Reliability-based design optimization of shells with uncertain geometry using adaptive Kriging metamodels

Optimal design under uncertainty has gained much attention in the past ten years due to the ever increasing need for manufacturers to build robust systems at the lowest cost. Reliability-based design optimization (RBDO) allows the analyst to minimize some cost function while ensuring some minimal performances cast as admissible failure probabilities for a set of performance functions. In order to address real-world engineering problems in which the performance is assessed through computational models (e.g., finite element models in structural mechanics) metamodeling techniques have been developed in the past decade. This paper introduces adaptive Kriging surrogate models to solve the RBDO problem. The latter is cast in an augmented space that "sums up" the range of the design space and the aleatory uncertainty in the design parameters and the environmental conditions. The surrogate model is used (i) for evaluating robust estimates of the failure probabilities (and for enhancing the computational experimental design by adaptive sampling) in order to achieve the requested accuracy and (ii) for applying a gradient-based optimization algorithm to get optimal values of the design parameters. The approach is applied to the optimal design of ring-stiffened cylindrical shells used in submarine engineering under uncertain geometric imperfections. For this application the performance of the structure is related to buckling which is addressed here by means of a finite element solution based on the asymptotic numerical method

The effect of increasing the thickness of the ship’s structural members on the Generalised Life Cycle Maintenance Cost (GLCMC)

In the context of the EU funded IMPROVE project, the research work of a Generalised Life Cycle Maintenance Cost (GLCMC) was initiated in order to investigate the influence of a weight oriented ship structural design on its production and operational characteristics. Following this, an increase in the structural scantlings of the ship was examined following the IACS Common Structural Rules (CSR) for double hull oil tankers. A case study for a Chemical tanker is shown considering an addition in its bottom plate thickness and three different cases of mean annual corrosion rates applied. A comparison regarding the “Gross gains”, “Gross expenses” and “Net gains” for this ship is also presented. Moreover, an evaluation of the extra cost for the additional steel weight used is shown together with the outcome on the repair-free operation of the ship for different additional plate thickness. Finally, a sensitivity analysis is carried out for the most likely case (“Case 2”) and the variation of different amount of days spent in the ship repair yard

Designing efficient and contemporary ship recycling yards through discrete event simulation

Ship recycling, similar to any other recycling industry, can be considered as the most environmentally friendly option for end-of-life ships than the other alternatives. However, lack of safety, lack of environmental awareness as well as lack of a global and local regulatory framework resulted in ships being dismantled in undesirable conditions which forced international regulators to focus on developing international regulations and standards.;The International Maritime Organization's (IMO) Hong Kong Convention and the European Union's Ship Recycling Regulation are examples of the aforementioned new regulations. Both regulations require ship recycling yards to improve existing HSE standards to stay compliant. These HSE measures will negatively impact on running costs, therefore, ship recycling yards will need to increase their production efficiency to remain competitive.;Even though the industry requires support during this transition, there is no study within the current body of literature that focuses on increasing the productivity of the ship recycling facilities. Hence, there is a need to develop a framework to design contemporary and efficient ship recycling yards. Increasing production efficiency in ship recycling yards will not only decrease the costs, but it will also increase the throughput of the yards which will generate more income and positively impact on overall profitability.;Therefore, this PhD study addresses this gap through the development of a simulation framework for ship recycling industry to design and optimise the ship recycling yards. The study adopts a case-based approach where numerous design alternatives will be studied through the proposed framework. The main aim of this study is to increase the productivity of ship recycling yards and optimise their procedures towards achieving cost-efficient facilities.;Overall research conducted in this study will be significant contribution to the maritime literature as a novel framework for ship recycling yard design and optimisation is developed. The process models of this framework are developed based on real ship recycling procedures, therefore, the framework can be considered ready for practical implementation.Ship recycling, similar to any other recycling industry, can be considered as the most environmentally friendly option for end-of-life ships than the other alternatives. However, lack of safety, lack of environmental awareness as well as lack of a global and local regulatory framework resulted in ships being dismantled in undesirable conditions which forced international regulators to focus on developing international regulations and standards.;The International Maritime Organization's (IMO) Hong Kong Convention and the European Union's Ship Recycling Regulation are examples of the aforementioned new regulations. Both regulations require ship recycling yards to improve existing HSE standards to stay compliant. These HSE measures will negatively impact on running costs, therefore, ship recycling yards will need to increase their production efficiency to remain competitive.;Even though the industry requires support during this transition, there is no study within the current body of literature that focuses on increasing the productivity of the ship recycling facilities. Hence, there is a need to develop a framework to design contemporary and efficient ship recycling yards. Increasing production efficiency in ship recycling yards will not only decrease the costs, but it will also increase the throughput of the yards which will generate more income and positively impact on overall profitability.;Therefore, this PhD study addresses this gap through the development of a simulation framework for ship recycling industry to design and optimise the ship recycling yards. The study adopts a case-based approach where numerous design alternatives will be studied through the proposed framework. The main aim of this study is to increase the productivity of ship recycling yards and optimise their procedures towards achieving cost-efficient facilities.;Overall research conducted in this study will be significant contribution to the maritime literature as a novel framework for ship recycling yard design and optimisation is developed. The process models of this framework are developed based on real ship recycling procedures, therefore, the framework can be considered ready for practical implementation

