김경종
222 lines
16 KiB
Markdown
222 lines
16 KiB
Markdown
<!-- source-page: 751 -->
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# Copying or moving a substructure definition
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You can copy a substructure definition from one library to another or from one substructure to another within the same library. You must identify the substructure being copied and assign a name to the substructure being created.
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When copying substructures from library to library, you can identify the name of the library containing the substructure being copied. Similarly, you can identify the name of the new library to which the substructure will be copied. This new library need not exist prior to the substructure being copied; it will be created in this case.
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If the original substructure is to be deleted, you can follow the copy with a delete (see above).
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Input File Usage: \*SUBSTRUCTURE COPY, OLD TYPE=Zn, NEW TYPE=Zn, OLD LIBRARY=substructure\_library\_name, $\mathrm { N E W \ L I B R A R Y } { = } s u b s t r u c t u r e \ L i b r a r y \_ n a m e$
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Abaqus/CAE Usage: Substructure libraries are not supported in Abaqus/CAE.
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# Renaming substructure libraries
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Once a substructure library has been generated, the disk file should not be renamed manually. To rename a substructure library, copy the existing substructures to a new library. The new library need not exist prior to the first substructure being copied. You can then delete the original disk file manually if you do not need it anymore.
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<!-- source-page: 752 -->
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<!-- source-page: 753 -->
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# 10.2 Submodeling
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• “Submodeling: overview,” Section 10.2.1
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• “Node-based submodeling,” Section 10.2.2
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• “Surface-based submodeling,” Section 10.2.3
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# 10.2.1 SUBMODELING: OVERVIEW
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Products: Abaqus/Standard Abaqus/Explicit Abaqus/CAE
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# References
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• “Node-based submodeling,” Section 10.2.2
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• “Surface-based submodeling,” Section 10.2.3
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• \*SUBMODEL
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• Chapter 38, “Submodeling,” of the Abaqus/CAE User’s Guide
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# Overview
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The submodeling technique:
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• is used to study a local part of a model with a refined mesh based on interpolation of the solution from an initial (undeformed), relatively coarse, global model;
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• is most useful when it is necessary to obtain an accurate, detailed solution in a local region and the detailed modeling of that local region has negligible effect on the overall solution;
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• can be used to drive a local part of the model by nodal results, such as displacements (see “Nodebased submodeling,” later in this section), or by the element stress results (see “Surface-based submodeling,” later in this section) from the global mesh;
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• can be used to analyze an acoustic model driven by displacements from a structural, global model when the acoustic fluid has negligible effect on the structural solution;
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• can be used for the analysis of a structure driven by acoustic pressures from an acoustic or coupled acoustic-structural, global model;
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• can use a combination of Abaqus/Explicit and Abaqus/Standard procedures;
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• can use a combination of linear and nonlinear procedures; and
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• cannot be used in an import analysis.
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# Terminology
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The model whose solution is interpolated onto the relevant parts of the boundary of the submodel is referred to as the “global” model (even though it may itself be a submodel of a larger “global” model). Driven variables are defined as those variables in the submodel that are constrained to match results from the global model. Driven variables can be degrees of freedom at nodes in the node-based technique, or they can be components of stress tensor at the integration points of element faces in the surface-based technique.
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Submodeling can be applied quite generally in Abaqus. The material response defined for the submodel may be different from that defined for the global model. Both the global model and the submodel can have nonlinear response. See “Shell-to-solid submodeling and shell-to-solid coupling of a pipe joint,” Section 1.1.10 of the Abaqus Example Problems Guide, for an example application of the submodeling technique.
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Vehicle-occupant/pedestrian interaction simulations are an example where the submodeling technique can be used efficiently. Crash safety simulation generally includes interaction between a vehicle and its occupant or a vehicle and a pedestrian. In some cases the influence of the human on the structural response of the vehicle is so small as to be negligible. In these cases, the global analysis of the vehicle is performed without the human or with a simple representation of the human, and the part of the vehicle surrounding the human is then used via the submodeling technique to study the detailed interaction with a number of human models.
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Submodeling is classified first according to which of two basic techniques is used. The most common, and more general technique, is node-based submodeling, which uses a nodal results field (including displacement, temperature, or pressure degrees of freedom) to interpolate global model results onto the submodel nodes. The alternative surface-based technique uses the stress field to interpolate global model results onto the submodel integration points on the driven element-based surface facets.
