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Modelling of a medium-term dynamics in a shallow tidal sea, based on combined physical and neural

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Modellingofamedium-termdynamicsinashallowtidalsea,

basedoncombinedphysicalandneuralnetworkmethods

AgnieszkaHerman*,RalfKaiser,HanzD.Niemeyer

CoastalResearchStation,LowerSaxonyWaterManagement,CoastalDefenceandNatureConservationAgency,AnderMu¨hle5,26548Norderney,Germany

Received2August2006;receivedinrevisedform23February2007;accepted26February2007Availableonline12March2007

Abstract

Thepaperpresentsanapproachtowardsamedium-term($decades)modellingofwaterlevelsandcurrentsinashallowtidalseabymeansofcombinedhydrodynamicandneuralnetworkmodels.Thetwo-dimensionalversionofthehydrody-namicmodelDelft3D,forcedwithrealisticwaterlevelandwindfields,isusedtoproduceatwo-year-databaseofwaterlevelsandcurrentsinthestudyarea.Thelinearprincipalcomponentanalysis(PCA)oftheresultsisperformedtorevealdominatingspatialpatternsintheanalyzeddatasetandtosignificantlyreducethedimensionalityofthedata.Itisshownthatonlyafewprincipalcomponents(PCs)arenecessarytoreconstructthedatawithhighaccuracy(over95%oftheoriginalvariance).Feed-forwardneuralnetworksaresetupandtrainedtoeffectivelysimulatetheleadingPCsbasedonwaterlevelandwindspeedanddirectiontimeseriesinasingle,arbitrarilychosenpointinthestudyarea.AssumingthatthespatialmodesresultingfromthePCAare‘universally’applicabletothedatafromtimeperiodsnotmodelledwithDelft3D,thetrainedneuralnetworkscanbeusedtoveryeffectivelyandreliablysimulatetemporalandspatialvariabilityofwaterlevelsandcurrentsinthestudyarea.Theapproachisshowntobeabletoaccuratelyreproducestatisticaldistri-butionofwaterlevelsandcurrentsinvariouslocationsinsidethestudyareaandthuscanbeviewedasareliablecomple-mentarytoole.g.,forcomputationallyexpensivehydrodynamicmodelling.Finally,adetailedanalysisoftheleadingPCsisperformedtoestimatetheroleoftidalforcingandwind(includingitsseasonalandannualvariability)inshapingthewaterlevelandcurrentclimateinthestudyarea.Ó2007PublishedbyElsevierLtd.

Keywords:Tidalinlets;Hydrodynamicmodelling;Principalcomponentanalysis;Neuralnetworks;NorthSea;WaddenSea;EastFrisianIslands

1.Introduction

Theinvestigationofmanyimportantaspectsofthecoastalzoneprocesses–e.g.,theanalysisofsediment

transportorstudiesconcerningthesafetyofvariouscoastalprotectionstructuresandthecoastitself–is

1463-5003/$-seefrontmatterÓ2007PublishedbyElsevierLtd.

doi:10.1016/j.ocemod.2007.02.004*Correspondingauthor.Presentaddress:InstituteofOceanography,UniversityofGdan´sk,Pilsudskiego46,81-378Gdynia,Poland.Tel.:+48585236879.E-mailaddress:herman@ocean.univ.gda.pl(A.

Herman).OceanModelling17(2007)

277–299www.elsevier.com/locate/ocemodpossibleonlyifdataconcerningmedium-term($decades)variabilityofwavesandcurrentsinthestudyarea

areavailable.Becauseofenormouscostsandtechnicaldifficultiesoflong-termmeasuringcampaignsonthe

onehand,andtypicalshortageofinputdatarequiredby(usuallyextremelycomputationallyexpensive)

numericalmodelsontheotherhand,theknowledgeoftemporalandspatialvariabilityofwavesandcurrents

inthecoastalzoneisusuallyverylimited.

TheworkpresentedinthisstudyispartofaresearchprojectMOSES(‘‘Modellingofthemedium-term

waveclimatologyattheGermanNorthSeacoast”),oneofthepurposesofwhichistoproduceamedium-

termdatabaseofwaterlevels,currentsandmeanwaveparametersforacoastalareaintheGermanWadden

Sea.Althoughthestate-of-the-arthydrodynamicandwavemodelsareabletoreproducethewaveandcurrent

processesinshallowtidalseaswithhighaccuracy,theirapplicationtomedium-termmodellingislimited

becauseofenormouscomputerresourcesthatarerequiredtoreachspatialandtemporalresolutionsufficient

toresolvealldetailsofthecomplicatedgeometryofthecoastalzone.Themethodstypicallyusedtoaddress

theseproblems,e.g.,nestingorgridswithvaryingspatialresolution,onlyinsomecasesprovideasatisfactory

solution.Moreover,theamountofdataproducedbythemodelsmakestheirdirectusageinfurtherapplica-

tions(e.g.,asinputformorphodynamicmodelling)practicallyimpossible.Therefore,evenifoneisableto

conductsufficientlylongsimulations,additionaldataanalysistoolsarenecessary,enablingthereductionof

theamountofdatawithoutlossofinformationcrucialfortheunderstandingoftheprocessesanalyzed

andforfurtherapplicationofthemodellingresults.

