http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
유도탄 노즈 형상 변화에 따른 공력 산출 기법의 비교 연구
한서음,박윤식,홍슬기,이복직 한국전산유체공학회 2023 한국전산유체공학회지 Vol.28 No.1
Aerodynamic coefficients of baseline missile noses and deformed missile noses at Mach 5 and 7 were calculated and compared using three kinds of approaches: 1) a density-based solver for CFD, 2) Newtonian theory, and 3) modified Newtonian theory. A blunt-cone shape was used as a baseline missile nose, and a deformed missile nose was generated by adapting the ablation model of a missile in the hypersonic region. The difference between the aerodynamics coefficients obtained from CFD and those obtained from the two theories was decreased as the Mach number increased. In terms of aerodynamic coefficient changes with the deformation of missile noses, the changes in drag and lift coefficients were similar for all three methods, but the changes in pitching moment coefficients were significant between CFD and the two theories.
GPGPU를 활용한 OpenFOAM 기반 해석자 성능 분석
한서음(Seoeum Han),정황희(Hwanghui Jeong),이복직(Bok Jik Lee) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.2
Two benchmark tests were carried out to analyze the performance of OpenFOAM-based CFD solvers using General-Purpose computing on Graphics Processing Units(GPGPU). In the present study, RapidCFD, which is an implementation of OpenFOAM capable of running most of the functions of OpenFOAM on GPUs, was used to apply GPGPU to OpenFOAM. The numerical simulations of 1) 3D lid-driven cavity incompressible flows and 2) steady flows around a motorbike were conducted on two kinds of CPU, single-GPU, and multi-GPU systems, and the computational times were analyzed. For the test of cavity flows, as the number of cells increased, the performance and the scalability of GPGPU were improved. When the number of cells was 2503, a system with 8-GPUs showed the highest performance with 42 times of speedup over a CPU system. For the test of flows around a motorbike, a system with 8-GPUs showed the highest performance with 20 times of speedup over a CPU system. For both single precision and double precision calculations, the performance improvements using GPGPU were efficient. The results demonstrate that GPGPU would be more efficient than computing on CPUs when computing large-scale flows and practical problems that require massive parallelism.
2차원 압축성 유동 해석자의 OpenACC를 이용한 GPU 활용
김승래,한서음,이복직 한국전산유체공학회 2022 한국전산유체공학회지 Vol.27 No.3
A two-dimensional compressible flow solver was ported to GPU using OpenACC. The performance of this program was tested in three cases: viscous flow on a flat plate, inviscid transonic flow in a channel with a bump, and inviscid transonic flow around n0012 airfoil. The GPU program running on RTX 3090 showed up to 20 times of speedup compared to the original program using a single core of Ryzen 5950X, and up to 10 times of speedup compared to the program that uses all resources on the CPU. Among the computation steps of the program, implicit residual smoothing was the worst performing step on the GPU. To address this problem, skipping residual smoothing and using the Cyclic Reduction algorithm were tried as alternatives. These approaches improved speedup in almost every case, increasing the maximum speedups to 24 times compared to the single core program and 11 times compared to the 16-core program. The results show that GPU is a suitable tool for accelerating CFD solvers due to its memory bandwidth and parallel computing capability and using OpenACC is a viable method for porting programs to GPU.
고엔탈피 풍동에서의 모델 스크램제트 흡입구 유동에 관한 수치해석적 연구
박윤식,남준혁,한서음,이복직,이양지 한국전산유체공학회 2023 한국전산유체공학회지 Vol.28 No.2
In order to assess the performance of a hypersonic air-breathing propulsion system under high-altitude conditions, blow-down type high-enthalpy wind tunnel tests are commonly conducted. However, it should be noted that accurately reproducing the high-altitude freestream conditions is challenging due to various factors, such as the nozzle boundary layer, nozzle back pressure, and the configuration and placement of the test engine. Therefore, in this study, numerical simulations were performed for the scramjet inlet flow under the blow-down type high-enthalpy wind tunnel environment and the freestream conditions, and the results were compared. It was observed that the nozzle boundary layer had negligible influence on the inlet flow, even when the test engine was positioned close to the nozzle wall. Furthermore, while the core flow in the nozzle exhibited similarities to conditions at an altitude of 23 km and Mach 5, the formation of over-expansion shock waves at the nozzle exit due to high nozzle back pressure was observed, interfering with the inlet internal flow. Lastly, a quantitative analysis was conducted to examine the effect of the over-expansion shock waves on the performance parameters of the inlet, including the mass flow rate and total pressure recovery.