Rosemary Norman

Hybrid MCDM based methodology for selecting the optimum maintenance strategy for ship machinery systems

The key to achieving optimum ship system reliability and safety is to have a sound maintenance management system in place for mitigating or eliminating equipment/component failures. Maintenance has three key elements; risk assessment, maintenance strategy selection and the process of determining the optimal interval for the maintenance task. The optimisation of these three main elements of maintenance is what constitute a sound maintenance management system. One of the challenges that marine maintenance practitioners are faced with is the problem of maintenance selection for each equipment item of the ship machinery system. The decision making process involves utilising different conflicting decision criteria in selecting the optimum maintenance strategy from among multiple maintenance alternatives. In tackling such decision making problems the application of a multi-criteria decision making (MCDM) method is appropriate. Hence in this paper two hybrid MCDM methods; Delphi-AHP and Delphi-AHP-PROMETHEE, are presented for the selection of appropriate maintenance strategies for ship machinery systems and other related ship systems. A case study of a ship machinery system maintenance strategy selection problem is used to demonstrate the suitability of the proposed methods.

A New Tool for Prioritising the Risk of Failure Modes for Marine Machinery Systems

Failure Mode Effect and Analysis (FMEA) is one of the most powerful techniques for performing risk analysis for marine machinery systems, with risk being quantified through evaluating Risk Priority Numbers (RPNs) for all failure modes of the systems. The RPN is traditionally evaluated as the product of three risk criteria; occurrence (O), severity (S) and Detection (D). FMEA has several limitations such as the challenge of aggregating experts’ risk criteria rating that may be imprecise or incomplete.In this paper some of the limitations in the conventional FMEA technique are addressed using two approaches; AVeraging technique integrated with conventional Risk Priority Number (AVRPN) and AVeraging technique integrated with TOPSIS (AVTOPSIS). Both proposed techniques use a novel approach simple average in aggregating imprecise experts’ risk criteria ratings. A case study illustrates the suitability of both techniques for use in risk prioritisation jointly or independently as the results generated by both techniques are very similar. Furthermore, the AVRPN technique has been applied to an example from the literature and it has been demonstrated to be both computationally simple and capable of producing results which almost completely match those generated by modified Dempster-Shafer evidence theory techniques.Copyright

Design of a high-temperature thermal ballast water treatment system

The introduction of non-indigenous marine species to foreign environments through the medium of ballast water has led to a research focus on the design of onboard ballast water treatment systems. Such systems must be capable of meeting new International Maritime Organization (IMO) standards while also having minimal effect on the environment and on the operational costs and safety of the vessel. Thermal treatment of ballast water appears to be a promising solution, although the application of low-temperature treatment methods may be limited by the time required for the process. A thermodynamic model is presented for a two-stage heat exchanger system to be used for high-temperature treatment of ballast water during discharge. The model may be used for estimation of ballast water treatment requirements during the design phase for a vessel. It was also used to size a pilot-scale, high-temperature treatment system that has been tested onboard ship with regard to the biological effectiveness of the treatment method.

Design of an underwater positioning sensor for crawling ship hull maintenance robots

In recent years there has been a significant increase in the automation of ship hull maintenance tasks such as cleaning, paint stripping, and in-water inspection. This is driven by several factors including reduction in cost, environmental hazard, and impact on the health of workers. The development of autonomous systems has been limited by the availability of suitable position sensors capable of providing accurate and repeatable information to a robot control system. This paper presents the development of an optical position sensor (OPS) suitable for use both underwater and in air, and designed to operate on a crawling ship hull robot. The OPS provides dead-reckoning position data which may be used in conjunction with a landmark position sensor for navigation of a robot. The OPS was based on an optical mouse sensor and telecentric lens and has been shown to provide accurate position information over a range of test speeds and working distances and when operating under non-ideal conditions in terms of angle with respect to the ship hull surface.

Holistic Study of Liquefied Natural Gas Carrier Systems

Abstract Natural gas, one of the fossil fuels, has shown promising growth due to its price and lower pollutant emissions compared to other fossil fuels. One option for transporting natural gas is the use of Liquefied Natural Gas (LNG) carriers. An LNG carrier is one of the most expensive, complex and potentially hazardous cargo carriers that is operating across the worlds oceans due to its cargo. The aim of this paper is to identify the relationship of seven main components involved in constructing an LNG carrier. It can be done through an understanding of the principals involved in the LNG carrier design process. Understanding each component and the inter-component relationships requires detailed investigation into the behaviour of components relative to any changes in the multitude of variables. The main challenge is to consider and adapt all of the possible constraints within each component. Here, each component is required to communicate with each other in one language. As a result a comprehensive ‘system of systems’ of an LNG carrier relationship will be developed to be used as a tool to construct a new LNG carrier efficiently.

