EFFICIENT GENERATION OF CFDBASED LOADS FOR THE FEMANALYSIS OF SHIP STRUCTURES


 Samuel Lawrence
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1 EFFICIENT GENERATION OF CFDBASED LOADS FOR THE FEMANALYSIS OF SHIP STRUCTURES H Ese ad C Cabos, Gemasche Lloyd AG, Gemay SUMMARY Stegth aalyss of shp stuctues by meas of FEM eques ealstc loads. The most ealstc loads wll esult fom CFD smulatos. GL have specfed gudeles fo a desg vefcato pocess by meas of FEMaalyss wth CFDbased loads based o the equvalet desg wave appoach. The GL ShpLoad pogam tegates all algothms ecessay to access ad combe the data of the CFD computatos ad the FEMmodel fo geeatg the appopate CFDbased FEM loads. It also povdes a GUI to easly cotol the above load geeato pocess a tme ad costsavg mae. Ths pape descbes the techology fo couplg CFD ad FEM computatos ad fo selectg the appopate desg waves. Oe coe compoet fo lkg CFD ad FEM s a epostoy fo the shp hydodyamc esults (SHR). Aothe mpotat compoet s a algothm whch maps CFD pessues to FEM odal loads whee CFD ad FEM meshes eed ot cocde. Both the exchage fle ad the mappg algothm ae depedet of the CFD method. Theefoe, the cuetly appled effcet stp method ca be eplaced by moe advaced pocedues. 1. INTRODUCTION Stegth aalyss of shp stuctues by meas of FEM eques ealstc loads. The most ealstc loads wll esult fom CFD smulatos. GL have specfed gudeles fo a desg vefcato pocess by meas of FEMaalyss wth CFDbased loads based o the equvalet desg wave appoach [1]. The stuctual aalyss eeds to accout fo exteal loads (caused by hydodyamc pessues oto the shp hull) as well as fo teal loads (weght ad eta foces caused by the hull stuctue ad cago). Thus, pefomg desg vefcato based o CFD loads volves seveal tasks: Geeatg a FEM mesh matchg the stuctual popetes of the whole hull Selectg a set of loadg codtos to be used fo stuctual aalyss Addg masses to the fte elemet model, such as cago ad cosumables elated to those loadg codtos Geeatg a CFD mesh matchg the hull s shell Selectg appopate wave stuatos whee loads ae to be based o Computg elated pessues at the hull suface by meas of CFD smulato Computg the exteal FEM loads by mappg the pessue loads fom the CFD mesh to the FEM mesh Balacg the exteal FEM loads by appopate teal loads Pefomg the stuctual aalyss based o those FEM loads Pefomg most of the above subtasks s faly state of the at. CFD ad FEM codes ae use fo a log tme. Ad pepocessos whch assst settg up the elated meshes ae commecally avalable. I cotast, modellg cago loads a effcet mae s athe specfc to shp desg ad ot addessed by stadad tools. Thee ae some FEM codes whch povde eadytouse solutos fo applyg CFD pessue loads. Howeve, each of those FEM codes oly suppots some dedcated CFD codes (usually the CFD code fom the same softwae house ad ot the specal potetalbased codes pefeed fo shp desg). Futhemoe, some solutos mply meshg costats (such as equg cocdg FEM ad CFD meshes). Eve whe softwae compoets fo all of the above poblems ae avalable, pefomg a CFDbased stuctual aalyss wll ema a complex ad tme cosumg task: Pogams fom dffeet vedos eed to be tefaced ad executed a coodated mae. Thee mght also be ogazatoal challeges, too: Expets fom the CFD ad FEM depatmets wll eed to wok close coopeato. The GL ShpLoad pogam has bee desged to addess those poblems. It tegates all algothms ecessay to access ad combe the data of the CFD computatos ad the FEMmodel fo geeatg the appopate CFDbased FEM loads. It also povdes a GUI to easly cotol the above load geeato pocess a tme ad costsavg mae. Ths pape focuses o the techology fo couplg CFD ad FEM computatos ad fo selectg the appopate desg waves. Fo detals o othe compoets, such as
