• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.28-40
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• 2002

Turbulent flows around two-dimensional wing sections in ground effect are analysed by incompressible RANS equations and a finite difference method. The Baldwin-Lomax algebraic turbulence model is used to simulate high Reynolds number flows. The main purpose of this study is to clarify the two-dimensional ground effect and its flow characteristics due to different ground boundary conditions, i.e., moving and fixed bottom boundary. As a first step, to validate the present numerical code, the computational result of Clark-Y(t/C 11.7%) is compared with published numerical results and experimental data. Then, NACA4412 section in ground effect is calculated for various ground clearances with two bottom boundary conditions. According to the computational results, the difference in the lift and moment simulated with the two bottom boundary conditions is negligible, but the drag force simulated by the fixed bottom is to some extent smaller than that by the moving bottom. Therefore, it can be concluded that the drag force measured in a wind tunnel with the fixed bottom could be smaller than that with the moving bottom.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.780-785
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• 2016

Heavy oil used as ship propulsion has a serious issue regarding exhaust emission of global warming. Recently, among large-scale merchant ships are using LNG as green ships so called ech-ships. In this study, an vaporizer and pipes under cryogenic and high pressure load were considered to evaluate structural integrity according to codes. Structural analysis of the vaporizer and pipes was performed using the commercial code, ANSYS. Integrity evaluation of the vaporizer based on von Mises stress was performed in accordance with allowable stress specified in ASME Boiler & Pressure Vesssel Section VIII Division 2. To assess structural integrity of the pipes, stress components were combined and compared with ASME B31.3. The calculated stresses for all load cases are lower than allowable stresses, therefore the structural integrity of equipments are verified.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.318-328
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• 1991

The present paper describes the experimental study on the fixed-type wave-energy conversion system, consisting of the OWC-type wave-energy absorbing chamber and the duct for the air turbine. For simplicity, a screen of wire mesh was employed in place of an air turbine in order to simulate its effects on OWC chamber. Experiments were performed at the towing tank in regular waves with the frequency range of 0.22-0.75Hz. Comparison wish the numerical prediction using a potential flow-based method [4] was made to validate the capability of numerical code. It was shown that the agreements between measured and calculated results are quite good, giving a confidence in prediction method. Simulation of air turbine using a wire-mesh screen was successful, at least in a qualitative sense, to investigate the inter action between the OWC chamber and an air turbine. Results also showed that the effects of a wire-mesh screen on chamber efficiency are negligible, and the present model can be effectively utilized for the practical use in ocean waves with the frequency range under 0.3Hz.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.11-19
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• 2010

The performance of the crossover system of a centrifugal compressor stage consisting of static components of $180^{\circ}$ U-bend, return channel vanes and exit ducting with a $90^{\circ}$ bend is investigated. This study is confined to the assessment of performance of the crossover system by varying the shape of the return channel vanes. For this purpose two different types of Return Channel Vanes (RCV1 and RCV2) were experimentally investigated. The performance of the crossover system is discussed in terms of total pressure loss coefficient, static pressure recovery coefficient and vane surface pressure distribution. The experimentation was carried out on a test setup in which static swirl vanes were used to simulate the flow at the exit of an actual centrifugal compressor impeller with a design flow coefficient of 0.053. The swirl vanes are connected to a mechanism with which the flow angle at the inlet of U-bend could be altered. The measurements were taken at five different operating conditions varying from 70% to 120% of design flow rate. On an overall assessment RCV1 is found to give better performance in comparison to RCV2 for different U-bend inlet flow angles. The performance of RCV2 was verified using numerical studies with the help of a CFD Code. Three dimensional sector models were used for simulating the flow through the crossover system. The turbulence was predicted with standard k-$\varepsilon$, 2-equation model. The iso-Mach contour plots on different planes and development of secondary flows were visualized through this study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.63-71
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• 2018

Strands with ultimate strength of 2,400 MPa was developed and applied in the KCI Code and the KS standard. A high-strength prestressed strand to be applied to a structure, a suitable anchorage system should be used together. Recently, a post tension anchorage for 2,400 MPa strands was developed. but there is not much research on performance evaluation. Therefore, in this study, structural analysis of local zone with 9 strands, 15 strands, and 19 strands anchorage were investigated respectively, which are most widely used for post tensioning anchorages with 2,400 MPa strands, according to PTI anchorage zone design method, and Load transfer performance from ETAG013 and/or KCI-PS101 was evaluated. Furthermore, the adequacy of the test was also analyzed by nonlinear numerical analysis. As results, the anchorages with 2,400 MPa strands satisfied the structural performance of the local area and satisfied the load transfer performance condition.

• Journal of Biosystems Engineering
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• v.35 no.6
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• pp.434-442
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• 2010

This study was carried out to determine necessary conditions for optimal ventilation of small windowless piglet house (4.0 (W) $\times$ 11.0 (L) $\times$ 2.6(H) m) with corridor and attic for preheating using CFD (Computational Fluid Dynamics) simulation. The experimental weaning piglet house was consisted of a corridor, an attic, 4 rooms (3.0 (W) $\times$ 2.75(L) m), 3 fences (0.7(H) m), 5 air inlets and 2 exhaust fans (0.4 (D) m) and simulated using CFD code, FLUENT. The simulation results for the experimental weaning piglet house showed that each room was uniformly ventilated under all the experimental conditions and air velocities at 0.1 m above floor are less than 0.15 m/s for 0.75 m/s and 1.0 m/s of air inlet velocity but 0.61 m/s for 1.25 m/s. The simulation results are similar to the measured results. Considering the air flow pattern, ventilating efficiency, air velocity at 0.1 m above floor and cold stress of weaning piglets and so on, the optimum velocity of air inlet might be 1.0 m/s.

