The Determination of Dynamic Stiffness of Dish-Shaped Metal Corrugated Pipe by Use of Random Vibration Method

2012 ◽  
Vol 468-471 ◽  
pp. 1393-1397
Author(s):  
Li Ming Rui ◽  
Mei Sheng Zheng ◽  
Lian Jun Tian
Keyword(s):  
Random Vibration ◽  
Dynamic Stiffness ◽  
Static Stiffness ◽  
Mass System ◽  
Single Degree Of Freedom ◽  
Vibration Method ◽  
Single Degree ◽  
Wide Range ◽  
Random Vibration Method

This paper simplifies the dish-shaped metal corrugated pipe into a elastic element, constitutes a single degree of freedom spring-mass system, then applicants the random vibration method to measure its natural frequency, further to calculate the dynamic stiffness of dish-shaped metal corrugated pipe. At the same time its static stiffness test is done. By comparison of two results, static and dynamic stiffness values fit well, and dynamic stiffness is closer to the actual working conditions. Random vibration method for dynamic stiffness is convenient, accurate and has application values in a wide range of engineering.

Effectiveness of neoprene pad vibration isolators at high frequencies

2021 ◽  
Vol 263 (4) ◽  
pp. 2172-2183
Author(s):  
Jerry Lilly
Keyword(s):  
Natural Frequency ◽  
Insertion Loss ◽  
Dynamic Stiffness ◽  
Degree Of Freedom ◽  
Frequency Wave ◽  
Single Degree Of Freedom ◽  
High Frequencies ◽  
Vibration Isolators ◽  
Single Degree ◽  
Wide Range

The natural frequency, dynamic stiffness, and insertion loss of commercially available neoprene pad vibration isolators have been measured in a simple, single degree of freedom system over a wide range of pad loadings out to a maximum frequency of 10 kHz. The results reveal that dynamic stiffness can vary significantly with pad loading as well as the durometer of the material. It will also be shown that insertion loss follows the theoretical single degree of freedom curve only out to a frequency that is about 5 to 10 times the natural frequency, depending upon the pad durometer rating. Above that frequency wave resonances in the material cause the insertion loss to deteriorate significantly out to a frequency near 1 kHz, above which the insertion loss maintains a relatively constant value, again depending upon the pad durometer rating. In some instances the insertion loss values can approach 0 dB or even become negative at specific frequencies in the frequency region that is 10 to 20 times the natural frequency of the system.

On the Stability Properties of a Periodically Forced, Time-Varying Mass System

2009 ◽  
Author(s):  
W. T. van Horssen ◽  
O. V. Pischanskyy ◽  
J. L. A. Dubbeldam
Keyword(s):  
Periodic Solutions ◽  
Forced Vibrations ◽  
Time Varying ◽  
Mass System ◽  
Single Degree Of Freedom ◽  
Stability Properties ◽  
Single Degree ◽  
Existence Of Periodic Solutions ◽  
The Stability ◽  
Varying Mass

In this paper the forced vibrations of a linear, single degree of freedom oscillator (sdofo) with a time-varying mass will be studied. The forced vibrations are due to small masses which are periodically hitting and leaving the oscillator with different velocities. Since these small masses stay for some time on the oscillator surface the effective mass of the oscillator will periodically vary in time. Not only solutions of the oscillator equation will be constructed, but also the stability properties, and the existence of periodic solutions will be discussed.

The Measurement of Nonlinear Damping in Single-Degree-of-Freedom Systems

1991 ◽  
Vol 113 (1) ◽  
pp. 132-140 ◽  
Author(s):  
H. J. Rice ◽  
J. A. Fitzpatrick
Keyword(s):  
Nonlinear Distortion ◽  
Nonlinear Damping ◽  
Degree Of Freedom ◽  
Crucial Importance ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Wide Range ◽  
Impulse Excitation ◽  
Excitation Techniques ◽  
Quadratic Damping

The measurement and correct modelling of damping is of crucial importance in the prediction of the dynamical performance of systems for a wide range of engineering applications. In most cases, however, the experimental methods used to measure damping coefficients are extremely basic and, in general, poorly reported. This paper shows that damping is a deceptive parameter which is prone to subtle nonlinear distortion which often appears to satisfy general linear criteria. An efficient experimental method which provides for the measurement of both the linear and nonlinear damping for a single-degree-of-freedom system is proposed. The results from a numerical simulation study of a model with “drag” type quadratic damping are shown to give reliable estimates of parameters of the system when both random and impulse excitation techniques are used.

