Earticle

컴퓨터의 성능이 향상되면서 시뮬레이션 기반의 자연 현상 표현 기법에 대한 수요가 늘어나고 있다. 특히 컴퓨터 게임의 배경으로 많이 나오는 바다와 강의 표면을 표현하기 위해 다양한 수면 시뮬레이션 기술이 소개되고 있다. 이 러한 수면 표현 기법은 사실적인 효과를 줄 수 있지만 계산의 복잡성으로 인해 게임에는 제한적으로 적용되어왔다. 본 논문에서는 컴퓨터 게임을 위한 빠르고 자연스러운 수면 표현 기법을 제시한다. 제시된 기법은 게임 엔진 등에 적 용되어 다양한 삼차원 컴퓨터 게임에 응용될 것으로 예상된다.

According to the advance of computing capability, more demands for simulation-based natural phenomena representation are required. Demands for wave simulation technologies used to express ocean and river become bigger and bigger. These simulation-based technologies ensure realistic results. However, they are time-consuming. This paper presents a wave simulation algorithm which is fast and generates realistic results. The presented algorithm can be applied to existing game engines and various 3D computer games.

This paper describes the control simulation of pitch hydroplane motion with the input flapping arm reference in the oscillating flapping arm in tidal wave system power generation. Dynamic model of the system consists of a pitch hydroplane connected to a flapping arm where flapping arm is connected to a gear. By calculating the forces and the moments, dynamic equation of the model system is obtained. Then by using the transfer function of the system, PID control were simulated on Matlab® to investigate the motions of the flapping arm due to up and down of pitch hydroplane motions. The hydroplane structure is following the characteristic of NACA0012.

연안에서 각종 개발사업과 항만 운영 등을 안전하게 수행하고 관리하기 위해서는 해당지역의 파랑을 산정하는 것이 중요하다. 파랑을 정확히 산정하기 위해서는 장기간의 관측 자료가 필요하다. 특히 평상파랑의 경우 최소 10년 이상의 파랑관측 자료가 필요하나 우리나라의 경우 이와 같은 자료가 매우 부족한 실정이다. 본 연구에서는 기상대에서 관측한 바람자료가 비교적 장기간에 걸쳐 축척되어 있음에 착안하여 수치파랑모형을 이용하여 평상파랑을 모의하였다. 모의결과를 관측된 파랑과 비교한 결과, 지형의 방향과 풍향이 일치하는 경우에는 관측파랑을 비교적 잘 재현하는 것으로 나타났다.

Wave calculation is very an important thing to select operable wave condition for use in coastal and ocean desing or in marine operation planning. Wave measurement data which is measured over 10 years is needed to calculate wave correctly, but, there is few long-term wave measurement data in Korea. As long-term wind data is much more than wave data, in this study, wind data was used to simulate wave by numerical wave model. As a result, when the geographical direction of study area is similar to the direction of wind, the simulated wave coincide with the measured wave.

이 논문은 MPM(Material Point Method) 기반의 탄성체 소성변형 시뮬레이션의 정확도를 향상시키기 위해 응 력파(Stress Wave) 속도에 대한 손상위상장(Damage Phase Field)을 MPM 시뮬레이션과 결합하는 새로운 접 근법을 제시한다. 기존의 MPM 시뮬레이션은 소성변형에 대해서 각 입자의 Cauchy 응력을 계산하고 APIC (Affine Particle in Cell) 접근법을 사용하여 입자 간에 힘의 전달을 표현하였다. 그러나 각 입자의 수직 응력에 대한 아핀(affine) 연산만으로는 다양한 소성변형으로부터 물체의 연속적인 손상 진화를 표현하는데 한계가 있다. 이 한계점에 대응하기 위해 본 연구에서는 응력에 대한 미분연산을 통해 응력파 속도를 계산하여 연속적인 손상 진 화를 손상위상장으로 나타내고 이를 MPM과 결합한다. 동일한 환경에서 기존 MPM과 제안한 방법의 비교 실험을 수행하였으며, 시뮬레이션한 탄성 물체의 소성변형과 손상의 시각적인 정확도가 향상되었음을 확인했다.

