• Title/Summary/Keyword: Shock reduction

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An Experimental Study on Installation of the Shielding Material to Reduce the Shock Noise of a Gun (화포소음 저감을 위한 차폐재 설치에 관한 실험적 연구)

  • Lee, Haesuk;Hong, Junhee
    • Journal of the Korea Institute of Military Science and Technology
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    • v.19 no.4
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    • pp.453-461
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    • 2016
  • The paper represents the experimental analysis of the shock noise of medium caliber guns when a projectile is passed through the shielding material. In the study, the shielding material was constructed and tested in three separate experiments. The shielding material was not installed for medium caliber gun in Case 1. A medium caliber gun was fully covered with shielding material in Case 2, and another one was put with shielding material near muzzle in Case 3. In each experiment, the experimental data was compared with each other. Results showed the firing shielding material achieved a significant noise reduction in $90^{\circ}$ to the noise source. Case 3 is confirmed to be better effective than Case 2 in the near field. But, the noise reduction in the far field is small in quantity due to the low frequency. The paper is considered that further study is necessary for the shielding material which can absorb a low frequency noise in the future.

Experimental study of compression waves propagating porous walls (다공벽을 전파하는 압축파의 실험적 연구)

  • Kim, Hui-Dong;Setoguchi, Toshiaki
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.12
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    • pp.4036-4043
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    • 1996
  • When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

Improved Detection of ${\gamma}-Irradiated$ Vibrio vulnificus after Heat and Cold Shock Treatment by Using Ethidium Monoazide Real-time PCR

  • Lee, Jung-Lim;Levin, Robert E.
    • Food Science and Biotechnology
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    • v.18 no.3
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    • pp.788-792
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    • 2009
  • Gamma $({\gamma})-irradiation$ can be used to control pathogens such as Vibrio vulnificus in seafood. The effects of irradiation on microbial cell populations (%) have been studied in order to develop detection methods for irradiated foods. The method used in this study was ethidium bromide monoazide (EMA) real-time polymerase chain reaction (PCR), using V. vulnificus specific primer, EMA, and $SYBR^{(R)}$ Green to discriminate between ${\gamma}-irradiated$ and non-irradiated cells. Confocal microscope examination showed that ${\gamma}-irradiation$ damaged portions of the cell membrane, allowing EMA to penetrate cells of irradidated V. vulnificus. ${\gamma}-Irradiation$ at 1.08 KGy resulted in log reduction ($-1.15{\pm}0.13$ log reduction) in genomic targets derived from EMA real-time PCR. The combination cold/heat shock resulted in the highest ($-1.74{\pm}0.1$ log reduction) discrimination of dead irradiated V. vulnificus by EMA real-time PCR.

Theoretical study on compression wave propagating in a sudden reduction duct (급축소관을 전파하는 압축파에 관한 이론적 연구)

  • Kim, Hui-Dong;Kim, Tae-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.1
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    • pp.89-98
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    • 1997
  • Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.

Enhanced Efficacy of the Commissural Transmission between Lateral Giants in the Sensitization of Crayfish Escape Behavior

  • C.Lee, Sun-Hee
    • The Korean Journal of Physiology
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    • v.29 no.2
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    • pp.291-299
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    • 1995
  • Lateral giant (LG)-mediated escape response of crayfish is sensitized by natural traumatic events. Such sensitization has previously been shown to be associated with increased transmission between primary afferents and sensory interneurons at the cholinergic synapse of LG escape reflex circuit. In the present study, it was firstly investigated as to whether transmission is also altered at other synapses of the LG-escape reflex circuit by traumatic shock-induced sensitization. Evidence that traumatic shock also directly affects the excitability of lateral giants is now provided by the finding that traumatic shock produces a significant reduction of the time needed for LG to recruit its contralateral homologue, which is defined as commissural delay. Octopamine, a naturally occurring neuromodulator in the crayfish nerve cord, has also been shown to enhance transmission at the cholinergic synapse between primary afferents and sensory interneurons, and has been conjectured to mediate sensitization. Like traumatic shock, $octopamine\;(10^{-5}-5{\times}10^{-4}\;M)$ also enhanced the efficacy of commissural transmission between lateral giants, as indicated by a significant reduction of commissural delay. This effect was blocked by an octopamine antagonist phentolamine, suggesting a specific action of octopamine on the octopamine receptor present on LGs. These observations suggest that both traumatic shocks and octopamine may cause a rather broad alteration in the excitability of the crayfish nervous system that contributes to the sensitization of the LG escape response.

