• Title/Summary/Keyword: piston effect

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Effect of Applying Pressure of High Pressure Diecasting Process Using Salt core (용탕단조 시 저온염코어 적용 가압력의 영향)

  • Lee, Jun-Ho;Moon, J.H.;Lee, Dock-Young
    • Journal of Korea Foundry Society
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    • v.28 no.3
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    • pp.136-140
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    • 2008
  • A new concept of salt core, a melting temperature of which is lower than the solidus temperature of cast alloy, was introduced to produced an integrated casting part having a complicated inner shape or requiring under-cut in high pressure die casting or squeeze casting process. The main goal of this study is to develop a new integrated net-shape forming technology using fusible core of lower melting temperature than that of a casting alloy. This integrated net-shape forming technology would be very successful and cost-effective for producing the integrated products having a complicated inner shape or requiring under-cut. The technology for measuring and evaluating a various property of fusible core such as a thermal conductivity and thermal expansion coefficient, melting temperature was established. Also, the work space can be cleaned without a pollution inducing products.

Geoacoustic Characteristics of Shelf Sediment in the South Sea and Southeastern Sea of Korea (남해 및 남동해역 대륙붕 퇴적물의 지음향 특성)

  • KIM Dae Choul;SEO Young Kyo;JUNG Ja Hun;KIM Gil Young
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.37 no.4
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    • pp.312-322
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    • 2004
  • Physical and geoacoustic properties of inner shelf sediment in the South and Southeastern Seas of Korea have been studied based on six piston core samples. The sediments are largely composed of homogeneous mud except the core from the southeasternmost part of the area. Both physical and geoacoustic properties and mean grain size are relatively uniform with sediment depth, suggesting little effect of sediment compaction and/or consolidation. Mean grain size appears to be the most Important variable to determine the physical and acoustic properties. In contrast, the attenuation shows more or less fluctuations. Correlations between physical properties and sediment texture show slight deviations from those of the compared data, caused by the difference of sedimentary processes, mineral composition, and the difference of measurement system. In particular, the velocity is lower (approximately 20-30 m/s) than that of the previous data measured in the same area. This is probably due to the difference in velocity measurement system (particularly, error by a length of sample). We propose new relationships for physical and geoacoustic characteristics of shelf sediment in the study area.

A Study of vibration Characteristics of Compressors with FEM model (유한요소 모델을 이용한 압축기의 진동특성에 관한 연구)

  • Ju, Jung-Ham;Hwang, Won-Gul;Choi, Gi-Seob;Ryu, Ki-O;SeoMoon, Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.11a
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    • pp.967-971
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    • 2004
  • Today, as the demands for home appliances are increasing, the understanding of noise and vibration characteristics have become more important. It is hard to control its vibration and noise characteristics, because its mechanical structure is very complex. In this study a model of reciprocating compressor is developed. Spring, frame, and LDT are modeled as flexible body, and the other parts are modeled as rigid. FEM model of frame is simplified in order to save the simulation time. We validated the simple model by comparing their natural frequencies and mode shapes. Motor torque is applied to a rotor, and the piston is subjected to a gas pressure. The vibrational characteristics of compressor is analyzed with LS-DYNA. Its results are compared with the simulation results of rigid body frame. The effect of LDT is also studied by comparing the vibration of frame with the results of simulation with no LDT.

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Development of Aerodynamic Thermal Load Element for Structural Design of Hypersonic Vehicle (극초음속 비행체의 구조설계를 위한 공력 열하중 요소 개발)

  • Kang, Yeon Cheol;Kim, Gyu Bin;Kim, Jeong Ho;Cho, Jin Yeon;Kim, Heon Ju
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.11
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    • pp.892-901
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    • 2018
  • An efficient aerodynamic thermal load element is developed to reflect the effect of coupled aero-thermo-elastic behaviors in the early design stage of hypersonic vehicle. To this aim, semi-analytic relationships depending on structural deformation are adopted for pressure and thermal load, and the element is formulated based on the relations. The proposed element is implemented in the form of ABAQUS user subroutine, and coupled finite element analysis is carried out to investigate the aero-thermo-elastic behaviors of control surface of hypersonic vehicle. Through the analysis, usefulness of the proposed aerodynamic thermal load element is identified.

