Effective Mean Field Approach to Kinetic Monte Carlo Simulations in Limit Cycle Dynamics with Reactive and Diffusive Rewiring

The dynamics of complex reactive schemes is known to deviate from the Mean Field (MF) theory when restricted on low dimensional spatial supports. This failure has been attributed to the limited number of species-neighbours which are available for interactions. In the current study, we introduce effective reactive parameters, which depend on the type of the spatial support and which allow for an effective MF description. As working example the Lattice Limit Cycle dynamics is used, restricted on a 2D square lattice with nearest neighbour interactions. We show that the MF steady state results are recovered when the kinetic rates are replaced with their effective values. The same conclusion holds when reactive stochastic rewiring is introduced in the system via long distance reactive coupling. Instead, when the stochastic coupling becomes diffusive the effective parameters no longer predict the steady state. This is attributed to the diffusion process which is an additional factor introduced into the dynamics and is not accounted for, in the kinetic MF scheme.Comment: 8 pages, 6 figure

An integrated methodology for the design of Ro-Ro passenger ships

The present paper provides a brief introduction to the holistic approach to ship design, defines the generic ship design optimization problem and demonstrates its solution by use of advanced optimization techniques

Mitigating Risk Factors for Disease Progression in Patients with Varus Gonarthrosis

Knee osteoarthritis (OA) is a leading cause of disability worldwide. Its growing burden is related to an aging population, obesity and physical inactivity. The progression of knee OA involves both biomechanical and systemic mechanisms. Known risk factors that might be altered through interventions include lower limb alignment, the distribution of loads across the knee during walking, body composition and muscular strength. The overall purpose of this thesis was to evaluate the effects of multi-modal, rehabilitative and surgical interventions that target different risk factors for disease progression in patients with medial compartment knee OA and varus mal-alignment (varus gonarthrosis). The thesis included three studies. Study 1 demonstrated that patients with substantial bilateral varus alignment who underwent unilateral medial opening wedge high tibial osteotomy (HTO) experienced large decreases in the external knee adduction moment during walking two years after surgery. However, they also experienced increased knee adduction moments in the mal-aligned, non-operated limb, explained most by increases in both body mass and gait speed. Study 2 demonstrated that body composition measurements in patients with knee OA using air displacement plethsmography (BodPod©)had excellent test-re-test reliability. It also provided estimates of measurement error and minimal detectable change to be used when evaluating body composition changes in individual patients with knee OA. Study 3 was a proof of principle study that demonstrated combined, multi-modal physiotherapy and medial opening wedge HTO decreased fat mass, increased muscular strength, decreased knee adduction moments and varus mal-alignment in patients with varus gonarthrosis. Rehabilitative intervention was required to improve body composition and strength, whereas surgical intervention was required to improve alignment and knee adduction moments. Overall, the results of these studies suggest that a combination of treatment approaches that target different risk factors for knee OA are necessary. Multi-modal rehabilitative and surgical intervention for patients with varus gonarthrosis is recommended

Stability upgrade of a typical Philippine ferry

The waterborne transport in the Philippines has been a sensitive subject amplified by the lack of rules and regulations to restrict ship-owners profit-driven decisions, leading to overloading, with significant impact on ship stability. Most of the Tier-II vessels are using solid ballast to balance trim and increase static stability at the expense of freeboard. To improve matters whilst facilitating the currently adopted process, solutions are required that offer additional buoyancy with increased stability. To this end, a solution is proposed here through the addition of sponsons, providing the required level of intact stability and residual floatability/stability, using a typical Ro-Pax. In this paper, a case study is presented to demonstrate the validity of the proposed solution

Computational investigation of ship propulsion performance in rough seas

In this paper, the performance of a merchant vessel propulsion system during acceleration is evaluated under different sea state conditions. The various parts of the main propulsion system have been modelled by using a mean value approach for the engine model with differential equations to calculate the engine crankshaft and turbocharger shaft speeds. Ship propulsion system has been modelled by using differential equations to calculate vessel speed and speed of advance. The output of the engine model has been validated under steady conditions according to the main engine shop test performance data. The calm water resistance is calculated following the ship sea trials results, whilst Wageningen polynomials have been used to simulate the propeller performance for the given hull resistance and speed. In order to estimate the added resistance for different weather conditions, the recommended procedures by International Standards have been followed. Then, the propulsion system performance is evaluated, both in calm water and waves, to investigate the main engine response during acceleration. Based on the simulation results, the propulsion system performance is discussed in respect for the engine response and vessel hydrodynamic performance, predicting the maximum vessel speed for the available engine power and speed

