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Full Matrix Capture (FMC)

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Oliver Mashari
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In this tutorial we will learn how to set up a simple 2D model of a Full Matrix capture (FMC) data acquisition of a steel block with a defect positioned at the centre of the block. We will be using the CAD importation functionality.

We will learn:

  • How to set up a 2D model from CAD importation
  • How to assign a time dependent load
  • How to create the 2D geometry using simple geometry shapes
  • How to solve the model to calculate the acoustic pressure on each of the inactive elements

Problem Definition

Characteristics of the model

Model:

Steel block of dimensions 10mm x 18mm with a defect of radius 0.25mm centered in the middle of the block.

8 elements of dimensions 8mm x 0.2mm seperated by a 2mm gap
Mesh Size: 15 Elements / Wavelength 
Analysis Time: 6e-05 seconds
Output Results:

- Time History of Acoustic Pressure at each element

 Material Data

Name Mild Steel, Generic
Code Name steel
Density 7900 kg.m-3
Bulk Velocity 5900 ms-1
Shear Velocity 3200 ms-1

Note: Material Data in OnScale are generally defined using the bulk velocity and the shear velocity parameters instead of the more traditional Elastic Modulus and Poisson's Ratio. You can check this page if you want to understand the relation between those parameters.

Why This Simulation?

Full Matrix Capture (FMC) is a data acquisition strategy, FMC allows for the capture of A-Scan signals from every transmit-receive combination for a given ultrasonic phased array transducer.

For example for a 16-element probe the probe will be pulsed 16 times and 256 A-scans are gathered. This model uses 8 elements we are only pulsing one of the elements and receiving on the remaining 7, in total if we simulated this in full we would gather 64 A-scans.

From this raw A-scan signals stored on a drive, it is possible to generate images from this data post-process.

The Simulation Process

Let's go through the step by step tutorial and see how to simulate this in OnScale!

Step 1 - Create a New Project

  1. In the Home tab of the ribbon, click New Project. The New Project window shows.
  2. Type a name for the project.
  3. If desired, change the save location and/or project file name by clicking … beside Project File.
  4. For Analysis, select Mechanical Dynamic.
  5. For Model Type, select 2D Model.
  6. Select the Advanced checkbox.
  7. For Distance, select mm.
  8. Click OK.
fmc-new-project.png

Step 2 - Import STEP file

Note: As of OnScale 1.30.3, this step can now be performed from the New Project window. As such, you can perform steps 1 and 2 as a single step.

Download: FMC STEP file 

  1. Select Import icon in toolbar
  2. Select ... and open the downloaded file 'FMC_2D.step'
  3. Select Import
import.png

Step 3 - Add Material to Project Materials 

  1. Click Project Materials 
  2. Expand Misc
  3. Add Vacm to the project materials database (double click)
3.AddVACM.png
  1. Right click vacm and select Copy Material 
  2. Rename vacm to vacm2
  3. Click OK
4.copyvacm.png

Repeat steps 1-3 and add the material Steel to the project material database by expanding the dropdown menu METAL

Step 4 - Change Project Setting

  1. Click Setup
  2. Click Project Settings 
  3. Enable the option to change Frequency of Interest
  4. Expand the dropdown menu
  5. Change the Frequency of Interest to 5e6
6.projectsettings.png

Step 5 - Assign Materials to Parts

Assign steel 

  1. Click and Expand Geometry
  2. Select part_9
  3. Assign material Steel
7.assignsteel.png

 Assign vacm to the first element

  1. Select part_8
  2. Assign material vacm
8.assignvacm.png

 Assign vacm to the remaining elements element

  1. Select part_1 to part_7
  2. Assign material vacm2
9.assignvacm2.png

Step 6 - Define a Time Function

We will now add a Ricker Wavelet drive function for later use as out loads require a time function be set.

  1. Expand Forcing Functions
  2. Click '+' to open the Define Input Time function window
  3. Change to Ricker Wavelet 
  4. Set Frequency to 5e6
  5. Click Insert to close the window. A record called timefunc_1 will be added to the window
10.timefunc.png

Step 7 - Mesh Settings

  1. Expand Model
  2. Expand Mesh
  3. Click Configuration
  4. Change Definitions to Wavelength Based
  5. Set Elements per Wavelength to 20
  6. Expand Mesh Velocity 
  7. Set Mesh Velocity to Defined 
  8. Set Mesh Velocity Value to 3200
mceclip0.png

Step 8 - Create Loads

  1. Expand Boundary Conditions and, beside Loads, click +.
  2. For Creation Mode, select Geometry Interface.
  3. For Geometry, select part_8 (vacm) (or click it in the model).
  4. For Interfacing Item, select part_9 (steel).
  5. For Amplitude Scale Factor, type 1.
  6. Click Create Load.
fmc-create-load.png

Step 9 - Change Domain Boundaries

Leave all other boundary conditions as Free this is the default boundary condition

  1. Click Domain Boundaries
  2. Expand X Minimum
  3. Change to Absorbing
  4. Expand X Maximum
  5. Change to Absorbing
15.boundaries.png

Step 10 - Set Simulation Time

  1. Click Analysis
  2. Change Simulation Time to 6e-6
16.analysis.png

Step 11 - Outputs

We will add 8 time history outputs that will record the particle velocity (yvel) on each element. Do not use acoustic pressure as this will be zero at a boundary with vacuum.

  1. Click '+' 8 times this will create 8 outputs
17.add8outputs.png

Change output properties

  1. Click output_1
  2. Expand Location (mm)
  3. Change X to 5.4
  4. Change Y to 10
18.output_properties.png

For all other outputs input the following location coordinates:

  X Y
output_2 6.4 10
output_3 7.4 10
output_4 8.4 10
output_5 9.4 10
output_6 10.4 10
output_7 11.4 10
output_8 12.4 10

Step 12 - Run on the Cloud

At this point the model is completely set up and it can now be run on the cloud.

  1. Click Run on Cloud 
  2. Click Estimate 
  3. Click Run
20.cloud.png

How to Get the Simulation Results?

The simulation results will need to be downloaded from the cloud storage in order to analyse the results in the post processor. More experience users may also be able to process Time Histories in Review.

  1. Click Storage this opens the window shown above
  2. Locate the job 
  3. Click Download 
  4. Select Download All
mceclip0.png

Step 13 - Check the Simulation Results 

Switch to the Post Processor 

  1. Click this icon to access the Post Processor
switch-post-processor.png

Open Results

  1. Locate the downloaded folder 
  2. Expand the folder containing the results just downloaded this will be folder 1
  3. Double click the flxhst file to open them
  4. Click Results Manager
22.filexplorer.png

Plot Time History

  1. Double click aprs
23.aprs1.png

Plot remaining Time History

  1. Double click aprs
  2. Change Plot Title to Acoustic Pressure on All Elements
  3. Set Y-Axis label to Acoustic Pressure 
24.allaprsplotted.png

 

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