FREQUENCY RESPONSE FUNCTIONS FOR THE FLOOR IMPACT SOUND BASED ON FEM FLOOR VIBRATION ANALYSIS AND BEM SOUND FIELD ANALYSIS : Study on simulation analysis for the floor impact sound of low frequency range Part 2

Characteristics of modal sound radiation of finite cylindrical shells are studied using finite element and boundary element methods in this paper. In the low frequency range, modal radiation efficiencies of finite cylindrical shells are found to asymptotically approach those of the corresponding infinite cylindrical shell when structural trace wavelengths of the cylindrical shells are greater than the acoustic wavelength. Modal radiation efficiencies for each group of modes having the same circumferential modal index decrease as the axial modal index increases. They converge to each other when the axial trace wavelength is much greater than the circumferential trace wavelength. The mechanism leading to lower radiation efficiency of modes with higher circumferential modal index of short cylinders is explained. Similar to those of flat plate panels, change in slope or waviness is observed in modal radiation efficiency curves of modes with higher order axial modal index at medium frequencies. This is attributed to the interference of sound radiated by neighboring vibrating cells when the distance between nodal lines of a vibrating mode is in the same order or smaller than the acoustic wavelength. The effects of the internal sound field on modal radiation efficiencies of a finite open-end cylinder are discussed.

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Active Control of Low-Frequency Sound Radiation From Vibrating Panel Using Planar Sound Sources

Journal of Vibration and Acoustics ◽

10.1115/1.1420197 ◽

2001 ◽

Vol 124 (1) ◽

pp. 2-9 ◽

Cited By ~ 7

Author(s):

Kean Chen ◽

Gary H. Koopmann

Keyword(s):

Active Control ◽

Near Field ◽

Low Frequency ◽

Sound Radiation ◽

Sound Field ◽

Sound Power ◽

Frequency Range ◽

Sound Sources ◽

Frequency Sound ◽

Secondary Sources

Active control of low frequency sound radiation using planar secondary sources is theoretically investigated in this paper. The primary sound field originates from a vibrating panel and the planar sources are modeled as simply supported rectangular panels in an infinite baffle. The sound power of the primary and secondary panels are calculated using a near field approach, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiate sound power. Finally, active reduction for a number of secondary panel arrangements is examined and it is concluded that when the modal distribution of the secondary panel does not coincide with that of the primary panel, one secondary panel is sufficient. Otherwise four secondary panels can guarantee considerable reduction in sound power over entire frequency range of interest.

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Advanced non-dimensional dynamic influence function method considering the singularity of the system matrix for accurate eigenvalue analysis of membranes

Advances in Mechanical Engineering ◽

10.1177/16878140211072960 ◽

2022 ◽

Vol 14 (1) ◽

pp. 168781402110729

Author(s):

Sangwook Kang

Keyword(s):

Influence Function ◽

Vibration Analysis ◽

Function Method ◽

Accurate Result ◽

Low Frequency ◽

Free Vibration Analysis ◽

System Matrix ◽

Frequency Range ◽

Influence Function Method ◽

Lower Frequency Range

An advanced non-dimensional dynamic influence function method (NDIF method) for highly accurate free vibration analysis of membranes with arbitrary shapes is proposed in this paper. The existing NDIF method has the weakness of not offering eigenvalues and eigenmodes in the low frequency range when the number of boundary nodes of an analyzed membrane is increased to obtain more accurate result. This paper reveals that the system matrix of the membrane becomes singular in the lower frequency range when the number of the nodes increases excessively. Based on this fact, it provides an efficient way to successfully overcome the weaknesses of the existing NDIF method and still maintain its accuracy. Finally, verification examples show the validity and accuracy of the advanced NDIF method proposed.