2 the tegated pepocesso fo modellg cago loads ad loadg codtos, we efe to [2]. Oe coe compoet fo lkg CFD ad FEM s a epostoy fo the shp hydodyamc esults (SHR). Aothe mpotat compoet s a algothm whch maps CFD pessues to FEM odal loads whee CFD ad FEM meshes eed ot cocde. Both the exchage fle ad the mappg algothm ae depedet of the CFD method. Theefoe, the cuetly appled effcet stp method ca be eplaced by moe advaced pocedues. 2. LOADS FOR FEM MODELS 2.1 DESIGN BENDING MOMENT APPROACH Classcal ule sets whch ae based o a beam model smply specfy some desg loads ad eque that the shp stuctue wll esst those desg loads. E.g. wth the IACS desg wave bedg momet actg, a secto modulus s equed such that pemssble stess s ot exceeded. The basc dea s that f the shp s desged to esst a appopate set of desg bedg momet loads, the shp wll esst all loads expected dug ts lfetme. Ths appoach s smple ad easly applcable. Despte ts smplcty, t s vey elable because the desg bedg momets ae based o expeece gatheed dug a log tme. The advatage of expeece desg loads s that they also accout fo ukow o uawae load effects. The dsadvatage s that expeece stogly holds oly fo desgs commo so fa. Fo ovatve desgs, expeece based desg ules mght be less elable. As the desg bedg momet appoach s based o a beam model, t does ot dectly apply to 3D FEM models. Thus, geeatg FEM loads eques geeatg a odal load dstbuto whch causes the desg bedg momets. But thee ae may odal load dstbutos whch cause the same bedg momet. Thus, thee s o uque appoach fo geeatg the coespodg FEM loads. Addtoal ules fo dstbutg the odal loads ae eeded. As a example, we efe to IACS commo stuctual ules fo takes [3] o bulkes [4] whch cota such (dffeet) ules. Rule sets typcally specfy some basc desg loads (such as hozotal bedg momet, vetcal wave ad stll wate hoggg ad saggg momets). Addtoal desg loads ae usually specfed tems of a combato of the above. The mae of combato mght also deped o the shp type ad the ule set. It should also be oted that physcal loads esult fom dffeet pheomea, such as wave pessue ad acceleatos. Applyg odal loads as above oly esues that the desg bedg momets ae eached. It does ot automatcally mply that the desg momets ae geeated by a physcally ealstc combato of pessue ad acceleato loads. 2.2 PHYSICAL LOAD APPROACH I pcple, physcally ealstc loads ca be obtaed by meas of a CFD smulato whch takes all majo hydodyamc effects to accout. Nodal loads ca be computed fom the esultg pessues ad acceleatos. A tmedepedet smulato based o the Nave Stokesequato wth a fee suface wll be eeded ode to captue all hydodyamc effects. Such smulatos eed to be caed out fo all wave stuatos whch mght occu whe opeatg the shp. Fally, a lage amout of FEesults eeds to be postpocessed. Although possble, ths would be a vey tmecosumg ad expesve task. It should also be oted that computg physcally ealstc loads lke ths does ot automatcally esult desg loads whch ae moe elable. The physcal load appoach wll oly accout fo the modelled physcal effects. Thus, makg the pope coclusos fom the physcal load smulatos s stll subject to expeece. I cotast, the expeecebased desg bedg momet appoach eve accouts fo ophyscal as well as fo ukow physcal effects. 2.3 EQUIVALENT DESIGN WAVE APPROACH The equvalet desg wave appoach s a compomse betwee the desg bedg momet ad the physcal load appoach. The appoach assumes that f the shp s desged to esst the loads caused be ceta desg waves, the shp wll esst all loads expected dug opeato. The method mplemeted GL ShpLoad chooses desg waves amog a set of hamoc waves. Each wave the set causes a ceta bedg momet whch s computed by meas of a hydodyamc smulato. The ampltude of the waves s the scaled such that at least oe wave of the set causes the desg bedg momet whle o wave wll cause lage momets. FEM loads ae computed by combg the pessue loads fom the hydodyamc calculatos wth the appopate eta loads. As a wave of the set causes the desg bedg momet, the coespodg FEM load case wll do so, too. Thus, the appoach ca also be tepeted as a specal method of geeatg FEM loads cosstet wth the desg momets. Theefoe, t hets the advatage of beg backed up by expeece. I addto to the classcal desg bedg momet appoach, t automatcally esues that loads coespod
