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1
Lu, Leo K. H. "Optimum Damping Selection by Statistical Energy Analysis." Journal of Vibration and Acoustics 112, no. 1 (January 1, 1990): 16–20. http://dx.doi.org/10.1115/1.2930090.
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It is widely accepted that for mitigating the vibration developed in structures, damping should be applied to the components with the largest response and be added at locations in the components’ energy transmission paths. However, it is difficult to determine the optimum damping location for some complicated dynamic systems. In this paper, the SEA concept is used to prove mathematically the reason for damping application and also to provide a convenient procedure for selecting the location of the damping treatment.
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Mace, B. R., and L. Ji. "The statistical energy analysis of coupled sets of oscillators." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2081 (March 6, 2007): 1359–77. http://dx.doi.org/10.1098/rspa.2007.1824.
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The paper concerns the statistical energy analysis (SEA) of two conservatively coupled oscillators, sets of oscillators and continuous subsystems under broadband excitation. The oscillator properties are assumed to be random and ensemble averages found. Account is taken of the correlation between the coupling parameters and the oscillator energies. For coupled sets of oscillators or continuous subsystems, it is assumed that the coupling power between a pair of oscillators is proportional to the difference of either their actual energies or their ‘blocked’ energies, and expressions for the ensemble averages and coupling loss factors (CLFs) are found. Various observations are made, some of which differ from those that are commonly assumed within SEA. The coupling power and CLF are governed by two parameters: the ‘strength of connection’ and the ‘strength of coupling’. The CLF is proportional to damping at low damping and independent of damping in the high damping, weak coupling limit. Equipartition of energy does not occur as damping tends to zero, except for the case of two oscillators that have identical natural frequencies. While attention is focused on spring-coupled oscillators, similar results hold for more general forms of conservative coupling. The examples of two spring-coupled rods and two spring-coupled plates are considered. Conventional SEA and the coupled oscillator results are in good agreement for weak coupling but diverge for strong coupling. For strong coupling and weak connection, the coupled oscillator results agree well with an exact wave analysis and Monte Carlo simulations.
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Yap, F. F., and J. Woodhouse. "INVESTIGATION OF DAMPING EFFECTS ON STATISTICAL ENERGY ANALYSIS OF COUPLED STRUCTURES." Journal of Sound and Vibration 197, no. 3 (October 1996): 351–71. http://dx.doi.org/10.1006/jsvi.1996.0536.
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Zhang, Guo Jun, and Yun Ju Yan. "Applications of Statistical Energy Analysis in Influencing Factors Analysis of Aircraft Vibro-Acoustic Response Characteristics." Applied Mechanics and Materials 300-301 (February 2013): 810–13. http://dx.doi.org/10.4028/www.scientific.net/amm.300-301.810.
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The SEA model of hypersonic aircraft is established based on statistical energy analysis (SEA) theory. Three parameters of the SEA model are established by the theory and experiential formula. According to damping loss factors of model subsystem and acoustic absorptivity of cavity, sensitivity analysis of vibro-acoustic response is discussed. The effect that division way of plate subsystem and material structure cause to vibro-acoustic response is analyzed. The analysis results show that the material structure, damping loss factors and material type have the great effect on the characteristics of vibro-acoustic response. The division way of plate subsystem can affect computational accuracy greatly. The influencing factors should be synthetically considered in the design of acoustics structure.
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Zhang, Xiao Feng, You Gang Xiao, Yu Shi, and Wu Yang Zeng. "Statistical Energy Analysis of Subway Wheel/Track Noise." Applied Mechanics and Materials 423-426 (September 2013): 1563–66. http://dx.doi.org/10.4028/www.scientific.net/amm.423-426.1563.
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Dividing wheel-track system of subway into a series of sub-systems, the statistical energy analysis (SEA) model of wheel/track system is established. The factors affecting the wheel/track noise, such as modal density, damping loss factors, coupling loss factors, are gotten by theoretical analysis combined with experiments. The calculated results show that the track noise is about 4.5 dB(A) higher than the wheel noise at 160 km/h, and the wheel noise is reduced by 2.8 dB(A) at 160 km/h and by 2.3 dB(A) at 90 km/h by attaching damped layer plates to the wheels, but the total reduction is only 0.9 dB(A) at 160 km/h and 0.4 dB(A) at 90 km/h, so the attempts to reduce the total noise should exert noise control measures on the track, not on the wheel.
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Lafont, T., N. Totaro, and A. Le Bot. "Review of statistical energy analysis hypotheses in vibroacoustics." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2162 (February 8, 2014): 20130515. http://dx.doi.org/10.1098/rspa.2013.0515.
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This paper is a discussion of the equivalence between rain-on-the-roof excitation, diffuse field and modal energy equipartition hypotheses when using statistical energy analysis (SEA). A first example of a simply supported plate is taken to quantify whether a field is diffuse or the energy is equally distributed among modes. It is shown that the field can be diffuse in a certain region of the frequency-damping domain with a single point force but without energy equipartition. For a rain-on-the-roof excitation, the energy becomes equally distributed, and the diffuse field is enforced in all regions. A second example of two plates coupled by a light spring is discussed. It is shown that in addition to previous conclusions, the power exchanged between plates agrees with the statistical prediction of SEA if and only if the field is diffuse. The special case of energy equipartition confirms this observation.
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Yang, Xiao Yan, You Gang Xiao, and Yu Shi. "Statistical Energy Analysis of Wind Noise in High-Speed Train Cab." Applied Mechanics and Materials 249-250 (December 2012): 307–13. http://dx.doi.org/10.4028/www.scientific.net/amm.249-250.307.
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Statistical energy analysis(SEA) method has many advantages in analysis of high frequency, high modal density and complex dynamic systems. Dividing high-speed train cab into a series of sub-systems, the SEA model of high-speed train cab was established. The factors affecting the cab noise, such as modal density, damping loss factors, coupling loss factors, were gotten by theoretical analysis combined with experiments. Using large eddy simulation method, the fluctuation pressures from train head surface were calculated. Using fluctuation pressure as excitation source, wind noise spectra and power flow of sub-systems in cab were obtained, which provided the basis for the control of high-speed train cab noise.
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Yang, Qiao, Hai Bo Chen, and Yong Yan Wang. "Statistical Energy Analysis of Fractional Derivative Model-Based Rubber Vibration Isolating System." Applied Mechanics and Materials 437 (October 2013): 114–19. http://dx.doi.org/10.4028/www.scientific.net/amm.437.114.
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The fractional derivative model and Coulomb friction model are introduced to describe the nonlinear characteristics of rubber isolators. Then the non-conservative coupling theory is used to calculate the statistical energy analysis (SEA) parameters of a typical non-conservative coupling system formed by two square plates and a rubber isolator. Numerical results are compared with those obtained by using the traditional viscous damping model, which shows that higher accuracy can be obtained by using the fractional derivative model in high-frequency band.
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Liu, Quanmin, Xiaozhen Li, Xun Zhang, Yunlai Zhou, and Y. Frank Chen. "Applying constrained layer damping to reduce vibration and noise from a steel-concrete composite bridge: An experimental and numerical investigation." Journal of Sandwich Structures & Materials 22, no. 6 (July 24, 2018): 1743–69. http://dx.doi.org/10.1177/1099636218789606.