We propose a new approach to combining the Damage Phase Field for Stress Wave velocity with MPM(Material Point Method) simulation to improve the accuracy of the elastic plastic deformation simulation based on the MPM. Existing MPM simulations have calculated the Cauchy stress of each particle for plastic deformation and expressed force transfer between particles using the APIC (Affine Particle in Cell) approach. However, there is a limit to expressing the continuous damage evolution of an object from various plastic deformations only by affine calculations on the vertical stress of each particle. To cope with this limitation, this study calculates the stress wave velocity through differential computation for stress to represent continuous damage evolution as a damage phase field and combines it with MPM. Comparative experiments of the proposed method with the existing MPM were conducted in the same environment, and it was confirmed that the visual accuracy of the simulating elastic object's plastic deformation and damage was improved.

본 연구는 스마트하이웨이 같은 첨단 도로 인프라가 구축이 되어 WAVE(Wireless Access for Vehicular Environments) 기술을 이용하여 차량의 정보를 수집하는 서비스를 시행할 경우, 차량데이터를 수집하는 전송간격의 결정 문제를 다루고 있다. 여기서 차량데이터는 위치정보이외에 속도, RPM, 연료소모량 및 DTC 코드와 같은 차량안전데이터를 포함하는 OBD II와 연계된 차량수집장치로부터 매초별로 수집될 수 있는 데이터이다. 이러한 차량데이터는 기존의 교통소통정보로 가공 및 제공이 가능할 뿐만 아니라 다각화된 서비스가 가능한 컨텐츠로 활용이 될 수 있다. 본 연구에서는 이러한 실시간 차량데이터를 일상적인 상황에서 수집될 경우 교통조건의 변화에 따라 전송간격(교통정보 수집주기)를 변경하는 방법으로 공간적, 시간적 교통상황을 고려하는 모델을 제안한다. 연구에서는 이러한 전송간격 결정모델에 대하여 교통상황묘사가 가능한 VISSIM이라는 미시적 교통시뮬레이터를 기반으로 시나리오를 약 32가지 설정하여 전송간격, 통신전송량, 통신간격, 통신수 및 BPS 등에 대하여 확인하여 보았다. 그 결과 2차로의 1km 고속도로 구간에서는 차량데이터를 2회 정도 수집할 경우에 통신전송량의 특성상 가장 적절할 것으로 확인되었다. 향후 다양한 도로상의 무선 통신 기술이 도입될 경우 교통 및 통신기술 특성을 동시적으로 고려한 전송간격 모델을 제시한 본 연구는 그 활용가치가 높을 것으로 판단되는 바이다.

This paper deals with the transmission interval of vehicle data in smart highway where WAVE (Wireless Access for Vehicular Environments) systems have been installed for advanced road infrastructure. The vehicle data could be collected at every second, which is containing location information of the vehicle as well the vehicle speed, RPM, fuel consuming and safety data. The safety data such as DTC code, can be collected through OBD-II. These vehicle data can be used for valuable contents for processing and providing traffic information. In this paper, we propose a model to decide the collection interval of vehicle information in real time environment. This model can change the transmission interval along with special and time-variant traffic condition based on the 32 scenarios using microscopic traffic simulator, VISSIM. We have reviewed the transmission interval, communication transmission quantity and communication interval, tried to confirm about communication possibility and BPS, etc for each scenario. As results, in 2-lane from 1km highway segment, most appropriate transmission interval is 2 times over spatial basic segment considering to communication specification. In the future, if a variety of wireless technologies on the road is introduced, this paper considering not only traffic condition but also wireless network specification will be utilized the high value.

Applications of nonlinear acoustics are getting popular in the field of nondestructive characterization of material microstructure and damage. Before the nonlinear acoustic technique is fully utilized, it is important to understand the behavior of nonlinear acoustic fields generated by finite amplitude excitation. A two wave mixing technique can be considered and the difference frequency component can be used to determine the nonlinear material properties. One important advantage of using the difference frequency component is known to minimize the source nonlinearity and to acquire low attenuating nonlinear signals. In this paper, the expression for the difference frequency sound beam is derived from the quasilinear theory of the Westervelt equation which includes the material nonlinearity, beam diffraction and material attenuation. Simulation results are presented and the beam properies are discussed in comparison with the behavior of the second harmonic beam fields.

In this paper, optical infrared thermography simulation using thermal wave imaging technique is performed to analyze the thermal characteristics of delamination defects. In this study, lock-in thermography(LIT) and pulsed thermography(PT) simulation was performed to analyze the samples of european traditional tiles with delamination defects, and the analytical modeler was developed through the ANSYS 19.2 transient thermal analysis tool. Applied sinusoidal heating with modulation frequency according to pulse heating and phase locking technique. The thermal response of the sample surface by heating was recorded and then data analysis was performed. The temperature gradient characteristics of each technique were compared, and phase angle was calculated for the LIT to analyze the parameters for the experiment setting. The simulation model was developed as a useful data for practical optical infrared thermography tests.

