ansys workbench 流固耦合计算实例

Oscillating Plate with Two-Way Fluid-Structure Interaction

Introduction This tutorial includes:

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Features

Overview of the Problem to Solve

Setting up the Solid Physics in Simulation (ANSYS Workbench)

Setting up the Fluid Physics and ANSYS Multi-field Settings in ANSYS CFX-Pre Obtaining a Solution using ANSYS CFX-Solver Manager Viewing Results in ANSYS CFX-Post

If this is the first tutorial you are working with, it is important to review the following topics before beginning:

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Setting the Working Directory Changing the Display Colors

Unless you plan on running a session file, you should copy the sample files used in this tutorial from the installation folder for your software (/examples/) to your working directory. This prevents you from overwriting source files provided with your installation. If you plan to use a session file, please refer to Playing a Session File. Sample files referenced by this tutorial include:

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OscillatingPlate.pre OscillatingPlate.agdb OscillatingPlate.gtm OscillatingPlate.inp

1. Features

This tutorial addresses the following features of ANSYS CFX.

Component Feature User Mode ANSYS CFX-Pre Simulation Type ANSYS Multi-field General Mode Transient Details Component Feature Fluid Type Domain Type Turbulence Model Heat Transfer Output Control General Fluid Single Domain Laminar None Monitor Points Details Transient Results File Wall: Mesh Motion = ANSYS MultiField Boundary Details Wall: No Slip Wall: Adiabatic Timestep Transient Animation ANSYS CFX-Post Plots Contour Vector In this tutorial you will learn about:

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Moving mesh

Fluid-solid interaction (including modeling solid deformation using ANSYS) Running an ANSYS Multi-field (MFX) simulation Post-processing two results files simultaneously.

2. Overview of the Problem to Solve

This tutorial uses a simple oscillating plate example to demonstrate how to set up and run a simulation involving two-way Fluid-Structure Interaction, where the fluid physics is solved in ANSYS CFX and the solid physics is solved in the FEA package ANSYS. Coupling between the two solvers is required throughout the solution to model the interaction between fluid and solid as time progresses, and the framework for the coupling is provided by the ANSYS Multi-field solver, using the MFX setup.

The geometry consists of a 2D closed cavity. A thin plate is anchored to the bottom of the cavity as shown below:

An initial pressure of 100 Pa is applied to one side of the thin plate for 0.5 seconds in order to distort it. Once this pressure is released, the plate oscillates backwards and forwards as it attempts to regain its equilibrium (vertical) position. The surrounding fluid damps the oscillations, which therefore have an amplitude that decreases in time. The CFX Solver calculates how the fluid responds to the motion of the plate, and the ANSYS Solver calculates how the plate deforms as a result of both the initial applied pressure and the pressure resulting from the presence of the fluid. Coupling between the two solvers is required since the solid deformation affects the fluid solution, and the fluid solution affects the solid deformation.

The tutorial describes the setup and execution of the calculation including the setup of the solid physics in Simulation (within ANSYS Workbench) and the setup of the fluid physics and ANSYS Multi-field settings in ANSYS CFX-Pre. If you do not have ANSYS Workbench, then you can use the provided ANSYS input file to avoid the need for Simulation. 3. Setting up the Solid Physics in Simulation (ANSYS Workbench)

This section describes the step-by-step definition of the solid physics in Simulation within ANSYS Workbench that will result in the creation of an ANSYS input file OscillatingPlate.inp. If you prefer, you can instead use the provided OscillatingPlate.inp file and continue from Setting up the Fluid Physics and ANSYS Multi-field Settings in ANSYS CFX-Pre. Creating a New Simulation

1. If required, launch ANSYS Workbench.

2. Click Empty Project. The Project page appears displaying an unsaved project. 3. Select File > Save or click Save button.

4. If required, set the path location to a different folder. The default location is your working

directory. However, if you have a specific folder that you want to use to store files created during this tutorial, change the path. 5. Under File name, type OscillatingPlate.

6. Click Save.

7. Under Link to Geometry File on the left hand task bar click Browse. Select the provided

file OscillatingPlate.agdb and click Open.

8. Make sure that OscillatingPlate.agdb is highlighted and click New simulation from the

left-hand taskbar.

Creating the Solid Material

1. When Simulation opens, expand Geometry in the project tree at the left hand side of the

Simulation window.

2. Select Solid, and in the Details view below, select Material.

3. Use the arrow that appears next to the material name Structural Steel to select New

Material.

4. When the Engineering Data window opens, right-click New Material from the tree view

and rename it to Plate.

5. Enter 2.5e06 for Young's Modulus, 0.35 for Poisson's Ratio and 2550 for Density.

Note that the other properties are not used for this simulation, and that the units for these values are implied by the global units in Simulation.

6. Click the Simulation tab near the top of the Workbench window to return to the

simulation.

Basic Analysis Settings

The ANSYS Multi-field simulation is a transient mechanical analysis, with a timestep of 0.1 s and a time duration of 5 s.