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You can choose either the node-based or surface-based technique or a combination of the two in your submodel. The following factors should be considered in deciding on the technique to be used:
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• Whether you are performing solid-to-solid submodeling in a general static analysis in Abaqus/Standard:
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– Surface-based submodeling is available only for solid models and static analyses.
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– For all other procedures use the node-based technique.
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• Whether the global model and submodel differ significantly in their average stiffness in the region of the submodel:
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When the stiffness of the models is comparable, node-based submodeling of displacements will provide comparable results to the surface-based technique with a lesser likelihood of numerical issues associated with rigid-body modes.
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– When the stiffness of the models differs and the global model is exposed primarily to a load-controlled environment, the surface-based technique will generally provide more accurate stress results. Stiffness differences may arise due to additional detail in the submodel, such as explicit modeling of a fillet or a hole. In other cases stiffness changes may result from minor geometry changes for which a reanalysis of the global model is not warranted.
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• Whether your model is subjected to large deformations or rotations:
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– Node-based submodeling of displacements will result in more accurate transmission of large deformation and rotation to the submodel.
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• Whether the displacement response of the global model corresponds to the displacement response of the submodel:
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– When the displacements in the global model correspond closely with the expected displacements in the submodel, node-based submodeling is generally preferable.
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– Surface-based submodeling should be used when the submodel displacement response is expected to differ from the global model response. This situation can occur when thermal strains are modeled and the temperature history of the submodel differs from that of the global model; for example, when heat transfer submodeling is performed as part of a sequential thermal-structural analysis.
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• The stiffness of the structure:
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– Surface-based submodeling may provide more accurate results for very stiff structures. When the structure is so stiff that only a small component of the global model displacement field contributes to the stress response, numerical roundoff in the displacement results can become significant; for example, when the global model displacement is dominated by a rigid-body motion component.
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• The type of output you are interested in from the submodel:
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– Node-based submodeling of displacements will result in more accurate transmission of a displacement field.
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– Surface-based submodeling will result in more accurate transmission of a stress field, and determination of reaction forces in the submodel.
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You can use both node-based submodeling and stress-based submodeling in the same model.
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# Node-based submodeling
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Node-based submodeling is the more general technique, supporting a variety of element type combinations and procedures in both Abaqus/Explicit and Abaqus/Standard.
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Input File Usage: \*SUBMODEL, TYPE=NODE
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Abaqus/CAE Usage: Load module: Create Boundary Condition: choose Other for the Category and Submodel for the Types for Selected Step: Driving region: Specify
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# Element types supported
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Different element types can be used in the submodel than those used to model the corresponding region in the global model.
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The following types of submodeling are provided for the node-based approach (global-tosubmodel):
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• Two-dimensional models:
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– Solid-to-solid
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– Acoustic-to-structure
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<!-- source-page: 758 -->
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• Three-dimensional models:
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– Solid-to-solid
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– Shell-to-shell
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– Membrane-to-membrane
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– Shell-to-solid
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– Acoustic-to-structure
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A global or submodel region that is meshed with continuum shell elements constitutes a three-dimensional solid region in the submodeling technique. Hence, the use of the submodeling technique for models involving continuum shell elements is the same as with models involving continuum solid elements such as C3D8R or C3D6.
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# Procedures supported
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Both the global model and the submodel can have nonlinear response and can be analyzed for any sequence of analysis procedures. These procedures do not have to be the same for both models. For example, the linear or nonlinear dynamic response of the global model can be used to drive the static, nonlinear response of the submodel on the grounds that the submodel is too small for dynamic effects to be significant in that local region. The global procedure can be performed in Abaqus/Standard to drive a submodeling procedure in Abaqus/Explicit and vice versa. For example, a static analysis performed in Abaqus/Standard can drive a quasi-static Abaqus/Explicit analysis in the submodel. The step time used in these analyses can be different; the time variable of the amplitude functions generated at the driven nodes can be scaled to the step time used in the submodel.
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Your submodel cannot refer to a global model step that includes multiple load cases (see “Multiple load case analysis,” Section 6.1.4). You must perform the global analysis with a single load definition for the step that will drive the submodel.
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# Surface-based submodeling
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Surface-based submodeling is provided as a complement to the node-based technique, enabling you to drive the submodel with stresses from the global model.