The Vibration Effect by Induced Pulsation Pressure to the Fatigue Crack of the Dampener Fitting Welding Zone (항공기용 유압 펌프의 맥동 압력에 의한 감쇄기 용접부위 균열 개선 연구)

  • Shin, Jae Hyuk;Kim, Tae Hwan;Kang, Gu Heon;Ha, Do Jun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.7
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    • pp.677-687
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    • 2017
  • Aircraft can often be exposed to a variety of environments and vibrations such as engine, hydraulic pump, aerodynamic force. These may cause cracking and destruction of the mechanical structure and sub-components by high-cycle fatigue. The axial piston type pump which is usually applied to the aircraft hydraulic pump can be necessarily accompanied by the fluid pulsation by continuous rotation of the axial piston. The fatigue crack was identified at the dampener fitting welding zone to prevent vibration damping during the running of aircraft equipped with this type of pulsation hydraulic pump. In order to understand the root cause of this matter, fracture and component analyses were carried out and also integral type dampener fitting was applied to prevent recurrence of the crack as a subject of design improvements. Structural integrity stress analysis, fatigue analysis, qualification test and aircraft system equipped test was conducted to verify the design validity in application to integral type dampener fitting. The test results were sufficiently satisfactory with the demand lifetime of the material from the various types of test as conducted and the subject of design improvement in this study could be objectively evaluated that shall be applied to the operational aircraft.

EFFECT OF INTAKE PORT GEOMETRY ON THE IN-CYLINDER FLOW CHARACTERISTICS IN A HIGH SPEED D.I. DIESEL ENGINE

  • LEE K. H.;RYU I. D.;LEE C. S.;REITZ R. D.
    • International Journal of Automotive Technology
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    • v.6 no.1
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    • pp.1-8
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    • 2005
  • Recently, the HSDI (High Speed Direct Injection) diesel engine has been spotlighted as a next generation engine because it has a good potential for high thermal efficiency and fuel economy. This study was carried out to investigate the in-cylinder flow characteristics generated in a HSDI diesel engine with a 4-valve type cylinder head. The four kinds of cylinder head were manufactured to elucidate the effect of intake port geometry on the in-cylinder flow characteristics. The steady flow characteristics such as coefficient of flow rate $(C_{f})$, swirl ratio (Rs), and mass flow rate (m,) were measured by the steady flow test rig and the unsteady flow velocity within a cylinder was measured by PIV. In addition, the in-cylinder flow patterns were visualized by the visualization experiment and these results were compared with simulation results calculated by the commercial CFD code. The steady flow test results indicated that the mass flow rate of the cylinder head with a short distance between the two intake ports is $13\%$ more than that of the other head. However, the non-dimensional swirl ratio is decreased by approximately $15\%$. As a result of in-cylinder flow characteristics obtained by PIV and CFD calculation, we found that the swirl center was eccentric from the cylinder center and the position of swirl center was changed with crank angle. As the piston moves to near the TDC, the swirl center corresponded to the cylinder center and the velocity distribution became uniform. In addition, the results of the calculation are in good agreement with the experimental results.

Lubrication Characteristics of Micro-Textured Slider Bearing: Effect of Dimple Density (Micro-Texturing한 Slider Bearing의 윤활특성 : 딤플 밀도의 영향)

  • Park, Tae Jo;Lee, Joon Oh
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.4
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    • pp.437-442
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    • 2013
  • In recent times, surface texturing methods have been widely applied to reduce friction and improve the reliability of machine components such as parallel thrust bearings, mechanical face seals, and piston rings. In this study, a numerical analysis is carried out to investigate the effect of uniformly spaced hemispherical dimples on the lubrication characteristics of a slider bearing using a commercial computational fluid dynamics (CFD) code, FLUENT. The pressure distributions, load capacity, leakage flowrate, and friction force are strongly affected by the dimple diameter and the number of dimples. In particular, the load capacity and friction force decrease linearly with the dimple density whereas the leakage increases. These results can be used for designing the optimum dimple characteristics in order to improve the lubrication performance of slider bearings, for which further studies are required.

