hypermesh很有用的问题与解答.doc

RADIOSS (Bulk Data Format), OptiStruct一、FEA Setup and Modeling【1】How can I apply multiple constraints or loads in a subcase?1.Put multiple loads in one load collector, and include that one load collector in the subcase. The same method can be used in the case of multiple constraints.2.Create load collectors for each and every load and constraint set. When you want to apply multiple loads in a subcase, a new load collector needs to be created with the LOAD card. Then, individual load collectors can be combined using the LOAD card. The LOAD card also enables you to associate an independent weighting factor to an individual load collector. In the case of applying multiple constraints, create a new load collector with the SPCADD card, and follow the same procedure as in the multiple load case. Once the combined load collectors are created, they can be applied in a subcase.一，设置有限元分析与建模 【1】如何申请多个约束在一个子用例或负载？ 1。把多个负载在一个负载收藏家，包括该子用例中的一个负载收藏家。同样的方法可用于多种约束条件。 2。创建每一个载荷和约束集负载收藏家。当你想用一个子用例多个负载，一个新的集电极负载需要用在LOAD卡创建的。然后，个人收藏家负载可以组合使用LOAD卡。在LOAD卡还可以让您联想到一个独立的个体因素加权负载收藏家。在应用多约束的情况下，创建一个新的负载SPCADD卡收藏家，并按照在多工况相同的程序。一旦联合负荷收藏家的创建，它们可以应用在子用例。【2】How can I specify an enforced displacement in a subcase (or loadstep) in an OptiStruct input deck?There are two ways to do this:1.Create a single SPC definition containing the enforced displacement information and reference this within the subcase (loadstep) definition. 2.Create an SPC, SPCD pair, with the SPC constraining the dof that is to have the enforced displacement and the SPCD defining the magnitude and dof of the enforced displacement. Both must be referenced in the subcase (loadstep) definition. 2】我可以指定如何在输入中的一个OptiStruct甲板子用例（或loadstep）被迫流离失所？ 有两种方法可以做到这一点： 1。建立一个单一的定义包含最高人民法院被迫流离失所的信息和参考在子用例（loadstep）的定义这一点。 2。创建最高人民法院，SPCD与SPC制约自由度是有强迫流离失所和SPCD确定的规模和实施的位移自由度一双。两者都必须被引用在子用例（loadstep）的定义。【3】What kinds of checking does the check run perform? What is the difference between the CHECK and ANALYSIS cards in the input deck?The check run checks for syntax errors, input errors (i.e. missing LOAD or SPC card in subcase), and gives the recommended memory for the analysis or optimization run. All errors or warning messages will be output to the .out file.If the CHECK card is included in the input file, chosen as a Run Option in HyperMesh, or added as a run option on the command line, OptiStruct will only perform the check run. If the ANALYSIS card is included in the input deck, chosen as a Run Option in HyperMesh, or added as a run option on the command line, OptiStruct will perform only baseline analysis and no optimization. Note:A request for a check run always takes precedence over a request for an analysis run, and a request for an analysis run always takes precedence over an optimization. 【3】种什么样的检查检查运行是否执行？之间有什么检查并分析卡，在输入甲板区别？ 检查错误的语法检查，运行，输入错误（即缺少子用例LOAD或最高人民法院卡），并给出了优化运行的分析或建议内存。所有的错误或警告信息将被输出到。出的文件。 如果支票卡是在输入文件作为在HyperMesh运行选项选择，或在命令行运行的选项添加，OptiStruct只会执行检查运行。 如果分析卡在输入甲板内，选择了作为一个HyperMesh运行选项，或在命令行运行的选项添加，OptiStruct只须执行基准分析，也没有优化。 注：为检查运行要求总是比一个请求的优先级运行的分析，并为分析运行的要求总是比一个优化的优先级。 【4】How can I specify the temporary directory (where all of the scratch files are written) to run OptiStruct jobs?In an OptiStruct input, the complete path to the temporary directory (which has enough disk space for the scratch files) can be entered on the TMPDIR card. The TMPDIR card is available in HyperMesh in the control cards panel. Also, please note that when a temporary directory is specified, it is important to verify that the directory has correct read and write permissions.3】种什么样的检查检查运行是否执行？之间有什么检查并分析卡，在输入甲板区别？ 检查错误的语法检查，运行，输入错误（即缺少子用例LOAD或最高人民法院卡），并给出了优化运行的分析或建议内存。所有的错误或警告信息将被输出到。出的文件。 如果支票卡是在输入文件作为在HyperMesh运行选项选择，或在命令行运行的选项添加，OptiStruct只会执行检查运行。 如果分析卡在输入甲板内，选择了作为一个HyperMesh运行选项，或在命令行运行的选项添加，OptiStruct只须执行基准分析，也没有优化。 注：为检查运行要求总是比一个请求的优先级运行的分析，并为分析运行的要求总是比一个优化的优先级。 