• Structural Engineering and Mechanics
• /
• v.25 no.2
• /
• pp.181-200
• /
• 2007

A decoupling technique for simulating near-field wave motions in two-phase media is introduced in this paper. First, an equivalent but direct weighted residual method is presented in this paper to solve boundary value problems more explicitly. We applied the Green's theorem for integration by parts on the equivalent integral statement of the field governing equations and then introduced the Neumann conditions directly. Using this method and considering the precision requirement in wave motion simulation, a lumped-mass FEM for two-phase media with clear physical concepts and convenient implementation is derived. Then, considering the innate attenuation character of the wave in two-phase media, an attenuation parameter is introduced into Liao's Multi-Transmitting Formula (MTF) to simulate the attenuating outgoing wave in two-phase media. At last, two numerical experiments are presented and the numerical results are compared with the analytical ones demonstrating that the lumped-mass FEM and the generalized MTF introduced in this paper have good precision.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.5
• /
• pp.866-873
• /
• 2001

The governing partial differential equations of a helical spring with a circular section were derived from Frenet formulas and Timoshenko beam theory. These were solved to give the dispersion relationship between wave number and frequency along with wave form. Wave motions of helical springs are categorized by 4 regimes. In the first regime, the lower frequency area, the torsional and extensional waves of the spring are predominant and two waves are composite wave motions involving lateral motion of the coils and rotation of the coils about a horizontal axis. All waves are propagating in the second regime. The wave of the extensional motion of the spring and one wave of transverse motion of a wire change from travelling waves to near field waves in the third regime. Both waves excited by both axial and transverse motion are predominant in the fourth regime.

• Journal of Korean Port Research
• /
• v.6 no.2
• /
• pp.33-42
• /
• 1992

In this paper we investigate the motion response of a moored ship in the fluid region sheltered by inclined breakwaters. The matched asymptotic expansion technique is employed to analyze the wave fields scattered by the inclined breakwaters. Fluid domain is subdivided into the ocean, entrance and sheltered regions. Unknown coefficients contained in each region can be determined by matching at the intermediate zone between two neighboring regions. The wave field generated by the ship motion can be analyzed in terms of Green's function method. To obtain the velocity jump across the ship associated with the symmetric motion modes, the sheltered region is further divided into near field of the ship and the rest field. The image method is introduced to consider the effect of the pier near the ship. The integral equation for the velocity jump is derived by the flux matching between the inner region and the outer region of a moored ship. Throughout the numerical calculation it is found that the inclined angle width of entrance of breakwaters as well as the location of moored vessel play an important role in the motion response of a moored ship.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2001.09a
• /
• pp.83-90
• /
• 2001

The site effects of local geological conditions on seismic ground motion are performed using 2D numerical method. For the analysis, a numerical method far ground response analysis using FE-BE coupling method is developed. The total system is divided into two parts so called far field and near field. The far field is modeled by boundary element formulation using the multi-layered dynamic fundamental solution that satisfied radiational condition of wave. And this is coupled with near field modeled by finite elements. In order to verify the seismic response analysis, the results are compared with those of commercial code. As a result, it is shown that the developed method can be an efficient numerical method to solve the seismic response analysis of the site effect in 2D problem.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.19 no.10
• /
• pp.1053-1061
• /
• 2009

The goal of this paper is to investigate the generation characteristics of the main impulsive noise sources generated by the supersonic flow discharging from a muzzle. For this, this paper investigates two fundamental mechanisms to sound generation in shocked flows: shock motion and shock deformation. Shock motion is modeled numerically by examining the interaction of a sound wave with a shock. The numerical approach is validated by comparison with results obtained by linear theory for a small disturbance case. Shock deformations are modeled numerically by examining the interaction of a vortex ring with a blast wave. A numerical approach of a dispersion-relation-preserving(DRP) scheme is used to investigate the sound generation and propagation by their interactions in near-field.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.6 s.73
• /
• pp.41-53
• /
• 2006

This experimental study investigated the flow characteristics for regular waves passing a rectangular floating structure in a two-dimensional wave tank. The particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The phase average was used to extract the mean flow and turbulence property from repeated instantaneous PIV velocity profiles. The mean velocity field represented the vortex generation and evolution on both sides of the structure. The turbulence properties, including the turbulence length scale and the turbulent kinetic energy budget were investigated to characterize the flow interaction between the regular wave and the structure. The results shaw the vortex generated near the structure corners, which are known as the eddy-making damping or viscous damping. However, the vortex induced by the wave is longer than the roll natural period of the structure, which presents the phenomena opposing the roll damping effect; that is, the vortex may increase the roll motion under the wave condition longer than the roll natural period.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.187-191
• /
• 2003

The motion and time-mean drift force of a 2-D floating BBDB in waves are studied with and without taking account of fluctuating air pressure in the air chamber. It has been found numerically that the drift for a of the BBDB is in the reverse direction of propagation of the incident waves over specific frequency ranges as found by McCormick through his experiment work. The drift force is calculated by Pinkster's near-field method. Since Maruo's formula method for the drift force is always positive, Maruo's formula is only approximate and should be replaced by the correct near-field method.

• Journal of Navigation and Port Research
• /
• v.33 no.1
• /
• pp.65-70
• /
• 2009

The hybrid numerical model is developed by combining BEM that can calculate the wave motion rapidly under the potential theory and CADMAS-SURF that solves Navier-Stokes equations for the free surface variation near the structure, In the hybrid model the calculation of wave motion in a wide field of wave reflection for deep water area is conducted by BEM but for shallow water area by CADMAS-SURF. Especially the hybrid model can calculate random wave motions for long term period more rapidly with almost similar accuracy than the calculation of wave motion which was carried out by CADMAS-SURF only. In this study the coupling model was applied to the calculation of the strong nonlinear wave motion such as wave runup and overtopping at the coastal structure on the mild-slope bottom and the results of numerical model were compared with the Toyosima's experiments of regular wave runup and Goda's design diagram of ramdom wave overtopping, respectively.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.03a
• /
• pp.117-124
• /
• 2002

The major purpose of this study is to determine the dynamic behavior of soil-pile-structure interaction system considering the underground cavity. For the analysis, a numerical method fur ground response analysis using FE-BE coupling method is developed. The total system is divided into two parts so called far field and near field. The far field is modeled by boundary element formulation using the multi-layered dynamic fundamental solution that satisfied radiational condition of wave. And this is coupled with near field modeled by finite elements. For the verification of dynamic analysis in the frequency domain, both forced vibration analysis and free-field response analysis are performed. The behavior of soil non-linearity is considered using the equivalent linear approximation method. As a result, it is shown that the developed method can be an efficient numerical method to solve the seismic response analysis considering the underground cavity in 2D problem.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.21 no.2
• /
• pp.196-208
• /
• 2009

In this paper, wave responses of buoyant flap-typed storm surge barriers was studied numerically. Wave motions were modeled by using a linear potential wave theory, and behaviors of structures were represented as a Newton's 2nd law of motion. The near field region of the fluid was discretized as conventional quadratic iso-parametric elements, while the far field was modeled as infinite elements. Comparisons with the results from hydraulic model tests show that the present model gives good results. By using the model, the applicability of a buoyant flap-typed storm surge barrier in Masan bay was investigated considering field environmental conditions.