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Structure-borne noise from railway bridges has become increasingly severe due to increased train speeds and axle loads. Constrained layer damping can suppress structural vibration and noise considerably across a wide frequency range by dissipating vibrational energy via damping layer shear deformation. This paper proposes a theoretical method of calculating the train-induced vibration and noise of a constrained layer damping-enhanced railway bridge based on the train–track–bridge coupled vibration, the modal strain energy method, and statistical energy analysis. First, the vibration responses of bridge decks were obtained via train–track–bridge coupled vibration calculations. Second, the constrained layer damping subsystem modal loss factors were determined via modal strain energy analysis and converted to damping loss factors in 1/3 octave band. Third, upon substituting the vibration energies of the decks and the damping loss factors of constrained layer damping subsystems into the statistical energy analysis power balance equations, the transmitted vibration energy results from various bridge subsystems were determined by solving the referenced equations. The structure-borne noise from the bridge was finally determined by analyzing the vibratory energies of all of the bridge subsystems using vibro-acoustic theory. Numerical analysis and field measurements of vibration and noise from a three-span steel–concrete composite bridge before and after constrained layer damping installation were performed. The predicted train-induced vibration and noise agreed well with the measured results. The stringer web and flange vibration velocity levels were reduced by 10.5 dB and 6.1 dB, respectively, and the sound pressure level at a measurement point 25 m (horizontal) from the track centerline and 1.5 m off the ground decreased by 4.3 dB(A).
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WADA, Hirofumi, Takayuki KOIZUMI, Nobutaka TSUJIUCHI, Hiroshi UEHARA, and Satoshi MORITA. "604 Damping Loss Factor Estimation Method of Statistical Energy Analysis Using Power Injection Method." Proceedings of Conference of Kansai Branch 2010.85 (2010): _6–4_. http://dx.doi.org/10.1299/jsmekansai.2010.85._6-4_.
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Liu, A. Q., S. P. Lim, and S. T. Chow. "Statistical energy analysis on the damping effect of the oil pan on engine vibration." Applied Acoustics 34, no. 2 (1991): 131–41. http://dx.doi.org/10.1016/0003-682x(91)90028-d.
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Sulla, Francesco, Matti Koivisto, Janne Seppanen, Jukka Turunen, Liisa C. Haarla, and Olof Samuelsson. "Statistical Analysis and Forecasting of Damping in the Nordic Power System." IEEE Transactions on Power Systems 30, no. 1 (January 2015): 306–15. http://dx.doi.org/10.1109/tpwrs.2014.2329489.
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KOIZUMI, Takayuki, Nobutaka TSUJIUCHI, Hirofumi WADA, and Mitsugu KANEKO. "1002 Damping Loss Factor Estimation Method by Using Finite Element Method in Statistical Energy Analysis." Proceedings of Conference of Kansai Branch 2012.87 (2012): _10–2_. http://dx.doi.org/10.1299/jsmekansai.2012.87._10-2_.
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Xu, Qianlong, Ye Li, Yingkai Xia, Weixing Chen, and Feng Gao. "Performance assessments of the fully submerged sphere and cylinder point absorber wave energy converters." Modern Physics Letters B 33, no. 13 (May 10, 2019): 1950168. http://dx.doi.org/10.1142/s0217984919501689.
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Fully submerged sphere and cylinder point absorber (PA), wave energy converters (WECs) are analyzed numerically based on linearized potential flow theory. A boundary element method (BEM) (a radiation–diffraction panel program for wave-body interactions) is used for the basic wave-structure interaction analysis. In the present numerical model, the viscous damping is modeled by an equivalent linearized damping which extracts the same amount of wave energy over one cycle as the conventional quadratic damping term. The wave power capture width in each case is predicted. Comparisons are also made between the sphere and cylinder PAs which have identical geometrical scales and submerged depths. The results show that: (i) viscous damping has a greater influence on wave power performance of the cylinder PA than that of the sphere PA; (ii) the increasing wave height reduces wave power performance of PAs; (iii) the cylinder PA has a better wave power performance compared to the sphere PA in larger wave height scenarios, which indicates that fully submerged cylinder PA is a preferable prototype of WEC.
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Ma, Du-Meng, Shu-Ling Zhang, Ying Zhang, and Wei Xu. "Stochastic analysis of a nonlinear electromagnetic energy harvesting system with fractional damping under additive and multiplicative stochastic excitation." International Journal of Modern Physics B 34, no. 14n16 (June 3, 2020): 2040113. http://dx.doi.org/10.1142/s021797922040113x.
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Electromagnetic energy harvester has been widely concerned in recent years due to its advantages of small size and high sensing frequency. In this paper, the stochastic behaviors of a nonlinear electromagnetic energy harvesting system (NEEH) with fractional damping are investigated under the additive and multiplicative stochastic excitation. Firstly, by applying the stochastic average method to the NEEH system, the mean square of the output current, and the steady-state probability density of vibration amplitude, displacement and velocity are obtained. Meanwhile, the validity of the theoretical results is verified by comparing with the numerical results given by the Monte Carlo method. Secondly, by investigating the theoretical and numerical results, the influences of noise intensity and fractional order on the NEEH system are explored. It is obvious that a higher output voltage can be obtained by the larger intensity of the stochastic excitation, and the smaller coefficient and fractional order of the fractional damping.
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Chen, Shuming, Dengfeng Wang, and Yingfeng Lei. "Automotive Interior Noise Prediction Based on Single Sound Cavity Using Statistical Energy Analysis Method." Noise & Vibration Worldwide 42, no. 11 (December 2011): 36–43. http://dx.doi.org/10.1260/0957-4565.42.11.36.
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In order to predict car interior noises at the car design and development stage, the statistical energy analysis (SEA) method was used. All the input parameters – modal density (MD), damping loss factor (DLF) and coupling loss factor (CLF) were calculated with SEA principle. Meanwhile, the sound excitation was calculated with sound power experiment data of internal combustion engine given by the engine manufacturer and sound source radiation formula. Engine mount excitation was also computed through the acceleration at initiative side of the engine mount and the transmissibility. A car virtual prototype was built to calculate a car body suspension receiving excitation from road roughness. A computational fluid dynamics (CFD) model was also built up to analyze the wind excitation on the outside surfaces. The car interior noises were predicted by the SEA model with all of the parameters and excitations. A good agreement was indicated by comparing predicted results with measured ones. The maximum relative error between prediction and measurement results is less than 3%, and the maximum absolute error is less than 2.5 dB (A). The above predicted results satisfy engineering precision requirements and as well as showing that using SEA method to predict car internal noises is feasible. The acoustic sensitivity analysis was made at the end. The car internal noise prediction method presented in the paper can be used at car design and development stage.
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Fang, X., and J. Tang. "A Direct Simulation Monte Carlo Approach for the Analysis of Granular Damping." Journal of Computational and Nonlinear Dynamics 2, no. 2 (November 13, 2006): 180–89. http://dx.doi.org/10.1115/1.2447502.
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Granular damping, which possesses promising features for vibration suppression in harsh environments such as in turbo-machinery and spacecraft, has been studied using empirical analysis and more recently using the discrete element method (DEM). The mechanism of granular damping is nonlinear and, when numerical analyses are employed, usually a relatively long simulation time of structural vibration is needed to reflect the damping behavior. The present research explores the granular damping analysis by means of the direct simulation Monte Carlo (DSMC) approach. Unlike the DEM that tracks the motion of granules based upon the direct numerical integration of Newton’s equations, the DSMC is a statistical method derived from the Boltzmann equation to describe the velocity evolution of the granular system. Since the exact time and locations of contacts among granules are not calculated in the DSMC, a significant reduction in computational time/cost can be achieved. While the DSMC has been exercised in a variety of gas/granular systems, its implementation to granular damping analysis poses unique challenges. In this research, we develop a new method that enables the coupled analysis of the stochastic granular motion and the structural vibration. The complicated energy transfer and dissipation due to the collisions between the granules and the host structure and among the granules is directly analyzed, which is essential to damping evaluation. Also, the effects of granular packing ratio and the excluded volume of granules, which may not be considered in the conventional DSMC approach, are explicitly incorporated in the analysis. A series of numerical studies are performed to highlight the accuracy and efficiency of the new approach.
