• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.43-51
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• 1997

Steady and unsteady numerical simulations are conducted for the experiments performed to investigate the ram accelerator flow field by using the expansion tube facility in Stanford University. Navier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state assumption shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$+$O_2$+$17N_2$, it fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$+$O_2$+$12N_2$, mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. The experimental result is revealed to be an instantaneous result during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

• Journal of the Korea Society for Simulation
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• v.24 no.2
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• pp.19-29
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• 2015

M&S techniques are utilized for various purposes on the national defense, and its importance is increasing than ever. For analyzing RAM (Reliability, Availability and Maintainability) of weapon system, using M&S techniques can be more effective and practical way than deterministic approach, because M&S approach can consider uncertain variables and various constraints in the ILS (Integrated Logistics support) field. For design of ILS M&S, we first set up a purpose of M&S, attributes of real system and other similar ILS M&S tool. Then, we convert real system into model which consists of mathematical formula and logical expression. In this thesis, we introduce modeling procedures of M&S that describes total life cycle of 'OO guided weapon system' and the contents proposed in this paper can provide references for developing other M&S tool.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.33.1-33.1
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• 2018

Ram pressure stripping by intracluster medium (ICM) can play a crucial role in galaxy evolution in the high-density environment as seen by many examples of cluster galaxies. Although much progress has been made by direct numerical simulations of galaxies (or a galaxy) as a whole in a cluster environment, the interstellar medium (ISM) in galactic disks is not well resolved to understand responses of the ISM in details. In order to overcome this, we utilize the TIGRESS simulation suite that focuses on a local region of galactic disks and resolves key physical processes in the ISM with uniformly high resolution. In this talk, we present the results from the solar neighborhood TIGRESS model facing the ICM winds with a range of ram pressures. When ram pressure is weaker than and comparable to the ISM weight, the ICM winds simply reshape the ISM to the one-sided disk, but star formation rates remain unchanged. Although there exist low-density channels in the multiphase ISM that allow the ICM winds to penetrate through, the ISM turbulence quickly closes the channels and prevents efficient stripping. When ram pressure is stronger than the ISM weight, a significant amount of the ISM can be stripped away rapidly, and star formation is quickly quenched. While the low-density gas is stripped rapidly, star formation still occurs in the extraplanar dense ISM (1-2kpc away from the stellar disk). Finally, we quantify the momentum transfer from the ICM to the ISM using the mass-and momentum-weighted velocity distribution functions of each gas phase.

• Journal of Environmental Impact Assessment
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• v.20 no.6
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• pp.797-813
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• 2011

Frequently occurring flood and drought due to abnormal climate and global warming have increased the necessity of an effective water resources control and management of river flows. The various hydraulic structures are constructed in river as part of an effective water resources management. It is very important to analyse characteristics of flow according to installing hydraulic structures in this situations. The objective of this study is to investigate the hydraulic behaviors of flow considering affections of hydraulic structures using 2-D numerical model. To do this, both RMA-2 model and developed RAM2 model are used to analyse flow phenomena before and after installation of hydraulic structures in Nakdong river. As a result of, the water surface elevation at upstream regions increased about 22cm~66cm and the velocity around the structures sharply increased after installation of structures. The measures for the rise of water surface at upstream and local scour due to high velocity around the structures must be established when the structures is constructed.

• Journal of computational fluids engineering
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• v.5 no.2
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• pp.55-63
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• 2000

In this paper, the numerical study has been done for the improvement of the superdetonative ram accelerator performance and for the design optimization of the system. The objective function to optimize the premixture composition is the ram tube length, required to accelerate projectile from initial velocity V/sub 0/ to target velocity V/sub e/. The premixture is composed of H₂, O₂, N₂ and the mole numbers of these species are selected as design variables. RSM(Response Surface Methodology) which is widely used for the complex optimization problems is selected as the optimization technique. In particular, to improve the non-linearity of the response and to consider the accuracy and the efficiency of the solution, design space stretching technique has been applied. Separate sub-optimization routine is introduced to determine the stretching position and clustering parameters which construct the optimum regression model. Two step optimization technique has been applied to obtain the optimal system. With the application of stretching technique, we can perform system optimization with a small number of experimental points, and construct precise regression model for highly non-linear domain. The error compared with analysis result is only 0.01% and it is demonstrated that present method can be applied to more practical design optimization problems with many design variables.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.159-165
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• 2000

In this paper, numerical study has been done for the improvement of the superdetonative ram accelerator performance and for the design optimization of the system. The objective function to optimize the premixture composition is the ram tube length required to accelerate projectile from initial velocity $V_o$ to target velocity $V_e$. The premixture is composed of $H_2,\;O_2,\;N_2$ and the mole numbers of these species are selected at design variables. RSM(Response Surface Methodology) which is widely used for the complex optimization problems is selected as the optimization technique. In particular, to improve the non-linearity of the response and to consider the accuracy and efficiency of the solution, design space stretching technique has been applied. Separate sub-optimization routine is introduced to determine the stretching position and clustering parameters which construct the optimum regression model. Two step optimization technique has been applied to obtain the optimal system. With the application of stretching technique, we can perform system optimization with a small number of experimental points, and construct precise regression model for highly non-linear domain. The error to compared with analysis result is only $0.01\%$ and it is demonstrated that present method can be applied more practical design optimization problems with many design variables.

