Mass Spring Damper

Overview

The mass spring damper digital twin (DT) has two mass spring dampers and shows how a co-simulation based DT can be used within DTaaS.

Example Diagram

Mass Spring Damper System

Example Structure

The study includes two simulators, each representing a mass spring damper system. The first simulator calculates the mass displacement and speed of \(m_1\) for a given force \(F_k\) acting on mass \(m_1\). The second simulator calculates force \(F_k\) given a displacement and speed of mass \(m_1\). By coupling these simulators, the evolution of the position of the two masses is computed.

Mass Spring Damper Structure

Digital Twin Configuration

This example uses two models and one tool:

Asset Type	Names of Assets	Visibility	Reuse in Other Examples
Models	MassSpringDamper1.fmu	Private	Yes
	MassSpringDamper2.fmu	Private	Yes
Tool	maestro-2.3.0-jar-with-dependencies.jar	Common	Yes

The cosim.json and time.json files configure the execution of the digital twin. Edit them to customise the DT.

Lifecycle Phases

Lifecycle Phase	Completed Tasks
Create	Installs the Java runtime for the Maestro tool
Execute	Produces and stores output in data/mass-spring-damper/output directory
Clean	Clears run logs and outputs

DevOps Automation

This example uses the DevOps features of the DTaaS platform, which the DTaaS provides through GitLab DevOps pipelines.

The .gitlab-ci.yml file sets the order in which the lifecycle scripts of the example run. Its configuration format lets you split a program into stages. This first example runs the create and execute scripts in a single stage named build_and_run.

GitLab saves the co-simulation outputs as job artefacts. You can find them at https://<gitlab-host>/<group>/<username>/-/artifacts. Replace <gitlab-host>, <group>, and <username> with the values for your GitLab instance and project.

Run the example

To run the example, go to the following directory.

1	`cd /workspace/examples/digital_twins/mass-spring-damper`

If required, make the lifecycle scripts executable, for example:

1	`chmod +x lifecycle/create`

Now, run the following scripts:

Create

Installs the OpenJDK 17 Java runtime in the workspace.

1	`lifecycle/create`

Execute

Runs the digital twin. Because this is a co-simulation based digital twin, the Maestro co-simulation tool runs a co-simulation of the two FMU models.

1	`lifecycle/execute`

Examine the results

The results are in the /workspace/examples/data/mass-spring-damper/output directory.

The run logs are in the /workspace/examples/digital_twins/mass-spring-damper directory.

Terminate phase

Removes the debug files and co-simulation output files.

1	`lifecycle/terminate`

References

More information about co-simulation techniques and the mass spring damper case study is available in:

1 2	`Gomes, Cláudio, et al. "Co-simulation: State of the art." arXiv preprint arXiv:1702.00686 (2017).`

The source code for the models used in this DT is available in the mass spring damper GitHub repository.