共查询到20条相似文献,搜索用时 31 毫秒
1.
V. YILDIRIM 《Journal of sound and vibration》2002,252(3):479-491
Numerical and analytical studies are performed for the free vibration analysis of non-cylindrical (conical, barrel and hyperboloidal types) helical springs. The stiffness matrix method is used in the numerical analysis. A total of 12 degrees of freedom (six displacements and six rotations) is described for an element. The exact element stiffness matrix and the exact concentrated element inertia matrix are used in the formulation. The rotary inertia, the shear and extensional deformation effects are considered in the analysis. Comparison of the numerical results with the reported results obtained numerically and experimentally gives satisfactory values. After verification of the numerical frequencies, the non-dimensional fundamental frequencies of fixed-fixed non-cylindrical helical springs with circular section are expressed in a simple formula with a maximum absolute relative error of 5% using those numerical values for the constant helix pitch angles (5°, 10°, and 15°). These expressions restricted to the fundamental frequencies are also verified with ANSYS results. 相似文献
2.
L M Van Immerseel J P Martens 《The Journal of the Acoustical Society of America》1992,91(6):3511-3526
In this paper, an accurate pitch and voiced/unvoiced determination algorithm for speech analysis is described. The algorithm is called AMPEX (auditory model-based pitch extractor) and it performs a temporal analysis of the outputs emerging from a new auditory model. However, in spite of its use of an auditory model, AMPEX should not be regarded as a substitute for any psychophysical theory of human auditory pitch perception. What is mainly described is the design of a computationally efficient auditory model, the perceptually motivated determination of the model parameters, the conception of a reliable pitch extractor for speech analysis, and the elaboration of an experimental procedure for evaluating the performance of such a pitch extractor. In the course of the evaluation experiment several kinds of speech stimuli including clean speech, bandpass-filtered speech, and noisy speech were presented to three different pitch extractors. The experimental results clearly indicate that AMPEX outperforms the best algorithms available. 相似文献
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K. K. Jee J. H. Han Y. B. Kim D. H. Lee W. Y. Jang 《The European physical journal. Special topics》2008,158(1):261-266
This work is related to a SMA coil spring which shows perfect recovery and greater recovery force. When tension spring of
common metals is fabricated, `initial tension' can be provided by minus pitch winding. The initial tension is the force for
tension springs to contract further in closed state. If a SMA spring has the initial tension, perfect recovery is expected
with a greater recovery force. However, the initial tension cannot be given to SMA coils in the conventional way, since heat
treatment for shape setting eliminates the tension generated by the minus pitch winding. We have developed a new method of
supplying the initial tension to SMA springs by changing coil orientation after the shape setting treatment. In this paper,
some examples are introduced that a perfect recovery with a greater force, though permanent deformation is involved in the
deformation, can be attained by the initial tension. 相似文献
5.
Furuno D.S. McDermott D.B. Luhmann M.C. Jr. Vitello P. Ko K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1988,16(2):155-161
An experimental four-cavity, fifth-harmonic gyroklystron is described that separates at 11.3 GHz in a 1.2-KG magnetic field. This device used longer drift regions than previous configurations. Principal results reported include 45 dB of small-signal gain and 0.6 kW of output power. Other results include the measurement of phase noise characteristics and the identification of spurious output signals. An improved beam diagnostic which determines the pitch of the electron orbits was used together with a fluorescent uranium-glass witness plate and beam-current diagnostics to characterize the electron beam. This information was used to perform analytic modelling and computer simulation of the amplifier. The experimental results are compared with the predictions of the analytic theory and simulation, and substantial agreement is demonstrated 相似文献
6.
A light intensity modulation fiber-optic sensor, which can measure curvature directly, has been developed. It is suitable for the measurement of thin, embedded or highly flexible structures. An experimental analysis on the static and dynamic characteristics of sensor has been undertaken. The results show that the output voltage has polarity and a good linear relationship with curvature when the curvature radius is larger than 60 mm. The mathematical model relating the relative output loss, parameters of sensitive zone’s configuration (depth, number, height and half angle of tooth) and bending radius is described analytically based on the geometric optics. Curvature fiber-optic sensors can be used to build a quasi-distributed fiber-optic sensor system, which can measure curvature and torsion angle simultaneously. 相似文献
7.
