• Journal of KSNVE
• /
• v.8 no.2
• /
• pp.239-250
• /
• 1998

Traditionally, intake noise from internal combustion engine has not recevied much attention compared to exhaust noise. But nowadays, intake noise is a major contributing factor to automotive passenger compartment noise levels. The main objective of this paper is to identify the mechanism of generation, propagation and radiation of the intake noise. With a simplest geometric model, one of the main noise sources for the intake stroke is found to be the pressure surge, which is generated after intake valve closing. The pressure surge, which has the nonlinear acoustic behavior, propagates and radiates with relatively large amplitude. In this paper, unsteady compressible Navier-Stokes equations are employed for the intake stroke of axisymmetric model having a single moving cylinder and a single moving intake valve. To simulate the periodic motion of the piston and the valve, unsteady deforming mesh algorithm is employed and Thompson's non-reflecting boundary condition is applied to the radiation field. In order to resolve the small amplitude waves at the radiation field, essentially non-oscillatory(ENO) schemes with an artificial compression method (ACM) are used.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.2
• /
• pp.179-185
• /
• 2008

Simulating combustion tests have been performed to elucidate the effect of baffle gaps on the optimal damping characteristics in liquid rocket combustors where coaxial injectors are installed. Amplitude of pressure oscillation in model combustion chamber and the combustion stability margin are used to quantify the damping capacitance of baffles. Satisfactory agreement has been achieved with the results of cold acoustic tests. Present results have shown that the optimal gap for high acoustic damping capacity has also the large combustion stability margin in simulating combustion tests. Therefore, the present results can be utilized to determine the baffle length and optimal gap in full-scaled rocket combustors.

• Journal of Environmental Impact Assessment
• /
• v.21 no.5
• /
• pp.609-615
• /
• 2012

In recent years, the development of computer technique was possible to the simulation analysis of the structure caused by ground vibration. Generally, finite element method(FEM) has been used in these structural analysis. In this study, it was calculated to the vibration energy as measuring vibration waveform, and estimated about principal stress due to medium characteristics of the ground as processing dynamic analysis by the vibration energy. The results are as follows : Firstly, the principal stress distribution in all mediums was different due to a medium condition, and the principal stress at concrete medium was represented to difference due to physical characteristics. Secondly, the principal stress by time increasing was represented to maximum amplitude within 0.03 second. And also, the principal stress after maximum amplitude was very large at concrete medium, which was considered to be formed compression or tension range at a medium boundary. Thirdly, the variation of principal stress at concrete medium was represented in the order of RC medium, NC=H medium, NC=S medium. It was considered that the vibration energy propagated fast when a medium have a big elasticity and density.

• Steel and Composite Structures
• /
• v.22 no.2
• /
• pp.353-368
• /
• 2016

This paper extends our recent work on the fatigue behavior of stud shear connectors in steel and recycled tyre rubber-filled concrete (RRFC) composite beams. A series of 16 fatigue push-out tests were conducted using a hydraulic servo testing machine. Three different recycled tyre rubber contents of concrete, 0%, 5% and 10%, were adopted as main variable parameters. Stress amplitudes and the diameters of studs were also taken into consideration in the tests. The results show that the fatigue lives of studs in 5% and 10% RRFC were 1.6 and 2.0 times greater of those in normal concrete, respectively. At the same time, the ultimate residual slips' values of stud increased in RRFC to highlight its better ductility. The average ultimate residual slip value of the studs was found to be equal to a quarter of studs' diameter. It had also been proved that stress amplitude was inversely proportional to the fatigue life of studs. Moreover, the fatigue lives of studs with large diameter were slightly shorter than those of smaller ones and using larger ones had the risk of tearing off the base metal. Finally, the comparison between test results and three national codes was discussed.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.6 no.2
• /
• pp.97-104
• /
• 2015

Compared with a strong axial rigidity due to large intial tension, cable has a weak laterally flexural rigidity. A variety of dynamic loads such as traffic loads and wind loads etc. cause the cables to vibrate significantly and affect the mechanical properties and the performance of cables. Therefore, vibration reduction design is an urgent task to control the vibration of cable-supported bridges. Because a various kind of dampers have shown to reduce the amplitude and duration time of vibration of cable from measured date in field test, damper can be considered that it is effective device significantly to reduce the amplitude and duration time in vibration of cable. Vibration characteristics of cable can change according to manufacturing method and type of established form, and damper has been designed according to distribution of natural frequencies and vibration modes. In this study, numerical analysis is used to show the reduction effects of vibrations and present the design of damper for vibration reduction of cable.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.10a
• /
• pp.73-77
• /
• 2003