Exact determination of critical damping in multiple exponential kernel-based viscoelastic single-degree-of-freedom systems

2019 ◽  
Vol 24 (12) ◽  
pp. 3843-3861 ◽  
Author(s):  
Mario Lázaro
Keyword(s):  
Past History ◽  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Critical Curves ◽  
History Of ◽  
Definition Of ◽  
Analytical Expressions ◽  
Critical Damping

In this paper, exact closed forms of critical damping manifolds for multiple-kernel-based nonviscous single-degree-of-freedom oscillators are derived. The dissipative forces are assumed to depend on the past history of the velocity response via hereditary exponential kernels. The damping model depends on several parameters, considered variables in the context of this paper. Those parameter combinations which establish thresholds between induced overdamped and underdamped motion are called critical damping manifolds. If such manifolds are represented on a coordinate plane of two damping parameters, then they are named critical curves, so that overdamped regions are bounded by them. Analytical expressions of critical curves are deduced in parametric form, considering certain local nondimensional parameters based on the Laplace variable in the frequency domain. The definition of the new parameter (called the critical parameter) is supported by several theoretical results. The proposed expressions are validated through numerical examples showing perfect fitting of the determined critical curves and overdamped regions.

A New Magnetorheological Mount for Vibration Control

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
David York ◽  
Xiaojie Wang ◽  
Faramarz Gordaninejad
Keyword(s):  
Vibration Control ◽  
Phenomenological Model ◽  
Dynamic Performance ◽  
Small Displacement ◽  
Rectilinear Motion ◽  
Single Degree Of Freedom ◽  
Sdof System ◽  
Single Degree ◽  
Performance Predictions ◽  
Wide Range

In this study, the performance of a new controllable mount design utilizing a magnetorheological material encapsulated in an elastomer matrix is investigated. A magnetorheological fluid-elastomer (MRF-E) mount is designed and fabricated, and its dynamic performance is studied under harmonic oscillatory vibrations for a wide range of frequencies and various applied magnetic fields. Also, a theoretical analysis is conducted by proposing a three-element phenomenological model for replicating the dynamic behavior of the MRF-E mount under oscillation loadings, and the results are compared with the experimental data. In order to further evaluate the effectiveness of the MRF-E mount for vibration control, a single degree-of-freedom (SDOF) system incorporated with this device is developed. Theoretically, the equation of motion utilizing the proposed phenomenological model is derived to provide performance predictions on the effectiveness of the semiactive device at suppressing unwanted vibrations. Experimentally, a SDOF system constrained to rectilinear motion and composed of a mass, four linear springs, and the MRF-E mount is designed and manufactured. This work demonstrates the performance of the proposed MRF-E mount and its capability in attenuating undesirable system vibrations for a range of small-displacement amplitudes and frequencies.

scholarly journals The Spectrum Dip of Deck Mounted Systems

2010 ◽  
Vol 17 (1) ◽  
pp. 55-69
Author(s):  
R.J. Scavuzzo ◽  
G.D. Hill ◽  
P.W. Saxe
Keyword(s):  
Vertical Motion ◽  
Base Point ◽  
Degree Of Freedom ◽  
Mass System ◽  
Detailed Model ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Fixed Base ◽  
Grid Points ◽  
Modal Mass

In this paper, a detailed model of a ship deck and attached dynamic systems was developed and subjected to dynamic studies using two different shock inputs: a triangular shaped velocity pulse and the vertical motion of the innerbottom of the standard Floating Shock Platform (FSP). Two studies were conducted, one considering four single degree-of-freedom systems attached at various deck locations and another considering a three-mass system attached at one location. The two shock inputs were used only for the multi-mass system study. The triangular pulse was used for the four single degree-of-freedom systems study. For the single degree-of-freedom systems study, shock spectra were first calculated at the four mounting locations assuming the oscillators were not present. Then the oscillator systems were added to these grid points to determine the change in the shock spectra. First, the oscillators were added one at a time, and then all the oscillators were added to the deck. The multi-mass system was analyzed using both shock inputs. First, the fixed-base modal masses and frequencies were determined. Then, the system as a whole was attached to the deck and the spectrum values at the base point were determined and compared to those for the free deck case. In the last step each mode of the multi-mass system, represented by a single degree-of-freedom system with the modal mass and appropriate spring stiffness, was considered individually to determine the spectrum responses. Results of the free deck, the entire system and individual modal responses are compared.

Transient Vibration Experiments for Determination of Properties for Viscoelastic Structures

1975 ◽  
Vol 42 (1) ◽  
pp. 205-208 ◽  
Author(s):  
M. J. Forrestal ◽  
M. J. Sagartz
Keyword(s):  
Complex Modulus ◽  
Strain Gages ◽  
Transient Vibration ◽  
Single Degree Of Freedom ◽  
Complex Moduli ◽  
Bending Mode ◽  
Wide Range ◽  
Spatially Distributed ◽  
Circular Rings

Two experimental techniques devised to determine the mechanical properties for viscoelastic structures are demonstrated with experiments on polymethyl methacrylate (PMMA). Circular rings are loaded with an axisymmetric impulse which excites the fundamental membrane mode and free-free beams are loaded with a spatially distributed impulse which excites the fundamental bending mode. Because only one mode of vibration is excited, these structures can be regarded as single-degree-of-freedom systems in free vibration. Loading is produced by magnetic pressure pulses and the response is measured with strain gages. The complex modulus is obtained from period of vibration and logarithmic decrement of the strain response. Geometry of the specimens is varied to obtain complex moduli over a wide range of frequencies.

