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
Characteristics of the 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|
- Time History of Acoustic Pressure at each element
|Name||Mild Steel, Generic|
|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!
- In the Home tab of the ribbon, click New Project. The New Project window shows.
- Type a name for the project.
- If desired, change the save location and/or project file name by clicking … beside Project File.
- For Analysis, select Mechanical Dynamic.
- For Model Type, select 2D Model.
- Select the Advanced checkbox.
- For Distance, select mm.
- Click OK.
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.
- Select Import icon in toolbar
- Select ... and open the downloaded file 'FMC_2D.step'
- Select Import
- Click Project Materials
- Expand Misc
- Add Vacm to the project materials database (double click)
- Right click vacm and select Copy Material
- Rename vacm to vacm2
- Click OK
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
- Click Setup
- Click Project Settings
- Enable the option to change Frequency of Interest
- Expand the dropdown menu
- Change the Frequency of Interest to 5e6
- Click and Expand Geometry
- Select part_9
- Assign material Steel
Assign vacm to the first element
- Select part_8
- Assign material vacm
Assign vacm to the remaining elements element
- Select part_1 to part_7
- Assign material vacm2
We will now add a Ricker Wavelet drive function for later use as out loads require a time function be set.
- Expand Forcing Functions
- Click '+' to open the Define Input Time function window
- Change to Ricker Wavelet
- Set Frequency to 5e6
- Click Insert to close the window. A record called timefunc_1 will be added to the window
- Expand Model
- Expand Mesh
- Click Configuration
- Change Definitions to Wavelength Based
- Set Elements per Wavelength to 20
- Expand Mesh Velocity
- Set Mesh Velocity to Defined
- Set Mesh Velocity Value to 3200
- Expand Boundary Conditions and, beside Loads, click +.
- For Creation Mode, select Geometry Interface.
- For Geometry, select part_8 (vacm) (or click it in the model).
- For Interfacing Item, select part_9 (steel).
- For Amplitude Scale Factor, type 1.
- Click Create Load.
Leave all other boundary conditions as Free this is the default boundary condition
- Click Domain Boundaries
- Expand X Minimum
- Change to Absorbing
- Expand X Maximum
- Change to Absorbing
- Click Analysis
- Change Simulation Time to 6e-6
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.
- Click '+' 8 times this will create 8 outputs
Change output properties
- Click output_1
- Expand Location (mm)
- Change X to 5.4
- Change Y to 10
For all other outputs input the following location coordinates:
At this point the model is completely set up and it can now be run on the cloud.
- Click Run on Cloud
- Click Estimate
- Click Run
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.
- Click Storage this opens the window shown above
- Locate the job
- Click Download
- Select Download All
Switch to the Post Processor
- Click this icon to access the Post Processor
- Locate the downloaded folder
- Expand the folder containing the results just downloaded this will be folder 1
- Double click the flxhst file to open them
- Click Results Manager
Plot Time History
- Double click aprs
Plot remaining Time History
- Double click aprs
- Change Plot Title to Acoustic Pressure on All Elements
- Set Y-Axis label to Acoustic Pressure