scholarly journals A Case Study of Analysis of Natural Frequency Variability Related to Manufacturing Process

2010 ◽  
Vol 17 (4-5) ◽  
pp. 537-550
Author(s):  
T. Uhl ◽  
W. Lisowski
Keyword(s):  
Rapid Prototyping ◽  
Natural Frequency ◽  
Manufacturing Process ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Point Of View ◽  
Modal Testing ◽  
Fe Model ◽  
Structural Dynamic ◽  
Traditional Manufacturing

One of the important challenges present nowadays in the automotive industry is minimizing of a car components design time. Traditional manufacturing of a prototype is usually a time and a cost consuming process. Alternatively, rapid prototyping techniques can be used in such a case. In the reported research a brake caliper was investigated, since it is an example of an element, which should have very strictly defined structural dynamic properties. As a technique of rapid prototyping of the considered caliper the 3D printing of a mould was selected. A process of the caliper casting with the use of the "prototype" mould is different than the one with the use of the metal form. Thus it is very likely that the both considered types of the caliper would possess different properties from the point of view of structural dynamics.Structural dynamic properties can be analyzed both numerically and experimentally. Simulation of the caliper FE model with uncertain parameters was used to analyze influence of various caliper parameters on its natural frequency values. Modal testing of the caliper was performed with the aim of investigation of applicability of Experimental Modal Analysis for determination of variability of natural frequencies resulting from the manufacturing process. In the course of this research, the natural frequencies of the prototype caliper and the standard caliper were compared.

Detection of Damage Extension in Cantilever Beams Using Change Ratio of Frequency Response Functions

2011 ◽  
Vol 50-51 ◽  
pp. 875-879
Author(s):  
Hai Lei Jia ◽  
Yin Zhao
Keyword(s):  
Frequency Response ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Damage Index ◽  
High Sensitivity ◽  
Cantilever Beams ◽  
Response Functions ◽  
Full Spectrum ◽  
Structural Dynamic ◽  
Low Dimensional

Frequency response function (FRF) is a fundamental dynamic index, which is capable of reflecting structural dynamic properties using full-spectrum information. In spite of distinct merits over conventional modal parameters, the FRF has an observable drawback of multi-dimensionality, unsuited for damage characterization. Such a situation motivates an interesting subject, i.e., extracting low-dimensional, high-sensitivity damage index from the FRF. This study focuses on developing a valid damage index, called FRF change ratio, to detect extension of damage. An experiment towards cantilever beams is systemically conducted. The results show that the FRF change ratio can effectively reflects damage extension, and it is more sensitive than conventional natural frequencies. This new damage index holds promise for practical damage detection in beam-like structures.

Shaking Table Experimental Study on Damage Mechanism of the Disconnecting Switch under Seismic Excitation

2011 ◽  
Vol 488-489 ◽  
pp. 351-354
Author(s):  
Paweł Dembowski ◽  
Robert Jankowski
Keyword(s):  
High Voltage ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Safety Issue ◽  
Damage Mechanism ◽  
Shaking Table ◽  
Seismic Excitation ◽  
Structural Dynamic ◽  
Electric Circuits ◽  
Seismic Tests

The efficiency of the energetic network is a very import safety issue in the region experienced by the earthquake. High voltage disconnecting switches are important elements of the energetic infrastructure used to separate electric circuits (i.e. during repairs), which should not be damaged remaining fully operational. The aim of the paper is to show the results of the shaking table experimental investigation focused on damage mechanism of a high voltage disconnecting switch under seismic excitation. The real example of the two-column pantograph-type disconnecting switch was considered in the study. First, the tests were carried out by exciting the unit with the sweep-sine function. Based on the results, the structural dynamic properties of undamaged structure (natural frequencies, damping ratios) could be determined. Then, the so called rumbling seismic tests were conducted in order to determine the seismic strength of disconnecting switch according to the standards PN-EN 60068-3-3. After each experiment, the sweep-sine test was carried out so as to check the decrease in the natural frequencies of the unit. The results of the study show that the lower parts of the columns, which serve as isolators, are the most critical locations of the disconnecting switch considered. The unit was damaged due to failure of one of the rotational mechanisms installed at the bottom of columns.

