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Material MAT_005 (Soil and Crushable Foam) was used to model the soil. Volumetric compaction is determined by a tabulated curve of pressure versus volumetric strain defined from a hydrostatic compression test. A pressure-dependent flow rule governs the deviatoric behavior of the model: ( ) (3.14) Where: , , are user-defined constants obtained from triaxial compression test. An example of such failure surface definition is shown in Figure 3.28. Figure 3.28 Strength envelope in terms of yield surface- second invariant of deviatoric stress and pressure The shear failure of the soil is occurring when the s defined in Equation (3.14) becomes zero. It means that the stress state defined by the second stress invariant is located on the yield surface. This material definition has a simple implication stating that if the confining pressure of the material is very low, accordingly low shear stress would cause the material to fail. In the case of scour slope stability lack of confinement of the sand is causing fluid-like flow of material. 3.3.3. Procedure Flowchart The procedure consists of the following steps: 1. Run the analysis in STAR-CCM+ up to the point where the slope angle exceeds significantly the natural angle of repose of the sand. (This is the state where deviatoric shear stress in the soil can cause the slope to slide.) 2. Extract the shape of the scour hole in the NASTRAN file format. 3. Import the NASTRAN file to LS-PrePost – a pre and post processor for LS-DYNA. TRACC/TFHRC Y1Q3 Page 72
4. Build a shell container with the shape of the scour for soil volume initialization in the LS-DYNA simulation. 5. Analyze the slope stability problem using LS-DYNA MM-ALE capabilities. 6. Export final shape of the scour to the NASTRAN file that can be imported back to STAR-CCM+. 3.3.4. Simplifying Assumptions The procedure of this coupling has several simplifications: 1. The shear stresses on the bed surface resulting from the water flow are not transferred in the coupling process – only the geometry is transferred. Due to this assumption the surface shear stress is not contributing to the further slope slide. 2. If the LS-DYNA simulation is executed too early in the scouring process the gravitational forces may have small effect on the soil behavior. That may require long computations for achieving the equilibrium position. 3. State of stress in the soil from LS-DYNA is not transferred back to STAR-CCM+. Gravitational compaction will be occurring each time the transfer between STAR-CCM+ and LS-DYNA is executed. For these reasons it is not recommended to perform multiple transfers between the two codes. Limiting the transfers to one or two would reduce the errors generated in the coupling process. 3.3.5. Example of Use of the Procedure Geometry of scour hole with noticeable steep walls was obtained from STAR-CCM+ simulation. Its initial shape is shown in Figure 3.29. Figure 3.29 Initial scour shape based on STAR-CCM+ calculation Subsequently the geometry was used to build a volume for soil material initialization in LS-DYNA. Only a portion of the domain around the pier was modeled to save the computational cost. The modeled domain had approximate dimensions of 300 mm x 300 mm x 750 mm for width, height and length respectively. The base size of the background element was ~2.5 mm which resulted in ~3,450,000 uniform hexahedral elements and about 10 elements through the width of the initial scour hole localized deformation. This is a rather large number of elements and should be sufficient to capture the deformation precisely. Figure 3.30 shows the Finite Element model of the scour hole. Only soil and the TRACC/TFHRC Y1Q3 Page 73
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ANL/ESD/11-39 Computational Mechani
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ANL/ESD/11-39 Computational Mechani
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Computational Mechanics Research an
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3.3.4. Simplifying Assumptions ....
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Figure 2.22: Velocity distribution
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List of Tables Table 2.1: Boundary
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experiments at TFHRC continued. A m
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2. Computational Fluid Dynamics for
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( ) ( ) (2.8) where A 0, A 1, and n
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efine the rate function to improve
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The objective of this work is to de
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2.3.2. Mesh Refinement Study As det
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Page 33 and 34: Mesh 1 Mesh 2 Mesh 3 Mesh 4 Mesh 5
Page 35 and 36: Figure 2.20: Dimensional details of
Page 37 and 38: Figure 2.22: Velocity distribution
Page 39 and 40: Figure 2.25: CFD velocity contour p
Page 41 and 42: Figure 2.27: CFD velocity contour p
Page 43 and 44: Conclusions for Comparison with Exp
Page 45 and 46: 3.1.1.1. Approach To date, an initi
Page 47 and 48: Figure 3.4: Sampling domain [3] A c
Page 49 and 50: present. In addition during the sum
Page 51 and 52: For each level, the figures below s
Page 53 and 54: 0.0 sec 0.5 sec 1.0 sec 1.5 sec 2.0
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Page 61 and 62: ̇ = steer angle These equations co
Page 63 and 64: ̈ With the success to the above an
Page 65 and 66: command. This requires the creation
Page 67 and 68: Figure 3.17: FEM Model of a Ford F-
Page 69 and 70: 3) Chen, F. and Chen, S., “Assess
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Page 73 and 74: while the passive system has fixed
Page 75: the controllable EMSA. Simulations
Page 79 and 80: Figure 3.32 Comparison of the initi
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