OWEC(Overtopping Wave Energy Converter)는 월파된 파도를 이용한 파력발전시스템이라한다. OWEC의 성능 및 안전성은 파고, 주기 등 파도의 특성에 의해 영향을 받는다. 따라서 해역 특성에 따른 OWEC의 최적 형상과 구조안전성에 관한 연구가 필요하다. 본 연구 에서는 울릉읍 연안 해양 환경 데이터를 이용하였으며, SPH(Smoothed Particle Hydrodynamics) 입자법 해석을 통해 기존 케이슨 하부 구조에 변화를 준 모델 4개를 비교하여 월파 효율을 분석하였다. 그 결과, 하부 구조의 변경 및 경량화가 가능함을 확인하였다. 최적화 해석을 통 해 설계 하중에 내하력을 가지는 하부 구조인 새로운 트러스형 구조를 제안하였다. 이후 부재 직경 및 두께를 설계변수로 하는 사례 연구 를 통해 허용응력조건 하에서 구조 안전성의 확보를 확인하였다. 주기적인 파랑 하중을 받기 때문에 제안하는 구조의 고유 진동수와 해 당 해역의 파주기를 비교하였으며, 1년 재현 주기의 파랑을 하중으로 한 조화응답해석을 수행하였다. 제안하는 하부 구조는 동일 가진력 에서 기존 설계 대비 응답의 크기가 감소하였으며, 기존 대비 32% 이상의 중량 절감을 수행하였다.

I present here one approach to general relativistic radiation hydrodynamics. It is based on covariant tensor conservation equations and considers only the frequency-integrated total energy and momentum exchange between matter and the radiation field. It is also a mixed-frame formalism in the sense that, the interaction between radiation and matter is described with quantities in the comoving frame in which the interaction is often symmetric in angle while the radiation energy and momentum equations are expressed in the fixed frame quantities in which the derivatives are simpler. Hence, this approach is intuitive enough to be applied straightforwardly to any spacetime or coordinate. A few examples are provided along with caveats in this formalism.

A numerical model analysis was performed to analyze the motion and mooring tension response of submersible fish cage systems in irregular waves and currents. Two systems were examined: a submersible cage mooring with a single, high tension mooring and the same system, but with an additional three point mooring. Using a Morison equation type model, simulations of the systems were conducted with the cage at the surface and submerged. Irregular waves(JONSWAP spectrum) with and without a co-linear current with a magnitude of 0.5m/s were simulated into the model as input parameters. Surge, heave and pitch dynamic calculations were made, along with tension responses in the mooring lines. Results were analyzed in both the time and frequency domains and linear transfer functions were calculated.

Radiation hydrodynamics in high. velocity or high optical-depth flow should be treated under rigorous relativistic formalism. Relativistic radiation hydrodynamic moment equations are summarized, and its application to the near-critical accretion onto neutron star is discussed. The relativistic effects can dominate the dynamics of the flow even when the gravity is weak and the velocity is small. First order equations fail to describe the intricate relativistic effects correctly.

We present preliminary numerical simulations of tilted-disk accretion around a rotating black hole. Our goal is to explore whether hydrodynamic instabilities near the Bardeen-Petterson radius could be responsible for generating moderate-frequency quasi-periodic oscillations in X-ray binaries. We review the relevant general relativistic hydrodynamic equations, and discuss preliminary results on the structure and dynamics of a thin, Keplerian disk.

To examine the structure and dynamics of thick accretion disks, we use a two-dimensional viscous hydrodynamic code coupled with radiation transport. The α-model and the full viscous stress-tensor description for the kinematic viscosity are used. The radiation transport is treated in the gray, flux-limited diffusion approximation. The finite difference methods used are based on an explicit-implicit method. We apply the numerical code to the Super-Eddington black-hole model for SS 433.@The result for a very small viscosity parameter a reproduces well the characteristic features of SS 433, such as the relativistic jets with ~0.26c, the small collimation degree of the jets, the mass-outflow rate of ≥ 5 × 10 -7 M⊙yr-1, and the formation of the X-ray iron emission lines.

SPH is the shorthand for Smoothed Particle Hydrodynamics. This method is a Lagrangian method which means that it involves following the motion of elements of fluid. These elements have the characteristics of particles and the method is called a particle method. A useful review of SPH (Monaghan 1992) gives the basic technique and how it can be applied to numerous problems relevant to astrophysics. You can get some basic SPH programs from http) /www.maths.monash.edu.au/jjm/sphlect In the present lecture I will assume that the student has studied this review and therefore understands the basic principles. In today's lecture I plan to approach the equations from a different perspective by using a variational principle.

