• Title/Summary/Keyword: Propagation constant

Search Result 534, Processing Time 0.031 seconds

Acoustical Properties of Polyester Sound Absorbing Materials (폴리에스테르 흡음재의 음향특성)

  • 주경민;용호택;이동훈
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 2001.11b
    • /
    • pp.1347-1352
    • /
    • 2001
  • In this study, the acoustic properties of polyester sound absorbing materials with three different bulk densities were investigated by calculating and measuring the acoustic parameters in terms of characteristic impedance, propagation constant, and absorption coefficient. For the calculations, Delany and Bazley's empirical equation was used together with the experimentally obtained specific flow resistivities under steady flow conditions. For the experimental measurements, the well-known two-thickness method was accessed. The experimentally measured values of characteristic impedance and propagation constant were generally agreed well with the corresponding calculated values. Based on the comparisons between the calculations and measurements, it was found that the magnitude of the absorption coefficient was closely related to the characteristic impedance and the real part of the propagation constant. Especially, the maximum magnitude of the absorption coefficient was depended upon the imaginary part of the propagation constant indicating the phase change of the propagation constant.

  • PDF

A Study on the Fatigue Crack Propagation Behavior in the SB41 Welding Material (SB41용접재의 피로크랙 진전거동에 관한 연구)

  • 최병기;장경천
    • Transactions of the Korean Society of Machine Tool Engineers
    • /
    • v.11 no.2
    • /
    • pp.43-49
    • /
    • 2002
  • SB41 material is welded automatically and is investigated some effects of the welding residual stress in the growth and propagation of fatigue crack, so as to study the fatigue behaviour in the welding residual stress field. The summarized results are as follows; 1) In case of the load amplitude is constant, as the stress ratio is changing to 0.1, 0.33 and 0.5 the propagation life is constant but the growth life decreases. And than, when maximum load or minimum load is constant as the stress ratio increases the growth life and propagation life. 2) It was shown that fatigue crack propagation ratio da/dN was almost constant regardless of the stress ratio change at constant load amplitude and that the larger stress ratio, the slower was the fatigue crack propagation ratio. 3) The opening ratio U is influenced by $K_max$ but it isn't only the function of $K_max$ because data range is very large. 4) The fatigue life of the specimens on tensile compressive residual stress field was decreased and increased respectably more than that of the base metal.

A Study on the Fatigue Crack Growth Behavior in Residual Stress Field of the SS41 Welding Material (SS41 용접재의 잔류응력장내에서의 피로균열 성장거동에 관한 연구)

  • Choi, Byung-Ki
    • Journal of the Korean Society of Safety
    • /
    • v.17 no.1
    • /
    • pp.33-38
    • /
    • 2002
  • SS41 material is welded automatically and is investigated some effects of the welding residual stress on the growth and propagation of fatigue crack, so as to study the fatigue behaviour in the welding residual stress field. The summarized results are as follows; 1) In case of the load amplitude is constant, as the stress ration is changing to 0.1, 0.33 and 0.5 the propagation life is constant but the initiation life decreases. And than, when maximum load or minimum load is constant, s the stress ration increases the initiation life and propagation life. 2) It was shown that the fatigue crack propagation ratio da/dn was almost constant regardless of the stress ratio change at constant load amplitude and that the larger stress ratio, the slower was the fatigue crack propagation ratio. 3) The opening ratio U is influenced by $K_{max}$ but it isn't only the function of $K_{max}$ because data range is very large. 4) The fatigue life of the specimens on tensile compressive residual stress field was decreased and increased respectably more than that of the base metal.

Flame Propagation Characteristics of Propane-Air Premixed Mixtures (프로판-공기 예혼합기의 화염전파 과정에 관한 연구)

  • Bae, Choong-Sik
    • Journal of the Korean Society of Combustion
    • /
    • v.1 no.2
    • /
    • pp.21-29
    • /
    • 1996
  • Flame propagation characteristics of propane-air mixtures were experimentally investigated in constant-volume combustion chambers. Flame propagation process was observed as a function of mixture strength, initial mixture temperature and initial mixture pressure in quiescent mixtures. A cylindrical combustion chamber and a spherical combustion chamber contain a pair of parallel windows through which optical access into the chamber can be provided. Laser two beam deflection method was adopted to measure the local flame propagation, which gave information on the flame size and flame propagation speed. Pressure development was also measured by a piezoelectric pressure transducer to characterize combustion in quiescent mixtures. Burning velocity was calculated from flame propagation and pressure measurements. The effect of flow on flame propagation was also investigated under flowing mixture conditions. Laser two beam method was found to be feasible in measuring flame propagation of quiescent mixtures. Flame was observed to propagate faster with higher initial mixture temperature and lower initial pressure. Combustion duration was shortened in the highly turbulent flowing mixtures.

