Tutorial for Assignment #2 Gantry Crane Analysis By ANSYS (Mechanical APDL) V.13.0

Transcription

1 Tutorial for Assignment #2 Gantry Crane Analysis By ANSYS (Mechanical APDL) V Problem Description Design a gantry crane meeting the geometry presented in Figure 1 on page #325 of the course textbook Daryl L. Logan, A First Course in the Finite Element Method, 5 th Edition (a modified version of problem 5-70 on page # ). Assume that structural steel is used for all the truss members (ASTM- A36). The design should: 1. be as light as possible, 2. have a beam structure at the top that is well removed from the possibility of material yield due to bending (using a FOS of 5.0), and 3. have vertical columns that are well removed from the possibility of yield and buckling due to internal compression (using a FOS of 5.0). 4. have corner braces that are well removed from the possibility of yield and buckling due to internal compression (using a FOS of 5.0). You can assume that all joints are welded except the corner braces which are connected to the columns and beams with idealized spherical joints. When calculating the threshold for buckling you can use Euler s buckling formula (which assumes pinned-pinned conditions). Using Appendix F (pages # ), you can choose from the wide flange sections listed for the beam elements (one size used for all beams), the rectangular hollow structural sections (HSS) for the vertical columns (one size used for all columns) and the pipe sections for the corner bracing (one size used for all braces). Material properties can be located inside the back cover of the textbook. 1.1 Deliverables: From your simulation results, provide: 1. An ANSYS plot of the undeformed and the deformed space frame. Choose a scaling factor for the elastic displacements such that they are appreciable in the plot. 2. A table of output values that compares the nodal displacements (translations only) to those calculated with your MATLAB Code. By: Majid Soleimaninia Page 1

2 Figure 1: Structural drawing of problem 5-70 on page # of the course textbook Daryl L. Logan, A First Course in the Finite Element Method, 5th Edition. By: Majid Soleimaninia Page 2

3 2 Start ANSYS (Mechanical APDL) V.13.0 Begin ANSYS (Mechanical APDL) with Start All Programs ANSYS 13.0 Mechanical APDL (ANSYS). That will bring you to the main ANSYS Utility Menu as seen in Figure 2. Figure 2: Opening ANSYS to the Utility Menu and graphics window. By: Majid Soleimaninia Page 3

4 3 Preprocessing: Defining the Problem 3.1 Select job name and analysis type The various menus below will sometimes get moved to a back (hidden) window. If you think that has occurred hit the Raise Hidden button,. You will always need a job name: 1. Utility Menu File Change Jobname. 2. Change_Jobname, type in the new name, OK (as seen in Figure 3). Figure 3: Setting the new job name. The ANSYS file sizes for real engineering problems get to be quite large, so have a directory dedicated to ANSYS: 1. Utility Menu File Change Directory. 2. Browse for Folder Change Working Directory, pick your directory (ANSYS Tutorial_P5-70 in Figure 4), OK. By: Majid Soleimaninia Page 4

5 Figure 4: Establish a directory for the analysis files. To keep up with your analysis studies over time create descriptive titles: 1. Utility Menu File Change Title. 2. Change Title, enter a descriptive title, OK (see Figure 5). Figure 5: Provide a descriptive title. By: Majid Soleimaninia Page 5

6 3.2 Element type data You will need a 3D structural line element, or frame member, that transmits axial forces, axial torsion, and transverse bending moments and also 3D structural link element for your truss members. Open and add to element types you need: 1. Main Menu Preferences Preferences for GUI Filtering. 2. Check Structural, accept default h-method, OK, as in Figure 6. Figure 6: Declare the selection of a structural analysis. 3. Main Menu Preprocessor Element Type Add/Edit/Delete, as in Figure In Element Types, seen in Figure 7, pick Add Library of Element Types. 5. Select (Structural) Beam and 2 node 188 (that is, BEAM188), OK. 6. In Element Types window, select BEAM188 element and then pick Options to modify your BEAM188 element type options, as in Figure In Element Types pick Close. By: Majid Soleimaninia Page 6

7 Figure 7: Select beam element type. Figure 8: Modify BEAM188 element type options. Now you defined your beam element and need to add truss element as well. In order to add other elements, open and add to element types you need: 1. Main Menu Preprocessor Element Type Add/Edit/Delete, as in Figure In Element Types, seen in Figure 9, pick Add Library of Element Types. 3. Select (Structural) Link and 3D finit stn 180 (that is, LINK180), OK. By: Majid Soleimaninia Page 7

