scholarly journals On the Force Drop Off Phenomenon in Shaker Testing in Experimental Modal Analysis

2002 ◽  
Vol 9 (4-5) ◽  
pp. 165-175 ◽  
Author(s):  
Paulo Sergio Varoto ◽  
Leopoldo Pisanelli Rodrigues de Oliveira
Keyword(s):  
Input Signal ◽  
Modal Testing ◽  
Analytical Models ◽  
Vibration Exciter ◽  
Electromechanical Device ◽  
Vibration Tests ◽  
Operational Modes ◽  
Electrodynamic Vibration ◽  
Force Drop

The Electrodynamic Vibration Exciter (shakers) has been one of the most employed excitation sources in modal tests. The shaker is an electromechanical device that provides a mechanical motion due to the input signal sent to its coil. Despite being widely used, it is well known that the shaker interacts with the structure under test. In particular, when the structure passes through a given resonance, the force delivered by the shaker abruptly decreases, causing the so called drop off phenomenon. This paper aims to study this force drop off phenomenon in the single shaker modal testing. Analytical models are developed to help in understanding the physical principles involved in the interaction between the shaker and the structure under test. Experimental analyses are performed using different shakers as well as excitation signals, in order to evaluate the effects of the input signal, as well as the power amplifier operational modes, on the structure dynamics. Preliminary tests revealed that significant distortions might occur during vibration tests using shakers and these distortions significantly affect the determination of the structure response.

A New Approach for Determining Joint Stiffness of Bolted Joints

2014 ◽  
Vol 670-671 ◽  
pp. 1041-1044 ◽  
Author(s):  
Xi Wang Wang ◽  
Xiao Yang Li ◽  
Lin Lin Zhang ◽  
Xiao Guang Wang
Keyword(s):  
Accurate Determination ◽  
Joint Stiffness ◽  
Fatigue Loading ◽  
Bolted Joints ◽  
Analytical Models ◽  
Bolted Connection ◽  
New Approach ◽  
Axisymmetric Model ◽  
Force Equilibrium

Joint member stiffness in a bolted connection directly influence the safety of a design in regard to both static and fatigue loading as well as in the prevention of separation in the connection. Thus, the accurate determination of the stiffness is of extreme importance to predict the behavior of bolted assemblies. In this paper, An analytical 3D axisymmetric model of bolted joints is proposed to obtain the joint stiffness of Bolted Joints. Considering many different analytical models have been proposed to calculate the joint stiffness, the expression based force equilibrium can be a easy way to choose the best expression for the joint stiffness as a judgment criteria.

scholarly journals Using Bayesian Model Selection to Advise Neutron Reflectometry Analysis from Langmuir-Blodgett Monolayers

2019 ◽  
Author(s):  
Andrew McCluskey ◽  
Tom Arnold ◽  
Joshaniel F. K. Cooper ◽  
Tim Snow
Keyword(s):  
Experimental Data ◽  
Soft Matter ◽  
General Framework ◽  
Neutron Reflectometry ◽  
Analytical Models ◽  
Colloid Interface ◽  
X Ray ◽  
Langmuir Blodgett ◽  
Generic Framework

The analysis of neutron and X-ray reflectometry data is important for the study of interfacial soft matter structures. However, there is still substantial discussion regarding the analytical models<br>that should be used to rationalise relflectometry data. In this work, we outline a robust and generic framework for the determination of the evidence for a particular model given experimental data, by<br>applying Bayesian logic. We apply this framework to the study of Langmuir-Blodgett monolayers by considering three possible analytical models from a recently published investigation [Campbell et al., J. Colloid Interface Sci, 2018, 531, 98]. From this, we can determine which model has the most evidence given the experimental data, and show the effect that different isotopic contrasts of neutron reflectometry will have on this. We believe that this general framework could become an important component of neutron and X-ray reflectometry data analysis, and hope others more regularly consider the relative evidence for their analytical models.<br>

scholarly journals Experimental and Numerical Study on Dynamics of Two Footbridges with Different Shapes of Girders

