Mass Spring Damper

Overview

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

Example Diagram

Example Structure

There are two simulators included in the study, 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.

Digital Twin Configuration

This example uses two models and one tool. The specific assets used are:

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 co-sim.json and time.json are two DT configuration files used for executing the digital twin. These two files can be modified to customise the DT as required.

Lifecycle Phases

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

DevOps Automation

This example demonstrates the use of DevOps features of the DTaaS platform. The GitLab DevOps pipelines are used for providing this feature in the DTaaS.

The .gitlab-ci.yml file controls the sequence of executing the lifecycle scripts of the example. The configuration format of .gitlab-ci.yml permits specifying stages for execution of a program. In this first example, all the lifecycle scripts are put in single stage, namely build_and_run.

This example produces co-simulation outputs which are then saved in the artefacts repository of the GitLab. These can be accessed 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, navigate to the following directory.

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

If required, change the execute permission of the lifecycle scripts to be executed, for example:

chmod +x lifecycle/create

Now, run the following scripts:

Create

Installs Open Java Development Kit 17 in the workspace.

lifecycle/create

Execute

Run the Digital Twin. Since this is a co-simulation based digital twin, the Maestro co-simulation tool executes co-simulation using the two FMU models.

lifecycle/execute

Examine the results

The results can be found in the /workspace/examples/data/mass-spring-damper/output directory.

You can also view run logs in the /workspace/examples/digital_twins/mass-spring-damper.

Terminate phase

Terminate to clean up the debug files and co-simulation output files.

lifecycle/terminate

References

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

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 are available in mass spring damper github repository.