8 4. In Element Types window, select LINK180 element and then pick Options to modify your LINK180 element type options, as in Figure In Element Types pick Close. Figure 9: Select truss element type. Figure 10: Modify LINK180 element type options. By: Majid Soleimaninia Page 8

9 3.3 Element geometric properties data For truss element, LINK180, we need to set real constant (Cross-sectional area) which we can get the value from Table 1-14 on page#907 of the course textbook. To set up the real constant you need: 1. Main Menu Preprocessor Real Constants Add/Edit/Delete, as in Figure In Real Constants, seen in Figure 11, pick Add Element Types for Real Constants. 3. Select LINK180 element, OK. 4. In Real Constants Set Number 1, for LINK180 window, type selected area in Crosssectional area... AREA, to modify Real Constant Set for LINK180, OK, as in Figure In Real Constants pick Close. Figure 11: Setup real constant for LINK180 element. For beam element, BEAM188, we need to define two different element geometry and sections, the wide flange sections listed for the horizontal beam elements (one size used for all beams), the rectangular hollow structural sections (HSS) for the vertical columns (one size used for all columns). Every element type requires one or more real constants, like area or moment of inertia, to describe it. Here, you need several geometric items for each type of beam, which we can get the values from Appendix F on page# of the course textbook. To enter the wide flange sections geometry, you need: 1. Main Menu Preprocessor Sections Beam Common Sections, as in Figure In Beam Tool, seen in Figure 12, Type 1 in ID and Flange in Name section to define beam type you are modifying, and then pick the correct section for wide flange in Sub- Type. Also type the dimensions for selected wide flange section, APPLY. By: Majid Soleimaninia Page 9

10 3. To check your wide flange geometry and dimensions, you can pick Preview in Beam Tool, as in Figure In Beam Tool pick Close. Figure 12: Setup beam section geometry for wide flange section. To enter the rectangular hollow structural sections (HSS) geometry, you need: 1. Main Menu Preprocessor Sections Beam Common Sections, as in Figure In Beam Tool, seen in Figure 13, Type 2 in ID and Tube in Name section to define beam type you are modifying, and then pick the correct section for Rectangular HSS in Sub- Type. Also type the dimensions for selected Rectangular HSS, APPLY. 3. To check your wide flange geometry and dimensions, you can pick Preview in Beam Tool, as in Figure In Beam Tool pick Close. By: Majid Soleimaninia Page 10

11 Figure 13: Setup beam section geometry for Rectangular HSS section. 3.4 Define member material properties Here you will use the simplest linear, isotropic, 1D material description. ANSYS has full anisotropic (completely directionally dependent), as well as non-linear material constitutive laws. Activate the material properties with: 1. Main Menu Preprocessor Material Props Material Models. 2. Material Model Number 1 appears in Define Material Model Behavior. 3. Double click on Structural, then Linear, then Elastic, then Isotropic. 4. In Linear Isotropic Properties for Material Number 1 enter 29e6 (psi) for elastic modulus, EX, and for Poisson s ratio (PRXY), as in Figure 14, OK. 5. Close (X) the Define Material Model Behavior window. By: Majid Soleimaninia Page 11

12 Figure 14: Define the isotropic elastic properties. 3.5 Define nodal data Of course, ANSYS has powerful mesh generation capabilities. However, for beginners or small problems with only a few nodes you can type in the coordinates, or use cursor input via the graphics window, or read them from a file. Use the first approach: 1. Main Menu Preprocessor Modeling Create Nodes In Active CS. 2. In Create Nodes in Active Coordinate System of Figure 15 enter 1 for Node number, X = 0., Y = 0., Z = 0 (in), Apply, enter 2 for Node number, X = 0., Y = 0., Z = 144., Apply, enter 3 for Node number, X = 24., Y = 0., Z = 180., Apply, enter 4 for Node number, X = 0., Y = 0., Z = 180., Apply, enter 22 for Node number, X = 96., Y = 72., Z = 180., OK. 3. You can also add a non-structural node for beam orientation purposes. 4. If you make a mistake you can return and correct it in the above window, or delete them all with Main Menu Preprocessor Modeling Delete. Now, plot the nodal values input (node 1 may be hidden behind the axis symbol): 1. Utility Menu PlotCtrls Numbering. 2. In Plot Numbering Controls check node numbers and select element numbers in the pull down menu, OK. 3. Utility Menu PlotCtrls Numbers and review the plot that is similar to Figure. 4. To get the reverse video white background of that figure use PlotCtrls Style Color Reverse Video. By: Majid Soleimaninia Page 12

