w25 riser viv

Copyright 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.

Workshop 25 Riser VIV


Riser VIV

Purpose of the Workshop

Set up a Practical FSI simulation (P-FSI)

Gain experience using ALE mesh motion

Use Surface Manager to assign boundary condition types

Use Eigenmode Manager for transfering structural data onto CFD mesh

Use the Propagate feature to copy settings from one group to another

Run AcuSolve

Monitor solution with AcuProbe

Post process in AcuFieldView

2


Flexible Riser Problem Description

In this workshop, we perform a P-FSI simulation of a flexible riser suspended in cross

flow. Note that this is a contrived configuration used for training purposes only.

The following diagram illustrates the problem set up and the constraints that are placed

on the ring.

Riser VIV

3

OD= 0.15 m

Top an bottom are constrained in all directions to have zero displacement

and zero rotation

ID= 0.125 m

Youngs Modulus = 2.0 x 109 Pa Density = 1500 kg/m3 Poissons Ratio = 0.3

6 m


Riser VIV

Create a new database

File New

Browse to problem directory

Provide a file name riser and click Save

Import Geometry

File > Import

Browse to the problem directory, select the

parasolid file and click Open

In the Import Geometry dialog set,

Surface Group Option to By attributes

Surface attribute string to SDL/TYSA_NAME

By setting the above, we are getting the surface set tags from cad into AcuConsole

Click Ok to import the geometry

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Riser VIV

Set the data tree to Basic

Ensure that the BAS button is selected in the Data

tree Manager

Expand Model > Surfaces

All the surfaces are placed in the appropriate sets.

This is due to the tagging of faces in SolidWorks and

importing the model using By attributes option

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Riser VIV

Set up global parameters

Expand Global branch

Double-click Problem Description

Enter the problem title and subtitle

Set Analysis Type' to Transient

Set Turbulence equation to Spalart-Allmaras

Set Mesh Type to Arbitrary mesh movement

(ALE)

Set solution strategy

Double-click Auto Solution Strategy

Set Max time steps to 4000

Set Initial time increment to .005 sec

Set Max stagger iterations to 6

Verify that Flow and Mesh are set to On

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Riser VIV

Material model

Water is used as the fluid which is already defined

Set the nodal output frequency

Double-click on Nodal Output

Set Time step frequency to 5

Set Output initial condition to On

Nodal Initial Condition

Set the X velocity to 1.5 m/s

Eddy viscosity to 1.0e-05 m2/sec

7


Riser VIV

Separating Volume sets

Right-click on Surfaces and select Display off

Right-click on Volumes and select Display on

Right-click on Volumes again and select New

Rename Volume 1 to fluid

Right-click on fluid and click Add To. Select the

model. Outer region is selected which is the fluid

region.

Remaining is the pipe volume

Rename default to solid

Now turn off volumes display and turn on

surfaces.

Right-click on Surfaces and select Purge to

delete any empty surface sets.

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Riser VIV

Mesh Parameters

Click on MSH in the Datatree Manager

Double click on Global Mesh Attributes

Set Mesh size type to Absolute

Absolute mesh size = 0.16

Right-click on Zone Mesh Attributes and select New

Rename Zone Mesh Attributes 1 to Box_Large

Set the Mesh zone type to Box

Click on Open Array next to Box center

Specify the center as (0.2, 1.0, 0.0) and click Ok.

Set Box lengths to 0.9 m, 2.1 m and 0.6 m

Set Mesh size to 0.04 m

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Riser VIV

Again right-click on Zone Mesh Attributes and

select New

Rename Zone Mesh Attributes 1 to Cylinder

Set the Mesh zone type to Cylinder

Click on Open Array next to Base centers array

Set the base centers as (0, -0.05, 0) and (0, 2.05, 0)

Set Radius to 0.15 m

Set Mesh size to 0.02 m

Expand Volumes > solid

Enable Volume Mesh Attributes and set Mesh

size type to NoMesh

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Riser VIV

Expand Surfaces > Pipe

Enable Surface Mesh Attributes

Set Mesh size type to Absolute

Absolute mesh size = 0.015

Boundary layer flag = On

Boundary layer type = Full control

Resolve = Total layer height

First Element height = 0.002 m

Growth rate = 1.3

Number of layers = 6

Click on Tools > Generate Mesh

Click Ok in the Launch AcuMeshSim dialog to run the mesher

~ 81,000 nodes will be generated

Right-click on Surfaces and set the Display type to Solid&wire to see the mesh

Also visualize the mesh around pipe using the cut-plane feature.

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Riser VIV

Scaling the mesh

In the menu bar, select MeshOp > Transform Coordinates

In the Transform Coordintes Dialog select Scale from the drop downlist next to

Transformation

Specify 3 in the second box to scale the model 3 times in Y direction

Click Apply and Close

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Riser VIV

Create some monitor points

Expand the Output branch

Right click on Time History Output and select New

Rename Time History Output 1 to Monitor Points

Double-click Monitor Points

Change Type to Coordinates

Click Open Array next to Coordinates

In the Array Editor click Read and select monitor.dat file. It has the coordinates of the monitor points. Click Ok

13


Riser VIV

Create Multiplier Function

Multiplier function is used to ramp up the fluid forces initially

Click PB* in the datatree manager

Right-click on Multiplier Function and select New

Rename Multiplier Function 1 to Ramp

Set the Type to Piecewise linear

Curve fit variable to Time step

Click on Open Array next to Curve fit values

Provide the following from the image below.