3 to a physcally possble stuato. Fally, the desg wave loads wll be cosstet wth the classfcato socety s ules (whch ae based o the same desg momets). I cotast to the physcal load appoach, the magtude of the load depeds o the expeecebased desg momets ad ot o the physcal elablty of the CFD method. Modeate eos caused by the CFD method ae eglgble because the fally appled loads ae calbated by meas of the desg bedg momets, ayway. Thus, t s suffcet to use a smple but fast (e.g. stp) method stead o a expesve fee suface NaveStokessolve. Rule sets based o the desg bedg momet appoach usually ely o explctly specfed combatos of desg loads ode to accout fo cocdg load stuatos. I cotast, the desg wave appoach as suppoted by GL ShpLoad does ot specfy the elated desg wave apoy. Istead, t aalyses the hydodyamc esults ode to fd waves whch cause ctcal loads. 3. CONTROLING LOAD CALCULATION 3.1 MODELING The load calculato cotol pocess GL ShpLoad s desged to ely pmaly o the FE model because ths s avalable ayway. The model wll be set up by the use s favoute FEM pepocesso. I addto to the FEMmodel the pocess eques a CFD model. Fo the cuetly tegated stp method, the model ca be set up dectly by meas of the use s favoute tool. I addto, GL ShpLoad cotas a module whch ca compute a stp model fom the FE model. Thus, the use ca pefom desg wave calculatos wthout the eed of settg up a CFD model explctly. The thd class of put data cossts of mass dstbutos whch ae eeded by GL ShpLoad ode to popely accout fo weghts ad eta loads. GL ShpLoad povdes a sophstcated pepocesso fo ths task because thee ae o stadad tools avalable. Ths pepocesso allows the use to defe dffeet type of basc mass tems o a hgh level (e.g. taks, cotae bays) as well as o a low level (e.g. FEM loads o odes located wth a ceta aea). Fally, the use ca defe seveal loadg codtos tems of those mass tems. The fst step s to set up ad mpot the FE model because evey automated modellg task suppoted by GL ShpLoad s based o the FE geomety. The ext step s to set up the basc mass tems whch epeset the stuctue, equpmet, cago, o cosumables. The complete mass dstbuto fo each loadg codto s fally defed tems of those mass tems ad elated load factos. A hydostatc equlbum calculato based o these loadg codtos ad the FE geomety s fally pefomed ode to compute statc loads. 3.2 SELECTING DESIGN WAVES I cotast to modellg, whch s usually pefomed oce the begg of the load calculato pocess, selectg the appopate desg waves s a teatve pocess: A full set of waves s specfed by paametes A hydodyamc calculato elated to these waves s pefomed The esultg pessue loads ae combed wth the appopate eta loads ode to obta the total load actg o the shp stuctue. The total loads ae aalysed Based o ths load aalyss, ceta desg waves mght be selected Wave paametes o selecto ctea may be modfed ad the calculato pocess s epeated. The use ca cotol most of these steps hmself. Howeve, fo ceta stadad tasks (such as calbatg the wave ampltudes ad selectg the desg waves accodg to GL s pocedue) automatc cotol modules ae also povded. The teal desg of GL ShpLoad ams to decouple the hydodyamc calculato fom the load selecto cotol as much as possble. The CFD code deposts ts esults a hydodyamc esult database whch s depedet of the CFD method. Ths wll allow eplacg the cuetly bult stp solve wth othe CFD codes easly. As the equvalet desg wave appoach ams at beg compatble wth the desg bedg momet appoach, load aalyss s based o secto load dstbutos. A exteal secto load dstbuto s computed fom the pessues whch ae ead fom the esult database. The teal secto load dstbuto s computed fom the mass dstbuto elated to the loadg codto. Ths s doe by computg the sx eta foce dstbutos esultg fom ut acceleatos wth espect to the shps gd body modes. A appopate lea combato of these sx foce dstbutos s added to the exteal foce dstbuto such that the total foce s zeo. Plots of the secto load dstbutos ca be spected dectly by the use. Selectg ctcal desg waves automatcally s suppoted by a seach featue. The use specfes a fuctoal tems of the secto load
