內(nèi)容教程講稿subs-l12practices

1、Lesson content:Perturbation Analysis Changing Procedures The Frequency Domain Submodeling and Thermal Stress AnalysisExample: Thermal Strain in a BarSubmodeling in Dynamic Procedures Example: Speaker Diaphragm (1/7)Lesson 12: Submodeling Practices1 hourPerturbation AnalysisThe linear perturbation st

2、atic procedure allows you to study a submodels linearized response corresponding to a particular point in time in the global solution.The INC parameter on the *BOUNDARY, SUBMODEL option is used:*BOUNDARY, SUBMODEL, STEP=k, INC=i where step k, increment i is the point in time in the global solution f

3、or which local, detailed response is sought.If the INC parameter is omitted, the last increment of the selected step is used.The INC parameter cannot be used in a general (nonperturbation) submodel step.Changing Procedures (1/4)It is possible to treat general analysis steps as linear perturbation st

4、eps during submodeling, and vice versa.For example, in a three-step global analysis:Static preload (general analysis step).Natural frequency extraction including preload effects (perturbation step).Analyze 5 seconds of modal dynamic response (perturbation step). Surface-based and Node-basedChanging

5、Procedures (2/4)Model for the global analysis would include:*Step, nlgeom Apply static preload*Static 0.1, 1.0 : loads, : boundary conditions, : output requests, etc.*Node output, nset=detail U*End step*Step Get eigenmodes and eigenfrequencies*Frequency :*Node output, nset=detail U*End step*Step Mod

6、al dynamic response*Modal dynamic 0.01, 5.0 :*End stepChanging Procedures (3/4)Now examine the submodel:If the submodel region of the global model is small enough that dynamic effects need not be modeled locally inertia effects are negligible then the submodel analysis can be done in two general sta

7、tic analysis steps.Changing Procedures (4/4)*Heading :* define submodel boundary via nset PERIM*SubmodelPERIM*Step, nlgeom* Static preload*Static 0.1, 1.0*Boundary, submodel, step=1 :*End step*Step* Local static response to global modal dynamic step*Static 0.01, 5.0*Boundary, submodel, step=3 :*End

8、stepSubmodel driven by results of static preload stepStatic response of submodel is driven by dynamic response of global modelThe Frequency Domain (1/2)Submodeling in the frequency domain is available only with the direct steady state dynamics procedure.Other options do not allow driven boundary con

9、ditions.The frequency range of the submodel must lie within the maximum and minimum frequencies calculated in the global model, or the results will not be accurate.Both the amplitude and the phase of the nodal displacements in the global model must be saved to drive the submodel.Abaqus will interpol

10、ate the global solutions spatially and in the frequency domain.Results are most accurate when the frequencies requested in the submodel match the frequencies at which the response was calculated in the global modelparticularly in the vicinity of the global models natural frequencies.Node-based OnlyT

11、he Frequency Domain (2/2)Submodeling in the frequency domain is available only with the direct steady state dynamics procedure.Other options do not allow driven boundary conditions.The frequency range of the submodel must lie within the maximum and minimum frequencies calculated in the global model,

12、 or the results will not be accurate.Both the amplitude and the phase of the nodal displacements in the global model must be saved to drive the submodel.Node-based OnlySubmodeling and Thermal Stress Analysis (1/4)The steps for the sequentially-coupled case are as follows:Run a global heat transfer j

13、ob (mesh1).If necessary:Run a submodel heat transfer job (mesh2).Use the global heat transfer job results to drive the submodel boundary temperatures.Run a global thermal stress job (mesh3; may be different from mesh1). Read the temperatures from the global heat transfer job.Run a submodel thermal s

14、tress job (mesh4; may be different from mesh2).Use the global thermal stress job results to drive the submodel boundary displacements and rotations.Read the temperatures from any of the preceding analyses.Submodeling and Thermal Stress Analysis (2/4)Schematic:Global model (mesh1)*Heat transferSubmod