【5】What is the OptiStruct equivalent of the Nastran K6ROT parameter?In Nastran, shell elements have five degrees of freedom per node, three displacements and two rotations. The K6ROT parameter provides an in-plane rotational stiffness (so-called drilling stiffness) accounting for the missing sixth degree of freedom. The absolute stiffness value provided by K6ROT is applied to all shell elements in the same manner. This way a singular stiffness matrix is avoided for shell models.In OptiStruct, the shell elements have a built-in drilling stiffness. Each elements drilling stiffness is calculated from the element properties using a shape function. This way, the shell elements in OptiStruct have six degrees of freedom per node, three displacements and three rotations. The OptiStruct approach is more accurate, since it derives the drilling stiffness from the structural properties of each element. This leads to somewhat different results between OptiStruct and Nastran for shell models.An alternative shell element formulation is available in OptiStruct that matches more closely with the Nastran formulation. The primary difference with respect to the default OptiStruct shells is the absence of drilling stiffness. Some stabilization terms and other adjustments are added for reliable performance. The resulting elements are generally more flexible than the default OptiStruct shell elements, especially on curved geometries. 【5】什么是Nastran的K6ROT参数OptiStruct相像？ 在Nastran的，有五度壳单元，每节点的自由，两三个位移和旋转。该K6ROT参数提供了一个平面旋转刚度失踪自由第六度（所谓的钻劲度）会计。绝对刚度值K6ROT提供适用于所有以相同的方式壳单元。这是一个奇异的壳刚度矩阵模型避免的方法。 在OptiStruct，外壳元素有一个内置的钻井刚度。每个元素的钻井刚度计算元素使用形状函数的性质。这样，在OptiStruct壳元素六度每个节点自由，三位移和三个旋转。该OptiStruct方法更准确，因为它源于从每个元素的结构性能自钻刚度。这导致有些不同之间OptiStruct和Nastran的结果壳模型。 另一种是在壳单元制定OptiStruct可用的匹配更加紧密地与Nastran的制定。相对于默认OptiStruct炮弹的主要区别是钻井刚度缺席。稳定条款和其他一些调整，增加了可靠的性能。由此产生的元素通常比默认OptiStruct壳单元灵活，特别是在弯曲的几何形状。 【6】Is OptiStruct benchmarked?OptiStruct finite elements are benchmarked with the MacNeal-Harder tests, NAFEMS benchmarks, and some other problems posted by individuals and companies.The NAFEMS benchmark problems and results are documented in the OptiStruct manual. 【6】是OptiStruct基准？ OptiStruct有限元素基准与MacNeal -哈德测试，NAFEMS基准，以及其他一些问题，由个人和企业发布。 该NAFEMS基准问题和结果都记录在OptiStruct手册。二、Optimization Problem Set Up【7】What is the difference between volumefrac response and volume response?Volumefrac response is the material fraction of the designable material volume. The volume response is the total volume, which includes design and non-design volume. 【8】Is minimizing mass identical to minimizing volume in OptiStruct?Both formulations are identical as long as the same density is used for all materials in the model. When minimizing the volume, the density value in the material card does not have to be given.If different densities exist in the design and the non-design space, then the optimization result may be different for minimizing mass and minimizing volume.In a case where the design mass and the non-design mass are almost identical, but the design volume is much smaller than the non-design volume (Vdesign Vnon-design), minimizing mass will give better results.On the other hand, when the design volume and the non-design volume are almost identical, but the design mass is much smaller than the non-design mass (design non-design), minimizing volume will yield better results.【9】Is there a way I can control the step size of the optimization?You can change the move limits (the allowable change of the design variable in each iteration step) for the first iteration. The move limits are defined for each optimization type differently. The parameters are DELTOP, DELSHP, DELSIZ on the DOPTPRM statement. They can also be defined for size and shape variables on the DESVARcard. In HyperMesh, use the opti control subpanel in the optimization panel on the Analysis page【10】What is the procedure for restarting an OptiStruct job?To restart an OptiStruct job, two files are needed: filename.fem (containing input data) and filename.sh (containing design variable information from the end of last complete iteration). Please refer to Restarting OptiStruct in the Orientation and Fundamentals/Running OptiStruct section of the documentation. 【11】Is it possible to obtain rib pattern information on shell models using topology optimization?Yes, but in order to do this, you must define the topology optimization problem differently. Instead of defining the complete thickness of the shell element as designable, a core non-designable thickness, T0, must be provided in addition to a maximum thickness, T, which includes the core thickness and a designable region (where the ribs can be grown). The topology optimization can then be performed as usual.The rib patterns can be interpreted by visualization of the density contour plots. Wherever the density values reach 1.0, a rib with the height of the -core plus the designable