Myung-Il Roh

An improved genetic algorithm for facility layout problems having inner structure walls and passages

This study proposes an improved genetic algorithm to derive solutions for multi-floor facility layouts that are to have inner structure walls and passages. The proposed algorithm models the multi-floor layout of facilities on gene structures. These gene structures consist of a five-segmented chromosome. Improved solutions are produced by employing genetic operations known as selection, crossover, inversion, mutation, and refinement of these genes for successive generations. All relationships between the facilities, passages, and lifts are represented as an adjacency graph. The shortest path and distance between two facilities is calculated using Dijkstras algorithm of the graph theory. Comparative testing shows that the proposed algorithm performs better than other existing algorithm for the multi-floor facility layout design. Finally, the proposed algorithm is applied to the multi-deck compartment layout problem of the ship with the computational result compared with the multi-deck compartment layout of the actual ship.

An initial hull structural modeling system for computer-aided process planning in shipbuilding

At the initial stage of ship design, it is difficult for designers to define all design information of a hull structure on 2D drawings. Thus, other designers must undertake the arduous task of translating such information to generate a 3D CAD model of the hull structure which is required at the following design stage such as the initial process planning stage. Since this task needs much time and effort, the 3D CAD model is not being generated at the initial design stage. For solving this problem, an initial hull structural modeling system is developed in this study. The applicability of the developed system is demonstrated by applying it to a deadweight 300,000 ton VLCC (Very Large Crude oil Carrier). The results show that the developed system can quickly generate the 3D CAD model of the hull structure and accurately extract the production material information for computer-aided process planning at the initial design stage.

Dynamic response simulation of an offshore wind turbine suspended by a floating crane

Recently, a number of wind turbines are being installed due to the increase of the interest in green energy. Such wind turbines are installed on land or offshore, and most of them are being installed on land because of easy installation. However, because it is possible to get better wind quality in offshore, the request for an offshore wind turbine is increasing and some heavy industries including shipyards are producing different sizes of offshore wind turbines. A floating crane is used for constructing the offshore wind turbine because its weight amounts to several hundred tons. Thus, it is very important to secure the safety during the construction. In this study, a dynamic response simulation of the offshore wind turbine suspended by the floating crane is performed. For this, we supposed that the motion of the floating crane and the wind turbine has 14 degrees of freedom, and there is the interaction by constraints among them. In addition, hydrostatic and hydrodynamic forces which are independent of each other are considered as external forces acting on the floating crane. The simulation result can be used for the verification of the safety of the construction method which the offshore wind turbine is constructed by the floating crane and the application guidance of this method.

Multibody system dynamics simulator for process simulation of ships and offshore plants in shipyards

A simulator was developed for dynamic analysis of operations in shipyards.We based the simulator on six kernels including multibody dynamics kernel.The simulator contains some functions for motion analysis of floating platforms.The graphical user interfaces were also included for the convenience.The simulator was verified by applying to the operations in shipyards. Since various existing simulation tools based on multibody system dynamics focus on conventional mechanical systems, such as machinery, cars, and spacecraft, there are some problems with the application of such simulation tools to shipbuilding domains due to the absence of specific items in the field of naval architecture and ocean engineering, such as hydrostatics, hydrodynamics, and mooring forces. Thus, in this study, we developed a multibody system dynamics simulator for the process simulation of ships and offshore structures. We based the simulator on six kernels: the multibody system dynamics kernel, the force calculation kernel, the numerical analysis kernel, the hybrid simulation kernel, the scenario management kernel, and the collision detection kernel. Based on these kernels, we implemented a simulator that had the following Graphic User Interfaces (GUIs): the modeling, visualization, and report GUIs. In addition, the geometric properties of blocks and facilities in shipyards are needed to configure the simulation for the production of ships and offshore plants, so these are managed in a database and connected to a specific commercial CAD system in shipyards. We used the simulator we developed in various cases of the process simulation of ships and offshore plants. The results show that the simulator is useful for various simulations of operations in shipyards and offshore industries.

Rapid generation of the piping model having the relationship with a hull structure in shipbuilding

At the initial stage of ship design, a hull structural model, that is, 3D CAD model of a hull structure is not generated by the existing shipbuilding CAD system because it is time-consuming and requires much effort. As a result, a designer is generating a piping model, that is, 3D CAD model of the pipes in the hull structure, independently of the hull structural model at the detailed design stage. The designer must manually modify the piping model whenever the hull structural model changes. To lighten the burden imposed on the designer, a generation method of the piping model based on the hull structural model is developed in this study. The applicability of the developed method is demonstrated by applying it to a deadweight 300,000ton VLCC (Very Large Crude Oil Carrier). The result shows that the developed method can quickly generate the piping model having the relationship with the hull structure in early time.

