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Optimization of prismatic moon pool configuration by operability criteria

A moon pool is an opening inside the hull of a floating system that allows access to the sea isolated from horizontal environmental forces. Despite those benefits, some disadvantages may occur when a resonant response to waves happens. Exaggerated oscillations might cause poor operation conditions o...

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Main Author: MICHIMA, Paula Suemy Arruda
Other Authors: PRIMO, Ana Rosa Mendes
Format: doctoralThesis
Language: eng
Published: Universidade Federal de Pernambuco 2019
Subjects:
Engenharia Mecânica
Drill ship
Navio-sonda de perfuração
Moon pool
Otimização
Operabilidade
Algoritmo genético
Online Access: https://repositorio.ufpe.br/handle/123456789/28383
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spelling ir-123456789-283832019-10-26T05:36:05Z Optimization of prismatic moon pool configuration by operability criteria MICHIMA, Paula Suemy Arruda PRIMO, Ana Rosa Mendes KAWABE, Hiroshi http://lattes.cnpq.br/3434875455344412 http://lattes.cnpq.br/0107672521253580 Engenharia Mecânica Drill ship Navio-sonda de perfuração Moon pool Otimização Operabilidade Algoritmo genético A moon pool is an opening inside the hull of a floating system that allows access to the sea isolated from horizontal environmental forces. Despite those benefits, some disadvantages may occur when a resonant response to waves happens. Exaggerated oscillations might cause poor operation conditions or interruption of drilling procedures. The aim of this work is to, given a hull, find an optimal moon pool configuration that would result in the best stationary operation conditions for a typical sea state of the operation region. The proposal restricts it to be prismatic, free of appendages, recess, or any solution other than adequate contour shape. A drill ship is chosen as an example, but the method suits for floating systems in short and long term operation, granted that the response spectra can be calculated. Through an altered genetic algorithm applied to the set of parameters that define the shape and dimensions of the moon pool border, the optimum shape is searched based on hull and internal water response to wave excitation in various incidence angles and significant wave periods. A detailed development of the potential model used to describe the ship and free surface motions is presented, proposing a Rayleigh damping term and a boundary condition at the free surface inside the moon pool. The derivation of a set of formulae to transform into threshold significant wave height the acceptable limit values of each criterion: free surface height, ship motion, hull structure strength and positioning in azimuthal plane are also shown to determine a grade of fitness based on resultant operable conditions. Although there still are spaces for improvement of the resultant parameters’ values due to computational limitations, transversal dimensions and border shape parameters have converged, and the small variation of longitudinal dimensions is limited by order of length and Length/Breadth ratio values range of the moon pool. It was found possible to define, from user input: hull geometry and limit values for operability, what is the optimum prismatic moon pool configuration, which can be very different from the standard rectangle. Further, once the results of optimization are obtained, still in design stage, it is possible to identify characteristics of the system (or ship) that would improve operability. The output of the optimization program provides a visualization file of the mesh of the hull with optimum moon pool, and a radar chart with the operable zone of a given sea state. The latter can be used for quick decision making upon interruption of procedures during operation. In terms of construction complexity the moon pool shape doesn’t seem to present any limitations, since it is prismatic. A bow or stern shape is much more complex than the moon pool, and from mesh definition it is composed of only flat plates, demanding no extra work in plate conformation. Um moon pool é uma abertura no casco de um sistema flutuante que permite o acesso ao mar isolado das forças horizontais provindas do ambiente. Apesar desse benefício, algumas desvantagens podem existir quando a resposta à excitação de ondas é ressonante. Oscilações exageradas podem provocar baixas condições de operação ou interrupção dos procedimentos de perfuração. O objetivo deste trabalho é, dado um casco, encontrar a configuração ótima do moon pool que resultará nas melhores condições de operação estacionária para um estado de mar típico da região de operação. A proposta restringe-o a ser prismático, livre de apêndices, recessos, ou qualquer outra solução que não seja o formato de sua borda. Um navio-sonda de perfuração (drill ship) foi escolhido como exemplo, mas o método se aplica a sistemas flutuantes em operação de curto e longo prazo, se os espectros de resposta puderem ser calculados. Utilizando um algoritmo genético alterado aplicado aos parâmetros que definem a forma e dimensões de seu contorno, a configuração ótima do moon pool é buscada para o casco, dada a resposta à excitação de ondas em vários ângulos de incidência e períodos significativos de onda. O modelo potencial usado para descrever os movimentos do navio e da superfície livre do moon pool é apresentada, com a proposta do termo de amortecimento de Rayleigh e a condição de contorno correspondente. A dedução das fórmulas para converter as informações de valores dos limites aceitáveis para cada critério (altura da superfície livre do moon pool, resposta do navio, resistência estrutural do casco e manutenção do posicionamento) é apresentada. As