CFD Analysis of the Acoustic and Mean Flow Performance of Simple Expansion Chamber Mufflers

2004 ◽  
Author(s):  
J. M. Middelberg ◽  
T. J. Barber ◽  
S. S. Leong ◽  
K. P. Byrne ◽  
E. Leonardi
Keyword(s):  
Transmission Loss ◽  
Time History ◽  
Mean Flow ◽  
Inlet Pipe ◽  
Expansion Chamber ◽  
Acoustic Performance ◽  
Time Histories ◽  
History Of ◽  
Simple Expansion ◽  
The Mean

The acoustic and mean flow performance of different configurations of simple expansion chamber mufflers has been considered. The different configurations include extended inlet/outlet pipes and baffles inside the expansion section of the muffler. Both the acoustic and mean flow performance has been evaluated for each muffler. The acoustic CFD model of the muffler uses an axisymmetric grid with no mean flow and a single period sinusoid of suitable amplitude and duration imposed at the inlet boundary. The time history of the acoustic pressure and particle velocity are recorded at two points, one in the inlet pipe and the other in the outlet pipe. These time histories are Fourier transformed and the transmission loss of the muffler is calculated. The mean flow model of the muffler uses the same geometry, but has a finer mesh and has a suitable inlet velocity applied at the inlet boundary and the pressure drop across the muffler is found. The acoustic performance is compared with published experimental results.

Stationary and Transient Response of Cylindrical Shells Under Random Excitation

1988 ◽  
Vol 110 (2) ◽  
pp. 205-209
Author(s):  
A. V. Singh
Keyword(s):  
Transient Response ◽  
Random Vibration ◽  
Time History ◽  
Wide Band ◽  
Random Excitation ◽  
Mode Shapes ◽  
The Finite Element Method ◽  
History Of ◽  
The Mean ◽  
Random Vibration Analysis

This paper presents the random vibration analysis of a simply supported cylindrical shell under a ring load which is uniform around the circumference. The time history of the excitation is assumed to be a stationary wide-band random process. The finite element method and the condition of symmetry along the length of the cylinder are used to calculate the natural frequencies and associated mode shapes. Maximum values of the mean square displacements and velocities occur at the point of application of the load. It is seen that the transient response of the shell under wide band stationary excitation is nonstationary in the initial stages and approaches the stationary solution for large value of time.

Time Progression of Hemolysis of Erythrocyte Populations Exposed to Supraphysiological Temperatures

1979 ◽  
Vol 101 (3) ◽  
pp. 213-217 ◽  
Author(s):  
N. A. Moussa ◽  
E. N. Tell ◽  
E. G. Cravalho
Keyword(s):  
Statistical Model ◽  
Distribution Curve ◽  
Time History ◽  
Kinetic Scheme ◽  
First Order ◽  
Arrhenius Dependence ◽  
History Of ◽  
The Mean ◽  
Two Parameters ◽  
Microscope Stage

Populations of erythrocytes in solution were heated “instantaneously” to and maintained at temperatures in the range of 44 to 60°C on a microscope stage specifically designed for this purpose. Simultaneously, the visually observed hemolysis-time history of these cells was measured. The results were successfully correlated on the basis of two models: 1) a kinetic scheme assuming two sequential, first-order reactions by which the cells are first reversibly altered and then irreversibly damaged; and 2) a statistical model for which the number of cells that are damaged at each instant is assumed to be normally distributed. From the experimental data the rate constants for the two reactions in the kinetic model were determined and were found to have an Arrhenius dependence on temperature. By applying the statistical model to the data, we were able to determine the mean and standard deviation of the distribution curve for this model. The logarithms of these latter two parameters vary with temperature in a linear fashion.