An alternative system for damage stability enhancement

There is an ongoing and continuous initiative to improve the survivability of passenger vessels and in the past increasing safety standards have generally been catered for through the use of design(passive) measures. However, this approach is becoming saturated and any such measures to improve damage stability severly erode ship earning potential and are being resisted by industry. In a change of direction, this paper aims to explore the use of operational(active) measures for damage stability enhancement in line with IMO Circular 1455 on equivalents. An alternative system for damage stability enhancement is intorduced that involves injecting highly expandable foam in the compartment(s) undergoing flooding during the initial post-accident flooding phase thus enhancing damage stability and survivability of RoPax vessels well beyond the design levels in the most cost-effective way currently available. This is a mind-set changing innovation that is likely to revolutionise design and operation of most ship types and RoPax, in particular. A case study has been performed on a large RoPax vessel with impressive results that will challenge the current established practice and open possibilities for novel and innovative design configuration

Energy efficiency parametric design tool in the framework of holistic ship design optimization

Recent International Maritime Organization (IMO) decisions with respect to measures to reduce the emissions from maritime greenhouse gases (GHGs) suggest that the collaboration of all major stakeholders of shipbuilding and ship operations is required to address this complex techno-economical and highly political problem efficiently. This calls eventually for the development of proper design, operational knowledge, and assessment tools for the energy-efficient design and operation of ships, as suggested by the Second IMO GHG Study (2009). This type of coordination of the efforts of many maritime stakeholders, with often conflicting professional interests but ultimately commonly aiming at optimal ship design and operation solutions, has been addressed within a methodology developed in the EU-funded Logistics-Based (LOGBASED) Design Project (2004–2007). Based on the knowledge base developed within this project, a new parametric design software tool (PDT) has been developed by the National Technical University of Athens, Ship Design Laboratory (NTUA-SDL), for implementing an energy efficiency design and management procedure. The PDT is an integral part of an earlier developed holistic ship design optimization approach by NTUA-SDL that addresses the multi-objective ship design optimization problem. It provides Pareto-optimum solutions and a complete mapping of the design space in a comprehensive way for the final assessment and decision by all the involved stakeholders. The application of the tool to the design of a large oil tanker and alternatively to container ships is elaborated in the presented paper

A study on the effects of bilge keels on roll damping coefficient

A study of the roll damping of a two-dimensional FPSO model produced by bilge keels using CFD method is presented in this paper. The tool to be utilized is the well-known code Star-CCM+, which uses the Volume of Fluid (VOF) approach to capture the free surface. The results are validated by comparison with experiments. Using the results from a number of simulations, the roll damping coefficient resulting from locating the bilge keels at different positions will be calculated. The analysis of the rolling damping coefficients for the different locations will provide a useful design tool for optimising the roll damping of vessels with bilge keels

Quantification of the maritime security problem onboard passenger ship

Given the large number of recent terror attacks worldwide, there is a growing concern over the security issue in the maritime world. Aim of this paper is to address a scenario pertinent to the maritime security problem using the evacuation simulation software tool EVI. The vessel chosen for this case study is a 13-deck cruise ship. The scenario investigated deals with the evacuation of a large density populated area within the vessel, where an explosive device has been placed and assesses the potential loss of life, according to the distance of the agents relative to the explosion blast. Three different positions of the explosive device are examined in this study and for each position six different cases are examined, in which the effect of prior warning to the explosion is taken into consideration. In the first case, the explosion takes place at the beginning of the simulation (t=0) in order to replicate such a scenario in which those agents within the restaurant are un-alerted to the presence of the explosive device. In the rest of the cases the explosion takes place after warning times of 0.5, 1, 1.5, 2 and 2.5 minutes respectively in order to assess the sensitivity of the fatality rate and evacuation to prior warning time