  • PDF

A Study on the Effects of Ignition Energy and Systems on the Flame Propagation in a Constant Volume Combustion Chamber (정적연소기에서 점화에너지와 점화장치가 화염전파속도에 미치는 영향에 관한 연구)

  • 송정훈;서영호;선우명호
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.9 no.1
    • /
    • pp.45-56
    • /
    • 2001
  • A constant volume combustion chamber is employed to investigate the initial flame kernel development and flame propagation of gasoline-air mixtures with various ignition systems, ignition energy and spark plug electrodes. To do this research, four ignition systems are designed and manufactured, and the ignition energy is controlled by varying the dwell time. Several kinds of spark plugs are also made to analyze the effects of electrodes on flame kernel development. The velocity of flame propagation is measured by the laser deflection method. The output laser beam from He-Ne laser is divided into three parallel beams by a beam splitter. The splitted beams pass through the combustion chamber. They are deflected when contacted with flame front, and the voltage signals from photodiodes change due to deflection. The results show that higher ignition energy raises the flame propagation speed especially under the fuel lean operation. The wider electrode gap, smaller electrode diameter and sharper electrode tip make the speed of the initial flame propagation faster. The speed of the initial flame propagation is affected by electrode material as well. Electrode material with lower melting temperature help the initial flame propagation.

  • PDF

A Stochastic Analysis of Crack Propagation Life under Constant Amplitude Loading (균일진폭 하중하에서의 확률론적 균열진전 수명해석)

  • 윤한용;양영순;윤장호
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.16 no.9
    • /
    • pp.1691-1699
    • /
    • 1992
  • The experimental results of fatigue crack propagation under constant amplitude loading show that intra-and inter-specimen variability exist. In this paper, a stochastic model for the estimation of mean and variance of crack propagation life is presented To take into account the intra-specimen variability, the material resistance against crack propagation is treated as an 1-dimensional spatial stochastic process, i. e. random field, varying along the propagation path. For the inter-specimen variability, C in paris equation is assumed to be a random variable. Compared with experimental results reported, the present method well estimate the variation in fatigue crack propagation life. And it is confirmed that the thicker the specimen thickness is, the less the variation of propagation life is.

Prediction of Fatigue Crack Propagation Life under Constant Amplitude and Overloading Condition (일정진폭 및 과대하중 하에서의 피로 균열 성장 수명 예측)

  • 이억섭;김승권
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.15 no.10
    • /
    • pp.113-119
    • /
    • 1998
  • Ship structures and aircraft structures are consisted of thin sheet alloy, so it is very important to understand the characteristics of fatigue crack propagation of that material and to establish the data base. The data for fatigue crack propagation behavior scatter very much even under identical experimental conditions with constant loading. The behavior of fatigue crack propagation under regular and irregular cyclic loadings is known to be highly affected by complicated factors such as plastic zone developed at the vicinity of crack tip and reduction of cross sectional area. In this paper, the controlled stress amplitude and overload fatigue crack propagation tests have been conducted to investigate the effect of varying factors such as plastic zone size near the crack tip and area reduction factor (AF) on the fatigue crack propagation behavior A better simulation of fatigue crack propagation behavior is found to be obtainable by using Wheeler and Willenborg models with AF effect.

  • PDF

Analysis of Combustion and Flame Propagation Characteristics of LPG and Gasoline Fuels by Laser Deflection Method

  • Lee, Ki-Hyung;Lee, Chang-Sik;Ryu, Jea-Duk;Park, Gyung-Min
    • Journal of Mechanical Science and Technology
    • /
    • v.16 no.7
    • /
    • pp.935-941
    • /
    • 2002
  • This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than 5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a grate effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.

Dynamic Stress Intensity Factor $K_{III}$ of Crack Propagating with Constant Velocity in Orthotropic Disk Plate Subjected to Longitudinal Shear Stress (길이방향의 전단응력을 받은 직교이방성 원판에 내재된 외부균열의 등속전파 응력확대계수 $K_{III}$)

  • 최상인
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.4 no.2
    • /
    • pp.69-79
    • /
    • 1996
  • Dynamic stress intensity factors are derives when the crack is propagating with constant velocity under longitudinal shear stress in orthotropic disk plate. General stress fields of crack tip propagating with constant velocity and least square method are used to obtain the dynamic stress intensity factor. The dynamic stress intensity factors of GLV/GTV=1(=isotropic material or transversely isotropic material) which is obtained in out study nearly coincides with Chiang's results when mode Ⅲ stress is applied to boundary of isotropic disk. The D.S.I.F. of mode Ⅲ stress is greater when α(=angle of crack propagation direction with fiber direction) is 90° than that when α is 0°. In case of a/D(a:crack length, D:disk diameter)<0. 58, the faster crack propagation velocity, the less D.S.I.F. but when crack propagation velocity arrive on ghear stress wave velocity, the D.S.I.F. but when crack propagation velocity arrive on shear stress wave velocity, the D.S.I.F. unexpectedly increases and decreases to zero.

  • PDF

A Study of the Propagation of Turbulent Premixed Flame Using the Flame Surface Density Model in a Constant Volume Combustion Chamber

  • Lee, Sangsu;Kyungwon Yun;Nakwon Sung
    • Journal of Mechanical Science and Technology
    • /
    • v.16 no.4
    • /
    • pp.564-571
    • /
    • 2002
  • Three-dimensional numerical analysis of the turbulent premixed flame propagation in a constant volume combustion chamber is performed using the KIVA-3V code (Amsden et. al. 1997) by the flame surface density (FSD) model. A simple near-wall boundary condition is eaployed to describe the interaction between turbulent premixed flame and the wall. A mean stretch factor is introduced to include the stretch and curvature effects of turbulence. The results from the FSD model are compared with the experimental results of schlieren photos and pressure measurements. It is found that the burned mass rate and flame propagation by the FSD model are in reasonable agreement with the experimental results. The FSD combustion model proved to be effective for description of turbulent premixed flames.