2020 ◽  
Vol 10 (13) ◽  
pp. 4505 ◽  
Author(s):  
Anna Banas ◽  
Robert Jankowski
Keyword(s):  
Natural Vibration ◽  
Numerical Study ◽  
Numerical Results ◽  
Vibration Exciter ◽  
Structural Vibrations ◽  
Impulse Load ◽  
Different Shapes ◽  
Comfort Criteria ◽  
Good Agreement

The paper presents the experimental and numerical results of the dynamic system identification and verification of the behavior of two footbridges in Poland. The experimental part of the study involved vibration testing under different scenarios of human-induced load, impulse load, and excitations induced by vibration exciter. Based on the results obtained, the identification of dynamic parameters of the footbridges was performed using the peak-picking method. With the impulse load applied to both structures, determination of their natural vibration frequencies was possible. Then, based on the design drawings, detailed finite element method (FEM) models were developed, and the numerical analyses were carried out. The comparison between experimental and numerical results obtained from the modal analysis showed a good agreement. The results also indicated that both structures under investigation have the first natural bending frequency of the deck in the range of human-induced excitation. Therefore, the risk of excessive structural vibrations caused by pedestrian loading was then analysed for both structures. The vibration comfort criteria for both footbridges were checked according to Sétra guidelines. In the case of the first footbridge, the results showed that the comfort criteria are fulfilled, regardless of the type of load. For the second footbridge, it was emphasized that the structure meets the assumptions of the guidelines for vibration severability in normal use; nevertheless, it is susceptible to excitations induced by synchronized users, even in the case of a small group of pedestrians.

Determination of Some Mechanical Properties of Welded Reinforcing Steel with Self-Shielded Wires by Vibration Tests

2014 ◽  
Vol 1029 ◽  
pp. 206-211 ◽  
Author(s):  
Liviu Bereteu ◽  
Mircea Burcă ◽  
Raul Moisa ◽  
Dorin Simoiu ◽  
Gheorghe Drăgănescu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Welding Process ◽  
Steel Reinforcement ◽  
Reinforcing Steel ◽  
Coated Electrode ◽  
Major Disadvantage ◽  
Steel Bars ◽  
Vibration Tests ◽  
The Cost

Reinforced concrete is a material formed by pouring concrete over reinforcement steel bars and wires and sometimes by a polymer that turns by drying in a hard and rigid composite. Welding of steel reinforcement concrete is a relatively difficult operation and with a large amount of work, given by the large number of welds that are needed and when this work is make in site conditions. The most common method of steel reinforcement welding is manual welding with coated electrode. The major disadvantage of this process is low productivity in welding effects on execution time, and the cost of welding. An alternative to manual welding with coated electrode for steel reinforcement welding on site is the welding process with self-shielded tubular wires.The aim of this paper is to determine the mechanical properties of welded reinforcing steel PC 52 with self-shielded wires, using a vibroacustic technique. To validate this method, the results obtained by vibroacoustic signal processing are compared with those determined by the tensile stresses of the same samples.

Dynamic Characteristics of Plastic Plates With Bolted Joints

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Akira Saito ◽  
Hideyoshi Suzuki
Keyword(s):  
Dynamic Characteristics ◽  
Vibration Mode ◽  
Acrylonitrile Butadiene Styrene ◽  
Bolted Joints ◽  
Modal Testing ◽  
Analytical Models ◽  
Plate Motion ◽  
Tightening Torque ◽  
Modeling Strategy ◽  
Torque Values

