• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.32-39
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• 2005

Recently, renewed interest on the scramjet engine has been demonstrated through the many international activities along the several Asia-Pacific countries. Here, a short review of current activities on supersonic combustion in a scramjet engine will be addressed followed by the discussions on the review of numerical simulation on supersonic combustion phenomena related with scramjet engine combustors and ram accelerator. Emphasis was put on the grid refinement, scheme, unsteadiness and phenomenological differences.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.2
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• pp.21-30
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• 2000

Numerical design optimization techniques are implemented for the improvement of the ram accelerator performance. The design object is to find the minimum 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 as design variables. The objective function and the constraints are linearized during the optimization process and gradient-based Simplex method and SLP(Sequential Linear Programming) have been employed. With the assumption of two dimensional inviscid flow for internal flow field, the analyses of the nonequilibrium chemical reactions for 8 steps 7 species have been performed. To determined the tube length, ram tube internal flow field is assumed to be in a quasi-steady state and the flow velocity is divided into several subregions with equal interval. Hence the thrust coefficients and accelerations for corresponding subregions are obtained and integrated for the whole velocity region. With the proposed design optimization techniques, the total ram tube length had been reduced 19% within 7 design iterations. This optimization procedure can be directly applied to the multi-stage, multi-premixture ram accelerator design optimization problems.

• 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 Korean Society of Combustion
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• v.5 no.1
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• pp.31-41
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• 2000

A numerical study was conducted to investigate the combustion phenomena of regular start and unstart processes based on ISL#s RAMAC 30 experiments with different diluent amounts in a ram accelerator. The initial projectile launching speed was 1800m/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with $5CO_2\;or\;4CO_2$. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1800m/s, as was found in the experiments using a steel-covered projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the regular start and unstart processes found in the experiments with an aluminum-covered projectile. The numerical results matched almost exactly to the experimental results. As a result, it was found that the regular start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.358-365
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• 2016

In this study, one-dimensional analysis under the assumption of an inviscid flow was conducted for the experiment initiated by the French-German Research Institute of Saint-Louis (ISL) in order to investigate the energy effect of aluminum combustion. Previous theoretical analysis based on the assumptions of isentropic compression and a constant specific heat derived by ISL claimed that the experiment was not affected by the heat of aluminum combustion. However, rigorous analysis in present investigation that considered the average properties behind the shock wave compression and temperature-dependent specific heat showed that the S225 experiment was partially affected by the aluminum combustion. The increase in heat due to aluminum combustion was estimated from the rigorous analysis.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2B
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• pp.1-10
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• 2005

TCP/IP protocols have been implemented in software program running on CPU in end systems. As the increased demand of fast protocol processing, it is required to implement the protocols in hardware, and Host Interface is responsible for communication between external CPU and the hardware blocks of TCP/IP implementation. The Host Interface follows AMBA AHB specification for the communication with external world. For control flow, the Host Interface behaves as a slave of AMBA AHB. Using internal Command/status Registers, the Host Interface receives commands from CPU and transfers hardware status and header information to CPU. On the other hand, the Host Interface behaves as a master for data flow. Data flow has two directions, Receive Flow and Transmit Flow. In Receive Flow, using internal RxFIFO, the Host Interface reads data from UDP FIFO or TCP buffer and transfers data to external RAM for CPU to read. For Transmit Flow, the Host Interface reads data from external RAM and transfers data to UDP buffer or TCP buffer through internal TxFIFO. TCP/IP hardware blocks generate packets using the data and transmit. Buffer Descriptor is one of the Command/Status Registers, and the information stored in Buffer Descriptor is used for external RAM access. Several testcases are designed to verify TCP/IP functions. The Host Interface is synthesized using the 0.18 micron technology, and it results in 173 K gates including the Command/status Registers and internal FIFOs.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.123-132
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• 2002

A numerical study was conducted to investigate the combustion phenomena of normal start and unstart processes based on ISL's RAMAC 30 experiments with different diluent amounts and fill pressures in a ram accelerator. The initial projectile launching speed was 1.8 km/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with 5 $CO_2$ or 4 $CO_2$. Experiments with same condition except for projectile surface material demonstrated that ignition was successful with an aluminum projectile, but no combustion was observed in case of a steel projectile. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1.8 km/s, as was found in the experiments using a steel projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the normal start and unstart processes found in the experiments with an aluminum projectile. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations coupled with a Baldwin-Lomax turbulence model and detailed chemistry reaction equations of $H_2/O_2/CO_2$ suitable for high-pressure gaseous combustion were considered. The governing equations were discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit, time accurate integration method. The numerical results matched almost exactly to the experimental results. As a result, it was found that the normal start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.83-91
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• 1996

A numerical study is carried out to examine the ignition and propagation process of detonation wave in SCRam-accelerator operating in superdetonative mode. The time accurate solution of Reynolds averaged Navier-Stokes equations for chemically reacting flow is obtained by using the fully implicit numerical method and the higher order upwind scheme. As a result, it is clarified that the ignition process has its origin to the hot temperature region caused by shock-boundary layer interaction at the shoulder of projectile. After the ignition, the oblique detonation wave is generated and propagates toward the inlet while constructing complex shock-shock interaction and shock-boundary layer interaction. Finally, a standing oblique detonation wave is formed at the conical ramp.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.12
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• pp.1609-1617
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• 2019

Described in this paper is a design of hardware accelerator for implementing public-key cryptographic protocols (PKCPs) based on Elliptic Curve Cryptography (ECC) and RSA. It supports five elliptic curves (ECs) over GF(p) and three key lengths of RSA that are defined by NIST standard. It was designed to support four point operations over ECs and six modular arithmetic operations, making it suitable for hardware implementation of ECC- and RSA-based PKCPs. In order to achieve small-area implementation, a finite field arithmetic circuit was designed with 32-bit data-path, and it adopted word-based Montgomery multiplication algorithm, the Jacobian coordinate system for EC point operations, and the Fermat's little theorem for modular multiplicative inverse. The hardware operation was verified with FPGA device by implementing EC-DH key exchange protocol and RSA operations. It occupied 20,800 gate equivalents and 28 kbits of RAM at 50 MHz clock frequency with 180-nm CMOS cell library, and 1,503 slices and 2 BRAMs in Virtex-5 FPGA device.