Determination of the Optimal Operating Condition of the Hamworthy Mark I Cycle for LNG-FPSO

In this study, optimization was performed to improve the conventional liquefaction process of offshore plants, such as a LNG-FPSO(Liquefied Natural Gas-Floating, Production, Storage, and Offloading unit) by maximizing the energy efficiency of the process. The major equipments of the liquefaction process are compressors, expanders, and heat exchangers. These are connected by stream which has some thermodynamic properties, such as the temperature, pressure, enthalpy or specific volume, and entropy. For this, a process design problem for the liquefaction process of offshore plants was mathematically formulated as an optimization problem. The minimization of the total energy requirement of the liquefaction process was used as an objective function. Governing equations and other equations derived from thermodynamic laws acted as constraints. To solve this problem, the sequential quadratic programming(SQP) method was used. To evaluate the proposed method in this study, it was applied to the natural gas liquefaction process of the LNG-FPSO. The result showed that the proposed method could present the improved liquefaction process minimizing the total energy requirement as compared to conventional process.

A method for intermediate flooding and sinking simulation of a damaged floater in time domain

Abstract When a floater such as a ship or an offshore structure is damaged in the sea, it is necessary to determine whether the floater will sink in water or not. If the floater will sink, the time to sink should be estimated to make an emergency plan. In addition, causes of the flooding should be investigated carefully. For this purpose, a method for performing intermediate flooding and sinking simulation of the damaged floater in time domain is proposed in this study. Overall process of the proposed method consists of several steps. In the first step, data of the damaged floater such as hull form and compartments are prepared. In the second step, physical characteristics of the floater such as the increased weight considering incoming water, the center of gravity, the changed buoyancy, and the center of buoyancy are calculated at every time step. In the third step, the quasi-static equilibrium position of the floater is calculated. The second and third steps are repeated until the floater reaches to sink or to be in equilibrium. As a result, the final condition of the floater can be determined. To check the feasibility of the proposed method, it is applied to a simple box problem. Finally, it is applied to intermediate flooding simulation of a barge-type damaged floater. Two cases having damaged holes of different locations are selected. As a result, it was confirmed that the floater can be in equilibrium or sink according to the damaged position. The time to be in equilibrium or the time to sink was estimated.

Optimal module layout for a generic offshore LNG liquefaction process of LNG-FPSO

Constraints related to offshore projects such as liquefied natural gas floating, production, storage, and offloading (LNG-FPSO) have been considered more important than those in onshore areas because topside process systems are located on the limited hull space. Therefore, the layout of the LNG-FPSO topside equipment shall be designed as multi-deck instead of single-deck, and this layout shall be optimised in order to reduce the area occupied by the topside equipment at the front-end engineering design stage. In this study, an optimal module layout for a generic offshore LNG liquefaction process system is derived, considering the deck penetration of long-length equipment across several decks. By considering the above, we formulate a mathematical model, which consists of 1652 unknowns, 1624 equality constraints, and 1048 inequality constraints. This mathematical model can be regarded as the optimisation problem, in which the number of unknowns is larger than the total number of equality constraints and given variables. To obtain the optimal layout, the minimisation of the total layout cost was defined as an objective function. The optimal module layout was then obtained using a mixed integer nonlinear programming.

Design of controller for mobile robot in welding process of shipbuilding engineering

Abstract The present study describes the development of control hardware and software for a mobile welding robot. This robot is able to move and perform welding tasks in a double hull structure. The control hardware consists of a main controller and a welding machine controller. Control software consists of four layers. Each layer consists of modules. Suitable combinations of modules enable the control software to perform the required tasks. Control software is developed using C programming under QNX operating system. For the modularizing architecture of control software, we designed control software with four layers: Task Manager, Task Planner, Actions for Task, and Task Executer. The embedded controller and control software was applied to the mobile welding robot for successful execution of the required tasks. For evaluate this imbedded controller and control software, the field tests are conducted, it is confirmed that the developed imbedded controller of mobile welding robot for shipyard is well designed and implemented.

Multi-floor Layout for the Liquefaction Process Systems of LNG FPSO Using the Optimization Technique

A layout of an LNG FPSO should be elaborately determined as compared with that of an onshore plant because many topside process systems are installed on the limited area; the deck of the LNG FPSO. Especially, the layout should be made as multi-deck, not single-deck and have a minimum area. In this study, a multi-floor layout for the liquefaction process, the dual mixed refrigerant(DMR) cycle, of LNG FPSO was determined by using the optimization technique. For this, an optimization problem for the multi-floor layout was mathematically formulated. The problem consists of 589 design variables representing the positions of topside process systems, 125 equality constraints and 2,315 inequality constraints representing limitations on the layout of them, and an objective function representing the total layout cost. To solve the problem, a hybrid optimization method that consists of the genetic algorithm(GA) and sequential quadratic programming(SQP) was used in this study. As a result, we can obtain a multi-floor layout for the liquefaction process of the LNG FPSO which satisfies all constraints related to limitations on the layout.