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Turkdogru Gurun, Nurkan, Jonathan Chen, Frederick Ward, Matthew Wilcox, and Zhiming Luo. "Prediction and Improvement of Aircraft Cabin Acoustics using Statistical Energy Analysis and Sound Quality Evaluation." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 6 (August 1, 2021): 257–66. http://dx.doi.org/10.3397/in-2021-1382.
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Aircraft interior acoustic design is a key influencer for cabin comfort. An essential part of the design is optimization of acoustic insulation systems under weight restrictions to create a pleasant environment for human ear. Considering the complexity of aircraft geometry, noise sources, and transfer paths, computational prediction techniques become invaluable tools for increasing the accuracy in material selection while reducing design time and costs. In this study, a procedure that integrates sound quality evaluation with Statistical Energy Analysis (SEA) to design aircraft acoustic insulation systems is described. SEA is employed to predict the cabin sound pressure levels of a narrow body aircraft insulated with sound absorption and vibration damping materials. Aircraft cabin including under-floor sections is modelled based on 3D airframe and VIP style interior design and the model is validated with flight test data. Transfer functions obtained from SEA model for selected transfer paths are utilized to filter the noise signal recorded with a binaural recording system during flight. Sound quality metrics are computed in order to map perceptive response. An iterative process is introduced to improve acoustic design by investigating the effects of different sound insulation systems and room absorption values on noise levels and sound quality metrics.
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Victor, Tyrode, Nicolas Totaro, Laurent Maxit, and Alain Le Bot. "Vibrational energy distribution in plate excited with random white noise." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 6 (August 1, 2021): 965–69. http://dx.doi.org/10.3397/in-2021-1712.
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In Statistical Energy Analysis (SEA) and more generally in all statistical theories of sound and vibration, the establishment of diffuse field in subsystems is one of the most important assumption. Diffuse field is a special state of vibration for which the vibrational energy is homogeneously and isotropically distributed. For subsystems excited with a random white noise, the vibration tends to become diffuse when the number of modes is large and the damping sufficiently light. However even under these conditions, the so-called coherent backscattering enhancement (CBE) observed for certain symmetric subsystems may impede diffusivity. In this study, CBE is observed numerically and experimentally for various geometries of subsystem. Also, it is shown that asymmetric boundary conditions leads to reduce or even vanish the CBE. Theoretical and numerical simulations with the ray tracing method are provided to support the discussion.
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DEKKER, H. "KINETICS OF NEARLY DEGENERATE METASTABLE SYSTEMS WITH OHMIC DISSIPATION: THE NON-GAUSSIAN QUANTUM STATISTICAL PATH INTEGRAL." International Journal of Modern Physics B 04, no. 04 (March 20, 1990): 549–67. http://dx.doi.org/10.1142/s0217979290000279.
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Using a generalized version of Langer's "imaginary part of the free energy" method the quantum decay rate Γ = A exp (−B) of a metastable ohmic oscillator — with harmonic frequency ω0 and quantum friction coefficient α — is studied for an almost symmetric barrier and a "free" exit space, involving an "inflection scattering" center. The unstable anomalous fluctuation mode (of the "breathing bounce" configuration in the partition function) is analytically continued in a fully "dynamical" manner. At zero friction and zero temperature the result for Γ agrees with the escape rate found from the pertinent Schrodinger equation by means of an extended WKB "outgoing waves" analysis. At slightly elevated temperatures — removing the earlier restrictions 12B exp (− ħω0/2k B T) → 0 and 2πk B T/ħω0 → 0 arising from the "two-state" and "sudden-flip" approximations — in the weak quantum damping regime (α ≲ 1) the decay rate shows a characteristic transition from quantal to thermal dependence on the bias energy ε. In the strong quantum damping regime (α ≳ 1) this dependence is always thermal while — in that case — at zero bias the oscillator becomes "dissipatively frozen" at zero temperature.
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Clarkson, B. L. "Estimation of the Coupling Loss Factor of Structural Joints." Proceedings of the Institution of Mechanical Engineers, Part C: Mechanical Engineering Science 205, no. 1 (January 1991): 17–22. http://dx.doi.org/10.1243/pime_proc_1991_205_085_02.
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This paper shows how Bishop's receptance method can be used to derive the transmission of vibrational energy across a structural joint. The results are averaged over frequency bands and on the assumption of light damping an approximate formula for the coupling loss factor is obtained. This is an important parameter in the statistical energy analysis method of estimating the response of structures to broad-band random forces. The results compare well with those obtained by the travelling wave method.
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Hinze, Matthias, André Schmidt, and Remco I. Leine. "Lyapunov Stability of a Fractionally Damped Oscillator with Linear (Anti-)Damping." International Journal of Nonlinear Sciences and Numerical Simulation 21, no. 5 (July 28, 2020): 425–42. http://dx.doi.org/10.1515/ijnsns-2018-0381.
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AbstractIn this paper, we develop a Lyapunov stability framework for fractionally damped mechanical systems. In particular, we study the asymptotic stability of a linear single degree-of-freedom oscillator with viscous and fractional damping. We prove that the total mechanical energy, including the stored energy in the fractional element, is a Lyapunov functional with which one can prove stability of the equilibrium. Furthermore, we develop a strict Lyapunov functional for asymptotic stability, thereby opening the way to a nonlinear stability analysis beyond an eigenvalue analysis. A key result of the paper is a Lyapunov stability condition for systems having negative viscous damping but a sufficient amount of positive fractional damping. This result forms the stepping stone to the study of Hopf bifurcations in fractionally damped mechanical systems. The theory is demonstrated on a stick-slip oscillator with Stribeck friction law leading to an effective negative viscous damping.
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He, Li, and Xian Guo Ye. "A Study on Elastic Input Energy Spectra Based on the Compound Intensity Indicator." Advanced Materials Research 446-449 (January 2012): 140–45. http://dx.doi.org/10.4028/www.scientific.net/amr.446-449.140.
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Determination of a SDOFS elastic input energy is the primary problem to solve for energy-based design approach. The effect of ground motion and damping ratio were analyzed on the input energy spectra. is selected as the compound ground motion intensity indicator to represent the damage potential of strong ground motion. Through inputting of 188 seismic records according to the site classification of Chinese seismic code, three-segment elastic energy spectra are proposed based on normalization methods. The calculation formula of the peak and the value of long-period section of the input energy spectra are presented for four categories of site conditions by statistical analysis. Moreover, calculation procedure of the total energy input is given in the paper.
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Sen'kevich, S. E., YE N. Il'chenko, Z. A. Godzhayev, and V. V. Duryagina. "Results of field studies of a tractor of traction class 1,4 with an elastic damping mechanism in a power drive." Izvestia MGTU MAMI 1, no. 4 (2020): 70–79. http://dx.doi.org/10.31992/2074-0530-2020-46-4-70-79.
