• Journal of computational fluids engineering
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• v.17 no.3
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• pp.75-86
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• 2012

We developed a preliminary CFD analysis methodology to predict a pressure build up due to hydrogen flame acceleration in the APR1400 IRWST on the basis of CFD analysis results for test data of hydrogen flame acceleration in a scaled-down test facility performed by Korea Atomic Energy Research Institute. We found out that ANSYS CFX-13 with a combustion model of the so-called turbulent flame closure and a model constant of A = 5.0, a grid model with a hexahedral cell length of 5.0 mm, and a time step size of $1.0{\times}10^{-5}$ s can be a useful tool to predict the pressure build up due to the hydrogen flame acceleration in the test results. Through the comparison of the simulated results with the test results, we found out that the proposed CFD analysis methodology enables us to predict the peak pressure within an error range of about ${\pm}29%$ for the hydrogen concentration of 19.5%. However, the error ranges of the peak pressure for the hydrogen concentration of 15.4% and 18.6% were about 66% and 51%, respectively. To reduce the error ranges in case of the hydrogen concentration of 15.4% and 18.6%, some uncertainties of the test conditions should be clarified. In addition, an investigation for a possibility of flame extinction in the test results should be performed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.2
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• pp.106-113
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• 2017

Attitude determination algorithms for aircraft and land vehicles use earth gravitational vector and geomagnetic vector; hence, magnetometers and accelerometers are employed. In dynamic situation, the output from accelerometers includes not only gravitational vector but also motional acceleration, thus it is hard to determine accurate attitude. The acceleration compensation method treated in this paper solves the problem to compensate the specific force vector for motional acceleration calculated by a GPS receiver. This paper analyzed the error from the corrected vector regarded as a constant by conventional acceleration compensation method, and improve the error by rederivation from measurements. The analyzed error factors and improvements by the proposed algorithm are verified by computer simulations.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.690-696
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• 2011

A number of conventional railway bridge is more than 2600. Non-ballast plate girder bridge is about 700 and this is 27% of all bridge numbers. Non-ballast plate girder has advantages that self load is more lighter than moving load and construction cost is more inexpensive than concrete bridge. But non-ballast plate girder has disadvantages that vibration and noise is bigger than concrete bridge. This study had analyzed behavior of non-ballast plate girder according to the arrangement of supports and driving conditions to review the proper arrangement of support. Measurements were performed in single line and disel locomotive of 7400type were used as test vehicle. The vehicle's driving conditions are as follows; Change of driving direction, Constant speed driving, Deceleration driving, Acceleration driving. Main measurement contents were horizontal displacement and vertical vibration acceleration in girder of vicinity support. Results of measurement are as follows; In case that a vehicle drives from fixed support to movable support, vertical vibration acceleration of the girder was smaller than opposition case.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.106-111
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• 2008

In this paper, study about property evaluation for the metal matrix composites fabricated by low pressure infiltration process. Aluminum alloy composite which is reinforced by Metal fiber preform was fabricated by low pressure casting process. Infiltration condition was changed the pressure infiltration time of 1 sec, 2 sec and 5 sec under a constant pressure of 0.4 MPa. The molten alloy completely infiltrated the FeCrSi metal perform regardless of the increase in the pressure acceleration time. The the porosity in the FeCrSi/AC8A composite was investigated. The porosity was reduced as the pressure acceleration time as shorter. The FeCrSi/AC8A composite was investigated the wear test for to know the relationship between Porosity and wear resistance. FeCrSi/AC8A composite at pressure acceleration time of 1sec is shown excellent wear resistance.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1018-1024
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• 2011

Liquid sloshing occurs when a partially filled liquid tank is subjected to undesirable external forces or acceleration/deceleration for positioning control. Installation of baffles is still the most popular way to suppress the sloshing, but recent successes of input shaping in reducing structural vibrations may give a possible alternative. We aim at investigating the applicability of input shaping to sloshing suppression by numerically solving fluid motions in a rectangular tank. The tank is partially filled with water and it is suddenly put into a sequence of horizontal motions of acceleration and constant speed. The flow is assumed to be two-dimensional, incompressible, and in viscid, and a VOF two-phase model is used to capture the free surface. Results show that the sloshing can be successfully suppressed by shaping the input, i.e., the velocity or acceleration profile of tank. Three different input shapers (ZII, ZVD, and two-mode convolved ZV shapers) are tested and compared in this study Among them, the convolved ZV shaper shows a best performance to eliminate the sloshing almost completely.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.4
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• pp.513-528
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• 2013

