Kyu-Yeul Lee

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.

Estimation of hydrodynamic coefficients for an AUV using nonlinear observers

Hydrodynamic coefficients strongly affect the dynamic performance of an autonomous underwater vehicle. Although these coefficients are generally obtained experimentally such as through the planar-motion-mechanism (PMM) test, the measured values are not completely reliable because of experimental difficulties and errors involved. Another approach by which these coefficients can be obtained is the observer method, in which a model-based estimation algorithm predicts the coefficients. In this paper, the hydrodynamic coefficients are estimated using two nonlinear observers - a sliding mode observer and an extended Kalman filter. Their performances are evaluated by comparing the estimated coefficients obtained from the two observer methods with the values as determined from the PMM test. By using the estimated coefficients, a sliding mode controller is constructed for the diving and steering maneuver. It is demonstrated that the controller with the estimated values maintains the desired depth and path with sufficient accuracy.

An algorithm for automatic 2D quadrilateral mesh generation with line constraints

Finite element method (FEM) is a fundamental numerical analysis technique widely used in engineering applications. Although state-of-the-art hardware has reduced the solving time, which accounts for a small portion of the overall FEM analysis time, the relative time needed to build mesh models has been increasing. In particular, mesh models that must model stiffeners, those features that are attached to the plate in a ship structure, are imposed with line constraints and other constraints such as holes. To automatically generate a 2D quadrilateral mesh with the line constraints, an extended algorithm to handle line constraints is proposed based on the constrained Delaunay triangulation and Q-Morph algorithm. The performance of the proposed algorithm is evaluated, and numerical results of our proposed algorithm are presented.

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.

Generation of the 3D CAD model of the hull structure at the initial ship design stage and its application

Currently, all design information of a hull structure is being first defined on 2D drawings not 3D CAD model at the initial ship design stage and then transferred to following design stages through the 2D drawings. This is caused by the past design practice, limitation on time, and lack of shipbuilding CAD systems supporting the initial design stage. As a result, the following design tasks such as the process planning and scheduling are being manually performed using the 2D drawings. For solving this problem, a data structure for shipbuilding CAD systems supporting the initial design stage is proposed and a prototype system is developed based on the data structure. The applicability of the system is demonstrated by applying it to various examples. The results show that the system can be effectively used for generating the 3D CAD model of the hull structure at the initial design stage.

Modeling and simulation of target motion analysis for a submarine using a script-based tactics manager

Various types of simulation are required for underwater vehicles such as submarines or torpedoes. These include engineering-level simulations for predicting the performance and engagement-level simulations for examining the effectiveness of certain tactics. For this reason, a tactics manager that can change the behavior of a simulation model according to tactics defined outside the model is needed. This paper describes a tactics manager that supports a scripting language that can represent various tactics and can help users to easily define external input tactics. Python and Lua, representative scripting languages, are compared and analyzed from the viewpoint of a tactics manager, and a tactics manager using those script languages is implemented. A target motion analysis simulation of the engagement between a submarine and a surface ship is conducted to demonstrate the effectiveness of the tactics manager. We generated a simulation model based on the Discrete Event System Specification formalism and provided it with an interface to the tactics manager.

Depth and heading control for autonomous underwater vehicle using estimated hydrodynamic coefficients

Depth and heading control of an AUV are considered for the predetermined depth and heading angle. The proposed control algorithm is based on a sliding mode control using estimated hydrodynamic coefficients. The hydrodynamic coefficients are estimated with the help of conventional nonlinear observer techniques such as sliding mode observer and extended Kalman filter. By using the estimated coefficients, a sliding mode controller is constructed for the combined diving and steering maneuver. The simulation results of the proposed control system are compared with those of control system with true coefficients. It is demonstrated that the proposed control system makes the system stable and maintains the desired depth and heading angle with sufficient accuracy.

Optimal liquefaction process cycle considering simplicity and efficiency for LNG FPSO at FEED stage