1. Select New Analysis > Flexible Dynamic from the toolbar.

2. Select Analysis Settings from the tree view and in the Details view below, set Auto Time

Stepping to Off. 3. Set Time Step to 0.1.

4. Under Tabular Data at the bottom right of the window, set End Time to 5.0 for the

Steps = 1 setting.

Inserting Loads

Loads are applied to an FEA analysis as the equivalent of boundary conditions in ANSYS CFX. In this section, you will set a fixed support, a fluid-solid interface, and a pressure load. Fixed Support

The fixed support is required to hold the bottom of the thin plate in place.

1. Right-click Flexible Dynamic in the tree and select Insert > Fixed Support from the

shortcut menu.

2. Rotate the geometry using the Rotate

solid is visible, then select Face

button so that the bottom (low-y) face of the

and click the low-y face.

That face should be highlighted to indicate selection.

3. Ensure Fixed Support is selected in the Outline view, then, in the Details view, select

Geometry and click 1 Face to make the Apply button appear (if necessary). Click Apply to set the fixed support.

Fluid-Solid Interface

It is necessary to define the region in the solid that defines the interface between the fluid in CFX and the solid in ANSYS. Data is exchanged across this interface during the execution of the simulation.

1. Right-click Flexible Dynamic in the tree and select Insert > Fluid Solid Interface from

the shortcut menu.

2. Using the same face-selection procedure described earlier, select the three faces of the

geometry that form the interface between the solid and the fluid (low-x, high-y and high-x faces) by holding down to select multiple faces. Note that this load is automatically given an interface number of 1.

Pressure Load

1. Click Global Initialization 2. Apply the following settings:

Tab .

Setting Value Initial Conditions > Cartesian Velocity 0 [m s^-1] Components > U Initial Conditions > Cartesian Velocity 0 [m s^-1] Components > V Global Settings Initial Conditions > Cartesian Velocity 0 [m s^-1] Components > W Initial Conditions > Static Pressure > Relative 0 [Pa] Pressure 3. Click OK. Setting Solver Control

Various ANSYS Multi-field settings are contained under Solver Control under the External Coupling tab. Most of these settings do not need to be changed for this simulation.

Within each timestep, a series of “coupling” or “stagger” iterations are performed to ensure that CFX, ANSYS and the data exchanged between the two solvers are all consistent. Within each stagger iteration, ANSYS and CFX both run once each, but which one runs first is a user-specifiable setting. In general, it is slightly more efficient to choose the solver that drives the simulation to run first. In this case, the simulation is being driven by the initial pressure applied in ANSYS, so ANSYS is set to solve before CFX within each stagger iteration.

1. Click Solver Control

.

2. Apply the following settings:

Tab Setting Transient Scheme > Option Value Second Order Backward Euler Basic Settings Convergence Control > Minimum Number of (Selected) Coefficient Loops Convergence Control > Minimum Number of [a]2 Coefficient Loops > Min. Coeff. Loops Convergence Control > Max. Coeff. Loops 3 External Coupling Coupling Step Control > Solution Sequence Before CFX Fields Control > Solve ANSYS Fields Tab [a] Setting Value This setting is optional. The default value of 1 is also acceptable. 3. Click OK. Setting Output Control

This step sets up transient results files to be written at set intervals. 1. Click Output Control

.

2. On the Trn Results tab, create a new transient result with the default name. 3. Apply the following settings to Transient Results 1:

Setting Option Output Variable List Selected Variables Pressure, Total Mesh Displacement, Velocity [a]Value Output Frequency > Option Every Coupling Step [a] This setting writes a transient results file every multi-field timestep. 4. Click the Monitor tab. 5. Select Monitor Options.

6. Under Monitor Points and Expressions: 7. Click Add new item

and accept the default name.

8. Set Option to Cartesian Coordinates.

9. Set Output Variables List to Total Mesh Displacement X. 10. Set Cartesian Coordinates to [0, 1, 0]. 11. Click OK.

Writing the Solver (.def) File

1. Click Write Solver File

.

2. If the Physics Validation Summary dialog box appears, click Yes to proceed. 3. Apply the following settings

Setting File name Quit CFX–Pre [a] [a]Value OscillatingPlate.def (Selected) If using ANSYS CFX-Pre in Standalone Mode. 4. Ensure Start Solver Manager is selected and click Save.

5. If you are notified the file already exists, click Overwrite.

6. This file is provided in the tutorial directory and will exist in your working folder if you

have copied it there.

7. Quit ANSYS CFX-Pre, saving the simulation (.cfx) file at your discretion. 5. Obtaining a Solution using ANSYS CFX-Solver Manager

The execution of an ANSYS Multi-field simulation requires both the CFX and ANSYS solvers to be running and communicating with each other. ANSYS CFX-Solver Manager can be used to launch both solvers and to monitor the output from both.

