• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.4
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• pp.1024-1040
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• 2014

The theoretical background and a numerical solution procedure for a time domain hydroelastic code are presented in this paper. The code combines a VOF-based free surface flow solver with a flexible body motion solver where the body linear elastic deformation is described by a modal superposition of dry mode shapes expressed in a local floating frame of reference. These mode shapes can be obtained from any finite element code. The floating frame undergoes a pseudo rigid-body motion which allows for a large rigid body translation and rotation and fully preserves the coupling with the local structural deformation. The formulation relies on the ability of the flow solver to provide the total fluid action on the body including e.g. the viscous forces, hydrostatic and hydrodynamic forces, slamming forces and the fluid damping. A numerical simulation of a flexible barge is provided and compared to experiments to show that the VOF-based flow solver has this ability and the code has the potential to predict the global hydroelastic responses accurately.

• Nuclear Engineering and Technology
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• v.46 no.2
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• pp.263-272
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• 2014

Scattering source calculations using conventional spherical harmonic expansion may require lots of computation time to treat full-coupled three-dimensional photon-electron transport in a highly anisotropic scattering medium where their scattering cross sections should be expanded with very high order (e.g., $P_7$ or higher) Legendre expansions. In this paper, we introduce a modified scattering kernel approach to avoid the unnecessarily repeated calculations involved with the scattering source calculation, and used it with parallel computing to effectively reduce the computation time. Its computational efficiency was tested for three-dimensional full-coupled photon-electron transport problems using our computer program which solves the multi-group discrete ordinates transport equation by using the discontinuous finite element method with unstructured tetrahedral meshes for complicated geometrical problems. The numerical tests show that we can improve speed up to 17~42 times for the elapsed time per iteration using the modified scattering kernel, not only in the single CPU calculation but also in the parallel computing with several CPUs.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.3
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• pp.232-248
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• 2009

Numerical methodology to solve ship springing problem, which is basically fluid-structure interaction problem, was explored in this study. Solution of this hydroelasticity problem was sought by coupling higher order B-spline Rankine panel method and finite element method in time domain, each of which is introduced for fluid and structure domain respectively. Even though varieties of different combinations in terms of numerical scheme are possible and have been tried by many researchers to solve the problem, no systematic study regarding the characteristics of each scheme has been done so far. Here, extensive case studies have been done on the numerical schemes especially focusing on the iteration method, FE analysis of beam-like structure, handling of forward speed problem and so on. Two different iteration scheme, Newton style one and fixed point iteration, were tried in this study and results were compared between the two. For the solution of the FE-based equation of motion, direct integration and modal superposition method were compared with each other from the viewpoint of its efficiency and accuracy. Finally, calculation of second derivative of basis potential, which is difficult to obtain with accuracy within grid-based method like BEM was discussed.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.233-241
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• 2010

Scaffolding system in the membrane LNG carrier is a steel structure composed of various pipe-shaped members connected by specific coupling devices. In this study, the automatic design program for scaffolding system in membrane LNG carrier has been developed. It enables user to arrange members easily considering design constraints and input variables such as size of tank, position of legs, level height and so on. In addition to that, it creates finite element analysis model with loading and boundary conditions automatically and carries out structural analysis. With post processor based a state-of-the-art computer graphics, users can easily check the results of structural analysis and make a report for structural safety of scaffolding system.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.1
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• pp.29-34
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• 2015

DC bus electrolytic capacitors are used in variety of equipments as smoothing element of the power converters because it has high capacitance for its size and low price. It is responsible for frequent breakdowns of many static converters and inverter drive systems. Therefore it is important to diagnosis monitoring the condition of an electrolytic capacitor in real-time to predict the failure of power converter. In this paper, the on-line remote diagnosis monitoring system for DC BUS electrolytic capacitors of power converter using low-cost type Zigbee communication modules is developed. To estimate the health status of the capacitor, the equivalent series resistor(ESR) of the component has to be determined. The capacitor ESR is estimated by using RMS computation using AC coupling method of DC link ripple voltage/current. The Zigbee communication-based experimental results show that the proposed remote DC capacitor diagnosis monitoring system can be applied to DC/DC converter and UPS successfully.

• Wind and Structures
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• v.18 no.1
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• pp.1-20
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• 2014

Modern design of long suspension bridges must satisfy at the same time spanning very long distances and limiting their response against several external loads, even if of high intensity. Structural Control, with the solutions it provides, can offer a reliable contribution to limit internal forces and deformations in structural elements when extreme events occur. This positive aspect is very interesting when the dimensions of the structure are large. Herein, an updated numerical model of an existing suspension bridge is developed in a commercial finite element work frame, starting from original data. This model is used to reevaluate an optimization procedure for a passive control strategy, already proven effective with a simplified model of the buffeting wind forces. Such optimization procedure, previously implemented with a quasi-steady model of the buffeting excitation, is here reevaluated adopting a more refined version of the wind-structure interaction forces in which wind actions are applied on the towers and the cables considering drag forces only. For the deck a more refined formulation, based on the use of indicial functions, is adopted to reflect coupling with the bridge orientation and motion. It is shown that there is no variation of the previously identified optimal passive configuration.