Observed Soil-Water Interaction in the Centrifuge Dynamic Test

2011 ◽  
Vol 243-249 ◽  
pp. 2978-2984
Author(s):  
Dong Su ◽  
Xiang Song Li
Keyword(s):  
Pore Pressure ◽  
Earthquake Engineering ◽  
Dynamic Test ◽  
Time History ◽  
Excess Pore Pressure ◽  
Geotechnical Earthquake Engineering ◽  
Time Histories ◽  
History Of ◽  
Input Motion ◽  
Excess Pore

Centrifuge physical modeling technique has been increasingly used in geotechnical earthquake engineering. A centrifuge dynamic model test has been conducted on the centrifuge on a saturated sand deposit model. The input motion at the base of the model was a strong earthquake waveform with a peak acceleration of 0.55 g in prototype. Some interesting phenomena, which include disappearance and reappearance of acceleration in soils during the shaking event, and existence of double plateaus or one plateau and one peak in the time histories of excess pore pressure, were recorded. The mechanism behind the phenomena was investigated by comparing the time history of excess pore pressure with the time history of acceleration, and with the derived shear modulus.

A Green’s Function Solution for Acoustic Attenuation by a Cylindrical Chamber With Concentric Perforated Liners

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
D. Veerababu ◽  
B. Venkatesham
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Velocity Potential ◽  
Transmission Loss ◽  
Analytical Models ◽  
Mean Flow ◽  
Cylindrical Chamber ◽  
Function Solution ◽  
Grazing Flow ◽  
The Mean

Abstract In this study, a Green’s function-based semi-analytical method is presented to predict the transmission loss (TL) of a circular chamber having concentric perforated screens. Initially, the Green’s function is developed for a single-screen configuration as the summation of eigenfunctions of the inner pipe in the absence of the mean flow. The inlet and the outlet ports are modeled as oscillating piston sources. A transfer matrix is formulated from the velocity potential generated by the piston sources. The results obtained from the proposed method are validated with the numerical and analytical models and with the experimental results available in the literature. Later, the method has been extended to the double-screen configuration. The effect of the additional perforated screen on the TL is studied in terms of the surface impedance of the chamber. Along with grazing flow considerations, guidelines are provided to incorporate more concentric perforated screens into the formulation.

On the Motion of Single and Twin Oblique Particle Clouds in Stagnant Water

2021 ◽  
Author(s):  
Mahsa Janati ◽  
Amir Azimi
Keyword(s):  
Vortex Motion ◽  
Time History ◽  
Particle Interactions ◽  
Stagnant Water ◽  
Cloud Properties ◽  
Image Velocimetry ◽  
Particle Clouds ◽  
Time Histories ◽  
History Of ◽  
Nozzle Spacing

Abstract The evolution of single and twin oblique particle clouds in stagnant water was investigated using a series of laboratory experiments and the effects of controlling parameters such as sand mass and nozzle spacing were studied. The time variations of particle cloud properties such as frontal position, horizontal and vertical centroids, cloud width, and frontal velocity were measured using image analysis and Particle Image Velocimetry (PIV) techniques. The entrainment coefficients were extracted from the measurements. It was found that the main vortex motion of the frontal heads altered after the collision and a new integrated frontal head was formed. The effects of release angle and particle interactions were studied by comparing the time histories of maximum centerline velocities. It was found that the centerline velocity of twin oblique particle clouds in comparison with twin vertical particle clouds increased with increasing nozzle spacing. The time history of the ratio of horizontal to vertical centroids in oblique particle clouds determined the potential location of sand particles and a practical model was developed to determine the size and location of particle clouds with time. The time histories of normalized cloud width indicated a significant change after the frontal head collision. The particle interactions due to frontal head collision in twin oblique particle clouds significantly increased the cloud width until particle clouds reached the swarm phase. The time at which twin oblique particle clouds reached the swarm phase was recorded and a linear model was proposed to link the time to reach the swarm phase with the cloud aspect ratio and nozzle spacing.

Acoustic Characteristics of an Expansion Chamber With Constant Mass Flow and Steady Temperature Gradient (Theory and Numerical Simulation)

1990 ◽  
Vol 112 (4) ◽  
pp. 460-467 ◽  
Author(s):  
Yang-Hann Kim ◽  
Jae Woong Choi ◽  
Byung Duk Lim
Keyword(s):  
Temperature Gradient ◽  
Transmission Loss ◽  
Matching Condition ◽  
Present Theory ◽  
Flow Speed ◽  
Gradient Theory ◽  
Mean Flow ◽  
Acoustic Wave Propagation ◽  
Expansion Chamber ◽  
Twisting Angle

