Academic literature on the topic 'Coupling Loss Factor'

Statistical Energy Analysis (SEA) is one of the methods in literature to estimate high frequency vibrations. The inputs required for the SEA power balance equations are damping and coupling loss factors, input powers to the subsystems. In this study, the coupling loss factors are derived for two and three plates joined with a stiffener system. Simple formulas given in the literature for coupling loss factors of basic junctions are not used and the factors are calculated from the expressions derived in this study. The stiffener is modelled as line mass, Euler beam, and open section channel having double and triple coupling. Plate is modelled as Kirchoff plate. In the classical SEA approach the joint beam is modelled as another subsystem. In this study, the beam is not a separate subsystem but is used as the characteristics of the joint and to calculate the coupling loss factor between coupled plates. Sensitivity of coupling loss factors to system parameters is studied for different beam approaches. The derived coupling loss factors and input powers are used to calculate the subsystem energies by SEA. The last plate is joined to the first one to simulate the fuselage structure. A plate representing floor structure and acoustic volume are also added. The different modelling types are assessed by applying pressure wave excitation. It is shown that deriving the parameters as given in this study increases the efficiency of the SEA method.

Este trabalho baseia-se no estudo e aplicação da Análise Estatística de Energia (SEA). Tal técnica é amplamente empregada nos estudos de vibrações em altas freqüências, dominadas por altas densidades modais e oferecendo toda a solução para o modelo em termos de parâmetros estatísticos. Aplica-se SEA tanto a modelos teóricos e numéricos quanto a modelos experimentais. Qualquer uma das duas abordagens descrita anteriormente tem como objetivo a obtenção dos parâmetros SEA, conhecidos por fator de perda por dissipação interna, fator de perda por acoplamento e densidade modal. Para o estudo e aplicação experimental da técnica SEA utiliza-se o Método de Injeção de Potência, sendo este aplicado a estruturas acopladas do tipo viga, numa configuração em T e estruturas acopladas do tipo placa que formam uma caixa. O estudo numérico e analítico também faz parte deste trabalho, tendo como base o desenvolvimento de uma formulação para vigas relativamente espessas, mostrando a influência geométrica na transmissão da vibração entre subsistemas. Comparações também são feitas entre os resultados obtidos experimentalmente na caixa e na viga T com os obtidos analiticamente e computacionalmente e em ambos os casos estes apresentaram uma boa correlação. Por fim, uma estrutura composta por uma cavidade acústica é estudada e um aparato o para injeção de potência é construído com base no estudo em altas freqüências.<br>This work is based in the study and application of the Statistical Energy Analysis (SEA), which is applied to high frequencies vibrations characterized by high modal densities and the solution, is given in statistical terms. This analysis is used in numerical, analytical and experimental models and the principal objective is the estimative of the SEA parameters, known by damping loss factors, coupling loss factors and modal densities. The experimental model is based on the Power Injection Method (PIM), and this was applied in coupled structures, like beam type, that was coupled in a T-beam configuration and the other type of coupling was studied in a box type structure. An analytical model was developed in this thesis, it was based on the Timoshenko beam formulation and the possible geometrical effects were studied. The results obtained as experimentally as numerically or analytically were compared and showed a good agreement. Finally, an acoustic cavity was studied and a new display was constructed to inject power in the cavity and a high frequency study was performed.

