aqwa-intro 14 5 ws05 1 load mapping

2012 ANSYS, Inc. March 21, 2013 1 Release 14.5

14.5 Release

Workshop 5.1

Load Mapping


Worked Example

We are going to create a simple box shaped model to demonstrate the load mapping process

The structural model will include some simple stiffeners to show how to handle internal elements

The Steps of the exercise include:

Create Structural Geometry Create Structural Model and Information Create Hydrodynamic Geometry Create Hydrodynamic Model and Information Extract the Hydrodynamic Load Information (Load Mapping) Include the Hydrodynamic loading to Structural model Investigate the final results


Step 1: Create the Structural Geometry Open Workbench

Create a Geometry instance and open DM for editing


...Create Structural geometry Create Hull

Select length units as meters Create box primitive Set details of box

Generate


...Create Structural geometry Create a thin surface

Set Selection Type to Bodies Only Graphically select box for Geometry Set thickness to 0m (acts as shell rather than solid)


...Create Structural geometry Create Stiffener

We are going to generate a series of simple plate stiffeners

First generate a new horizontal plane


...Create Structural geometry

Create stiffener

Use the new plane to slice the model First Freeze the model to allow the slice Slice all bodies using the plane created in

the last step


...Create Structural geometry Create stiffener

Create a second box that will be used to remove the interior of the plate to generate the desired stiffener



Create the plate surface for the stiffener using the edges generated with the Slice command

Edges are selected using the



Remove interior of plate to create desired stiffener

Use a Boolean operation (Subtract)

Target body is the plate generated in last step

To select the plate use the layer selection image to step through the surfaces

Tool body is the second box


...Create Structural geometry Generate copies of stiffener

Use Pattern to create 5 copies of stiffener Linear pattern type with 5m offset

Geometry is the stiffener created in the last step

Use the face normal of the stiffener surface to define direction.

Note the use of the red and black arrows to define actual direction.



Resulting stiffener definition


...Create Structural geometry Complete stiffener connection

Stiffeners are not automatically connected to hull

Use Joint command to make connections Select all surface bodies as Target Bodies.

Can use Box Select mode to simplify selection.


...Create Structural geometry Create a single part

Model currently has 8 bodies and 8 parts To improve meshing create a single part Rename the new Part to Hull



Geometry for structure is now complete

Exit DesignModeler

Now we need to create a structural meshed model for use in the load mapping stage


Step 2: Create Structural Model and Information

Add Static Structural System to project, linking geometry to that created in DesignModeler.

Double click on Model cell.


...Create Structural Model and Information Define plate thickness

DesignModeler set plate thickness to 0.0

Results in Geometry as ?

Set thickness for hull bodies to 32mm

Set thickness for stiffener plate to 50mm


...Create Structural Model and Information

Mesh

Use default meshing for this model


...Create Structural Model and Information Define wetted surface

Load transfer requires definition of wetted (external) surfaces

Use dummy pressure case to define required geometry

Select surfaces manually, or use named selections


...Create Structural Model and Information Model Interface definition

AQWA WAVE requires structural model in ASAS format

ANSTOASAS command generates required data In Workbench insert Commands in object tree Add ANSTOASAS in Worksheet view


...Create Structural Model and Information Add Point Masses

Masses represent ballast & storage Associate mass with hull surface adjacent to position First mass is at 5,5,-32.5 Mass value of 1000 tonnes


...Create Structural Model and Information Add Point Masses

Add two more additional masses 1000 tonnes at 5,5,-27.5

1000 tonnes at 5,5,-22.5

Associate these masses to appropriate hull surfaces



Disable weak springs

ANSYS Mechanical defaults to including weak springs to remove rigid body motions

AQWA WAVE does not recognize the springs generated, so disable this feature



Solve

In order to implement the ANSTOASAS command a Solve must be instigated. Can ignore any warnings and errors related to solution since results from this analysis

are not used, only the generated ASAS interface file and mass information


...Create Structural Model and Information Mass Extraction

The hydrodynamic model requires an accurate definition of the mass inertia information for the model.

In the absence of better data this can be extracted from the structural model

Select Solution Information and review Worksheet for the mass data


...Create Structural Model and Information Review structural interface file

The ANSTOASAS command generates a text file called file.asas This contains the structural definition in ASAS format

Copy file.asas to a new directory where you will perform the load mapping


Step 3: Create Hydrodynamic Geometry

Structural definition model for AQWA WAVE is now complete

Exit ANSYS Mechanical

Now we need to create a hydrodynamic model for use in the load mapping stage


...Create Hydrodynamic Geometry Duplicate structural geometry created earlier. Rename system as Hydrodynamic Geometry and double click in the geometry cell of the new system


...Create Hydrodynamic Geometry The hydrodynamic geometry is much simpler, it is just the hull

Suppress items in the tree that were used for the stiffener generation


...Create Hydrodynamic Geometry

Modify Geometry

AQWA requires model that is meshed up to water line

Slice the model horizontally

Use XYPlane as the Base Plane (global Z is 0 for this)

