• Bulletin of the Korean Chemical Society
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• v.31 no.7
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• pp.1920-1926
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• 2010

Yoon et $al.^1$ presented an approximate mathmatical model to describe ammonia removal from an experimental batch reactor system with gaseous headspace. The development of the model was initially based on assuming instantaneous equilibrium between ammonia in the aqueous and gas phases. In the model, a "saturation factor, $\beta$" was defined as a constant and used to check whether the equilibrium assumption was appropriate. The authors used the trends established by the estimated $\beta$ values to conclude that the equilibrium assumption was not valid. The authors presented valuable experimental results obtained using a carefully designed system and the model used to analyze the results accounted for the following effects: speciation of ammonia between $NH_3$ and $NH^+_4$ as a function of pH; temperature dependence of the reactions constants; and air flow rate. In this article, an alternative model based on the exact solution of the governing mass-balance differential equations was developed and used to describe ammonia removal without relying on the use of the saturation factor. The modified model was also extended to mathematically describe the pH dependence of the ammonia removal rate, in addition to accounting for the speciation of ammonia, temperature dependence of reactions constants, and air flow rate. The modified model was used to extend the analysis of the original experimental data presented by Yoon et $al.^1$ and the results matched the theory in an excellent manner.

• Coupled systems mechanics
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• v.5 no.3
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• pp.235-254
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• 2016

A numerical model for fluid-structure interactions (abbr. FSI) is presented in the context of sloshing effects in movable, partially filled tanks to improve understanding of interactions between the fluid and the dynamics of a tank flexibly attached to a vehicle. The purpose of this model is to counteract the penalizing impact of the added mass effect on classical partitioned FSI coupling scheme: the proposed investigation is based on an added mass corrected version of the classical strongly coupled partitioned scheme presented in (Song et al. 2013). Results show that this corrected version systematically allows convergence to the coupled solution. In the rare cases where convergence is already obtained, the corrected version significantly reduces the number of iterations required. Finally, it is shown that the convergence limit imposed by added mass effect for the non-corrected coupling scheme, is directly dependent on the aspect ratio of the fluid domain and highly related to the precision order of the temporal discretization scheme.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.638-641
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• 1995

The model-technology has been conduced to a large quantity of automobile and electric products. However, many problems in mold-technology have been solved through trial and error of experts. So it has given rise to overdesign of mold and generated other problems in production line. In this paper we choosed the lower-mold of a cool chamber in refrigerator as the model of the study and mass reduced overdesigned mold. In mass reduction process, several cases in plane processing error were selected for the sample case through FEM analysis & simplicated theory analysis and each case was evaluated for mass reduction.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.445-452
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• 1998

The dynamic performance design of catenary-pantograph system which collects current for the next generation Korean high speed train(KHST) was considered. Used was the same dynamic model of the catenary-pantograph system as that of TGV-K which will be introduced for Kyung-bu corridor. Using the model , sensitivity analysis fer design variables were made to improve dynamic performance of KHST system. The results of sensitivity analysis and performance improvement are as follows: (1) It was found that aerodynamic force, tension of contact wire, mass of contact strip, mass of supporting contact strip, mass of clamp, mass of steady arm, and stiffness of plunger were the design variables most influencing the dynamic performance of the system. (2) Pantograph with reductions of 20% aerodynamic force, 34% weight of supporting contact strip, 20% spring constant of plunger, and 34% equivalent mass of steady arm was very possible system for the KHST which will be running at maximum operating speed 350 km/h.

• Structural Engineering and Mechanics
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• v.82 no.2
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• pp.191-204
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• 2022

A three-mass vehicle model including one rigid mass and two unsprung masses is adopted to predict the vehicle-bridge interaction (VBI) and to establish the nonlinear coupled governing equations. To overcome the numerical instability and large computation problems concerning the vehicle-bridge system, the perturbation method is used to convert the nonlinear coupled governing equations into a set of linear uncoupled equations. Formulas for bridge's natural frequencies considering both the VBI and the dynamic responses of bridge and vehicle are proposed. Compared with the numerical results obtained by the Newmark-β method, the theoretical solutions for natural frequencies and dynamic responses are validated. The effects of the important factors of unsprung mass, vehicle damping, surface irregularity on the natural frequencies and dynamic responses of bridge and vehicle are discussed, based on the theoretical solutions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.213-214
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• 2010

• Journal of Sensor Science and Technology
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• v.16 no.3
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• pp.165-173
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• 2007

A differential floating mass transducer has been developed in Korea for fully implantable middle ear hearing devices (F-IMEHDs). In particular, the performance of a differential floating mass transducer (DFMT) is very important among the parts of the F-IMEHDs because the mechanical vibration generated by DFMT is delivered to the inner ear directly. In this paper, the electrical model is proposed to analyze the DFMT vibration characteristic using the mechanical model of the DFMT. The electrical model enables the simple analysis of DFMT vibration characteristics using a computer program. The proposed electrical model is simulated through PSpice as changing the values of passive elements in the electrical model. To verify the proposed model, the DFMT has been implemented on the basis of the simulated results and the experiment for vibration measurement has been carried out. Through the comparison, it is verified that the proposed model is useful to analyze the vibration characteristics of the DFMT.

• Tunnel and Underground Space
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• v.29 no.5
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• pp.318-331
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• 2019

A three-dimensional(3D) equivalent continuum modeling was performed to analyze hydraulic behavior of rock mass considering discontinuities by using DFN model and smeared fracture model. DFN model was generated by FLAC3D and smeared fracture model was applied by using FISH functions, which is built-in functions in FLAC3D, for equivalent continuum model of fractured rock mass. Comparative analysis with 3DEC, which is for discontinuum analysis, was conducted to verify reliability of equivalent continuum analysis by using FLAC3D. Similar results of hydraulic analysis under the same conditions could be achieved. Equivalent continuum analysis of fractured rock mass by using DFN model was implemented to compare with existing analytical methods for inflow into the tunnel.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.6
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• pp.483-495
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• 2008

The paper presents a numerical study to evaluate the phase velocities and attenuations of the average longitudinal and shear ultrasonic waves resulting from multiple scattering in fiber-reinforced composites. A computational procedure developed in this work is first used to produce a random, yet largely even distribution of fibers. Both the viscoelastic epoxy matrix and lossless randomly distributed graphite fibers are modeled using the mass-spring-dashpot lattice model, with no damping for the latter. By numerically simulating ultrasonic through-transmission tests using this direct model of composites, phase velocities and attenuations of the longitudinal and shear waves through the composite are found as functions of frequency or fiber concentration. The numerical results are observed to generally agree with the corresponding results in the literature. Discrepancies found in some detail aspects, particularly in the attenuation results, are also addressed.

• Structural Engineering and Mechanics
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• v.59 no.6
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• pp.1019-1035
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• 2016

This paper proposes a new foundation model called "Dynamic foundation model" for the dynamic analysis of plates on foundation subjected to a moving oscillator. This model includes a linear elastic spring, shear layer, viscous damping and the special effects of mass density parameters of foundation during vibration. By using finite element method and the principle of dynamic balance, the governing equation of motion of the plate travelled by the oscillator is derived and solved by the Newmark's time integration procedure. The accuracy of the algorithm is verified by comparing the numerical results with the other numerical results in the literature. Also, the effects of mass and damping ratio of system components, stiffness of suspension system, velocity of moving oscillator, and dynamic foundation parameters on dynamic responses are investigated. A very important role of these factors will be shown in the dynamic behavior of the plate.