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The Neutral Grounding Resistor Sizing Using an Analytical Method Based on Nonlinear Transformer Model for Inrush Current MitigationGholamabas M.H.Hajivar Shahid Chamran University,Ahvaz, Iranhajivar@S.S.MortazaviShahid Chamran University,Ahvaz, IranMortazavi_s@scu.ac.irMohsen SanieiShahid Chamran University,Ahvaz, IranMohsen.saniei@Abstract-It was found that a neutral resistor together with 'simultaneous' switching didn't have any effect on either the magnitudes or the time constant of inrush currents. The pre-insertion resistors were recommended as the most effective means of controlling inrush currents. Through simulations, it was found that the neutral resistor had little effect on reducing the inrush current peak or even the rate of decay as compared to the cases without a neutral resistor. The use of neutral impedances was concluded to be ineffective compared to the use of pre-insertion resistors. This finding was explained by the low neutral current value as compared to that of high phase currents during inrush. The inrush currents could be mitigated by using a neutral resistor when sequential switching is implemented. From the sequential energizing scheme performance, the neutral resistor size plays the significant role in the scheme effectiveness. Through simulation, it was found that a few ohms neutral grounding resistor can effectively achieve inrush currents reduction. If the neutral resistor is directly selected to minimize the peak of the actual inrush current, a much lower resistor value could be found.This paper presents an analytical method to select optimal neutral grounding resistor for mitigation of inrush current. In this method nonlinearity and core loss of the transformer has been modeled and derived analytical equations.Index Terms--Inrush current, neutral grounding resistor, transformerI.I NTRODUCTIONThe energizing of transformers produces high inrush currents. The nature of inrush currents have rich in harmonics coupled with relatively a long duration, leads to adverse effects on the residual life of the transformer, malfunction of the protection system [1] and power quality [2]. In the power-system industry, two different strategies have been implemented to tackle the problem of transformer inrush currents. The first strategy focuses on adapting to the effects of inrush currents by desensitizing the protection elements. Other approaches go further by 'over-sizing' the magnetic core to achieve higher saturation flux levels. These partial countermeasures impose downgrades on the system's operational reliability, considerable increases unit cost, high mechanical stresses on the transformer and lead to a lower power quality. The second strategy focuses on reducing the inrush current magnitude itself during the energizing process. Minimizing the inrush current will extend the transformer's lifetime and increase the reliability of operation and lower maintenance and down-time costs. Meanwhile, the problem of protection-system malfunction is eliminated during transformer energizing. The available inrush current mitigation consist "closing resistor"[3], "control closing of circuit breaker"[4],[5], "reduction of residual flux"[6], "neutral resistor with sequential switching"[7],[8],[9].The sequential energizing technique presents inrush-reduction scheme due to transformer energizing. This scheme involves the sequential energizing of the three phases transformer together with the insertion of a properly sized resistor at the neutral point of the transformer energizing side [7] ,[8],[9] (Fig. 1).The neutral resistor based scheme acts to minimize the induced voltage across the energized windings during sequential switching of each phase and, hence, minimizes the integral of the applied voltage across the windings.The scheme has the main advantage of being a simpler, more reliable and more cost effective than the synchronous switching and pre-insertion resistor schemes. The scheme has no requirements for the speed of the circuit breaker or the determination of the residual flux. Sequential switching of the three phases can be implemented through either introducing a mechanical delay between each pole in the case of three phase breakers or simply through adjusting the breaker trip-coil time delay for single pole breakers.A further study of the scheme revealed that a much lower resistor size is equally effective. The steady-state theory developed for neutral resistor sizing [8] is unable to explain this phenomenon. This phenomenon must be understood using transient analysis.Fig. 1. The sequential phase energizing schemeUPEC201031st Aug - 3rd Sept 2010The rise of neutral voltage is the main limitation of the scheme. Two methods present to control the neutral voltage rise: the use of surge arrestors and saturated reactors connected to the neutral point. The use of surge arresters was found to be more effective in overcoming the neutral voltage rise limitation [9].The main objective of this paper is to derive an analytical relationship between the peak of the inrush current and the size of the resistor. This paper presents a robust analytical study of the transformer energizing phenomenon. The results reveal a good deal of information on inrush currents and the characteristics of the sequential energizing scheme.II. SCHEME PERFORMANCESince the scheme adopts sequential switching, each switching stage can be investigated separately. For first-phase switching, the scheme's performance is straightforward. The neutral resistor is in series with the energized phase and this resistor's effect is similar to a pre-insertion resistor.The second- phase energizing is one of the most difficult to analyze. Fortunately, from simulation studies, it was found that the inrush current due to second-phase energizing is lower than that due to first-phase energizing for the same value of n R [9]. This result is true for the region where the inrush current of the first-phase is decreasing rapidly as n R increases. As a result, when developing a neutral-resistor-sizing criterion, the focus should be directed towards the analysis of the first-phase energizing.III. A NALYSIS OF F IRST -P HASE E NERGIZING The following analysis focuses on deriving an inrush current waveform expression covering both the unsaturatedand saturated modes of operation respectively. The presented analysis is based on a single saturated core element, but is suitable for analytical modelling of the single-phase transformers and for the single-phase switching of three-phase transformers. As shown in Fig. 2, the transformer's energized phase was modeled as a two segmented saturated magnetizing inductance in series with the transformer's winding resistance, leakage inductance and neutral resistance. The iron core non-l inear inductance as function of the operating flux linkages is represented as a linear inductor inunsaturated ‘‘m l ’’ and saturated ‘‘s l ’’ modes of operation respectively. (a)(b)Fig. 2. (a) Transformer electrical equivalent circuit (per-phase) referred to the primary side. (b) Simplified, two slope saturation curve.For the first-phase switching stage, the equivalent circuit represented in Fig. 2(a) can accurately represent behaviour of the transformer for any connection or core type by using only the positive sequence Flux-Current characteristics. Based on the transformer connection and core structure type, the phases are coupled either through the electrical circuit (3 single phase units in Yg-D connection) or through the Magnetic circuit (Core type transformers with Yg-Y connection) or through both, (the condition of Yg-D connection in an E-Core or a multi limb transformer). The coupling introduced between the windings will result in flux flowing through the limbs or magnetic circuits of un-energized phases. For the sequential switching application, the magnetic coupling will result in an increased reluctance (decreased reactance) for zero sequence flux path if present. The approach presented here is based on deriving an analytical expression relating the amount of inrush current reduction directly to the neutral resistor size. Investigation in this field has been done and some formulas were given to predict the general wave shape or the maximum peak current.A. Expression for magnitude of inrush currentIn Fig. 2(a), p r and p l present the total primary side resistance and leakage reactance. c R shows the total transformer core loss. Secondary side resistance sp r and leakage reactance sp l as referred to primary side are also shown. P V and s V represent the primary and secondary phase to ground terminal voltages, respectively.During first phase energizing, the differential equation describing behaviour of the transformer with saturated ironcore can be written as follows:()())sin((2) (1)φω+⋅⋅=⋅+⋅+⋅+=+⋅+⋅+=t V (t)V dtdi di d λdt di l (t)i R r (t)V dt d λdt di l (t)i R r (t)V m P ll p pp n p P p p p n p PAs the rate of change of the flux linkages with magnetizing current dt d /λcan be represented as an inductance equal to the slope of the i −λcurve, (2) can be re-written as follows;()(3) )()()(dtdi L dt di l t i R r t V lcore p p P n p P ⋅+⋅+⋅+=λ (4) )()(L core l p c l i i R dtdi−⋅=⋅λ⎩⎨⎧==sml core L L di d L λλ)(s s λλλλ>≤The general solution of the differential equations (3),(4) has the following form;⎪⎩⎪⎨⎧>−⋅⋅+−⋅+−−⋅+≤−⋅⋅+−⋅+−⋅=(5) )sin(//)()( )sin(//)(s s 22222221211112121111λλψωττλλψωττt B t e A t t e i A t B t e A t e A t i s s pSubscripts 11,12 and 21,22 denote un-saturated and saturated operation respectively. The parameters given in the equation (5) are given