La recherche vise à étendre les études existantes sur les métastructures hétérogènes présentant des caractéristiques de fort contraste et de forte dissipation. Les dynamiques multi-échelles, les indicateurs vibroacoustiques, l'effet de couplage des ondes et les ondes d'ordre élevé sont étudiés dans le cadre des méthodologies basées sur les ondes. Les modèles pour les structures à forts contrastes (Highly Contrasted Structures, HCS) et haute dissipation (Highly Dissipative Structures, HDS) sont explorés. Diverses méthodes de calcul des indicateurs vibroacoustiques tels que l'espace des nombres d'onde, le facteur de perte par amortissement (Damping Loss Factor, DLF) et la perte de transmission sonore (Sound Transmission Loss, STL) sont passées en revue. L'attention particulière est accordée à la méthode d'homogénéisation asymptotique (Asymptotic Homogenization Method, AHM) exploitant le modèle Zig-Zag et la technique d'homogénéisation pour prédire les dynamiques multi-échelles des HCS par les nombres d'onde de flexion. Parallèlement, la méthode analytique de la matrice de transfert (Transfer Matrix Method, TMM) et sa généralisation pour les structures complexes par le modèle des éléments finis (General Transfer Matrix Method, GTMM), le modèle stratifié général (General Laminate Model, GLM) utilisant la théorie de déplacement de Mindlin, et le schéma d'éléments finis d'ondes (Wave Finite Element, WFE) sont présentés. L'évaluation de la robustesse et de la précision de AHM et GLM est réalisée en comparant l'espace des nombres d'onde et le DLF avec la méthode de référence WFE. Le problème des valeurs propres nonlinéaires (Nonlinear Eigenvalue Problem, NEP) dans le schéma WFE pour les ondes se propageant dans diverses directions est résolu par un solveur d'intégrale de contour (Contour Integral, CI), les nombres d'ondes complexes sont suivis en fonction des critères de continuité de l'énergie dans le domaine fréquentiel. Les limites de validité d'AHM et GLM sont vérifiées. La faisabilité d'appliquer la méthode WFE aux structures sandwich avec des composants non-homogènes est démontrée en utilisant la méthode d'entrée de puissance basée sur les éléments finis (FE-based Power Input Method, PIM-FEM). Le cadre WFE est étendu pour prédire avec précision le DLF global des HDS. Il commence par dériver les réponses forcées d'une cellule unitaire (Unit Cell, UC) représentative de la structure périodique lorsqu'elle est excitée par une onde incidente. Ensuite, il calcule le DLF de l'onde via l'équation de bilan de puissance. En utilisant l'expansion de Bloch, la réponse à une force ponctuelle appliquée à la structure périodique est décomposée dans la zone de Brillouin, permettant la prédiction de la réponse totale par intégration sur l'espace des nombres d'onde. Le DLF global est dérivé sur la base du principe de PIM. Pour les HDS, les résultats du GLM sont exploités pour valider le DLF des ondes, tandis que l'approche PIM-FEM est utilisée comme référence pour le DLF global. L'influence réduite des ondes de flexion sur l'estimation du DLF pour les HDS est discutée, ainsi que l'importance des ordres des modes de Bloch. Les coefficients de transmission du son sont exploités pour représenter la contribution des nombres d'onde à la STL des métastructures hétérogènes. La méthode WFE est appliquée pour étudier les mécanismes de couplage des ondes influençant la performance d'isolation acoustique des HCS et HDS, ainsi que l'importance du mouvement symétrique pour les structures sandwich avec un couche centrale souple très épais. La même approche est utilisée pour les guides d'ondes avec des sections transversales complexes afin d'analyser l'effet de couplage des ondes et des ondes d'ordre élevé sur l'estimation précise de la STL par les approches TMM, WFE et GTMM. Une attention particulière est accordée aux structures courbées. Les mécanismes de couplage entre les ondes de flexion et de membrane influençant la STL sont également étudiés<br>The research aims to extend existing studies for heterogeneous metastructures with high contrast and high dissipation features. The multi-scale dynamics, vibroacoustic indicators, wave coupling effect, and high-order waves of heterogeneous metastructures are investigated within the wave-based frameworks. The wave-based models for Highly Contrasted Structures (HCS) and Highly Dissipative Structures (HDS) are explored. Various methods for computing the vibroacoustic indicators, such as the wavenumber space, Damping Loss Factor (DLF), and Sound Transmission Loss (STL), are reviewed. Special attention is placed on the Asymptotic Homogenization Method (AHM) exploiting the Zig-Zag model and homogenization technique to predict the multi-scale dynamics of HCS by the bending