对动载荷，影响系统强度和NVH性能除了载荷的大小，还有载荷的频率，即载荷变化的快慢。如果系统含有旋转件，则载荷的频率分布和转速有一定的关系，常采用瀑布图及阶次切片进行分析。
主要步骤：利用Motion对曲柄连杆滑块机构进行动力学仿真，再用数据处理模块MathData Processing和DSP进行后处理。
一、Motion建模分析。
1、曲柄连杆滑块机构Motion仿真，4 Bodies,4 Joints,1 Driver(TimeAngle Function)
2、插入新的Motion Analysis Case...
然后：Insert ->Analysis Cases->
Solution Set ->
Speed sweep Element.
3、定义Driver的转速工况及每转的采样点数（2^n，以便用FFT），注意新的工况将覆盖Driver原设置的TimeAngle Function。
This results in a discontinuous speed sweep which will be run on the joint driver with a starting rpm of 1000 t/min, an increment of 250 rpm up to 2000 rpm. At each rpm, the steady state results are written to the Motion output file. Per rotation, 512 print steps are taken (Note: This number should be a power of 2 for a smooth FFT operation afterwards).
4、Edit the Solution set and ensure that the Matrix Scaling is set to Standard. This is found in the System (Advanced) tab of the Solution Set definition.
5.计算Solution set 并查看动画，注意每稳态转速4转，每转512点，另转速变换时2转，每转1个点。
二、MathData Processor
Prior to inserting the MathData Processor (MDP) case we need to prepare the Motion results set for the specific channels to process.
1、双击Motion result set,选择要分析的载荷单元。
2、From the Insert menu, select Data Processing->MathData Processing Case.
选择输入函数Motion Results Set ，设置输出函数类型为 Load Waterfall of Frequency Spectra.，处理方法设为 FFT of speedsweep.
3、设置FFT窗口参数
4、右键点击特征树solution->update,然后right-clicking on the Load Function Set created under the Solution and selecting New Function Display. For example, select a Colormap Display and click Finish.
5、The Select Data window that appears has a list of all the reaction forces available from the channel we selected in the Motion Results set. Highlight the Revolute Joint.1_b1:+Y and click Display. Change the x-scale to range from 0 to 200 Hz. An order cursor can be added to the graph by right-clicking in the graph window and select Cursor Order. Your plot should look similar to the following:
6、新建一个 MathData Processing case，输入函数设为刚处理完的Load Function Set.10(瀑布图）,输出类型设为Load Ordercuts,并设置阶次切片的参数。
7、Postprocess the results by creating a New Function Display as before create a Color Bars + 2D Displays. The Select Data window will let you display the desired orders as for each of the reaction forces of the rev joint.
三、DSP（Digital Signal Processor）
1、From the Insert menu select DataProcessing ->DSP Case....
设置输入输出函数。
2、Double-click the DSP – Load Function Solution2 to set the parameters. Change the Fourier Transform Options Window to Rectangular.
Notice the Block Size and Overlap are automatically set due to the data in the Motion Results set.（DSP与MDP不同之处）
3、Compute the DSP case by right-clicking on the DSP – Load Function Solution and click Compute.
4、Plotting is similar to the MDP case. Create a New Function Display: Colormap + 2D Ordercuts Displays. Plot the Revolute Joint.1_b1:+Y.
5、Set the x-scale to range from 0 to 200. Insert an order cut cursor, double-click the cursor and set it to snap to every .5 cut. Once the cursor is moved across the waterfall plot, the upper graph changes to display the current order cut.