by;() )(/12221σ⋅++⎟⎟⎠⎞⎜⎜⎝⎛⋅−++⋅=m p c p m n p c m m x x R x x R r R x V B()2222)(/1σ⋅++⎟⎟⎠⎞⎜⎜⎝⎛⋅−++⋅=s p c p s n p c s m x x R x x R r R x V B⎟⎟⎟⎟⎟⎠⎞⎜⎜⎜⎜⎜⎝⎛⋅−+++=⋅−−⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛−c p m n p m p c m R x x R r x x R x σφψ111tan tan ⎟⎟⎟⎟⎟⎠⎞⎜⎜⎜⎜⎜⎝⎛⋅−+++=⋅−−⎟⎟⎟⎠⎞⎜⎜⎜⎝⎛−c p s n p s p c m R R r x x R x σφψ112tan tan )sin(111211ψ⋅=+B A A )sin(222221s t B A A ⋅−⋅=+ωψ mp n p m p m p m p c xx R r x x x x x x R ⋅⋅+⋅−⋅+−⋅+⋅⋅⋅=)(4)()(21211σστm p n p m p m p m p c xx R r x x x x x x R ⋅⋅+⋅−⋅++⋅+⋅⋅⋅=)(4)()(21212σστ s p n p s p s p s p xx R r x x x x x x c R ⋅⋅+⋅−⋅+−⋅+⋅⋅⋅=)(4)()(21221σστ sp n p s p s p sp c xx R r x x x x x x R ⋅⋅+⋅−⋅++⋅+⋅⋅⋅=)(4)()(21222σστ ⎟⎟⎠⎞⎜⎜⎝⎛−⋅==s rs s ri i λλλ10 cnp R R r ++=1σ21221112 , ττττ>>>>⇒>>c R , 012≈A , 022≈A According to equation (5), the required inrush waveform assuming two-part segmented i −λcurve can be calculated for two separate un-saturated and saturated regions. For thefirst unsaturated mode, the current can be directly calculated from the first equation for all flux linkage values below the saturation level. After saturation is reached, the current waveform will follow the second given expression for fluxlinkage values above the saturation level. The saturation time s t can be found at the time when the current reaches the saturation current level s i .Where m λ,r λ,m V and ωare the nominal peak flux linkage, residual flux linkage, peak supply voltage and angular frequency, respectivelyThe inrush current waveform peak will essentially exist during saturation mode of operation. The focus should be concentrated on the second current waveform equation describing saturated operation mode, equation (5). The expression of inrush current peak could be directly evaluated when both saturation time s t and peak time of the inrush current waveform peak t t =are known [9].(10))( (9) )(2/)(222222121//)()(2B eA t e i A peak peak t s t s n peak n n peak R I R R t +−⋅+−−⋅+=+=ττωψπThe peak time peak t at which the inrush current will reachits peak can be numerically found through setting the derivative of equation (10) with respect to time equal to zero at peak t t =.()(11) )sin(/)(022222221212221/ψωωττττ−⋅⋅⋅−−−⋅+−=+−⋅peak t s t B A t te A i peak s peakeThe inrush waveform consists of exponentially decaying'DC' term and a sinusoidal 'AC' term. Both DC and AC amplitudes are significantly reduced with the increase of the available series impedance. The inrush waveform, neglecting the relatively small saturating current s i ,12A and 22A when extremely high could be normalized with respect to theamplitude of the sinusoidal term as follows; (12) )sin(/)()(2221221⎥⎦⎤⎢⎣⎡−⋅+−−⋅⋅=ψωτt t t e B A B t i s p(13) )sin(/)()sin()( 22221⎥⎦⎤⎢⎣⎡−⋅+−−⋅⋅−⋅=ψωτωψt t t e t B t i s s p ))(sin()( 2s n n t R R K ⋅−=ωψ (14) ωλλλφλφωλλφωmm m r s s t r m s mV t dt t V dtd t V V s=⎪⎭⎪⎬⎫⎪⎩⎪⎨⎧⎥⎥⎦⎤⎢⎢⎣⎡⎟⎟⎠⎞⎜⎜⎝⎛−−+−⋅=+⋅+⋅⋅==+⋅⋅=−∫(8) 1cos 1(7))sin((6))sin(10The factor )(n R K depends on transformer saturation characteristics (s λand r λ) and other parameters during saturation.Typical saturation and residual flux magnitudes for power transformers are in the range[9]; .).(35.1.).(2.1u p u p s <<λ and .).(9.0.).(7.0u p r u p <<λIt can be easily shown that with increased damping 'resistance' in the circuit, where the circuit phase angle 2ψhas lower values than the saturation angle s t ⋅ω, the exponential term is negative resulting in an inrush magnitude that is lowerthan the sinusoidal term amplitude.B. Neutral Grounding Resistor SizingBased on (10), the inrush current peak expression, it is now possible to select a neutral resistor size that can achieve a specific inrush current reduction ratio )(n R α given by:(15) )0(/)()(==n peak n peak n R I R I R α For the maximum inrush current condition (0=n R ), the total energized phase system impedance ratio X/R is high and accordingly, the damping of the exponential term in equation (10) during the first cycle can be neglected; [][](16))0(1)0()0(2212=⋅++⎥⎦⎤⎢⎣⎡⋅−+===⎟⎟⎠⎞⎜⎜⎝⎛+⋅⋅n s p c p s pR x n m n peak R x x R x x r R K V R I c s σ High n R values leading to considerable inrush current reduction will result in low X / R ratios. It is clear from (14) that X / R ratios equal to or less than 1 ensure negative DC component factor ')(n R K ' and hence the exponential term shown in (10) can be conservatively neglected. Accordingly, (10) can be re-written as follows;()[](17) )()(22122n s p c p s n p R x m n n peak R x x R x x R r V R B R I c s σ⋅++⎥⎦⎤⎢⎣⎡⋅−+=≈⎟⎟⎠⎞⎜⎜⎝⎛+⋅Using (16) and (17) to evaluate (15), the neutral resistorsize which corresponds to a specific reduction ratio can be given by;[][][](18) )0()(1)0( 12222=⋅++⋅−⋅++⋅−+⋅+=⎥⎥⎦⎤⎢⎢⎣⎡⎥⎥⎦⎤⎢⎢⎣⎡=n s p c p s p n s p c p s n p n R x x R x x r R x x R x x R r R K σσα Very high c R values leading to low transformer core loss, it can be re-written equation (18) as follows [9]; [][][][](19) 1)0(12222s p p s p n p n x x r x x R r R K +++++⋅+==α Equations (18) and (19) reveal that transformers require higher neutral resistor value to achieve the desired inrush current reduction rate. IV. A NALYSIS OF SECOND-P HASE E NERGIZING It is obvious that the analysis of the electric and magnetic circuit behavior during second phase switching will be sufficiently more complex than that for first phase switching.Transformer behaviour during second phase switching was served to vary with respect to connection and core structure type. However, a general behaviour trend exists within lowneutral resistor values where the scheme can effectively limitinrush current magnitude. For cases with delta winding or multi-limb core structure, the second phase inrush current is lower than that during first phase switching. Single phase units connected in star/star have a different performance as both first and second stage inrush currents has almost the same magnitude until a maximum reduction rate of about80% is achieved. V. NEUTRAL VOLTAGE RISEThe peak neutral voltage will reach values up to peak phasevoltage where the neutral resistor value is increased. Typicalneutral voltage peak profile against neutral resistor size is shown in Fig. 6- Fig. 8, for the 225 KVA transformer during 1st and 2nd phase switching. A del ay of 40 (ms) between each switching stage has been considered. VI. S IMULATION A 225 KVA, 2400V/600V, 50 Hz three phase transformer connected in star-star are used for the simulation study. The number of turns per phase primary (2400V) winding is 128=P N and )(01.0pu R R s P ==, )(05.0pu X X s P ==,active power losses in iron core=4.5 KW, average length and section of core limbs (L1=1.3462(m), A1=0.01155192)(2m ), average length and section of yokes (L2=0.5334(m),A2=0.01155192)(2m ), average length and section of air pathfor zero sequence flux return (L0=0.0127(m),A0=0.01155192)(2m ), three phase voltage for fluxinitialization=1 (pu) and B-H characteristic of iron core is inaccordance with Fig.3. A MATLAB program was prepared for the simulation study. Simulation results are shown in Fig.4-Fig.8.Fig. 3.B-H characteristic iron coreFig.4. Inrush current )(0Ω=n RFig.5. Inrush current )(5Ω=n RFig.6. Inrush current )(50Ω=n RFig.7. Maximum neutral voltage )(50Ω=n RFig.8. Maximum neutral voltage ).(5Ω=n RFig.9. Maximum inrush current in (pu), Maximum neutral voltage in (pu), Duration of the inrush current in (s)VII. ConclusionsIn this paper, Based on the sequential switching, presents an analytical method to select optimal neutral grounding resistor for transformer inrush current mitigation. In this method, complete transformer model, including core loss and nonlinearity core specification, has been used. It was shown that high reduction in inrush currents among the three phases can be achieved by using a neutral resistor .Other work presented in this paper also addressed the scheme's main practical limitation: the permissible rise of neutral voltage.VIII.R EFERENCES[1] Hanli Weng, Xiangning Lin "Studies on the UnusualMaloperation of Transformer Differential Protection During the Nonlinear Load Switch-In",IEEE Transaction on Power Delivery, vol. 24, no.4, october 2009.[2] Westinghouse Electric Corporation, Electric Transmissionand Distribution Reference Book, 4th ed. East Pittsburgh, PA, 1964.[3] K.P.Basu, Stella Morris"Reduction of Magnetizing inrushcurrent in traction transformer", DRPT2008 6-9 April 2008 Nanjing China.[4] J.H.Brunke, K.J.Frohlich “Elimination of TransformerInrush Currents by Controlled Switching-Part I: Theoretical Considerations” IEEE Trans. On Power Delivery, Vol.16,No.2,2001. [5] R. Apolonio,J.C.de Oliveira,H.S.Bronzeado,A.B.deVasconcellos,"Transformer Controlled Switching:a strategy proposal and laboratory validation",IEEE 2004, 11th International Conference on Harmonics and Quality of Power.[6] E. Andersen, S. Bereneryd and S. Lindahl, "SynchronousEnergizing of Shunt Reactors and Shunt Capacitors," OGRE paper 13-12, pp 1-6, September 1988.[7] Y. Cui, S. G. Abdulsalam, S. Chen, and W. Xu, “Asequential phase energizing method for transformer inrush current reduction—part I: Simulation and experimental results,” IEEE Trans. Power Del., vol. 20, no. 2, pt. 1, pp. 943–949, Apr. 2005.[8] W. Xu, S. G. Abdulsalam, Y. Cui, S. Liu, and X. Liu, “Asequential phase energizing method for transformer inrush current reduction—part II: Theoretical analysis and design guide,” IEEE Trans. Power Del., vol. 20, no. 2, pt. 1, pp. 950–957, Apr. 2005.[9] S.G. Abdulsalam and W. Xu "A Sequential PhaseEnergization Method for Transformer Inrush current Reduction-Transient Performance and Practical considerations", IEEE Transactions on Power Delivery,vol. 22, No.1, pp. 208-216,Jan. 2007.。

