Introduction

Railguns (Figure 1) are an interesting combination of electrical and mechanical design, testing the capabilities of Model-Based Systems Engineering (MBSE) to connect these domains. In Part 2 of this blog series, we described the composition of the system and the requirements governing it. In this section, we will create a generalized electrical schematic using a SysML internal block diagram and use the Intercax MBSE interoperability platform, Syndeia, to connect the mechanical CAD model of a key system component, the Rail, to the SysML architecture model for the quantitative analyses and requirements verification in the final parts of this series.

Figure 1 Simplified physics of electromagnetic railgun

Modeling the Railgun, Connectivity and Geometry

Reference - Part 2, Figure 3 RailGun decomposition, SysML block definition diagram

The block definition diagram in Part 2, Figure 3, represents the composition of the RailGun system. The related internal block diagram in Figure 2 shows the connectivity inside this system. Ports typing the inputs and outputs of each part or subsystem are linked by connectors. As we will discuss in Part 5, this model can provide the foundation by model transformation of an analytical model in MATLAB Simulink.

Figure 2 RailGun internal connections, SysML internal block diagram

Jumping forward in the design process, mechanical CAD will be used to design individual components, including the critical rails. In Figure 3, a U-channel beam design in a 3D CAD model in NX will serve as a proxy for the rail. One key parameter in determining railgun performance is the length of the rail. It would be valuable to make this parameter available in the SysML model for analysis, and to be able to update that value as the CAD design changes.

Figure 3 3D CAD design, railgun rail beam (Siemens NX). Inset shows SysML parametric diagram linking model1 z-axis length in mm with Rail length in meters

Using Syndeia, we can accomplish this using a model transform connection, which takes the CAD model in NX and creates a block in SysML containing key CAD parameters. This block, labeled model1, is shown at the bottom of Part 2, Figure 3. and contains a set of value properties whose default values are taken from the CAD design.  These values include mass, volume, the center of gravity, and bounding box dimensions. If the design changes, Syndeia allows the SysML values to be updated from the CAD file (NX does not allow a reverse update because these are calculated values and not over-writable from outside).

In Part 2, Figure 3, model1 is linked to the Rail, but we need to specify exactly how the length parameter in Rail relates to the dimensions of model1. For this we use a simple SysML parametric diagram, shown as an inset in Figure 3, which connects length to upper_right_z dimension of the CAD part bounding box. The parametric constraint also incorporates unit conversion into the model, from millimeters in the CAD file to meters in the SysML and analysis models. Updates of the rail length are automatically converted to the correct units as the design evolves.

Next Steps

In the final part of this blog series, we examine analysis of the RailGun system. We will examine both intrinsic (constraints inside the SysML model) and extrinsic (external to the SysML model) modes of analysis and the use of external solvers, Mathematica and Simulink, to execute the analyses. The combination of these tools with system requirements from Jama and geometric dimensions from NX demonstrate the power of distributed digital total system model managed by Syndeia.

Related posts:

• MBSE for Railgun Design | Part 1
• MBSE for Railgun Design | Part 2
• MBSE for Railgun Design | Part 3 (this post)
• MBSE for Railgun Design | Part 4
• MBSE for Railgun Design | Part 5

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