4 dstbuto whch should be maxmsed o mmsed. Fo example, t s possble to automatcally fd the wave whch causes the lagest value of hozotal plus vetcal bedg momet. 3.3 GENERATING FEM LOADS Afte a set of ctcal desg waves has bee selected, FEM loads elated to these waves ca be geeated. The pessue loads elated to the selected waves ae ead fom the hydodyamc esult database. GL ShpLoad cotas a sophstcated module whch aalyses the geomety of the CFD mesh ad the FEM mesh ad maps the CFD pessue to FEM odal loads. The esultg exteal FEM loads ae balaced agast teal loads such that the total load oto the FEM model s zeo. 4. THE SHIP HYDRODYNAMIC RESULT REPOSITORY (SHR) 4.1 PURPOSE AND GENERAL IDEAS The SHR data model ad fle fomat ams at povdg a commo teface fom CFD codes to othe pogams. The CFD codes wll stoe the esults a eutal data fle. Othe pogams fo shp stuctual aalyss ad desg wll ead the CFD esults fom that eutal data fle. It s estcted to data eeded by shp desg tools whch wat to apply CFD based loads. It s ot teded to be a eutal hydodyamc model fle ay way (would be dffcult wth all those athe dffeet hydodyamc methods use). The focus s o stog the esults of the hydodyamc calculatos. These ae usually pessues, but othe esult types such as flud potetals ae also possble. The fle also stoes some basc fomato about the CFD model geomety a CFDmethoddepedet mae. Ths s estcted to data whch s eeded by stuctual aalyss codes ode to apply pessueduced loads. It s geeally ot possble to epoduce the CFD model geomety fom the fomato peset the SHR fle. Pessue esults ae stoed oly fo locatos whee the flud doma bouday faces the shp stuctue. Results elated to othe locatos ae ot eeded fo computg stuctual loads (ad some CFD methods do t compute them, ayway). I addto to the esults of CFD computatos the fle fomats suppots stog of the load attbutes (such as wave paametes) elated to the esults. Thus, the load paametes ca be accessed by subsequet pogams ode to select ceta esults, to pefom evaluatos whch deped o ceta load paametes explctly o to tepolate betwee esults. The data model s based o the followg pcples: pcpal esults ae pessue felds actg o a twodmesoal suface pessue esults ae peset fo seveal load cases load attbutes (e.g. wave paametes) ca be stoed sepaately. Fo each stoed load case esult, a efeece to elated load attbutes s mataed. 4.2 GEOMETRY Pessue esults ae stoed fo a dscete set of pessue feld pots located at the hull s shell. Oly some vey basc geometc fomato elated to those pessue esult pots ae mataed by two spatal attbutes: The locato x of each pessue esult pot s stoed by meas of ts catesa coodates. The decto ad sze of the pessue aea whch s dscetzed by pot s stoed by meas of a aea vecto o a. Ths basc fomato s ecessay ad suffcet fo locatg close fte elemets ad odes, computg pessueduced foces f = p a. No patcula sematcs wth espect to the CFD model s mpled by ths. Depedg o the CFD method, the values mght be obtaed fom dffeet model tems, e.g.: Pael method: locato = pael s cete of gavty, aea vecto = omal vecto of pael. Stp method: locato = collocato pot of coss secto cuve, aea vecto paallel to coss secto plae, legth detemed fom dstace to eghbou stps ad eghbou collocato pots. Fte volume method: aea vecto = omal vecto of those cell faces fomg the flud doma bouday, locato = cete of gavty of these faces. The computato of pessueduced foces as well as seach stateges fo locatg close fte elemet tems does ot deped o the ogal sematcs of these spatal attbutes. Thus, the esults stoed a SHR fle ca be used depedetly fom the CFD pogam whch has wtte the fle. Although the above spatal attbutes ae suffcet fo pocessg the pessue esults we mght be teested moe specfc fomato about the aea whch s dscetzed by a pessue esult pot. Wth most CFD models, such aeas ae (o ca be appoxmated by) polygos. As a optoal thd spatal attbute, the SHR