stored energy 储存能thermal（internal）energy 热（内）能potential energy 势能位能kinetic energy 动能chemical energy 化学能nuclear（atomic）energy 核能heat workflow work 流动功saturated liquid 饱和液体subcooled liquid 过冷液体compressed liquid 压缩液体superheated vapor 过热蒸气coefficient of performance （COP）性能系数expansion valve 膨胀阀condenser 冷凝器compressor 压缩机evaporator 蒸发器equation of state 状态方程heat rejection 排热热损失heat addition 供热reference plane 基准面参考面single-stage cycle 单级循环multistage cycle 多级循环specific volume 比容specific enthalpy 比焓shearing stress 切应力lateral velocity gradient 速度梯度square root 平方根kinematic viscosity 运动粘度velocity normal 法向速度laminar flow 层流turbulence 紊流cross section 横截面differential equation 微分方程inertia 惯性惯量viscosity 黏质粘性thermal conduction 热传导thermal convection 热对流thermal radiation 热辐射laminar sublayer 层流底层buffer layer 缓冲层过渡层thermal resistance 热阻natural convection 自然对流secondary influences 次要因素be directly proportional to 和…成正比be inversely proportional to 和…成反比characteristic length 特征长度critical point（temperature、pressure）临界点（温度、压力）momentum 动量proportionality factory 比例系数transition 过渡区psychrometrics 焓湿学dry air 干空气moist air 湿空specific humidity 比湿度degree of saturation 饱和度relative humidity 相对湿度dew-point temperature 露点温度wet-bulb temperature 湿球温度water vapor partial pressure 水蒸气分压力humidity ratio 含湿量（湿度比）precision 精度精密度精确quality 干度single-phase 单相physical constant 物理常数leading edge of the plate 平板起始端psychrometrics 焓湿学1.Work is the mechanism that transfer energy across the boundary of systems with differing pressures (or force of any kind),always toward the lower pressure. If the total effect produced in the system can be reduced to the raising of a weight, then nothing but work has crossed the boundary .Work is positive when energy is removed from the system(see Figure 1).功是指通过存在压差（任一种力）的系统边界传递能量的作用过程，总是指向低压。

专业名称•动力工程及工程热物理：Power Engineering and Engineering Thermophysics工程热物理：Thermal Physics of Engineering •动力工程：Power Engineering;Dynamic Engineering•热能工程：Thermal Engineering(Thermal Energy Engineering)•制冷与低温工程：Refrigeration and Cryogenic[ˌkraɪəˈdʒɛnɪk]Engineering•流体机械及工程：Fluid Mechanics and Engineering•热能动力工程：Thermal Energy and Dynamic Engineering•能源与动力工程学院：School of Energy and Power Engineering热力学thermodynamics1.adiabatic process[ˌædiəˈbætɪk]绝热过程2.aerodynamics[ˌeroʊdaɪˈnæmɪks]空气动力学,空气动力学专家，n,adj空气动力学的3.buoyancy[ˈbɔɪənsi,ˈbujən-]浮升力pressibility压缩性5.gasdynamics气体动力学6.hydraulics[haɪˈdrɔlɪks]水力学7.hydrodynamics流体水力学8.hydrostatics[ˌhaɪdrə'stætɪks]流体静力学9.open system开口系统10.reversible process[rɪˈvɚsəbəl]可逆过程11.thermodynamics equilibrium[ˌikwəˈlɪbriəm]热力平衡12.viscous[ˈvɪskəs]粘性的13.inviscid[ɪn'vɪsɪd]无粘性的14.thermodynamics、thermodynamic property热力学、热力性质15.entropy[ˈɛntrəpi]熵16．enthalpy[en'θælpɪ]焓17．internal energy内能18．potential energy势能19．kinetic energy动能20．work功21．mechanical/shaft work机械功/轴功22．flow work流动功23．specific volume比容24.cycle循环25.Saturated temperature/pressure/liquid/ vapor[ˈsætʃəreɪtɪd]饱和温度/压力/液体/蒸汽26.subcooled liquid过冷液体27.quality（蒸汽）干度28.dry saturated vapor干饱和蒸汽29.superheated vapor过热蒸汽30.the first/second law of thermodynamics热力学第一/二定律31.the law of the conservation of energy能量守恒定律32.reversible/irreversible process可逆/不可逆过程33.pressure drop压降34.heat exchanger热交换器35.entropy production熵产[ˈɛntrəpi]36.coefficient of performance性能系数37.refrigerating capacity/effect制冷量38.Carnot cycle卡诺循环/nit/39.refrigerating efficiency制冷效率40.equation of state状态方程41.ideal gas constant理想气体常数42.isotherm等温线43.triple point三相点44.hydrocarbons碳氢化合物/烃45.cryogenic低温学[ˌkraɪəˈdʒenɪk]46.least-square fitting最小二乘法47.specific heat/specific heat capacity比热/比热容48.azeotropic mixture共沸混合物[əˌzi:ə'trɒpɪk]49.zeotropic mixture非共沸混合物50.dew point(temperature)露点（温度）[dju: pɔint][du pɔɪnt]51.isentropic compression/process等熵压缩/过程[aɪsen'trɒpɪk]52.condenser冷凝器53.evaporator蒸发器54.expansion valve膨胀阀55.throttling valve节流阀pressor压缩机pressor displacement压缩机排气量58.volumetric efficiency容积效率59.single-stage/two-stage/double-stage/compound compression单/双级压缩60.intercool/intercooler中间冷却（器）61.intermediate pressure中间压力62.pressure ratio压力比63.insulating material保温材料流体力学1.流体力学fluid mechanics2.动力粘度absolute/dynamic viscosity3.速度梯度velocity gradient英[ˈgreɪdiənt]美[ˈɡrediənt]4.运动粘度kinematic viscosity英[ˌkɪnɪ'mætɪk]美[ˌkɪnə'mætɪk]英[vɪ'skɒsətɪ]美[vɪˈskɑsɪti] 5.伯努力方程Bernoulli Equation英[bə:ˈnu:li iˈkweiʃən]6.体积流量volumetric flow rate7.质量流量mass flow rate8.层流laminar flow9.紊流turbulence/turbulent flow10.雷诺数Reynolds number11.摩擦力friction/frictional force12.摩擦系数coefficient of friction13.微分方程differential equation14.阻力drag force或resistance15.阻力系数drag coefficient传热学1.热传递heat transfer2.热传导thermal conduction3.热对流thermal convection4.热辐射thermal radiation5.层流底层laminar sublayer6.过渡层buffer layer,缓冲区或人，buffer dinner 自助餐buffet英[ˈbʌfit]7.强迫对流forced convection8.自然/自由对流natural/free convection9.稳态导热steady-state conduction10.导热系数thermal conductivity11.热阻thermal resistance12.（总）传热系数(overall)heat transfer coefficient13.表面积surface area14.串联series系列15.并联parallel英[ˈpærəlel]并行，Parallel computing并行计算16.接触热阻contact thermal resistance17.（对数）平均温差(logarithmic)mean temperature difference[ˌlɒɡə'rɪðmɪk]18.顺流parallel flow19.逆流counter flow20.相变phase change21.冷库cold storage热库thermal reservoir/heat bath22.边界条件boundary condition23.黑体辐射blackbody radiation24.辐射力emissive power25.维恩位移定律Wien’s displacement Law26.半球发射率hemispherical emittance[ˌhemɪˈsferɪkl]27.吸收率absorptance英[əb'sɔ:ptəns]28.透射率transmittance英[træns'mɪtns]n.播送;发射;传动;透明度;29.反射率reflectance30.漫射辐射diffuse radiation31.(充分发展的)层流/紊流fully developed laminar/turbulent flow湿空气1.湿空气学psychrometrics2.干空气dry air3.湿空气moistair4.大气压barometricpressure5.热力学温标thermodynamic temperature scale6.含湿量humidity ratio7.比焓specific enthalpy英[en'θælpɪ]8.比熵specific entropy英[ˈentrəpi]9.绝对湿度absolute humidity10.饱和含湿量saturation humidity ratio英[ˌsætʃəˈreɪʃn]英[ˈreɪʃiəʊ]11.相对湿度relative humidity12.热力学湿球温度thermodynamic wet-bulb temperature13.分压力partial pressure14.总压total pressure15.通用气体常数universal gas constant16.湿球/干球温度dry-bulb/wet-bulb temperature17.焓湿图psychrometric chart制冷空调1.集中/分散供冷central/decentralized cooling英[ˌdi:'sentrəlaɪzd]2.锅炉boiler3.往复/螺杆/离心/涡旋式压缩机/冷水机组reciprocating/helical rotary(或screw)/centrifugal/scroll compressor/water chiller unit4.吸收式制冷/冷水机组absorption refrigeration/water chiller unit5.热回收heat reclaim/recovery6.冷却塔cooling tower7.空气/水冷却冷凝器air-cooled/water-cooled condenser8.蒸发式冷凝器evaporative condenser9.净正吸入压力/压头netpositive suction pressure/head10.供/回干管main supply/return line11.二/三通阀two/three-way valve12.平衡阀balancing valve13.一次/二次冷冻水系统primary/secondary chilled water system14.备用泵spare pump15.疏水器、存水弯、水封trap16.水/冰蓄冷water/ice thermal storage17.空气/水/地源热泵air/water/ground source heat pump18.定/变风量constant/variable air volume19.经济器economizer20.静/动压static/dynamic pressure21.毛细管capillary tube英[kəˈpɪləri]22.全封闭压缩机hermetically sealed/hermetic compressor英[hɜ:ˈmetɪk]23.半封闭式压缩机semi-hermetic/semi-hermetically sealed compressor24.直接膨胀direct expansion26.离心/轴流式风机centrifugal/axial fan英[ˈæksiəl]27.立管riser英['raɪzə]28.内/外平衡式热力膨胀阀internally/externally equalized thermostatic expansion valve29.吸/排气管suction/discharge line30.电磁阀solenoid valve美['solə,nɔɪd]31.恒压阀constant pressure valve32.迎风面积/速度face area/velocity33.（一拖多）分体式空调器(multi-)split air conditioner34.水环热泵water loop heat pump35.能效比energy efficiency ratio36.变容压缩/压缩机positive displacement compression/compressor37.速度/动压式压缩/压缩机velocity/dynamic compression/compressor38.流量系数flow coefficient39.水锤water hammer40.闸阀gate valve41.球阀ball valve42.蝶阀butterfly valve43.平衡阀balancing valve44.安全阀safety/relief valve n.救济；减轻，解除；安慰；浮雕45.止回阀check/backflow prevention valve boiler锅炉1.air heater空气预热器2.auxiliary辅助的，辅机[ɔ:gˈzɪliəri]3.bare tube光管4.blast[英][blɑ:st]鼓风5.blowdown排污6.capacity[英][kəˈpæsəti]出力7.cogenerator热电联产机组pressor压缩机bustion燃烧10.condenser凝汽器11.counterflow逆流12.critical pressure临界压力13.diesel oil柴油gasoline,gaslene, gas,petro(英),汽油14.drainage疏水、排水设备,排水系统15.drum汽包16.economizer[英][i:'kɒnəmaɪzə]省煤器17.excess air[英][ɪkˈses]过量空气18.extended surface扩展受热面19.fin鳍片、肋片、散热片、翅片20.flue gas烟气21.fluid(-)bed流化床(fluidizedbed)[英]['flu:ɪdaɪzd22.furnace炉膛23.fouling污垢，击球出界（羽毛球）[英]['faʊlɪŋ]24.generator发电机25.header联箱、集箱,集管26.hopper[英][ˈhɒpə(r)]斗、料斗l磨煤机(pulverizer)[英]['pʌlvəraɪzə]28.motor汽车、马达、电动机29.platen屏、管屏[美]['plætən]30.Prandtl numbers普朗特数31.pressure loss压力损失32.regenerator回热器，蓄热器，再生器[英][rɪ'dʒenəˌreɪtə]33.Reynolds numbers雷诺数34.slag结渣美[slæɡ]35.sootblower吹灰器美[su:tb'ləʊər]36.steam line blowing蒸汽管路吹洗37.superheater过热器38.turbine汽轮机39.suction真空，负压steam turbine蒸汽轮机40.gas turbine燃气轮机41.back pressure背压42.blower送风机、吹灰器43.boundary layer边界层44.chimney英[ˈtʃɪmni]烟囱、烟道、烟筒45.cooling tower冷却水塔46.coupling连接，连接法兰,耦合47.critical speed临界转速48.cylinder圆筒、汽缸49.head汽包封头、扬程、水头50.impeller叶轮、推进器、压缩器rge turbine-generator unit大型汽轮发电机组52.non-destructive testing(NDT)无损检验53.digital-controlled machine数控机床54.fixed blade固定叶片，导向叶片55.operational speed运行转速56.outing casing外缸57.inner casing内缸58.rigid coupling刚性连轴器solid coupling59.rotor转子60.stress concentration应力集中61.two-shift operation两班制运行62.wake尾流Thermal Power Plant:热电厂1.automatic control system:自动控制系统2.boiler feed pump:锅炉给水泵feed pump:给水泵3.chamber:燃烧室/ei/4.circulating water:循环水5.check valve:止回阀，逆止阀6.non-return valve:逆止阀，止回阀7.controlling valve:控制阀，调节阀8.cooling water（CW）:冷却水9.cycle efficiency:循环效率10.data processing system:数据处理系统11.de-aerator[英]['eɪəreɪtə]除氧器12.de-aerator tank:除氧水箱13.desuperheater:减温器14.desuperheater spraywater:喷水减温15.drain pump:疏水泵16.full-load:满负荷erning system:调速系统（governing:调节，调整）18.heat-transfer coefficient:换热系数19.isolating valve:隔离阀20.load rejection:甩（抛）负荷21.main steam:主汽22.motorized isolating valve:电动隔离阀23.lubricating oil:润滑油24.nuclear plant:核电厂25.orifice:[orifis]孔，口，孔板26.pipework:管路27.power station:电厂28.pressure reducing valve:减压装置29.reliability:安全性，可靠性30.relief valve:安全阀31.running speed:运行转速32.sealing:密封，封闭，焊封33.self-sealing:自密封的34.stainless steel:不锈钢35.stop valve:断流阀，截止阀36.strainer:滤盆，滤器，滤网，拉紧装置37.supercritical plant:超临界机组38.synchronizer:英]['sɪŋkrənaɪzə]同步器，同步机，同步装置39.throttle:节流阀[美]/ˈθrɑ:tl/喉咙，气管，vt.&vi.扼杀，压制;勒死，使窒息;使节流40.turbine-generator unit:汽轮发电机组41.ultra-supercritical:超超临界英][ˈʌltrə] [美]['ʌltrə]42.vacuum:真空43.vent:通道，通风口44.actuator:/aiktjueite/执行机构45.brake:闸，制动器46.damper:[美]['dæmpər]挡板，调节风门47.distributed control system(DCS)分散控制系统48.disturbance:干扰，扰动49.feedback control:反馈控制50.forced draught（FD）fan:送风机[英][fɔ:st drɑ:ft/51.furnace purge:炉膛吹扫ernor valve:调节阀53.induced draught（ID）fan:引风机54.make-up pump:补水泵55.overheating:过热，超温56.preamp:前置放大器/ˈpriæmp/57.primary air fan:一次风机58.sensor:传感器59.shutdown:停机，停炉，停运，关机，关闭；倒闭，停工，停业，停播。

