Mass Spring Damper with NuRV Runtime Monitor

Overview

This digital twin is derived from the Mass Spring Damper digital twin.

The mass spring damper digital twin (DT) has two mass spring dampers. It shows how to use a co-simulation based DT within the DTaaS. This version of the example adds a monitor generated by NuRV. More information about NuRV is available on the NuRV tool page.

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 displacement and speed of mass \(m_1\) for a given force \(F_k\) acting on \(m_1\). The second simulator calculates the force \(F_k\) from a given displacement and speed of mass \(m_1\). Coupling the two simulators computes how the positions of the two masses evolve.

A monitor added to the simulation checks at runtime whether the displacement of the two masses stays below a maximum threshold.

Mass Spring Damper Structure

Digital Twin Configuration

This example uses four models, one specification and one tool:

Asset Type	Names of Assets	Visibility	Reuse in Other Examples
Models	MassSpringDamper1.fmu	Private	Yes
	MassSpringDamper2.fmu	Private	Yes
	m2.fmu	Private	No
	RtI.fmu	Private	Yes
Specification	m2.smv	Private	No
Tool	maestro-4.1.0-jar-with-dependencies.jar	Common	Yes

The DT is executed with two configuration files, cosim.json and time.json. Edit them to customise the DT.

Lifecycle Phases

Lifecycle Phase	Completed Tasks
Create	Installs Java Development Kit for Maestro tool Generates and compiles the monitor FMU
Execute	Produces and stores output in data/mass-spring-damper-monitor/output directory
Analyze	Processes the co-simulation output and produces a plot
Clean	Clears run logs and outputs

Run the example

To run the example, change to the example directory.

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

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

1	`chmod +x lifecycle/create`

Then run the following scripts.

Create

Installs Open Java Development Kit 21 and the pandas and matplotlib Python packages in the workspace.
Generates and compiles the monitor FMU from the NuRV specification.

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 FMU models.

1	`lifecycle/execute`

Analyze phase

Processes the co-simulation output and saves a plot in /workspace/examples/data/mass-spring-damper-monitor/output/plots.

1	`lifecycle/analyze`

Here is a sample plot.

sample plot

The plot uses three colours. The blue line is the distance between the two masses, and the green line is the monitor's verdict. The red dashed line marks the distance threshold that the monitor checks. The distance between the masses always stays below the threshold, so the monitor output stays at unknown (0).

Examine the results

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

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

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 in the mass spring damper GitHub repository.