• Title/Summary/Keyword: Critical Dynamic Pressure

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Control of Processing Conditions for Improvement of vibration Characteristics of Injection Molded Disk (사출성형 디스크의 진동특성 향상을 위한 공정조건 제어)

  • Sin Hyo-Chol;Nam Ji-Geun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.6 s.249
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    • pp.615-621
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    • 2006
  • Increased application of optical disks requires more improved dynamic stability of rotating disks. In this study, a new concept of controlling the processing conditions of injection molded disks was developed to improve vibration characteristics. The critical speed, which shows stiffness and dynamic stability of disk, is affected by the residual stress distribution; this varies as functions of distance from the gate and processing condition. The critical speed of disk was calculated with the initial stress taken into consideration, which was determined from injection molding simulation. Choosing melt temperature, mold temperature, filling speed and packing pressure as design parameters, critical speed is maximized with the method of response surface. It is shown that the stability of injection molded disk has been improved for the new condition obtained as a result of the study proposed.

Seismic Safety Evaluation of Concrete Gravity Dams Considering Dynamic Fluid Pressure (동수압을 고려한 콘크리트 중력식 댐의 내진안전성 평가)

  • Kim, Yoog-Gon
    • Journal of the Korean Society of Safety
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    • v.21 no.1 s.73
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    • pp.120-132
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    • 2006
  • Seismic safety evaluation of concrete gravity dams is very important because failure of concrete gravity dam may incur huge loss of life and properties around the dam as well as damage to dam structure itself. Recently, there has been growing much concerns about earthquake resistance or seismic safety of existing concrete gravity darns designed before current seismic design provisions were implemented. This research develops the dynamic fluid pressure calculation using 'added mass simulation'. The actual analysis using structural analysis package was performed. According to the analysis results, the vibration which is transverse to water flow seems to be very critical depending on the shape of the dam.

A Study on the Dynamic Stress Analysis of an Engine Block using Flexible-body Dynamic Analysis (유연체 동역학적 해석을 이용한 엔진블록의 동응력 해석에 관한 연구)

  • Son, Chang-Su;Cheon, Ho-Jeong;Seong, Hwal-Gyeong;Yoon, Keon-Sik
    • Journal of the Korean Society for Precision Engineering
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    • v.28 no.7
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    • pp.805-813
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    • 2011
  • The dynamic stress of the diesel engine block is analyzed by using flexible-body dynamic analysis. Multiple loadings including the pressure load due to gas combustion, thermal load, and dynamic load are considered. Thermal load is assumed constant, however, pressure load and dynamic load are treated as time dependent. The present work is focused on the dynamic stress analysis, especially on finding critical points of the engine block. The analysis model includes four parts - engine block, generator, bed, and mounts. On the other hand, crank shaft, pistons, and main bearings are excluded from the model. However, their dynamic effects are applied by dynamic forces, obtained in the separate analysis. Dynamic stress is found by using flexible body dynamic analysis, and compared to the measured data.

Experimental and numerical investigation of composite conical shells' stability subjected to dynamic loading

  • Jalili, Sina;Zamani, Jamal;Shariyat, M.;Jalili, N.;Ajdari, M.A.B.;Jafari, M.
    • Structural Engineering and Mechanics
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    • v.49 no.5
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    • pp.555-568
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    • 2014
  • In this article, stability of composite conical shells subjected to dynamic external pressure is investigated by numerical and experimental methods. In experimental tests, cross-ply glass woven fabrics were selected for manufacturing of specimens. Hand-layup method was employed for fabricating the glass-epoxy composite shells. A test-setup that includes pressure vessel and data acquisition system was designed. Also, numerical analyses are performed. In these analyses, effect of actual geometrical imperfections of experimental specimens on the numerical results is investigated. For introducing the imperfections to the numerical models, linear eigen-value buckling analyses were employed. The buckling modes are multiplied by very small numbers that are derived from measurement of actual specimens. Finally, results are compared together while a good agreement between results of imperfect numerical analyses and experimental tests is observed.