5 data model suppots stog the vetces of these polygos. Fo pael o fte volume methods, whch aleady defe the model tems of vetces, these ca be dectly take fom the flud mesh. Fo stp methods, a easoable choce mght to compute fou vetces by shftg x half the way towads eghbou odes ad eghbou stps. Aga, futhe computatos do ot deped o the ogal sematcs of the polygo vetces. Pogams pocessg the SHR esults ema depedet of the CFD method. 4.3 LOAD PARAMETERS Load esults wll elate to ceta load paametes. Thee ae seveal classes of load paametes, such as wave paametes (e.g. wave vecto, ampltude) evometal paametes (e.g. wate desty, depth) opeatoal paametes (e.g. speed, cete of gavty, mass) Pogams accessg the CFD esults wll fequetly also eed access to the load paametes elated to the esults. Theefoe, the SHR data model also suppots stog load attbutes. Ufotuately, the load attbutes whch chaacteze a ceta load mght deped o the hydodyamc method. Fo example, loads elated to tme step fom a tme doma smulato wll be chaactesed by a `tme attbute. Fo a CFD pogam opeatg fequecy doma, a `tme attbute wo t make sese but a `fequecy attbute wll be appopate. Fo ths easo, the SHR data model keeps load attbute data ad CFD esult data as sepaated as possble. Applcatos mght access load attbutes wthout eadg CFD esults. O they mght access the CFD esults wthout eadg the load attbutes. The elatoshp betwee the esults ad the coespodg load attbutes s also stoed sepaately. Ths allows addg ew types of load attbutes at wll wthout beakg exstg applcatos. Nevetheless, ay applcato teested the ew load attbute type wll be able to access t. 4.4 PRESSURE RESULTS A pessue esults elates to a dscetzed pessue feld ad a load case. Thus, a logcal aay s used fo stog such esult. The fst dmeso exteds alog the spatal attbutes axs, the secod alog a load case axs. I addto to the pessue esults pope, a load case detfe s stoed alog the load case axs wheeve a pessue esult s wtte. The same load case s also used to mak load attbute data elated to the just wtte esults. Ths wll allow eadg applcatos to match CFD esults ad elated load attbutes by meas of the load case detfe. It mght sometmes be useful to stoe dffeet esult compoets whch elated to the same pessue feld ad load data. E.g. t s sometmes usefully to hydodyamc ad dstctly fom the quasstatc pessue. Ths s suppoted by meas of a thd dmeso elated to the esult compoet. The physcal sematcs of the values elated to each esult compoet mght be emembeed by stog some esult type detfes as compoet attbutes. Some CFD methods yeld complexvalued esults. Iteally, the eal ad magay pat mght ae teated as a fouth dmeso. 4.5 IMPLEMENTATION BY MEANS OF HDF5 HDF5 [5] s a stoage scheme whch was desged ad mplemeted by NCSA fo stog lage amouts of scetfc umec data. It ogazes the data lke a fle system: Thee ae datasets (whch coespod to fles). The datasets ae stuctued lke multdmesoal aays. The data s stoed compactly a bay mae. The data stoage s potable. It ca be wtte ad ead usg dffeet opeatg systems ad hadwae achtectues. Thee ae HDF5 goups (coespodg to dectoes) whch cota datasets o othe HDF5 goups. Ths allows ogazg the data a heachcal mae. The ope souce lcese does ot estct commecal use. Due to these featues, the SHR epostoy ca be mplemeted easly ad effcetly o top of HDF5. Pessue esult aays ae dectly mplemeted as HDF5 datasets. Radom access to selected load cases s suppoted by HDF5 methods. Tableoeted data ca be easly epeseted by a HDF5 goup cotag datasets coespodg to the table colums. 5. MAPPING PRESSURES TO FEMLOADS 5.1 GENERAL CONSIDERATIONS I ode to keep geealty ad flexblty, a algothm fo mappg CFD pessue esults to FEM loads should ethe deped o the FEM pogam o o the CFD method. As the FE model ad the CFD model wll dffe, the fte elemets subject to the pessue loads wll ot cocde wth a elated CFD model tem. Eve wose, thee wll usually be gaps betwee both mesh sufaces.
