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Robust control methodology for the design of supplementary damping controllers for FACTS devices

KUIAVA, Roman; RAMOS, Rodrigo A.; BRETAS, Newton G.
Fonte: Sociedade Brasileira de Automática Publicador: Sociedade Brasileira de Automática
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.81%
In this paper, a new procedure to design Supplementary Damping Controllers (SDCs) for Flexible Alternating Current Transmission System (FACTS) devices is proposed. The control design problem is formulated as a search for a feasible controller subject to restrictions in the form of Linear Matrix Inequalities (LMIs). The main objective, from the application viewpoint, is the improvement of the damping ratios associated to inter-area oscillation modes. Unlike other types of formulations existing in the literature, this new formulation is capable of explicitly modeling the constraints on the controller bandwidth, which are crucial to avoid undesired amplification of high frequency noise signals coming into the controller input. To illustrate the efficiency of the proposed procedure, the design of an SDC for a Thyristor Controlled Series Capacitor (TCSC) placed in the New England/New York benchmark test system is carried out. The results show the designed controllers are able to provide adequate damping for the oscillations modes of interest for several different operating conditions.; Este artigo propõe um novo procedimento para projeto de controladores suplementares de amortecimento (ou SDCs, do inglês Supplementary Damping Controllers) para dispositivos FACTS. O problema de projeto do controlador é formulado como uma busca por um controlador que satisfaça um conjunto de restrições na forma de desigualdades matriciais lineares (ou LMIs...

Dissipação e ruído de dipolos magnéticos coletivamente acoplados a um circuito ressonante; Damping and noise of magnetic dipoles collectively coupled with a resonant circuit

Faria, Alencar José de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/03/2008 PT
Relevância na Pesquisa
36.81%
Estudamos o amortecimento radiativo e o ruído de spins de um material magnético acoplado a um circuito ressonante. O amortecimento radiativo em ressonância magnética é um fenômeno de dissipação, na qual a magnetização preparada após um pulso de Rabi sofre um decaimento até seu estado de equilíbrio. O material magnético perde energia através do seu acoplamento com o circuito ressonante, que deve estar sintonizado na freqüência de Larmor dos spins do material. Apesar deste fenômeno ter sido estudado há vários anos, nenhuma descrição quântica completa lhe foi dada. Apresentamos um modelo hamiltoniano quântico que descreve o amortecimento radiativo. Para isto usamos o método de equações de Langevin quânticas. Mostramos que além do amortecimento radiativo do material magnético, se o circuito está em um estado inicial coerente, a magnetização adquire um movimento complicado não-trivial. Usando as mesmas equações de Langevin, estudamos a influência da amostra no ruído do circuito ressonante. Calculamos a densidade espectral da corrente no caso em que todo o sistema está em equilíbrio térmico. Pudemos verifcar a efcácia do método comparando-o com estudos anteriores. Além disso, estudamos as alterações do ruído do circuito quando uma tensão oscilante externa é aplicada. Nesta situação surgem dois outros picos laterais ao pico central do espectro de absorção da amostra magnética. Isso leva a três depressões no espectro da corrente do circuito. Este efeito deve-se à separação dupla dos estados de energia dos spins. Comentamos sobre a analogia deste fenômeno com a fluorescência ressonante observada na Óptica Quântica.; We study the radiation damping and the spin noise of a magnetic material coupled with a resonant circuit. Radiation damping in magnetic resonance is a dissipation phenomenon...

Simulação de modelos dinâmicos com amortecimento não-proporcional; Dynamic simulations of mechanical systems with non-proportional damping