• Nuclear Engineering and Technology
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• v.39 no.3
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• pp.193-206
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• 2007

The Korea Atomic Energy Research Institute has developed an advanced fast reactor concept, KALIMER-600, which satisfies the Generation IV reactor design goals of sustainability, economics, safety, and proliferation resistance. The concept enables an efficient utilization of uranium resources and a reduction of the radioactive waste. The core design has been developed with a strong emphasis on proliferation resistance by adopting a single enrichment fuel without blanket assemblies. In addition, a passive residual heat removal system, shortened intermediate heat-transport system piping and seismic isolation have been realized in the reactor system design as enhancements to its safety and economics. The inherent safety characteristics of the KALIMER-600 design have been confirmed by a safety analysis of its bounding events. Research on important thermal-hydraulic phenomena and sensing technologies were performed to support the design study. The integrity of the reactor head against creep fatigue was confirmed using a CFD method, and a model for density-wave instability in a helical-coiled steam generator was developed. Gas entrainment on an agitating pool surface was investigated and an experimental correlation on a critical entrainment condition was obtained. An experimental study on sodium-water reactions was also performed to validate the developed SELPSTA code, which predicts the data accurately. An acoustic leak detection method utilizing a neural network and signal processing units were developed and applied successfully for the detection of a signal up to a noise level of -20 dB. Waveguide sensor visualization technology is being developed to inspect the reactor internals and fuel subassemblies. These research and developmental efforts contribute significantly to enhance the safety, economics, and efficiency of the KALIMER-600 design concept.

• Tunnel and Underground Space
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• v.15 no.2 s.55
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• pp.145-156
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• 2005

MODFLOW, 3-D finite difference code, is widely used to model groundwater flow and has been used to assess the effect of excavations on the groundwater system due to construction of subways and mountain tunnels. The results of numerical analysis depend on boundary conditions, initial conditions, conceptual models and hydrogeological properties. Therefore, its accuracy can only be enhanced using more realistic and field oriented input parameters. In this study, SA(simulated annealing) was used to integrate hydraulic conductivities from a few of injection tests with geophysical reference images. The realizations of hydraulic conductivity random field are obtained and then groundwater flows in each geostatistically equivalent media are analyzed with a numerical simulation. This approach can give probabilistic results of groundwater flow modeling considering the uncertainty of hydrogeological medium. In other words, this approach makes it possible to quantify the propagation of uncertainty of hydraulic conductivities into groundwater flow.

• Journal of Korea Foundry Society
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• v.42 no.4
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• pp.218-225
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• 2022

For hydrogen-vehicle applications (air pressure control valve housing, APCVH), an investigation was conducted to determine how micro-defects in a high- pressure die-casted Al alloy (industrial code: ALDC12) could be controlled by means of a post-treatment using an organic-based impregnation solution in order to improve the air- tightness of the die-casted Al sample. Two different impregnation solutions were proposed and its test results were compared to a imported product from Japan with respect to the processing variables used. A structural investigation of the components under study was conducted by means of computer tomography and 3D X-ray micro-CT. These observations revealed that the use of the impregnation treatment to seal micro-defects led to highly significant and beneficial changes which were attributed mainly to interconnections among inherent micro-pores. A leak test after impregnation revealed that the performance improvement rate of the die-casted Al sample was ~70% for INNO-01. Therefore, the developed impregnation solutions offer an effective strategy to control the micro-defects found in various vehicle parts via die-casting.

• Journal of Radiation Protection and Research
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• v.47 no.3
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• pp.111-133
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• 2022

The exciting advancement related to the "modeling of digital human" in terms of a computational phantom for radiation dose calculations has to do with the latest hype related to deep learning. The advent of deep learning or artificial intelligence (AI) technology involving convolutional neural networks has brought an unprecedented level of innovation to the field of organ segmentation. In addition, graphics processing units (GPUs) are utilized as boosters for both real-time Monte Carlo simulations and AI-based image segmentation applications. These advancements provide the feasibility of creating three-dimensional (3D) geometric details of the human anatomy from tomographic imaging and performing Monte Carlo radiation transport simulations using increasingly fast and inexpensive computers. This review first introduces the history of three types of computational human phantoms: stylized medical internal radiation dosimetry (MIRD) phantoms, voxelized tomographic phantoms, and boundary representation (BREP) deformable phantoms. Then, the development of a person-specific phantom is demonstrated by introducing AI-based organ autosegmentation technology. Next, a new development in GPU-based Monte Carlo radiation dose calculations is introduced. Examples of applying computational phantoms and a new Monte Carlo code named ARCHER (Accelerated Radiation-transport Computations in Heterogeneous EnviRonments) to problems in radiation protection, imaging, and radiotherapy are presented from research projects performed by students at the Rensselaer Polytechnic Institute (RPI) and University of Science and Technology of China (USTC). Finally, this review discusses challenges and future research opportunities. We found that, owing to the latest computer hardware and AI technology, computational human body models are moving closer to real human anatomy structures for accurate radiation dose calculations.