Integration of the CASTLE simulation executive with SIMULINK

Abstract

The Controls Analysis and Simulation Test Loop Environment (CASTLE) is a Navy in-house developed aircraft simulation executive application that has been in use at the Manned Flight Simulator (MFS) facility in Patuxent River, Maryland and elsewhere for over 15 years. In addition to supporting real-time hi-fidelity pilot-in-the-loop simulations in the MFS facility, CASTLE also includes integrated tools used for development and analysis of airframe simulations on various platforms. Much of the work with CASTLE includes exchanging and analyzing data with MATLAB® and Simulink®. In support of recent flight controls projects at Patuxent River, there was a requirement to integrate MATLABSimulink models with the CASTLE simulation. This led to the development of a new capability that enables a Simulink model to be modified and executed continuously with the CASTLE simulation, without having to exit and restart. The only interaction with CASTLE required by the user is to launch the specific airframe executable desired. Using an S-Function (System function) user definable block in Simulink, a MATLAB C-MEX file was created to interface Simulink with the CASTLE airframe using TCP/IP networking. In this scheme, when the Simulink model is executed and the SFunction block is called, a connection to CASTLE is established and a list of input and output variable names and values are sent for setup. The input values to the SFunction are then sent across the connection to the CASTLE airframe simulation. The simulation is then run through a simulation frame, halted, and output values requested are sent across the connection as the outputs to the S-Function block. This loop is continued for the duration of the Simulink model end run time, at which point the connection is terminated. In this manner, a hi-fidelity airframe simulation running under CASTLE can be used to develop, test and evaluate Simulink models of any type. Background The design of the CASTLE software is based on a C/C++ graphical user interface (GUI) and a C and FORTRAN airframe executive shell. The CASTLE environment was designed to be platform independent and is currently hosted on PC's running Microsoft Windows 98/NT/2000 operating system, DEC Alpha's running the VMS operating system, and SGI's running the Unix operating system. The design of the CASTLE software is very modular on several levels. It consists of several tasks running simultaneously, with the CASTLE GUI being the controlling entity of the simulation in most instances. Other processes include the actual airframe simulation, the plotting package and a 3D visualization software package. The airframe is used for analysis and development by simulation engineers and in real time pilot-in-the-loop simulations. These processes communicate via several methods, including local or global shared memory, and a TCP/IP protocol. In addition to these specific processes, CASTLE can communicate to other external processes by using either of these methods.