15、el (mesh2) - optional*Submodel*Heat transferGlobal model (mesh3)*Static*Temperature, file=global_heat.odbSubmodel (mesh4)*Submodel *Static*Temperature,file=global_u.odb or*Temperature,file=global_heat.odbor*Temperature,file=submodel_heat.odbglobal_heat.odbInterpolate from mesh1 to mesh3global_heat.f

16、ilglobal_heat.odbsubmodel_heat.odbInterpolate from mesh2 to mesh4global_u.filglobal_u.odbglobal_heat.odbInterpolate frommesh1 to mesh4Submodeling and Thermal Stress Analysis (3/4)Sequential thermal-stress analysesThere are two approaches to submodeling within a sequential thermal-stress analysisTher

17、mal global modelStress global modelThermal submodelStress submodelSubmodel procedureSubmodel procedureResult MappingResult MappingResult MappingThermal global modelStress global modelStress submodelSubmodel procedureResult MappingSubmodeling and Thermal Stress Analysis (4/4)In cases where complex he

18、at transfer effects occur within the submodel, performing a heat transfer submodel may yield more accurate results than mapping temperatures directly from the global stress model.In these cases, there will generally be a temperature discrepancy between the global thermal solution and the submodel th

19、ermal solution.This discrepancy can lead to unnatural thermal straining in the structural submodel, which can affect stress results when displacement based submodeling boundary conditions are used.Use of stress-based submodeling in these cases can result in more accurate stress results.Without therm

20、al submodeling, stress based submodeling will provide results comparable with displacement based submodeling, except in other noted cases (stiffness changes, etc.). Example: Thermal Strain in a Bar (1/14)OverviewThis example demonstrates how a different modeling approaches can yield dramatically dif

21、ferent resultsIt highlights the importance of understanding the problem before designing your analysis procedureThe example shows a simple 2-D bar loaded with a highly varied, non-uniform body heat fluxSchematic of thermal strain problemapplied across this body Non-uniform heat flux Thermal BC: Pres

22、cribed temperatureStructural BC: Symmetry Example: Thermal Strain in a Bar (2/14)Reference solutionFor the purposes of comparison, we run a reference analysis, with a suitable mesh to capture the thermal and stress profilesReference thermal results contour plotReference stress results contour plotEx

23、ample: Thermal Strain in a Bar (3/14)The procedure is the same as in previous examples, and the circled numbers refer to the workflow described earlierThis is the global model mesh, showing the submodel region in red and the applied heat flux load aboveRun the global thermal model, then the global s

24、tructural model (mapping the temperatures from the global thermal solution)12Example: Thermal Strain in a Bar (4/14)The global model resultsResults for both the thermal and the structural modelGlobal thermal results contour plotGlobal stress results contour plot3Example: Thermal Strain in a Bar (5/1

25、4)Thermal submodelThermal submodel definition4Heat flux applied to bodySubmodel boundary conditions applied (temperatures)56Example: Thermal Strain in a Bar (6/14)Structural submodelStructural submodel definitiononly one of these options requiredTemperatures mapped to all nodesSubmodel boundary cond

26、itions OR surface tractions applied654Example: Thermal Strain in a Bar (7/14)Submodeling approachWith the submodel defined, there are two possible approaches to considerMethod 1 Drive the structural submodel with results from the structural global model and the thermal global modelMethod 2 Perform a

27、 thermal submodel analysis first, then drive the structural submodel with results from the structural global model (as before) and the thermal submodelEach method can be performed using surface-based or node based submodeling to drive the stress submodel Example: Thermal Strain in a Bar (8/14)Method

28、 1 Without a thermal submodelThis method skips the thermal submodel, and drives the structural submodel with temperatures from the global thermal model and loads from the global structural modelIn this case the nodes of the submodel are driven by the global structural modelNode-based SolutionLegend

29、scale different to reference results for clarity8aExample: Thermal Strain in a Bar (9/14)Method 1 Without a thermal submodelThis method skips the thermal submodel, and drives the structural submodel with temperatures from the global thermal model and loads from the global structural modelIn this cas