Stability rating of KSR-III rocket engine is conducted based on stability rating tests in the course of development of KSR-III rocket engine. Rocket engine is approved to have combustion stabilization ability when it can suppress the external perturbation or pressure oscillation with finite amplitude and recover the original stable combustion. Rocket engine in flight nay be perturbed with unexpectedly large amplitude and thus a designer should not only assure combustion stabilization ability of the engine but also quantify the stabilization capacity. For this, several quantitative parameters and their evaluation are introduced. To verify dynamic stability of KSR-III rocket engine, five stability rating tests have been conducted. Based on these test results, such parameters are quantified and thereby, the stabilization capacity of KSR-III rocket engine is evaluated.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.91.2-91.2
• /
• 2012

Kokubun (1983) reported the local time variation of normalized amplitude of sudden commencement (SC) with a strong day-night asymmetry at geosynchronous orbit with 81 SC events. Further careful inspection of Kokubun's local time distribution reveals that the normalized SC amplitudes in the prenoon sector are larger than those in the postnoon sector. That is, there is a morning-afternoon asymmetry in the normalized SC amplitudes. Until now, however, there are no studies on this SC-associated morning-afternoon asymmetry at geosynchronous orbit. Motivated by this previous observation, we investigate a large data set (422 SC events in total) of geosynchronous SC observations and confirm that the geosynchronous SC amplitudes is larger in the morning sector than in the afternoon sector. This morning-asymmetry is probably caused by the enhancement of partial ring current, which is located in the premidnight sector, due to solar wind dynamic pressure increase. We also examine the latitudinal and seasonal variations of the normalized SC amplitude. We find that the SC-associated geosynchronous magnetic field perturbations are dependent on the magnetic latitude and season of the year. This may be due to the location of the magnetopause and cross-tail currents enhanced during SC interval with respect to geosynchronous spacecraft position.

• Journal of computational fluids engineering
• /
• v.6 no.3
• /
• pp.32-40
• /
• 2001

Viscous solutions of supersonic jet impinging on a flat plate normal to the flow are simulated using three-dimensional Navier-Stokes solver. The jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. In the present study, the nozzle contour and the pressure ratio are held fixed, while the jet impinging distance is varied to illuminate the characteristics of the jet plume with the distance. As the plate is placed close to the nozzle at 3D high, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. Here D is the nozzle exit diameter. The amplitude of wall pressure fluctuations subsides as the distance increases, but the maximum mean pressure level at the plate is achieved when the distance is about 4D high. The frequency of the wall pressure is estimated at 6.0 kHz, 9.3 kHz, and 10.0 kHz as the impinging distance varies from 3D, 4D, to 6D, respectively.

• 한국전산유체공학회:학술대회논문집
• /
• 2007.10a
• /
• pp.127-133
• /
• 2007

This paper represents the numerical study on Taylor flow according to the radius ratio and the angular velocity for flow between tow cylinder. The numerical model is consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8 mm, the numerical parameters are angular velocity and radius ratio. The numerical method is compared with the experimental results by Wereley, and the results are very good agreement. The critical Taylor number is calculated by theoretical and numerical analysis, and the results is showed the difference about ${\pm}10\;%$. As $Re/Re_c$ is increased, Taylor vortex is changed to wavy vortex, and then the wave number for azimuthal direction is increased. Azimuthal wave according to the radius ratio is showed high amplitude and low frequence in case of small radius ratio, and is showed low amplitude and high frequence in case of large radius ratio.

• Advances in nano research
• /
• v.3 no.1
• /
• pp.29-37
• /
• 2015

In the current study, the nonlinear vibration properties of an embedded zigzag single-walled carbon nanotube (SWCNT) are investigated. Winkler-type model is used to simulate the interaction of the zigzag SWCNTs with a surrounding elastic medium. The relation between deflection amplitudes and resonant frequencies of the SWCNT is derived through harmonic balance method. The equivalent Young's modulus and shear modulus for zigzag SWCNT are derived using an energy-equivalent model. The amplitude - frequency curves for large-amplitude vibrations are graphically illustrated. The simulation results show that the chirality of zigzag carbon nanolube as well as surrounding elastic medium play more important roles in the nonlinear vibration of the single-walled carbon nanotubes.