Tutorial: narrowTmember

Prepared by Philip Cardiff

Tutorial Aims

• Demonstrate how to perform a linear-static stress analysis of a 3-D engineering component in solids4foam;
• Compares the performance of two finite volume solid models: (i) the coupled cell-centred coupledUnsLinearGeometryLinearElastic model, and (ii) the segregated cell-centred linearGeometryTotalDisplacement model.
• Shows how to modify a case, which uses the coupledUnsLinearGeometryLinearElastic solid model, to use the linearGeometryTotalDisplacement solid model.

Case Overview

This case comprises a narrow engineering component with a T cross-section (Figure 1). This case was proposed as a benchmark by Demirdzic et al., 1997, Benchmark solutions of some structural analysis problems using the finite-volume method and multigrid acceleration. Int J Numer Methods Eng. Due to symmetry, the solution domain consists of one-quarter of the component. A constant negative pressure of 1 MPa is applied to the lower surface, and the upper left surface is fully clamped (Figure 1). The Young's modulus is 210 GPa, and Poisson's ratio is 0.3. A radius \(R = 5\) mm hole is located at the expected stress concentration. Four separate systematically refined hexahedral meshes (624, 4992, 39 936, and 319 488 cells) are examined here, mimicking the meshes employed by Demirdzic et al.; the coarsest mesh is shown in Figure 2.

Figure 1: Geometry and loading with dimensions in mm.

Figure 2: Coarest hexahedral mesh (624 cells)

Running the Case

The tutorial case is located at solids4foam/tutorials/solids/linearElasticity/narrowTmember. The case can be run using the included Allrun script, i.e. ./Allrun. In this case, the Allrun simply consists of creating the mesh using blockMesh (./blockMesh) followed by running the solids4foam solver (./solids4Foam).

To modify the case to run with the segregated linearGeometryTotalDisplacement solid model, the following changes are required:

• In 0/D
  • Replace blockSolidTraction with solidTraction
  • Replace blockFixedDisplacement with fixedDisplacement
  • Replace blockFixedDisplacementZeroShear with fixedDisplacementZeroShear
• In constant/solidProperties
  • Replace solidModel coupledUnsLinearGeometryLinearElastic; with solidModel linearGeometryTotalDisplacement;
  • (This is already present in the tutorial case) Add the following dictionary linearGeometryTotalDisplacementCoeffs {}
• In system/fvSchemes
  • Set the default gradSchemes to pointCellsLeastSquares for OpenFOAM.com/OpenFOAM.org, or leastSquares for foam-extend
  • Set the default divSchemes to Gauss linear
  • Set the default laplacianSchemes to Gauss linear skewCorrected 1
  • Set the default interpolationSchemes to linear

The case can the be run as before, i.e. > blockMesh && solids4Foam.

Expected Results

Figure 3 shows the \(\sigma_{xx}\) and \(\sigma_yy\) stress distributions on the plane z = 0 m (symmetry plane) for the finest mesh. The predictions agree closely with the results of Demirdzic et al. Further comparisons can be found in Cardiff et al., 2016, A block-coupled Finite Volume methodology for linear elasticity and unstructured meshes, Comp. and Struct.

Figure 3: Predicted stress component distributions on the plane z = 0:0 m (right) compared with results from Demirdzic et al. (left).

The wall-clock times and memory requirements for each run are given in Table 1, where the results for the coupled and segregated solid models are compared. The coupled solver used a bi-conjugate gradient stabilised linear solver with ILU(0) preconditioner, while the segregated solver used a conjugate gradient linear solver with ILU(0) preconditioner. Both approaches used a solution tolerance of \(1 \times 10^{-6}\). In this case, the coupled solver is approximately four times faster than the segregated solver but requires about four times more memory.

Table 1: Wall-clock time (in s) and maximum memory usage (in MB).