• Structural Engineering and Mechanics
• /
• 제25권2호
• /
• 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.

• 대한기계학회논문집A
• /
• 제25권5호
• /
• 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.

• 한국항만학회지
• /
• 제6권2호
• /
• 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.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
• /
• 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.

• 한국소음진동공학회논문집
• /
• 제19권10호
• /
• 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.

• 한국해양공학회지
• /
• 제20권6호
• /
• 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.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2003년도 추계학술대회 논문집
• /
• 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.

• 한국항해항만학회지
• /
• 제33권1호
• /
• pp.65-70
• /
• 2009

대수심의 유체운동을 포텐셜 운동으로 가정하여 자유수면의 거동을 신속히 해석하는 BEM 해석법과 구조물 근방에서 유체의 자유 수면 변화를 계산하기 위하여 NS방정식의 해석으로 CADMAS-SURF 기법을 결합하여 하이브리드 수치기법을 개발하였다. 하이브리드 해석법에서는 반사파를 고려해야 할 넓은 영역에서, 대수심의 영역은 BEM이, 천수역은 CADMAS-SURF가 계산하게 된다. 특히, 하이브리드 모델은 장시간에 걸친 불규칙파의 운동에 대해서는 단독의 CADMAS-SURF을 이용한 계산에 비해 거의 동일한 정확도로 월등히 신속하게 계산할 수 있다. 본 연구에서는 완경사 해저면을 가진 넓은 해역에서, 호안구조물에 내습하는 파랑의 처오름과 월파와 같은 강비선형 파랑장 계산에 결합해석모델을 적용하였다. 계산결과는 각각 토요시마(풍도(豊島))의 규칙과 처오름 실험과 고다(합전(合田))가 제안한 불규칙파의 월파량 산정도와 비교하였다.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2002년도 춘계 학술발표회 논문집
• /
• 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.

• 한국해안·해양공학회논문집
• /
• 제21권2호
• /
• pp.196-208
• /
• 2009

본 논문에서는 부유 플랩형 고조방파제의 응답특성에 대해서 연구하였다. 효율적인 연구를 위하여 파동장은 선형 포텐셜 이론을 적용하여 모형화하였으며, 구조물의 운동은 Newton의 운동 제2법칙을 사용하여 나타내었다. 유체 영역은 통상의 2차 보간함수를 갖는 등매개변수요소로 모형화하였으며, 방사경계조건에 접하는 외부 영역은 무한요소로 처리하였다. 수리실험결과와의 비교를 통하여 수립된 수치모델의 타당성을 입증하였으며, 개발된 수치모델을 이용하여 마산만에 부유 플랩형 고조방파제 적용가능성에 대해서 살펴보았다.