1、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 co
2、llectors 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 weigh
3、ting 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
4、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 su
5、bcase (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 t
6、he 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 S
7、PC 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
8、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
9、 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,
10、 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
11、，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
12、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
13、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 O
14、ptiStruct 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
15、. 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
16、 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 t
17、o 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 sti
18、ffness. 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 K6R
19、OT 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
20、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 problem
21、s 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 th
22、e 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
23、 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 no
24、n-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
25、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
26、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
27、 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 O
28、ptiStruct 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 des
29、ignable, 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
30、 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 thickn
31、ess 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 w
32、ith 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
33、 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 mode
34、s. 【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 (suc
35、h 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 u
36、sed 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 usi
37、ng 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 Complianc
38、e 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). OptiSt
39、ruct 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 arr
40、ive 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: Com
41、pliance 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 complian
42、ce 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 c
43、onstraint 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 ca
44、n 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
45、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 recommend
46、ed, 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, acce
47、ss 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 optim
48、ization.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
49、 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 rese