In this paper, the offshore selection criteria for the optimal liquefaction process system are studied to contribute to the future FEED engineering for the liquefied natural gas (LNG) floating, production, storage, and offloading (LNG FPSO) liquefaction process system. From the foregoing, it is clear that offshore liquefaction plants have process requirements different from those of the traditional onshore liquefaction plants. While thermodynamic efficiency is the key technical process selection criterion for large onshore liquefaction plants, the high-efficiency pre-cooled mixed refrigerant and optimized cascade plants that dominate the onshore LNG installations are unlikely to meet the diverse technical and safety needs of offshore liquefaction facilities. Offshore liquefaction technology developers are rightly focusing on process simplicity, low weight, small footprint, and other criteria. The key criteria that influence process selection and plant optimization for the offshore liquefaction cycle lead to some trade-offs and compromises between efficiency and simplicity. In addition, other criteria for offshore liquefaction cycles should also be considered, such as flexibility, safety, vessel motion, refrigerant storage hazard, proven technology, simplicity of operation, ease of start-up/shutdown, and capital cost. First of all, this paper proposes a generic mixed refrigerant (MR) liquefaction cycle based on four configuration strategies. The 27 feasible MR liquefaction cycles from such generic MR liquefaction cycle are configured for optimal synthesis. From the 27 MR liquefaction cycles, the top 10 are selected based on the minimum amount of power required for the compressors. Then, one MR liquefaction cycle is selected based on simplicity among the 10 MR process cycles, and this is called a “potential MR liquefaction cycle.” Second, three additional offshore liquefaction cycles – DMR for SHELL LNG FPSO, C3MR for onshore projects, and the dual N2 expander for FLEX LNG FPSO – are considered for comparison with the potential MR liquefaction cycle for the selection of the optimal offshore liquefaction cycle. Such four cycles are compared based on simplicity, efficiency, and other criteria. Therefore, the optimal operating conditions for each cycle with four LNG capacities (4.0, 3.0, 2.0, and 1.0 MTPA) are calculated with the minimum amount of power required for the compressors. Then the preliminary equipment module layout for the four cycles are designed as multi-deck instead of single-deck, and this equipment module layout should be optimized to reduce the area occupied by the topside equipment at the FEED stage. In this paper, the connectivity cost, the construction cost proportional to the deck area, and the distance of the main cryogenic heat exchanger (MCHE) and separators from the centerline of the hull are considered objective functions to be minimized. Moreover, the constraints are proposed to ensure the safety and considering the deck penetration of the long equipment across several decks. Considering the above, mathematical models were formulated for them. For example, the potential MR liquefaction cycle has a mathematical model consisting of 257 unknowns, 193 equality constraints, and 330 inequality constraints. The preliminary optimal equipment module layouts with four LNG capacities (4.0, 3.0, 2.0, and 1.0 MTPA) are then obtained using mixed-integer nonlinear programming (MINLP). Based on the above optimal operating conditions and equipment module layouts for the four potential offshore liquefaction cycles, trade-offs between simplicity and efficiency are performed for actual offshore application, and finally, the potential MR liquefaction cycle is selected for the optimal liquefaction cycle for LNG FPSO.

Knowledge-based nonmonotonic reasoning process in ship compartment design system

Abstract Recently marine pollution has been a hot issue in shipbuilding fields especially in the design of crude oil tanker ships. There are many significant constraints to be considered at the design stage. In this paper, an expert system to support compartment design of a crude oil tanker is developed so as to treat many of the constraints and design changes according to their conflicts effectively. The nonmonotonic reasoning concept helps a designer to perform his/her design in spite of complicated and cross-related design constraints. In addition, this system focuses on the integration of the knowledge base, database, case base, and CAE programs, hence reliable solutions can be assured. The validation of the system was examined and verified by applying the system to the 250,000 ton crude oil tanker.

Design of a teaching pendant program for a mobile shipbuilding welding robot using a PDA

Teaching pendant is a handheld device by which a human can control a robot. The main functions of a teaching pendant are moving the robot, teaching it about the locations, running robot programs, and jogging the axes. A teaching pendant is usually connected to the robot by a cable. The cable connection and the size of the teaching pendant generally do not pose a problem when the robot controller is separate from the robot. However, a large teaching pendant connected by a cable is not suitable for a self-propelled mobile robot with an internal controller. This paper describes the communication network of a personal data assistant (PDA) as a wireless teaching pendant for a mobile shipbuilding welding robot with embedded controller system that welds and moves autonomously inside the double hull structure of a ship. A double hull is a closed structure that has only a few access holes. It is very difficult and dangerous to weld components inside a double hull structure because of fumes, poisonous gas, and high temperatures. Using a wireless teaching pendant has the following advantages: (1) there are no limits to the welding activities that can take place, (2) the safety level increases because no workers are in close proximity to the robot, (3) workers are far away from the dangerous environmental conditions, (4) it is possible to reduce the weight of the cable connected to the robot, and (5) it is possible to reduce the weight of the robot because of the reduced load of the teaching pendant and the cable. We demonstrate the functionality and performance capabilities of our wireless teaching pendant through field-testing experiments.