Inthepresentstudytheresultsofhigh-resolutionhydrodynamicsimulationsofwaterlevelsandcurrents

(wavemodellinginthestudyareawillbetreatedindetailelsewhere)areusedasastartingpointforthedevel-

opmentofaneuralnetwork-basedmodellingsystem,whichenablesfastandsufficientlyaccuratehindcasting

oftemporalandspatialpatternsofwaterlevelsandcurrentsinthestudyarea.Themainideabehindthe

approachdevelopedistodecomposethedatasetintoa(small)numberoffixedmodes,assumed‘universal’

overthefourdecadesstudied,andtomodelthetimevariationsofthosemodesonly,thusreducingthedimen-

sionalityoftheproblembymorethanthreeordersofmagnitude.Theresultspresentedinthispapershowthat

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基于Delft3D的离岸堤附近波浪与波生流数值模拟

基于Delft3D的离岸堤附近波浪与波生流数值模拟

基于Delft3D的离岸堤附近波浪与波生流数值模拟

许忠厚;董晓红;尹亚军

【摘 要】Based on 3D numerical model Delft3D,coupling wave and

current,a numerical model was estab-lished to simulate the waves and

currents near the offshore dyke out of water.The distribution of wave

height and wave-induced current along the section are consistent with the

test results of physical model,indicating that Delft 3D is a reliable model to

simulate the physical phenomenon of wave deformation, refraction,

diffraction and breaking in shallow water area.Based on the reasonable

validation of the model,the flow patterns under different angles of wave

attack and different wave heights were studied.It is demonstrated when

the wave angle increases,the longshore cur-rent increases accordingly and

the circulation behind the breakwater moves downstream of the wave

基于FVCOM的泉州湾海域三维潮汐与潮流数值模拟

基于FVCOM的泉州湾海域三维潮汐与潮流数值模拟

基于FVCOM的泉州湾海域三维潮汐与潮流数值模拟

林作梁;朱学明;鲍献文;刘钦政

【摘 要】Based on a finite-volume coastal ocean model (FVCOM) ,

adopting an unstructured triangle grid, a three-dimensional tide and tidal

current numerical modeling with high resolution (26 m) is applied to

Quanzhou Bay. The simulated results agree well with the observed data

from two tide-gauges and three continuing current stations , and

reproduce the distribution features of the tide and tidal currents in the

Quanzhou Bay famously. The distributions of co-tidal charts and tidal

ellipses on the surface layer for four major constituents (M2 , S2, K1 ,O1)

are obtained. What's more, the distributions of the maximum probable

tidal range and tidal currents velocity and tidal residual currents on the

surface and bottom layers are obtained, too. By analyzing, the maximum

超大型浮体单模块在浅水斜底系泊下的动态响应

超大型浮体单模块在浅水斜底系泊下的动态响应

超大型浮体单模块在浅水斜底系泊下的动态响应

徐剑峰;徐胜文;汪学锋;王磊;丁爱兵

【摘 要】Waters around the islands is usually very shallow and has a

sloped seabed. The hydrodynamic performance of a floating structure in

this environment could be very different from its performance in deep

water. This paper investigates the dynamic response of a very large

floating structure's single module over an uneven seabed in shallow water.

The time-do-main motions, and the statistical results of sway and roll

motion are respectively obtained by numerical simulations in Or-caFlex

and model tests, as well as the line tension statistical results. Results show

that the constant wind has little effect on the motion stability and the

maximum line tension, while the wave loads have significant influence on

the module's motions and the maximum line tension.%岛礁附近的海域通常水深极浅且海底为斜坡,在这类海域中,浮式结构物对环境载荷的动态响应与其在深水中的表现会有较大差别.本文研究超大型浮体的单模块在浅水斜底海域中对风浪载荷的动态响应,分别通过OrcaFlex数值计算和模型试验得到了单模块横荡和横摇运动的时历及统计数据以及锚链张力的统计结果.结果显示定常风对单模块运动的稳定性以及锚链的最大张力影响较小,而波浪载荷对单模块运动及锚链最大张力都有显著的影响.

涉海英语读写教程课后题答案第六单元

涉海英语读写教程课后题答案第六单元

涉海英语读写教程课后题答案第六单元

涉海英语读写教程课后答案（第六单元）Unit 6 Marine Resources Exploitation

Text A

Part I

Understanding and Learning

Background information

1.Green energy

It is also called sustainable energy or renewable energy. It is the sustainable provision of energy that meets the needs of thepresent without compromising the ability of future generations to meet their needs. It includes hydroelectricity, solar energy,wind energy, wave power, geothermal energy, and tidal power,etc.

2.Tidal power

It is also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainlyelectricity.

Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than windenergy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high costand limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability.However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidallagoons) and turbine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal powermay be much higher than previously assumed, and that economic and environmental costs may be brought down tocompetitive levels.