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Input File Usage: \*SUBMODEL, TYPE=SURFACE
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Abaqus/CAE Usage: Load module: Create Load: choose Mechanical for the Category and Submodel for the Types for Selected Step: Driving region: Specify
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# Element types supported
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The following types of submodeling are provided for the surface-based approach (global-to-submodel):
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• Two-dimensional models:
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– Solid-to-solid
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• Three-dimensional models:
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– Solid-to-solid
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<!-- source-page: 759 -->
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Different element types can be used in the submodel than those used to model the corresponding region in the global model. Continuum elements supported for the static analysis procedure are supported for surface-based submodeling, with the following exceptions:
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• Cylindrical elements are not supported.
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• Continuum shell elements are not supported.
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# Procedures supported
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The surface-based technique is implemented only for static analysis in Abaqus/Standard.
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Your submodel cannot refer to a global model step that includes multiple load cases (see “Multiple load case analysis,” Section 6.1.4). You must perform the global analysis with a single load definition for the step that will drive the submodel.
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# Performing a submodeling analysis
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A submodeling analysis consists of:
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• running a global analysis and saving the results in the vicinity of the submodel boundary;
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• defining the total set of driven nodes or driven surfaces in the submodel;
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• defining the time variation of the driven variables in the submodel analysis by specifying the actual nodes and degrees of freedom or element-based surfaces to be driven in each step; and
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• running the submodel analysis using the “driven variables” to drive the solution.
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# Linking the global model and the submodel
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The submodel is run as a separate analysis from the global analysis. The only link between the submodel and the global model is the transfer of the time-dependent values of variables saved in the global analysis to the relevant boundary nodes of the submodel or to the relevant boundary surfaces. The results from the global model are saved in the results (.fil) file, in the output database (.odb) file, or in the SIM database (.sim) file for the node-based technique. For the stress-based technique, the global model results are saved either in the output database (.odb) file or in the SIM database (.sim) file. The transfer is achieved by then reading these results into the submodel analysis. If the global model is defined in terms of an assembly of part instances, the part (.prt) file from the global model is required for the submodel analysis. Since the submodel is a separate analysis, submodeling can be used to any number of levels; a submodel can be used as the global model for a subsequent submodel.
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# Accuracy
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The global model in a submodeling analysis must define the submodel boundary response with sufficient accuracy. It is your responsibility to ensure that any particular use of the submodeling technique provides physically meaningful results. In general, the solution at the boundary of the submodel must not be altered significantly by the different local modeling. There is no built-in check of this criterion in Abaqus; it is a matter of judgment on your part. In general, accuracy can be checked by comparing contour plots of important variables near the boundaries of the submodeled region.
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<!-- source-page: 760 -->
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By default, the global model in the vicinity of the submodel is searched for elements that encompass the locations of driven nodes or driven surfaces’ faces; the submodel is then driven by the response of these elements. In some cases more than one element can encompass the location of a driven node. For example, adjacent bodies in the global model may have temporarily coincident nodes or surfaces, as depicted in Figure 10.2.1–1.
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<details>
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<summary>text_image</summary>
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Global model
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A B
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contact
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interface
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x
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C D E
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Local model
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driven
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node
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</details>
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Figure 10.2.1–1 A global model with coincident surfaces in the area of the local model’s driven nodes.
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In this case the location of the driven node in the corresponding global model is touching both element A and element C; however, only the results from element A should drive the node in the submodel.
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To preclude certain elements from driving the submodel, you have the option of specifying a global element set to limit the search to an appropriate subset of the global model.
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Input File Usage: \*SUBMODEL, GLOBAL ELSET=name
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If the global model is defined in terms of an assembly of part instances, give the complete name—including the assembly and part instance names—when specifying the global element set. For example, an element set named top in part instance I-1 of assembly Assembly-1 must be referred to by Assembly-1.I-1.top.
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If the submodel is not defined in terms of an assembly of part instances, the dots in the global element set name must be replaced by underscores: Assembly-1\_I-1\_top.
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If the global element set is defined at the assembly level, you may provide the element set name without qualifying it with the assembly name in a submodel analysis.
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Abaqus/CAE Usage: Load module: Create Boundary Condition: choose Other for the Category and Submodel for the Types for Selected Step: Driving region: Specify
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