We are ramping linearly for the first 10 time steps.

14


Riser VIV

Set the Datatree Manager to FSI mode

Ensure that the FSI button is selected in the

Data tree Manager

This only shows settings associated with set-up

of FSI models

Create a Flexible Body

Right-click on Flexible Body and select New

Right-click on Flexible Body 1 and select

Rename rename to Flexible Riser

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Riser VIV

Double-click on Flexible Riser to open it

In the panel, click on the Open Refs button

next to Surface outputs

This opens the list editor to specify the name

of the surface outputs that AcuSolve will use

to determine the forces on the flexible body:

Select Add Row, then select Pipe from the pull-down

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Riser VIV

Set the data tree back to Basic

Click on the BAS button in the Data tree Manager

Set the element set properties

Collapse the Global branch

Expand the Model branch

Expand the Volumes and Surfaces branches

Expand the fluid branch under Volumes

Double-click Element Set

Set Material Model to Water

Boundary Conditions

Right-click on Surfaces and select Surface

Manager

Expand the Model branch

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Riser VIV

Set the boundary condition types

Right click on Surfaces, then Surface Manager

Click Columns and make sure Simple BC Type is enabled

Set the boundary conditions using the Simple BC Type column according

to the following:

Bottom Symmetry

Inlet Inflow

Outlet Outflow

Pipe Wall

Side_MaxZ Symmetry

Side_MinZ Symmetry

Top Symmetry

Close surface manager

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Riser VIV

Set the boundary condition details

Expand the surface named Pipe

Ensure that the Surface Output box is toggled

on

Double click on Simple Boundary Condition

Ensure that Wall Velocity Type is set to Match Mesh Velocity

Set the Mesh displacement BC Type to Flexible Body

Set the Flexible Body to Flexible Riser

These settings tell the mesh on the BODY walls to

move based on the Flexible Body parameters

that we will define later

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Riser VIV

Expand the surface named Side_MaxZ


Set Mesh displacement BC Type to Slip

Repeat the same for Side_MinZ

Set Mesh displacement BC Type to Slip

These settings allow the mesh on the

Side_MinZ surface to slip tangentially along

the surface

Expand the surface named Inlet


Set X velocity to 1.5 m/sec

Eddy viscosity to 1.0e-05 m2/sec

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Riser VIV

We will now create a set of nodes surrounding the

ring that we will force to move in conjunction with the

body

Right-click on Nodes and select New

Rename the node set to 8Layers

Right-click on 8Layers and select Define

When the Node Define dialog box opens, set the type

to Surface, then select Pipe as the surface, and set

Number of Layers to 8.

Select OK

This creates a node set containing 8 layers of nodes starting from the surface named Pipe

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Riser VIV

The next step is to import the structural model and project the eigenvectors onto

the CFD mesh

Well project the eigenvectors onto the surface of the ring as well as the node set that was just created.

This projection step tells AcuSolve to move the nodes according to the solution of the flexible body

The Eigenmode Manager will be used to perform this projection and update the boundary conditions with the appropriate data.

Note that this projection step relies on nodal coordinates and ids

If the mesh is changed, this step needs to be performed again!

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Riser VIV

Open the Eigenvalue manager by clicking on

the appropriate icon in the main toolbar

Click on Add, then type Modes for the

name.

Click on Open next to Import, then

navigate to the Radioss directory and select

the structural data file (Riser_PFSI.op2)

Make sure the file filter is set according to the type of results file to be loaded

Click on Open to load the file

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Riser VIV

Click on the Show tab in the Eigenmode

Manager, then toggle the animation button on

to visualize the modes of the structure.

Experiment with the Animation mode id slider

to look at the different modes of the structure.

You can also change the amplitude, speed, and

visualization properties of the animation using

this panel.

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Riser VIV

Click on the Transfer tab in the Eigenmode Manager.

Select Transfer next to the Flexible Body label.

Ensure that Flexible Riser is selected, then click on OK

This will transfer the mass, stiffness, and damping arrays from the structural model over to the Flexible Walls flexible body that was created earlier.

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Riser VIV

Select Transfer next to the Simple BC label.

Select the simple boundary condition named Pipe from the Reference Editor, then click on OK.

This will project the eigenvectors of the structure onto the nodes of the surface named Pipe.

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Riser VIV

Select Transfer next to the Nodal BC label.

Select the node set named 8Layers, then click on OK.

This will project the eigenvectors of the structure onto the nodes of the set named 8 Layers and activate the appropriate boundary conditions.

This projection step causes the nodes of this set to move directly with the structure

Note that there is an option to scale the eigenvectors for more complex applications.

Close the Eigenmode Manager

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Riser VIV

Save the model

Click on the save icon in the toolbar, or type

Ctrl+S

Write the AcuSolve input files and launch the

solver:

Click on the solve icon in the toolbar, or type

Ctrl+Shift+S

Select OK.

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Riser VIV

Launch acuProbe

Plot the mesh displacements at the time history output points to get an idea of how

much the pipe is deforming

Expand Time History

Expand Node 11

Plot the X mesh displacement

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Riser VIV

Post-process using AcuFieldView

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w25 riser viv

Documents

riser viv copyright

altair engineering

surface set tags

set output initial condition

riser viv purpose

import geometry dialog

spalartallmaras set

riser viv material model