Tutorial: Heave and Pitch Simulation of Ship hull moving through head sea waves Step 10: Dynamic Mesh Setup 1. Set the dynamic mesh parameters. Dynamic Mesh (a) Enable Dynamic Mesh. (b) Enable Six DOF Solver. Six DOF Solver Settings includes Gravitational Acceleration setting and the Write Motion History option. You already have set the Gravitational Acceleration in the Operating Conditions dialog box. If you want the motion history, enable Write Motion History and specify the File Name. (c) Ensure that Smoothing is enabled. (d) Enable Remeshing from the Mesh Methods group box ans click Settings.... i. Click Smoothing tab and set the Spring Constant Factor to 0.5. ii. Click Remeshing tab and set the remeshing parameters. 14 c ANSYS, Inc. February 25, 2011
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Tutorial: Heave and Pitch Simulation of Ship hull moving through head sea waves
Step 10: Dynamic Mesh Setup
1. Set the dynamic mesh parameters.
Dynamic Mesh
(a) Enable Dynamic Mesh.
(b) Enable Six DOF Solver.
Six DOF Solver Settings includes Gravitational Acceleration setting and the WriteMotion History option. You already have set the Gravitational Acceleration in theOperating Conditions dialog box. If you want the motion history, enable WriteMotion History and specify the File Name.
(c) Ensure that Smoothing is enabled.
(d) Enable Remeshing from the Mesh Methods group box ans click Settings....
i. Click Smoothing tab and set the Spring Constant Factor to 0.5.
ii. Click Remeshing tab and set the remeshing parameters.
Tutorial: Heave and Pitch Simulation of Ship hull moving through head sea waves
A. Enter 0.011 m for Minimum Length Scale and 0.65 m for MaximumLength Scale.
The Minimum Length Scale and the Maximum Length Scale can be ob-tained from the Mesh Scale Info dialog box. Click on the Mesh ScaleInfo... button to open the Mesh Scale Info dialog box.
Tutorial: Heave and Pitch Simulation of Ship hull moving through head sea waves
Note: Open the six dof property.c file and check the properties of the hull body spec-ified. Mass and Moment of inertia are specified here. In addition to this followingcommands have been written,
prop[SDOF ZERO TRANS X] = TRUE;
prop[SDOF ZERO TRANS Y] = TRUE;
prop[SDOF ZERO ROT X] = TRUE;
prop[SDOF ZERO ROT Z] = TRUE;
These macros have been used to restrict the motion in the particular direction. Forexample first command restricts the translation motion in X direction. Like this wayfour motions have been restricted using four commands. Only two motions are allowedwhich is translation along Z axis and rotation about Y axis.
Tutorial: Heave and Pitch Simulation of Ship hull moving through head sea waves
6. Run the calculation.
Run Calculation
(a) Enter 0.005 s for Time Step Size.
Make sure that the time step size is in the range of 1/100 to 1/200 of the Period
(b) Enter 3000 for Number of Time Steps.
(c) Set Max Iterations/Time Step to 20.
Write the initial case and data files with the name hull-2dof-init.cas.gz beforeclicking Calculate
File −→ Write −→Case & Data
(d) Click Calculate.
Now you need to monitor the drag residual plot.Run the simulation till the dragvalue stabilize(Figure 3); after stabilization drag curve will become periodic.
Tutorial: Heave and Pitch Simulation of Ship hull moving through head sea waves
5. Create Heave and Pitch plots from the motion history data
In the dynamic mesh properties we have switch on the Write Motion History in thesix DOF options, so a motion history file (Figure 6) is written which consists of linearand angular positions. In the file, CG Z is the heave and THETA Y is the pitch.
Figure 6: Motion History File
(a) Create a text file heave.xy by copying the time and CG Z columns. Plot this fileto get the heave curve.