Notched impact behavior of polymer blends: Part 1: New model for particle size dependence

A model is proposed to explain the observed relationships between particle size and fracture resistance in high-performance blends, which typically reach maximum toughness at particle diameters of 0.2–0.4 μm. To date there has been no satisfactory explanation for the ductile–brittle (DB) transition at large particle sizes. The model is based on a recently developed criterion for craze initiation, which treats large cavitated rubber particles as craze-initiating Griffith flaws. Using this criterion in conjunction with Westergaard's equations, it is possible to map the spread from the notch tip of three deformation mechanisms: rubber particle cavitation, multiple crazing and shear yielding. Comparison of zone sizes leads to the conclusion that maximum toughness is achieved when the particles are large enough to cavitate a long way ahead of a notch or crack tip, but not so large that they initiate unstable crazes and thus reduce fracture resistance

The angle guidance path planning algorithms for unmanned surface vehicle formations by using the fast marching method

By deploying multiple USVs as a formation fleet, benefits such as wide mission area, improved system autonomy and increased fault-tolerant resilience can be achieved. To efficiently and effectively navigate the USV formation, path planning algorithms are required to generate optimal trajectories and provide practical collision avoidance manoeuvres. In particular, as the USV is underactuated and is restricted by various motion constraints, this paper has presented a new algorithm named the ‘angle-guidance fast marching square’ (AFMS), to make the generated path compliant with vehicle's dynamics and orientation restrictions. Based upon the AFMS, a formation path planning algorithm has been proposed to guide the USVs safely navigating in a cluttered environment. In addition, the formation forming problem has been specifically investigated with the algorithm being developed to make the USVs capable of forming the desired shape by following the trajectories from random initial configurations (positions and orientations). In order to eliminate the potential collision risks occurring on the route, a novel priority scheme based upon the distance to the closest point of approaching (DCPA) has also been proposed and developed. Algorithms have been validated on the computer-based simulations and are proven to work effectively in different environments

On the design of plug-in hybrid fuel cell and lithium battery propulsion systems for coastal ships

A plug-in hybrid propulsion system comprising of a proton exchange membrane fuel cell (PEMFC) and lithium battery capable of being recharged in port offers a promising low carbon propulsion system for small coastal ships, e.g. small container ships, tankers and ferries, which typically sail over short routes at modest speeds. PEMFC operate at high efficiency and emit no harmful emissions, but their poor transient performance necessitates the need for an energy storage system such as a lithium battery. A shore-to-ship electrical connection is needed to recharge the lithium battery from the grid so as to improve the propulsion system performance both environmentally and economically. Production of both H2 and grid electricity have a carbon footprint. In this paper a two-layer optimisation based methodology is used for the design of plug-in hybrid fuel cell and lithium battery propulsion systems for coastal ships. Results from a case study suggest that the design of hybrid PEMFC and battery propulsion systems should be influenced by the ‘well-to-propeller’ carbon footprint

Assessing battery energy storage for integration with hybrid propulsion and high energy weapons

In the future warship power and propulsion systems need to be designed for increased flexibility, in part to sustain the demand of changing load profiles such as those characterised by high ramp-rates of new weapons and sensors intended to support enhanced future warfighting capability. Lithium-ion based battery performance is improving at a prominent pace in the automotive sector, increasing in both energy and power density, thus there is now an opportunity to exploit these characteristics for naval power systems. A common use energy storage system could facilitate benefits such as reduced fuel burn and prime mover running hours by reducing the number of running generator sets. Importantly, the improvement in battery systems, has reached a juncture where the technology could be considered to support directed energy weapons. The feasibility of a Lithium-ion NMC based energy storage system, capable of high discharge rates, to power predicted laser directed energy weapons using time domain simulation is investigated in this paper. Results verify that the simulated system is capable of high rates of fire for extended periods subject to state of charge operating limitations

Investigating the Performance Capability of a Lithium-ion Battery System When Powering Future Pulsed Loads

The supply of pulsed power loads is considered a key driver for the integration of energy storage systems (ESSs) with warship power systems. ESSs are identified as a means to offer fast response dynamics capable of driving pulsed loads for sustained periods. This paper contributes a novel investigation into the performance of a Nickel Manganese Cobalt based lithium-ion battery system to supply laser directed energy weapon (LDEW) loads for future warship combat power systems using time-domain simulation methodology. The approach describes a second order Thévenin equivalent circuit battery model validated against a battery module of a type used in commercial marine ESS. The ability of the battery system to power LDEW loads peaking at 2 MW for up to periods of four minutes were simulated for beginning of life (BoL) and degraded conditions. The repeatability of the pulsed power supply with ESS is also reported. Simulation results show that Quality of Power Supply (QPS) is maintained within acceptable transient tolerance using a feed-forward control circuit that controls the DC-DC converter interface between the battery system and the LDEW load. The results of the study demonstrate the battery system operating envelope for the LDEW under investigatio

A multi-layered fast marching method for unmanned surface vehicle path planning in a time-variant maritime environment

