SECTION 9 SCUBA TANK S9-1 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation

SECTION 9 SCUBA TANK S9-2 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation

SECTION 9 SCUBA TANK S9-3 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Topics covered in this section u Axisymmetric modeling techniques u Importing Geometry u Mesh Density Control u Perform quality checks on stress results u Create and manipulate viewports

SECTION 9 SCUBA TANK S9-4 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Problem Description u Scuba tanks are designed to withstand cyclic pressurization and depressurization loads. They must also survive loads induced during transportation and actual service. You are asked to analyze a new scuba tank design. n Analysis Objectives u Determine stresses in the scuba tank under an internal pressure of 3000 psi. The maximum stress must be below the yield point of the tank material.

SECTION 9 SCUBA TANK S9-5 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Getting started on the scuba tank analysis u The scuba tank is a thick shell structure. We expect the state of stress to be 3 dimensional in the tank shell. Solid elements should be used. u Solid element models tend to get large and take a lot of CPU time to solve. This is especially true for non-linear or transient analysis. It is often advisable to simplify the model in order to speed up the analysis process. u Several ways to simplify finite element models are presented next.

SECTION 9 SCUBA TANK S9-6 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Simplifying Finite Element Models u Finite element models can be simplified by using a 2D (planar) representation of a 3D model. There are three ways to do this: l Plane Stress l Plane Strain l Axisymmetric u Finite element models can also be simplified by taking advantage of symmetry. There are two primary types of symmetry - reflective symmetry and cyclic symmetry. Symmetry techniques will be presented in detail in the advanced course.

SECTION 9 SCUBA TANK S9-7 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n The Plane Stress Model u Assumptions: l Z stress is zero l Stresses do not vary through the thickness u One way to identify a plane stress model is to look for structures in which the thickness is small compared to the other two dimensions.

SECTION 9 SCUBA TANK S9-8 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n The Plane Strain Model u Assumptions: l Z strain is zero u The depth of the plane strain model is large compared to the cross section. u Plane strain problems are common in civil engineering and are used to model retaining walls or dams.

SECTION 9 SCUBA TANK S9-9 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n The Axisymmetric Model u Assumptions: The geometry, loads, and boundary conditions are not a function of. l Another way to state this is that the geometry, loads, and boundary conditions do not vary in the circumferential direction. u Axisymmetry is commonly used to analyze pressure vessels and tanks.

SECTION 9 SCUBA TANK S9-10 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Simplification of the scuba tank model u Since the scuba tank is axisymmetric and the pressure load is axisymmetric, we can simplify the problem using axisymmetry. We will solve this problem using two different axisymmetric methods: 1. Build a sector of the tank using 3D solid elements 2. Build the tank cross section using 2D solid elements

SECTION 9 SCUBA TANK S9-11 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Creating the geometry for the tank u A geometry file for the scuba tank generated by a CAD package is available so there is no need to re-create the geometry. u Use File/Import to import the geometry file directly into PATRAN.

SECTION 9 SCUBA TANK S9-12 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select the file type to be imported

SECTION 9 SCUBA TANK S9-13 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Models created by the following CAD packages can be imported into PATRAN: u CATIA u Unigraphics u Pro/ENGINEER u EUCLID 3 u I-DEAS

SECTION 9 SCUBA TANK S9-14 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Additional types of geometry files can also be imported into PATRAN u ACIS solid geometry files l Typical file extension is.sat l Generated by CAD systems such as Autocad, SolidEdge, and Mechanical Desktop u Parasolid solid geometry files l Typical file extension is.xmt l Generated by CAD systems such as SolidWorks u IGES geometry files l Typical file extension is.igs l Generated by most CAD systems u STEP geometry files l Typical file extension is.stp l Generated by CAD systems such as CATIA

SECTION 9 SCUBA TANK S9-15 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n The scuba tank geometry file we have is a parasolid solid geometry model. Lets import this file into PATRAN.