Methodology for managing shipbuilding projectby integrated optimality

PhD ThesisSmall to medium shipyards in developing shipbuilding countries face a persistent challenge to contain project cost and deadline due mainly to the ongoing development in facility and assorted product types. A methodology has been proposed to optimize project activities at the global level of project planning based on strength of dependencies between activities and subsequent production units at the local level. To achieve an optimal performance for enhanced competitiveness, both the global and local level of shipbuilding processes must be addressed. This integrated optimization model first uses Dependency Structure Matrix (DSM) to derive an optimal sequence of project activities based on Triangularization algorithm. Once optimality of project activities in the global level is realized then further optimization is applied to the local levels, which are the corresponding production processes of already optimized project activities. A robust optimization tool, Response Surface Method (RSM), is applied to ascertain optimum setting of various factors and resources at the production activities. Data from a South Asian shipyard has been applied to validate the fitness of the proposed method. Project data and computer simulated data are combined to carry out experiments according to the suggested layout of Design of Experiments (DOE). With the application of this model, it is possible to study the bottleneck dynamics of the production process. An optimum output of the yard, thus, may be achieved by the integrated optimization of project activities and corresponding production processes with respect to resource allocation. Therefore, this research may have a useful significance towards the improvement in shipbuilding project management

Resource constrained scheduling problem at U.S. Naval Shipyards

CIVINS (Civilian Institutions) Thesis documentSubmarine repair schedules are some of the most complex schedules seen in project management. Repairs of a nuclear U.S. submarine are resource constrained since resources are divided among approximately thirty shops (e.g., electricians, welders, and pipefitters). The system complexity, the tight spaces, the operational nuclear reactor, the challenges inherent in repair, and resource competition all contribute to a dense integrated schedule. Minimizing the overall length of each project, the "makespan," is the primary objective function of this thesis. This thesis uses a commercially available simulation package, @Risk, to analyze a realistic submarine repair schedule. Simulation is used to analyze uncertainty in the task durations and identify crucial tasks that highly impact the makespan. Finally, a genetic algorithm is tested to assign resources to tasks and 7723 constraints or ties. A simulation assigned all 4038 tasks a triangle probability distribution with the duration set at plus or minus 10 percent of the original duration estimate. Sensitivity analysis of the simulation identified key task nodes having significant impact on the overall duration. These top ten crucial tasks were then given similar probability distributions and another simulation was run keeping the remaining 4028 tasks as determiniatic durations. Minimizing the makespan could only be executed on a small subset of data, 25 tasks, due to limiting assumptions on reducing task durations by assigning more resources. An overall improvement of 5.5-15.6% was achieved: this gives an indication of the approximate makespan optimization potential in current U.S. submarine repair, maintenance and overhaul operations.http://archive.org/details/resourceconstrai1094540243US Navy (USN) autho

Assessing the suitability of ship design for human factors issues associated with evacuation and normal operations

Evaluating ship layout for human factors (HF) issues using simulation software such as maritimeEXODUS can be a long and complex process. The analysis requires the identification of relevant evaluation scenarios; encompassing evacuation and normal operations; the development of appropriate measures which can be used to gauge the performance of crew and vessel and finally; the interpretation of considerable simulation data. In this paper we present a systematic and transparent methodology for assessing the HF performance of ship design which is both discriminating and diagnostic. The methodology is demonstrated using two variants of a hypothetical naval ship

Optimal Design of Ship’s Hybrid Power System for Efficient Energy

The International Maritime Organization regulations on the reduction of greenhouse gas emissions (GHGs) from ships require efficient dealing with this complex techno-economic and highly political problem through joint efforts of all major stakeholders from the shipbuilding industry and ship operations. The key problems of any research in the field of renewable energy, including power generation, storage, transformation and distribution, and the issues associated with limited power generation for specific loads, are the same issues that are experienced in the implementation of electric distribution technologies onboard ships. This paper analyses the effects of efficient shipping using the solar panel system and batteries to ensure continuous power supply, regardless of the weather conditions. The logistics chain of this control architecture is modelled by Colored Petri Nets. The economic analysis examines the annual costs of fuel consumption, the initial capital cost, total net cost and CO2 emissions

A generalized likelihood-weighted optimal sampling algorithm for rare-event probability quantification

In this work, we introduce a new acquisition function for sequential sampling to efficiently quantify rare-event statistics of an input-to-response (ItR) system with given input probability and expensive function evaluations. Our acquisition is a generalization of the likelihood-weighted (LW) acquisition that was initially designed for the same purpose and then extended to many other applications. The improvement in our acquisition comes from the generalized form with two additional parameters, by varying which one can target and address two weaknesses of the original LW acquisition: (1) that the input space associated with rare-event responses is not sufficiently stressed in sampling; (2) that the surrogate model (generated from samples) may have significant deviation from the true ItR function, especially for cases with complex ItR function and limited number of samples. In addition, we develop a critical procedure in Monte-Carlo discrete optimization of the acquisition function, which achieves orders of magnitude acceleration compared to existing approaches for such type of problems. The superior performance of our new acquisition to the original LW acquisition is demonstrated in a number of test cases, including some cases that were designed to show the effectiveness of the original LW acquisition. We finally apply our method to an engineering example to quantify the rare-event roll-motion statistics of a ship in a random sea