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1、Training ManualTraining ManualDYNAMICS 11.0 定义和目的定义和目的 Workbench随机振动分析功能随机振动分析功能 分析流程分析流程Training ManualDYNAMICS 11.0什么是随机振动分析什么是随机振动分析 基于概率的谱分析基于概率的谱分析. 典型应用如火箭发射时结构承受的载荷谱，每次发射典型应用如火箭发射时结构承受的载荷谱，每次发射的谱不同，但统计规律相同的谱不同，但统计规律相同.Reference: Random vibrations in mechanical systems by Crandall & MarkTraini
2、ng ManualDYNAMICS 11.0 和确定性谱分析不同，随机振动不能用瞬态动和确定性谱分析不同，随机振动不能用瞬态动力学分析代替力学分析代替. 应用基于概率的功率谱密度分析，分析载荷作应用基于概率的功率谱密度分析，分析载荷作用过程中的统计规律用过程中的统计规律Image from “Random Vibrations Theory and Practice” by Wirsching, Paez and Ortiz.Training ManualDYNAMICS 11.0什么是什么是PSD? PSD是激励和响应的方差随频率的变化。是激励和响应的方差随频率的变化。 PSD曲线围成的面积
3、是响应的方差曲线围成的面积是响应的方差. PSD的单位是的单位是 方差方差/Hz (如加速度功率谱的单位是如加速度功率谱的单位是G2/Hz). PSD可以是位移、速度、加速度、力或压力可以是位移、速度、加速度、力或压力.Training ManualDYNAMICS 11.0输入输入: 结构的自然频率和阵型结构的自然频率和阵型 功率谱密度曲线功率谱密度曲线输出输出: 1s s位移和应力位移和应力 （用于疲劳分析）（用于疲劳分析）.Training ManualDYNAMICS 11.0 载荷载荷: 单点激励单点激励 得到结果得到结果: 相对或绝对的相对或绝对的1s s 输出输出 整体结构的结果
4、，可以进行云图显示整体结构的结果，可以进行云图显示. 1s s位移位移, 速度或加速度速度或加速度 后处理后处理: 1s s 可以进行云图显示可以进行云图显示.Training ManualDYNAMICS 11.0 Model: 输电铁架输电铁架 Analysis: 地面激励地面激励PSD分析分析. Steps: 进行模态和随机进行模态和随机振动分析，并显示结果振动分析，并显示结果.Training ManualDYNAMICS 11.0打开打开, Tower.dsdb. Browse to file if not in listTraining ManualDYNAMICS 11.0打开分
5、析向导打开分析向导Training ManualDYNAMICS 11.0 利用分析向导可以简单利用分析向导可以简单地建立分析流程地建立分析流程.可以看可以看到运行随机振动分析之到运行随机振动分析之前需要进行模态分析前需要进行模态分析.Training ManualDYNAMICS 11.0点击点击OK可以看到如图所示信息可以看到如图所示信息当提示当提示“Specify Number of Modes” ，输入，输入12Training ManualDYNAMICS 11.0下一步是插入约束，插入下一步是插入约束，插入fixed support. Training ManualDYNAMICS
6、 11.0模态分析结束模态分析结束. 可以查看模态结果，如右图所示可以查看模态结果，如右图所示.可以查看动画可以查看动画.Training ManualDYNAMICS 11.0 可以看到在谱分析中的初始条件已经可以看到在谱分析中的初始条件已经自动设置成模态分析的结果自动设置成模态分析的结果. 设置阻尼（恒定阻尼比）设置阻尼（恒定阻尼比）0.05Training ManualDYNAMICS 11.0插入一个插入一个PSD Base Excitation.在弹出的在弹出的PSD Base Excitation详情串口，选择新的详情串口，选择新的PSD载荷载荷.选择带选择带G的加速度的加速度PS
7、D，单位，单位G2/Hz. 设置设置PSD曲线曲线Training ManualDYNAMICS 11.0选择激励方向为选择激励方向为Y.选择选择Solve.求解结束后可以查看结果，可以选择求解结束后可以查看结果，可以选择1sigma到到3sigma结果结果.Training ManualDYNAMICS 11.0如果列出了结果如果列出了结果更改阻尼比为更改阻尼比为0.05，查看结果，查看结果.Training ManualDYNAMICS 11.0按阻尼比按阻尼比0.05重新计算重新计算. Training ManualDYNAMICS 11.0 查看如图所示查看如图所示结构在加速度结构在加
8、速度PSD激励下的响激励下的响应应Training ManualDYNAMICS 11.0目标是研究桁架结构的振动特性目标是研究桁架结构的振动特性. .这个练习将检查钢结构桁架由于加速度谱产生的这个练习将检查钢结构桁架由于加速度谱产生的位移和应力位移和应力. .PSDPSD谱可分为加速度、速度和位移谱可分为加速度、速度和位移. . The spectrum will typically be measured during physical tests or documented in a written specification relating to the system or comp
9、onent. The data points can be entered for each Freq & Amplitude, or a function can be entered.AccelerationFrequencyF1F2F3F4A2A3A4A1Training ManualDYNAMICS 11.0The Girder has fixed constraints along all lower edges.The boundary conditions will be applied to edges.Training ManualDYNAMICS 11.0From the
10、WorkBench Project Launcher start Simulation.if already in Simulation use FileNew For training purposes, choose “No: do not save any items” Once in Simulation click on GeometryFrom File to browse for and open girder.agdbTraining ManualDYNAMICS 11.0When the Geometry has loaded, choose “Random Vibratio
11、n” from the Map of Analysis TypesNote, the map will automatically highlight “Modal” too since modal is a precursor to Random Vibration simulation.Click OK, thus accepting the default number of modesChoose the U.S. inch pound unit system. “Units U.S. Customary (in, lbm, lbf, )”123Training ManualDYNAM
12、ICS 11.0The Girder geometry consists of surface bodies (for shell meshing)The first preprocessing task is to specify the thickness of all the surfaces.Click to fully expand the Girder “Geometry” branch. In the Details pane, notice that the “Thickness” field are displayed in yellow to indicate they a
13、re undefined. Select all the bodies to assign a uniform thickness LMB to select the top Body in the Part list.Hold and LMB on the last Surface Body.Note: By highlighting “all”, we can set the thickness on the first one, and the same thickness gets assigned to all of them.Of course one or more indivi
14、dual bodies can be redefined to different thicknesses later if necessary.Left click in the thickness field and set the thickness = 0.5 ”54Training ManualDYNAMICS 11.0The assembly to be shell meshed consists of multiple surface bodies separated by small offsets that account for the physical spacing b
15、etween the neutral (axis) planes of each piece of steel.We need to use “Bonded” Contact in order to simulate the effect of welded and/or bolted assembly connectivity.Click on ConnectionsCreate Automatic Contact6.The Default definition is “Bonded”6Training ManualDYNAMICS 11.0The assembly consists of