造纸专业词汇————————————————————————————————作者：————————————————————————————————日期：Weld: 焊接,焊缝end product: 成品Hexagon nut: 六脚螺栓spare part: 备品Valid: 有效的,正确的leveling screw: 水准螺旋Tolerance: 容忍,公差commutator: 换向器Anchor bolt: 地脚螺栓UPS: 不间断电源Rag bolt: 棘螺栓goggle: 护目镜Foundation bolt: 地脚螺栓apparel: 衣服Grout: 水泥浆,用水泥浇灌entrust: 委任Galvanize: 电镀jolt: 摇晃Louver: 天窗crate: 板条箱Hand over: 手柄,移交state: 国家,声明,规定,陈述Surplus: 剩余,剩余的forwarder: 代运人,转运公司Saturate: 使饱和,浸透synchro motor: 同步电机Ambient: 周围的squirrel motor: 鼠笼电机Electrical cubicle: 配电房slip ring motor: 滑环电机Insulated strand: 绝缘线perforated plate: 孔板Cablet: 电缆钢索contour: 轮廓Copperbusbar: 铜线beak suction tubes: 鸭嘴吸入管Transformer room: 变压器室lode cell: 测压元件Air impingement: 空起冲击haul: 拖拉,改变方向Incidental: 附带的,伴随的,偶然的dismantle：拆除In charge:看管，主管withdrawal:取回收回，取消Hazardous: 危险的consignment: 交托，交货，发货Supplementary:辅助的，增补的defect: 过失缺点Corrodible:会腐蚀的peripheral: 外围的Preservative: 防护剂grease: 油脂贿赂Axes: 轴workmanshop: 手艺，技巧做工Staircases and walkways: 楼梯和过道instrumentation: 使用仪表Positioner: 远程位置调节器issue: 发布,发给,出版发行Hose: 软管prerequisite: 先决条件Rubberized roll: 包胶辊built-in: 内置的,固定的Rinse: 冲洗ventilation: 通风,暖通Insulation: 绝缘sling: 吊索Broad padded sling: splinter: 裂片,碎片Nail: 钉,指甲rope lashing:Timber: 木材chill: 寒冷,变冷,使冷冻Monorail: 单轨铁路cotter bolt: 销螺栓,牵条螺栓,地脚螺栓Magnetic flow meter: 磁流量测量计spacer plate: 隔板Align: 使成行,排列,结盟false work: 脚手架Scaffold: 脚手架elevation: 标高Volute: 涡形的implementation: 执行Halloween: 万圣节前夕Hallowmas:万圣节Vigour: 气势,元气responsible: 有责任的,负责的Dedicated to: 献身,专注于battery limit: 界区Conquer: 战胜,克服deactivation: 钝化Client: 客户exclude: 不包括Saturated steam: 饱和蒸汽viscosity: 粘度Specific gravity: 比重sulphate: 硫酸盐Potassium: 钾sodium: 钠Anti-foaming agent: 消泡剂optimize: 使优化Coefficient: 系数efficiency: 效率temperature profile: 温度曲线图rotator: 转子rotate: 旋转sag: 下垂disassembly: 拆卸take-down: 拆卸,病倒,记下knock down: 拆卸,击倒gradient: 梯度,倾斜的scaling: 结垢top nut: 顶部螺帽top washer: 顶部垫片base frame: 底架tough: 艰苦的,坚强的fantastic: 幻想的,奇异荒谬的vapour body: 蒸汽室vapour: 二次蒸汽,闪蒸汽stripping system : 汽提系统reflux : 回流precipitate : 沉淀crystal :结晶plug : 堵塞velocity : 速度,速率previously : 以前,先前,优先的neutral : 中性的atmospheric mix tank: 常压混合槽medium steam: 中压蒸汽tube surface condenser: 管式表面冷凝器plus: 加上segregation baffle : 隔板volatile : 不稳定的,挥发deviate : 背离,偏离rectification : 精馏,纠正,校正tray : 塔板,板exitine : 外壁内层ions : 离子persistent : 持久稳固的plate heat exchanger : 板式换热器strainer : 过滤器,滤网(油,汽) arrestor : 捕集器wreck : 破坏,毁坏compliance with : 遵守comply : 遵守accomplish : 完成,实现carbide : 碳化物live steam : 新鲜蒸汽corrosion allowance : 腐蚀余量cladding : 包裹层mild steel : 软钢vent gas : 排气inspection : 检查,视察chevron : v形mist elimination : 汽膜分离器shop-built : 车间制造tube sheet : 管程,管板plenum : 充满,高压subcooling :低温冷却weld rod : 焊条cone : 锥形物,使成锥形stipper column :汽提塔valve tray : 浮阀塔板trim condenser: 平衡冷凝器plate heater: 板式加热器tube heater: 管式加热器pending: 悬而味觉的whip-lash: 鞭打,反方向猛扭hammering: 捶打dead point: 盲点dynamic: 动力的,动力学的thermodynamic: 使用热动力的, cement: 水泥,结合self regulating: 自我调节trace pipe: 伴管potable water: 可饮用水trench: 沟渠spill: 溢流overflow: 溢流conductivity meter: 电导计level indication: 液位指示here in: 在此parameter: 参数“AI” signal: 模拟输入信号“AO” signal: 模拟输出信号“DI” signal: 数字输入信号“DO” signal: 数字输出信号Deviation: 偏差remote: 遥控Via: 通过philosophy: 哲学,原理Principle: 原理elements: 原理基础Oscillating: 振荡,摆动filtrate: 滤液Boost: 增强booster: 加压机Sump: 地坑stabilization: 稳定性Day tank: 储槽(一天) sedimentation: 沉淀Diesel engine: 柴油机submittal: 服从,屈服helmet头盔toe-plates鞋尖铁片entanglement纠缠illumination照明，阐明，启发abrasive material磨擦材料grinding研磨welding焊接spark火花explosive gas爆炸性气体intact完整无缺的ultraviolet紫外线的，紫外线辐射ventilation通风fume（浓烈和难闻的）烟，气体property damage财产损失squeeze挤压defect过失，缺点，缺陷crushing挤压shearing剪切cutting or severing切割或切断entanglement纠缠drawing-in or trapping抽进或捕捉impact碰撞stabbing or puncture刺穿或刺破friction or abrasion磨擦或磨损a self-priming pump自吸式泵high pressure fluid ejection高压液体喷出electrical shock电击live parts带电部件burns and scalds灼伤或烫伤inhalation吸入a full-body safety harness全身安全带safety belt asbuilt document竣工文件custom clearance清关material takeoff所需材料的估算run out condition跳动、变动（机械：变工况）条件closeout出清存货progressive cavity pump渐进容积泵（螺杆泵）trip out断路，跳闸，甩负荷characteristics特征concentration浓度residual alkali残碱chloride氯化物magnesium镁calcium钙methanol甲醇aluminium铝silica硅sodium carbonate碳酸钠sodium sulphate硫酸钠electronic file电子文档eliminate消除steam trap疏水器desuperheated water减温水washing connection冲洗水甩头drainer排放导淋sog汽提塔臭气disclaimer不承担责任的声明tag标签a unique consecutive number唯一的连续编号prerequisite前提auxiliary equipment辅助设备architectural engineering drawings建筑设计图supplementary增补物sheet-metal working板金工加工X-Y coordinates X-Y座标obstacle障碍torque wrench扭矩板钳lubrication with grease用油脂润滑scaffolding脚手架mandatory强制的，命令的foremost最先的，最重要的safety precaution安全防范immunity to Electro-magnetic and radio frequency interference(EMI and RFI)免受电磁和无线电频率干扰solenoid valve电磁阀intermediate relay中间继电器hazardous area危险区域limit switch限位开关on-off valve开关阀analogue signal模拟信号auxiliary power supply辅助电源main power supply主电源differential pressure transmitter压差变送器capillary毛细管manifold歧管diaphragm seal膜片封rmoured 铠装的thermowell 热电偶套管vibration resistant抗振signal linearization线性信号even figure偶数coil excitation线圈励磁magnetic flow meter磁通量计anticorrosion 防腐automatic temperature compensation自动温度补偿tropicalized耐热的complete dossier全部档案elevation device起重装置manual valve手动阀mecharical cartridge seal 机械封筒密封ceramic coat陶瓷涂层feed back反馈minutes of meeting会议记录design liaison meeting设计联络会keep a log on记入日志pending issue未决事项authority approval官方批准heat expansion热膨胀buffer缓冲器isometric drawing三维图fire fighting消防fire hose灭火水龙头lightning conductor避雷针coder编码器position switch位置开关expansion joint膨胀连接frequency converter变频器assembly drawing组装图isolating valve隔离阀fuse保险丝blow tank喷放槽sump pit pump污水坑泵junk trap除渣器sand separator除砂器drain排水沟sewer下水道recausticizing system苛化系统suspended solids悬浮物causticizing efficiency苛化率sulfidity (of a.a.)硫化度（aa）total titrateable alkali(asna2o)总可滴定碱（na2o）reburnt lime再生石灰lime mud白泥actuator执行器linearization mode线性模式check valve止逆阀in verbal口头的dosing screw加药螺旋rake：耙screw classifier螺旋提渣机booster compressor增压机lime mud vessel白泥网槽advance payment预付款polymer絮凝剂freight forwarder运输行stevedore搬动工prevail胜过，优先discrepancy矛盾，差异oil day tank 常用油箱shrink tank收缩槽jet condenser喷射冷凝器eyewash system洗眼系统continuous precoat renewal (CPR) system连续预挂更新系统safety shower安全喷淋infrastructure基础结构steam drum汽包furnace燃烧炉generating section产汽区economizer省煤器economizer header省煤器联箱superheater过热器steam attemperator蒸汽调温器sweet water condenser净水冷凝器drain排水vent放空hanger rod悬臂buckstay支架、支柱ash hopper灰斗refractory耐火材料start up burner开车烧嘴flame scanner火焰扫描器sootblower吹灰器primary air一次风secondary air二次风tertiary air三次风flue gas duct烟气导管combustion air燃烧空气control damper控制挡板electrostatic precipitator静电除尘器ash dilution tank飞灰稀释槽vent stack烟囱smelt spout熔融物出口vent scrubber排放洗涤器continuous blowdown tank连续排污槽reserve water tank贮水槽chemical dosing system加药系统special tool专用工具maintenance platform检修平台raw green liquor tank绿液缓冲槽digester蒸煮器field instrument现场仪表field junction box现场接线箱special cable特殊电缆cable tray电缆沟，电缆架cable fitting电缆接头pneumatic air tube气动空气管MC discharge scraper中浓出口刮料机tower bottom dropleg塔底水腿vacuum pump真空泵drum displacer washer鼓式置换洗浆机（dd洗浆机）perforated plate孔板digester blowtank蒸煮器喷放槽agitator搅拌器filtrate pump滤液泵integrated knot separator and brown stock primary screen集成节子分离器和未漂浆初筛机secondary screen二次筛选机tertiary screen三次筛选机knot and reject washer节子和浆渣洗涤机pressure thickener压力浓缩机surface condenser表面冷凝器stripper unit汽提塔trim condenser平衡冷凝器preheater预热器flash tank闪蒸槽level tank液位槽stripper reflux tank汽提塔回流槽spill liquor tank溢流槽insulation and lagging保温和保温材料pipe bridge管廊soil excavation and filling挖填土process sewer工艺排水沟dregs filter hood ventilation blower绿泥过滤器送风机reburned lime再生石灰lime slaker classifier石灰消化提渣机causticizer tank苛化器lime bin dust collection system石灰仓除尘系统filtration compressor压滤机kiln shell石灰窑体bricklining砖衬riding ring 滚圈carrying roller set支承辊（传送辊）thrust roller set推力辊girth gear矢圈（矢轮）driving mechanism驱动机械firing hood燃烧罩feed head进料端（窑尾）burnt lime crusher燃烧石灰粉碎机burnt lime bucket elevator燃烧石灰斗提机control philosophy控制原理limestone discharge vibrator石灰石排放振动机others pending其他未确定事项infrastructure: 基础,结构buckstay: 支柱,支架hanger rod: 悬臂control damper: 控制挡板turbo-generator: 汽轮机turbine: 透频,涡轮发电机rear end: 后端thrust bearing: 推力轴承sketch: 草图impeller: 叶片thermo-electricity plant: 热电设备casing: 缸abstract: 抽提back pressure: 背压grease: 油脂parameter: 参数governor: 控制器,危急保安器converter: 转换器pressure guage: 压力计thermo couple: 热电偶balance test: 平衡测试static: 静态的critical speed: 临界速度turbulence: 震动,絮流trip: 跳车baseplate: 底板integrate: 集成tack welding: 点焊string welding: 线焊welding rod: 焊条sight glass: 视镜hatch: 开口,策划slop: 溢出oil mist eliminator: 油雾消除器bore: 孔submerge: 进入bridge over: 从旁边接通nitrogen: 氮气adjustable oil orifice: 可调节油孔板turbine generator set: 发电机组accessory: 附件gland steam: 密封蒸汽atmospheric: 常压sub-contractor: 分包商medium: 介质,中间的coupling: 连接,耦合turning device: 盘车装置coupling house: 连轴箱rear bearing house: 后轴承箱jaw: 钳夹,狭长入口stroke: 行程,冲程abbreviation: 缩写terminal strip: 接线条implement: 工具,器具,执行rated load: 额定负载hood: 盖子cooling plate: 冷却板forged-on: 铸造exciter machine: 励磁设备rectifier: 校正者,整流器voltage: 电压resistance thermometer: 电阻温度计ground fault: 接地故障leakage: 泄漏test bay: 试验间winding: 绕组stator: 定子trip-valve: 截断阀insulation resistance: 绝缘电阻tilting-pad: 倾斜垫,可倾瓦overspeed test: 超速试验protection relay: 继电保护器phase: 相位circuit breaker: 