Mamede, Ana Lúcia Grici Zacarin
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/12/2008 PT
Relevância na Pesquisa
36.97%
Alguns métodos aproximados são sugeridos na literatura relacionada para encontrar a resposta de sistemas com amortecimento não-proporcional. Muitas vezes procura-se estabelecer um critério para aproximar o amortecimento não-proporcional por um modelo de amortecimento proporcional. Neste trabalho foram utilizadas simulações de modelos dinâmicos com três graus de liberdade, com amortecimento não proporcional, a fim de analisar os valores obtidos para as freqüências naturais, estimados a partir dos autovalores resultantes desses modelos. Os cálculos das freqüências naturais e dos amortecimentos modais foram feitos admitindo-se a validade das relações entre estes parâmetros e os autovalores do problema como são bem conhecidas no caso do amortecimento proporcional. Observa-se que, para o caso de amortecimento não-proporcional, este procedimento pode levar a erros significativos na avaliação destes parâmetros. Nos problemas simulados é possível quantificar os erros nas avaliações das freqüências naturais, sendo significativos para fatores de amortecimentos altos. Observa-se que para os fatores de amortecimento não é possível quantificar estes erros, sendo que seus valores são apenas aproximações baseadas na teoria de amortecimento proporcional. Este trabalho apresenta dados que possibilitam uma discussão sobre as diferenças encontradas entre os valores das freqüências naturais e os valores estimados pelas expressões clássicas do amortecimento proporcional.; Some approximate methods are suggested in the related literature to find the output of mechanical systems with non-proportional damping. Often they try to establish a criterion that approximates the non-proportional damping to proportional damping model. In this work...

Algoritmo de determinação do coeficiente de amortecimento em materiais refratários de alta alumina; Algorithm for damping factor calculus in high alumina castables

Musolino, Bruno de Castro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/07/2011 PT
Relevância na Pesquisa
36.85%
O amortecimento, fenômeno pelo qual energia mecânica em um sistema dinâmico é dissipada, é uma das propriedades mais sensíveis dos materiais quanto a presença de trincas e microtrincas. O estudo do amortecimento já é bem estabelecido em áreas como engenharia civil, em que é de importância na resistência mecânica de um sistema sujeito a abalos sísmicos e vibrações, porém vem sendo cada vez mais estudado na indústria de materiais para analisar e quantificar o dano em concretos refratários que sofrem ciclos de choque térmico. Este trabalho apresenta uma metodologia e algoritmo para a determinação do amortecimento das ressonâncias de um material, para avaliação de danos em concretos refratários, através da análise espectral de tempo-frequência. São também apresentados os resultados obtidos para um sinal simulado, uma barra de alumina densa e um par de barras de concreto refratário comercial de alta alumina, sendo uma com e outra sem dano por choque térmico. Com o uso do método foi possível recuperar o valor do amortecimento e a frequência usada para gerar o sinal simulado. O resultado apresentado para a alumina é compatível com o valor encontrado em literatura e, com o resultado obtido para os concretos refratários...

A comparison of two nonlinear damping mechanisms in a vibration isolator

Tang, Bin; Brennan, M. J.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 510-520
ENG
Relevância na Pesquisa
36.85%
The vibration transmissibility characteristics of a single-degree-of- freedom (SDOF) passive vibration isolation system with different nonlinear dampers are investigated in this paper. In one configuration, the damper is assumed to be linear and viscous, and is connected to the mass so that it is perpendicular to the spring (horizontal damper). The vibration is in the direction of the spring. The second configuration is one in which the damper is in parallel with the spring but the damping force is proportional to the cube of the relative velocity across the damper (cubic damping). Both configurations are studied for small amplitudes of excitation, when some analysis can be conducted based on analytical expressions, and for large amplitudes of excitation, where the analysis is based on numerical simulations. It is found that the two nonlinear systems can outperform the linear system when force transmissibility is considered. However, for displacement transmissibility, the system with the horizontal damper exhibits some desirable properties, but the system with cubic damping does not. © 2012 Elsevier Ltd.

Storage moduli, loss moduli and damping factor of GaAs and Ga1-xMnxAs thin films using DMA 2980

Kemei, S. K.; Kirui, M. S. K.; Ndiritu, F. G.; Odhiambo, P. M.; Ngumbu, R. G.; Leite, D. M. G.; Pereira, A. L. J.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 23-26
ENG
Relevância na Pesquisa
36.91%
The spin injector part of spintronic FET and diodes suffers from fatigue due to rising heat on the depletion layer. In this study the stiffness of Ga1-xMnxAs spin injector in terms of storage modulus with respect to a varying temperature, 45 degrees C <= T <= 70 degrees C was determined. It was observed that the storage modulus for MDLs (Manganese Doping Levels) of 0%, 1% and 10% decreased with increase in temperature while that with MDLs of 20% and 50% increase with increase in temperature. MDLs of 20% and 50% appear not to allow for damping but MDLs <= 20% allow damping at temperature range of 45 degrees C <= T <= 70 degrees C. The magnitude of storage moduli of GaAs is smaller than that for ferromagnetic Ga1-xMnxAs systems. The loss moduli for GaAs were found to reduce with increase in temperature. Its magnitude of reducing gradient is smaller than Ga1-xMnxAs systems. The two temperature extremes show a general reduction in loss moduli for different MDLs at the study temperature range. From damping factor analysis, damping factors for ferromagnetic Ga1-xMnxAs was found to increase with decrease in MDLs contrary to GaAs which recorded the largest damping factor at 45 degrees C <= T <= 70 degrees C Hence, MDL of 20% shows little damping followed by 50% while MDL of 0% has the most damping in an increasing trend with temperature. (C) 2013 Elsevier Ltd. All rights reserved.