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A Flow Starvation Model for Tilting Pad Journal Bearings and Evaluation of Frequency Response Functions: A Contribution Toward Understanding the Onset of Low Frequency Shaft Motions

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4038043 ◽

2018 ◽

Vol 140 (5) ◽

Cited By ~ 2

Author(s):

Luis San Andrés ◽

Bonjin Koo ◽

Makoto Hemmi

Keyword(s):

Frequency Response ◽

Low Frequency ◽

Journal Bearings ◽

Response Functions ◽

Frequency Range ◽

Flow Conditions ◽

Force Coefficients ◽

Lubricant Flow ◽

Tilting Pad ◽

Tilting Pad Journal Bearings

Direct lubrication tilting pad journal bearings (TPJBs) require less oil flow, reduce power consumption, and offer cooler pad temperatures for operation at high surface speeds. Although apparently free of hydrodynamic instability, the literature shows that direct lubrication TPJBs exhibit unexpected shaft vibrations with a broadband low frequency range, albeit small in amplitude. Published industrial practice demonstrates the inlet lubrication type, a reduced supply flow rate causing film starvation, and the bearing discharge conditions (evacuated or end sealed) affect the onset, gravity, and persistency of the subsynchronous vibration (SSV) hash motions. The paper presents a physical model to predict the performance of TPJBs with flow conditions ranging from over flooded to extreme starvation. Lubricant starvation occurs first on an unloaded pad, thus producing a (beneficial) reduction in drag power. As the supplied flowrate decreases further, fluid starvation moves toward the loaded pads and affects the film temperature and power loss, increases the journal eccentricity, and modifies the dynamic force coefficients of each tilting pad and thus the whole bearing. For a point mass rotor supported on a TPJB, the analysis produces eigenvalues and frequency response functions (FRFs) from three physical models for lateral rotor displacements: one with frequency reduced (4 × 4) bearing stiffness (K) and damping (C) coefficients and another with constant K–C–M (inertia) coefficients over a frequency range. The third model keeps the degrees of freedom (DOF) (tilting) of each pad and incorporates the full matrices of force coefficients including fluid inertia. Predictions of rotordynamic performance follow for two TPJBs: one bearing with load between pads (LBP) configuration, and the other with a load on a pad (LOP) configuration. For both examples, under increasingly poor lubricant flow conditions, the damping ratio for the rotor-bearing low frequency (SSV) modes decreases, thus producing an increase in the amplitude of the FRFs. For the LOP bearing, a large static load produces a significant asymmetry in the force coefficients; the rotor bearing has a small stiffness and damping for shaft displacements in the direction orthogonal to the load. A reduction in lubricant flow only exacerbates the phenomenon; starvation reaches the loaded pad to eventually cause the onset of low frequency (SSV) instability. The bearing analyzed showed similar behavior in a test bench. The predictions thus show a direct correlation between lubricant flow starvation and the onset of SSV.

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Vibration Analysis and Optimal Design for Cab’s Isolation System of Vibratory Roller

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.199-200.936 ◽

2011 ◽

Vol 199-200 ◽

pp. 936-940 ◽

Cited By ~ 1

Author(s):

Le Van Quynh ◽

Jian Run Zhang ◽

Guo Wang Jiao ◽

Xiao Bo Liu ◽

Yuan Wang

Keyword(s):

Optimal Design ◽

Optimization Model ◽

Vibration Analysis ◽

Ride Comfort ◽

Dynamic Test ◽

Low Frequency ◽

Frequency Range ◽

Working Capacity ◽

Forward Motion ◽

Isolation System

In recent years, vibration roller market has required increasingly not only on working capacity but also ride comfort. Thus, in order to reduce the effect of vibration to operators, identification and elimination of vibration sources are the most important tasks to achieve optimum design. In this paper, the attention is paid to cab’s low-frequency sloshing analysis and optimal design for cab’s isolation system of vibratory roller. When working, it often exists the problem of cab’s low-frequency sloshing in the direction of forward motion. In order to solve this problem, the dynamic test and simulations analysis are carried out; and the main reasons causing cab’s low-frequency sloshing are found out. The optimization model according to the two points response amplitude in the direction of forward motion on the cab to reach the minimum value in the low frequency range is proposed in this paper. And also, the auxiliary vibrations isolator for solving the low-frequency sloshing in the direction of forward motion is designed.

