Multidisciplinary Design Optimization of Airborne Surveillance System

Abstract

Aircraft is a complex and multidisciplinary airborne system. Aerodynamics, Structures, Propulsion and Controls are the major design disciplines in an airborne system. Airborne Surveillance Systems are modified flying platforms which carry one or more electromagnetic sensors to perform surveillance of threats from enemies. Maritime Patrol System (MPS) is used for surveillance of sea surface for various types of ships and low flying aircraft. RADAR, an acronym for Radio Detection and Ranging, is a critical sensor integrated on airborne surveillance platforms. In MPS aircraft, antenna of the radar system is generally mounted under the belly of the aircraft and protected by a cover called Radome (a portmanteau of radar and dome). Design of this radome involves structural, aerodynamic and electro-magnetic disciplines. Modeling the interactions among these disciplines is essential to bring out the synergy between the disciplines. Design optimization is an effective tool or method to explore or achieve best compromise of design in terms of all involved disciplines, where the disciplines are not at their individual best, but at a combined best. newline Optimization methods can be broadly classified as indirect search or direct search methods. Indirect search methods or gradient based methods use first order derivatives to search the optimum point in a defined problem. When such derivatives are not quite well defined in a system model, direct search or evolutionary algorithms provide better results for finding global optimums. These algorithms use nature s process of evolution to achieve better and better designs. newline When more than one parameter is to be optimized, there is no single minimum or maximum point for design but a set of optimized points with varying degree of importance for each involved discipline. Collection of these points is referred as Pareto front. This condition is called Pareto optimality condition in which any point is a compromise in objective value of at least one discipline when compared to any other point. newline Multi-disciplinary multi-objective optimization of Maritime Patrol Radar radome involving the design disciplines of aerodynamics, structures and electromagnetics is carried out in this study with evolutionary algorithms to arrive at Pareto front. Drag, weight and electro-magnetic losses are optimized in radome design. In one of the possibly first efforts reported in literature, all the three design disciplines involved in radome design are integrated on MDO framework in this optimization study. newline Firstly, the aerodynamic analysis was integrated on MDO software framework. The CFD software has to be invoked in batch mode, re-adjust the mesh as per changed radome shape. The software will calculate the drag value based on surface area and pressure contour. newline Structural discipline is integrated next. Communication between CFD and FEM software was to be configured. The radome shape, analyzed in CFD had to be transferred to FEM software along with mesh and pressure contour details. FEM software, invoked in batch mode, will automatically create FE mesh based on the parameters defined. The FEM software will check compliance of radome for structural requirement and estimate the weight of the radome. The aerodynamic and structures, in the course of optimization, move the objectives in quite opposite directions. Although aerodynamic analysis helps to arrive at optimized shape of the radome, a physical radome can be realized only with addition of the structural analysis. newline To this the electromagnetic analysis has to be integrated in final step, to estimate the sidelobe loss (with and without radome). The structural information and the shape of radome analyzed in FEM software to be transferred to CEM software for this. Radome model will be created by CATIA invoked by batch mode and input this to CEM software. The CEM software, again invoked in batch mode, will read the radome model, material properties etc, will refine CEM mesh and estimate the sidelobe loss. All these are integrated on MDO software with proper interfaces and script files to invoke respective software codes, read outputs from software and supply the same to next software. newlineand#8195; newline newline