wavenumbers. Meanwhile, the analytical Transfer Matrix Method (TMM) and its generalization for complex structures by the Finite Element (FE) model (General Transfer Matrix Method, GTMM), the semi-analytical General Laminate Model (GLM) employing Mindlin's displacement theory, the numerical Wave Finite Element (WFE) scheme are presented. Evaluation on the robustness and accuracy of AHM and GLM is made by comparing the wavenumber space and DLF with the reference WFE method. The Nonlinear Eigenvalue Problem (NEP) in the WFE scheme for waves propagating in varying directions is solved by a Contour Integral (CI) solver, the complex wavenumbers are tracked based on the energy continuity criteria in the frequency domain. The validity limits of AHM and GLM are verified. The feasibility of applying the WFE method to sandwich structures with non-homogeneous components is shown using the classical FE-based Power Input Method (PIM-FEM). The WFE framework is extended for accurately predicting the global DLF of HDS. It starts by deriving the forced responses of a Unit Cell (UC) representative of the periodic structure when excited by an impinging wave. Then it computes the DLF of the wave via the power balance equation. By employing the Bloch expansion, the response to a point force applied to the periodic structure is decomposed in the Brillouin zone, allowing the prediction of total response via integration over the wavenumber space. The global DLF is derived based on the principle of PIM. For HDS, results of GLM are exploited for validating the wave DLF, the PIM-FEM approach is provided as reference approach for the global DLF. The shrinking influence of bending waves on the DLF estimation for HDS is discussed, as well as the importance of Bloch mode orders. \newline Sound transmission coefficients can be exploited to depict the contribution from the wavenumber space to the STL of the heterogeneous metastructures. The WFE method is applied to study the wave coupling mechanisms influencing the sound insulation performance of HCS and HDS, as well as the importance of symmetric motion to the sandwich structures with a very thick soft core. The same approach is applied to waveguides with complex cross-sections to investigate the wave coupling effect and high-order waves on the accurate STL estimation by analytical TMM, WFE, and GTMM approaches. Special attention is paid to curved periodic structures, the bending-membrane coupling mechanisms influencing the STL are also investigated

This thesis describes methods of high frequency noise and vibrations computation of cabin part of EV–55M (aircraft developed by Evektor Kunovice). There is a brief summary of methods used for determining high frequency noise and vibrations in the first part of the thesis. Detailed explanation is given for Statistical Energy Analysis (SEA) which is nowadays the most dominant method in this area. The energy balance equation is derived in this chapter and SEA parameters such as modal density, damping loss factor, coupling loss factor and power input are introduced here. Next part deals with main noise sources of propeller driven and jet aircraft and passive and active noise controls are discussed. Practical part of this thesis deals with modeling aircraft EV–55M fuselage using VA One SEA module. Two models were created. First of them is only an outside fuselage with aircraft flooring and the second one is extended by interior trim panels and is applicable for simulation of noise control treatments. Computational modeling is accompanied by experimental measurement of passive noise control material characteristics. Postprocessing of information obtained from impedance tube measurement was performed in FOAM – X. Determined characteristics of porous material were used as inputs to VA One and reduction of sound pressure level in fuselage cavities by using noise control treatment was found. In conclusion there is a summary of noise transmission paths from sources to interior cavity and some treatments of them are simulated

The mechanisms underpinning the immediate torque loss induced by acute, static muscle stretching are still not clear. The current research was designed to examine the neuromuscular factors influencing this torque loss. In Study 1, the contributions of central versus peripheral factors to the stretch-induced torque loss were investigated. Measures of central drive, including the EMG amplitude normalised to the muscle compound action potential amplitude (EMG:M), percent voluntary activation (%VA) and first volitional wave amplitude (V:M), and measures of peripheral function, including the twitch peak torque and 20:80 Hz tetanic torque ratio were made before, and immediately and 15 min after a 5-min continuous plantar