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The topic of this paper is analyzing the results of field studies of a tractor with an elastic damping mechanism in a power drive and its operational efficiency assessment in comparison with a serial tractor. The subject of the research is a tractor with an elastic damping mechanism in a power drive as part of a plowing unit with a mounted plow. The purpose of this work is a detailed analysis of the influence of the parameters of the elastic-damping mechanism on the performance of a tractor with a plow. Carrying out such studies makes it possible to obtain new experimental data on the operation of the elastic damping mechanism in-stalled in the power drive of a tractor when aggregated with a plow. The control experiments were carried out in the same field during the summer and autumn peri-ods of one year. The benchmark for comparative experiments was the same tractor, but with a blocked elastic damping mechanism (for brevity, it is called “serial”). The results were processed on a personal computer using a software package. To analyze energy efficiency, a conditional classifi-cation of sample variability based on the coefficient of variation was used. Spectral analysis was performed to study numerical slip data. The indicators of the energy assessment show that the unit with an elastic damping mechanism in the power drive of the tractor has better performance (travel speed, productivity and fuel consump-tion per hectare) than a similar unit with a more rigid transmission. The elastic damping mechanism creates more favorable conditions for the formation of the nature of the load of the nodes, with un-steady and steady-state modes of motion. Statistical analysis of numerical data on slipping showed that the use of the mechanism makes it possible to reduce the mathematical expectation of slipping. Analysis of spectral characteristics indicates that the elastic-damping mechanism absorbs frequen-cies, being a filter when aggregated with various tools. Everything mentioned above indicates a sig-nificant improvement in the characteristics of the unit when using an elastic damping mechanism.
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Weissman, Karen, Mark McNelis, and William Pordan. "Implementation of Acoustic Blankets in Energy Analysis Methods with Application to the Atlas Payload Fairing." Journal of the IEST 37, no. 4 (July 1, 1994): 32–39. http://dx.doi.org/10.17764/jiet.2.37.4.a5k692w88170707q.
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Energy analysis methods are commonly used to predict the vibroacoustic response of a spacecraft inside a launch vehicle payload fairing during liftoff. The payload fairing wall is often lined with acoustic blankets which can be difficult to model. This paper shows the development of a practical working method for accurately representing acoustic blankets in a VAPEPS statistical energy analysis model. A clear scaling relationship between the acoustic absorption coefficient and the blanket thickness is established. The scaling procedure is demonstrated using two sets of data for different absorption materials. The absorption data are implemented in VAPEPS by converting them to frequency-dependent damping loss factors. A post-processing procedure is derived to account for the increase in transmission loss due to the addition of the blanket layer. The entire process is used to predict the noise reduction in a VAPEPS model of the Atlas 14-ft-diameter payload fairing. Comparisons to ground-test and flight data for the blanketed fairing are presented to validate the procedure.
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Gordaninejad, F., and R. Bindu. "THE EFFECT OF SCALE FACTOR ON THE PERFORMANCE OF ELECTRO-RHEOLOGICAL FLUID DAMPERS." International Journal of Modern Physics B 10, no. 23n24 (October 30, 1996): 3133–41. http://dx.doi.org/10.1142/s0217979296001574.
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Theoretical and experimental scale analyses are conducted to investigate the effects of length of the damper and electric field strength on the damping and stiffness coefficients of electrorheological fluid (ERF) dampers. It is demonstrated that by employing the results obtained from smaller size prototypes, the energy absorbing capacity of larger dampers can be estimated.
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DROZDOV, V. A., D. O. EREMENKO, O. V. FOTINA, S. Yu PLATONOV, O. A. YUMINOV, G. GIARDINA, G. FAZIO, F. MALAGUTI, P. OLIVO, and V. TOGO. "FISSION TIME OF α-INDUCED REACTIONS MEASURED BY THE CRYSTAL BLOCKING TECHNIQUE." International Journal of Modern Physics E 19, no. 05n06 (June 2010): 1227–35. http://dx.doi.org/10.1142/s0218301310015710.
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A large set of experimental observables for the 232 Th , 235 U (α, xnf ) reactions has been analyzed within the dynamic-statistical approach with allowance for the nuclear dissipation phenomenon, the double humped structure of fission barrier, and also the temperature damping of shell effects. The energy dependences of the lifetime effect (experimentally measured by the crystal blocking technique) along the corresponding data on the fission fragment angular anisotropy and also fission probabilities of U and Pu isotopes produced in the reactions were chosen for the analysis. Reliable information on the nuclear viscosity at the low excitation energies (< 30 MeV) was obtained.
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Yan, Feng, Robin Wilson, and Peter Rutherford. "Prediction of acoustic transmission in heavily damped system using hybrid Ray-Tracing-SEA method." Noise Control Engineering Journal 68, no. 3 (May 20, 2020): 226–36. http://dx.doi.org/10.3397/1/376819.
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Classic statistical energy analysis mainly deals with the energy transmission of system with relatively low damping. With the application of passive damping treat- ments, one of the fundamental assumptions in SEA, i.e., a diffused field, tends to fail. The energy attenuation along transmission path becomes so significant that there may exist large energy level difference within one structural component. In light of this, this study proposes to use a hybrid ray-tracing-SEA method to predict the acoustic transmission in heavily damped system. Heavily damped structural compo- nents are treated as â–œcoupling elementsâ–? instead of normal â–œsubsystems.â–? The en- ergy transmission from one structural element to a connected structural element through the edge can be represented by using certain number of point sources and assuming each point source radiates certain number of acoustic rays. By tracing the travelling history of each ray, the energy attenuation along the travelling path can be achieved. With the information of energy input and energy attenuation, the equivalent coupling loss factors can be computed. By rebuilding a hybrid ray- tracing-SEA model, the energy level differences between different subsystems can be determined. Numerical validation of the ray tracing algorithm is conducted by comparing the calculated coupling loss factor with normal SEA method. Numerical study of a one-room system is given. The room is assumed to consist of six homoge- neous concrete plates and the analysis assumes no coupling between in-plan and out- plane waves. Comparisons between classic and hybrid method show that when a small number of the structural components are heavily damped, classic SEA gives similar results with the hybrid method because the prediction errors tend to cancel with each other and the transmission is dominated by paths that are not damped. With the increasing number of damped elements, SEA tends to underestimate the energy level difference.
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De Francesco, Alessio, Luisa Scaccia, Marco Maccarini, Ferdinando Formisano, Eleonora Guarini, Ubaldo Bafile, and Alessandro Cunsolo. "Interpreting the Terahertz Spectrum of Complex Materials: The Unique Contribution of the Bayesian Analysis." Materials 12, no. 18 (September 9, 2019): 2914. http://dx.doi.org/10.3390/ma12182914.
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In the last few decades, experimental studies of the terahertz spectrum of density fluctuations have considerably improved our knowledge of the mesoscopic dynamics of disordered materials, which also have imposed new demands on the data modelling and interpretation. Indeed, lineshape analyses are no longer limited to the phenomenological observation of inelastic features, as in the pioneering stage of Neutron or X-ray spectroscopy, rather aiming at the extraction from their shape of physically relevant quantities, as sound velocity and damping, relaxation times, or other transport coefficients. In this effort, researchers need to face both inherent and practical obstacles, respectively stemming from the highly damped nature of terahertz modes and the limited energy resolution, accessible kinematic region and statistical accuracy of the typical experimental outcome. To properly address these challenges, a global reconsideration of the lineshape modelling and the enforcement of evidence-based probabilistic inference is becoming crucial. Particularly compelling is the possibility of implementing Bayesian inference methods, which we illustrated here through an in-depth discussion of some results recently obtained in the analysis of Neutron and X-ray scattering results.
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Treszkai, Marcell, and Daniel Feszty. "Effect of junction type on the vibroacoustic response of a system of plates." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 2 (August 1, 2021): 3953–62. http://dx.doi.org/10.3397/in-2021-2565.