AQWA also requires one part for each vessel

Form new part and name as Hull

Close DesignModeler


Step 4: Create Hydrodynamic Model and Information Add a Hydrodynamic Diffraction to the Hydrodynamic Geometry

Double click on Model


...Create Hydrodynamic Model and Information Add Point Mass

Add a point mass and manually define the mass and inertia values obtained from structural model

Ensure position of point mass is correctly defined (also obtained from structural model)


...Create Hydrodynamic Model and Information

Generate Mesh

In general the load mapping process requires a more refined hydrodynamic mesh than normally required for motions analysis

For this exercise, to reduce run time use maximum element size of 2.5m (and defeaturing tolerance of 1m)



Adjust the General Settings for Hydrodynamic Analysis

To reduce run time for the exercise set the number of intermediate frequency values to 8



Check Hydrostatics

Insert Hydrostatic Result to Solution Solve Hydrostatics to check that we have a valid model



Check Hydrostatics

When solution has completed select Hydrostatic Report and review results


...Create Hydrodynamic Model and Information Solve

Select Solve and review pressures using Pressures and Motions results object Save AQWA files in the project directory to your load mapping directory


Step 5: Load Mapping

Hydrodynamic model for AQWA WAVE is now complete

Exit AQWAWB

Now we need to create a steering information data file for use in the load mapping stage


...Load Mapping

AQWA WAVE Steering file

Create a new *.dat file in the load mapping directory

Copy the text in the slide to the *.dat file

This file directs AQWA WAVE to the appropriate structural and hydrodynamic information, and defines load data required

For more information on the Steering file refer to AQWA WAVE Manual

* Standard lines for ASAS style data:

SYSTEM DATA AREA 5000000

JOB NEW LINE

PROJECT ANSY *At present ANSYS files default to project ANSY

* Extension of the output files (*.txt)

EXTENSION txt

END

* Define structural model (in this case output from anstoasas command)

stru asas file.asas

* Define hydrodynamic model

hydr aqwa analysis

END

AQWAID

* Following commands set target structural analysis system as ANSYS Mechanical

FELM

FEPG ANSYS

END

LOAD

* Load information

* Case Current_ID Frequency_ID Direction_ID Wave_Height Phase

CASE 0 5 1 2.0 0

CASE 0 5 1 2.0 90

CASE 0 7 1 2.0 0

CASE 0 7 1 2.0 90

END

*Stop processing this file.

STOP


...Load Mapping Run AQWA WAVE

Running the program will bring up a dialogue box requesting the steering data file discussed on previous slide


...Load Mapping

AQWA WAVE creates (in this instance) 4 ANSYS APDL load files


Step 6: Include the Hydrodynamic loading to Structural model

Create second structural model

Create a second structural process by dragging the Static Structural system onto the first and sharing the first three cells (B2:B4)


...Include the Hydrodynamic loading to Structural model

Apply generated loads

Open the second structural model In Analysis Settings set the number of steps

to 4

In Workbench insert Commands in object tree of Static Structural 2

Use /INPUT command to reference the first of the loading files

! Commands inserted into this file will be executed just prior to the Ansys SOLVE command.

! These commands may supersede command settings set by Workbench.

! Active UNIT system in Workbench when this object was created: Metric (m, kg, N, s, V, A)

/INPUT,C:\ANSYS\TrainingWorkArea\LoadMapWorking_files\user_files\file_aqld1001.dat



Apply generated loads

Set Step Selection Mode for the command object to By Number

Set Step Number to 1 Repeat command insertion for the other

three load cases, incrementing the step number by 1 each time



Solve

The standard load file generated by AQWAWAVE includes a SOLVE command for use in Mechanical APDL, not required for Workbench so comment out (or delete)

Note this time we allow weak springs to be used

SFE, 1011, 2,PRES,0, 1.7681E+02, 1.9584E+02, 1.5090E+02, 1.3224E+02

SFE, 1012, 2,PRES,0, 2.2709E+02, 2.4616E+02, 1.9584E+02, 1.7681E+02

SFE, 1013, 2,PRES,0, 3.0239E+02, 3.0313E+02, 2.4616E+02, 2.2709E+02

SFE, 1014, 2,PRES,0, 2.4616E+02, 3.0313E+02, 3.0239E+02, 2.3488E+02

SFE, 1015, 2,PRES,0, -2.1617E+02, -2.0395E+02, -1.3253E+02, -1.3314E+02

SFE, 1016, 2,PRES,0, -1.3253E+02, -2.0395E+02, -2.1617E+02, -1.3811E+02

ACEL, 5.6327E-02, -5.7843E-07, 1.1702E-03

CGLOC, 5.0000E+00, 5.0000E+00, -2.4600E+01

DCGOMG, -2.8427E-08, 6.1327E-03, 3.6777E-08

! SOLVE


Step 7: Investigate the final results Review Results

Results are now ready for review Add a Force Reaction object to check for load balance

aqwa-intro 14 5 ws05 1 load mapping

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