flexor stretch. There was a 15.7% (p Alternatively, intermittent (i.e. repeated) stretching commonly performed by athlete and clinical populations causes cycles of ischaemia-reperfusion, increasing the likelihood of contractile failure. Therefore, Study 2 was designed to determine whether intermittent stretch might cause greater torque loss when compared to continuous stretch, and to quantify the potentially greater peripheral effect. The main findings were that intermittent stretch induced a greater torque loss (-23.8%; p Central drive failure can clearly be of spinal origin, and it is reasonable to speculate that muscle stretch might affect the afferent-mediated motor neurone facilitatory system. Thus, in Study 3 a vibration-stimulation protocol (vib+stim) was used to elicit reflexmediated muscular contractions during two experiments. In Experiment 1, vib+stim was imposed with the ankle joint plantar flexed (+10°), neutral (0°) and dorsiflexed (-10°). Torque and EMG amplitudes during vibration and during the self-sustained torque period after vib+stim were greater in dorsiflexion, providing method validation. In Experiment 2, vib+stim was imposed twice before (Control) and immediately, 5, 10 and 15 min after a 5-min intermittent stretch protocol. Torque and EMG amplitude were depressed immediately after stretching during both vibration (-60% and –41%, respectively; p

Fatigue can accumulate sufficiently to limit muscular force production during repeated, forceful muscle contractions, including those that occur in the occupational, clinical and athletic settings. Fatigue during such efforts is likely to result from disturbances to multiple processes in the nervous system and muscle. However, previous research examining the mechanisms underpinning fatigue have typically required subjects to perform low-level constant-force contractions or to repeat maximal efforts in a single set format. Such tasks do not translate well to occupational, daily living or athletic situations where high-intensity, yet submaximal, repeated efforts may be performed in work bouts (or sets) with brief rest periods for recovery. Therefore, the overall aim of the present research was to investigate the neuromuscular mechanisms contributing to force loss after repeated, high-intensity muscular efforts with longer (90 s) periods of rest separating repetitions into sets of contractions. In Experiment 1, 16 resistance trained men performed 6 sets of unilateral isometric plantar flexor contractions of the right leg (3 s contraction/2 s rest) reaching a target level of 85% maximal voluntary contraction (MVC). Sets were separated by a 90-s inter-set rest and completed to failure (i.e. In Experiment 1, a significant reduction in maximum voluntary isometric plantar flexion torque (12.2%; p < 0.001) was observed post-exercise, which did not recover by POST-20. Significant reductions in triceps surae EMG/M (-6%; p = 0.024) and MEP/M amplitude (9%; p = 0.01) were found post-exercise but recovered by POST-10. Cortical silent period (an indicator of GABAB-mediated intracortical inhibition) was reduced (-4%; p = 0.016) post-exercise and did not recover by POST-20. In Experiment 2, temporal changes in torque were similar to Experiment 1. Significant reductions in the evoked torque response from 20 Hz (p < 0.001), 80 Hz (p < 0.001) and VFT (p < 0.001) stimulations were observed at POST and did not recover by POST-20, however no changes in 20:80 and 20:VFT ratios were observed. Finally, significant reductions in both Tvib (-13%; p = 0.035) and Tsust (-25%; p = 0.035) were found post-exercise but recovered by POST-10. The ingestion of caffeine allowed for a greater overall torque production and neural drive (EMG/M) but the lack of condition  time interaction effect indicated that it did not clearly affect the time course of fatigue or recovery. Further, no detectable effects were observed compared to the non-caffeine condition in corticospinal excitability, MN excitability or E-C coupling, as shown by the negligible changes in MEP/M amplitude, PIC facilitation, and torque during 20-Hz, 80-Hz and VFT stimulations. These data suggest that corticospinal tract efficiency and PIC-mediated facilitation of the MN pool can be compromised and are likely to account in part for the force loss immediately following an acute bout of repeated, high-intensity muscular efforts performed in sets (with 90 s rest). However, changes in E-C coupling efficiency (i.e. ‘peripheral fatigue) are likely to explain the ongoing, prolonged loss of force, at least to 20 min post-exercise. Therefore, it is likely that both changes in the nervous system as well as the muscle contribute to the loss of force following repeated, high-intensity muscular efforts.