Dynamic Properties of Delaminated Braided Textile Composite Beams

2008 ◽  
Author(s):  
Benjamin Dauda ◽  
S. Olutunde Oyadiji ◽  
Prasad Potluri
Keyword(s):  
Natural Frequency ◽  
Vibration Analysis ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Experimental Testing ◽  
Composite Beams ◽  
Textile Composite ◽  
Element Analysis ◽  
Frequency Shifts ◽  
Cantilevered Beams

In this paper, vibration analysis of through-width single- and multi-delaminated cantilevered composite beams is carried out using Finite Element Analysis (FEA) approach. Different configurations of multiple delaminations are considered. The FEA results for single delaminations are validated via experimental testing. It is found that changes in the natural frequencies of delaminated cantilevered beams are related to the number, type and distributions of delaminations within a beam. Also, the natural frequency shifts due to single or multiple delaminations are influenced by the thickness-wise locations of the delaminations. As the delamination is moved from the outermost inter-laminar layer towards the mid-plane of the beam, the natural frequency decreases and reaches a minimum value when the delamination is located at the midplane. Single delaminations have a more significant effect on natural frequencies than multiple delaminations of the same overall dimension as the single delamination. Furthermore, it is found that there is a greater reduction in natural frequency when multiple delaminations are close together than when they are spread out. However, where the locations of multiple delaminations coincide with nodal or antinodal vibration points, the effect is significantly altered.

Estimation of the dynamic properties of floors using Heel Drop Tests

2021 ◽  
Author(s):  
Mehdi Setareh ◽  
Jiang Li
Keyword(s):  
Dynamic Response ◽  
Natural Frequency ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Accurate Estimate ◽  
Inexpensive Method ◽  
Structure Interaction ◽  
Modal Damping ◽  
Drop Tests ◽  
Interaction Phenomenon

<p>To evaluate the dynamic response of floors, it is important to estimate their dynamic properties, in particular natural frequencies and modal damping ratios. Heel drop test is a simple and inexpensive method of floor excitation to measure its dynamic properties. Even though this test can result in a relatively accurate estimate of the floor natural frequency, this may not be the case for the modal damping ratios. With the help of a number of volunteers, heel drop tests were conducted on a force platform placed on a test floor. The tests were also repeated using an instrumented hammer. The results showed that the measured natural frequency using heel drops was close to that found using the instrumented hammer. However, the modal damping ratios found using the heel drop tests were higher, which can be attributed to the human-structure interaction phenomenon.</p>

Dynamic Properties of a Heliostat Structure Determined by Numerical and Experimental Modal Analysis

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
J. Felipe Vásquez-Arango ◽  
Reiner Buck ◽  
Robert Pitz-Paal
Keyword(s):  
Modal Analysis ◽  
Vortex Shedding ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Simple Approach ◽  
Operating Conditions ◽  
Mode Shapes ◽  
Fe Model ◽  
Damping Coefficients ◽  
Operating Points

An experimental and numerical modal analysis was performed on an 8 m2 T-shaped heliostat structure at different elevation angles. The experimental results were used to validate a finite element (FE) model by comparing natural frequencies and mode shapes. The agreement between experiments and simulations is good in all operating points investigated. In addition, damping coefficients were determined experimentally for each mode, in order to provide all necessary information for the development of a dynamic model. Furthermore, potentially critical operating conditions caused by vortex shedding were identified using a simple approach.