Mechanical properties of tissue are often related to the pathological state of tissue. Therefore, non-invasively measuring tissue stiffness has important clinical applications. With the assumption of isotropy, incompressibility and linearity, the shear modulus of tissue is related to its shear wave propagation speed. Acoustic radiation force from a focused ultrasound beam can be used to generate shear waves at the focal region within tissue, which propagate orthogonally to the direction of the pushing ultrasound beam. The shear wave speed can be estimated based on the so called time-to-flight principle. The shear wave arrival time determined at several lateral positions along the shear wave propagation path can be measured by the displacement profiles, which can be tracked using correlation-based method by pulse-echo ultrasound. This approach has been successively used with various modifications by several groups. The purpose of this study is to design a simulation method to generate the pulse-echo ultrasound signal, calculate the displacement profile in the spatial and time domain, and estimate the shear wave speed using RANSAC, Radon Sum and robust linear regression method, compare and analyze the algorithm performance of these methods.

Based on the characteristics of shock wave which are produced by spherical projectiles hypervelocity impact on nitrogen-filled pressure vessels, apply ingone-dimensional shock wave theory and numerical simulation method, at the condition of the debris clouds is completely ablated, the process of shock wave propagation in the gas is analyzed, and model of shock wave propagation is built. The law of shock wave propagation, the pressure of shock wave and the pressure pulse duration are obtained. The result shows that at the same impact velocity, the pressure of shock wave is increasing with gas pressure and projectile diameter. Fracture of pressure vessels impacted by hypervelocity projectiles with a diameter less than 3mm is governed by inflation pressure for projectile impact velocities of 7 km/s.

Due to the fact that theoretical analysis and instrument construction for antenna array of synthetic aperture imaging radiometer (SAIR) are both complicated, and designers usually hope to predict the imaging effect and analysis the influence of relevant parameters of SAIR before the system design. The imaging simulation is a very useful method in the system design of SAIR. This paper is devoted to establishing an accurate imaging model for simulating the process of near-field millimeter wave SAIR. In this model, the target radiation signals and received signals of receivers are represented by the accurate signals in the time domain, which improves the efficiency of this simulation model significantly. The visibility function is collected by the cross-correlation between I/Q signals of the antenna pairs just as the imaging process of the practical SAIR. Some characteristics (such as the coherence between targets, the resolution and no-aliasing FOV of SAIR and so on) are verified by the corresponding 1D and 2D simulation experiments, and the effectiveness of this imaging model is also tested by these simulation experiments. The simulation experiment results show that this model is an efficient, accurate imaging simulation model, and can be employed in the system design of near-field millimeter wave SAIR.

The property of magnetic field and properties of EMW(Electro Magnetic Wave) absorption with multi-shaped EMW absorber was simulated. As a magnetic field having high density was showed at bottom of EMW absorber, simulation showed that overall EMW was absorbed at the bottom of multi-shaped absorber. The absorption properties of EMW according to thickness of absorber showed that it enhanced about 50-60 percent. Also, EMW absorption properties was checked with surface area of EMW absorber. A cylinder-shaped EMW absorber exhibited good property among multi-shaped EMW absorber based on these result.

The wave mode calculation of a large-scale optical system in comparison to the working wavelength is practically impossible because the computational cost increases exponentially. In this paper, we propose a method that can obtain the optical mode in a large-scale optical system. The method carries out simulations by dividing the calculation area into blocks and moving along the light axis along which the light propagates. By applying this method to the calculation of resonant modes in a ring-type optical resonator, which is mainly used for ring laser optical gyro sensors, the efficiency of the proposed method was verified.