Innovative low noise surfaces : comparison of damping and absorption

Freitas, Elisabete F.; Rodrigues, José Dias; Rocha, Jorge de Araújo; Silva, Hugo Manuel Ribeiro Dias da
Fonte: Australian Acoustical Society Publicador: Australian Acoustical Society
Tipo: Conferência ou Objeto de Conferência
Publicado em /11/2014 ENG
Relevância na Pesquisa
36.81%
While sound absorption is an acoustic related property reasonably well known and currently used to characterize low noise surfaces, damping is a property commonly used in other domains to define the energy dissipation of a material but rarely used to characterize this important mechanism in road pavements. This paper compares noise related properties such as damping and absorption of five road pavement surfaces. Two of which are innovative and therefore expected to be low noise since they have high voids content, incorporate fine grading aggregates and expanded clay. Other two incorporate rubber and waste high-density polyethylene giving them an elastic and stiff behaviour respectively. The fifth is a conventional material, asphalt concrete, used for control. Sound absorption tests and mechanical impedance tests were carried out in 30x30 cm slabs at 20ºC. To measure absorption, an impedance tube with an open end was put on the surfaces. To determine damping, the response of a hammer impact measured by an accelerometer on suspended slabs was analysed. Results show that the innovative surfaces have better acoustic related properties while the surface with high-density polyethylene provided the worst results. Furthermore, a strong correlation of damping and air voids was found.

A comparative analysis of energy dissipation and equivalent viscous damping of RC columns subjected to uniaxial and biaxial loading

Rodrigues, H.; Varum, H.; Arêde, A.; Costa, A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.81%
The hysteretic behaviour of RC columns has been object of many experimental studies over the past years. However, the majority of these studies are focused on unidirectional loading. An experimental program was carried out where 24 columns were tested for different loading histories, under uniaxial and biaxial conditions. The experimental results are presented in this paper and are discussed in terms of global column behaviour, and particularly with regards to energy dissipation and damping capacity. The energy dissipation capacity of the columns was evaluated in terms of cumulative dissipated energy, comparing uniaxial and biaxial test results, and individual cycle dissipated energy. Ultimately, an equation relating the normalised dissipated energy with the displacement ductility is proposed. The equivalent viscous damping was analysed by comparing the uniaxial with biaxial test results, demonstrating the high influence of the load path in the biaxial response of RC columns. Proposals for estimating the equivalent viscous damping given by other authors are compared with the experimental results. Finally, simplified expressions are proposed to estimate equivalent viscous damping in RC columns under biaxial loading.

Chemical treatment of papaya seeds aiming at long-term storage and control of damping off

Botelho,Silvia de Carvalho Campos; Silveira,Silvaldo Felipe da; Silva,Roberto Ferreira da; Viana,Alexandre Pio
Fonte: Universidade Federal de Viçosa Publicador: Universidade Federal de Viçosa
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
Relevância na Pesquisa
36.85%
Damping off is a nursery disease of great economic importance in papaya and seed treatment may be an effective measure to control. The aim of this work was to evaluate the quality of papaya seeds treated with fungicides and stored under two environmental and packaging conditions. Additionally, the efficiency of fungicide treatments in the control of damping-off caused by Rhizoctonia solani was evaluated. Papaya seeds were treated with the fungicides Captan, Tolylfluanid and the mixture Tolylfluanid + Captan (all commercial wettable powder formulations). Seeds of the control group were not treated. The seeds were stored for nine months in two conditions: packed in aluminum coated paper and kept at 7 ± 1ºC and in permeable kraft paper and kept in non-controlled environment. At the beginning of the storage and every three months the seed quality (germination and vigor tests), emergence rate index, height, dry mass and damping of plants in pre and post-emergence (in contaminated substrate and mycelia-free substrate) were analyzed. Both storage conditions as well as the fungicide treatments preserved the germination and seed vigor. In the infested substrate, seedling emergence was favored by fungicides, but in post-emergence, fungicides alone did not control the damping off caused by R. solani. Symptoms of damping off were not observed in the clean substrate. The results showed that the fungicide treatments may be used to pretreat papaya seed for long-term storage and commercialization.