A Theory Treatment of Pedestrian-Induced Lateral Vibration of Structure

2017 ◽  
Vol 140 (6) ◽  
Author(s):  
Qingshan Yang ◽  
Yanan Gao
Keyword(s):  
Natural Frequency ◽  
Dynamic Properties ◽  
Damping Capacity ◽  
Lateral Vibration ◽  
Structural Damping ◽  
Step Width ◽  
Step Frequency ◽  
Public Attention ◽  
Structural Dynamic ◽  
Dynamic Performances

The lateral excessive sway motion caused by pedestrian traffic has attracted great public attention in the past decades years. However, the theories about exploring the effect of pedestrian on the lateral dynamic properties of structure are scarce. The new contribution of this paper is that a new pedestrian-structure system is proposed for exploring the effect of human on structural dynamic properties based on a sway assumption. Study shows that pedestrian deteriorates the natural frequency of structure and improves structural damping. The influence tendencies of pedestrian on structure can be supported by measurements. The further parametric study shows that the changes of human dynamic parameters have some evident impacts on structural dynamic performances. For example, the increase of leg damping can trigger an improvement of structural damping capacity. In addition, the walking step frequency closing structural harmonic natural frequency can incur the worst response. The increase of step width deteriorates lateral vibration and structural frequency but can slightly improve structural damping. One of essential reasons influencing structural lateral dynamic properties is the dynamic human system including body mass, damping, stiffness, and its motion behavior such as step frequency. This theory is proposed to analyze how pedestrian alters the lateral dynamic performances on those sensitive structures such as the footbridges or stadium bleachers. For example, how the variation of step width influences the change of natural frequency of structure?

Dynamic Characteristic of an Artificial Wing Mimicking a Beetle Hind Wing

2011 ◽  
Author(s):  
Ngoc San Ha ◽  
Nam Seo Goo ◽  
Tailie Jin ◽  
Quoc Viet Nguyen ◽  
Hoon Cheol Park
Keyword(s):  
Dynamic Characteristic ◽  
Natural Frequency ◽  
Natural Frequencies ◽  
Hind Wing ◽  
Damping Factor ◽  
Laser Sensor ◽  
Lateral Direction ◽  
Structural Dynamic ◽  
Artificial Wing ◽  
Beetle Hind Wing

Biomimetics is one of the most important paradigms as researchers seek to invent better engineering designs over human history. However, the observation of insect flight is a relatively recent work. Several researchers have tried to address the aerodynamic performance of flapping creatures and other natural properties of insects, although there are still many unsolved questions. In this study, we have attempted to investigate the structural dynamic characteristic of an artificial wing that mimicked the wing shape and main venation structure of a beetle hind wing using a non contact measurement method. The structural dynamic characteristic of the artificial wing was measured and compared to the real beetle hind wing by determining the natural frequencies and damping factor. The artificial wing was glued with the cyanoacrylate adhesive at the wing base onto the acrylic stand which was attached to the base of a shaker. The shaker produces the translation motion in the lateral direction of the wing plane. A non-contact laser sensor was used to measure the displacement history of the painted spots on the hind wing. A Bru¨el & Kjær FFT analyzer was adopted to calculate the frequency response functions where the natural frequencies of the wing structure can be extracted. The fundamental natural frequency of artificial wing is 51.3 Hz while the natural frequency of the beetle hind wing is 48.8 Hz. In addition, the wing structures were lightly damped with damping factor around 3.1% that is close to the one of beetle hind wing. We found that, in terms of the wing elasticity, the plastic wing frame of artificial wing was suitable for beetle-like flight.

The Modal Twist Axis: A Method for Describing the Dynamical Characteristics of Single Track Vehicles

2015 ◽  
Author(s):  
Alberto Doria ◽  
Luca Taraborrelli
Keyword(s):  
Natural Frequencies ◽  
Resonance Condition ◽  
Dynamic Properties ◽  
Point Of View ◽  
Experimental Results ◽  
Single Track ◽  
Structural Element ◽  
Lumped Elements ◽  
Axis Position ◽  
The Stability