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A Study on Balanced-Type Oscillating Mole Drainer (II) (Model Test For Vibration) (평형식진동탄환암거천공기의 연구(II) -모수실험 : 진동에 대하여-)

  • 김용환
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.17 no.4
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    • pp.3962-3969
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    • 1975
  • 1. When the frame of the experimental apparatus was directly fixed on the platform, result from the spectrum density analysis showed that the generated vibration frequecy of the system was nearly-same as the system's own characteristic vibration frequency, 80Hz, in the case of the forcing vibration frequency was 7.5 to 22.5Hz. The reduction ratio of acceleration by balanced type model compare to non-balanced type one was 26.66 percent. 2. When the frame of experimental apparatus was fixed on the platform with putting a shock absorbing rubber between the frame and the platform, the generated vibration frequency of the system was same as forcing vibration frequency. When either frequency or the amplitude of the forcing vibration was increased, the acceleration ratio was increased too. The average reduction ratio was resulted 44.77 per cent. It was concluded that this method of acceleration measurement(the method using a shock absorbing rubber) was a reaonable method, because actual machine will work under such condition. As the vibration frequency and aptitude were increased, the absolute magnitude of acceleration was increased. 3. unbalanced rotating parts, and unbalanced moment of inertia of links were supposed to be causing factors of residual vibration in spite of using the balanced type oscillating mole drainer. This fact suggested that the attachment of the counter weight on the rotating parts which satisfy the condition mw$.$rw=m0e, was necessary. And also, it was expected that the shock absorbing effect could be improved by putting the shock absorbing materials between the moving parts and their supports.

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Numerical Investigation for Multi-layer Shock Absorber to Improve Survivability of Fuze at High Impact (고충격에 신관의 생존성을 향상시키기 위한 다층 충격완충장치 전산해석 연구)

  • Soh, Kyoung Jae;Kim, Minkyum;Lee, Daehee
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.33 no.4
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    • pp.255-261
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    • 2020
  • This study proposes a method of constructing an effective shock absorber. The existing shock absorber is fabricated only with polyethylene; however, the new shock absorber comprises polyethylene on the outside and a high-density material on the inside. The shock was mostly reduced when the density difference between the inner and outer materials was large. Aluminum, titanium, and copper were chosen as the outer structure of two-layer. Shock reduction was most effective in copper with the highest density, and the maximum deceleration was reduced by 43% while the impulse was reduced by 51% in the proposed shock absorber than the traditional shock absorber. In the cases of four-layer and six-layer shock absorbers, the impulse was reduced, but the maximum deceleration was increased. The fuze must survive from the biggest shock and the remaining shock waves should not exceed the threshold. Thus, a two-layer structure shock absorber using polyethylene-copper was proposed.

The Characteristics of Electric Shock Accidents and Their Countermeasures for Portable Electrical Tools (이동형 전기기기의 감전재해 특성 및 그 대책)

  • Choi, Sang-Won
    • Journal of the Korean Society of Safety
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    • v.32 no.2
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    • pp.21-26
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    • 2017
  • According to the data of Korea Occupational Safety and Health Agency, electric shock accidents during recent 11 years exceeded more than 60% in architecture/other and construction work, the countermeasures for safety are required in the harsh environment of a construction site where moving electric machines and equipments are widely used. The establishment of countermeasure for insulation degradation and defect is required, in consideration of increasing trend for accidents caused by defective insulation among low voltage electrical installation each year. The aim of this study is to propose the policy about portable electrical tool standards and/or worker's safety standards for preventing electric shock accidents on safety workings, and is to develop the technology and the safety device to prevent electric shock for accident prevention reduction through experiments. It obtained the followings through this study; statistical data analysis of late about 10 years of electric shock-related industrial accidents analysis and portable electric tools; safety device development of 'device for testing continuous grounding and power shut-down' to prevent electric shock from portable electric tools. Furthermore, developed results and proposal in this study will help to prevent the electric shock accidents from portable electric tools and will be expected the utilization of policy formulation, educational data and field supplement of the safety device, and etc.

Study of the Weak Shock Wave Propagating through an Exhaust Pipe Silencer System (배기 소음기내를 전파하는 비정상 충격파의 수치해석)

  • Kweon, Y.H.;Kim, H.D.
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.462-467
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    • 2001
  • The present study addresses a computational work of the weak shock wave propagatings inside a silencer system of automobile exhaust pipe. Four different types of the silencer systems and the initial shock wave Mach number $M_s$ of $1.01\sim1.30$ are applied to investigate their effects on the noise reduction and the flow field in a silencer system. The results obtained from the present computational work are compared with the experimental results. The second order total variation diminishing (TVD) scheme is employed to solve the two dimensional, compressible, unsteady, Euler equations. The present computational results predict the experimental results with a quite good accuracy. Of the four silencer systems applied, the most desirable silencer system to reduce the peak pressure at the exit of the exhaust pipe is discussed.

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A Study on MR Insert for Shock Wave Attenuation (MR Insert 의 충격저감 성능 연구)

  • 강병우;김재환;최승복;김경수
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.121-126
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    • 2001
  • This paper presents the experimental study for the reduction of transmitted shock waves in smart structures incorporating MR insert. MR fluid is filled within the two aluminum layers and two piezoceramic disks are embedded on the host plate as a transmitter and a receiver of the shock wave. Pulse wave generated by the transmitter is transmitted to the receiver through the MR insert and the plate. By applying magnetic field to the MR insert, the amplitude of the transmitted shock wave is reduced remarkably. The attenuation performance is tested by changing the applied magnetic field on MR inserts in two ways: by changing angle of permanent rubber magnet from 90 to 5 with 5 decrements, by using electromagnet in which magnetic field is controllable. The propagating wave speed of MR insert is also investigated.

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