SECTION 9 SCUBA TANK S9-16 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Import the parasolid model tank.xmt

SECTION 9 SCUBA TANK S9-17 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select Parasolid xmt options and select Model Units. Select Inches. This converts the units in the parasolid model from meters to inches.

SECTION 9 SCUBA TANK S9-18 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finish importing the parasolid model

SECTION 9 SCUBA TANK S9-19 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Rotate and shade the model

SECTION 9 SCUBA TANK S9-20 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Break the solid into two halves

SECTION 9 SCUBA TANK S9-21 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Delete half the tank

SECTION 9 SCUBA TANK S9-22 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Break the remaining solid into two halves

SECTION 9 SCUBA TANK S9-23 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Delete the upper quarter of the tank

SECTION 9 SCUBA TANK S9-24 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Lets create a coarse mesh. Select Tet10 elements. Select TetMesh Parameters and deselect curvature check to ensure a coarse mesh. Select the solid. Use a global edge length of to create one element thru the thickness. Click apply in thick

SECTION 9 SCUBA TANK S9-25 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation A relatively coarse mesh is created.

SECTION 9 SCUBA TANK S9-26 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Create Boundary Conditions u Since the scuba tank is axisymmetric, we need to create a cylindrical coordinate system to define the symmetry boundary conditions.

SECTION 9 SCUBA TANK S9-27 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a cylindrical coordinate system

SECTION 9 SCUBA TANK S9-28 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a symmetric constraint in the tangential (theta) direction

SECTION 9 SCUBA TANK S9-29 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Constrain translation in the theta direction and select coordinate system 1 as the analysis coordinate system

SECTION 9 SCUBA TANK S9-30 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select the two faces located on the planes of symmetry

SECTION 9 SCUBA TANK S9-31 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finish creating the theta symmetry boundary condition

SECTION 9 SCUBA TANK S9-32 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select Display- Loads/BC/Element Prop to change the display to show on FEM only. Also turn off LBC/Prop values to simplify the display.

SECTION 9 SCUBA TANK S9-33 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Next create a symmetry constraint in the radial direction

SECTION 9 SCUBA TANK S9-34 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Constrain the radial translation

SECTION 9 SCUBA TANK S9-35 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select the edge along the tank centerline

SECTION 9 SCUBA TANK S9-36 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finish creating the radial constraint

SECTION 9 SCUBA TANK S9-37 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a final constraint in the Z direction

SECTION 9 SCUBA TANK S9-38 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Constrain the z translation

SECTION 9 SCUBA TANK S9-39 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select the cylindrical surface at the valve interface

SECTION 9 SCUBA TANK S9-40 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finish creating the z constraint

SECTION 9 SCUBA TANK S9-41 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a pressure load

SECTION 9 SCUBA TANK S9-42 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select all the internal wetted surfaces

SECTION 9 SCUBA TANK S9-43 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finish creating the pressure load

SECTION 9 SCUBA TANK S9-44 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Create the scuba tank material properties u The tank is made from 17-4 PH stainless steel forging heat treated to the H1025 condition. l E = 28.5 x 10 6 psi = 0.27 l Ultimate strength = 155 ksi l Yield strength = 145 ksi

SECTION 9 SCUBA TANK S9-45 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create an isotropic material named 17-4PH

SECTION 9 SCUBA TANK S9-46 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a 3D solid physical property set for the tank

SECTION 9 SCUBA TANK S9-47 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Select the solid and apply.

SECTION 9 SCUBA TANK S9-48 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Submit the model to NASTRAN for a static analysis.

SECTION 9 SCUBA TANK S9-49 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Read the NASTRAN results into PATRAN

SECTION 9 SCUBA TANK S9-50 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create the deformation plot. The maximum deformation is in which is reasonable.

SECTION 9 SCUBA TANK S9-51 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create 3 additional viewports to display the results

SECTION 9 SCUBA TANK S9-52 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Tile the 4 viewports.

