scholarly journals An analytical model for determining the effect of damping on 3D natural frequency of reinforced walls

2018 ◽  
Vol 6 (1) ◽  
pp. 35-52
Author(s):  
Alireza Darvishpour ◽  
Ali Ghanbari ◽  
S. A. A. Hosseini ◽  
Masoud Nekooei ◽  
Tayyebeh Darvishpour
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Reinforced Walls

scholarly journals Analysis and Experimental Validation of a Piezoelectric Harvester with Enhanced Frequency Bandwidth

Materials ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1243 ◽  
Author(s):  
Haim Abramovich ◽  
Idan Har-nes
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Vibrational Energy ◽  
Total Output ◽  
Frequency Bandwidth ◽  
Parametric Investigation ◽  
Two Factors ◽  
Set Up ◽  
Spring Constants ◽  
Advanced System

The use of a single bimorph as a harmonic oscillator aimed at harvesting vibrational energy is not effective due to its inherent narrow frequency bandwidth stemming from the need to adjust the natural frequency of the harvester to the platform excitation frequencies. Therefore, the present research focuses on the development, manufacturing, and testing of an advanced system based on three bimorphs, capable of adjusting their natural frequencies using tip end masses, and interconnected by springs, thus enlarging the system’s bandwidth. An analytical model was developed for three bimorphs interconnected by two springs with three end masses. The model can predict the output generated voltage from each bimorph, and then the total output power is measured on a given outside resistor as a function of the material properties, the geometric dimensions of the vibrating beams, the end-masses, and the spring constants. The analytical model was then compared with data in the literature, yielding a good correlation. To further increase the reliability of the model, a test set-up was designed and manufactured that included three bimorphs with three end-masses connected by two springs. The system was excited using a shaker, and the output voltage was measured for each bimorph for various configurations. Then, the analytical model was tuned based on the test results by introducing two factors, the quality and the stiffness factors, and the predictions of the calibrated analytical model were compared with the experimental results, yielding a good correlation. The calibrated analytical model was then used to perform a comprehensive parametric investigation for two and three bimorphs systems, in which the influences of various parameters—like spring constant, mass value, thickness, and width and length of the bimorph and the substrate beam—on the output generated power were investigated. The main conclusion from this parametric investigation was that by correctly choosing the geometric sizes of the cantilevers, the adequate tip end masses, and the ratio between constants of the springs, the frequency bandwidth is expanded yielding a higher harvested power. Typical harvested power of the present designed system can reach up to 20 mW at the first natural frequency and up to 5 mW for the second natural frequency.

Hydrostatic Gas Journal Bearings for Micro-Turbomachinery

2004 ◽  
Vol 127 (2) ◽  
pp. 157-164 ◽  
Author(s):  
L. X. Liu ◽  
C. J. Teo ◽  
A. H. Epstein ◽  
Z. S. Spakovszky
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
High Speed ◽  
Experimental Testing ◽  
Fluid Dynamic ◽  
Damping Ratio ◽  
Journal Bearings ◽  
Fiber Optic Sensor ◽  
Gas Bearings ◽  
Aspect Ratios

Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500m∕s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L∕D<0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the micro-bearing designs to an exotic spot in the design space for hydrostatic gas bearings. This paper presents a new analytical model for axially fed gas journal bearings and reports the experimental testing of micro gas bearings to characterize and to investigate their rotordynamic behavior. The analytical model is capable of dealing with all the elements of, (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy. First, a newly developed analytical model for hydrostatic gas journal bearings is introduced. The model consists of two parts, a fluid dynamic model for axially fed gas journal bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundary for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.

Isothermal Modeling of Meniscus Oscillation in the Continuous Strip Casting Process

2010 ◽  
Author(s):  
Kevin W. Wilcox ◽  
A. Gordon L. Holloway ◽  
Andrew G. Gerber
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Cold Work ◽  
Casting Process ◽  
Contact Angles ◽  
Strip Casting ◽  
Water Model ◽  
Working Fluid ◽  
Contact Points ◽  
Continuous Strip

In the continuous strip casting process a meniscus forms a compliant boundary between the casting nozzle and transporting conveyor. Movement of this meniscus during casting has been shown to create surface defects, which require extensive cold work to remove and limit the minimum thickness for which sections may be cast. This paper discusses experimental work conducted to test an analytical model of the meniscus oscillation. A high frame rate shadowgraph technique was used on an isothermal water model of the casting process to observe meniscus motion, and thus allowing the calculation of meniscus frequency, amplitude, contact points and contact angles. Both natural frequency and flow excited tests were conducted. Natural frequency tests were also conducted using mercury as the working fluid, having a non-wetting contact angle, typical of molten metals. The experimental results were found to be in good agreement with the predictions of theory for both wetting and non-wetting conditions. The experimentally verified analytical model for meniscus motion is valuable to the design of the continuous casting process, because it offers an opportunity to mitigate the effects of boundary motion on surface quality.