Successful High Flow Nasal Oxygen Therapy for Excessive Dynamic Airway Collapse: A Case Report

  • Park, Jisoo;Lee, Yeon Joo;Kim, Se Joong;Park, Jong Sun;Yoon, Ho Il;Lee, Jae Ho;Lee, Choon-Taek;Cho, Young-Jae
    • Tuberculosis and Respiratory Diseases
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    • v.78 no.4
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    • pp.455-458
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    • 2015
  • Excessive dynamic airway collapse (EDAC) is a disease entity of excessive reduction of the central airway diameter during exhalation, without cartilage collapse. An 80-year-old female presented with generalized edema and dyspnea at our hospital. The patient was in a state of acute decompensated heart failure due to pneumonia with respiratory failure. We accordingly managed the patient with renal replacement therapy, mechanical ventilation and antibiotics. Bronchoscopy confirmed the diagnosis of EDAC. We scheduled extubation after the improvement of pneumonia and heart condition. However, extubation failure occurred due to hypercapnic respiratory failure with poor expectoration. Her EDAC was improved in response to high flow nasal oxygen therapy (HFNOT). Subsequently, the patient was stabilized and transferred to the general ward. HFNOT, which generates physiologic positive end expiratory pressure (PEEP) effects, could be an alternative and effective management of EDAC. Further research and clinical trials are needed to demonstrate the therapeutic effect of HFNOT on EDAC.

Investigation of hyperbolic dynamic response in concrete pipes with two-phase flow

  • Zheng, Chuanzhang;Yan, Gongxing;Khadimallah, Mohamed Amiine;Nouri, Alireza Zamani;Behshad, Amir
    • Advances in concrete construction
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    • v.13 no.5
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    • pp.361-365
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    • 2022
  • The objective of this study is to simulate the two-phase flow in pipes with various two-fluid models and determinate the shear stress. A hyperbolic shear deformation theory is used for modelling of the pipe. Two-fluid models are solved by using the conservative shock capturing method. Energy relations are used for deriving the motion equations. When the initial conditions of problem satisfied the Kelvin Helmholtz instability conditions, the free-pressure two-fluid model could accurately predict discontinuities in the solution field. A numerical solution is applied for computing the shear stress. The two-pressure two-fluid model produces more numerical diffusion compared to the free-pressure two-fluid and single-pressure two-fluid models. Results show that with increasing the two-phase percent, the shear stress is reduced.

A simulation study on the dynamics of an antiskid brake systems for automotive vehicles (자동차용 미끄럼 방지 제동 장치의 동특성에 관한 시뮬레이션 연구)

  • 김경훈;조형석;홍예선
    • 제어로봇시스템학회:학술대회논문집
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    • 1988.10a
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    • pp.315-320
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    • 1988
  • This paper considers modelling and control of ABS(Anti-skid Brake System) which avoids dangerous wheel locking due to excessive brake pressure during the vehicle braking. The brake pressure is controlled by on and off's of solenoid valves via the variation of the wheel circumferential deceleration measured using tacho-sensors. The dynamic model between the brake pressure and the wheel acceleration of a vehicle is mathematically derived. The computer simulation shows that the threshold value of the on-off control is critical to the performance of the ABS.

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Local dynamic buckling of FPSO steel catenary riser by coupled time-domain simulations

  • Eom, T.S.;Kim, M.H.;Bae, Y.H.;Cifuentes, C.
    • Ocean Systems Engineering
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    • v.4 no.3
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    • pp.215-241
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    • 2014
  • Steel catenary riser (SCR) is a popular/economical solution for the oil/gas production in deep and ultra-deep water. The behavioral characteristics of SCR have a high correlation with the motion of floating production facility at its survival and operational environments. When large motions of surface floaters occur, such as FPSO in 100-yr storm case, they can cause unacceptable negative tension on SCR near TDZ (touch down zone) and the corresponding elastic deflection can be large due to local dynamic buckling. The generation, propagation, and decay of the elastic wave are also affected by SCR and seabed soil interaction effects. The temporary local dynamic buckling vanishes with the recovery of tension on SCR with the upheaval motion of surface floater. Unlike larger-scale, an-order-of-magnitude longer period global buckling driven by heat and pressure variations in subsea pipelines, the sub-critical local dynamic buckling of SCR is motion-driven and short cycled, which, however, can lead to permanent structural damage when the resulting stress is greatly amplified beyond the elastic limit. The phenomenon is extensively investigated in this paper by using the vessel-mooring-riser coupled dynamic analysis program. It is found that the moment of large downward heave motion at the farthest-horizontal-offset position is the most dangerous for the local dynamic buckling.