13 Figure 15: Build the nodal coordinates. 3.6 Define element attributes Next you have to associate each of the elements with your previous material numbers and real constant sets. Plan ahead and input those elements of the same type in sequence. To make vertical columns from our defined Rectangular HSS section element: 1. Main Menu Preprocessor Modeling Create Elements Elem Attributes. 2. In Element Attributes, seen in Figure 16, select (Element type number = 1 BEAM188, Material number = 1, Real constant set = 1, Section number = 2 Tube, Target element shape = Straight line), OK. 3. Main Menu Preprocessor Modeling Create Elements Auto numbered Thru Nodes, as in Figure In Elements from nodes verify that Pick is checked on. 5. In the graphics window, seen in Figure 17, define the first element by picking node 1 (a square symbol appears) then node 2, OK, and the next element number (1) appears in the graphics area. By: Majid Soleimaninia Page 13

14 6. Repeat this process for the other 7 members (all vertical columns) sharing the current real constants set and section: Thru Nodes pick nodes 2 and 4for element 2 and so on. Figure 16: Confirm the beam attributes for the first 8 vertical columns members. Figure 17: Define 8 vertical columns (HHS) elements for second section set (Tube). By: Majid Soleimaninia Page 14

15 For the next 14 horizontal beam elements you need to change the number of its section number data set from 2 to 1. If those data were still correct but the next element was made of a different material then a similar change would be required at this point. To make horizontal beam elements from our defined wide flange section element: 1. Main Menu Preprocessor Modeling Create Elements Elem Attributes. 2. In Element Attributes, seen in Figure 18, select (Element type number = 1 BEAM188, Material number = 1, Real constant set = 1, Section number = 1 Flange, Target element shape = Straight line), OK. 3. Main Menu Preprocessor Modeling Create Elements Auto numbered Thru Nodes, as in Figure In Elements from nodes verify that Pick is checked on. 5. In the graphics window, seen in Figure 17, define the first element by picking node 4 (a square symbol appears) then node 5, OK, and the next element number (9) appears in the graphics area. 6. Repeat this process for the other 13 members (all horizontal beam elements) sharing the current real constants set and section: Thru Nodes pick nodes 4 and 3for element 10 and so on. Figure 18: Confirm the beam attributes for the 14 horizontal beam members. To make corner braces elements from our defined pipe section element: 1. Main Menu Preprocessor Modeling Create Elements Elem Attributes. By: Majid Soleimaninia Page 15

16 2. In Element Attributes, seen in Figure 19, select (Element type number = 2 LINK180, Material number = 1, Real constant set = 1, Section number = No Section, Target element shape = Straight line), OK. 3. Main Menu Preprocessor Modeling Create Elements Auto numbered Thru Nodes, as in Figure In Elements from nodes verify that Pick is checked on. 5. In the graphics window, seen in Figure 17, define the first element by picking node 2 (a square symbol appears) then node 3, OK, and the next element number (23) appears in the graphics area. 6. Repeat this process for the other 7 members (all corner braces elements) sharing the current real constants set and section: Thru Nodes pick nodes 2 and 5 for element 24 and so on. Figure 19: Confirm the truss attributes for the 8 corner braces members. Figure 20 shows the final element model for our problem. By: Majid Soleimaninia Page 16

17 Figure 20: Final element model. 3.7 Check element data It is wise to check such element input by plotting the nodes and elements, and/or the element s real constant set numbers, and/or section number via: 1. Utility Menu PlotCtrls Numbers 2. Plot Numbering Controls Elem /Attrib numbering pick Section number in Figure 21 to create the associated display. Likewise, you can view a list of the data with, Figure 22 : 1. Utility Menu List Elements Nodes+Attr+RealConst. 2. When the ELIST (ELement LIST) window appears checks those data and close it. By: Majid Soleimaninia Page 17

18 Figure 21: Displaying the Section numbers. Figure 22: Listing the element attributes for checking. 3.8 Apply displacement restraints The displacement restraints must be applied to reflect the physical support (often the most unclear part of an analysis) as well as eliminating all the rigid body motions (RBM). Here By: Majid Soleimaninia Page 18