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Modelling of junctions is one of the most challenging tasks in vibroacoustics, especially for Statistical Energy Analysis (SEA), where the results heavily depend on the damping (DLF) and coupling loss factors (CLF). Also, it is an interesting question to determine that to what extent does the DLF or CLF contribute to the overall vibroacoustic characteristics of a structure? The aim of this paper is to investigate via measurements and SEA simulations the effect of the ratio of DLF and CLF on the response of a system for various junctions, such as riveting, bolting, line and point welding, between two steel plates. Loss matrices are determined experimentally by the Power Injection Method in the 200-1600 Hz frequency range. The simulation was performed in the ESI VA One software by using its analytical CLF formulations and compared to experimental data. For the reference case, a bended plate structure was considered, representing an ideal junction between two subsystems. This was equipped with damping foils to ensure the same weight and then compared to the results from other joints. Results showed that increasing the CLF could be more effective than focusing on increasing the DLF.
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Senkevich, S. E., and N. S. Kryukovskaya. "Analysis of experimental studies of the tractor equipped with an elastic-damping mechanism in the transmission when moving as part of a transport tractor unit." Traktory i sel'hozmashiny 1, no. 6 (2020): 59–66. http://dx.doi.org/10.31992/0321-4443-2020-6-59-66.
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The cargo transportation is an integral and energy-consuming part of agricultural production. To improve the energy performance of transport tractor units (TTU), an elastic-damping mechanism (EDM) installed in the tractor transmission was developed. An experimental study was conducted to identify the influence of the EDM on the operation of the tractor as part of the TTU, when it is moving on a dirt road in the 9th gear of the main speed range of the gearbox (GB) of the tractor. A tractor of traction class 1.4 was used. Energy sensors were installed on the main elements of the tractor. The energy performance of the tractor with a transmission equipped with the EDM and the tractor with a factory transmission are determined. A decrease in fuel consumption by 7.3%, a decrease in traction forces from an aggregated trailer by 19.9%, a decrease in the amplitude of fluctuations in traction forces by 28.3% and a decrease in skidding of the driving units by an average of 9.7% were revealed. A graph describing the dynamics of changes in the skidding of the driving units of a serial tractor and a tractor with the EDM in time is constructed. The statistical processing of the skidding indicators is performed. A decrease in the amplitude of fluctuations in the coefficient of skidding by 16.3% was revealed. The obtained results of experimental studies indicate that the tractor as part of the TTU with the EDM in the transmission has better performance compared to a serial tractor and has a lower load on the engine, gearbox elements and driving wheels of the tractor.
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Mao, Jie, Zhi Yong Hao, Xin Rui Chen, and Ji Yang. "The Application of SEA in Automobile Dash Sound Transmission Loss Numerical Calculation." Applied Mechanics and Materials 152-154 (January 2012): 894–99. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.894.
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In order to study the structure-borne sound radiation, statistical energy analysis (SEA) was adopted and an automobile dash was divided into 31 subsystems; the modal density, damping loss factor (DLF) and coupling loss factor (CLF) were acquired, which were the basic parameters of SEA; then dash transmission loss (TL) at the middle and high frequency (MHF) ranging from 100 Hz to 10k Hz was calculated. The most outstanding advantage of SEA was that calculation could be fast done, which was more convenient than FEM (Finite Element Method) and BEM (Boundary Element Method). Finally, a TL experiment was designed to verify the feasibility and reliability of numerical calculation. The 1/3 octave TL curves of the simulation and experiment show a good consistency and the error is engineering permitted, which means SEA simulation possesses high credibility and can guide the engineering research.
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CHANG, WEN-TENG. "CLAMPING LOSSES OF FOLDED- AND STRAIGHT-BEAM MEMS RESONATORS MADE FROM POLYCRYSTALLINE 3C-SiC FILMS." International Journal of Modern Physics B 25, no. 06 (March 10, 2011): 885–96. http://dx.doi.org/10.1142/s0217979211057980.
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This paper presents an analysis of clamping losses in microelectromechanical systems (MEMS)-based, flexural mode silicon carbide (SiC) lateral resonators. The study includes folded- and straight-beam resonators made from (111) polycrystalline 3 C - SiC side by side. The device testing was conducted at 30 μTorr using a transimpedance-amplifier-based circuit to measure the total quality factor. It was found that thermoelastic damping (TED) in SiC MEMS-based lateral resonators has minimal contributions to overall energy dissipation in the aforementioned devices. Moreover, the difference in material losses of these devices is negligible due to their similar microstructure. In this case, clamping losses are responsible when one is comparing the energy dissipation mechanism of these two types of resonators. The findings showed that the total losses for a folded-beam resonator were reduced by more than 10 times that for a straight-beam resonator when the beam lengths were set at 150 μm and operated at the same level of resonant frequency. The clamping coefficient of the folded-beam resonator was between 0.7 and 1.8, suggesting that the effective dimension of a folded-beam resonator should include part of the proof mass.
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Piersol, Allan. "Preliminary Design Procedures for Equipment Exposed to Random Vibration Environments." Journal of the IEST 44, no. 1 (December 19, 2001): 23–27. http://dx.doi.org/10.17764/jiet.44.1.b44215m70k35l246.
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A New NASA Handbook presents recommended procedures for the preliminary and final design of equipment items exposed to various dynamic loads, including random vibration excitations.1 For the final design when the geometric details of the equipment items have been largely determined, finite element method (FEM) and statistical energy analysis (SEA) procedures can be employed to predict the maximum stresses in equipment items due to random vibration excitations at their mounting points. In the preliminary design phase, however, more approximate prediction techniques are often needed, as summarized in the Handbook. The purpose of this paper is to detail the rationale behind these preliminary procedures. Included are simple techniques to predict a maximum instantaneous stress during a short duration vibration environment and fatigue damage during a long-duration vibration environment, based only upon estimates for the frequency and damping ratio of the first significant resonance of the equipment.
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XIAO, Z., M. WAN, S. CHEN, and G. L. EYINK. "Physical mechanism of the inverse energy cascade of two-dimensional turbulence: a numerical investigation." Journal of Fluid Mechanics 619 (January 25, 2009): 1–44. http://dx.doi.org/10.1017/s0022112008004266.
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We report an investigation of inverse energy cascade in steady-state two-dimensional turbulence by direct numerical simulation (DNS) of the two-dimensional Navier–Stokes equation, with small-scale forcing and large-scale damping. We employed several types of damping and dissipation mechanisms in simulations up to 20482 resolution. For all these simulations we obtained a wavenumber range for which the mean spectral energy flux is a negative constant and the energy spectrum scales as k−5/3, consistent with the predictions of Kraichnan (Phys. Fluids, vol. 439, 1967, p. 1417). To gain further insight, we investigated the energy cascade in physical space, employing a local energy flux defined by smooth filtering. We found that the inverse energy cascade is scale local, but that the strongly local contribution vanishes identically, as argued by Kraichnan (J. Fluid Mech., vol. 47, 1971, p. 525). The mean flux across a length scale ℓ was shown to be due mainly to interactions with modes two to eight times smaller. A major part of our investigation was devoted to identifying the physical mechanism of the two-dimensional inverse energy cascade. One popular idea is that inverse energy cascade proceeds via merger of like-sign vortices. We made a quantitative study employing a precise topological criterion of merger events. Our statistical analysis showed that vortex mergers play a negligible direct role in producing mean inverse energy flux in our simulations. Instead, we obtained with the help of other works considerable evidence in favour of a ‘vortex thinning’ mechanism, according to which the large-scale strains do negative work against turbulent stress as they stretch out the isolines of small-scale vorticity. In particular, we studied a multi-scale gradient (MSG) expansion developed by Eyink (J. Fluid Mech., vol. 549, 2006a, p. 159) for the turbulent stress, whose contributions to inverse cascade can all be explained by ‘thinning’. The MSG expansion up to second order in space gradients was found to predict well the magnitude, spatial structure and scale distribution of the local energy flux. The majority of mean flux was found to be due to the relative rotation of strain matrices at different length scales, a first-order effect of ‘thinning’. The remainder arose from two second-order effects, differential strain rotation and vorticity gradient stretching. Our findings give strong support to vortex thinning as the fundamental mechanism of two-dimensional inverse energy cascade.