Dynamic Characteristics and Instability of Submerged Plain Journal Bearings in accordance with the Cavitation Model (공동현상 모델에 따른 침수형 평면 저널베어링의 동특성 및 회전 안정성에 대한 연구)

  • Moonho Choi
    • Tribology and Lubricants
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    • v.39 no.4
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    • pp.139-147
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    • 2023
  • Cavitation phenomena observed during the operation of a submerged plain journal bearing (PJB) can affect bearing performance parameters such as dynamic coefficients, whirl frequency ratio, and critical mass. This study presents numerical solutions of the Reynolds equation for steadily and dynamically loaded submerged PJBs with half-Sommerfeld (HS), Reynolds, and Jakobsson-Floberg-Olsson (JFO) cavitation models when the supply pressure is larger or equal to the cavitation pressure. The loads at various eccentricity ratios are identical; however, the attitude angle is approximately 6% smaller when the eccentricity ratio is between 0.2 and 0.7 and the JFO model is used, compared to that when the Reynolds model is used. Dynamic coefficients obtained with the HS and Reynolds model show good agreement with each other, except for kxz, which is sensitive to changes in the force normal to the rotor weight, and is attributed to the difference in the attitude angle obtained with each cavitation model. Stiffness coefficients are determined using the pressure distribution in the film, and therefore, when the JFO model is used, the direct stiffness coefficients are affected and show opposite signs for most eccentricity ratios. The mass-conservative JFO model can predict at least a 30% smaller critical mass compared to that using the HS and Reynolds models. Thus, the instability analysis results can change based on the cavitation model used in a submerged PJB. The results of this research indicate that the JFO model should be used when designing a rotor system supported by submerged PJBs.

A Study on the Dynamic Characteristics of Axial Vibration Damper for Two Stroke Low Speed Diesel Engine (저속 2행정 디젤엔진의 종진동 댐퍼 동특성에 관한 연구)

  • 이돈출;김정렬;김의간
    • Journal of Advanced Marine Engineering and Technology
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    • v.18 no.2
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    • pp.113-121
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    • 1994
  • Since two oil shocks in 1970s, all of engine makers have persevered in their efforts to reduce specific fuel consumption and to increase engine power rate as much as possible in marine diesel engines. As a result, the maximum pressure in cylinders of these engines has been continuously increased. It causes direct axial vibration. The axial stiffness of crank shaft is low compared to old types of engine models by increasing the stroke/bore ratio and its major critical speed might occur within engine operation range. An axial damper, therefore, needs to be installed in order to reduce the axial vibration amplitude of the crankshaft. Usually the main critical speed of axial vibration for the propulsion shafting system with a 4-8 cylinder engine exists near the maximum continuous revolution(MCR). In this case, when the damping coefficient of the damper is increased within the allowance of the structural strength, its stiffness coefficient is also increased. Therefore, the main critical speed of axial vibration can be moved beyond the MCR. It has the same function as a conventional detuner. However, in the case of a 9-12 cylinder engine, the main critical speed of axial vibration for the propulsion shafting system exists below the MCR and thus the critical speed cannot be moved beyond the MCR by using an axial damper. In this case, the damping coefficient of an axial damper should be adjusted by considering the range of engine revolution, the location and vibration amplitude of the critical speed, the fore and aft vibration of the hull super structure. It needs to clarify the dynamic characteristics of the axial vibration damper to control the axial vibration appropriately. Therefore authors suggest the calculation method to analyse the dynamic characteristics of axial vibration damper. To confirm the calculation method proposed in this paper, it is applied to the propulsion shafting system of the actual ships and satisfactory results are obtained.

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