Concerns regarding the influence of the marine environment, such as surface currents and winds, on autonomous marine vehicles have been raised in recent years. A number of researchers have been working on the development of intelligent path planning algorithms to minimise the negative effects of environmental influences, however most of this work focuses on the platform of autonomous underwater vehicles (AUVs) with very little work on unmanned surface vehicles (USVs). This paper presents a novel multi-layered fast marching (MFM) method developed to generate practical trajectories for USVs when operating in a dynamic environment. This method constructs a synthetic environment framework, which incorporates the information of planning space and surface currents. In terms of the planning space, there are repelling and attracting forces, which are evaluated using an attractive/repulsive vector field construction process. The influence of surface currents is weighted against the obstacles in the planning space using a 4-regime risk strategy. A trajectory is then calculated using the anisotropic fast marching method. The complete algorithm has been tested and validated using simulated surface currents, and the performance of generated trajectories have been evaluated in terms of different optimisation criteria, such as the distance and energy consumption

The Advanced Technology Corvette - Railgun (ATK-R) Design Study - Future Weapons and Small Ship Power Systems

High-power electric weapons, such as the ElectroMagnetic RailGun (EMRG), laser and High Power Microwave devices are moving closer to practical utilisation by navies, and prototype EMRG systems are being tested at militarily useful energy levels. Previous work in the UCL Department of Mechanical Engineering includes; preliminary design studies for surface combatants with an all electric weapons outfit; and detailed marine engineering analysis, to PhD level, of the implications for future power and propulsion systems of these weapons. Design studies for electrically armed ships have generally examined large destroyer-sized surface combatants, with significant installed electrical power. This paper describes a concept design study for a small corvette-sized combatant, ATK-R, developed as the “minimum sized ship” capable of supporting an EMRG as its primary armament This paper describes the UCL ZEOLIT design tool, the ship design impacts and marine engineering integration of this future concept including the use of Energy Storage Systems (ESS) and the choice between power limited (Patrol vessel -like) and power dense (Fast attack craft –like) power and propulsion systems

The design of an autonomous maritime navigation system for unmanned surface vehicles

This paper presents the development of an autonomous maritime navigation system for unmanned surface vehicles (USVs). In the autonomous system various maritime navigational devices are connected to obtain necessary navigational information but with uncertainties. To improve signal accuracy as well as robustness, a novel multi-sensor data fusion algorithm is proposed and developed. Then, a new predictive path planning algorithm is employed to provide an advisory collision-free trajectory. Practical trials and computer based simulations are carried out to prove the effectiveness of the developed syste

Aspects of a Reliable Autonomous Navigation and Guidance System for an Unmanned Surface Vehicle

This paper describes a novel navigation and guidance (NG) system designed to address the issue of receiving unreliable navigational data considering an unmanned surface vehicles (USVs). In the NG system, a confidence rate determination method has been designed to identify the uncertainty of the acquired data. According to the confidence rate, the risks from inaccurate data can be properly analysed facilitating the system generating a more reliable guidance route. The route is calculated using a newly developed algorithm named the constrained FM*. The new NG system has been verified in simulation environments with results proving the effectiveness and capabilities of the system

Optimised MOPSO with the grey relationship analysis for the multi-criteria objective energy dispatch of a novel SOFC-solar hybrid CCHP residential system in the UK

In the quest to achieve home comfort with the highest possible efficiency, there is an increasing interest in combined cooling, heating and power (CCHP) systems. These can be fuelled by natural gas and potentially by hydrogen enriched natural gas and ultimately by hydrogen. The optimised designs largely depend on the energy dispatch algorithms that take into account aspects of economic and environmental impacts as well as system efficiency. This paper details a new algorithm to optimise the operation of a novel hybrid solid oxide fuel cell (SOFC)-solar hybrid CCHP residential system. The proposed algorithm is based on the multi-objective particle swarm optimization (MOPSO) and the grey relationship analysis (GRA) (named as MOPSO-GRA) with the capability of resolving the objective energy dispatch issues within the system by effectively avoiding local optimum problem. More specifically, the grey incidences are first integrated into MOPSO to analyse the degree of closeness between non-ideal solutions and the ideal solution. Then, the relationship of degree is introduced to give objective energy dispatch in order to maximise the efficiency of energy utilization while minimising the system capital cost, operating costs, maintenance costs, fuel costs and emissions. Finally, the new algorithm is validated on the proposed new design of CCHP system. Ten cases are studied to evaluate the technical, economic and environmental performance of the MOPSO-GRA algorithm when being applied to an SOFC-based CCHP system under both the grid-connected and the island modes. A comparison is made with the conventional MOPSO method and system structure, and the impact of a plug-in EV is also evaluated. Based on a detailed cost and emissions analysis, the results indicate the environmental and economic advantages, in addition to the higher efficiency of the proposed methodology and system structure. The impact of these results and observations leads to the promotion of intelligent FC-based multi-energy system technologies for residential use