1. Ensure the Define Run dialog box is displayed.

There is a new MultiField tab which contains settings specific for an ANSYS Multi-field simulation.

2. On the MultiField tab, check that the ANSYS input file location is correct (the location is

recorded in the definition file but may need to be changed if you have moved files around).

3. On UNIX systems, you may need to manually specify where the ANSYS installation is if

it is not in the default location. In this case, you must provide the path to the v110/ansys directory. 4. Click Start Run.

The run begins by some initial processing of the ANSYS Multi-field input which results in the creation of a file containing the necessary multi-field commands for ANSYS, and then the ANSYS Solver is started. The CFX Solver is then started in such a way that it knows how to communicate with the ANSYS Solver.

After the run is under way, two new plots appear in ANSYS CFX-Solver Manager:

ANSYS Field Solver (Structural) This plot is produced only when the solid physics is set to use large displacements or when other non-linear analyses are performed. It shows convergence of the ANSYS Solver. Full details of the quantities are described in the ANSYS user documentation. In general, the CRIT quantities are the convergence criteria for each relevant variable, and the L2 quantities represent the L2 Norm of the relevant variable. For convergence, the L2 Norm should be below the criteria. The x-axis of the plot is the cumulative iteration number for ANSYS, which does not correspond to either timesteps or stagger iterations. Several ANSYS iterations will be

performed for each timestep, depending on how quickly ANSYS converges. You will usually see a somewhat “spiky” plot, as each quantity will be unconverged at the start of each timestep, and then convergence will improve.

ANSYS Interface Loads (Structural) This plot shows the convergence for each quantity that is part of the data exchanged between the CFX and ANSYS Solvers. In this case, four lines appear, corresponding to two force components (FX and FY) and two displacement components (UX and UY). Since the analysis is 2D, FZ and UZ are not exchanged. Each quantity is converged when the plot shows a negative value. The x-axis of the plot corresponds to the cumulative number of stagger iterations (coupling iterations) and there are several of these for every timestep. Again, a spiky plot is expected as the quantities will not be converged at the start of a timestep.

The ANSYS out file is displayed in ANSYS CFX-Solver Manager as an extra tab. Similar to the CFX out file, this is a text file recording output from ANSYS as the solution progresses.

1. Click the User Points tab and watch how the top of the plate displaces as the solution

develops.

2. When the solvers have finished and ANSYS CFX-Solver Manager puts up a dialog box

to tell you this, click Yes to post-process the results. 3. If using Standalone Mode, quit ANSYS CFX-Solver Manager. 6. Viewing Results in ANSYS CFX-Post

For an ANSYS Multi-field run, both the CFX and ANSYS results files will be opened up in ANSYS CFX-Post by default if ANSYS CFX-Post is started from a finished run in ANSYS CFX-Solver Manager.

Plotting Results on the Solid

When ANSYS CFX-Post reads an ANSYS results file, all the ANSYS variables are available to plot on the solid, including stresses and strains. The mesh regions available for plots by default are limited to the full boundary of the solid, plus certain named regions which are automatically created when particular types of load are added in Simulation. For example, any Fluid Solid Interface will have a corresponding mesh region with a name such as FSIN 1. In this case, there is also a named region corresponding to the location of the fixed support, but in general pressure loads do not result in a named region.

You can add extra mesh regions for plotting by creating named selections in Simulation - see the Simulation product documentation for more details. Note that the named selection must have a name which contains only English letters, numbers and underscores for the named mesh region to be successfully created.

Note that when ANSYS CFX-Post loads an ANSYS results file, the true global range for each variable is not automatically calculated, as this would add a substantial amount of time onto how long it takes to load such a file (you can turn on this calculation using Edit > Options and using the Pre-calculate variable global ranges setting under CFX-Post > Files). When the global range is first used for plotting a variable, it is calculated as the range within the current timestep. As subsequent timesteps are loaded into ANSYS CFX-Post, the Global Range is extended each time variable values are found outside the previous Global Range.

1. Turn on the visibility of Boundary ANSYS (under ANSYS > Domain ANSYS). 2. Right-click a blank area in the viewer and select Predefined Camera > View Towards

-Z. Zoom into the plate to see it clearly.

3. Apply the following settings to Boundary ANSYS:

Tab Setting Value Mode Variable Color Variable Von Mises Stress 4. Click Apply.

5. Select Tools > Timestep Selector from the task bar to open the Timestep Selector

dialog box. Notice that a separate list of timesteps is available for each results file loaded, although for this case the lists are the same. By default, Sync Cases is set to By Time Value which means that each time you change the timestep for one results file, ANSYS CFX-Post will automatically load the results corresponding to the same time value for all other results files.

6. Set Match to Nearest Available.

7. Change to a time value of 1 [s] and click Apply.

The corresponding transient results are loaded and you can see the mesh move in both the CFX and ANSYS regions.

1. Clear the visibility check box of Boundary ANSYS.

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