Ju-Hwan Cha

Dynamic Response of a Floating Crane in Waves by Considering the Nonlinear Effect of Hydrostatic Force

Abstract The dynamic response of a floating crane and a suspended heavy cargo is analyzed. A mathematical model of the 6-degree-of-freedom floating crane and the 6-degree-of-freedom heavy cargo is developed based on multibody system dynamics. The hydrostatic forces are calculated as nonlinear. The motions of the floating crane and the cargo in waves are calculated and the tension of the wire rope between the two is compared with the measured data

Development of a simulation framework and applications to new production processes in shipyards

Recently, a floating crane is frequently used for the block lifting, transportation, turn-over, and assembly processes in waves. For these production processes, it is important to detect collision in advance between assembly blocks or the block and the other facilities like the wire rope and the barge which are carrying the block. The tension of the wire rope also needs to be calculated to check that the maximum value is less than the safety criteria. In this paper, a mathematical model is constructed based on multibody system dynamics considering the external forces such as the hydrostatic, hydrodynamic, wind force, etc. To observe the dynamic motions of the floating crane and the block, and to calculate the tension of the wire rope, the time and event simulations are performed by solving the mathematical model in the computer. For applying the simulations to the various production processes in shipyards, a simulation framework is developed. The simulation framework consists of a simulation kernel, application-specific modules, a simulation coordinator, development tools, and post-processing tools. The simulation kernel manages both DEVS (discrete event system specification) and DTSS (discrete time system specification) to deal with various simulation requests. The application-specific modules provide the functions used in application systems, such as dynamic analysis, collision detection, visualization, wire rope force calculation, hydrostatic force calculation and hydrodynamic force calculation. The simulation coordinator manages the data of the simulation kernel and the application-specific modules. The development tools provide a development process, a scenario manager, and a simulation model generator. The post-processing tools are used to report the simulation results. The examples of block lifting, transportation, turn-over, and assembly simulations are developed based on the framework to show that the framework is useful for the simulations of the production processes using one or more floating cranes.

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.

Offshore Process FEED(Front End Engineering Design) Method for Integrated Process Engineering

In this study, an offshore process FEED(Front End Engineering Design) method is systematically established to perform integrated process engineering for topsides systems of LNG FPSO(Floating, Production, Storage, and Off-loading unit) based on the concepts and procedures for the process FEED of general offshore production plants. First, various activities of the general process FEED engineering are summarized, and then the offshore process FEED method, which is suitable for application to all t ypes of offshore oil and gas production plants, is proposed. Second, an integrated process engineering environment is　 built based on the proposed FEED method. Finally, the integrated process engineering environment is applied to topsides systems of an LNG FPSO in order to verify the validity and applicability of the proposed FEED method. As a result, it is shown that the proposed FEED method can be applied to the process FEED engineering of F PSOs and moreover will be able to contribute to perform successful offshore projects in the future.

Analysis of Dynamic Response of a Floating Crane and a Cargo with Elastic Booms Based on Flexible Multibody System Dynamics

This study analyzes the dynamic response of a floating crane with a cargo considering an elastic boom to evaluate(or for evaluation of) its flexibility effect on their dynamic response. Flexible multibody system dynamics is applied in order to establish a dynamic equation of motion of the multibody system, which consists of flexible and rigid bodies. In addition, a floating reference frame and nodal coordinates are used to model the boom as a flexible body. The study also simulates the coupled surge, pitch, and heave motions of the floating crane carrying the cargo with three degrees of freedom by numerically solving the equation. Finally, the simulation results of the elastic and rigid booms are comparatively analyzed and the effects of the flexible boom are discussed.

Optimal Block Transportation Scheduling Considering the Minimization of the Travel Distance without Overload of a Transporter

A main issue about production management of shipyards is to efficiently manage the work in process and logistics. However, so far the management of a transporter for moving building blocks has not been efficiently performed. To solve the issues, optimal block transporting scheduling system is developed for minimizing of the travel distance without overload of a transporter. To implement the developed system, a hybrid optimization algorithm for an optimal block transportation scheduling is proposed by combining the genetic algorithm and the ant algorithm. Finally, to evaluate the applicability of the developed system, it is applied to a block transportation scheduling problem of shipyards. The result shows that the developed system can generate the optimal block transportation scheduling of a transporter which minimizes the travel distance without overload of the transporter.

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.

Optimal Block Transportation Path Planning of Transporters considering the Damaged Path

Nowadays, a transporter manager plans the schedule of the block transportation by considering the experience of the manager, the production process of the blocks and the priority of the block transportation in shipyard. The schedule planning of the block transportation should be rearranged for the reflection of the path blocking cases occurred by unexpected obstacles or delays in transportation. In this paper, the optimal block transportation path planning system is developed for rearranging the schedule of the block transportation by considering the damaged path. algorithm is applied to calculate the new shortest path between the departure and arrival of the blocks transported through the damaged path. In this algorithm, the first node of the damaged path is considered as the starting position of the new shortest path, and then the shortest path calculation is completed if the new shortest path is connected to the one of nodes in the original path. In addition, the data structure for the algorithm is designed. This optimal block transportation path planning system is applied to the Philippine Subic shipyard and the ability of the rapid path modification is verified.

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.

Determination of the Optimal Operating Condition of Dual Mixed Refrigerant Cycle of LNG FPSO Topside Liquefaction Process

In this study, the optimal operating conditions for the dual mixed refrigerant(DMR) cycle were determined by considering the power efficiency. The DMR cycle consists of compressors, heat exchangers, seawater coolers, valves, phase separators, tees, and common headers, and the operating conditions include the equipment`s flow rate, pressure, temperature, and refrigerant composition per flow. First, a mathematical model of the DMR cycle was formulated in this study by referring to the results of a past study that formulated a mathematical model of the single mixed refrigerant(SMR) cycle, which consists of compressors, heat exchangers, seawater coolers, and valves, and by considering as well the tees, phase separators, and common headers. Finally, in this study, the optimal operating conditions from the formulated mathematical model was obtained using a hybrid optimization method that consists of the genetic algorithm(GA) and sequential quadratic programming(SQP). Moreover, the required power at the obtained conditions was decreased by 1.4% compared with the corresponding value from the past relevant study of Venkatarathnam.