16、multiple slender bodies plus a large flat Roof plate. We want to specify a relatively fine mesh size on the slender members but a larger element up top.By assigning larger elements on the large roof, we preserve CPU time and are able to use finer (usually more accurate) elements elsewhere.Change to
17、Body Select.On the Outline Tree, RMB on the Mesh objectInsertSizing (for slender bodies)In Details, Replace “Default” size with 2 (inches)RMB in Graphics Window, Select AllBut then hold and LMB single select on the “roof body” to unselect that part from this Size object. ApplyInsertSizing (for the l
18、arge “roof” body)Enter “4” for size in Details (for the large top plate).Use Single Select and LMB on the large Body.ApplyPreview the mesh, MeshGenerate Mesh 7.If desired, repeat the steps above to increase or decrease element sizes as desired to enhance the model or reduce CPU time. Larger Elements
19、on roof 78,910Training ManualDYNAMICS 11.0For the lower edges of the truss, highlight the “Modal” branch in the Outline and Insert Fixed Supports. Switch to edge selection mode as necessary Reorient model as necessary throughout.an end view might be most convenient.Switch to Box SelectDrag the LMB t
20、o select the edges at the bottom of the lower girders. Click “Apply” in the Details window111213Training ManualDYNAMICS 11.0For the PSD Base Excitation loads, at the Random Vibration Branch, InsertPSD Base Excitation In the Details of the PSD Load, change “Direction” to “Y Axis” for this particular
21、XYZ orientation.For Load Data chose New PSD Load141516AccelerationFrequencyF1F2F3F4A2A3A4A1Training ManualDYNAMICS 11.0PDS data in this case is “Acceleration” Table data points, so insure that “PSD Acceleration” and “Table” is selected. Click on OKThen enter the table data for FREQ vs. Acceleration.
22、The graph automatically updates with each data point.Eventually, click on the Simulation tab (at the very top) to exit “Engineering Data” and return Simulation mode.1718Training ManualDYNAMICS 11.0Insure that the Details “Initial Condition” for the Random Vibration object is “Modal”With the branches
23、 for Modal (as well as Random Vibration) prepared, we are ready to solve this simulation. As a final check verify the status symbols next to the branches. All branches should have either:Lightening bolt (ready)Green check mark (complete)Solve.ToolBar Button SolveNote: solving from the Toolbar “thund
24、erbolt” causes all unsolved branches to be solved. 19. Had we wished to solve only one branch (such as “Modal” in this case) we could have highlighted only the branch or object to be solved and use RMB Solve.19Training ManualDYNAMICS 11.0After the solution is completed you can review the (precursor)
25、 modal shapes for each frequency.In the Outline Tree pertaining to Modal, click on Solution (within the Modal branch) Click on the Modal Solution Branch in the Tree. Then LMB on the top of the Frequency Column in the “Tabular Data” region, and RMBCreate Mode Shape Results This will insert “Total Def
26、ormation” objects in the Tree for all modes solved.Click on Click on “Solve” toolbar button so the new “result” objects can be evaluated20Training ManualDYNAMICS 11.0Now review Random Vibration results. Due to the applied spectrum, you can Insert DeformationsStrainsStresses InsertDeformationDirectio
27、nalSpecify the Z “Orientation” direction in the Details PaneInsertStrainNormalFor instance, specify Y “Orientation” in the Details PaneInsertStressEquivalent (von Mises) Click on Solve or RMBEvaluate All Results to evaluate any new objects you have added to the outline tree. Note: Only the new objec
28、ts get evaluated21.This saves CPU and wall clock time.RMB21222324Training ManualDYNAMICS 11.0查看和评估结果查看和评估结果.要点要点: 模态分析的节点位移是相对值而模态分析的节点位移是相对值而非真实值。非真实值。 The PSD simulation generates statistically “Probable” resultant magnitudes that depend on the energy input magnitude and spectrum applied to the sy
29、stem. The Damping data also plays a roll in the magnitude of the response. Review available results, and change the settings under the “Edges” toolbar button.You may choose to show (or not show) elements (edges) and un-deformed model.Element edges WireFrame can become “distracting” during Post-Processing. Turn wireframe off.25looks better without wireframe edges