Noise and vibration damping of Fe-Cr-x alloys

Pulino-Sagradi,Débora; Sagradi,Marcello; Martin,Jean-Luc
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2001 EN
Relevância na Pesquisa
36.88%
The aim of the present work is to study the noise and vibration damping capacity of ferromagnetic Fe-16%Cr base alloys (before and after heat treatment) with different Al and Mo contents. The noise damping was evaluated by the level of sound emission after an impact. The vibration damping was studied using a cantilever device. In addition to these tests, the magnetic structure of the materials was also investigated by Kerr effect. It was verified that the materials can decrease noise level in the frequency range of human earring. The vibration damping is influenced by heat treatment and chemical composition of the alloy. The improvement of vibration damping after heat treatment is ascribed to the decrease of internal stresses in materials and changes in magnetic domain structures.

Multimodal vibration damping through piezoelectric patches and optimal resonant shunt circuits

Viana,Felipe Antonio C.; Steffen, Jr,Valder
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2006 EN
Relevância na Pesquisa
36.88%
Piezoelectric elements connected to shunt circuits and bonded to a mechanical structure form a dissipation device that can be designed to add damping to the mechanical system. Due to the piezoelectric effect, part of the vibration energy is transformed into electrical energy that can be conveniently dissipated. Therefore, by using appropriate electrical circuits, it is possible to dissipate strain energy and, as a consequence, vibration is suppressed through the added passive damping. From the electrical point of view, the piezoelectric element behaves like a capacitor in series with a controlled voltage source and the shunt circuit, commonly formed by an RL network, is tuned to dissipate the electrical energy, more efficiently in a given frequency band. It is important to know that large inductances are frequently required, leading to the necessity of using synthetic inductors (obtained from operational amplifiers). From the mechanical point of view, the vibration energy can be attenuated in a single mode, or in multiple modes, according to the design of the damping device and the frequency band of interest. This work is devoted to the study of passive damping systems for single modes or multiple modes, based on piezoelectric patches and resonant shunt circuits. The present contribution discusses the modeling of piezoelectric patches coupled to shunt circuits...

Chemical treatment of papaya seeds aiming at long-term storage and control of damping off

CAMPOS, S. de C.; SILVEIRA, S. F. da; SILVA, R. F. da; VIANA, A. P.
Fonte: Revista Ceres, v. 61, n. 3, p. 384-391, mai/jun., 2014 Publicador: Revista Ceres, v. 61, n. 3, p. 384-391, mai/jun., 2014
Tipo: Artigo em periódico indexado (ALICE)
EN
Relevância na Pesquisa
36.85%
Damping off is a nursery disease of great economic importance in papaya and seed treatment may be an effective measure to control. The aim of this work was to evaluate the quality of papaya seeds treated with fungicides and stored under two environmental and packaging conditions. Additionally, the efficiency of fungicide treatments in the control of damping-off caused by Rhizoctonia solani was evaluated. Papaya seeds were treated with the fungicides Captan, Tolylfluanid and the mixture Tolylfluanid + Captan (all commercial wettable powder formulations). Seeds of the control group were not treated. The seeds were stored for nine months in two conditions: packed in aluminum coated paper and kept at 7 ± 1°C and in permeable kraft paper and kept in non-controlled environment. At the beginning of the storage and every three months the seed quality (germination and vigor tests), emergence rate index, height, dry mass and damping of plants in pre and post-emergence (in contaminated substrate and mycelia-free substrate) were analyzed. Both storage conditions as well as the fungicide treatments preserved the germination and seed vigor. In the infested substrate, seedling emergence was favored by fungicides, but in post-emergence, fungicides alone did not control the damping off caused by R. solani. Symptoms of damping off were not observed in the clean substrate. The results showed that the fungicide treatments may be used to pretreat papaya seed for long-term storage and commercialization.; 2014