• Smart Structures and Systems
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• v.12 no.5
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• pp.523-545
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• 2013

Piezoelectric and dielectric behaviors of a piezoceramic patch adhesively centered on a carbon composite plate are identified using a robust multi-objective optimization procedure. For this purpose, the patch piezoelectric stress coupling and blocked dielectric constants are automatically evaluated for a wide frequency range and for the different identifiable behaviors. Latters' symmetry conditions are coded in the design plans serving for response surface methodology-based sensitivity analysis and meta-modeling. The identified constants result from the measured and computed open-circuit frequencies deviations minimization by a genetic algorithm that uses meta-model estimated frequencies. Present investigations show that the bonded piezoceramic patch has effective three-dimensional (3D) orthotropic piezoelectric and dielectric behaviors. Besides, the sensitivity analysis indicates that four constants, from eight, dominate the 3D orthotropic behavior, and that the analyses can be reduced to the electromechanically coupled modes only; therefore, in this case, and if only the dominated parameters are optimized while the others keep their nominal values, the resulting piezoelectric and dielectric behaviors are found to be transverse-isotropic. These results can help designing piezoceramics smart composites for various applications like noise, vibration, shape, and health control.

• Ocean Systems Engineering
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• v.7 no.4
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• pp.329-344
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• 2017

This paper introduces a BEM/RANS interactive scheme to predict the contra-rotating propeller (CRP) performance. In this scheme, the forward propeller and the aft propeller are handled by two separate BEM models while the interactions between them are achieved by coupling them with a RANS solver. By using the body force field and mass source field to represent the propeller in the RANS model, the number of RANS cells and the number of required RANS iterations reduce significantly. The method provides an efficient way to predict the effective wake, the steady/unsteady propeller forces, etc. The BEM/RANS interactive scheme is first applied to a CRP in both an axisymmetric manner and a non-axisymmetric manner. Results are shown in good agreement with the experimental data in moderate to high advance ratios. It is proved that the difference between the axisymmetric scheme and the non-axisymmetric scheme mainly comes from the non-axisymmetric bodies. It is also found that the error is larger at lower advance ratios. Possible explanations are given. Finally, some additional cases are tested which justifies that the non-axisymmetric BEM/RANS scheme is able to handle a podded CRP working at given inclination angles.

• Structural Engineering and Mechanics
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• v.62 no.4
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• pp.465-475
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• 2017

Photovoltaic (PV) panels are used in high-rise buildings to convert solar energy to electricity. Due to the considerable energy consumption of high-rise buildings, applying PV technology is of great significance to energy saving. In the application of PV panels, one of the most important construction issues is the connection of the PV panel with the main structures. One major difficulty of the connection design is that the PV panel connection consists of two separate components with coupling and indeterminate dimension. In this paper, the gap element is employed in these two separated but coupled components, i.e., hook and catch. Topology optimization is applied to optimize and design the cross-section of the PV panel connection. Pareto optimization is conducted to operate the optimization subject to multiple load scenarios. The initial design for the topology optimization is determined by the common design specified by the Technical Code for Glass Curtain Wall Engineering (JGJ 102-2003). Gravity and wind load scenarios are considered for the optimization and numerical analysis. Post analysis is conducted for the optimal design obtained by the topology optimization due to the manufactory requirements. Generally, compared with the conventional design, the optimized connector reduces material use with improved structural characteristics.

• Smart Structures and Systems
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• v.26 no.3
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• pp.263-275
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• 2020

This research is dedicated to slope stability analysis using novel intelligent models. By coupling a neural network with spotted hyena optimizer (SHO), salp swarm algorithm (SSA), shuffled frog leaping algorithm (SFLA), and league champion optimization algorithm (LCA) metaheuristic algorithms, four predictive ensembles are built for predicting the factor of safety (FOS) of a single-layer cohesive soil slope. The data used to develop the ensembles are provided from a vast finite element analysis. After creating the proposed models, it was observed that the best population size for the SHO, SSA, SFLA, and LCA is 300, 400, 400, and 200, respectively. Evaluation of the results showed that the combination of metaheuristic and neural approaches offers capable tools for estimating the FOS. However, the SSA (error = 0.3532 and correlation = 0.9937), emerged as the most reliable optimizer, followed by LCA (error = 0.5430 and correlation = 0.9843), SFLA (error = 0.8176 and correlation = 0.9645), and SHO (error = 2.0887 and correlation = 0.8614). Due to the high accuracy of the SSA in properly adjusting the computational parameters of the neural network, the corresponding FOS predictive formula is presented to be used as a fast yet accurate substitution for traditional methods.