thickness is needed. Where the density values go to 0.0, no rib is required and it just retains the core thickness.Example: Component minimum core thickness: 1.5 mm max thickness with ribs: 3.5 mm The thickness on the PSHELL card is set to 3.5 mm and T0 on the DTPL card is set to 1.5. This can lead to 2mm high ribs (max). Note:T0 is the mid-layer thickness. Ribs are placed within (T0/2) + (T/2) and (-T0/2) - (T/2) about the shell model, (i.e. the shell model coincides with the mid-plane of the elements).Since shell elements are being used, the aspect ratio has to be taken into account. Do not let the expected thickness be greater than the in-plane dimensions of the elements.【12】How can I assign and/or change the modeweights in a subcase (load case)?Modeweights are assigned from within a model analysis subcase using the MODEWEIGHT subcase information entry. From within the HyperMesh panels, access the optimization panel and the responses subpanel. If the wfreq or comb is chosen as the response type, you can assign up to six modeweights to six different modes. 【13】How do I calculate the NORM factor for a combined compliance and frequency optimization problem?【14】If the value of the subcase information entry NORM is left as 0.0 (default), then the normalization factor is estimated during the zero-th (analysis only) iteration of the optimization run (such that the static compliance and weighted frequencies are equally weighted). If you provide a value other than 0.0, that value will be used in the optimization. In HyperMesh, the value of NORM may be defined in the response panel when the response type is comb. The normalization factor (NORM) is used for normalizing the contributions of static load case compliances and the inverse of eigenvalues when using the combined compliance index as the objective function. A typical structural compliance value is on the order of 1.e4 to 1.e6. However, a typical inverse eigenvalue, as in the case of using the combined compliance index as the objective function, is on the order of 1.e-5. If NF is not used, the linear static compliance requirements dominate the solution. Please refer to the Responses page of the Users Guide section of the documentation for more information on the Combined Compliance Index and the use of the NORM value. 【15】What is the difference between specifying a constraint on the designable volume and minimizing the designable volume?In the first method, you can tell OptiStruct to use only a certain fraction of the designable volume (i.e. constraining the volume). OptiStruct will redistribute and reorient the amount of the material within the design domain while optimizing the objective function and satisfying any other constraints specified.In the second method, you can choose their objective to minimize the volume. Here, OptiStruct will minimize the volume to arrive at a final topology that satisfies other constraints.【16】What is the difference between using forces and prescribed displacements?In order to increase stiffness, minimize compliance should be used with forces and maximize compliance with prescribed displacements.The compliance is defined as: Compliance Force DisplacementWhen prescribed displacements are used, the reaction force must be increased to increase the stiffness. This means that the compliance has to be maximized. In case the forces are given, a stiffer structure means having lower displacements. To achieve this goal, the compliance needs to be minimized.【17】What is the initial value of material fraction at the beginning of an optimization run (iteration 0)?If the objective of the design problem is to minimize volume response or mass response, the initial material fraction will be set to 0.9 by default. If a mass or volume constraint is used in the design problem, the initial material fraction will be the value corresponding to the value defined on the constraint. When mass or volume response is not being used to define the objective or the constraint, the material fraction will default to 0.6 at iteration 0.【18】How can I assign material fraction to 1 at iteration 0?The initial volume fraction can be assigned to 1.0 (or any other value between 0.0 and 1.0) by defining the MATINIT parameter on the DOPTPRM bulk data entry. This can be done from the HyperMesh interface by changing the value of the MATINIT parameter and checking the corresponding check box in the opti control subpanel, under the optimization panel (located on the Analysis page).