• International Journal of Naval Architecture and Ocean Engineering
• /
• v.3 no.4
• /
• pp.286-292
• /
• 2011

In order to design a shear coaxial injector of solid particles for underwater propulsion system, basic experiments on gas-liquid shear coaxial injector are necessary. In the gas-liquid coaxial injector self-pulsation usually occurs with an intense scream. When self-pulsation occurs, mass flow rate oscillation and intense scream are detected by the interactions between the liquid and gas phase. Self-pulsation must be suppressed since this oscillation may cause combustion instabilities. Considerable research has been conducted on self-pulsation characteristics, but these researches are conducted in swirl coaxial injector. The main objective of this research is to understand the characteristics of self-pulsation in shear coaxial injector and reveal the mechanism of the phenomenon. Toward this object, self-pulsation frequency and spray patterns are measured by laser diagnostics and indirect photography. The self-pulsation characteristics of shear coaxial injector are studied with various injection conditions, such as the pressure drop of liquid and gas phase, and recess ratio. It was found that the frequency of the self-pulsation is proportional to the liquid and gas Reynolds number, and proportional to the L/d.

• Asian-Australasian Journal of Animal Sciences
• /
• v.5 no.3
• /
• pp.475-480
• /
• 1992

The effect of mechanical factors and season of the year on milking characteristics (milk yield, time of milking, rate of milk flow, stripping time and tripping milk) were studied on 26 Holstein Friesian cows, raised under Saudi Arabia environmental conditions. Cows were in the third and fourth lactation and reached the peak. Cows milked twice a day with equal intervals. Three vacuum levels (34, 38 and 42 cfm) and two pulsation ratios were used to form six vacuum-pulsation combinations. The study was carried during two seasons Autumn-Winter (S1) and Spring-Summer (S2). After absorbing the cow equations least square analysis was used to analyze the data. Vacuum level 38 cfm and pulsation ratio 70:30 was the best among all combinations of vacuum level-pulsation ratio. No significant effect (p < .01) for season, up to the seventh half minute, on the rate of milk flow. However, season of the year has a significant effect on total milk yield, stripping time and stripping milk.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.1
• /
• pp.186-192
• /
• 2007

In general, pulsation damper is installed in fuel rail for conventional MPI engine to decrease undesirable noise in vehicle cabin room. However, pulsation damper is so expensive that there are prevailing studies to reduce fuel pressure pulsations with integrated damping effect. This paper is one of basic studies for development of fuel rail to abate pulsations with self-damping effect. Primarily, the pressure pulsation characteristics was investigated with aspect ratio of cross section, wall thickness, and materials of fuel rail. A high aspect ratio or thin wall was found to absorb the pressure pulsations effectively. But volume effects on the fuel pressure pulsation reductions were not especially significant than cross section effects because volume increment rate is larger than pressure pulsation reduction rate. The fuel rail made of aluminum is effective for reduction of pressure pulsation than that of low-carbon steel. Pressure change period increases on the basis of same lengths of supply line and fuel rail as the volume is enlarged and/or the thickness of wall is thinned.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.332-336
• /
• 2008

A pulsation damper is usually mounted on the fuel rail to diminish undesirable noise in the vehicle cabin room. However, pulsation dampers are quite expensive. Therefore, several studies have focused on reducing fuel pressure pulsations by increasing the self-damping characteristics of the fuel rail. This paper is a basic study in the development of a fuel rail that can reduce pulsations via a self-damping effect. In this study, the pressure pulsation characteristics were of investigated with respect to the aspect ratio of the cross section, wall thickness, and fuel rail material through oil hammer simulations. An oil hammer simulation was performed in advance to simulate the pressure pulsations at the resonant speed, which is a time-saving way. The pressure pulsation peak of fuel rail was observed to rise as the injection period increases. Increase of the aspect ratio and decrease of the wall thickness can reduce the pressure pulsation efficiently.