回路断路器redundancy: 冗余undercxcitation: 欠励磁unbalance load: 失衡负载over current: 电流过载impedance resistance: 阻抗电阻cubicle: 室core: 芯synchronization: 同期,同步angular velocity: 角速度paralleling: 平行的,相似的diode: 二极管power factor: 功率因素switchgear: 开关设备trigger: 激发tracing: 伴管protocol: 协议smolder: 自燃divergence:分歧eradicate:根除irrevocable:不能取消的scaling:缩放比例hoist:提升间,升起scratch:乱写,抓痕,打草稿用的stiffen:变硬,使变硬bulge:凸出部分,膨胀manhole:人孔socket:空穴,插座pickle:盐汁,泡腌circumference:圆周,周围pitch:斜度,掷投reduction gear: 减速齿轮器bevel gear:锥齿轮line shaft:主传动轴master signal:主信号reference signal:参考信号taut:张紧的,拉紧的reference speed: 基准速度,给定的计算速度strain gauge:应变仪,变形测量器rheostat:可变电阻器double acting:双重作用的parallel:平行的air lock:气塞surplus:剩余,过剩的plenum:充实,充满,高压guide vane:导流叶片orifice:孔orifice plate:孔板facilitate:使容易,使便利,推动pneumatic cylinder: piston:活塞angle iron:角钢,角铁time relay: 时间电阻器local regulation:局部调节in force:有效的,大规模的commence:开始,着手control package:成套控制设备power converter:整流器vendor:卖主longitudinal:纵向的spiral:螺旋形的,螺旋bushing:轴衬,套管pivot:轴支点,中心点,枢轴,枢轴上转动interlayer:夹层,隔层side force:侧力vertical alignment:竖向定线vice versa:反之亦然cylinder rod:活塞杆draft:草图,草稿,起草,气流cutting edge:刀刃bearing stand:轴承座(台)house shoe:马蹄铁,装马蹄铁于bearing race:轴承座圈journal:轴颈oxyacetylene:氧乙炔的ignite:点燃spacer ring:隔离环,隔离垫圈soak:浸泡eccentric:偏心的eccentric bolt:偏心螺栓ring gear:齿圈,环形齿轮relocate:重新布置cap screw:螺帽closure:封条,贴封,关闭angular position:角位,角坐标cover screw:盖用螺钉helical:螺旋状的noise abatement:噪音消除控制taper wedge:调整楔hold down bolt:抑制螺栓,锁紧螺栓slack off:松懈jack screw:顶丝螺旋worm:蜗杆,螺纹lock screw:锁紧螺丝bearing house:轴承座foreign matter:杂质heel:跟部drive down:压低knife edge:刀口dial indicator:千分表,刻度盘指示器cap screw:帽螺栓clamping screw:紧固螺栓,夹紧螺钉clean cut:净切割dynamic load:动载荷static load:静载荷jut out:伸出antiskid:防滑装置loose flange:活套法兰loose collar:活动环implementation: 执行weld bead:焊缝,焊珠bipolar:有两极的,双极的bipartite:双向的rangeability:可调整范围splash ring:润滑油环valve stem::阀杆hysteresis:滞后现象backlash:后座,反冲resolution:分辨率,决心discrete:不连续的feed back:反馈duration:持续时间,为期pulse:脉冲remote:远程的,遥控downtime:停工期compatible:一致兼容fore side:操作侧analog:类似的,相似的vicinity:附近roller chain:滚子链refrain:节制避免tail:引纸窄条tail cutter:切纸水针tail end:引纸窄条trim:纸边,冲边trim squirt:切边水针wire ring:磨损环voltage drop:电压降落delivery head:压头,压力差vent screw:放气螺旋overrunning clatch:超越离合器overrunning coupler:超越离合器open draw:开式引纸steering frame:转向架lateral:横向的span跨度,范围,跨距,横跃flow pattern::流型,流态circular hole:圆孔triangular hole:三角孔skew:倾斜的carriage:机架pinion:小齿轮fluorescent:荧光的telescopic:伸缩杆staggered:交错排列的vice:老虎钳light armature:电枢halogen:卤素knurled roll:槽纹扎辊retractable:可回收的chute:斜道,瀑布counterweight :平衡物Brittleness：脆性Intact：完整无缺Remedial maintenance：补救维修Rectify：改正矫正Malfunction：故障Solvent：溶剂auxiliary sealing（O-ring）：o型环negligence：忽略other than：除了consent : 同意patch up：修补supplement：增补downtime：停工期Intend for：为…..准备Withstand：抵档，经受住Detachable：可分开的Dimension：尺寸尺度Append：附加的Short-term：短期的Hoisting：提升起重Depressurize：使减压Transport pallet：转运货物的货架Enclosed：被附上的Dispatch note：发货票据Centralization：集中Overrunning clutch：超越离合器Sprocket：链轮齿Bearing lid：轴承盖Grease gun：润滑油脂抢Taper bush：锥形衬套Shaft sleeve：轴套Sliding face：滑动面Lifting eye screw：吊耳Fastening screw：紧固螺丝Dimensional drawing：尺寸图Junk trap：渣浆收集管Shaft seal：轴封Crate：板条箱柳条箱Regulating valve：调节阀Magnetic flow meter：电磁流量计Jack：千斤顶Chain plug：手动葫芦Bracket：托架支架Concrete：混泥土LWC：low weight coating paperSCP：Super calender paper Innovation：创新Stuff box：高位箱Degasser：脱气器Pitch：树脂Microbiological：微生物的Flocs：絮凝Reflocculation：再絮凝Pulsation：脉冲Cavitation：气蚀Compressibility：可压缩性Pinhole：针孔Agglomeration：聚集Hydrophobic trash：气泡附着物疏水垃圾Intense：强烈的剧烈的Conventional machine：传统设备Biocide：杀菌剂Change over loss：改产损失Grade change：等级改变Retention aid：助留剂Dispersant：分散剂Dedusting system：除尘系统Hopper：加料斗漏斗Dosing：定量给料Bentonite：斑脱土Cationic starch：阳离子淀粉Optical Brightener：增白剂Sizing：胶料Defoamer：消泡剂Web sizing：sizing surface：surface sizing：表面施胶Fine paper：高级纸张Calender：压光机Scale：结垢Grammage：定量Slice opening：开口宽度（流浆箱）Filler：填料Chemical aid：化学助剂First pass retention：一次留着率Air permeability：透气度Porosity：透气度气孔度Surface strength：表面强度Gloss：光泽度Printability：适印性Delamination strength：层间强度（scott bond表示J/m2）Tensile：抗张强度CSF：游离度Stiffness：挺度Offset paper：胶版纸Fiber support index：纤维支撑指数Yarn：单丝线（网子毛布）Mesh：网密目数Extended nip：宽压区Slush pulp：液体浆湿浆Base paper：原纸Reel：卷纸机Winder：复卷机Predryer：预热烘缸Formation：匀度Uniformity：均匀度Smoothness：平滑度Bulk：松厚度Newsprint：新闻纸Profile：横向成型分布Unwind：unwinding：退纸展开Unwinder：unwind stand：退纸架Runnability：运转性能Hybrid former：混合成型器Deflocculation：抗絮聚Attenuator：衰减器Electropolish：电解法抛光Turbulence generator：湍动发生器Transition pipe connection：大小头接管Inlet header：进浆总管Disturbance：扰动Tubular：管状的Geometry：几何学Enlarging：扩大Manifold tube bank：（进浆总管之后的）管束Equalizing chamber：管束之后的平衡室Weir：堰Contraction：渐缩式收缩Compact：紧凑的简洁的Eddying：涡流Groove：凹槽Pedestal：基架基础Subassembly：部件组件Fourdrinier：长网纸机Rigid：刚性的Vacufoil：真空脱水板Foil：案板Girder：梁Tilt：倾斜度Irrespective：无关的不考虑Drop leg：大气水腿Vacushoe：真空靴Amplitude：振幅丰富Clad：覆层Worm gear：涡轮Electromechanical：电动机械Mist collector：集雾器Intermittent：间歇的Hydrant：消防栓Socket wrench：管钳Torque wrench：扭矩扳手Impact wrench：套筒扳手Spacer sleeve：间隔套Spacer ring：间隔环Circlip：卡簧Gasket：垫子Shim：薄垫片Retaining ring：扣环定位环Converge：聚合会聚Beneath：在…之下Compatibility：兼容性Straight press：正压榨Patent：专利Helical：螺旋状的Hydrostatic：流体静力学Deflection：偏差偏斜Momentum：动力要素Tackle：工具滑车装备Sling ：Strap：吊装带Winch：绞盘Implement：工器具执行Dummy head：仿真头人工头Siphon：虹吸管Negative pressure：负压Intake：（水气）进口Cast iron：铸铁Insulation：绝缘隔热Elongation：延长伸长Drive pin：定位销传动销Crown：Crowning：中高Toothed rod：带齿的杆Linear velocity：线速度Hood：（烘缸）罩子Hoist：提升吊升Trolley：电车Dolly：移动推车Clearance gauge：塞尺Compliance：依据Applicator：施胶装置Solid content：固形物含量Thermostatic：温度调节装置的Drip pan：接水盘Universal shaft：万向轴Chrome：铬合金Chromium：铬Conduit：导管穿线管Antifriction bearing：抗磨轴承Circumference：周围Caliper：厚度Conical grinding：圆锥磨法Spherical plain bearing：球面滑动轴承Roller bearing：滚柱轴承Serrate：锯齿状的Induction coil：感应线圈电感器Profiler：横向调节器Parent roll：大卷筒Reel drum：卷纸缸Oblique loading：斜加载Sheave：滑轮Synchronizing shaft：同步轴Turn-up：换卷Pick up：引纸Dryer bar：扰流杆Press fit：压配合Deflaker：纤维疏解机Instantaneous production：瞬时产量Destacker：卸包机Integral：完整的整体的Aggregate：合计集合体Dewiring machine：除铁丝机Metal detector：金属探测器Adjustable bearing：可调轴承Dump tower：出料塔Intermediate chest：中间池Refiner：磨浆机OCC：废箱板纸制浆ONC：废新闻纸制浆DIP：脱墨浆Packing cord：填料绳Squeeze：压榨挤压Flush joint：齐平接缝Butt joint：对接接头Lantern ring：套环Undo：松开Symmetric：均衡的Homogeneous：均一的均匀的相似的Disintegration：瓦解Disperse：使分散使散开Composite：合成物合成的Coefficient：系数Impingement：冲击侵犯Robust：精力充沛Fluidization：使液化Instantly：立即地即刻地Pick-up felt：引纸毛毯Magnification：扩大放大倍数dtex=g/L*100 其中g为丝线的重量(克),L为丝线的长度(米)Underpressure：真空抽空Wiper：拭擦器拭擦布Entrainment：夹走带走Pigment：色素颜料Bill of lading：提货单Fibril：细纤维Sand blasting：喷砂Shock absorber：减震器Potentiometer：电位计Rear drum：后底辊Bowing rool：弧形辊Tungsten carbide：碳化钨Aluminium：铝Blade steel：刀片钢Chuck：复卷机纸芯夹头Rewinding head：复卷机纸芯夹头Saw tooth：锯齿状Roll lowering table：复卷机卸纸台。

Unsaturated Soil Mechanics in Engineering PracticeDelwyn G.Fredlund1Abstract:Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems͑or challenges͒.The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics.The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows:͑1͒The need to understand the fundamental,theoretical behavior of an unsaturated soil;͑2͒the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships;͑3͒the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods;͑4͒the determination of indirect techniques for the estimation of unsaturated soil property functions,and͑5͒in situ and laboratory devices for the measurement of a wide range of soil suctions.This paper explains the nature of each of the previous challenges and describes the solutions that have emerged from research puter technology has played a major role in achieving practical geotechnical engineering puter technology has played an important role with regard to the estimation of unsaturated soil property functions and the solution of nonlinear partial differential equations.Breakthroughs in the in situ and laboratory measurement of soil suction are allowing unsaturated soil theories and formulations to be verified through use of the“observational method.”DOI:10.1061/͑ASCE͒1090-0241͑2006͒132:3͑286͒CE Database subject headings:Unsaturated soils;Soil mechanics;Geotechnical engineering;Research.PreambleKarl Terzaghi is remembered most for providing the“effective stress”variable,͑␴−u w͒,that became the key to describing the mechanical behavior of saturated soils;where␴=total stress and u w=pore–water pressure.The effective stress variable became the unifying discovery that elevated geotechnical engineering to a science basis and context.As a graduate student I was asked to purchase and study the textbook,Theoretical Soil Mechanics,by Karl Terzaghi͑1943͒.I had already selected the subject of unsaturated soil behavior as myfield of research and was surprised tofind considerable infor-mation on this subject in this textbook.Two of the19chapters of the textbook contribute extensively toward understanding unsat-urated soil behavior;namely,Chapter14on“Capillary Forces,”and Chapter15,on“Mechanics of Drainage”͑with special atten-tion to drainage by desiccation͒.These chapters emphasize the importance of the unsaturated soil portion of the profile and in particular provide an insight into the fundamental nature and importance of the air–water interface͑i.e.,contractile skin͒. Considerable attention was given to soils with negative pore–water pressures.Fig.1shows an earth dam illustrating how waterflowed above the phreatic line through the capillary zone ͑Terzaghi1943͒.The contributions of Karl Terzaghi toward unsaturated soil behavior are truly commendable and still worthy of study.Subsequent reference to the textbook Theoretical Soil Mechan-ics during my career,has caused me to ask the question,“Why did unsaturated soil mechanics not emerge simultaneously with saturated soil mechanics?”Pondering this question has led me to realize that there were several theoretical and practical challenges associated with unsaturated