Static and dynamic properties of single-track vehicles components (such as frames, front forks and swing-arms) play a fundamental role from the point of view of vehicle stability, which is a key issue of single-track vehicles dynamics and safety. Nowadays, the stability of a vehicle is studied by means of multi-body codes, in which it is possible to implement models of the tires and of the components of the vehicle. Actually, the chassis and the forks of motorcycles are mechanical systems with distributed mass and stiffness properties, but in most simulation codes the elastic properties of the structural elements are modeled with lumped stiffness and damping elements. Very few research has been carried out on the identification of the lumped elements, of their natural frequencies and damping from laboratory tests. In the first section of the paper, the concept of modal twist axis is proposed to characterize the dynamic deformability of a structural element. The twist axis is defined as the intersection between the un-deformed plane of the structural element and the plane tangent to the free end of the structural element in deformed condition. If the identification of the twist axis is carried out in resonance condition, the modal twist axis is found. A method for measuring the modal twist axis position and orientation is described. It is based on impulse excitation by means of a modally tuned hammer and three accelerometers which are used for defining the deformed plane. In the second section of the paper, experimental results obtained on two motorcycle frames are shown. In order to know the modal shapes of the components at the measured natural frequencies, modal analysis is carried out. A correlation between the modal twist axis position and the mode of vibration is shown and discussed. In order to study the influence of the constraints on dynamic properties, the frames are tested in two different constraint conditions: rear constrained and front constrained. The last section of the paper shows the experimental results obtained by applying the proposed method to other motorcycle components, such as a front fork and a frame with the engine.

Structural Modification of a Pipe Under Harmonic Excitation Using an Hybrid Numerical/Experimental Method

2011 ◽  
Author(s):  
Charles Bodel
Keyword(s):  
Modal Analysis ◽  
Nuclear Power ◽  
Natural Frequencies ◽  
Harmonic Excitation ◽  
Experimental Modal Analysis ◽  
Point Of View ◽  
Mode Shapes ◽  
Design Stage ◽  
Centrifugal Pumps ◽  
Structural Dynamic

Vibrations generated by centrifugal pumps are difficult to predict at the design stage, for it is hardly possible to accurately determine the natural frequencies of pipes and to avoid coincidences with the blade pass frequency of the pump and its harmonics. One is often led to modify the existing structure, by adding stiffness, mass or damping. This paper illustrates this point on a pipe connected to a pump in a nuclear power plant operated by EDF (E´lectricite´ de France). In October 2010, abnormal vibrations were measured on a thin pipe at the outlet of a pump in a powerplant in France. The French nuclear regulatory commission asked EDF to perform a diagnosis and to define solutions within a few months. EDF/R&D division has used an original method developed in 2004 based on hybrid data, and called LMME-SDM (for Local Model Mode-shapes Expansion Structural Dynamic Modification). The main objective is to define a structure modification able to remove all natural frequencies close to the harmonic excitation. For the purpose of the study, we need a numerical model, which should be fairly correct from a static point of view, but which is not necessarily updated from a dynamic point of view, and an experimental modal analysis carried out under real conditions on the pipe. During the experimental modal analysis, a test of added mass has been carried out so that the method can be validated by comparing the predicted and the observed frequency. This method has already been used in industrial cases in former studies [3], however the study presented here has reached a higher level in complexity. Even if this method is able to give reasonable results compared to measurements, it is close to its limits.

Dynamic Characterization of Car Door and Hood Panels Using FEA and EMA

2013 ◽  
Vol 471 ◽  
pp. 89-96 ◽  
Author(s):  
Zahir Hanouf ◽  
Waleed F. Faris ◽  
Mohd Jailani Mohd Nor
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Modal Analysis ◽  
Dynamic Properties ◽  
Experimental Modal Analysis ◽  
Modal Testing ◽  
Dynamic Characterization ◽  
Element Analysis ◽  
Structural Dynamic

The dynamic characterization of vehicle structures is a crucial step in NVH analysis and helps in refining the vibration and noise in new vehicles. This paper investigates the dynamic properties of two parts of the vehicle structure which are door and hood panels. Theoretical modal analysis which is referred to as Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA) or modal testing has been used as investigative tools. The paper investigates the structural dynamic properties of door and hood panels of a local car. ME'scope software was used to analyze the data obtained from Pulse to extract the dynamic properties of the panels. LS-DYNA software was used to analyze the dynamic behavior of the structure. The comparison between the results obtained from both analyses showed some similarity in frequencies and mode shapes. Finally the paper concludes that experimental modal analysis and finite element analysis can both be used to extract dynamic properties of structures.

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