Impact analysis of LNG carrier modelling systems

Global energy demand especially natural gas is expected to grow due to high world oil prices. Natural gas composed mostly of methane is the cleanest burning fossil fuel. Thus, offering an alternative fuel and at the same time has ability to reduces the environment impact. LNG carrier has been successfully used to transport this fuel across the globe, despite being complex, expensive and potentially hazardous cargo. However, there is some area need to pay more attention in order to reduce the overall costs of this carrier.

Numerical Simulation of a Tidal Turbine Based Hydrofoil With Leading-Edge Tubercles

The tubercles along the leading edges of the humpback whale flippers can provide these large mammals with an exceptional maneuverability. This is due to the fact that the leading-edge tubercles have largely a 3D benefit for the finite hydrofoils, which can maintain the lift, reduce the drag and delay the stall angle. Newcastle University launched a series study to improve a tidal turbine’s performance with the aid of this concept. This paper presents a numerical simulation of the tested hydrofoil, which is representative of a tidal turbine blade, to investigate the flow around the foil and also to numerically model the experiment. This hydrofoil was designed based on an existing tidal turbine blade with the same chord length distribution but a constant pitch angle. The model tests have been conducted in the Emerson Cavitation Tunnel measuring the lift and drag. The results showed that the leading-edge tubercles can significantly improve the performance of the hydrofoil by improving the lift-to-drag ratio and delaying the stall. By applying Shear Stress Transport (SST), Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) via using the commercial CFD solver, Star-CCM+, the tested hydrofoil models were simulated and more detailed flow information has been achieved to complement the experiment. The numerical results show that the DES model is in close agreement with the experimental results. The flow separation pattern indicates the leading-edge tubercles can energize the flow around the hydrofoil to keep the flow more attached and also separate the flow into different channels through the tubercles.

Learning from humpback whales for improving the energy capturing performance of tidal turbine blades

This paper summarizes a project on the potential of further improving the performance of horizontal axis tidal turbines via the application of leading-edge tubercles to the turbine blades inspired by humpback whales. Within this framework, a wide variety of experimental investigations, supported by numerical studies, have been conducted.

Dynamic Positioning Reliability Index (DP-RI) and Offline Forecasting of DP-RI During Complex Marine Operations

The Dynamic Positioning (DP) System is a complex system with significant levels of integration between many sub-systems to perform diverse control functions. The extent of information managed by each sub-system is enormous. The complex level of integration between sub-systems creates more possible failure scenarios. A systematic analysis of all failure scenarios is tedious and for an operator to handle any such catastrophic situation is breath taking. There are many accidents where a failure in a DP system has resulted in fatalities and environmental pollution. Therefore, reliability assessment of a DP system is critical for safe and efficient operation of marine and offshore vessels. Traditionally, the reliability of a DP system is assessed during the design stage by methodologies such as Failure Mode Effects and Analysis (FMEA), Proving Trials, Hardware In-the Loop (HIL) testing, Site-Specific Risk Analysis, DP capability Analysis and during operation by annual trials to verify functionality. All these methods are time consuming, involving a lot of human effort and notably no analysis of previous accidents are indicated in the reliability assessment. This imposes in-built uncertainty and risk in DP system during operation. In this paper, a new concept of Dynamic Positioning Reliability Index (DP-RI) is introduced and a state-of-the-art advisory decision making tool is proposed. This tool is developed based on information from various sources including Offshore Reliability Data (OREDA), International Marine Contractors Association (IMCA) Accident database, DP vendor equipment failure databases, DP System supplier’s manuals, previous system level FMEA and HIL testing results, Site specific risk analysis documents, Project design specification and Operator’s operational experiences. Thus, DP-RI addresses the pitfalls of existing reliability assessment methods and will be an efficient tool in reducing the number of DP-related accidents.

The development of a model for determining scheduled replacement Intervals for marine machinery systems

One of the challenges of maintenance management of a marine machinery system is the problem of selecting the optimum interval for replacement of equipment items. Most of the approaches that are given in the literature for selecting optimum replacement intervals are based on a single criterion model such as cost. This approach may be satisfactory for some industries but for the marine industry disruption in services will result in a considerable cost penalty and, as such, other factors such as system downtime and system reliability must be taken into consideration when determining the optimum replacement interval for the system. These decision criteria have been proven to be in conflict with one another. On this basis, a multi-criteria decision-making tool, Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS), is proposed in this article for aggregating multiple criteria in order for them to be used simultaneously in determining the optimum scheduled replacement interval for the equipment items of the system. The use of a multi-criteria decision-making tool allows the decision-maker to express preference for the decision criteria in terms of their levels of importance. To achieve this aim, a compromise decision weighting technique is integrated with TOPSIS. The compromise weighting technique was obtained from a combination of the variance method (an objective decision criteria weighting technique) and analytical hierarchy process (a subjective decision criteria weighting technique). In order to demonstrate the applicability of the proposed innovative methodology for determining the optimum replacement intervals for a marine machinery system and also validate the technique, a case study involving some equipment items of a marine diesel engine is presented. Although results show that it produces the same optimum solution as the methods in the literature, the proposed method is more flexible and less computationally intensive.