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Kang H.C.,Korea Basic Science Institute | Kim S.-S.,Chungnam National University | Lee C.-H.,Korea Research Institute of Ships & Ocean Engineering
Journal of Mechanical Science and Technology | Year: 2015

In this paper, parallel processing of a vehicle analysis based on the subsystem synthesis method was developed in a multi-core CPU environment. The subsystem synthesis method provides independent computation of each suspension subsystem module, and so is ideally suited for parallel processing. For parallel program implementation, OpenMP API (Application program interface) for a shared memory multi-core CPU was utilized. Three different parallel implementations were applied to examine the performance of parallel processing. In the first, parallel processing was applied only to the identified parallel regions in the subsystem synthesis method within the integration time loop. In the second, parallel processing was applied from the beginning of the program in order to avoid overhead due to the creation of parallel threads in every time step. The 3rd implementation was the same as the 2nd one, except that unnecessary data synchronization overhead was removed. In order to investigate the performance of the proposed parallel processing, parallel programs with three different implementations were created for a 6 x 6 unmanned robot vehicle model. Rough terrain run simulations were carried out. Performances of the 1st and 2nd implementation methods were worse than that of the sequential program. When parallel processing with proper treatment of overheads was used, a three times increase in computational speed was achieved from the 3rd implementation, compared with serial computation. © 2015, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source

Sohn J.M.,Korea Research Institute of Ships & Ocean Engineering | Kim S.J.,Pusan National University | Seo J.K.,Pusan National University | Kim B.J.,Pusan National University | Paik J.K.,Lloyds Register
Ships and Offshore Structures | Year: 2015

Offshore installations are exposed to hydrocarbon explosions and/or fire accidents. Especially, explosions lead to serious damages to human, safety, and environment. To minimise and prevent the damage from explosions, blast walls are generally installed in oil and gas production structures. Typical blast walls are classified into flat, corrugated, and stiffened types. Among them, corrugated blast walls are frequently used for reasons such as construction, cost, and energy absorption. However, it has been known that a corrugated type of blast wall buckles between the web and flange under the explosion loads, and loses its stiffness. It means that the buckling phenomenon of a blast wall is closely related to the structural strength. This study investigates on the structural characteristics of a blast wall under quasi-static and dynamic (explosion) loads with or without a flat-plated stiffener. Finally, it can be concluded that the flat type of stiffeners are located at the buckling region to delay the buckling and improve the strength of blast walls. © 2015 Taylor & Francis Source

Yang K.-K.,Seoul National University | Kim Y.,Seoul National University | Nam B.-W.,Korea Research Institute of Ships & Ocean Engineering
Journal of Marine Science and Technology (Japan) | Year: 2015

An Euler equation solver based on a Cartesian-grid and non-uniform staggered grid system is applied to simulate and analyze the ship motion and added resistance in waves. Water, air, and solid phases are distinguished using a volume fraction function for each phase and in each cell. To capture the water interface, the tangent of hyperbola for interface capturing scheme is used with a weighted line interface calculation method. The volume fraction of a solid body embedded in a Cartesian-grid system is calculated using a level-set algorithm, and the body boundary condition is imposed using a volume-weighted formula. Numerical simulations for a Wigley III hull and an S175 containership in regular waves are carried out to validate the newly developed code and to compare the effects of numerical methods for calculating the added resistance. All the results are compared with experimental data, and a calculation for the KRISO’s very large crude carrier 2 is also performed. From the grid convergence test for incident wave generation and the added resistance calculation, the sensitivity of the grid spacing is investigated, and the minimum requirements for the number of gird points are suggested to reliably calculate the added resistance in waves. © 2014, JASNAOE. Source

Cho S.-G.,Hanyang University | Cho S.-G.,Korea Research Institute of Ships & Ocean Engineering | Jang J.,Hanyang University | Kim J.,Hanyang University | And 4 more authors.
Journal of Mechanical Science and Technology | Year: 2015

Sequential surrogate model-based global optimization algorithms, such as super-EGO, have been developed to increase the efficiency of commonly used global optimization technique as well as to ensure the accuracy of optimization. However, earlier studies have drawbacks because there are three phases in the optimization loop and empirical parameters. We propose a united sampling criterion to simplify the algorithm and to achieve the global optimum of problems with constraints without any empirical parameters. It is able to select the points located in a feasible region with high model uncertainty as well as the points along the boundary of constraint at the lowest objective value. The mean squared error determines which criterion is more dominant among the infill sampling criterion and boundary sampling criterion. Also, the method guarantees the accuracy of the surrogate model because the sample points are not located within extremely small regions like super-EGO. The performance of the proposed method, such as the solvability of a problem, convergence properties, and efficiency, are validated through nonlinear numerical examples with disconnected feasible regions. © 2015, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source

Lee C.-H.,Korea Research Institute of Ships & Ocean Engineering | Hong S.,Korea Research Institute of Ships & Ocean Engineering | Kim H.-W.,Korea Research Institute of Ships & Ocean Engineering | Kim S.-S.,Chungnam National University
Journal of Mechanical Science and Technology | Year: 2015

In this paper, in order to select a suitable method that is applicable to the large deflection with a small strain problem of pipe systems in the deep seabed mining system, the finite difference method with lumped mass from the field of cable dynamics and the substructure method from the field of flexible multibody dynamics were compared. Due to the difficulty of obtaining experimental results from an actual pipe system in the deep seabed mining system, a thin cantilever beam model with experimental results [7] was employed for the comparative study. Accuracy of the methods was investigated by comparing the experimental results and simulation results from the cantilever beam model with different numbers of elements. Efficiency of the methods was also examined by comparing the operational counts required for solving equations of motion. Finally, this cantilever beam model with comparative study results can be promoted to be a benchmark problem for the flexible multibody dynamics. © 2015, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source

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