In this paper, we present a real-time physical simulation model of water surfaces with a novel method to represent the water mass flow in full three dimensions. In a physical simulation model, the state of the water surfaces is represented by a set of physical values, including height, velocity, and the gradient. The evolution of the velocity field in previous works is handled by a velocity solver based on the Navier-Stokes equations, which occurs as a result of the unevenness of the velocity propagation. In this paper, we integrate the principle of the mass conservation in a fluid of equilateral density to upgrade the height field from the unevenness, which in mathematical terms can be represented by the divergence operator. Thus the model generates waves induced by horizontal velocity, offering a simulation that puts forces added in all direction into account when calculating the values for height and velocity for the next frame. Other effects such as reflection off the boundaries, and interactions with floating objects are involved in our method. The implementation of our method demonstrates to run with fast speed scalable to real-time rates even for large simulation domains. Therefore, our model is appropriate for a real-time and large scale water surface simulation into which the animator wishes to visualize the global fluid flow as a main emphasis.

탐사 지구물리학에서 수치 모사는 지하매질에서의 탄성파 전파 현상을 이해하는데 중요한 통찰력을 제공한다. 탄성파 모사는 음향파 근사에 의한 수치 모사보다 계산시간이 많이 소요되지만 전단응력 성분을 포함하여 보다 현실적인 파동의 모사를 가능하게 한다. 그러므로 탄성파 모사는 탄성체의 반응을 탐사하는데 적합하다고 할 수 있다. 계산 시간이 길다는 단점을 극복하기 위해 본 논문에서는 그래픽 프로세서(GPU)를 이용하여 탄성파 수치 모사 시간을 단축하고자 하였다. GPU는 많은 수의 프로세서와 광대역 메모리를 갖고 있기 때문에 병렬화된 계산 아카텍쳐에서 사용할 수 있는 장점이 있다. 본 연구에서 사용한 GPU 하드웨어는 NVIDIA Tesla C1060으로 240개의 프로세서로 구성되어 있으며 102 GB/s의 메모리 대역폭을 갖고 있다. NVIDIA에서 개발된 병렬계산 아카텍쳐인 CUDA를 사용할 수 있음에도 불구하고 계산효율을 상당히 향상시키기 위해서는 GPU 장치의 여러 가지 다양한 메모리의 사용과 계산 순서를 최적화해야만 한다. 본 연구에서는 GPU 시스템에서 시간영역 유한차분법을 이용하여 2차원과 3차원 탄성과 전파를 수치 모사하였다. 파동전파 모사에 가장 널리 사용되는 유한차분법 중의 하나인 엇갈린 격자기법을 채택하였다. 엇갈린 격자법은 지구물리학 분야에서 수치 모델링을 위해 사용하기에 충분한 정확도를 갖고 있는 것으로 알려져 있다. 본 논문에서 제안한 모델링기법은 자료 접근 시간을 단축하기 위해 GPU 장치를 메모리 사용을 최적화하여 가능한 더 빠른 메모리를 사용한다. 이점이 GPU를 이용한 계산의 핵심 요소이다. 하나의 GPU 장치를 사용하고 메모리 사용을 최적화함으로써 단일 CPU를 이용할 경우보다 2차원 모사에서는 14배 이상, 3차원에서는 6배 이상 계산시간을 단축할 수 있었다. 세 개의 GPU를 사용한 경우에는 3차원 모사에서 계산효율을 10배 향상시킬 수 있었다.

Numerical simulation in exploration geophysics provides important insights into subsurface wave propagation phenomena. Although elastic wave simulations take longer to compute than acoustic simulations, an elastic simulator can construct more realistic wavefields including shear components. Therefore, it is suitable for exploration of the responses of elastic bodies. To overcome the long duration of the calculations, we use a Graphic Processing Unit (GPU) to accelerate the elastic wave simulation. Because a GPU has many processors and a wide memory bandwidth, we can use it in a parallelised computing architecture. The GPU board used in this study is an NVIDIA Tesla C1060, which has 240 processors and a 102 GB/s memory bandwidth. Despite the availability of a parallel computing architecture (CUDA), developed by NVIDIA, we must optimise the usage of the different types of memory on the GPU device, and the sequence of calculations, to obtain a significant speedup of the computation. In this study, we simulate two- (2D) and threedimensional (3D) elastic wave propagation using the Finite-Difference Time-Domain (FDTD) method on GPUs. In the wave propagation simulation, we adopt the staggered-grid method, which is one of the conventional FD schemes, since this method can achieve sufficient accuracy for use in numerical modelling in geophysics. Our simulator optimises the usage of memory on the GPU device to reduce data access times, and uses faster memory as much as possible. This is a key factor in GPU computing. By using one GPU device and optimising its memory usage, we improved the computation time by more than 14 times in the 2D simulation, and over six times in the 3D simulation, compared with one CPU. Furthermore, by using three GPUs, we succeeded in accelerating the 3D simulation 10 times.