Lubrication Analysis of Infinite Width Slider Bearing with a Micro-Groove: Part 1 - Effect of Groove Position (미세 그루브가 있는 무한폭 Slider 베어링의 윤활해석: 제1보 - 그루브 위치의 영향)

  • Park, TaeJo;Jang, InGyu
    • Tribology and Lubricants
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    • v.35 no.6
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    • pp.376-381
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    • 2019
  • Surface texturing is widely applied to reduce friction and improve the reliability of machine elements. Despite extensive theoretical studies to date, most research has been limited to parallel thrust bearings, mechanical face seals, piston rings, etc. However, most sliding bearings have a convergent film shape in the sliding direction and the hydrodynamic pressure is mainly generated by the wedge action. The results of surface texturing on inclined slider bearings are largely insufficient. This paper is the first part of a recent study focusing on the effect of the groove position on the lubrication performances of inclined slider bearings. We model a slider bearing with one rectangular groove on a fixed pad and analyze the continuity and Navier-Stokes equations using a commercial computational fluid dynamics (CFD) code, FLUENT. The results show that the film convergence ratio and the groove position have a significant influence on the pressure and velocity distributions. There are groove positions to maximize the supporting load with the film convergence ratio and the groove reduces the frictional force acting on the slider. Therefore, the proper groove position not only improves the load-carrying capacity of the slider bearings but also reduces its frictional loss. The present results apply to various surface-textured sliding bearings and can lead to further studies.

Lubrication Analysis of Infinite Width Slider Bearing with a Micro-Groove: Part 2 - Effect of Groove Depth (미세 그루브가 있는 무한폭 Slider 베어링의 윤활해석: 제2보 - 그루브 깊이의 영향)

  • Park, TaeJo;Jang, InGyu
    • Tribology and Lubricants
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    • v.35 no.6
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    • pp.382-388
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    • 2019
  • It is currently well known that surface textures act as lubricant reservoirs, entrap wear debris, and hydrodynamic bearings, which can lead to certain increases in load-carrying capacities. Until recently, the vast majority of research has focused on parallel sliding machine components such as thrust bearings, mechanical face seals, piston rings, etc. However, most sliding bearings have a convergent film shape in the sliding direction and their hydrodynamic pressure is mainly generated by the wedge action. Following the first part of the present study that investigates the effect of groove position on the lubrication performances of inclined slider bearings, this paper focuses on the effects of groove depths and film thicknesses. Using a commercial computational fluid dynamics (CFD) code, FLUENT, the continuity and Navier-Stokes equations are numerically analyzed. The results show that the film thickness and groove depth have a significant influence on the pressure distribution. The maximum pressure occurs at the groove depth where the vortex is found and, as the depth increases, the pressure decreases. There is also a groove depth to maximize the supporting load with the film thickness. The friction force acting on the slider decreases with deeper grooves. Therefore, properly designed groove depths, depending on the operating conditions, can improve the load-carrying capacity of inclined slider bearings as compared to the bearings without a groove.

A CONTROLLED CYCLIC LOADING ON THE SURFACE TREATED AND BONDED CERAMIC: STAIRCASE METHOD

  • Yi, Yang-Jin
    • The Journal of Korean Academy of Prosthodontics
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    • v.46 no.3
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    • pp.298-306
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    • 2008
  • STATEMENT OF PROBLEM: Effect of surface treatment of ceramic under loading does not appear to have been investigated. PURPOSE: The aim of this study was to investigate the effect of surface treatment of esthetic ceramic, which is performed to increase the bonding strength, on the fracture stress under controlled cyclic loading condition. MATERIAL AND METHODS: Sixty 1.0 mm-thick specimens were made from Mark II Vitablocs (Vita Zahnfabrik, Germany) and divided into 3 groups: polished (control), sandblasted, and etched. Specimens of each group were bonded to a dentin analog material base including micro-channels to facilitate the flow of water to the bonding interface. Bonded ceramics were cyclically loaded with a flat-end piston in the water (500,000 cycles, 15Hz). Following completion of cyclic loading, specimens were examined for subsurface crack formation and subsequent stress was determined and loaded to next specimen by the staircase method according to the crack existence. RESULTS: There were significant differences of mean fatigue limit in the sandblasted (222.86 ${\pm}$ 23.42 N) and etched group (222.86 ${\pm}$ 14.16 N) when compared to polished group (251.43 ${\pm}$ 10.6 N) (P<.05; Wald-type pair-wise comparison and post hoc Bonferroni test). Of cracked specimens, surface treated group showed longer crack propagation after 24 hours. All failures originated from the radial cracking without cone crack. Fracture resistance of this study was very low and comparable to failure load in the oral cavity. CONCLUSION: Well controlled cyclic loading could induce clinically relevant cracks and fracture resistance of Mark II ceramic was relatively low applicable only to anterior restorations. Surface treatment of inner surface of feldspathic porcelain in the matsicatory area could influence lifetime of restorations.