formulas definem a adequação do moon pool para as condições de operação resultantes. Embora haja pontos a serem melhorados nos valores dos parâmetros resultantes (devidos à limitação computacional), as dimensões transversais e parâmetros de forma convergiram, e a pequena variação nas dimensões longitudinais é limitada pela ordem de grandeza do comprimento e faixa de valores da razão de Comprimento/Boca do moon pool. Concluiu-se que é possível definir, a partir de dados de entrada do usuário: geometria do casco e valores limites para operabilidade, qual é a configuração ótima de moon pool prismático, que pode ser bastante diferente do retângulo convencional. Além disso, uma vez obtidos os resultados da otimização, ainda no estágio de projeto, é possível identificar características do sistema (ou navio) que podem melhorar a operabilidade se alterados de forma conveniente. Juntamente com os valores resultantes dos parâmetros de dimensões e forma, são fornecidos também a malha do casco com o moon pool ótimo integrado e um gráfico de radar com a zona operável em um dado estado de mar, que pode ser usado para tomadas rápidas de decisão sobre a interrupção das operações em curso. Em termos de complexidade construtiva, a forma do moon pool não parece 2019-01-03T12:27:29Z 2019-01-03T12:27:29Z 2017-10-20 doctoralThesis https://repositorio.ufpe.br/handle/123456789/28383 eng openAccess Attribution-NonCommercial-NoDerivs 3.0 Brazil http://creativecommons.org/licenses/by-nc-nd/3.0/br/ application/pdf Universidade Federal de Pernambuco UFPE Brasil Programa de Pos Graduacao em Engenharia Mecanica
institution REPOSITORIO UFPE
collection REPOSITORIO UFPE
language eng
topic Engenharia Mecânica
Drill ship
Navio-sonda de perfuração
Moon pool
Otimização
Operabilidade
Algoritmo genético
spellingShingle Engenharia Mecânica
Drill ship
Navio-sonda de perfuração
Moon pool
Otimização
Operabilidade
Algoritmo genético
MICHIMA, Paula Suemy Arruda
Optimization of prismatic moon pool configuration by operability criteria
description A moon pool is an opening inside the hull of a floating system that allows access to the sea isolated from horizontal environmental forces. Despite those benefits, some disadvantages may occur when a resonant response to waves happens. Exaggerated oscillations might cause poor operation conditions or interruption of drilling procedures. The aim of this work is to, given a hull, find an optimal moon pool configuration that would result in the best stationary operation conditions for a typical sea state of the operation region. The proposal restricts it to be prismatic, free of appendages, recess, or any solution other than adequate contour shape. A drill ship is chosen as an example, but the method suits for floating systems in short and long term operation, granted that the response spectra can be calculated. Through an altered genetic algorithm applied to the set of parameters that define the shape and dimensions of the moon pool border, the optimum shape is searched based on hull and internal water response to wave excitation in various incidence angles and significant wave periods. A detailed development of the potential model used to describe the ship and free surface motions is presented, proposing a Rayleigh damping term and a boundary condition at the free surface inside the moon pool. The derivation of a set of formulae to transform into threshold significant wave height the acceptable limit values of each criterion: free surface height, ship motion, hull structure strength and positioning in azimuthal plane are also shown to determine a grade of fitness based on resultant operable conditions. Although there still are spaces for improvement of the resultant parameters’ values due to computational limitations, transversal dimensions and border shape parameters have converged, and the small variation of longitudinal dimensions is limited by order of length and Length/Breadth ratio values range of the moon pool. It was found possible to define, from user input: hull geometry and limit values for operability, what is the optimum prismatic moon pool configuration, which can be very different from the standard rectangle. Further, once the results of optimization are obtained, still in design stage, it is possible to identify characteristics of the system (or ship) that would improve operability. The output of the optimization program provides a visualization file of the mesh of the hull with optimum moon pool, and a radar chart with the operable zone of a given sea state. The latter can be used for quick decision making upon interruption of procedures during operation. In terms of construction complexity the moon pool shape doesn’t seem to present any limitations, since it is prismatic. A bow or stern shape is much more complex than the moon pool, and from mesh definition it is composed of only flat plates, demanding no extra work in plate conformation.
author2 PRIMO, Ana Rosa Mendes
format doctoralThesis
author MICHIMA, Paula Suemy Arruda
author_sort MICHIMA, Paula Suemy Arruda
title Optimization of prismatic moon pool configuration by operability criteria
title_short Optimization of prismatic moon pool configuration by operability criteria
title_full Optimization of prismatic moon pool configuration by operability criteria
title_fullStr Optimization of prismatic moon pool configuration by operability criteria
title_full_unstemmed Optimization of prismatic moon pool configuration by operability criteria
title_sort optimization of prismatic moon pool configuration by operability criteria
publisher Universidade Federal de Pernambuco
publishDate 2019
url https://repositorio.ufpe.br/handle/123456789/28383
_version_ 1648655379603652608
score 13.657419

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