• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.3
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• pp.230-237
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• 2020

In order to design a diesel engine system and predict its performance, it is necessary to analyze the gas flow of the intake and exhaust system. A gas flow analysis in three-dimensional (3D) format needs a high-resolution workstation and enormous time for analysis. Therefore, the method of characteristics (MOC) was used for a gas flow analysis with a fast calculation time and a low-resolution workstation. An experiment was conducted on a single cylinder diesel engine to measure pressure in cylinder, intake pipe and exhaust pipe. The one-dimensional (1D) gas flow was analyzed under the same conditions as the experiment. The engine speed, valve timing and compression ratio were the same conditions and the intake pressure was inputted as the experimental results. Bent pipe such as an exhaust port that cannot be realized in 1D was omitted. As results of validation, the cylinder pressure showed accuracy, but the exhaust pipe pressure exhibited inaccuracy. This is considered as an error caused by the failure to implement a bent pipe such as an exhaust port. When analyzed in 3D, calculation time required 61 hours more based on a model of this study. In the future, we intend to implement a bent pipe that cannot be realized in 1D using 3D and prepare a method to supplement reliability by using 1D-3D coupling.

• Geomechanics and Engineering
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• v.14 no.6
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• pp.589-600
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• 2018

For foundations in permafrost regions, the displacement characteristics are uncertain because of the randomness of temperature characteristics and mechanical parameters, which make the structural system have an unexpected deviation and unpredictability. It will affect the safety of design and construction. In this paper, we consider the randomness of temperature characteristics and mechanical parameters. A stochastic analysis model for the uncertain displacement characteristic of foundations is presented, and the stochastic coupling program is compiled by Matrix Laboratory (MATLAB) software. The stochastic displacement fields of an embankment in a permafrost region are obtained and analyzed by Neumann stochastic finite element method (NSFEM). The results provide a new way to predict the deformation characteristics of foundations in permafrost regions, and it shows that the stochastic temperature has a different influence on the stochastic lateral displacement and vertical displacement. Construction disturbance and climate warming lead to three different stages for the mean settlement of characteristic points. For the stochastic settlement characteristic, the standard deviation increases with time, which imply that the results of conventional deterministic analysis may be far from the true value. These results can improve our understanding of the stochastic deformation fields of embankments and provide a theoretical basis for engineering reliability analysis and design in permafrost regions.

• Journal of Cadastre & Land InformatiX
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• v.46 no.1
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• pp.59-74
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• 2016

The collapses of retaining walls or embankments, the soil erosion and landslides around urban areas are occurring by heavy rainfalls because of the recent climate change. This study conducts the soil erosion modeling, while applying the spatial information such as soil maps, DEM and landcover maps to the RUSLE model. Especially this study draws up the soil erosion grade map and the unit soil erosion grade map by parcels through coupling the soil erosion with the cadastral map, and by that can calculate the number of parcels by soil erosion grades. Also the sediment disaster information system based on the mobile GIS is developed to identify the soil erosion grades of site in the urban plannings and the construction fields. The sediment disaster information system can identify the present conditions of the registers of lands, buildings and roads, and confirm the RUSLE factors, the soil erosion, the sediment disaster grades by parcels. Also it is anticipated that this system can support the sediment disaster work of site effectively through searching the locations and attributes of the specific parcels by Administrative Dong and the soil erosion grades.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.29-35
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• 2010

This paper studies causes of the L-1 blade damage of a low pressure turbine, which was found during the scheduled maintenance, in 500 MW fossil power plants. Many failures of turbine blades are caused by the coupling of aerodynamic forcing with bladed-disk vibration characteristics. In this study the coupled vibration characteristics of the L-1 turbine bladed-disk in a fossil power plant is shown for the purpose of identifying the root cause of the damage and confirming equipment integrity. First, analytic and experimental modal analysis for the bladed-disk at zero rpm as well as a single blade were performed and analyzed in order to verify the finite element model, and then steady stresses, natural frequencies and corresponding mode shapes, dynamic stresses were calculated for the bladed-disk under operation. Centrifugal force and steady steam force were considered in calculation of steady and dynamic stress. The proximity of modes to sources of excitation was assessed by means of an interference diagram to examine resonances. In addition, fatigue analysis was done for the dangerous modes of operation by a local strain approach. It is expected that these dynamic characteristics will be used effectively to identify the root causes of blade failures and to perform prompt maintenance.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.1
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• pp.51-57
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• 2009

In this study, a new topology optimization method is developed to design heat-dissipating structure with forced convection. To cool down electrical devices or mechanical machines, two types of convection models have been widely used: the natural convection model with a large Archimedes number and the forced convection with a small Archimedes number. In these days, lots of engineering application areas such as electrochemical conversion devices (Fuel cell) or rocket propulsion engines adopt the forced convection to dissipate the generated heat. Therefore, to our knowledge, it becomes an important issue to design flow channels inside which the generated heat dissipate. Thus, this paper studies optimal topological designs considering fluid-heat interactions. To consider the effect of the advection in the heat transfer problem, the incompressible Navier-stokes equation is solved. This paper numerically studies the coupling phenomena and presents optimal channel design considering forced convection.