Detection and location of a partial blockage in a pipeline using damping of fluid transients

Wang, X.; Lambert, M.; Simpson, A.
Fonte: ASCE-Amer Soc Civil Engineers Publicador: ASCE-Amer Soc Civil Engineers
Tipo: Artigo de Revista Científica
Publicado em //2005 EN
Relevância na Pesquisa
36.91%
The effects of a partial blockage on pipeline transients are investigated analytically. A partial blockage is simulated using an orifice equation, and the influence of the blockage on the unsteady pipe flow is considered in the governing equations using a Dirac delta function. A simplified, linear dimensionless governing equation has been derived, and an analytical solution expressed in terms of a Fourier series has been developed under nonvarying boundary conditions. The linear analysis indicates that pipe friction and a partial blockage both introduce damping on fluid transients. The friction damping and blockage damping are exponential for each of the individual harmonic components. For each individual harmonic component, the blockage-induced damping depends on the blockage magnitude and position and is also independent of measurement location and the transient event. A new blockage detection method using the blockage-induced transient damping is developed based on the analytical solution. The magnitude of the blockage-induced damping rate indicates the size of the blockage, and the ratios of different damping rates can be used to locate the blockage. The proposed blockage detection method has been successfully used in detecting...

Constrained viscoelastic layer damping of thick aluminum plates: design, analysis, and testing

Bateman, Michael John.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: vii, 109 p. ; ill.
EN_US
Relevância na Pesquisa
36.88%
Approved for public release, distribution is unlimited; Modern naval warfare has been increasingly dependent upon the acoustic silencing of the participants. Constrained viscoelastic layer damping of vibrating elements is one method which can be used to meet acoustic silencing goals. This paper considers constrained viscoelastic layer damping treatments applied to a thick aluminum plate, including single layer, double layer, a milled pocket plate, and a milled 'floating element' configuration. High modal damping values were obtained for each configuration. The Modal Strain Energy method, using finite element analysis to estimate modal loss factors, was investigated for use as a tool in constrained viscoelastic layer damping design. A comparison of experimentally measured frequency response and modal loss factors with those predicted by the modal strain energy method is presented to confirm the possible use of the modal strain energy method as a design tool.; Lieutenant, United States Navy

Damping in stiffener welded structures

Ehnes, Charles W.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xiv, 51 p. : ill. (some col.) ;
Relevância na Pesquisa
36.85%
Approved for public release, distribution is unlimited; Damping of welded structures is a subject of great interest and application for the navy as relates to ship shock survivability and acoustic transmission of ship noise. The purpose of this research is to study the effects of welding on damping. A generic model of a warship's hull structure was used to study damping effects. The model's natural frequencies and mode shapes were calculated using a finite element model prior to model testing. The frequency response and natural frequencies of the model were determined experimentally by exciting the model and measuring the response throughout the structure using Frequency Response Functions (FRF's). The results were compared with the finite element modeling. The damping ratio of the model in relation to position from excitation was calculated using the half-power point method and then a more detailed analysis of frequency dependent damping versus position was made using modal parameter extraction using the Complex Exponential Method.; Lieutenant, United States Navy

Damping of elastic-viscoelastic beams

West, Ray A.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.85%
The subject of this investigation is the dynamic behavior of a composite beam consisting of a main elastic core and two viscoelastic layers. The viscoelastic layers provide increased damping of vibrations. When the beam vibrates, damping is caused by energy dissipation in the viscoelastic layers due to their shear deformations. Thus, the goal of this investigation is the development of a method to assess the dynamic characteristics, including the effectiveness of damping, in the layered elastic-viscoelastic beam. Analysis of the resulting sixth-order partial differential equation along with the appropriate boundary conditions is the key to the dynamic characterization of the beam. The developed method will allow the design of beams with predictable dynamic characteristics. In addition, the methodology and analysis will provide insights to the effectiveness of surface damping treatments in general.

