• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.7
• /
• pp.1030-1040
• /
• 1998

One of the main unresolved issues in large-eddy simulation(LES) of wall-bounded turbulent flows is the requirement of high spatial resolution in the near-wall region, especially in the spanwise direction. Such high resolution required in the near-wall region is generally used throughout the computational domain, making simulations of high Reynolds number, complex-geometry flows prohibitive. A grid-embedding strategy using a nonconforming spectral domain-decomposition method is proposed to address this limitation. This method provides an efficient way of clustering grid points in the near-wall region with spectral accuracy. LES of transitional and turbulent channel flow has been performed to evaluate the proposed grid-embedding technique. The computational domain is divided into three subdomains to resolve the near-wall regions in the spanwise direction. Spectral patching collocation methods are used for the grid-embedding and appropriate conditions are suggested for the interface matching. Results of LES using the grid-embedding strategy are promising compared to LES of global spectral method and direct numerical simulation. Overall, the results show that the spectral domain-decomposition grid-embedding technique provides an efficient method for resolving the near-wall region in LES of complex flows of engineering interest, allowing significant savings in the computational CPU and memory.

• Journal of the military operations research society of Korea
• /
• v.32 no.1
• /
• pp.133-158
• /
• 2006

The change of information and communications technology affects into many parts of military battlefield as the future warfare will be information-oriented warfare, relying on information technology. The more IT-based military systems are deployed the more multimedia data traffic increase. To accommodate such user's requirements the bandwidth capacity of military communications network must be upgraded. The cost of upgrading network capacity is increasing as well. But there has no systematic estimation approach to analyze the amount of data traffic in the military network. In this paper we suggest an efficient data traffic estimation technique using network simulation with the respect of Input and output, scenario, toolset and technique, and experimental environments.

• International Journal of Aeronautical and Space Sciences
• /
• v.11 no.1
• /
• pp.1-9
• /
• 2010

Numerical simulation of unsteady flows around helicopters was conducted to investigate the aerodynamic interaction of main rotor and other components such as fuselage and tail rotor. For this purpose, a three-dimensional inviscid flow solver has been developed based on unstructured meshes. An overset mesh technique was used to describe the relative motion between the main rotor, and other components. As the application of the present method, calculations were made for the rotor-fuselage aerodynamic interaction of the ROBIN (ROtor Body INteraction) configuration and for a complete UH-60 helicopter configuration consisted of main rotor, fuselage, and tail rotor. Comparison of the computational results was made with measured time-averaged and instantaneous fuselage surface pressure distributions for the ROBIN configuration and thrust distribution and available experimental data for the UH-60 configuration. It is demonstrated that the present method is efficient and robust for the simulation of complete rotorcraft configurations.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.23 no.4
• /
• pp.265-275
• /
• 2011

Estimation of wave height is the most important factor in the design of coastal structures such as breakwaters. In the present study, typhoon wind distribution was constructed by applying the parametric model of Holland (1980), and numerical simulations on the typhoon-generated waves were carried out using the WAM. The typhoons which affected the southern coast of the Korean Peninsula and several hypothetical typhoons were selected to construct the training sets. Design wave heights were estimated using the empirical simulation technique for various return periods and wave directions. The estimated design wave heights were compared with those by the peaks-over-threshold method and the results of KORDI(2005).

• Proceedings of the KIEE Conference
• /
• summer
• /
• pp.666-670
• /
• 2004

This paper presents a new approach for determining an accurate incentive levels of Direct Load Control (DLC) program using sequential Monte Carlo Simulation (MCS) techniques. The economic analysis of DLC resources needs to identify the hourly-by-hourly expected energy-not-served resulting from the random outage characteristics of generators as well as to reflect the availability and duration of DLC resources, which results the computational explosion. Therefore, the conventional methods are based on the scenario approaches to reduce the computation time as well as to avoid the complexity of economic studies. In this paper, we have developed a new technique based on the sequential MCS to evaluate the required expected load control amount in each hour and to decide the incentive level satisfying the economic constraints. And also the proposed approach has been considered multi-state as well as two-state of the generating units. In addition, we have applied the variance reduction technique to enhance the efficiency of the simulation. To show the efficiency and effectiveness of the suggested method the numerical studies have been performed for the modified IEEE reliability test system.

