Mass Spring Damper with NuRV Runtime Monitor

Overview

This digital twin is derives from te Mass String Damper digital twin.

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. This version of the example is expanded with a monitor generated by NuRV. More information about NuRV is available here.

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.

Additionally, a monitor is inserted in the simulation to check at runtime whether the displacement of the two masses stays below a maximum threshold.

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
	m2.fmu	Private	No
	RtI.fmu	Private	Yes
Specification	m2.smv	Private	No
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. You can change these two files to customize the DT to your needs.

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
Clean	Clears run logs and outputs

Run the example

To run the example, change your present directory.

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

If required, change the execute permission of lifecycle scripts you need to execute, for example:

chmod +x lifecycle/create

Now, run the following scripts:

Create

• Installs Open Java Development Kit 17 in the workspace.
• Generates and compiles the monitor FMU from the NuRV specification

lifecycle/create

Execute

Run the 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

Analyze phase

Process the output of co-simulation to produce a plot at: /workspace/examples/data/mass-spring-damper-monitor/output/plots.

lifecycle/analyze

A sample plot is given here.

In the plot, three color-coded indicators are used to represent different values. The blue line shows the distance between the two masses, while the green indicates the monitor's verdict. A red dashed line serves as a reference point, marking the distance checked by the monitor. Since the distance of the masses is always below the threshold, the output of the monitor is fixed to unknown (0).

Examine the results

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

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

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.