Simulating a Transmit Receive Longitudinal (TRL) Inspection

In this tutorial we will learn how to simulate a full 3D model of a TRL (Transmit Receive Longitudinal) inspection of a steel pipe with water. We will use CAD importation for the model geometry.

We will learn:

  • How to import CAD
  • How to apply mechanical load to a surface
  • How to solve the model to calculate the acoustic pressure received

Problem Definition


Characteristics of the model

Model: TRL inspection with Block Angle = 15 degrees and Wedge Angle = 162 degrees
Mesh Size: 16 Elements / Wavelength
Analysis Time: 0.1 ms
Output Results:

- Time History of Acoustic Pressure at Receiver (0.025,0.02,0.035) m

- Maximum Acoustic Pressure Field

Material Data


Code Name


Bulk Velocity 

Shear Velocity



1060 kg.m-3

2340 ms-1

1100 ms-1

Stainless Steel, Generic 


7890 kg.m-3

5790 ms-1

3100 ms-1



0 ms-1

0 ms-1

0 ms-1

Water watr

1000 ms-1

1496 ms-1

0 ms-1

Why This Simulation?

There are many issues associated with inspection, including accessibility and critical defect sizes, but the most important issue regards the accurate positioning, sizing and characterisation of flaws. TRL is a popular method for near-surface inspection and simulating the inspection design is necessary for optimization.

In this simulation we will transmit from one probe on the wedge into the pipe and receive on the other probe.

The Simulation Process

Step 1 - Creating a New Project

Before we begin we must 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. Click OK.

Step 2 - Set the Frequency of Interest

First we will specify the frequency of interest.

  1. Select Project Settings in the Model Tree
  2. Expand the Frequency of Interest property
  3. Tick the box
  4. Enter a value of 150,000

Step 3 - Adding the Materials

First we will add the materials needed from the material database.

Stainless Steel

We need stainless steel for the pipe.

  1. Click Project Materials to open the Material Database
  2. Expand the Metal material tab
  3. Double click 'Stainless Steel, generic - stst' to add this to Project Materials

Rexolite & Vacuum

We require rexolite for the wedge and vacuum for the probes.

  1. Expand the Misc material tab
  2. Double click 'Rexolite - rxlt' to add this to Project Materials
  3. Double click 'Vacuum- vacm' to add this to Project Materials


  1. Expand the Fluid material tab
  2. Double click 'Water at 25C- watr' to add this to Project Materials
  3. Select Done to close the Project Material Database

Step 4 - Import Geometry

Note: As of OnScale 1.30.3, this step can now be performed from the New Project window. As such, you could alternatively perform steps 1 and 4 as a single step.

We will make use of this BDF File containing a model of a 3D TRL Inspection.

Download: TRL STEP File

  1. Select Import button
  2. Select ... and locate 'TRL.step'
  3. Select Import

Step 5 - Assign Materials to Parts

We must now assign each model part a material.


  1. Expand Geometry in the Model Tree
  2. Right click part_1 > Assign Material > rxlt


  1. Right click part_2 > Assign Material > vacm
  1. Right click part_3 > Assign Material > vacm


  1. Right click part_4 > Assign Material > stst


  1. Right click part_5 > Assign Material > watr

Step 6 - Setting up the Mesh

We will now change the mesh settings to use 16 elements per wavelength

  1. Expand Model in Model Tree
  2. Expand Mesh
  3. Select Configuration
  4. Set Definitions to Advanced
  5. Set Elements Per Wavelength to 16
  6. Expand Mesh Velocity and set to Defined
  7. Set Mesh Velocity Value to 1100

Step 7 - Creating a New Load

Adding a Time Function

We need to assign a pressure load to the transmit probe so we require a drive function. For this model we will use with a Sinusoidal drive function.

  1. Expand Forcing Functions in the Model Tree
  2. Click '+' to open the Time Function window
  3. Change Drive Frequency to 150,000
  4. Click Insert

Creating a Load

  1. In the Model Tree, expand Boundary Conditions and then, beside Loads, click +.
  2. In the Model Tree, under Geometry clear the part_1 checkbox to hide this part.
  3. Change Creation Mode to Geometry Interface
  4. Click part_2.
  5. For Interfacing Item select part_1 from the drop down menu.
  6. Set timefunc_1 as the forcuing function.
  7. Change Amplitude Scale Factor to 1
  8. Click Create Load


Step 8 - Setting up Boundary Conditions 

We will need to change all boundaries except Ymin to Absorbing conditions because we are only simulating part of the pipe and the waves would continue on and not reflect off of the boundaries. Ymin is free as this is the boundary at our probes.

  1. Click Domain Boundaries 
  2. Expand X Minimum and set Boundary Type to Absorbing
  3. Expand X Maximum and set Boundary Type to Absorbing
  4. Expand Y Minimum and set Boundary Type to Absorbing
  5. Expand Z Minimum and set Boundary Type to Absorbing
  6. Expand X Maximum and set Boundary Type to Absorbing

Step 9 - Setting Analysis Time

We will now set the model simulation time to be 0.0001 seconds

  1. Click Analysis 
  2. Set Simulation Run Time to 0.0001

Step 10 - Choosing Output Results

We will now define 2 outputs, a time history of the acoustic pressure at the receiver and the maximum pressure array.

1 - Time History of Acoustic Pressure at Receiver [0.025,0.02,0.035 ]m

  1. Click '+' this will create a new output 
  2. Change Output Type to Time History
  3. Set Location > X to 0.025
  4. Set Location > Y to 0.02
  5. Set Location > Z to 0.035

2- Maximum Acoustic Pressure Field

  1. Click '+' this will create a new output 
  2. Change Output Type to Field Data
  3. Change Field Type to Maximum

Step 11 - Launch the simulation 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

Step 12 - Post Processing Simulation Results 

Download the results from the cloud

The simulation results will need to be downloaded from the cloud storage in order to analyse the results in the post processor.

  1. Select Storage icon
  2. Locate the job from the dropdown menu
  3. CTRL + select the .flxdato and .flxhst file, right click and select Download Selection

Choose an appropriate save location when the file explorer pops up and click Select Folder to close the window.

Switch to the Post Processor 

Important: Once you downloaded the results from the cloud, those results will be available on your computer locally. You will then need to open them into the post-processor to visualize them.

  1. Click this icon to access the Post Processor 

Open Results 

  1. Click File Explorer
  2. Expand the job simulation folder
  3. Double click .flxdato file and .flxhst file to open them in Results Manager

Plot Time History 

  1. Double click 'aprs' in Results Manager to plot acoustic pressure curve

Plot Data Array (Maximum Pressure)

  1. Double click 'apmx' in Results Manager to plot maximum pressure data array
  2. Select Continue
  3. Set Scale Factor to 0.5
  4. Rotate model to view maximum pressure at different parts of the model

Try for yourself 

Now that we have introduced you to the tutorial try have a play around with some of the settings, add some other outputs, or use this model as a starting point for your own.