• Nuclear Engineering and Technology
• /
• v.53 no.6
• /
• pp.1846-1857
• /
• 2021

Ultrasonic nondestructive testing is important for monitoring the structural integrity of dissimilar metal welds (DMWs) in pressure vessels and piping in nuclear power plants. However, there is a low probability of crack detection via inspection of DMWs using ultrasonic waves because the grain structures (grain orientations) of the weld area cause distortion and splitting of ultrasonic beams propagating in anisotropic media. To overcome this issue, the grain orientation should be known, and a precise ultrasonic wave simulation technique in anisotropic media is required to model the distortion and splitting of the waves accurately. In this study, a method for nondestructive prediction of the DMW grain orientations is presented for accurate simulation of ultrasonic wave propagation behavior in the weld area. The ultrasonic wave propagation behavior in anisotropic media is simulated via finite-element analysis when ultrasonic waves propagate in a transversely isotropic material. In addition, a methodology to predict the DMW grain orientation is proposed that employs a simulation technique for ultrasonic wave propagation behavior calculation and an optimization technique. The simulated ultrasonic wave behaviors with the grain orientations predicted via the proposed method demonstrate its usefulness. Moreover, the method can be used to determine the focal law in DMWs.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.21 no.2
• /
• pp.235-246
• /
• 2023

Neutron resonance transmission technique was applied for assaying isotopic fissile materials produced in the pyro-process. In each process of the pyro-process, a different composition of the fissile material is produced. Simulation was basically performed on ²³⁵U and ²³⁹Pu assay for TRU-RE product, hull waste, and uranium addition. The resonance energies were evaluated for uranium and plutonium in the simulation, and the linearity in the detection response was examined on the fissile content variation. The linear resonance energies were determined for the analysis of ²³⁵U and ²³⁹Pu on the different fissile materials. For enriched TRU-RE assay, the sample condition was suggested; The sample density, content, and thickness are the key factors to obtain accurate fissile content. The detection signal is discriminated for uranium and plutonium in neutron resonance technique. The transmitted signal for fissile resonance has a direct relation with the content of fissile. The simulation results indicated that the neutron resonance technique is promising to analyze ²³⁵U and ²³⁹Pu for various types of the pyro-process material. An accurate fissile assay will contribute toward safeguarding the pyro-processing system.

• Proceedings of the KIEE Conference
• /
• 1979.08a
• /
• pp.164-165
• /
• 1979

Two dimensional kernels which reconstruct the tomographic image from the blurred one formed by simple back-projection are investigated and their performances are compared. These kernels are derived from tile point spread function of the tomographic system and have the form of a ramp filter modified by several window functions to suppress ringing in the reconstruction. Computer simulation using a computer generated phantom image data with different correction functions(kernels) has been carried out. In this simulation, filtering in frequency domain by 2-D FFT technique or in space domain by 2-D direct convolution is considered. It is found that the-computation time required for real space convolution technique is much larger than that of Fourier 2-D filtering technique in the pratical situation.

• Journal of Institute of Control, Robotics and Systems
• /
• v.17 no.7
• /
• pp.634-640
• /
• 2011

When a servo position controller of a robot or a driving units is composed of a PID controller, servomechanism which is modelled is composed of current, velocity and position control loops. After this model is simulated, the technique operating gain of each controller is suggested. The model consists of current, velocity and position controllers from the inside to the outside gradually. Also, to combine velocity and position controllers with 2 order system, simulation is performed after current controllers are composed, which are able for current loop to work ideally. If a current controller is treated with constant, it is possible for velocity and position controller to consist of controller into 2 order system. The technique is verified by applying T-company servo motor which is much more applied to current, velocity and position controller robots.

• Proceedings of the KIEE Conference
• /
• 1990.11a
• /
• pp.202-205
• /
• 1990

In this paper the development of new technique based on the travelling-wave information contained in the post fault voltage and current signals has been presented. To develop fault location methods which can cope with close-up fault and zero-inception angle problems, magnitude of the backward wave has been used. The technique developed can be incorporated in a generalized algorithm for application as a high speed distance scheme. In this way some of the problems and limitations associated with travelling wave schemes are avoided. Verification of the relay operating principles is presented through digital computer numerical simulation using an electromagnetic transient program(EMTP) in conjunction with simulation of the proposed algorithms.