【19】Can I combine various optimization types (size with shape and/or topography)?Yes, any type of combined optimization can be performed with OptiStruct. It is recommended, however, that different types of optimization be performed separately first. This will help you understand the performance of the structure with different kinds of optimization before attempting a combined optimization.To set up an optimization problem using more than one optimization type, access the optimization panel and choose the subpanels for the optimization types to be performed (topology, topography, size and/or shape). If more than one subpanel is chosen in the optimization panel, (both topology and topography, for example) OptiStruct will automatically perform the combined optimization.For details on setting up different types of optimization, please refer to the tutorial section of the manual. 【20】The results of iteration 0 in an attempted topology optimization are different from the results of a run with ANALYSIS. What is wrong?Nothing is wrong. You have defined a design space for your topology optimization. In an analysis-only run, the density of the design space is set to 1.0. In the first iteration of the topology optimization, the density of the design space is less than 1.0, unless you have expressly set the MATINIT value, defined on the DOPTPRM bulk data entry, to 1.0. Therefore, in the first iteration, the structure appears to be not as stiff as in an analysis-only run. For topology optimization runs with mass (volume) as the objective, the default for MATINIT is 0.9. For runs with constrained mass (volume), the default is reset to the constraint value. If mass (volume) is not the objective function and is not constrained, the default is 0.6. To perform an analysis only run with the modal parameters set to the values that will be used for the first optimization iteration, do not use the ANALYSIS command, and set MAXITER = 0.【21】How can I follow the iteration history while OptiStruct is running?You can open the iteration history file .hgdata using Altair HyperGraph (or HyperView) while OptiStruct is still running and create plots of the Objective, Constraints, and Design Variables against Iteration. Using the Apply button on the Edit Curves panel, the view can be updated periodically.【22】Can I use stress constraints with topology or free-size optimization?Von Mises stress constraints may be defined for topology and free-size optimization through the STRESS optional continuation line on the DTPL or the DSIZE card. There are a number of restrictions with this constraint:The definition of stress constraints is limited to a single von Mises permissible stress. The phenomenon of singular topology is pronounced when different materials with different permissible stresses exist in a structure. Singular topology refers to the problem associated with the conditional nature of stress constraints, i.e. the stress constraint of an element disappears when the element vanishes. This creates another problem in that a huge number of reduced problems exist with solutions that cannot usually be found by a gradient-based optimizer in the full design space. Stress constraints for a partial domain of the structure are not allowed because they often create an ill-posed optimization problem since elimination of the partial domain would remove all stress constraints. Consequently, the stress constraint applies to the entire model when active, including both design and non-design regions, and stress constraint settings must be identical for all DSIZE and DTPL cards. The capability has built-in intelligence to filter out artificial stress concentrations around point loads and point boundary conditions. Stress concentrations due to boundary geometry are also filtered to some extent as they can be improved more effectively with local shape optimization. Due to the large number of elements with active stress constraints, no element stress report is given in the table of retained constraints in the .out file. The iterative history of the stress state of the model can be viewed in HyperView or HyperMesh. Stress constraints do not apply to 1-D elements. 【23】Can I use buckling constraints on a topology or free-size optimization?There are several b