SECTION 9 SCUBA TANK S9-53 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Next lets plot the stresses u By default, the solid element stresses are computed in the basic coordinate system. u For the scuba tank, we are interested in the radial, hoop, and axial stresses which are defined in a cylindrical system. We need to transform the stresses from the basic coordinate system to the cylindrical coordinate system no. 1.

SECTION 9 SCUBA TANK S9-54 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Click the Plot Options icon. Select CID and coordinate system no. 1. This transforms the stresses into coordinate system 1.

SECTION 9 SCUBA TANK S9-55 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the radial (x component) stress.

SECTION 9 SCUBA TANK S9-56 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the hoop (y component) stress.

SECTION 9 SCUBA TANK S9-57 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the axial (z component) stress

SECTION 9 SCUBA TANK S9-58 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the Von Mises stress

SECTION 9 SCUBA TANK S9-59 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Zoom in to the critical area near the base of the tank. Notice that the stress gradient is high through the thickness of the tank.

SECTION 9 SCUBA TANK S9-60 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Turn off stress averaging. Notice that the stress fringes are jagged.

SECTION 9 SCUBA TANK S9-61 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the stress jumps at each node. The difference between the maximum stress and the minimum stress at each node is plotted.

SECTION 9 SCUBA TANK S9-62 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Scuba tank coarse-mesh model analysis summary: u The maximum Von Mises stress is 31,600 psi at the base of the tank near the fillet radius. u The stress gradient through the tank wall thickness is high. It ranges from 31,000 psi on the inside wall to about 7,000 psi on the outside wall. This stress gradient is captured by a single tet10 element through the thickness. u The un-averaged stress fringe plot is jagged, an indication that the mesh is too coarse. u The stress difference plot shows a maximum stress jump of 16,000 psi. This suggests that the mesh is too coarse in this area. n This first scuba tank model was relatively coarse. It helped us identify the critical area in the tank. We will now create a second model with a finer mesh in the critical area.

SECTION 9 SCUBA TANK S9-63 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a new database and import the tank geometry. Break the solid into 90-degree sectors as before and create a cylindrical coordinate system.

SECTION 9 SCUBA TANK S9-64 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a point 1 away from the fillet radius. Point 163 New point

SECTION 9 SCUBA TANK S9-65 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a plane at this new point.

SECTION 9 SCUBA TANK S9-66 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Use the plane to break the solid

SECTION 9 SCUBA TANK S9-67 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Mesh the bottom portion of the tank. Make sure curvature check is turned back on. Use an element size of inch.

SECTION 9 SCUBA TANK S9-68 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Move to the other end of the tank. Create a point 1 away from the dome/cylinder transition point and create a plane there. Break the solid using this plane.

SECTION 9 SCUBA TANK S9-69 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Mesh this end of the tank with an element size of 0.25 inch.

SECTION 9 SCUBA TANK S9-70 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finally mesh the cylindrical portion with an element size of inch. Under assembly parameters, turn on Match Parasolid Faces to match the mesh on two neighboring solids. Solid 9 Solid 7 Solid 8

SECTION 9 SCUBA TANK S9-71 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Equivalence the model

SECTION 9 SCUBA TANK S9-72 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Finish creating loads, boundary conditions, material properties, and element properties. Submit the model to NASTRAN for static analysis.

SECTION 9 SCUBA TANK S9-73 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Read the NASTRAN results into PATRAN.

SECTION 9 SCUBA TANK S9-74 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create the deformation plot. The maximum deformation of inch agrees with the coarse model.

SECTION 9 SCUBA TANK S9-75 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the Von Mises stress

SECTION 9 SCUBA TANK S9-76 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Zoom into the critical area. The maximum Von Mises stress is 29,400 psi. Notice that there are 5 elements through the thickness in the critical area.

SECTION 9 SCUBA TANK S9-77 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Turn off stress averaging. The maximum Von Mises stress is 30,100 psi

SECTION 9 SCUBA TANK S9-78 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the stress jumps across nodes.

