Advanced Approach to Electromagnetic & Signature Design of Modern Naval Platforms

In the context of this discussion, the Electromagnetic Design is intended as the part of the ship design process devoted to support the design cycles in optimising the antenna location and performances, controlling the undesired interferences among equipment, and the radiation hazard risks, together with a concurrent control and reduction of the different ship signatures.

2. Evolution of the EM Design Approach
As a consequence of the improvements in new ship mission requirements, the EM design (see Fig.1) discipline has evolved, quickly moving from a simple analysis role to a design process to be followed through all the ship design cycles.

Fig.1 – Concurrent Ship EM Design concept

In such a scenario, the role of the prediction tools increases, thanks to its capability to anticipate the trade off and feasibility assessment (see Fig.2 and 3). So the EM design process started moving from a basically experimental approach through an extended and systematic use of prediction, aimed at identifying and solving the potential risks since the earliest stage of a project and at controlling their impact as changes get introduced along the ship design cycles.

Fig.2 – Ship EMC Design (“Ship EDF” Prediction tool)

It becomes evident that the solution to these problems must be pursued in a concurrent way, through co-operation between naval architects, mission planners, equipment manufacturer and the EM design team. This kind of co-operation must start from the outset of the ship design process, when the preliminary design is carried out and where the major architecture, weapon and sensor choices are often made. During this initial stage, the timely contributions from the different engineering disciplines are more demanding but provide greatest benefits to the ship project.

Fig.3 – Ship RCS/IR Design (“Ship EDF” Prediction tool)

To be effective a prediction process must combine the features required for the electromagnetic solvers with the features for concurrent design into an integrated environment to provide a unified ship electromagnetic design. In this scenario the ship CAD and related combat system information must be shared by the different EM analysis areas (EMC, signature…) and must be open to data import from and export to other ship project areas.

Experience shows that very often naval architects, ship design specialists, RCS, IR and EMC engineers act independently and in many cases loose the ability to optimise the ship's configuration through balanced judgement and compromise. To achieve the best solution the following features should be provided to the naval engineer:

• Control of the configuration of the “Ship System” The environment must be capable of providing project management services to organise the EM analyses during the project evolution. It must also supply configuration control aids on the ship architectural (shapes, materials) and electromagnetic (fields, signatures) database, in order to keep track and have a synthetic vision of the electromagnetic performance of each project version. A simplified scheme describing a possible organisation of such procedure/information is given in Fig. 4.

Fig.4 – Organisation of data for the Ship EM Design

• Open and integrated modelling environment. The geometric and electromagnetic characterisation of the ship model should be performed in a unified CAD environment, closely interfaced to the CAD drawings that may be defined and manipulated using the different 3D modelling tools used by naval architects.
  
  
• Advanced electromagnetic prediction codes. The complex problems to be modelled need a full set of state-of-the-art electromagnetic computation techniques (radiated/scattered fields). The prediction framework must also provide advanced simulations of all the aspects related to ship electromagnetic design exploiting the capabilities of modern hardware resources to reduce computation time.

3. Signature management & requirements

The major reason of the growing complexity of mid size fast attack vessels comes from signatures requirements.

Signature management is increasingly crucial for the platform operational performance and consequently for its continued existence. Ship mission performance requires significantly improved signature as regards not only the absolute radar cross section (RCS) levels but accounting for the ship imaging features. These imply a strategic need to carefully identify and control the spatial distribution of the scattering centres, represented as hot spots in 3D analyses of the platform. It is the improved discrimination and recognition features of new radar sensors that have made it important to know the distribution of scattering centres and its related signature properties.

A first step to achieve the reduction of the signature and the margins for a signature management is to clean up the 3D geometry of the superstructure. For example fig. 5 shows how a new generation ship could appear with respect to one using old design philosophies.

Fig. 5 – Pictorial examples of old/new ship aspect

In addition, a ship’s ability to manage its own signature according to its mission is becoming crucial to military strategies. For instance, the possibility to modify a ship signature from peacetime status to war status will improve that ship’s chances of survival. So, suitable camouflaging criteria plays a strategic role to obtain the desired signature properties.

Signature management through camouflage techniques is a formidable engineering challenge to be addressed. The basic scope of signature management is to reduce the possibility of a ship being classified in peacetime and, thus, being recognisable in times of conflict. Furthermore, the ability to change ship signature can be used to optimise deception techniques. These aspects will have a dramatic impact on the ship design process, therefore requiring a major rethink of the design philosophy.

The achievement of this optimisation will require the appropriate application of suitable shipbuilding technology, innovative combat system design, advanced materials design capability and novel integration processes taking account of the whole range of ship requirements and constraints.

Such challenging design will increasingly involve industry and government departments into a real concurrent engineering process supported by suited methods and design tools.

Chiti Stefano
Naval Division Manager
IDS - Ingegneria Dei Sistemi, SpA
Via Livornese, 1019
56010 S.Piero A Grado (Pisa) - Italy

Tel: +39 050 3124 224

E-mail:s.chiti@ids-spa.it