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Pogorzelski, Stanisław, Paweł Rochowski, Maciej Grzegorczyk, Bogumił B. J. Linde, Ewa Skrodzka, and Łukasz Bielasiewicz. "Detection of Wavy Sea Surface Oil-Derivative Contamination with Forward Specular High-Frequency Scattering." Polish Maritime Research 27, no. 1 (March 1, 2020): 173–79. http://dx.doi.org/10.2478/pomr-2020-0018.
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AbstractA spectrum of low-frequency (20–30 Hz) amplitude fluctuations of the ultrasonic (10 MHz) signal specularly scattered from water surfaces covered with monomolecular and thicker crude oil origin films of well-defined, oceanographically relevant viscoelastic properties was examined in laboratory and at-sea conditions. The relationship between the surface water wave (30 Hz) damping coefficient and the oil layer thickness was established, and compared to the one predicted by the classical Stokes theory. The depression of the spectral energy density of wind-driven waves by surface films was inferred from the ratio of acoustic signal fluctuations spectra with/without films, and compared to that resulting from the Marangoni damping theory applicable to monolayers of particular surface viscoelasticity. The agreement between the theory and experimental data was satisfactory. As shown in at-sea experiments performed with a free-floating, buoy-like acoustic system, and an artificial oil slick spread over the Baltic Sea surface, the film’s rheological surface properties can be recovered from acoustic surface probing, as well as oil spill edge detection. Simultaneous statistical analyses of the scattered signal amplitude distribution parameters turned out to be unequivocally related to the oil substance fraction weight, oil layer thickness, and the form of oil contamination.
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Wan Mohtar, W. H. M., and A. ElShafie. "Characteristics of Low Reynolds Number Shear-Free Turbulence at an Impermeable Base." Scientific World Journal 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/683537.
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Shear-free turbulence generated from an oscillating grid in a water tank impinging on an impermeable surface at varying Reynolds number74≤Rel≤570was studied experimentally, where the Reynolds number is defined based on the root-mean-square (r.m.s) horizontal velocity and the integral length scale. A particular focus was paid to the turbulence characteristics for lowRel<150to investigate the minimum limit ofRelobeying the profiles of rapid distortion theory. The measurements taken at near base included the r.m.s turbulent velocities, evolution of isotropy, integral length scales, and energy spectra. Statistical analysis of the velocity data showed that the anisotropic turbulence structure follows the theory for flows withRel≥117. At lowRel<117, however, the turbulence profile deviated from the prediction where no amplification of horizontal velocity components was observed and the vertical velocity components were seen to be constant towards the tank base. Both velocity components sharply decreased towards zero at a distance of≈1/3of the integral length scale above the base due to viscous damping. The lower limit whereRelobeys the standard profile was found to be within the range114≤Rel≤116.
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Ou, Jin-Ping, Bo Wu, and T. T. Soong. "Performance Comparison of Passive Energy Dissipation Systems in Structural Applications – I: Linear Reference System." Advances in Structural Engineering 1, no. 4 (October 1998): 237–59. http://dx.doi.org/10.1177/136943329800100402.
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In this paper, an analysis is presented for the performance comparison of representative passive energy dissipation systems which have been developed and implemented in structures in recent years. They include viscous fluid dampers, viscoelastic solid dampers, metallic dampers, friction dampers, tuned mass dampers and tuned liquid dampers. A single-degree-of-freedom linear structural system is used as a standard reference system where ground excitations are simulated either as a white noise or a filtered white noise. The performance criteria are first established, followed by the formulation of computational models for each of the energy dissipators considered. For those exhibiting inherent nonlinear behavior, statistically equivalent linearized models are used for analyzing their modified dynamical properties, such as additional mass, stiffness and damping coefficients due to addition of the energy dissipators to the reference system. Finally, representative numerical models of the above six types of energy dissipators are used to make quantitative comparisons of their performances when added to the reference system by calculating their equivalent additional dynamical properties and their effectiveness in alleviating key response quantities of the system.
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Craik, Robert J. M. "The Effect of Design Changes on Sound Transmission through a Building." Building Acoustics 3, no. 3 (September 1996): 145–85. http://dx.doi.org/10.1177/1351010x9600300302.
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A statistical energy analysis model of a building was used to assess the effect of design changes on sound transmission. Systematic changes were made to the material properties (density, Young's modulus, Poisson's ratio and internal loss factor) and to the dimensions (thickness and room size). These changes resulted in a redistribution of the energy throughout the building causing the noise level to go up in some rooms and to go down in others. For each case examined it was found that the effect of several changes could be estimated from the sum of the individual changes. Thus a change of 20% in the density resulted in approximately double the change in DnTw that was obtained from a 10% change in density. The same additive effect was also found to apply if more than one variable was changed at the same time. Thus the change in DnTw resulting from a small change in Young's modulus for the floors and a small change in the density of the walls can be estimated from the sum of the two individual effects. Changes to the thickness and density of the walls and floors have the greatest effect on sound transmission whilst changes to Young's modulus and Poisson's ratio have a much smaller effect. Damping can also have a significant effect on transmission particularly far from the source.
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Santo, H., P. H. Taylor, E. Carpintero Moreno, P. Stansby, R. Eatock Taylor, L. Sun, and J. Zang. "Extreme motion and response statistics for survival of the three-float wave energy converter M4 in intermediate water depth." Journal of Fluid Mechanics 813 (January 17, 2017): 175–204. http://dx.doi.org/10.1017/jfm.2016.872.
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This paper presents both linear and nonlinear analyses of extreme responses for a multi-body wave energy converter (WEC) in severe sea states. The WEC known as M4 consists of three cylindrical floats with diameters and draft which increase from bow to stern with the larger mid and stern floats having rounded bases so that the overall system has negligible drag effects. The bow and mid float are rigidly connected by a beam and the stern float is connected by a beam to a hinge above the mid float where the rotational relative motion would be damped to absorb power in operational conditions. A range of focussed wave groups representing extreme waves were tested on a scale model without hinge damping, also representing a more general system of interconnected cylindrical floats with multi-mode forcing. Importantly, the analysis reveals a predominantly linear response structure in hinge angle and weakly nonlinear response for the beam bending moment, while effects due to drift forces, expected to be predominantly second order, are not accounted for. There are also complex and violent free-surface effects on the model during the excitation period driven by the main wave group, which generally reduce the overall motion response. Once the main group has moved away, the decaying response in the free-vibration phase decays at a rate very close to that predicted by simple linear radiation damping. Two types of nonlinear harmonic motion are demonstrated. During the free-vibration phase, there are only double and triple frequency Stokes harmonics of the linear motion, captured using a frequency doubling and tripling model. In contrast, during the excitation phase, these harmonics show much more complex behaviour associated with nonlinear fluid loading. Although bound harmonics are visible in the system response, the overall response is remarkably linear until temporary submergence of the central float (‘dunking’) occurs. This provides a strong stabilising effect for angular amplitudes greater than ${\sim}30^{\circ }$ and can be treated as a temporary loss of part of the driving wave as long as submergence continues. With an experimentally and numerically derived response amplitude operator (RAO), we perform a statistical analysis of extreme response for the hinge angle based on wave data at Orkney, well known for its severe wave climate, using the NORA10 wave hindcast. For storms with spectral peak wave periods longer than the RAO peak period, the response is controlled by the steepness of the sea state rather than the wave height. Thus, the system responds very similarly under the most extreme sea states, providing an upper bound for the most probable maximum response, which is reduced significantly in directionally spread waves. The methodology presented here is relevant to other single and multi-body systems including WECs. We also demonstrate a general and potentially important reciprocity result for linear body motion in random seas: the averaged wave history given an extreme system response and the average response history given an extreme wave match in time, with time reversed for one of the signals. This relationship will provide an efficient and robust way of defining a ‘designer wave’, for both experimental testing and computationally intensive computational fluid dynamics (CFD), for a wide range of wave–structure interaction problems.