6 Thee ae some fte elemet pogams whch allow defg loads tems of pessues oto elemet sufaces. Howeve, ths ca be msgudg. Although tutve at fst, we aleady u to tepetato poblems whe the meshes do t match: How should pessues be tepolated the? If flud elemets ad fte elemets ae ot alged paallel the decto of elated pessue foces wll be dffeet. Thus, foces ae hadly coseved by a aïve pessue mappg appoach. We should be awae that the eal poblem s ot to tasfe pessues fom the flud mesh to the FEM mesh but to tasfe the foces esultg fom the CFD smulato to foces oto the stuctual model. I cotast, mappg foces ca be coceptually vey smple. Fo each pessue esult, we just eed to select some FE odes ad dstbute the pessue foce oto those odes such that the sum of the output foces equals the put foce. Thus, tasfeg foces stead of pessues s theefoe moe obust ad cosevg the total foce actg o the model ca be acheved easly. Ad t keeps depedece because t s ot estcted to FEM codes suppotg pessue loads. I pcple, mappg foces lke ths cossts of the followg: Fo each pessue esult p (actg at locato x ), select some FEM odes (located at Compute the pessue foce x, f = p a Dstbute that pessue foce amog the selected odes such that foce s coseved: = f f, momet s coseved f ( x x ) = 0,, It s geeally possble to choose appopate weghts f w f ) (1) (2), =, (3) such that the above codtos ae fulflled. Ths geeal appoach s vey flexble about the selecto of FEM odes whee the mapped foces shall be actg. As log as each pessue esult s dstbuted oto the odes a mae cosevg foce ad momets of a local pessue esult, total foce ad momets wll be peseved. I pactce, we ae also teested the local qualty of the esultg foce dstbuto. Theefoe, we eed a moe specfc ad advaced algothm whch detemes appopate taget odes ad weghts. 5.2 FINDING MATCHING FINITE ELEMENTS Fo easoable local mappg qualty, oly the FEM odes the eghbouhood of a pessue esult pot shall be subject to the elated pessue foces. Thus, the fst step of a cocete mappg pocedue cossts of a algothm whch detemes a appopate set of `eghbouhood odes. Fo each pessue esult locato, the algothm appled GL ShpLoad fst selects a uque fte elemet whch s cosdeed closest to the pessue esult locato. The the odes of that closest elemet ae added to the eghbou ode set. Oly those elemets whch costtute the hull s shell ae cosdeed the seach. The same elemet set has aleady bee eeded a pevous (hydostatc) computato step. Theefoe, t has aleady bee defed by the tme whe the hydodyamc esults shall be mapped. A pessue esult at locato x actg decto of a suface aea vecto a defes a le 3D space L( t) = x + ta. (4) The elemets of the shell whch ae tesected by that le ae detemed. If thee ae seveal tesected elemets the the elemet wth the smallest dstace fom x (wth espect to decto a ) s selected. I pactce, the tesecto test s most easly pefomed afte pojectg the elemet vetces ad the esult locato to a twodmesoal plae whch s pepedcula to a. The tesecto test s the equvalet to a potpolygo test (pojecto of x s sde the polygo whch s fomed by the pojected elemet edges). 5.3 MAPPING TO SINGLE ELEMENTS GL ShpLoad suppots mappg pessue foces to the odes of tagula o quadlateal elemets. All odes wll eceve foces wth the same decto (paallel to a ). Thus, the poblem educes to detemg some odal weghts accodg to (3). GL ShpLoad detemes the tal odal weghts fom a fom fucto fomulato elated to the elemet. The odes of the suface elemets ae pojected oto the plae omal to the aea vecto a (`flud pael plae ). The pojected odes x wll defe a polygo (tagle o quadlateal). The pojecto of the pessue esult locato x wll be sde the polygo because the le (4) tesects the ogatg elemet.
