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This article investigates the size-dependent dynamic behavior of the viscoelastic functionally graded (FG) porous doubly-curved macro/nanosize shells rested on various foundations based on the nonlocal strain gradient theory (NSGT). Also, a parametric study was conducted to describe the impact of small-scale parameters, magneto-hygrothermal environments, as well as Winkler, Pasternak, and Kerr foundations on the vibration characteristics of the system. A novel quasi-3D shell model is developed to scrutinize the dynamics of the structure by dividing the transverse displacement into deflection and thickness stretching components. For porosity-dependent dynamic analysis, two different types of porosity distributions are considered. A novel higher-order shear deformation theory (HSDT) is employed to reflect the shear effects along the system thickness. Hamilton's principle and Kelvin--Voigt damping effects are utilized to obtain the governing equations of motion. The Navier solution approach is applied to acquire the dynamic response of the panel with simply-supported boundary conditions. It is indicated that the vibration frequency of the considered system is substantially affected by the porosity volume fraction, FG index, porosity distribution, foundation parameters, feedback control gain, viscoelastic structural damping, and length-to-thickness ratio of the structure. [ABSTRACT FROM AUTHOR]

In this article, a rotary valve is developed to obtain accurate high-frequency sinusoidal vibration waveforms. Then, a uniaxial electro-hydraulic shaking table controlled by a set of parallel rotary valves is constructed, which can superpose the sinusoidal vibration waveforms. The non-sinusoidal vibration waveforms including triangular vibration waveform, rectangular vibration waveform, sawtooth vibration waveform and trapezoidal vibration waveform are generated by adjusting the spool rotation speed based on the Fourier series. The results show that with one rotary valve, the uniaxial electro-hydraulic shaking table can output accurate high-frequency sinusoidal vibration waveforms and the total harmonic distortion is less than 1% at high vibration frequency. Compared with the standard vibration waveform, the error of the generated vibration waveform is very small. For the rectangular vibration waveform and sawtooth vibration waveform, the error is less than 6%, and for the triangular vibration waveform and trapezoidal vibration waveform, the error is less than 3%. The impacts of the working conditions on the error of the generated vibration waveform are very small. The proposed method for the accurate high-frequency non-sinusoidal vibration waveform is very effective and can be applied in high vibration frequency and different load masses. With the increase of the supply pressure, the amplitude of the generated vibration waveforms increases, while the error changes in a rather narrow range. The amplitude can be adjusted by changing the supply pressure with almost no effect on the accuracy of the vibration waveform. [ABSTRACT FROM AUTHOR]

In order to maximize the controllability of magnetorheological (MR) mount for engines, a novel (MR) mount with an internal bypass (MRM-IB), which provides particular advantages of large dynamic stiffness range, small field-off dynamic stiffness and long available stroke under full vibration frequency range, is proposed and investigated in this paper. The proposed MRM-IB consists of a main rubber spring unit for supporting static load and a MR damping unit for mechanical energy dissipation. The MR damping unit is composed of a piston assembly, a MR fluid chamber and an annular MR fluid channel sandwiched by two concentric cylinders, that is, the inner and outer cylinders. Electromagnetic coil winding is wound on the outside of the inner cylinder and continuous damping/dynamic stiffness of the MRM-IB is tuned by the applied current in the coils. Structural principle of the magnetic circuit of the proposed MRM-IB is validated and analyzed, and the mathematical model of the controllable damping force is then established. In addition, a frequency-based piecewise controller and a fuzzy controller for a specific MR semi-active automotive mount system are designed, and the theoretical simulation and the experimental tests of the system are conducted, compared and analyzed. [ABSTRACT FROM AUTHOR]

As a novel propulsion technology, ultrasonic electric propulsion is mainly applied to micro-satellite platforms (<10 kg). In this work, effects of vibration frequency and typical operating conditions on extraction process of charged droplets in ultrasonic electric propulsion are investigated by an ultra-high speed imaging technique. A long-distance microscope coupled with an ultra-high speed camera (NAC HX-6) is also used. A solution of formamide and lithium chloride is employed as propellant. Experimental results show that mean diameters of charged droplets are 43.3 ± 4.2 µm (120 kHz), 76.2 ± 5.8 µm (60 kHz), and 101.4 ± 7.1 µm (25 kHz), respectively. Besides, the theoretical diameter values are calculated, which are close to experimental ones and both values decrease with the increase of vibration frequency. Meanwhile, experimental results indicate that the diameter of charged droplets increases as the propellant flow rate rises, and such effect is obvious when the flow rate is ranging from 3 to 10 ml/h. It is also found that charged droplets are not uniformly accelerated and their motion directions are also divergent. [ABSTRACT FROM AUTHOR]