30、e the surfaces of the submodel are driven by the global structural modelSurface-based SolutionLegend scale different to reference results for clarity8bExample: Thermal Strain in a Bar (10/14)Method 1 results without the thermal submodelThese graphs compare the Mises stress results along the length o

31、f the submodeled region for the analysis without the thermal submodel.The global and submodel results agree well with each other, but not with the reference solutionMises Stress102030 x103Distance across submodeled regionNode- and surface-based submodel solutions (almost identical)Global modelRefere

32、nce solution9Example: Thermal Strain in a Bar (11/14)Method 2 Using a thermal submodelThis method performs a thermal submodel analysis driven by temperatures mapped from the global thermal model and loaded with the same surface heat flux There is clearly a complex thermal solution in the submodel7bE

33、xample: Thermal Strain in a Bar (12/14)Method 2 Using a thermal submodelThe results of both the thermal submodel AND the structural global model are mapped onto the structural submodelIn this case the nodes of the submodel are driven by the global structural modelNode-based Solution8bExample: Therma

34、l Strain in a Bar (13/14) Method 2 Using a thermal submodelThe results of both the thermal submodel AND the structural global model are mapped onto the structural submodelIn this case the surfaces of the submodel are driven by the global structural modelSurface-based Solution8cExample: Thermal Strai

35、n in a Bar (14/14)Method 2 results with the thermal submodelClearly, in these cases it is important to use the second method and run a thermal submodel to capture the local thermal behavior.Now, the node-based submodel results are improved, and the surface-based submodel results agree very well with

36、 the reference solution.Reference solutionGlobal modelMises Stress102030 x103Distance across submodeled regionNode-based submodelSurface-based submodel9Submodeling in Dynamic Procedures (1/3)The submodeling capability can be used in dynamic procedures using explicit integration (Abaqus/Explicit) and

37、 implicit direct integration (Abaqus/Standard). Thus, can drive an Abaqus/Standard submodel with either an Abaqus/Standard or an Abaqus/Explicit global model.Alternatively, can drive an Abaqus/Explicit submodel with either an Abaqus/Standard or an Abaqus/Explicit global model.Node-based OnlySubmodel

38、ing in Dynamic Procedures (2/3)Generally, the same time scales should be used in the global model and the submodel.This is particularly true in problems in which inertial forces are significant (i.e., highly dynamic problems).For quasi-static analyses, however, the time period of the global model an

39、d submodel can be different. Scale the time variable of each driven nodes amplitude function to match the submodel analysis step time.In dynamic submodeling, output from the global model should be at a high enough frequency to avoid aliasing problems (under sampling).The displacement results for the

40、 nodes that are used to drive the submodel should be saved for each increment.Submodeling in Dynamic Procedures (3/3)Acoustic-to-structure submodelingThis technique is useful in situations where the structural response is of primary interest and the presence of the (heavy) fluid is required mainly f

41、or the application of the load onto the structure. The global model is a coupled structural-acoustic analysisThe submodel is an uncoupled structural force-displacement analysisInterpolated acoustic pressures converted to concentrated loadsDriven nodes are specified by defining an element-based surfa

42、ceShell surfaces can be driven on both sides by different acoustic domainsUsage:*SUBMODEL, ACOUSTIC TO STRUCTURE surface_name*BOUNDARY,SUBMODEL, STEP=n node_set, 8Example: Speaker Diaphragm (1/7)The problem consists of a large over-pressure transient acting upon a speaker diaphragm and voice coil.Pl

43、astic (red)Copper (blue)Epoxy (green-solid)Rigid bodies (green-wire)region 2region 1pressure load applied to top surface of plasticspeakerdiaphragmvoice coilExample: Speaker Diaphragm (2/7)The acoustic and structural responses are assumed uncoupled since the scattered pressures induced by the diaphragm vibrations will be an order of magnitude less than the incident pulse. The pressure load and its variation are shown below.The region behi