7 Computg the weghts by meas of fom fuctos automatcally esues that oly oe ode s loaded f that ode cocdes wth the pessue esult locato. 5.4 HANDLING OVERLAPPING ELEMENTS Usg the ode selecto pocedue descbed so fa, oly the odes of a sgle elemet wll eceve foces elated to a patcula pessue esult pot. Ths usually yelds easoable foce dstbutos f the flud mesh s fe tha the FEM mesh. Ths s fequetly the case whe applyg the physcal load appoach whee athe fe flud meshes ae commo. I cotast, fo the equvalet desg wave appoach athe coase flud models ae suffcet. Wth GL ShpLoad s bult stp solve, adjacet stps typcally spa seveal fte elemets. If pessue foces ae oly dstbuted o the odes of the closest elemet, some odes wll be subject to lage cocetated pessue foces. I tu, some odes (of elemets whch ae ot tesected by ay le (4)) wll eceve o pessue foce at all. Ths s ot ctcal fo global stegth aalyss. But t mght become a coce whe local pessueduced bedg effects shall be vestgated. Fxg ths eques a lage set of odes subject to the pessue foces. Havg foud these odes, we deteme appopate odal weghts (3) fo the elaged ode set. Detemg above odes eques a moe specfc geometc descpto of the aea whch elates to each flud esult locato. That fomato s also ead fom the SHR fle whch eeds to cota the esult aeas vetces. GL ShpLoad detemes the ode set by detfyg those fte elemets whch ovelap wth the flud esult ego. The the odes of these elemets ae selected. The ovelappg elemets ae detemed ecusvely. It stats wth a tal elemet whch s detemed as descbed 5.2. Its adjacet elemets ae cosdeed. Adjacet ovelappg elemets ae added to the elemet lst. Lkewse, the adjacet eghbous of the ewly added elemets ae pocessed ecusvely. The above algothm depeds o a test whch detemes whethe a fte elemet ad the flud esult aea do ovelap. The tem ovelap does ot dectly make sese a theedmesoal cotext wth omatchg gds because flud esult aea ad fte elemets mght be sepaated by a ceta dstace. Theefoe, a specfc ovelap test (ad othe computatos) wll be pefomed afte pojectg the flud esult aea ad the fte elemets to the sgle efeece plae. Afte the odes ae selected, the weghts (3) eed to be detemed. Fo each flud esult the weghts wll be computed ad accumulated elemetwse: Loop ove all flud esult pots (at locato suface aea vecto a ): x, wth compute the pojected flud esult aea polygo P Deteme the ovelappg fte elemets e ad the odes v, Reset all odal weghts w : 0, = Loop ove all ovelappg elemets e : Compute the pojected elemet polygo Compute the tesecto polygo P E j j E j Compute the tesecto polygo s cete of gavty x j Compute local mappg weghts wk fo the odes of the cuet ovelappg elemet e j by meas of the same method as 5.3, but usg the tesectos cete of gavty x stead of x as pessue esult locato. Compute the aea a of the tesecto polygo j Update the odal weghts w a a w w + ( / ), ( k ) : =, ( k ) 5.5 FIXING CONSERVATION PROPERTIES The above algothm wll usually esult a odal foce dstbuto whch vsually matches the ogatg pessue foce dstbuto faly well. Howeve, total foce ad momet o the FEmodel wll usually slghtly devate fom the ogatg CFD esult. Thee ae seveal easos: The fom fucto method appled to sgle elemets does ot automatcally peseve the momets as (2) Flud mesh ad FEM mesh do t match exactly. At locatos close to model edges of the FE model, thee mght be some elemets whch ae oly