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

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

Applications of holistic ship theory for the simulation driven optimization of the design and operation of large bulk carriers

The change of scenery in shipping has been evident over the past 20 years. The changing fuel costs, tough and volatile market conditions, the constant societal pressure for a «green» environmental footprint combined with ever demanding international safety regulations create the new framework in which commercial ship designs are subject to. As a result of this current status of shipping commercial a change of attitude in the philosophy and process of ship design is required in order to shift towards new approaches where holistic approaches are deemed necessary. Apart from considering all the interrelationships between the subsystems that consist the vessel lifecycle and supply chain considerations are the key in successful and «operator oriented» designs. The methodology herein presented is built within the computer aided engineering (CAE) software CAESES that integrates in the design process CFD codes. It can be successfully used for the optimization of either of the basic design of a vessel or the operation of an existing vessel with regards to the maximization of the efficiency, safety and competitiveness of the final design. The model is created based on the design of a large bulk carrier and a simulation model consisting of modules that cover most aspects of ship design. Stability, strength, powering and propulsion, safety, economics, operational and maintenance and in service management considerations are tightly integrated within a fully parametric model. This tight integration enables the user to simulate the response of the model in variations of the geometrical, design variables of the vessel (including its propeller) under conditions of simulation and uncertainty. The uncertainty modelling is extensive and in several levels including but not limited to Economic, Environmental, and Operational uncertainty as well an accuracy modelling of the methodology itself

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

Material quality effects on structural design of rudder horns for bulk carriers and tankers

This paper addresses the assessment of the structural integrity of a rudder horn built of different materials and in particular, the material quality effects on the structural design of a typical rudder horn of a conventional Panama-Kamsarmax size ship in relation to IACS requirements. The minimum scantlings of the rudder horn were established and compared for different steels permitted in IACS UR S10. Furthermore, a FEA model of the rudder horn including its most critical part i.e. its connection to the hull structure, was developed in order to calculate and compare stress and deflections under the IACS prescribed loading conditions The findings suggest that the use of higher strength material may reduce substantially the fatigue life of the structure at the critical area of rudder horn to hull connection which may cause the initiation of cracking, with adverse impact to the safety of the ship and its crew

ELIGMOS: time domain simulation of the maneuvering of ships in deep and shallow waters

Calm water manoeuvring simulations are commonly used at the initial design stage as they provide useful an practical insight concerning ship's manoeuvrability and compliance with the relevant IMO criteria. In this paper the authors present ELIGMOS; a time-domain numerical code utilizing a 3-DOF manoeuvring model based on the MMG method. For the validation of the code's predictions, a comparison with the experimental results on the turning ability of S-175 has been conducted. The paper presents also the investigation performed regarding the accuracy of certain empirical formulas for the derivation of the manoeuvring derivatives is also investigated, especially for the case of shallow water where experimental data and results remain scarce. The code is written in C++ programming language, adopting a modular approach for the calculation of external forces and moment (i.e. hydrodynamic hull, rudder and propeller) which allows future enhancements with the introduction of additional terms

Wave-induced vertical bending moment estimation by onboard tiltmeters units on container ship

Full-scale measurements in oceangoing ships have shown that the relationship between bending moment with the curvature curve of hull girder. As part of the INCASS (Inspection Capabilities for Enhanced Ship Safety) EU FP7 project, this paper carried out an estimation of wave-induced vertical bending moment for cargo hold of the 4250 TEU container ship, based on the data of pitch angles processing from the Tiltmeter units placed on board. The results are enable to be processed to the Decision Support System (DSS), in order to assist to monitoring and risk analysis for ship structure and machinery the towards enhanced and efficient ship operations (Konstantinos, et al., 2015). The prediction values also provide a reference for the trend analy-sis of the past record signals (Ulrik Dam et al, 2015) for evaluation of longitudinal strength of container ship. The advance in different pitch angle response (deformation curvature) of hull girder can be as a development of modern decision support systems for guidance to the ship's master (Lloyd's Register, 2016

Tanker ship structural analysis for intact and damage cases

This paper presents the work carried out to assess the structural calculation of a tanker ship in intact and damage conditions, in order to know the areas of the central cargo ship exposed to greater stresses. Analysing the results obtained from the intact condition and damage conditions due to grounding. The method selected to simulate the damage conditions has been done applying a change in the mechanical properties of the material; reductions of 40, 60 and 80 % of Young Modules were applied. The validation of the results was made following the guidelines "Common Structural Rules for Bulk Carriers and Oil Tankers" from IACS. The finite element method and finite element analysis software (Ansys®) were used to analyse intact and ground-ing cases. For intact case only one scenario was done, full load condition. For grounding, three scenarios were done. The results presented correspond to the validation of the finite element model, and the results concern-ing the maximum value of Von Mises Stress for each load condition, verifying if the permissible stress has been exceeded in each of the conditions analysed

Analysis of the wave-induced vertical bending moment and comparison with the class imposed design loads for 4250 TEU container ship

The long-term predictions of vertical wave bending moment are made for the extreme design values on ship. As part of the INCASS (Inspection Capabilities for Enhanced Ship Safety), this paper carried out a short-term estimation of wave loads for 4250 TEU container ship by the hydrodynamic analysis software of ANSYS-Aqwa based on three-dimensional linear potential flow theories. Based on the short-term predic-tion and the wave statistic of the North Atlantic Ocean, a long-term prediction of vertical wave bending mo-ment is obtained. The results are required and processed to the Decision Support System (DSS), in order to assist to monitoring and risk analysis for ship structure and machinery the towards enhanced and efficient ship operations (Konstantinos, et al., 2015). The prediction values also provide a reference for the trend analysis of the past record signals (Ulrik Dam et al, 2015) for evaluation of longitudinal strength of container ship

Comparison of diesel-electric with hybrid-electric propulsion system safety using system-theoretic process analysis

Cruise ship industry is rapidly developing, with both the vessels size and number constantly growing up, which renders ensuring passengers, crew and ship safety a paramount necessity. Collision, grounding and fire are among the most frequent accidents on cruise ships with high consequences. In this study, a hazard analysis of diesel-electric and hybrid-electric propulsion system is undertaken using System-Theoretic Process Analysis (STPA). The results demonstrate significant increase in potential hazardous scenarios due to failures in automation and control systems, leading to fire and a higher number of scenarios leading to propulsion and power loss in hybrid-electric propulsion systems than on a conventional cruise-ship propulsion system. Results also demonstrate that STPA enhancement is required to compare the risk of two propulsion systems