19 there are three translational RBM plus three rotational ones. Apply the system nodal displacement restraints via: 1. Main Menu Preprocessor Loads Define Loads Apply Structural Displacement On Nodes (see Figure 23). 2. In Apply U, Rot on Nodes verifies that Pick and Single are checked on. 3. In the graphics window, Figure 24, select top node 1 (for complete restraints), OK. After the panel changes form, highlight the fixed option for all of the degrees of freedom components (UX, UY, UZ, ROTX, ROTY, ROYZ) as the DOF to be constrained 4. Under Constant value enter 0, OK. Note that these restraint operations are shown in the graphics window as triangles pointing in the direction of restraint, at each restrained node. To list the current restraints, Figure 25: 1. Utility Menu List Loads DOF Constraints On All Nodes. 2. When the (Displacement LIST) DLIST window appears check those data and close it Review the graphical restraint symbols in Figure 24 to verify the choice you picked from the list of available displacement restraints. Figure 23: Preparing to graphically assign displacement restraints. By: Majid Soleimaninia Page 19

20 Figure 24: Picking nodes to restrain all displacements and rotations. Figure 25: Nodal constraints list of all displacements and rotations. 3.9 Apply nodal loads This space frame is intended to carry a vertical load of (lb) at node 22. Specify that z component force with: By: Majid Soleimaninia Page 20

21 1. Main Menu Preprocessor Loads Define Loads Apply Structural Force/Moment On Nodes as in Figure In Apply F/M on Nodes verify that Pick and Single are on, and then pick node 22, OK. 3. When the window changes form (lower part of Figure 27, pick a vertical force (FZ) for the Direction of force and (lb) for the Constant value, OK. 4. Then the arrows representing the load should appear as in Figure 28. Figure 26: Preparing to graphically assign nodal force/moment. Figure 27: Apply nodal force/moment on selected node. By: Majid Soleimaninia Page 21

22 You may also wish to list the current loads, Figure 28: 1. Utility Menu List Loads Forces On All Nodes. 2. When the Force LIST (FLIST) window appears check those data and close it. Figure 28: Nodal forces list of all force/moment. 4 Solve for displacements and secondary variables To use the current (and only) load system (LS) enter: 1. Main Menu Solution Solve Current LS, review the listed summary, OK. 2. When the solution of the simultaneous equations is complete you will be alerted that the solution is done. By: Majid Soleimaninia Page 22

23 Figure 29: Solving displacements for the current load set. 5 Post-processing 5.1 Displacements It is always wise to visually check the computed displacements: 1. Main Menu General Postproc Plot Results Deformed Shape. 2. In Plot Deformed Shape pick the combined deflected and undeformed option for the Items to be plotted (KUND), OK. Check the plot in the graphics window, such as the one seen in Figure Animate the computed deflections with:utility Menu PlotCrtls Animate Deformed Shape. 4. Pick Def+undeformed in Animate Deformed Shape, OK. 5. If desired, employ the Animation Controller that appears, or simply pick Stop, Close. By: Majid Soleimaninia Page 23

24 Figure 30: The deformed and undeformed gantry crane. To create a hardcopy (you may need to try various background colors): By: Majid Soleimaninia Page 24

25 1. Utility Menu PlotCrtls Hard Copy Printer (or File), select your printer name, Print. 2. To get the reverse video white background of Figure 30 use PlotCtrls Style Color Reverse Video. Since displacements and (infinitesimal) rotations are vector quantities it is wise to plot them in that mode as a visual check of the response of the system. To do that: 1. General Postproc Plot Results Vector Plot Predefined. 2. In Vector Plot of Predefined Vectors select DOF solution, Translation U, Vector mode, and element nodes. The resulting color plot will display the vectors with scaled lengths and with a color matching the color bar scale, as seen in Figure 31. To see a (potentially long) list of displacement results: 1. Preferences General Postproc List Results Nodal Solution. 2. In List Nodal Solution Nodal Solutions DOF Solution Displacement vector sum, OK. 3. Examine the results in the PRNSOL (PRint Nodal SOLution) Command window of Figure 26 and close it. 4. Likewise, to see the nodal rotations, also in Figure 26, use List Nodal Solution Nodal Solutions DOF Solution Rotation vector sum, OK. By: Majid Soleimaninia Page 25

26 Figure 31: Nodal displacement vector plot. By: Majid Soleimaninia Page 26

27 Figure 32: Listing the nodal displacements and rotations. By: Majid Soleimaninia Page 27