This paper presents an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is then composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional side bands that contain the time-of-flight information on the defect location. One of the side band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free detection of a defect, so that experimental studies are needed to verify the proposed method and to be applied to real structure.

Offshore substructures have been developed to support structures against complex offshore environments. The load at offshore substructures is dominated by waves, and deformation of waves caused by interactions with the current is an important phenomena. Wave load simulation of fixed offshore substructures in waves with the presence of uniform current was carried out by numerical wave tank technique using the commercial software, FLUENT. The continuity and Navier-Stokes equations were applied as the governing equations for incompressible fluid motion, and numerical wavemaker was employed to reproduce offshore wave environment. Convergence test against grids number was carried out to investigate grid dependency and optimized conditions for numerical wave generation were derived including investigation of the damping effect against length of the damping domain. Numerical simulation of wave and current interactions with fixed offshore substructure was carried out by computational fluid dynamics, and comparison with other experiments and simulations results was conducted.

The present study numerically models the interaction between a regular wave and the roll motion of a rectangular floating structure. In order to simulate two-dimensional incompressible viscous two-phase flow in a numerical wave tank with the rectangular floating structure, the present study used the volume of fluid method based on the finite volume method. The sliding mesh technique is adopted to handle the motion of the rectangular floating structure induced by fluid-structure interaction. The effect of the wave period on the flow, roll motion and forces acting on the structure is examined by considering three different wave periods. The time variations of the wave height and the roll motion of the rectangular structure are in good agreement with experimental results for all wave periods. The present response amplitude operator is in good agreement with experimental results with the linear potential theory. The present numerical results effectively represent the entire process of vortex generation and evolution described by the experimental results. The longer wave period showed a different mechanism of the vortex evolution near each bottom corner of the structure compared to cases of shorter wave periods. In addition, the x-directional and z-directional forces acting on the structure are analyzed.

The interaction between advancing ships and the waves generated by them plays important roles in wave resistances and ship motions. Wave breaking phenomena near the ship bow at different speeds are investigated both numerically and experimentally. Numerical simulations of free surface profiles near the fore bodies of ships are performed and visualized to grasp the general trend or the mechanism of wave breaking phenomena from moderate waves rather than concentrating on local chaotic irregularities as ship speeds increase. Navier-Stokes equations are differentiated based on the finite difference method. The Marker and Cell (MAC) Method and Marker-Density Method are employed, and they are compared for the description of free surface conditions associated with the governing equations. Extra effort has been directed toward the realization of extremely complex free surface conditions at wave breaking. For this purpose, the air-water interface is treated with marker density, which is used for two layer flows of fluids with different properties. Adaptation schemes and refinement of the numerical grid system are also used at local complex flows to improve the accuracy of the solutions. In addition to numerical simulations, various model tests are performed in a ship model towing tank. The results are compared with numerical calculations for verification and for realizing better, more efficient research performance. It is expected that the present research results regarding wave breaking and the geometry of the fore body of ship will facilitate better hull form design productivity at the preliminary ship design stage, especially in the case of small and fast ship design. Also, the obtained knowledge on the impact due to the interaction of breaking waves and an advancing hull surface is expected to be applicable to investigation of the ship bow slamming problem as a specific application.

본 논문에서는 이상유체모델에서의 비선형 자유표면파의 발생, 전파 및 상호간섭에 대한 비정상 문제의 수치해법을 개발하였다. 본 수치해법은 매 시간 스텝에서 비선형 축차해법을 이용한 음함수적(implicit)방법이다. 속도장함수를 구하기 위하여 경계접합좌표계를 도입한 유한차분법을 이용하였다. 본 수치해법의 유효성과 효율성의 검증을 위하여 타원형 유체의 변형과 바닥의 일부분이 올라옴으로서 발생하는 자유표면파의 생성에 대한 두 가지 계산결과를 보여준다.

The present paper is devoted to constructing a numerical algorithm for solving un steady problems on generation, propagation and interaction of nonlinear waves at a surface of ideal fluid, within the framework of the potential-flow model. The numerical scheme is implicit. with non-linearity iteration at every step of time. the finite-difference method with boundary-fitted coordinates are presented in favor for validity and high efficiency of the numerical model developed. Among these arguments, there are the results of calculations of two test problems-on stretching of a liquid ellipse and on wave generation by lifting a portion of a bottom.