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Chen, Shujun, Na Wu, Jun Xiao, Tianming Li, and Zhenyang Lu. "Expulsion Identification in Resistance Spot Welding by Electrode Force Sensing Based on Wavelet Decomposition with Multi-Indexes and BP Neural Networks." Applied Sciences 9, no. 19 (September 26, 2019): 4028. http://dx.doi.org/10.3390/app9194028.
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Expulsion identification is of significance for welding quality assessment and control in resistance spot welding. In order to improve the identification accuracy, a novel wavelet decomposition and Back Propagation (BP) neural networks with the peak-to-peak amplitude and the kurtosis index were proposed to identify the expulsion from electrode force sensing signals. The rapid step impulse and resultant damping vibration of electrode force was determined as a robust indication of expulsion, and this feature was extracted from the electrode force waveform by seven-layer wavelet decomposition with Daubechies5 wavelets. Then, the energy distribution proportion of the decomposed detail signals were calculated, and the highest-energy one was selected as the target signal. Two statistical indexes were introduced in this paper to measure the target signal in overall situation and volatility. The bigger the peak-to-peak amplitude is, the more violent the fluctuation is. Moreover, the higher the kurtosis index is, the stronger the impact is, and the lower the dispersion degree of the data is. Experimental analysis showed that neither the peak-to-peak amplitude nor the kurtosis index could accurately judge the expulsion defect individually, because of the early signal fluctuation, likely affected by the work-piece clamping, work-piece clearance, or the oxide film thickness. Therefore, the BP neural networks were introduced to identify the expulsion defects, which is a mature and stable non-linear pattern recognition method. Testing experiments presented good results with the trained networks and improved the evaluable accuracy effectively in the quality assessment of the resistance spot welding.
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Samelson, R. M., D. B. Chelton, and M. G. Schlax. "The Ocean Mesoscale Regime of the Reduced-Gravity Quasigeostrophic Model." Journal of Physical Oceanography 49, no. 10 (October 2019): 2469–98. http://dx.doi.org/10.1175/jpo-d-18-0260.1.
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AbstractA statistical-equilibrium, geostrophic-turbulence regime of the stochastically forced, one-layer, reduced-gravity, quasigeostrophic model is identified in which the numerical solutions are representative of global mean, midlatitude, open-ocean mesoscale variability. Solutions are forced near the internal deformation wavenumber and damped linearly and by high-wavenumber enstrophy dissipation. The results partially rationalize a recent semiempirical stochastic field model of mesoscale variability motivated by a global eddy identification and tracking analysis of two decades of satellite altimeter sea surface height (SSH) observations. Comparisons of model results with observed SSH variance, autocorrelation, eddy, and spectral statistics place constraints on the model parameters. A nominal best fit is obtained for a dimensional SSH stochastic-forcing variance production rate of 1/4 cm2 day−1, an SSH damping rate of 1/62 week−1, and a stochastic forcing autocorrelation time scale near or greater than 1 week. This ocean mesoscale regime is nonlinear and appears to fall near the stochastic limit, at which wave-mean interaction is just strong enough to begin to reduce the local mesoscale variance production, but is still weak relative to the overall nonlinearity. Comparison of linearly inverted wavenumber–frequency spectra shows that a strong effect of nonlinearity, the removal of energy from the resonant linear wave field, is resolved by the gridded altimeter SSH data. These inversions further suggest a possible signature in the merged altimeter SSH dataset of signal propagation characteristics from the objective analysis procedure.
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RISSO, FRÉDÉRIC, and JEAN FABRE. "Oscillations and breakup of a bubble immersed in a turbulent field." Journal of Fluid Mechanics 372 (October 10, 1998): 323–55. http://dx.doi.org/10.1017/s0022112098002705.
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This work is an experimental study of the deformation and breakup of a bubble in a turbulent flow. A special facility was designed to obtain intense turbulence without significant mean flow. The experiments were performed under microgravity conditions to ensure that turbulence was the only cause of bubble deformation. A scalar parameter, characteristic of this deformation, was obtained by video processing of high-speed movies. The time evolution and spectral representation of this scalar parameter showed the dynamical characteristics of bubble deformation. The signatures of the eigenmodes of oscillation predicted by the linear theory were clearly observed and the predominance of the second mode was proved. In addition, numerical simulations were performed by computing the response of a damped oscillator to the measured turbulence forcing. Simulations and experiments were found to be in good agreement both qualitatively, from visual inspections of the signals, and quantitatively, from a statistical analysis. The role of bubble dynamics in the deformation process has been clarified. On the one hand, the time response of the bubble controls the maximum amount of energy which can be extracted from each turbulent eddy. On the other hand, the viscous damping limits the energy that the bubble can accumulate during its fluctuating deformation. Moreover, two breakup mechanisms have been identified. One mechanism results from the balance between two opposing dominant forces, and the other from a resonance oscillation. A new parameter, the mean efficiency coefficient, has been introduced to take into account the various aspects of bubble dynamics. Used together with the Weber number, this parameter allows the prediction of the occurrence of these two mechanisms. Finally, the influence of the residence time of the bubble on the statistics of the deformation has been analysed and quantified.
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Shringarpure, Mrugesh, Mariano I. Cantero, and S. Balachandar. "Dynamics of complete turbulence suppression in turbidity currents driven by monodisperse suspensions of sediment." Journal of Fluid Mechanics 712 (September 25, 2012): 384–417. http://dx.doi.org/10.1017/jfm.2012.427.
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AbstractTurbidity currents derive their motion from the excess density imposed by suspended sediments. The settling tendency of sediments is countered by flow turbulence, which expends energy to keep them in suspension. This interaction leads to downward increasing concentration of suspended sediments (stable stratification) in the flow. Thus in a turbidity current sediments play the dual role of sustaining turbulence by driving the flow and damping turbulence due to stable stratification. By means of direct numerical simulations, it has been shown previously that stratification above a threshold can substantially reduce turbulence and possibly extinguish it. This study expands the simplified model by Cantero et al. (J. Geophys. Res., vol. 114, 2009a, C03008), and puts forth a proposition that explains the mechanism of complete turbulence suppression due to suspended sediments. In our simulations it is observed that suspensions of larger sediments lead to stronger stratification and, above a threshold size, induce an abrupt transition in the flow to complete turbulence suppression. It has been widely accepted that hairpin and quasi-streamwise vortices are key to sustaining turbulence in wall-bounded flows, and that only vortices of sufficiently strong intensity can spawn the next generation of vortices. This auto-generation mechanism keeps the flow populated with hairpin and quasi-streamwise vortical structures and thus sustains turbulence. From statistical analysis of Reynolds stress events and visualization of flow structures, it is observed that settling sediments damp the Reynolds stress events (Q2 events), which means a reduction in both the strength and spatial distribution of vortical structures. Beyond the threshold sediment size, the existing vortical structures in the flow are damped to an extent where they lose their ability to regenerate the subsequent generation of turbulent vortical structures, which ultimately leads to complete turbulence suppression.