The dynamic response of the subgrade under moving train loads provides information on subgrade settlement prediction, condition evaluation, and so forth. This paper presents the field dynamics tests on the transition subgrade in the Shuo-Huang heavy-haul railway in China. The variation characteristics of the peak dynamic displacements along the track and subgrade slope were analyzed, and the random distribution characteristics of the peak dynamic displacements at the subgrade shoulder were studied. The response characteristics of the subgrade during the train passage were investigated, and the attenuation regularities of vibration along the subgrade slope were identified. The results indicated that the action of the train moving loads on the subgrade has obvious periodicity, and two bogies in the adjacent wagons should be considered as one loading unit. The peak dynamic displacements at the subgrade shoulder obey normal distribution under the repeated loading of the loading unit. The subgrade bed is dramatically influenced by the dynamic loadings of the trains, and the moving train loads have little influence on the part below the subgrade bed. The results of the research provide the basis for the evaluation of instantaneous and long-term dynamic stability of the subgrade and offer guidance for simulating train moving loads in the model test and numerical analysis to study the dynamic response of the subgrade. [ABSTRACT FROM AUTHOR]

In order to study the influence of yarn bundle vibration characteristics on the vibration and noise of tufted carpet looms, a yarn bundle vibration model was proposed in this paper, which was based on the viscoelasticity of the yarn bundle, and the correctness of the transverse vibration equation of the yarn bundle was verified by experiments. Different creep models of the yarn bundle were fitted with the experimental data, and the transverse vibration equation of the axial motion viscoelastic yarn bundle was established by using Burgers four-element constitutive model. Then, the Galerkin truncation method was used to solve the partial differential vibration equation of the yarn bundle and solve the equation. Finally, the correctness of the vibration equation is verified by comparison between the experimental results and the numerical simulation results. The results show that the vibration equation is suitable for studying the transverse dynamic vibration characteristics of the yarn bundle. [ABSTRACT FROM AUTHOR]

In this analytical study, free vibration analyses of a 3d mixed formulation beam element are performed by adopting forcebased consistent mass matrix that incorporates shear and rotary inertia effects. The force-based approach takes into account the actual distribution of mass of an element in the derivation of the mass matrix. Moreover, the force-based approach enables accurate determination of free vibration frequencies of members with varying geometry and material distribution without any need for specification of different displacement shape functions for each individual case. This phenomenon is justified by comparing free vibration frequencies of cantilever beams that have circular and rectangular cross-sections and various mass distribution configurations. Vibration frequencies of the mixed formulation element are compared with the frequencies obtained from closed-form solutions and finite element analyses. Fundamental frequency is computed with only one element per member span and higher order frequencies are determined with two or four elements with considerable accuracy by employing 3d mixed element and force-based consistent mass matrix. [ABSTRACT FROM AUTHOR]

When sinusoidal vibration waveform is required, the frequency bandwidth of conventional electro-hydraulic vibration exciter controlled by servo valve is always limited to a rather narrow range due to the limits of slide valve structure and response speed, and no parameter is available for defining and evaluating the waveform quality. In this paper, a novel electro-hydraulic vibration exciter controlled by electromotor driven rotary valve is proposed to significantly extend the frequency range compared to the conventional servo valve controlled counterpart. Total harmonic distortion (THD) theory which is usually used to cope with voltage and current in electric system is borrowed to evaluate the quality of theoretical and experimental vibration waveforms at different supply pressures and vibration frequencies, quantitatively and qualitatively. The results show that the waveform quality is mainly influenced by the 3rd harmonic resonance. The proposed vibration exciter can output sinusoidal waveform with THD less than 5% at the vibration frequency higher than 70 Hz. In this frequency domain, the supply pressure has an extremely low impact on the THD of the waveform. The amplitude of the waveform can be adjusted by changing the supply pressure with almost no effect to the waveform quality at a certain vibration frequency. [ABSTRACT FROM AUTHOR]

Since the chain-type weak-link theory was first proposed by Pierce in 1926, many items in the literature have referred to it in one form or another. There has, however, been little extensive testing of this theory for either yarns or individual fibers. In this paper, the hazard function is used as a sensitive test for the data of Pierce on cotton yarns, those of Moreton on carbon filaments, and data gathered in the authors' laboratory on viscose rayon filaments. In each of these cases, it is shown that the theory does not apply. Alternate models are proposed and the most tractable of these is discussed in detail. Parameters in this model are estimated for the viscose rayon data. [ABSTRACT FROM PUBLISHER]