2 An Investigation of Vibrational Characteristics of Lap Joints Using Experimental and Analytical Methods 15 Fig. 2.7 SEM with Shells window. Here the user inputs geometry, undamaged and damaged modes, and selects which modes to use in the computation The window shown in Fig. 2.6 is where the user accesses the UI’s three main functions – SEM with Beams, SEM with Shells, and Convert FE Data to Modes. The two strain energy methods work in similar ways and require the same inputs. Once given the correct input, each function executes its respective method and produces damage identification results. Figure 2.7 shows the window for executing the SEM with Shells function (the window for the SEM with Beams functions is visually identical with the exception of the figure’s title and resulting plot format). To utilize the SEM functions within the UI, the user must input a valid geometry file, an undamaged modes file, and a damaged modes file. The UI requires these files to be in MATLAB data format. Geometry is specified by Nodes, Tracelines, Beams, Quads, and Shells. Files for undamaged and damaged modes can be either direct modal analysis output from DIAMOND, or the user can generate their own mode shape files from other modal analysis software packages. The SEM UI only requires a MATLAB Structure data type of the nodal displacements that pertain to the geometry and a confirmation that the response degree-of-freedom is in the positive z-axis. Some notable assumptions within the SEM UI are that it requires planar geometries with the response degree-of-freedom being in the positive z-axis. The SEM with Beams function requires that the beams used in the computation be parallel in either the x- or y-axis, but beams need not be the same length in this function. The third function within the SEM UI is mapping FE mode shapes to geometry that can be used within the strain energy methods. The Convert FE Data to Modes window, shown in Fig. 2.8, has two capabilities – mapping FE mode shapes to an existing geometry and mapping FE mode shapes to a new geometry. The user inputs a reference geometry (the geometry in Fig. 2.8 is the same as shown in Fig. 2.2) MATLAB file and a Microsoft Excel file containing the FE mode shapes that are defined by paths in the geometry. The format required for the FE Displacement Excel File can be found in the open-source example data that accompanies the UI. The UI then configures itself to map the Current Path to the nodes that the user inputs in the Nodes for Path dialog box (node numbers separated by commas). This window in the UI relies on similar geometry assumptions as previously stated with some extra constraints. The Convert FE Data to Modes functions require that paths be parallel in either the x- or y-axis and the same length, and it is advantageous to list the paths in ascending order with the most negative x- or y-direction path first. ANSYS Workbench 19.1 was used in this work to create FE models and do the modal analysis. ANSYS allows the user to create paths along edges in a geometry, and this functionality allows the user to extract nodal displacements to be used in the SEM UI. Figure 2.9 shows a screen shot of a path and its corresponding data from within an ANSYS modal analysis. The second functionality of the Convert FE Data to Modes window (which is still in development) is mapping FE displacements to a new geometry. For this function, the user only inputs the FE Displacements Excel File and the number of nodes to discretize each path into. In this function it is critical that all paths be parallel, the same length, and listed in the correct order. Once given the proper information, the UI generates the mode shape data and the geometry file to be used
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