Accurate control of vocal pitch (fundamental frequency) requires coordination of sensory and motor systems. Previous research has supported the relationship between perceptual accuracy and vocal pitch matching accuracy. The purpose of this study was to investigate the role of memory for pitch in pitch matching and pitch discrimination ability. Three experimental tasks were used. First, a pitch matching task was completed, in which the participants listened to target tones and vocally matched the pitch of the tones. The second task was a pitch discrimination task that required the participants to judge the pitch (same or different) of complex tone pairs. The third task was pitch discrimination with memory interference task that was similar to the pitch discrimination task except interference tones were added. Results of the pitch matching and pitch discrimination tasks yielded a significant correlation between these values. When there was memory interference, pitch discrimination ability was poorer, and there was no significant correlation between pitch discrimination and pitch matching. These results support earlier findings of a relationship between pitch discrimination and pitch matching abilities. The results also suggest a possible role of pitch memory in both tasks. These findings may have implications for abilities related to accurate pitch control. 相似文献
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Propagation of shock and detonation waves in channels with U-shaped bends of limiting curvature 总被引:1,自引:0,他引:1
S. M. Frolov V. S. Aksenov I. O. Shamshin 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(5):759-774
Systematic experimental and theoretical studies of the propagation of shock and detonation waves in cylindrical tubes and planar channels with two U-shaped bends of limiting curvature were performed. It was demonstrated that U-shaped bends substantially facilitate detonation initiation in gases. The minimum shock wave velocity required to initiate the detonation of a stoichiometric propane-air mixture under normal conditions in a near-critical diameter tube with two U-shaped bends of limiting curvature was found to be ~800 m/s. 相似文献
10.
Wave propagation in pinned-supported, post-buckled beams can be described with the Korteweg de Vries (KdV) equation. Finite-element simulations however show that the KdV is applicable only to post-buckled beams with strong pre-compression. For weak and moderate pre-stress, a dispersive front is present and it is the aim of the current paper to analyze sources of dispersion beyond periodicity given three support types: guided, pinned, and free. Bloch theorem and a transfer-matrix method are employed to obtain numerical dispersion relations and characteristic wave modes, which are used to analyze the effects of pre-stress, initial curvature, and the influence of support types. Additionally, a new method is proposed to obtain a semi-analytical dispersion equation for the acoustic branch. Powers of frequency and the propagation constant are explicitly expressed and their coefficients are based on stiffness and mass-matrix components obtained from finite elements. This allows a physical interpretation of the dispersion sources, based on which, equivalent mass–spring models of post-buckled beam are proposed. It is found that mass and stiffness coupling are significant dispersion sources. In the present paper, a reduced form of Bloch theorem is presented exploiting glide-reflection symmetries, reducing the size of the unit cell and allowing an easier representation and interpretation of results. 相似文献
11.
Korobov A. I. Izosimova M. Yu. Agafonov A. A. Kokshaiskii A. I. Zhostkov R. A. 《Acoustical Physics》2020,66(3):228-234
Acoustical Physics - The article presents results of numerical simulation and experimental studies of elastic wedge wave propagation in cylindrical wedges with positive and negative curvature in... 相似文献
12.
This paper analyzes the propagation characteristics of the millimeter wave in various circular section tunnels. The received
power, path loss and delay spread are discussed in detail using the verified software of Wireless InSite. The investigated
tunnel models with circular section include the long straight tunnel, the tunnel with train inside and the curved tunnels
with different curvature. The simulated results are verified by the experimental value in the actual tunnel. Several valuable
conclusions are obtained, which would offer theoretical and practical references for the millimeter wave communication in
limited spaces. 相似文献
13.
根据光波导短程透镜母线曲率半径与光传输损耗的关系,利用数值计算的方法,通过计算不同母线参数条件下,四种解析解设计的短程透镜母线曲率半径,研究比较了短程透镜卷边对其损耗的影响,得出了短程透镜损耗与其有效区半径关系的曲线图,发现透镜凹面半径一定时,有效区半径越小,即卷边越大时,光传输损耗越小;短程透镜的解析改进解和最优解设计的透镜卷边存在曲率奇点.并由此得出了四种解析解设计的短程透镜有效区半径选取原则及其满足低损耗条件的取值范围. 相似文献
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The geometry of excitation wave front may play an important role on the propagation block and spiral wave formation. The wave
front which is bent over the critical value due to interaction with the obstacles may partially cease to propagate and appearing
wave breaks evolve into rotating waves or reentry. This scenario may explain how reentry spontaneously originates in a heart.