soil behavior that needed further re-search.Unsaturated soil mechanics would need to wait several decades before it would take on the character of a science that could be used in routine geotechnical engineering practice.I am not aware that Karl Terzaghi ever proposed a special description of the stress state in an unsaturated soil;however, his contemporary,Biot͑1941͒,was one of thefirst to suggest the use of two independent stress state variables when formulating the theory of consolidation for an unsaturated soil.This paper will review a series of key theoretical extensions that were required for a more thorough representation and formulation of unsaturated soil behavior.Research within the agriculture-related disciplines strongly influenced the physical and hydraulic model that Terzaghi developed for soil mechanics͑Baver1940͒.With time,further significant contributions have come from the agriculture-related disciplines͑i.e.,soil science,soil physics,and agronomy͒to geo-technical engineering.It can be said that geotechnical engineers tended to test soils by applying total stresses to soils through the use of oedometers and triaxial cells.On the other hand, agriculture-related counterparts tended to apply stresses to the water phase͑i.e.,tensions͒through use of pressure plate cells. Eventually,geotechnical engineers would realize the wealth of information that had accumulated in the agriculture-related disciplines;information of value to geotechnical engineering. Careful consideration would need to be given to the test proce-dures and testing techniques when transferring the technology into geotechnical engineering.1Professor Emeritus,Dept.of Civil and Geological Engineering,Univ. of Saskatchewan,Saskatoon SK,Canada S7N5A9.Note.Discussion open until August1,2006.Separate discussions must be submitted for individual papers.To extend the closing date by one month,a written request must befiled with the ASCE Managing Editor.The manuscript for this paper was submitted for review and pos-sible publication on February16,2005;approved on May1,2005.This paper is part of the Journal of Geotechnical and Geoenvironmental Engineering,V ol.132,No.3,March1,2006.©ASCE,ISSN1090-0241/ 2006/3-286–321/$25.00.An attempt is made in this paper to give the theory of unsat-urated soil mechanics its rightful position.Terzaghi ͑1943͒stated that “the theories of soil mechanics provide us only with the working hypothesis,because our knowledge of the average physical soil properties of the subsoil and the orientation of the boundaries between the individual strata is always incomplete and often utterly inadequate.”Terzaghi ͑1943͒also emphasized the importance of clearly stating all assumptions upon which the theories are based and pointed out that almost every “alleged contradiction between theory and practice can be traced back to some misconception regarding the conditions for the validity of the theory.”And so his advice from the early days of soil mechan-ics is extremely relevant as the theories for unsaturated soil be-havior are brought to the “implementation”stage in geotechnical engineering.IntroductionFundamental principles pivotal to understanding the behavior of saturated soils emerged with the concept of effective stress in the 1930s ͑Terzaghi 1943͒.There appeared to be considerable interest in the behavior of unsaturated soil at the First International Conference on Soil Mechanics and Foundation Engineering in 1936,but the fundamental principles required for formulating unsaturated soil mechanics would take more than another 30years to be forthcoming.Eventually,a theoretically based set of stress state variables for an unsaturated soil would be proposed within the context of multiphase continuum mechanics ͑Fredlund and Morgenstern 1977͒.There have been a number of challenges ͑i.e.,problems or difficulties ͒that have slowed the development and implement-ation of unsaturated soil mechanics ͑Fredlund 2000͒.Each of these challenges has provided an opportunity to develop new and innovative solutions that allow unsaturated soil mechanics to become part of geotechnical engineering practice.It has been necessary for geotechnical engineers to adopt a new “mindset”toward soil property assessment for unsaturated soils ͑Fredlund et al.1996͒.The primary objective of this paper is to illustrate the progres-sion from the development of theories and formulations to practical engineering protocols for a variety of unsaturated soil mechanics problems ͑e.g.,seepage,shear strength,and volume change ͒.The use of “direct”and “indirect”means of characteriz-ing unsaturated soil property functions has been central to the emergence of unsaturated soil mechanics.The key challenges faced in the development of unsaturated soil mechanics are described and research findings are presented that have made it possible to implement unsaturated soil mechanics into geotech-nical engineering practice.A series of unsaturated soil mechanics problems are presented to illustrate the procedures and methodology required to obtain meaningful solutions to plete and detailed case histories will not be presented but sufficient information is pro-vided to illustrate the types of engineering solutions that are feasible.Gradual Emergence of Unsaturated Soil Mechanics Experimental laboratory studies in the late 1950s ͑Bishop et al.1960͒showed that it was possible to independently measure ͑or control ͒the pore–water and pore–air pressures through the use of high air entry ceramic boratory studies were reported over the next decade that revealed fundamental differences be-tween the behavior of saturated and unsaturated soils.The studies also revealed that there were significant challenges that needed to be addressed.The laboratory testing of unsaturated soils proved to be time consuming and demanding from a technique standpoint.The usual focus on soil property constants was diverted toward the study of nonlinear unsaturated soil property functions.The increased complexity of unsaturated soil behavior extended from the laboratory to theoretical formulations and solutions.Originally,there was a search for a single-valued effective stress equation for unsaturated soils but by the late 1960s,there was increasing awareness that the use of two independent stress state variables would provide an approach more consistent with the principles of continuum mechanics ͑Fredlund and Morgenstern 1977͒.The 1970s was a period when constitutive relations for the classic areas of soil mechanics were proposed and studied with respect to uniqueness ͑Fredlund and Rahardjo 1993͒.Initially,constitutive behavior focused primarily on the study of seepage,shear strength,and volume change problems.Gradually it became apparent that the behavior of unsaturated soils could be viewed as a natural extension of saturated soil behavior ͑Fredlund and Morgenstern 1976͒.Later,numerous studies attempted to combine volume change and shear strength in the form of elasto-plastic models that were an extension from the saturated soil range to unsaturated soil conditions ͑Alonso et al.1990;Wheeler and Sivakumar 1995;Blatz and Graham 2003͒.The study of con-taminant transport and thermal soil properties for unsaturated soils also took on the form of nonlinear soil property functions ͑Newman 1996;Lim et al.1998;Pentland et al.2001͒.The 1980s was a period when boundary-value problems were solved using numerical,finite element,and finite difference mod-eling methods.Digital computers were required and iterative,numerical solutions became the norm.The challenge was to find techniques that would ensure convergence of highly nonlinear partial differential equations on a routine basis ͑Thieu et al.2001;Fig.1.An earth dam shown by Terzaghi ͑1943͒illustrating that water can flow above the phreatic line through the capillary zone ͑reprinted with permission of ErLC Terzaghi ͒Fredlund et al.2002a,b,c͒.Saturated–unsaturated seepage model-ing became thefirst of the unsaturated soils problems to comeinto common engineering practice.Concern for stewardshiptoward the environment further promoted interest in seepage andgeoenvironmental,advection-dispersion modeling.The1990s and beyond have become a period where therehas been an emphasis on the implementation of unsaturated soilmechanics into routine geotechnical engineering practice.A seriesof international conferences have been dedicated to the exchangeof information on the engineering behavior of unsaturated soilsand it has become apparent that the time had come for increasedusage of unsaturated soil mechanics in engineering practice.Implementation can be defined as“a unique and important stepthat brings theories and analytical solutions into engineeringpractice”͑Fredlund2000͒.There are several stages in the devel-opment of a science that must be brought together in an efficientand appropriate manner in order for implementation to becomea reality.The primary stages suggested by Fredlund͑2000͒,areas follows:͑1͒State variable;͑2͒constitutive;͑3͒formulation;͑4͒solution;͑5͒design;͑6͒verification and monitoring;and ͑7͒implementation.Research is required for all of the above-mentioned stages in order that practical,efficient,cost-effective,and appropriate technologies emerge.Primary Challenges to the Implementationof Unsaturated Soil MechanicsThere are a number of primary challenges that needed to beaddressed before unsaturated soil mechanics could become a partof routine geotechnical engineering practice.Several of thechallenges are identified here.Each challenge has an associatedsolution that is further developed throughout the manuscript.Insome cases it has been necessary to adopt a