patally coveed by flud elemets o some flud aeas whch ae oly patally coveed by fte elemets. At those locatos, some facto of the foce mght be lost ad some spuous momets wll be geeated. Thee mght be some locatos whee pojecto of the fte elemets esults degeeated polygos whch mght cause some computatos to fal. Uless thee ae seous model msmatches, the devatos wll be small ad acceptable fo applcatos lke the equvalet desg wave appoach. Howeve, compag total FEM wth CFD loads s a good eo check oly f the mappg algothm peseves the total foce. Some othe applcatos, lke tme doma smulatos, mght eve be sestve to spuous foces j k j j
8 ad momets duced by ocosevatve foce mappg. As a pagmatc measue, the mappg weghts w, ae fally modfed by addg a appopate lea combato of w,, ξ, w, ad ζ, w, such that the cosevato equatos (1) ad (2) ae fulflled ξ adξ ae the local coodates of the odes the (,, pojecto plae). 6. CONCLUSIONS Applyg the pevously descbed techologes, shp desges ae able to pefom stuctual FEMaalyss wth CFDbased loads, outely. The addtoal ovehead elated to fludstuctue couplg s eglgble. The majo computatoal esouces ae cosumed by the CFD smulato. Oly modeate esouces ae eeded whe applyg the equvalet desg wave appoach wth a stp method. Most huma wokg tme s eeded fo modellg the mass dstbutos elated to the loadg codtos. Ths task s aleady suppoted by GL ShpLoad a effcet mae. The eutal SHR fle ad the pogam lbay whch maps pessues to odal foces has also bee successfully used outsde the cotext of GL ShpLoad patcula fo geeatg FEM loads fom fte volume CFD smulatos. Ths cofms that depedece of the CFD methods s acheved pactce. 7. ACKNOWLEDGEMENTS Some deas whch ae appled the pessuetoodalfoce mappg have bee sped by the jot Euopea eseach poject ESPRIT `CISPAR (Ope Iteface fo Couplg of Idustal Smulato codes o Paallel Systems) whch was fuded by the Euopea Commsso. 8. REFERENCES 1. Gemasche Lloyd AG, GLGudele V, Pat 1, Chapte 2, Secto 2 Global Stegth Aalyss (Edto 2007), Gemasche Lloyd AG, Hambug, `Rules ad Gudeles 2007 (publshg pogess), Chsta Cabos, Hee Ese, Matthas Köme, GL.ShpLoad: A Itegated Load Geeato Tool fo FEAalyss, Poceedgs of the COMPIT 2006, Delft, IACS membes, Commo Stuctual Rules fo Double Hull Ol Takes, Edto Jauay 2006, Publshed by Gemasche Lloyd AG, Hambug, `Rules ad Gudeles 2007, IACS membes, Commo Stuctual Rules fo Bulk Caes, Edto Jauay 2006, Publshed by Gemasche Lloyd AG, Hambug, `Rules ad Gudeles 2007, The HDF Goup, HDF5 Home Page, August 15 th AUTHORS BIOGRAPHIES Hee Ese studed mathematcs ad physcs ad s wokg as a seo poject egee the CAE developmet depatmet of Gemasche Lloyd. He s pefomg eseach ad developmet data modellg ad computatoal methods, patcula elated to fludstuctueteacto ad stuctual fatgue smulato. Chsta Cabos studed mathematcs ad physcs ad dd hs PhD o methods fo computg shp vbato. He woks fo Gemasche Lloyd sce 1989 ad s esposble fo the depatmet CAE developmet sce He s pefomg eseach data modellg ad computatoal methods matme egeeg. A tal desg ad mplemetato of the SHR data model was caed out whle patcpatg the jot Gema eseach pogamme `WIPS (Wettbewebsvotele duch Ifomatostechsch utestützte Poduktsmulato m Schffbau Compettve Shp Techology though ITbased Poduct Smulato) whch was fuded by the Gema Fedeal Msty of Educato ad Reseach (BMBF).
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