Predictions of the Periodic Response of a Single-Degree-of-Freedom Foam-Mass System by Using Incremental Harmonic Balance

2012 ◽  
Author(s):  
Yousof Azizi ◽  
Patricia Davies ◽  
Anil K. Bajaj
Keyword(s):  
Steady State ◽  
Harmonic Balance ◽  
Driving Frequency ◽  
Steady State Response ◽  
Base Excitation ◽  
Mass System ◽  
Single Degree Of Freedom ◽  
State Response ◽  
Single Degree ◽  
Incremental Harmonic Balance

Vehicle occupants are exposed to low frequency vibration that can cause fatigue, lower back pain, spine injuries. Therefore, understanding the behavior of a seat-occupant system is important in order to minimize these undesirable vibrations. The properties of seating foam affect the response of the occupant, so there is a need for good models of seat-occupant systems through which the effects of foam properties on the dynamic response can be directly evaluated. In order to understand the role of flexible polyurethane foam in characterizing the complex seat-occupant system behavior better, the response of a single-degree-of-freedom foam-mass system, which is the simplest model representing a seat-occupant system, is studied. The incremental harmonic balance method is used to determine the steady-state behavior of the foam-mass system subjected to sinusoidal base excitation. This method is used to reduce the time required to generate the steady-state response at the driving frequency and at harmonics of the driving frequency from that required when using direct time-integration of the governing equations to determine the steady state response. Using this method, the effects of different viscoelastic models, riding masses, base excitation levels and damping coefficients on the response are investigated.

The Virtual Cam – Hexagon Method Authentication on Locating Key Instant Centers of All Planar Single Degree of Freedom Kinematically Indeterminate Linkages up to Ten-Bar

2018 ◽  
Author(s):  
Zhengqi Liu ◽  
Yin-ping Chang
Keyword(s):  
Degree Of Freedom ◽  
Universal Method ◽  
Single Degree Of Freedom ◽  
Graphical Approach ◽  
Single Degree ◽  
Wide Range ◽  
Different Types ◽  
Limited Application ◽  
Complete Sets ◽  
Improved Technique

At this moment all the methods which had been proposed have extremely limited application to only several specific constructions of kinematically indeterminate linkages, i.e. their complete sets of instant centers cannot be obtained simply from Kennedy Theorem due to lack of enough four-bar loop information in their constructions. Planar single degree of freedom linkages up to ten-bar include two different types of mechanisms, i.e. pure bar linkages, such as four-, six-, eight-, and ten-bar; and geared-bar linkages, i.e. geared-five, seven, and nine-bar. The huge varieties of different types and constructions can serve as great testbeds for these methods. This research systematically investigates and modifies the graphical approach, i.e. virtual cam method, whose employment will show it to be an almost-universal method which can be compliantly applied on very wide range of kinematically indeterminate linkages. The procedures and criteria of the methodology are proposed and examined thoroughly to help locate key instant centers of all planar single degree of freedom kinematically indeterminate linkages up to ten-bar so that their complete sets of instant centers can be located successfully. We call this modified and improved technique as Virtual Cam – Hexagon Method. The results are verified carefully against traditional Kennedy Theorem approach and CAD modeling.

Closed-Form Displacement Analysis of SDOF 8 Link Mechanisms

1996 ◽  
Author(s):  
Abdulaziz N. Almadi ◽  
Anoop K. Dhingra ◽  
Dilip Kohli
Keyword(s):  
Closed Form ◽  
Analysis Problem ◽  
Algebraic Form ◽  
Single Degree Of Freedom ◽  
Displacement Analysis ◽  
Kinematic Chains ◽  
Closed Form Solutions ◽  
Single Degree ◽  
Half Angle

Abstract This paper presents closed-form solutions to the displacement analysis problem of planar 8-link mechanisms with a single degree of freedom (SDOF). The degrees of I/O polynomials as well as the number of possible assembly configurations for all 71 8-link mechanisms resulting from 16 8-link kinematic chains are presented. Three numerical examples illustrating the applicability of the successive elimination procedure to the displacement analysis of 8-link mechanisms are presented. The first example deals with the determination of I/O polynomial for an 8-link mechanism containing no four-bar loops. The second and third examples, address in detail, some of the problems associated with the conversion of transcendental loop-closure equations into an algebraic form using tangent half-angle substitutions. These examples illustrate how extraneous roots can get introduced during the displacement analysis of mechanisms, and how one can derive an I/O polynomial devoid of the extraneous roots. Extensions of the proposed approach to the displacement analysis of SDOF spherical 8-link mechanisms is also presented.

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