• Smart Structures and Systems
• /
• v.23 no.1
• /
• pp.71-79
• /
• 2019

In general, it may be advantageous to measure the pressure pulsation near a valve to detect a valve defect in a linear compressor. However, the acceleration signals are more advantageous for rapid classification in a mass-production line. This paper deals with the performance improvement of fault classification using only the compressor-shell acceleration signal based on the relation between the refrigerant pressure pulsation and the shell acceleration of the compressor. A transfer function was estimated experimentally to take into account the signal noise ratio between the pressure pulsation of the refrigerant in the suction pipe and the shell acceleration. The shell acceleration signal of the compressor was modified using this transfer function to improve the defect classification performance. The defect classification of the modified signal was evaluated in the acceleration signal in the frequency domain using Fisher's discriminant ratio (FDR). The defect classification method was validated by experimental data. By using the method presented, the classification of valve defects can be performed rapidly and efficiently during mass production.

• Journal of Power System Engineering
• /
• v.11 no.1
• /
• pp.76-81
• /
• 2007

The objective of this study is to find the optimum design of a snubber using CFD analysis. Several dimensions such as snubber height(H), snubber diameter(D), buffer width and buffer angle are considered in this study. The present study shows that the CFD can be applied to study the pressure characteristics inside the snubber. The objective of the snubber design optimization are to minimize a pressure loss and the pulsation ratio. Numerical results such as particle track, pressure distribution and turbulent kinetic energy are used to analyze the critical area and pressure behavior inside the snubber. As a result, snubber model with H/D ratio of 3.23 and buffer angle of $40^{\circ}$ has a minimum pressure loss. On the other hand, snubber model with H/D ratio 4.41 and buffer angle $10^{\circ}$ has a minimum pulsation ratio.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.7
• /
• pp.512-519
• /
• 2009

Flow pulsation in the gap connecting with two parallel channels is investigated by RANS and URANS approaches. The two parallel channels are connected by a small channel called for a gap. The parallel channels are designed to have different cross section area with its ratio of 0.5. Computations are conducted using a CFX 11.0 code. The bulk Reynolds number is 60,000. Predicted results are compared with the previous experimental data. Mean velocity profile at the center of gap region are compared with experiments for its validation. Spectral analysis on the lateral velocity in the center of the gap was performed. Auto correlation for the axial-flow velocity pattern was presented. The unsteady structure of the flow pulsation was visualized in the region of the gap in the parallel channel.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.601-604
• /
• 2008

The flow pulsation of two parallel channels is investigated using RANS and URANS approaches. The parallel channels are connected with a small gap and have different cross section areas. The ratio of a right side area and a left side area ($A_R$ / $A_L$) is 0.5. Computations are conducted using a CFX code. Turbulence models adopted for RANS are Reynolds stress model and Shear Stress Transport (SST) model. The bulk Reynolds number is 60,000. Predicted results are compared with the experimental result of Lee et al. and show the flow pulsation with the frequency of about 100 Hz at the center of the gap.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.10a
• /
• pp.779-780
• /
• 2014

This paper dealt with numerical estimation of pressure pulsation of the refrigerant in a suction pipe of the compressor. To evaluate the effect of reduction of pressure pulsation, a pipe system with tube was simulated using F.S.I.(Fluid-structure interaction) analysis. A commercial program was used for calculating behavior of pressure. The numerical simulation for pressure ratio of before and after going though internal structure were carried out. As a result, it was verified that the pressure after passing structure is less than the pressure before passing internal structure depending on the longitudinal frequency of structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.813-816
• /
• 2006

Complex pressure pulsation phenomenon in fuel rails is generated by rapid opening and closing of injectors and it commonly causes undesirable noise. In this study, fluid-structure interaction analyses based on CFD and FEM have been conducted to examine the pulsation damping characteristics for different shapes of fuel rails. It is shown from the present results that the fuel rail with a high aspect ratio rectangular cross section seems to be best in order to reduce the pressure pulsations. It also agrees well with the previous experimental test by Mizuno, K. et al.