The governing equation of acoustic wave propagation in a circular expansion chamber with mean flow and temperature gradient is solved. The circular chamber is divided into N segments and the flow speed and temperature are assumed to be constant in each segment. The solution is obtained in recursive form by applying the matching condition on the boundary of adjacent elements. The solution is verified by comparing it with the experimental results. The results demonstrate that the present theory can well predict the transmission loss of an expansion chamber which has offset, a twisting angle, mean flow, and temperature gradient.

scholarly journals An Investigation of Acoustic Attenuation Performance of Silencers with Mean Flow Based on Three-Dimensional Numerical Simulation

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Wei Fan ◽  
Li-Xin Guo
Keyword(s):  
Flow Field ◽  
Flow Velocity ◽  
Cfd Simulation ◽  
Data Transfer ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
3D Fem ◽  
Expansion Chamber

Transmission loss (TL) is often used to evaluate the acoustic attenuation performance of a silencer. In this work, a three-dimensional (3D) finite element method (FEM) is employed to calculate the TL of some representative silencers, namely, circular expansion chamber silencer and straight-through perforated pipe silencer. In order to account for the effect of mean flow that exists inside the silencer, the 3D FEM is used in conjunction with the Computational Fluid Dynamics (CFD) simulation of the flow field. More concretely, the 3D mean flow field is computed by firstly using CFD, and then the obtained mean flow data are imported to an acoustic solution undertaken using FEM. The data transfer between the two steps is accomplished by mesh mapping. The results presented demonstrate good agreement between present TL predictions and previously published experimental and numerical works. Also, the details of the flow inside the silencers may be studied. Furthermore, the effect of mean flow velocity on acoustic attenuation performance of the silencers is investigated. It is concluded that for the studied silencers, in general, increasing flow velocity increases the TL and decreases the resonance peaks.

Numerical Flow Prediction in Inlet Pipe of Vertical Inline Pump

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Christopher Stephen ◽  
Shouqi Yuan ◽  
Ji Pei ◽  
Xing Cheng G
Keyword(s):  
Stokes Equations ◽  
Reverse Flow ◽  
Pressure Coefficient ◽  
Navier Stokes ◽  
Mean Flow ◽  
Inlet Pipe ◽  
Navier Stokes Equations ◽  
Computational Fluid Dynamics Cfd ◽  
The Mean ◽  
Good Agreement

For a pump, the inlet condition of flow determines the outlet conditions of fluid (i.e., energy). As a rule to minimize the losses at the entry of pump, the bends should be avoided as one of the methods. But for the case of vertical inline pump, it is unavoidable in order to save the space for installation. For the purpose of investigation in inlet pipe of vertical inline pump, the unsteady Reynolds-averaged Navier–Stokes equations are solved using the computational fluid dynamics (CFD) code. The results have been shown that there is a good agreement between the performance characteristics obtained from the simulation and experiments. The velocity coefficient from the simulation along the inlet pipe sections is well matched with the theoretical values and found to have variation near the exit of inlet pipe. The pressure and velocity coefficients studies depict the flow physics at each section along with the study of helicity at the exit of inlet pipe to determine the recirculation effects. It is observed that the vortices associated with the motion of the particles are moved toward the surfaces and are more intense than the mean flow. The trends of pressure coefficient at the exit of inlet pipe were addressed with reference to the various flow rates for eight set of radial lines. Hence, this work concludes that for inlet pipe, the generation of circulation was due to the stream path and the reverse flow from the impeller and was reconfirmed with the literature.

scholarly journals Application of harmonic balance method for solving non-linear equations of motion

2018 ◽  
Vol 182 ◽  
pp. 02024
Author(s):  
Robert Kostek
Keyword(s):  
Harmonic Balance ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Harmonic Balance Method ◽  
Time History ◽  
Balance Method ◽  
Non Linear ◽  
Time Histories ◽  
History Of ◽  
Non Linear Equations

This article presents the advantages and limitations of a harmonic balance method applied for solving non-linear equations of monition. This method provides an opportunity to find stable and unstable periodic solutions, which was demonstrated for a few equations. An error of solution decreases rapidly with increase of number of harmonics for smooth time history of acceleration, which shows convergence; whereas, for discontinuous time histories, this method is not effective.

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