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Brisset, J., T. Miletich, J. Metzger, A. Rascon, A. Dove, and J. Colwell. "Multi-particle collisions in microgravity: Coefficient of restitution and sticking threshold for systems of mm-sized particles." Astronomy & Astrophysics 631 (October 16, 2019): A35. http://dx.doi.org/10.1051/0004-6361/201936228.
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Context. The current model of planet formation lacks a good understanding of the growth of dust particles inside the protoplanetary disk beyond mm sizes. A similar collisional regime exists in dense planetary rings. In order to investigate the low-velocity collisions between this type of particles, the NanoRocks experiment was flown on the International Space Station (ISS) between September 2014 and March 2016. We present the results of this experiment. Aims. The objectives of our data analysis are the quantification of the damping of energy in systems of multiple particles in the 0.1–1 mm size range while they are in the bouncing regime, and the study of the formation of clusters through sticking collisions between particles. Methods. We developed statistical methods for the analysis of the large quantity of collision data collected by the experiment. We measured the average motion of particles, the moment of clustering, and the cluster size formed. In addition, we ran simple numerical simulations in order to validate our measurements. Results. We computed the average coefficient of restitution (COR) of collisions and find values ranging from 0.55 for systems including a population of fine grains to 0.94 for systems of denser particles. We also measured the sticking threshold velocities and find values around 1 cm s−1, consistent with the current dust collision models based on independently collected experimental data. Conclusions. Our findings have the following implications that can be useful for the simulation of particles in PPDs and planetary rings: (1) The average COR of collisions between same-sized free-floating particles at low speeds (<2 cm s−1) is not dependent on the collision velocity; (2) The simplified approach of using a constant COR value will accurately reproduce the average behavior of a particle system during collisional cooling; (3) At speeds below 5 mm s−1, the influence of particle rotation becomes apparent on the collision behavior; (4) Current dust collision models predicting sticking thresholds are robust.
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Kemp, Connor, and Gary Scavone. "Microstructure Contributions to Vibrational Damping and Identification of Damage Mechanisms in Arundo Donax L: Reed Cane for Woodwind Instruments." MRS Advances 2, no. 35-36 (2017): 1869–88. http://dx.doi.org/10.1557/adv.2017.223.
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ABSTRACTNatural cane reeds (Latin name Arundo Donax L and here termed ADL) have been used on woodwind instruments for centuries with little change. The reed acts as a mechanical valve controlling the energy input into the musical instrument and it is the musician’s first option for altering the instrument’s sound and response characteristics. Despite this, their consistency, variable performance, durability and sensitivity to ambient conditions make it difficult for the musician to find and maintain a reed that responds to their liking. Thus it is desirable to examine the material, microstructural and anatomical properties of the reed and their contributions to vibrational performance with input from mechanical engineers, materials scientists and musicians.The current study is part of an on-going research project, and this paper presents preliminary results. In the present work raw samples of ADL obtained from a manufacturer in pre-cut form are sectioned into longitudinal and transverse specimens for mechanical characterization. Prior to testing, samples are conditioned using an incubation system to 37 degrees Celsius and 90% relative humidity, mimicking in-use conditions of the reed. Initial microstructure analysis of each specimen is completed using optical microscopy to quantify fiber spatial arrangement, size and the existence of micro-cracks along the fiber-matrix interface. X-ray diffraction is also used to quantify the fraction of crystalline cellulose present in each sample. Specimens are then excited over a specific frequency range similar to that of in-use reeds using pressure waves in a non-contact setup. Values of internal friction are obtained as logarithmic decrement values for frequency-dependent decay. One set of specimens is then subjected to cyclic mechanical loading at low frequency (< 1Hz) and stresses up to 15MPa. The other set is maintained at the given environmental conditions using the incubator and aged through temperature and humidity cycling. Comparisons of post-testing microstructure damage and internal friction measurements are then completed to delineate specific degradation mechanisms due to mechanical/fatigue deterioration and moisture cycling. Internal friction is found to be dependent on both frequency, moisture and cyclic loading. Furthermore, the existence of microstructural cracks contributes to increasing decrement values at high frequencies in both fatigued and moisture cycled samples. Statistically significant correlations are discovered between logarithmic decrement and vascular bundle orientation at 700 Hz and logarithmic decrement and parenchyma cell diameter at 1000 Hz. Reductions in internal friction below 400 Hz indicate a decreasing loss modulus (E’’) with increased moisture cycles, although this trend will be tested against a larger sample set in further work.
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Le Bot, Alain. "Entropy in statistical energy analysis." Journal of the Acoustical Society of America 125, no. 3 (March 2009): 1473–78. http://dx.doi.org/10.1121/1.3075613.
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Du, W., H. F. Wang, P. Ju, and R. Dunn. "Damping torque analysis for DC bus implemented damping control." European Transactions on Electrical Power 20, no. 3 (April 2010): 277–89. http://dx.doi.org/10.1002/etep.310.
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Jiao, Fujun. "Oil damping energy loss analysis of landing gear shock absorber." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 8 (August 14, 2018): 3096–106. http://dx.doi.org/10.1177/0954410018793788.
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It is seen that previous research on falling vibration of landing gear only provides work–stroke diagram and damping force value. Nevertheless, the change process of buffering medium at a micro-level is yet to be analyzed. The velocity, pressure, and their change over time of fluid particle are rarely researched in reality. To improve the intuitive, concreteness, and accuracy of the falling vibration analysis, this paper uses theoretical calculation and simulation to analyze oil damping energy loss of shock absorber. On the basis of theoretical calculation, the paper provides a feasible solution for calculating oil damping energy loss in the drop test of landing gear. Based on the classical fluid mechanics, the research builds a series-parallel model for calculating oil damping coefficient, and the oil damping energy loss values are calculated. To the flow passage type with one inlet and two outlets, the best solution of volume flow rate weighting of two outlets is determined. With regard to simulation, ANSYS FLUENT is used to show the dynamic flow process of oil in damping orifice. Damping energy loss values are calculated by total pressure difference. By comparison, the results of the theoretical calculation, the simulation, and the drop test achieve a good consistency.
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YOO, JIN-HYEONG, and NORMAN M. WERELEY. "NONDIMENSIONAL ANALYSIS OF ANNULAR DUCT FLOW IN MAGNETORHEOLOGICAL/ELECTRORHEOLOGICAL DAMPERS." International Journal of Modern Physics B 19, no. 07n09 (April 10, 2005): 1577–83. http://dx.doi.org/10.1142/s021797920503061x.
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Approximate analytical expressions describing MR/ER damper performance for an axisymmetric annular duct under the assumption of uniform field are presented. The key performance metric is the damping coefficient, which is the ratio of the equivalent viscous damping constant, Ceq, to the Newtonian viscous damping constant, C. To develop these approximations, a quadratic equation was used to approximate the center of the plug location in the annular duct. This equation simplified the calculation of the annular duct solution without resorting to numerical methods to solve the boundary value problem. Approximations for the damping coefficient are developed on this basis.