Electromagnetic Risks Reduction and Control Process for Modern Ship Design

Configuration Control of new naval platforms during the whole designing process is becoming a key aspect for reducing the risks of poor ship performances with respect to the requested operational requirements stated at the beginning of the project. This paper addresses the configuration control applied to the electromagnetic design of ships based on an EM Risk Matrix approach. A dedicated EM Risk Management Tool that adopts the matrix approach has been integrated inside the Ship EDF software framework and has been employed successfully in new naval platform designs in the past ten years.

Electromagnetic Defense

There are several EM problems that impact the sensors and systems installed onboard military ship platforms. The Electromagnetic defense risks can be subdivided into different types such as: EMI, Antenna Coverage (degradation, due to the superstructure blockage), Radiation Hazard on electronic components, ordnance, avionics, fuel and personnel. The above requirements must account for other concurrent aspects concerning the EM signature, such as Radar and IR. All these problems lead to the risk of mission failure and reduced self defense capability.

Moreover in the last 20 years an ever growing number of systems have been installed onboard due to the new requirements of modern naval units. The increasing complexity implies an increasing number of potential EM problems and imposes the need for significant improvements in approaching ship EM designing. Configuration Control of new naval platforms during the whole designing process is becoming a key aspect for reducing the risks of poor ship performances with respect to the requested operational requirements stated at the beginning of the project. The logical process, currently in use in some ongoing new ship projects, is depicted in Fig.1.

Electromagnetic Risk

The Electromagnetic risk control process must follow the ship project from the preliminary design to the delivery in order to anticipate significant risks at the earliest stage of the project and to find solutions co-agreed between naval architects, mission planners and the EM design team. The Configuration Control approach is required to face some EM project demands:

• Use of EM (EMC, RCS, ...) risk files containing EM evaluations and clear and understandable explanations of risks in terms of impact with respect to the lack of performance of the ship and related combat system;
• The EM analysis of each possible or proposed design configuration must cycle through all the items involved in the design, not limiting the study of the means for mitigation to each single risk.
• For each given risk, a trade off analysis must be performed to propose alternative solutions to the Design Authority, providing the Design Authority with more flexibility, and allowing non EM expert team members to efficiently interact and contribute to the discussion. This approach helps the convergence of options where conflicts may arise.
• Necessity of an instrument able to manage the growing numbers and complexity of EM risks and to guide the EM system analyst in the risk mitigation process.
• Necessity of continuous verification and monitoring of the project by means of loop during the steps of the project, allowing the traceability of requirements and history of design choices.

An efficient way for answering these requirements is based on an EM Risk Matrix approach. The Risk Matrix contains a complete view of the ship’s overall risk status which is the results of an EM Design tools Operational requirements EM Risk Identification & Analysis Ship Configuration Risk Files and Risk Matrix.

EM Risk Assessment EM Experts Ship Design Authority Database analysis of all the relevant source and victim pairs covering different EM aspects with all the relevant impacts.

The matrix is generated by listing the EM risk sources in the rows and the EM risk victims in the columns subdivided by operative frequency bands and victim types. Each cell of the matrix represents an EM risk between a source and victim present onboard and contains a specific link to a tailored EM Risk File. The EM Risk File reports the assessment of the risk, derived from the EM specialist analysis and details the risk classification, the risk characterization and the proposed solution. The risk classification includes information about the Type(Electromagnetic Interference, Radiation Hazard, Coverage,…), the Level (High, Medium, Low or Null) and the Status (Potential, Assessed, Mitigated, Managed, or Residual) with the aim of tracing risk evolution. In order to identify the most critical risks and consequently, the issues to be solved or mitigated first, all the risks are characterized by their level. The Level is obtained taking into account the relevance of risk’s Impact and Probability. The Impact is estimated performing a weighted average of dedicated indexes that define victim priority and risk consequence, whilst the threshold overstepping and the risk occurrence contribute in characterizing Probability.

Risk Evolution

The goal of the EM system analyst team is to mitigate the risks or to reduce their level until it can be considered acceptable by the Design Authority. Risk evolution starts with identifying the potential risks considering the input data and assumptions, the operational requirements and specific C/S layout and topside configuration references. Then a detailed analysis is performed based on antenna and superstructure EM models. At this stage the suitability and efficiency of the prediction tools play a fundamental role in properly characterizing the EM risk. At the end of the analysis phase all the risks have been assessed and for each of them a level has been defined in accordance with the criteria described above. If the risk is null or acceptable can be closed; if not, some mitigation actions such as operational procedures or dedicated technical solutions must be proposed. After agreement of the Design Authority, the mitigation actions that need to be implemented, together with new additional requirements, contribute in defining the design changes and close the loop leading to a new ship external configuration. The evolution of the risk is reported in Fig.4.

The evaluation of the risks and the related mitigation solutions can help to define the best trade-off choices which, once recognised by the Design Authority and the end users, can provide a general increase of knowledge of the ship’s capability and of the ways to get the best operational performance from it. The effectiveness of the EM Matrix approach can be fully exploited if managed by automatic routines and supported by a dedicated database. For this reason an EM Risk Management Tool adopting the matrix approach has been created and integrated inside the Ship EDF software framework. The tool has been employed successfully in new naval platform designs in the past ten years.