new approach tosolving problems involving unsaturated soils.In this paper,anattempt is made to describe the techniques and procedures thathave been used to overcome the obstacles to implementation;thuspreparing the way for more widespread application of unsaturatedsoil mechanics.Challenge1:The development of a theoretically sound basisfor describing the physical behavior of unsaturated soils,startingwith appropriate state variables.Solution1:The adoption of independent stress state variablesbased on multiphase continuum mechanics has formed the basisfor describing the stress state independent of soil properties.The stress state variables can then be used to develop suitableconstitutive models.Challenge2:Constitutive relations commonly accepted forsaturated soil behavior needed to be extended to also describeunsaturated soil behavior.Solution2:Gradually it became apparent that all constitutiverelations for saturated soil behavior could be extended to embraceunsaturated soil behavior and thereby form a smooth transitionbetween saturated and unsaturated soil conditions.In each case,research studies needed to be undertaken to verify the uniqueness of the extended constitutive relations.Challenge3:Nonlinearity associated with the partial differen-tial equations formulated for unsaturated soil behavior resulted in iterative procedures in order to arrive at a solution.The conver-gence of highly nonlinear partial differential equations proved to be a serious challenge.Solution3:Computer solutions for numerical models have em-braced automatic mesh generation,automatic mesh optimization,and automatic mesh refinement͓known as adaptive grid refine-ment͑AGR͔͒,and these techniques have proved to be of greatassistance in obtaining convergence when solving nonlinear par-tial differential equations.Solution procedures were forthcomingfrom the mathematics and computer science disciplines.Challenge4:Greatly increased costs and time were required for the testing of unsaturated soils.As well,laboratory equipmentfor measuring unsaturated soil properties has proven to be tech-nically demanding and quite complex to operate.Solution4:Indirect,estimation procedures for the character-ization of unsaturated soil property functions were related to thesoil–water characteristic curve͑SWCC͒and the saturated soilproperties.Several estimation procedures have emerged for eachof the unsaturated soil property functions.The computer has alsoplayed an important role in computing unsaturated soil propertyfunctions.Challenge5:Highly negative pore–water pressures͑i.e., matric suctions greater than100kPa͒,have proven to be difficultto measure,particularly in thefield.Solution5:New instrumentation such as the direct,high suc-tion tensiometer,and the indirect thermal conductivity suctionsensor,have provided new measurement techniques for thelaboratory and thefield.Other measurement systems are alsoshowing promise.These devices allow suctions to be measuredover a considerable range of matric suctions.The null type,axis-translation technique remains a laboratory reference procedure forthe measurement of matric suction.Challenge6:New technologies such as those proposed for unsaturated soil mechanics are not always easy to incorporate intoengineering practice.The implementation of unsaturated soilmechanicsfindings into engineering practice has proven to be achallenge.Solution6:Educational materials and visualization systems have been assembled to assist in effective technology transfer ͑Fredlund and Fredlund2003͒.These are a part of teaching and demonstrating the concepts of unsaturated soil behavior;information that needs to be incorporated into the undergraduateand graduate curriculum at universities.Protocols for engineeringpractice are being developed for all application areas of geotech-nical engineering.Changes are necessary in geotechnical engineering practicein order for unsaturated soil mechanics to be implemented.Eachchallenge has been met with a definitive and practical solution.In the case of the determination of unsaturated soil propertyfunctions a significant paradigm shift has been required͑Houston2002͒.The new approaches that have been developed appearto provide cost-effective procedures for the determination ofunsaturated soil property functions for all classes of problems ͑Fredlund2002͒.Laboratory and Field Visualizationof Varying Degrees of SaturationClimatic conditions around the world range from very humid to arid,and dry.Climatic classification is based on the average net moistureflux at the ground surface͓i.e.,precipitation minus potential evaporation͑Thornthwaite1948͔͒.The ground surface climate is a prime factor controlling the depth to the groundwater table and therefore,the thickness of the unsaturated soil zone ͑Fig.2͒.The zone between the ground surface and the water table is generally referred to as the unsaturated soil zone.This is some-what of a misnomer since the capillary fringe is essentially saturated.A more correct term for the entire zone above the water table is the vadose zone ͑Bouwer 1978͒.The entire zone sub-jected to negative pore–water pressures is commonly referred to as the unsaturated zone in geotechnical engineering.The unsaturated zone becomes the transition between the water in the atmosphere and the groundwater ͑i.e.,positive pore–water pressure zone ͒.The pore–water pressures in the unsaturated soil zone can range from zero at the water table to a maximum tension of approximately 1,000,000kPa ͑i.e.,soil suction of 1,000,000kPa ͒under dry soil conditions ͑Croney et al.1958͒.The water degree of saturation of the soil can range from 100%to zero.The changes in soil suction result in distinct zones of saturation.The zones of saturation have been defined in situ as well as in the laboratory ͓i.e.,through the soil–water characteristic curve ͑Fig.3͔͒.Table 1illustrates the terminologies commonly used to describe saturation conditions in situ and in the laboratory.Soils in situ start at saturation at the water table and tend to become unsaturated toward the ground surface.Soils near to the ground surface are often classified as “prob-lematic”soils.It is the changes in the negative pore–water pressures that can result in adverse changes in shear strength and volume mon problematic soils are:expansive orswelling soils,collapsible soils,and residual soils.Any of the above-mentioned soils,as well as other soil types,can also be compacted,once again giving rise to a material with negative pore–water pressures.Unsaturated Soil as a Four-Phase MixtureAn unsaturated soil is commonly referred to as a three-phase mixture ͑i.e.,solids,air,and water ͒but there is strong justification for including a fourth independent phase called the contractile skin or the air–water interface.The contractile skin acts like a thin membrane interwoven throughout the voids of the soil,acting as a partition between the air and water phases.It is the interaction of the contractile skin with the soil structure that causes an unsatur-ated soil to change in volume and shear strength.The unsaturated soil properties change in response to the position of the contrac-tile skin ͑i.e.,water degree of saturation ͒.It is important to viewTable parison of Terminology Used to Describe In Situ and Laboratory Degrees of Saturation In situ zones of saturation Zones of saturation on the soil-watercharacteristic curveCapillary fringeBoundary effect Two phase fluid flowTransition Dry ͑vapor transport of water ͒ResidualFig.2.Illustration of the unsaturated soil zone ͑vadose zone ͒on a regional and localbasisFig. 3.Illustration of the in situ zones of desaturation defined by a soil–water characteristic curvean unsaturated soil as a four-phase mixture for purposes of stress analysis,within the context of multiphase continuum mechanics.Consequently,an unsaturated soil has two phases that flow under the influence of a stress gradient ͑i.e.,air and water ͒and two phases that come to equilibrium under the influence of a stress gradient ͑i.e.,soil particles forming a structural arrangement and the contractile skin forming a partition between the fluid phases ͒͑Fredlund and Rahardjo 1993͒.The contractile skin has physical properties differing from the contiguous air and water phases and interacts with the soil structure to influence soil behavior.The contractile skin can be considered as part of the water phase with regard to changes in volume–mass soil properties but must be considered as an independent phase when describing the stress state and phenom-enological behavior of an unsaturated soil.Terzaghi ͑1943͒emphasized the important role played by surface tension effects associated with the air–water interface ͑i.e.,contractile skin ͒.Distinctive Features of the Contractile Skin :Numerous research studies on the nature of the contractile skin point toward its important,independent role in unsaturated soil mechanics.Terzaghi ͑1943͒suggested that the contractile skin might be in the order of 10−6mm in thickness.More recent studies suggest that the thickness of the contractile skin is in the order of 1.5–2water molecular diameters ͑i.e.,5Å͒͑Israelachvili 1991;Townsend and Rice 1991͒.A surface tension of approximately 75mN/m translates into a unit stress in the order of 140,000kPa.Lyklema ͑2000͒showed that the distribution of water molecules across the contractile skin takes the form of a hyperbolic tangent function as shown in Fig.4.Properties of the contractile skin are different from that of ordinary water and have a water molecular structure similar to that of ice ͑Derjaguin and Churaev 1981;Matsumoto and Kataoka 1988͒.The Young–Laplace and Kelvin equations describe fundamen-tal behavioral aspects of the contractile skin but both equations have limitations.The Young–Laplace equation is not able to explain why an air bubble can gradually dissolve in water without any apparent difference between the air pressure and the water pressure.The validity of the Kelvin equation becomes suspect as the radius of curvature reduces to the molecular scale ͑Adamson and Gast 1997;Christenson 1988͒.Terzaghi ͑1943͒recognized the limitations of the Kelvin equa-tion and stated that if the radius of a gas bubble “approaches zero,the gas pressure …approaches infinity.However,within the range of molecular dimensions,”the equation “loses its validity.”Although Terzaghi recognized this limitation,later researchers would attempt to incorporate the Kelvin equation into formula-tions for the compressibility of air–water mixtures,to no avail ͑Schuurman 1966͒.The details of the laws describing the behav-ior of the contractile skin are not fully understood but the contractile skin is known to play a dominant role in unsaturated soil behavior.Terzaghi ͑1943͒stated that surface tension “is valid regardless of the physical causes.