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A Wave-Based Vibration Analysis of a Finite Timoshenko Locally Resonant Beam Suspended with Periodic Uncoupled Force-Moment Type Resonators

Crystals ◽

10.3390/cryst10121132 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1132

Author(s):

Hangyuan Lv ◽

Yimin Zhang

Keyword(s):

Vibration Analysis ◽

Low Frequency ◽

Bending Moment ◽

Analysis Approach ◽

Structural Elements ◽

Frequency Range ◽

Resonant Beam ◽

Force Moment ◽

A Cell ◽

Two Degree Of Freedom

This paper first employs and develops an exact wave-based vibration analysis approach to investigate a finite Timoshenko beam carrying periodic two-degree-of-freedom (2-DOF) uncoupled force-moment type resonators. In the approach, vibrations are described as structural waves that propagate along uniform structural elements and reflected and transmitted at structural discontinuities. Each uncoupled force-moment type resonator is considered as a cell which injects waves into the distributed beam through the transverse force and the bending moment at the attached point. By assembling wave relations of the cells into the beam, the forced vibration problem of the locally resonant (LR) structure is turned to be the solution to a related set of matrix equations. In addition, the parametric analysis provides an efficient method to obtain wide low-frequency range band-gaps. Accuracy of the proposed wave-based vibration analysis approach is demonstrated by the simulated and measured results of two sets of beam-like resonator samples.

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A Flow Starvation Model for Tilting Pad Journal Bearings and Evaluation of Frequency Response Functions: A Contribution Towards Understanding the Onset of Low Frequency Shaft Motions

Volume 7A: Structures and Dynamics ◽

10.1115/gt2017-64822 ◽

2017 ◽

Cited By ~ 1

Author(s):

Luis San Andrés ◽

Bonjin Koo ◽

Makoto Hemmi

Keyword(s):

Frequency Response ◽

Low Frequency ◽

Journal Bearings ◽

Response Functions ◽

Frequency Range ◽

Flow Conditions ◽

Force Coefficients ◽

Lubricant Flow ◽

Tilting Pad ◽

Tilting Pad Journal Bearings

Direct lubrication tilting pad journal bearings (TPJBs) require of less oil flow, reduce power consumption and offer cooler pad temperatures for operation at high surface speeds. Although apparently free of a hydrodynamic instability, the literature shows that direct lubrication TPJBs exhibit unexpected shaft vibrations with a broadband low frequency range, albeit small in amplitude. Published industrial practice demonstrates the inlet lubrication type, a reduced supply flow rate causing film starvation, and the bearing discharge conditions (evacuated or end sealed) affect the onset, gravity and persistency of the sub synchronous (SSV) hash motions. The paper presents a physical model to predict the performance of TPJBs with flow conditions ranging from over flooded to extreme starvation. Lubricant starvation occurs first on an unloaded pad, thus producing a (beneficial) reduction in drag power. As the supplied flowrate decreases further, fluid starvation moves towards the loaded pads and affects the film temperature and power loss, increases the journal eccentricity, and modifies the dynamic force coefficients of each tilting pad and thus the whole bearing. For a point mass rotor supported on a TPJB, the analysis produces eigenvalues and frequency response functions (FRFs) from three physical models for lateral rotor displacements: one with frequency reduced (4×4) bearing stiffness (K) and damping (C) coefficients and another with constant K-C-M (inertia) coefficients over a frequency range. The third model keeps the degrees of freedom (tilting) of each pad and incorporates the full matrices of force coefficients including fluid inertia. Predictions of rotordynamic performance follow for two TPJBs: one bearing with load between pads (LBP) configuration, and the other with a load on a pad (LOP) configuration. For both examples, under increasingly poor lubricant flow conditions, the damping ratio for the rotor-bearing low frequency (SSV) modes decreases, thus producing an increase in the amplitude of the FRFs. For the LOP bearing, a large static load produces a significant asymmetry in the force coefficients; the rotor-bearing has a small stiffness and damping for shaft displacements in the direction orthogonal to the load. A reduction in lubricant flow only exacerbates the phenomenon; starvation reaches the loaded pad to eventually cause the onset of low frequency (SSV) instability. The bearing analyzed showed similar behavior in a test bench. The predictions thus show a direct correlation between lubricant flow starvation and the onset of SSV.

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