A floating Oscillating Water Column (OWC) wave energy converter, a Backward Bent Duct Buoy (BBDB), was simulated using a state-of-the-art, two-dimensional, fully-nonlinear Numerical Wave Tank (NWT) technique. The hydrodynamic performance of the floating OWC device was evaluated in the time domain. The acceleration potential method, with a full-updated kernel matrix calculation associated with a mode decomposition scheme, was implemented to obtain accurate estimates of the hydrodynamic force and displacement of a freely floating BBDB. The developed NWT was based on the potential theory and the boundary element method with constant panels on the boundaries. The mixed Eulerian-Lagrangian (MEL) approach was employed to capture the nonlinear free surfaces inside the chamber that interacted with a pneumatic pressure, induced by the time-varying airflow velocity at the air duct. A special viscous damping was applied to the chamber free surface to represent the viscous energy loss due to the BBDB's shape and motions. The viscous damping coefficient was properly selected using a comparison of the experimental data. The calculated surface elevation, inside and outside the chamber, with a tuned viscous damping correlated reasonably well with the experimental data for various incident wave conditions. The conservation of the total wave energy in the computational domain was confirmed over the entire range of wave frequencies.

• Journal of ILASS-Korea
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• v.1 no.4
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• pp.46-53
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• 1996

The present study is aiming at improving the performance of main nozzle of an air jet loom with a modified reed and auxiliary nozzles. The double coaxial pipe jets consisting of a central air jet and an annular air jet have been experimentally investigated. The duter jet has a potential core and a constant velocity. The inner jet through an inner long pipe is induced by the subatmospheric pressure near the inner nozzle edge, and the jet velocity of an inner pipe is always lower than that of a outer pipe. The static pressures of the main nozzle over a wide range of the nozzle tank pressure were measured, and the nozzle velocity and Mach numbers were analytically calculated. Experiment81 results indicate that the critical condition of Mach number of unity to occur at the two positions in a main nozzle; one of them is the needle tip and the other is the acceleration tube exit An increase in the tank pressure causes the critical throat condition to occur at the two positions above. The velocity of acceleration-tube exit is maximum at the critical length L* and flow patter in acceleration-tube over critical lengh remains unstable.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.67-74
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• 1982

The dynamic behaviour of an elastically supported finite beam subjected to an axial force and moving loads with acceleration is investigated. Within the Euler beam theory the solutions are obtained by using finite Fourier and Laplace transformation methods with respect to space and time variable. Integrations involved in the theoretical results are carried out by Simpson's rule. From the results of the theoretical analysis, it is evident that dynamic behaviour of the beam are affected remarkably by acceleration and axial force.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.3
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• pp.266-272
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• 2004

In this paper, an observer-based adaptive controller is proposed to control the longitudinal motion of vehicles. The standard gradient method will be used to estimate the vehicle parameters such as mass, time constant, etc. The nonlinear model between the driving force and the vehicle acceleration will be chosen to design the state observer for the vehicle velocity and acceleration. It will be shown that the proposed observer is exponentially stable, and that the adaptive controller proposed in this paper is stable by the Lyapunov function candidate. It will be proved that the errors of the relative distance, velocity and acceleration converge to zero asymptotically fast, and that the overall system is also asymptotically stable. The simulation results are presented to investigate the effectiveness of the proposed method.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2997-3002
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• 2007

A manipulator is operated for the motion of mechanical hands or arms by mechanical mechanism. When a cup including liquid inside is shifted by a manipulator, it is important to know how a free surface of the liquid moves. In this study, non-dimensional parameters have been found that affect the rise of the free surface in a cup moving with constant acceleration. The non-dimensional parameters are the dimensionless time, the ratio of inertia effect to vicous effect (Reynolds number), aspect ratio of the liquid inside the cup and acceleration ratio (Froude number). Through this study, the height of the free surface rise in a cup has been predicted. Generally the maximum rise of the free surface is dependent on the Reynolds number and Froude number strongly, but on the aspect ratio weakly. But the influence of the aspect ratio on the maximum rise of the free surface in not negligible in the range 10 < Re < 100.