• Journal of the Korean Geotechnical Society
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• v.32 no.6
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• pp.17-26
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• 2016

Characteristic behaviors of geo-structure during freezing and thawing process have to be understood based on fundamental knowledge on phase change in porous soil and interaction between soil and structure. Inversion analysis using published one-dimensional soil freezing tests was conducted to suggest a mechanical model to consider an effect of the ice saturation on Young's modulus. Silty soil was more sensitive to temperature than weathered granite soil and sand, and weathered granite soil was more affected by initial water saturation in stiffness decrease than silty soil. Numerical simulations on chilled gas pipeline showed that shielding effect from surrounding frozen zone around the pipe decreases impact from external load onto the pipe. And a pipe installed in sand backfill showed more heaving due to relatively low stiffness of sand during freezing than that of surrounding in-situ weather granite soil. However, it had more stable stress condition due to effective stress redistribution from external load.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.359-365
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• 2018

Herein, electromagnetic shielding structures to reduce the external noise coupling to printed spiral coils (PSCs) and a design method for improving the bandwidth of shielded PSCs have been proposed. It has been demonstrated that the bandwidth of shielded PSCs is limited due to the parasitic capacitance between the coils and the shielding structures and is confirmed by the transfer function simulation of the shielded PSCs with a transmission line as the radio-frequency interference noise source. A design method for the bandwidth improvement of the shielded PSCs has been proposed based on the equivalent circuit model analysis and the case studies depending on PSC designs with a three-dimensional field simulation. With the design method, an optimized shielded PSC design has been presented and successfully confirmed by experimental verification in that the optimized design results in a significant bandwidth improvement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1967-1974
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• 1991

When the functional electrical stimulation is employed to recover mobility to the plegic, it is very important to understand functions of the selected muscles. I have investigated how a muscle acts to accelerate the body segments, since the body segements are connected by joints so that contraction of a muscle not only rotates the segments to which it is attached but also causes other segments to rotate by creation a reaction force at every joint, which is called the inertial coupling. I found that a single-joint muscle always acts to accelerate the spanned joint in the same direction as the joint torque produced by the muscle. However, a double-joint muscle can act to accelerate the spanned joint in the opposite direction to the joint torque produced by the muscle depending on (1) the body position, (2) the body-segmental parameters, and (3) the type of the movement. Investigating the condition number of the inertia matrix of the body-segmental model gave us some insights into how controllable the body-segmental system is for different values of the factors mentioned above. The results suggested that the upright position is the most undesirable position to independently control the three segments(trunk, thigh and shank) and that the controllability is the most sensitive to variation of the shank length and the trunk mass, which implies that accuracy is required particularly when we estimate these two body-segmental parameters before the paralyzed muscles are innervated by using electrical stimulation.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.1
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• pp.39-45
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• 2012

In the standard CFD code, Lagrangian-Eulerian method is very popular to simulate the liquid spray penetrating into gaseous phase. Though this method can give a simple solution and low computational cost, it have been reported that the Lagrangian spray models have numerical grid dependency, resulting in serious numerical errors. Many researches have shown the grid dependency arise from two sources. The first is due to unaccurate prediction of the droplet-gas relative velocity, and the second is that the probability of binary droplet collision is dependent on the grid resolution. In order to solve the grid dependency problem, the improved spray models are implemented in the KIVA-3V code in this study. For reducing the errors in predicting the relative velocity, the momentum gain from the gaseous phase to liquid particles were resolved according to the gas-jet theory. In addition, the advanced algorithm of the droplet collision modeling which surmounts the grid dependency problem was applied. Then, in order to validate the improved spray model, the computation is compared to the experimental results. By simultaneously regarding the momentum coupling and the droplet collision modeling, successful reduction of the numerical grid dependency could be accomplished in the simulation of the high-pressure injection diesel spray.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.583-591
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• 2014

The mathematical modeling on the free vibration and stability of a multi-stepped shaft of turbo compressor is performed in this study. The multi-stepped shaft is modeled as a non-uniform Timoshenko beam supported by anisotropic bearings. It is assumed that the shaft is spinning with constant speed about its longitudinal axis and subjected to a conservative axial force induced by front and rear impellers attached to the shaft. The structural model incorporates non-classical features such as transverse shear and rotary inertia. A structural coupling between vertical and lateral motions is induced by Coriolis acceleration terms. The governing equations are derived via Hamilton's variational principle and the equations are transformed to the standard form of an eigenvalue problem. The implications of combined gyroscopic effect, conservative axial force, bearing stiffness and damping are revealed and a number of pertinent conclusions are outlined. In this study analytical results are compared with those from ANSYS finite element analysis and experimental modal testing.