Electromechanical surface damping combining constrained layer and shunted piezoelectric matetrials with passive electrical networks of second order

Velazquez, Carlos
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Relevância na Pesquisa
36.95%
An electromechanical surface damping (EMSD) technique is proposed. This technique combines two surface damping methods, the shunted piezoelectric-ceramic damping with the viscoelastic constrained layer damping (CLD). The damping contribution of the shunted piezoelectric intends to enhance the effective frequency range of the CLD. Piezoelectric ceramics provide similar damping characteristics to viscoelastic material when they are shunted with resonant electrical networks. A resonant shunting circuit provides the opportunity of tuning (shifting) the effective damping range of the piezoelectric into an arbitrary frequency, enhancing the damping at the vicinity of such frequency. Also, the EMSD technique proposes the use of a multiple resonant network to shunt the piezoelectric ceramic. This concept enhances simultaneously the effective damping range at the vicinity of multiple and selected frequencies. This thesis assesses the dynamic behavior of a simple structure under EMSD treatment and it studies the effectiveness of multiple tuning also. A cantilever beam-like structure is adopted as a case study and a typical oscillator with two resonant networks has been selected to shunt the piezoelectric-ceramic. A viscoelastic material is attached on the structure and constrained by the piezoelectric ceramic. The EMSD is tuned to two natural frequencies of the main structure and its effectiveness in suppressing two vibration peaks simultaneously is evaluated. This study provides insight into the use of shunting networks of higher order. The constitutive equations of the EMSD differential element are developed and a finite element solution is obtained. Finally...

Evaluation of Turbine Blade Root Damping

Beck, Curtis
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.93%
A test program has been conducted to measure the vibration damping of three designs of steam turbine blades. These blades were tested in their root attachments, sectioned from retired rotors. Blade loading was accomplished in a new type of blade damping test rig and damping was evaluated in the lowest tangential and axial blade modes. The test environment was room temperature air. The damping rig concept and development is presented in detail as well as results of an intensive test program. The blade designs are designated as Types A, B, and C, where Types A and B were of a fir tree root design and Type C was a ball and shank design. A total of 86 blades were tested and the influence of vibration amplitude, applied axial (simulated centrifugal) load, and vibration mode on damping logarithmic decrement was studied. For the designs studied, the most important findings were: a) Logarithmic decrement was inversely related to blade centrifugal load. High centrifugal loads resulted in low damping ratios. b) Logarithmic decrements varied in an almost linear manner with vibration amplitude for most tests. Constant logarithmic decrement conditions were not observed. c) The damping test rig worked well in this test series. Long LP blades may cause problems without some design changes. d) Results were highly reproducable per each blade group tested. Typical scatter was observed when comparing the results of one blade group to another. e) Changing the initial excitation amplitude did not cause any changes in the vibration decay. There is one characteristic decay trace for each centrifugal load. Test data was reduced by hand...

Experimental investigation of electromechanical surface damping

Orsagh, Rolf Fisher
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.85%
Electromechanical Surface Damping (EMSD) is a hybrid technique that incorporates constrained layer damping (CLD) and shunted piezoelectric element methods for the suppression of vibration in light beam-like or plate-like structures. The EMSD technique enhances the damping effectiveness (peak amplitude suppression) at targeted resonant frequencies, and may therefore be used to extend the damping effectiveness of the constrained layer damping technique over a broader temperature and frequency range than CLD alone. This performance enhancement was demonstrated experimentally by comparing the steady state frequency response of cantilever beams that were partially treated with the CLD and EMSD techniques. The experimental results also agreed with the results of a corresponding finite element model.

Aerodynamic Damping of Randomly Excited Plates in Stationary and Moving Air

Tarnopolsky, Alex Z; Lai, J C S; Fletcher, Neville
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.85%
An experimental study of the aerodynamic damping of oscillating plates has been undertaken. Plates of various shapes were placed into an air flow normal to the plate and excited to oscillate parallel to the flow direction by electromagnetic forces of equal amplitudes and random frequencies. The aerodynamic damping of oscillating plates, evaluated in terms of a quality Q-factor from a frequency response resonance curve, was found to vary linearly with the absolute pressure in stationary surrounding air and with the air flow velocity in moving air. The flow velocity was also found to affect the aerodynamic damping more than the absolute pressure. A simple empirical model has been developed to predict the variation of the aerodynamic damping with the flow velocity.