• Asian Pacific Journal of Cancer Prevention
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• v.17 no.4
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• pp.1773-1777
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• 2016

Diagnostic and therapeutic radiation fields are planned so as to reduce side-effects while maximising the dose to site but effects on healthy tissues are inevitable. Radiation causes strand breaks in DNA of exposed cells which can lead to chromosomal aberrations and cause malfunction and cell death. Several researchers have highlighted the damaging effects of high dose radiation but still there is a lacuna in identifying damage due to low dose radiation used for diagnostic purposes. Blood is an easy resource to study genotoxicity and to estimate the effects of radiation. The micronucleus assay and chromosomal aberration can indicate genetic damage and our present aim was to establish these with lymphocytes in an in vitro model to predict the immediate effects low dose radiation. Blood was collected from healthy individuals and divided into 6 groups with increasing radiation dose i.e., 0Gy, 0.10Gy, 0.25Gy, 0.50Gy, 1Gy and 2Gy. The samples were irradiated in duplicates using a LINAC in the radiation oncology department. Standard protocols were applied for chromosomal aberration and micronucleus assays. Metaphases were stained in Giemsa and 200 were scored per sample for the detection of dicentric or acentric forms. For micronuclei detection, 200 metaphases. Giemsa stained binucleate cells per sample were analysed for any abnormality. The micronuclei (MN) frequency was increased in cells exposed to the entire range of doses (0.1-2Gy) delivered. Controls showed minimal MN formation ($2.0%{\pm}0.05$) with triple MN ($5.6%{\pm}2.0$) frequency at the lowest dose. MN formation increased exponentially with the radiation dose thereafter with a maximum at 2Gy. Significantly elevated numbers of dicentric chromosomes were also observed, even at doses of 0.1-0.5Gy, compared to controls, and acentric chromosomes were apparent at 2Gy. In conclusion we can state that lymphocytes can be effectively used to study direct effect of low dose radiation.

• Korean Chemical Engineering Research
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• v.59 no.4
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• pp.644-651
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• 2021

Alkyl amines are widely used in various industries. Nowadays these are also used in CO₂ capture technology because amines react with CO₂ and remove it from the flue gas. To make the amines more compatible towards this technology, physico chemical properties may be altered by mixing with other solvents. In the present report, we measured the refractive properties of pure diisopropylamine (DIPA) (1) + isomeric butanol (2) at 298.15 K to 308.15 K. The 𝚫n values were positive for DIPA + n-butanol or sec-butanol or isobutanol or tert-butanol mixtures. The measured data was correlated with Redlich-Kister equation. The excess molar volume data were predicted from refractive index data using Nakata and Sakurai model. The experimental data were also predicted by various correlations, and the prediction capability of these correlations was reported through standard deviation. Further, the deviation in refractive index (𝚫n) data was interpreted by the consideration of specific molecular interactions between DIPA and isomeric butanol.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.157-164
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• 2012

When designing a multifunctional system consisting of many components performing many functions or missions, it is important to determine the reliability, availability, and maintainability (RAM) of the system and components, and we consider system availability to be the optimization criterion. For given intervals of mean time between failure (MTBF) and mean time to repair (MTTR) of the components, we want to determine the values of MTBF and MTTR for all components that satisfy the target availability. A heuristic method is proposed for finding near-optimal solutions through simulation. We also study numerical examples to check effects of model parameters on the optimal solutions.

• Electrical & Electronic Materials
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• v.10 no.4
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• pp.349-354
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• 1997

This paper aims at studying the improvement of test method for t-weight sensitive fault (t-wsf) detect. The development of RAM fabrication technology results in not only the increase at device density on chips but also the decrease in line widths in VLSI. But, the chip size that was large and complex is shortened and simplified while the cost of chips remains at the present level, in many cases, even lowering. First of all, The testing patterns for RAM fault detect, which is apt to be complicated , need to be simplified. This new testing method made use of Local Lower Bound (L.L.B) which has the memory with the beginning pattern of 0(l) and the finishing pattern of 0(1). The proposed testing patterns can detect all of RAM faults which contain stuck-at faults, coupling faults. The number of operation is 6N at 1-weight sensitive fault, 9,5N at 2-weight sensitive fault, 7N at 3-weight sensitive fault, and 3N at 4-weight sensitive fault. This test techniques can reduce the number of test pattern in memory cells, saving much more time in test, This testing patterns can detect all static weight sensitive faults and pattern sensitive faults in RAM.