My contribution to these proceedings summarizes a general overview on High Resolution Shock Capturing methods (HRSC) in the field of relativistic hydrodynamics with special emphasis on Riemann solvers. HRSC techniques achieve highly accurate numerical approximations (formally second order or better) in smooth regions of the flow, and capture the motion of unresolved steep gradients without creating spurious oscillations. In the first part I will show how these techniques have been extended to relativistic hydrodynamics, making it possible to explore some challenging astrophysical scenarios. I will review recent literature concerning the main properties of different special relativistic Riemann solvers, and discuss several 1D and 2D test problems which are commonly used to evaluate the performance of numerical methods in relativistic hydrodynamics. In the second part I will illustrate the use of HRSC methods in several astrophysical applications where special and general relativistic hydrodynamical processes play a crucial role.

The kinetics of flocculation of heterodisperse suspension like those in water treatment plants and natural water system are usually described by the Smoluchowski equation, which incorporates collision frequency functions for particle collisions by Brownian motion, fluid shear, and differential sedimentation. These collisionfrequeney functions have been based on a rectilinear view of collisions, i.e., one that ignores short-range forces and changes in fluid motion as particles approach one another. In this research, a curvilinear approach, i.e., one that accounts for hydrodynamic forces and particle interaction in the collision of two different size particles is developed. Collision efficiency factors of each mechanism can be calculated by trajectory analysis (fluid shear and differential sedimentation) or the solution of diffusion equation (Brownian motion). The results are presented as a set of corrections to the rectilinear collision frequency functions for each mechanism.

We have constructed a 3-dim hydrodynamics code called BTSPH. The fluid dynamics part of the code is based on the smoothed particle hydrodynamics (SPH), and for its Poisson solver the binary tree (BT) scheme is employed. We let the smoothing length in the SPH algorithm vary with space and time, so that resolution of the calculation is considerably enhanced over the version of SPH with fixed smoothing length. The binary tree scheme calculates the gravitational force at a point by collecting the monopole forces from neighboring particles and the multipole forces from aggregates of distant particles. The BTSPH is free from geometric constraints, does not rely on grids, and needs arrays of moderate size. With the code we have run the following set of test calculations: one-dim shock tube, adiabatic collapse of an isothermal cloud, small oscillation of an equilibrium polytrope of index 3/2, and tidal encounter of the polytrope and a point mass perturber. Results of the tests confirmed the code performance.

The optimum design and scale-up of a fast pyrolysis reactor require a fundamental understanding of its hydrodynamics characteristics. Extensive investigations have been carried out, both theoretically and experimentally, to understand the hydrodynamic characteristics of gas-solid two-phase flow in a pyrolysis reactor, such as velocity field, solids concentration, and pressure drop. Numerical simulation can provide a promising alternative for studying the hydrodynamics of gas-solid flows in the fast pyrolysis reactor. In this study, computational particle fluid dynamics (CPFD) was used to investigate the hydrodynamic characteristics of bubbling fluidized bed (BFB) and conical spouted bed (CSB) reactors. These characteristics were analyzed in terms of pressure drop, solid distribution, and solid circulation rate. The BFB reactor was found to have a lower efficiency than the CSB reactor. The pressure drop of the CSB reactor was 25% less than that of the BFB reactor. The solid circulation rate of the CSB reactor was 68% greater than that of the BFB reactor.

고 밀집 상태의 군중 시뮬레이션은 객체 수에 따라 복잡도와 제작 비용이 크게 증가함으로 사실적인 움직임을 표현하는데 어려움이 있다. 본 논문에서는 고 밀집 군중 시뮬레이션 시 사실적인 움직임을 표현하기 위해 Smoothed Particle Hydrodynamics (SPH) 기법을 도입하였다. 본 연구에서는 유체 시뮬레이션에 사용되는 SPH 모델을 응용하여 객체 움직임에 필요한 회피력, 거리 유지력, 그룹 응집력을 새로이 제안하였다. 제안된 객체 운동 수식은 고 밀집 상태에서 유체와 같이 자연스런 객체 움직임을 표현하는데 효과적이다. 실험 결과, 본 시스템은 밀집도 높은 군중 시뮬레이션을 실시간으로 생성 가능함을 보였다.