Study on Isolation Device for Decrease of Displacement by Using Control of Friction

2005 ◽  
Author(s):  
Masanori Shintani ◽  
Yuichi Hattori ◽  
Tadashi Kotera
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Friction Force ◽  
External Force ◽  
Simulation Analysis ◽  
Relative Displacement ◽  
Earthquake Damage ◽  
Experimental Results ◽  
Isolation Device ◽  
Analytical Program

This paper deals with an isolation device by using friction force. An isolation device decreases response acceleration and external force. Therefore, earthquake damage is reduced. However, an isolation device has a demerit for large relative displacement. A low horizontal natural frequency decreases the response acceleration. Therefore, in this research, a soft spring is attached to the base of the structure. The purpose of this research is to decrease the relative displacement by using the friction force. Then, an analytical model in consideration of the friction force is proposed, and a simulation is analyzed with well-known earthquake waves. Consequently, as the friction force increases, the results show that the relative displacement decreases. However, it is found that the response acceleration increases. But it is thought that optimal friction force exists, and this force decreases both the response acceleration and the relative displacement. This is considered to change with the properties of earthquake waves. Therefore, it is thought that the response acceleration and the relative displacement are decreased by changing the friction force to the most suitable value for earthquakes. This isolation device is examined with simulation analysis. An experimental device is made under the same conditions as the proposed analytical model. The analytical results are compared with the experimental results, and the validity of an analytical program is examined.

scholarly journals Analytical Model For Approximately Calculating Of The Second Frequency Of Cross Vibrations For Complex Shape Barrel Of The Small ARM

2015 ◽  
Vol 21 (3) ◽  
pp. 803-808
Author(s):  
Conyu Grigorov Conev ◽  
Krasimir Stoianov Davidov
Keyword(s):  
Experimental Investigation ◽  
Natural Frequency ◽  
Analytical Model ◽  
Analytical Method ◽  
Complex Shape ◽  
Made In

Abstract The report scrutinizes an analytical model for approximately calculating of the second natural frequency of cross vibrations for complex shape barrel of the small arm. The model is based on known formulas, used for calculating on the second natural frequency of cross vibrations for cylindrical barrels. In suggested analytical model a coefficient, that gives an influence on form of the complex barrel is added. An experimental investigation is made in order to prove the workability of the analytical method.

Effects of Bearing Configuration on Spindle Dynamic Characteristics

2013 ◽  
Vol 437 ◽  
pp. 76-80
Author(s):  
Guo Ping An ◽  
Bing Bing Zhang ◽  
Yong Sheng Zhao ◽  
Li Gang Cai
Keyword(s):  
Modal Analysis ◽  
Natural Frequency ◽  
Analytical Model ◽  
Dynamic Characteristics ◽  
Response Analysis ◽  
Face To Face ◽  
Harmonic Response ◽  
Radial Stiffness ◽  
Proposed Model ◽  
Harmonic Response Analysis

This article investigates the effects of bearing configuration on the spindle dynamic characteristics. First, an analytical model of spindle is proposed and the bearing sets radial stiffness is calculated. Second, the spindle analytical model is developed to perform modal analysis and harmonic response analysis with ANSYS, and then obtain the natural frequency and FRF under different bearing configurations. The result suggests that bearing configuration has little effect on the natural frequency of spindle system and the FRF amplitude corresponding to the 1st natural frequency under back to back configuration or face to face configuration is relatively small. Finally, the proposed model is validated by modal experiment.

scholarly journals Analytical model for flexural damping responses of CFRP cantilever beams in the low-frequency vibration

2018 ◽  
Vol 37 (4) ◽  
pp. 669-681 ◽  
Author(s):  
Mo Yang ◽  
Yefa Hu ◽  
Jinguang Zhang ◽  
Guoping Ding ◽  
Chunsheng Song
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Natural Frequency ◽  
Analytical Model ◽  
Flexural Vibration ◽  
Maximum Error ◽  
Damping Capacity ◽  
Element Analysis ◽  
First Order ◽  
Specific Damping Capacity

In this paper, an analytical model for the flexural vibration damping of Carbon Fiber Reinforced Plastics (CFRP) cantilever beams was proposed, which is based on the Lamination Theory and Euler–Bernoulli Beam Theory. By using a finite element analysis and an analytical model, four sets of specific damping capacity with different pavement schemes were predicted, and flexural vibration test and damping analysis were carried out. Comparing the analytical model, finite element analysis, and test results, it could be found that the analytical model had relatively good accuracy in predicting the first-order natural frequency and specific damping capacity of the bending vibration of CFRP beams. The maximum error of the first-order natural frequency between the analysis result and the experimental result was 7.05%; the maximum specific damping capacity error was only 5.65%. Comparing the finite element analysis method and the experiment results, the maximum error of the first-order natural frequency was 7.8%, the error of the specific damping capacity was bigger, and the [±30°]5S specimen was as high as 18.7%. However, there was a significant error when the analytical model was used to predict the second-order natural frequency and the specific damping capacity of CFRP beam’s flexural vibration.

scholarly journals An analytical model for predicting the natural frequency of retaining structures

2020 ◽  
Vol 15 (1) ◽  
pp. 7-12
Author(s):  
Lyazid Guechi ◽  
Smaïn Belkacemi
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Current Model ◽  
Accurate Determination ◽  
Analytical Models ◽  
Retaining Structures ◽  
The Earth ◽  
Earth Pressures ◽  
Analytical Formulas ◽  
Failure Wedge

Abstract The importance of the retaining structures is crucial in geotechnical engineering and the accurate determination of static and seismic earth pressures and natural frequency is important for study the dynamic behavior of these structures. Usually analytical formulas which do not consider the earth pressures behind retaining structure are used. An analytical model for predicting the natural frequency of retaining structures including the earth pressures by failure wedges is proposed in the present analysis. The model considers the effect of Coulomb and Mononobe Okabe failure wedges. Backfill material is considered in the analysis as cohesionless. The failure wedge is an important factor which should be considered in determining the natural frequency of retaining structures. As the weight of failure wedge increases the natural frequency decreases significantly. The current model is validated using several analytical models reported in the literature of the earlier researcher.

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