Namkug Ku

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.

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.

Calculation of the Dynamic Contact Force between a Shipbuilding Block and Wire Ropes of a Goliath Crane for the Optimal Lug Arrangement

In this study, dynamic load and dynamic contact force between a building block and wire ropes of a goliath crane are calculated during lifting or turn-over of a building block for the design of an optimal lug arrangement system. In addition, a multibody dynamics kernel for implementing the system were developed. In the multibody dynamics kernel, the equations of motion are constructed using recursive formulation. To evaluate the applicability of the developed kernels, the interferences and dynamic contact force between the building block and wire ropes were calculated and then the hull structural analysis for the block was performed using the calculation result.

Modularized Control Architecture of an Embedded Controller for Mobile Welding Robot in the Shipyard

The present study describes the development of controller hardware and control software for a mobile welding robot, which can move in the transverse and longitudinal directions (Moving Tasks), perform the welding tasks of the U-shaped parts and bracket parts in a double hull structure (Welding Tasks), and detect points of the welding path (Sensing Tasks). Controller hardware consists of a main controller and a welding machine controller. The main controller, which is mounted on the mobile welding robot, consists of a CPU board, a motion controller, and an incremental encoder type AC servo motor driver. The welding machine controller, which is mounted on the welding machine located on the outside of the double hull structure, controls the welding machine. Communication between the two controllers is made via the RS485. Control software consists of 4 layers: Task Manager, Task Planner, Actions for Task, and Task Executer. Each Layer consists of modules such as the Action Module, Motion Generator Module, Servo Module, etc. Suitable combinations of modules enable the control software to perform the required tasks. Control software is developed using C programming under QNX Operating System, which is well known to have a reliable hard-realtime performance.

A tagline proportional–derivative control method for the anti-swing motion of a heavy load suspended by a floating crane in waves

This paper presents a tagline proportional–derivative control method for suppressing the swing motion of a heavy load suspended by a floating crane in an ocean environment. The tagline mechanism, which is connected between the floating crane and the heavy load, is applied to the floating crane. The winch, which is mounted on the deck of the floating crane, is used to control the tension of the tagline. A proportional–derivative control algorithm is applied to generate the control force of the winch. Swing angle feedback of the proportional–derivative control is supplied by the encoder attached at the boom tip of the floating crane. To demonstrate the performance of the tagline control method, numerical simulations are performed on a non-linear six-dimensional mathematical model of the floating crane and the heavy load. The mathematical model of the floating crane is constructed to consider both the three-degree-of-freedom principle of the floating crane and the heavy load, based on multi-body system dynamics. The numerical and experimental simulation results are compared using a one-hundredth-scale model of the floating crane in the model basin. The results of the numerical simulation and experiment show that the tagline proportional–derivative control method suppresses the swing motion of the load.

Dynamic Constrained Force of Tower Top and Rotor Shaft of Floating Wind Turbine

In this study, we calculate dynamic constrained force of tower top and blade root of a floating offshore wind turbine. The floating offshore wind turbine is multibody system which consists of a floating platform, a tower, a nacelle, and a hub and three blades. All of these parts are regarded as a rigid body with six degree-of-freedom(DOF). The platform and the tower are connected with fixed joint, and the tower, the nacelle, and the hub are successively connected with revolute joint. The hub and three blades are connected with fixed joint. The recursive formulation is adopted for constructing the equations of motion for the floating wind turbine. The non-linear hydrostatic force, the linear hydrodynamic force, the aerodynamic force, the mooring force, and gravitational forces are considered as external forces. The dynamic load at the tower top, rotor shaft, and blade root of the floating wind turbine are simulated in time domain by solving the equations of motion numerically. From the simulation results, the mutual effects of the dynamic response between the each part of the floating wind turbine are discussed and can be used as input data for the structural analysis of the floating offshore wind turbine.

Dynamic Response Simulation of a Heavy Cargo Suspended by Parallel Connected Floating Cranes

In this study, we performed a simulation of the dynamic response of a multibody system to calculate the tension acting on wire ropes connecting floating cranes and a heavy cargo such as a Giga Block weighing over 5000 tons when the cargo is salvaged using parallel connected floating cranes. In this simulation, we supposed that the motion of the floating cranes, barge ship, and heavy cargo has 6 degrees of freedom and that the interaction is determined by constraints among them. In addition, we considered independent hydrostatic and hydrodynamic forces as external forces acting on the floating cranes and barge ship. The simulation result can be a basis for verifying the safety of construction methods in which heavy cargo is salvaged by parallel connected floating cranes, and it can also be used to guide the development of such construction methods.