Abstract This paper discusses the dynamic characteristics of plastic plates with bolted joints. The effects of tightening torque on the modal properties of the plates are investigated. Experimental and numerical modal analyses have been conducted on the plates made of acrylonitrile butadiene styrene (ABS), that are clamped by bolted joints. First, the effect of tightening torque on the vibration mode of the plates is investigated by experimental modal analyses. Modal testing has been conducted for various tightening torque values, and the relationships between the modal parameters and the tightening torques are discussed. Second, the effects of tightening torque on the vibration mode are studied by using analytical models for the bolted joints based on the finite element method (FEM). Based on the comparisons between the experimental and the numerical results, a modeling strategy for the boundary conditions between the plates is introduced and its validity is discussed. From both experimental and numerical studies, it is shown that the natural frequencies of the structures with bolted joints tend to converge to specific values as tightening torque increases. Moreover, it is also shown that when modeling the bolted plates by FEM, the inter-plate motion should be constrained by a boundary condition to properly suppress the out-of-phase motion of the plates.

scholarly journals Failure Modes and Resistance of Perforated Steel Rib Shear Connectors under Uplift Forces

2019 ◽  
Vol 2019 ◽  
pp. 1-16 ◽  
Author(s):  
Xiaoqing Xu ◽  
Yuqing Liu
Keyword(s):  
Composite Structures ◽  
Failure Modes ◽  
Analytical Models ◽  
Shear Connectors ◽  
Steel Bar ◽  
Concrete Damage ◽  
Uplift Resistance ◽  
Transverse Steel ◽  
Uplift Forces

In recent years, there is a rapid increase in the application of perforated steel rib shear connectors in steel and concrete composite structures. The connectors must not only ensure shear transfer but also sufficient uplift resistance. The shear behavior of connectors has been extensively investigated. However, studies on uplift resistance are lacking so far. Therefore, three push-out test specimens were tested to investigate the shear and tension behavior of perforated L-shaped and plain steel rib shear connectors. The failure modes of connectors were analyzed, and analytical models for the determination of uplift resistance were derived based on test results. The results showed that the ductility of perforated steel rib shear connectors under uplift force was smaller than that under shear force, and more severe concrete damage surrounding the rib and larger bending deformation of transverse steel bar was observed. The rib flange of L-shaped perforated rib has a significant contribution to the uplift resistance. It was suggested to increase the rib height of L-shaped rib to avoid the horizontal crack at the height of the rib flange. The validity of the proposed analytical models was confirmed by comparing the failure modes and capacities of specimens.

scholarly journals Dynamic Modal Analysis of Vertical Machining Centre Components

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Anayet U. Patwari ◽  
Waleed F. Faris ◽  
A. K. M. Nurul Amin ◽  
S. K. Loh
Keyword(s):  
Modal Analysis ◽  
Mode Shape ◽  
Modal Testing ◽  
Machine Component ◽  
Vibration Modes ◽  
Structural Dynamic ◽  
Element Simulation ◽  
Analysis Technique ◽  
Design Software

The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Determination of dynamic rail properties by means of modal testing

2002 ◽  
Author(s):  
Shyh-Chour Huang ◽  
Ren-sheng Lin ◽  
Jiun-Rong Liao ◽  
Yung-Chuan Chen
Keyword(s):  
Modal Testing

Coupling of Turbomachine Blade Vibrations Through the Rotor

1967 ◽  
Vol 89 (4) ◽  
pp. 502-512 ◽  
Author(s):  
J. T. Wagner
Keyword(s):  
Forced Vibration ◽  
Natural Frequencies ◽  
Vibration Response ◽  
Analytical Models ◽  
Finite Mass ◽  
Blade Vibration ◽  
Resonant Frequencies ◽  
Vibration Tests ◽  
Flexible Disk ◽  
Turbomachine Blade

The forced vibration response of subsystems with different natural frequencies and damping, attached to a foundation with finite stiffness or mass, is calculated. Analytical models include simulations of turbomachine blading on a flexible disk or on a rotor with finite mass. Coupling through the disk or rotor explains variations in resonant frequencies and amplitudes that have been observed in blade-vibration tests. Effects on damping measurements are also determined.

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