SECTION 9 SCUBA TANK S9-79 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Scuba tank fine-mesh model analysis summary: u The maximum Von Mises stress is 30,100 psi at the base of the tank near the fillet radius. u There are 5 elements through the thickness in this critical area. The stress gradient is represented reasonably well through the thickness. u The un-averaged stress fringe plot is relatively smooth, indicating that the re-meshing effort paid off. u The stress difference plot shows a maximum stress jump of 4500 psi. Is further mesh refinement necessary? u A total of 114,019 nodes and 76,658 elements were used to model this problem. n Lets analyze the tank again using 2D axisymmetric elements.

SECTION 9 SCUBA TANK S9-80 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Using 2D Axisymmetric Elements u This converts a 3D problem into a planar problem by using 2D elements. u Only half of the tank cross section is modeled. u Geometry, boundary condition, and loads must all be axisymmetric. u A much finer mesh can be used to solve this problem.

SECTION 9 SCUBA TANK S9-81 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Open a new PATRAN database and import the scuba tank parasolid model.

SECTION 9 SCUBA TANK S9-82 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Break the tank twice as before. Keep the +X/-Y quadrant.

SECTION 9 SCUBA TANK S9-83 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Extract the tank face located in the X-Z plane. Delete the solid.

SECTION 9 SCUBA TANK S9-84 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Change the view by using Viewing Angles.

SECTION 9 SCUBA TANK S9-85 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Mesh the surface to generate triangular elements with a global edge length of inch. The axisymmetric elements must lie in the positive x half of the x-z plane of the basic coordinate system with the z axis as the centerline.

SECTION 9 SCUBA TANK S9-86 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation The use of planar elements allowed us to use a much finer mesh. There are now more than 10 elements through the thickness in the critical area.

SECTION 9 SCUBA TANK S9-87 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation The T2, R1, R2, and R3 degrees of freedom are not used in this axisymmetric problem. Constrain these unused degrees of freedom.

SECTION 9 SCUBA TANK S9-88 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Constrain the model in the z direction.

SECTION 9 SCUBA TANK S9-89 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Apply the z constraint to the curve at the valve interface. The radial constraint is automatically handled by NASTRAN.

SECTION 9 SCUBA TANK S9-90 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create a pressure load

SECTION 9 SCUBA TANK S9-91 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Apply the pressure to all the internal curves.

SECTION 9 SCUBA TANK S9-92 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create the material properties

SECTION 9 SCUBA TANK S9-93 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create the axisymmetric element properties

SECTION 9 SCUBA TANK S9-94 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Run the static analysis.

SECTION 9 SCUBA TANK S9-95 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Read the results back into PATRAN.

SECTION 9 SCUBA TANK S9-96 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Create the deformation plot. Maximum deformation is inch which agrees with the previous two models.

SECTION 9 SCUBA TANK S9-97 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the Von Mises stress. The maximum Von Mises Stress is 29,100 psi

SECTION 9 SCUBA TANK S9-98 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Turn off stress averaging. The maximum Von Mises stress remains at 29,100 psi

SECTION 9 SCUBA TANK S9-99 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Zoom in on the critical area. Note that the un- averaged stress fringes are relatively smooth.

SECTION 9 SCUBA TANK S9-100 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation Plot the stress jumps across nodes. The maximum stress difference in the critical area is low.

SECTION 9 SCUBA TANK S9-101 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation n Scuba tank 2D axisymmetric analysis summary u The maximum Von Mises stress is 29,100 psi at the base of the tank near the fillet radius. u There are more than10 elements through the thickness in this critical area. The stress gradient is represented reasonably well through the thickness. u The un-averaged stress fringe plot is very smooth, indicating that the mesh density is adequate. u The stress difference plot shows near zero values. u Using a 2D representation of the scuba tank, we were able to create a smaller model with a finer mesh compared to the 3D model.

SECTION 9 SCUBA TANK S9-102 NAS120, Section 9, May 2006 Copyright 2006 MSC.Software Corporation EXERCISE Perform Workshop 10 Support Bracket in your exercise workbook. Optional: Analyze the Scuba Tank covered in this section.