We studied highly curved excitation wave fronts in the cardiac tissue culture and found that in the conditions of normal,
non-inhibited excitability the curvature effects do not play essential role in the propagation. Neither narrow isthmuses nor
sharp corners of the obstacles, being classical objects for production of extremely curved wave front, affect non-inhibited
wave propagation. The curvature-related phenomena of the propagation block and wave detachment from the obstacle boundary
were observed only after partial suppression of the sodium channels with Lidocaine. Computer simulations confirmed the experimental
observations. The explanation of the observed phenomena refers to the fact that the heart tissue is made of finite size cells
so that curvature radii smaller than the cardiomyocyte size loses sense, and in non-inhibited tissue the single cell is capable
to transmit excitation to its neighbors. 相似文献
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Uncertainty analysis near bifurcation of an aeroelastic system 总被引:1,自引:0,他引:1
Variations in structural and aerodynamic nonlinearities on the dynamic behavior of an aeroelastic system are investigated. The aeroelastic system consists of a rigid airfoil that is supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. We follow two approaches to determine the effects of variations in the linear and nonlinear plunge and pitch stiffness coefficients of this aeroelastic system on its stability near the bifurcation. The first approach is based on implementation of intrusive polynomial chaos expansion (PCE) on the governing equations, yielding a set of nonlinear coupled ordinary differential equations that are numerically solved. The results show that this approach is capable of determining sensitivity of the flutter speed to variations in the linear pitch stiffness coefficient. On the other hand, it fails to predict changes in the type of the instability associated with randomness in the cubic stiffness coefficient. In the second approach, the normal form is used to investigate the flutter (Hopf bifurcation) boundary that occurs as the freestream velocity is increased and to analytically predict the amplitude and frequency of the ensuing LCO. The results show that this mathematical approach provides detailed aspects of the effects of the different system nonlinearities on its dynamic behavior. Furthermore, this approach could be effectively used to perform sensitivity analysis of the system's response to variations in its parameters. 相似文献
18.
Khalid Hadi Ryo Ichimura Nozomu Hashimoto Osamu Fujita 《Proceedings of the Combustion Institute》2019,37(3):2935-2942
The present study aims to clarify the effects of turbulence intensity and coal concentration on the spherical turbulent flame propagation of a pulverized coal particle cloud. A unique experimental apparatus was developed in which coal particles can be dispersed homogeneously in a turbulent flow field generated by two fans. Experiments on spherical turbulent flame propagation of pulverized coal particle clouds in a constant volume spherical chamber in various turbulence intensities and coal concentrations were conducted. A common bituminous coal was used in the present study. The flame propagation velocity was obtained from an analysis of flame propagation images taken using a high-speed camera. It was found that the flame propagation velocity increased with increasing flame radius. The flame propagation velocity increases as the turbulence intensity increases. Similar trends were observed in spherical flames using gaseous fuel. The coal concentration has a weak effect on the flame propagation velocity, which is unique to pulverized coal combustions in a turbulent field. These are the first reports of experimental results for the spherical turbulent flame propagation behavior of pulverized coal particle clouds. The results obtained in the present study are obviously different from those of previous pulverized coal combustion studies and any other results of gaseous fuel combustion research. 相似文献
19.
An ordered structure of noncohesive spherical beads constitutes a phononic crystal. This type of media combines the properties of wave propagation in phononic crystals (dispersion due to the geometrical periodicity) with the properties of wave propagation in granular media (nonlinearities, rotational degree of freedom) and gives the opportunity to have interesting features as tunable frequency band gaps for example.In this work, the acoustic bulk modes of a hexagonal close packed (hcp) structure of beads, considered as rigid masses connected by springs, are theoretically evaluated and their associated resonance frequencies are compared to experimental results. When friction is neglected, the elastic interaction between the beads are reduced to a normal spring interaction given by the Hertz theory. According to this theory, the rigidity of the contact depends on its static loading. The theory predicts the existence of elastic transverse and longitudinal acoustical-type modes and transverse and longitudinal optical-type modes.The acoustic transfer function of a hcp crystal slab built with stainless steel beads is measured and its resonance frequencies are compared to the theoretical predictions. Despite some differences between theory and experiments, which could come for instance from the disordered character of the contact loads, the developed theory and the experimental results show relatively good agreement. 相似文献
20.
Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable and unstable pitch modes for the lower and higher activation energies, respectively. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of two modes. The maximum pressure history in the stable pitch remained nearly constant, and the single Mach leg existing on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the unstable pitch due to the generation and decay of complex Mach interaction on the shock front shape. The high-frequency oscillation was self-induced because the intensity of the transverse wave was changed during propagation in one cycle. The high-frequency behavior was not always the same for each cycle, and therefore the low frequency oscillation was also induced in the pressure history. 相似文献