…The views concerning the molecular mechanism which produces the surface tension are still controversial.Yet the existence of the surface film was established during the last century beyond any doubt.”Designation of the Stress StateState variables can be defined within the context of continuum mechanics as variables independent of soil properties required for the characterization of a system ͑Fung 1965͒.The stress state variables associated with an unsaturated soil are related to equilibrium considerations ͑i.e.,conservation of energy ͒of a multiphase system.The stress state variables form one or more tensors ͑i.e.,3ϫ3matrix ͒because of the three-dimensional Cartesian coordinate system generally used for the formulation of engineering problems ͑i.e.,a three-dimensional world ͒.The description of the state variables for an unsaturated soil becomes the fundamental building block for an applied engineering science.The universal acceptance of unsaturated soil mechanics depends largely upon how satisfactorily the stress state variables can be defined,justified,and measured.Historically,it has been the lack of certainty regarding the description of the stress state for an unsaturated soil that has been largely responsible for the slow emergence of unsaturated soil mechanics.Biot ͑1941͒was probably the first to suggest the need for two independent stress state variables for an unsaturated soil.This is evidenced from the stress versus deformation relations used in the derivation of the consolidation theory for unsaturated soils.Other researchers began recognizing the need to use two independent stress state variables for an unsaturated soil as early as the 1950s.This realization can be observed through the three-dimensional plots of the volume change constitutive surfaces for an unsatur-ated soil ͑Bishop and Blight 1963;Matyas and Radakrishna 1968͒.It was during the 1970s that a theoretical basis and justi-fication was provided for the use of two independent stress state variables ͑Fredlund and Morgenstern 1977͒.The justification was based on the superposition of coincident equilibrium stress fields for each of the phases of a multiphase system,within the context of continuum mechanics.From a continuum mechanics stand-point,the representative element volume ͑REV ͒must be suffi-ciently large such that the density function associated with each phase is a constant.It should be noted that it is not necessary for all phases to be continuous but rather that the REV statistically represents the multiphase system.Although the stress analysis had little direct application in solving practical problems,it helped unite researchers on how best to describe the stress state of an unsaturated soil.Three possible combinations of independent stress state vari-ables were shown to be justifiable from the theoretical continuum mechanics analysis.However,it was the net normal stress ͓i.e.,␴−u a ,where ␴=total net normal stress and u a =pore–air pressure ͔and the matric suction ͑i.e.,u a −u w ,where u w =pore–water pres-sure ͒combination of stress state variables that proved to be the easiest to apply in engineering practice.The net normal stress primarily embraces the activities of humans which aredominatedFig.4.Density distribution across the contractile skin reprinted from Liquid–Fluid Interface ,V ol.3of Fundamental of Interface and Colloid Science,J.Lyklema ͑2000͒,with permission from Elsevierby applying and removing total stress͑i.e.,excavations,fills,and applied loads͒.The matric suction stress state variable primarily embraces the impact of the climatic environment above the ground surface.The stress state for an unsaturated soil can be defined in the form of two independent stress tensors͑Fredlund and Morgenstern1977͒.There are three sets of possible stress tensors, of which only two are independent.The stress state variables most often used in the formulation of unsaturated soil problems form the following two tensors:΄͑␴x−u a͒␶yx␶zx␶xy͑␴y−u a͒␶zy␶xz␶yz͑␴z−u a͒΅͑1͒and΄͑u a−u w͒000͑u a−u w͒000͑u a−u w͒΅͑2͒where␴x,␴y,and␴z=total stresses in the x,y,and z directions, respectively;u w=pore–water pressure;and u a=pore–air pressure.The stress tensors contain surface tractions that can be placed on a cube to represent the stress state at a point͑Fig.5͒.The stress tensors provide a fundamental description of the stress state for an unsaturated soil.It has also been shown͑Barbour and Fredlund 1989͒that osmotic suction forms another independent stress tensor when there are changes in salt content of either a saturated or unsaturated soil.All the stress state variables are independent of soil properties and become the“keys”to describing physical phenomenological behavior,as well as defining functional relationships for unsaturated soil properties.The inclusion of soil parameters at the stress state level is unacceptable within the context of continuum mechanics.As a soil approaches saturation,the pore–air pressure,u a, becomes equal to the pore–water pressure,u w.At this point,the two independent stress tensors revert to a single stress tensor that can be used to describe the behavior of saturated soils:΄͑␴x−u w͒␶yx␶zx␶xy͑␴y−u w͒␶zy␶xz␶yz͑␴z−u w͒΅͑3͒Variations in the Description of Stress StateStress tensors containing stress state variables form the basis for developing a behavioral science for particulate materials. The stress tensors make it possible to writefirst,second,and third stress invariants for each stress tensor.The stress invariants associated with thefirst and second stress tensors are shown in Fredlund and Rahardjo͑1993͒.It is not imperative that the stress invariants be used in developing constitutive models;however, the stress invariants are fundamental in the sense that all three Cartesian coordinates are taken into consideration.There have been numerous equations proposed that relate some of the stress variables to other stress variables through the inclusion of soil properties.It is important to differentiate be-tween the role of these equations and the description of the stress state͑at a point͒in an unsaturated soil.It is also important to understand the role that these equations might play in subsequent formulations for practical engineering problems.The oldest and best known single-valued relationship that has been proposed is Bishop’s effective stress equation͑Bishop 1959͒:␴Ј=͑␴−u a͒+␹͑u a−u w͒͑4͒where␴Ј=effective stress and␹=soil parameter related to water degree of saturation,and ranging from0to1.Bishop’s equation relates net normal stress to matric suction through the incorporation of a soil property,␹.Bishop’s equation does not qualify as a fundamental description of stress state in an unsaturated soil since it is constitutive in character.It would be erroneous to elevate this equation to the status of stress state for an unsaturated soil.Morgenstern͑1979͒explained the limitations of Bishop’s effective stress equation as follows:•Bishop’s effective stress equation“…proved to have little impact on practice.The parameter,␹,when determined for volume change behavior was found to differ when determined for shear strength.While originally thought to be a function of degree of saturation and hence bounded by0and1,experi-ments were conducted in which␹was found to go beyond these bounds.•The effective stress is a stress variable and hence related to equilibrium considerations alone.”Morgenstern͑1979͒went on to explain:•Bishop’s effective stress equation“…contains the parameter,␹,that bears on constitutive behavior.This parameter is found by assuming that the behavior of a soil can be expressed uniquely in terms of a single effective stress variable and by matching unsaturated soil behavior with saturated soil be-havior in order to calculate␹.Normally,we link equilibrium considerations to deformations through constitutive behavior and do not introduce constitutive behavior into the stress state.Another form of Bishop’s equation has been used by several researchers in the development of elastoplastic models͑Jommi 2000;Wheeler et al.2003;Gallipoli et al.2003͒.␴ij*=␴ij−͓S w u w+͑1−S w͒u a͔␦ij͑5͒where␴ij=total stress tensor;␦ij=Kroneker delta or substitutiontensor;␴ij*=Bishop’s average soil skeleton stress;and Sw=water degree of saturation.In this case,the water degree of saturation has been substituted for the␹soil parameter.The above-mentioned equation is once again empirical and constitutive in character.Consequently,the Fig.5.Definition of stress state at a point in an unsaturated soil。