Spectral finite element of a helix

Determination of a spectral (i.e. frequency dependent) finite element of a helix is the focus of this communication. The helix is treated as straight, linear elastic element, exhibiting coupling of axial with torsional responses. We derive explicit forms of all the coefficients of the stiffness matrix and plot their dependencies on the frequency and the parameter describing the said coupling. In general, the growth of that parameter leads to a progressively denser occurrence of the resonances of both axial and torsional motions.     

Non-Contact Eddy Current Excitation Method for Vibration Testing

When a conductive material is subjected to a time changing magnetic field, eddy currents are induced in that structure. The eddy currents circulate inside the conductor resulting in a magnetic field that interacts with the applied field. The eddy current field is such that it opposes the change in flux resulting in a force between the source and conductor. The time changing magnetic field necessary to induce an electrometric force in the materials can be generated through a variety of different ways. In the present study, a permanent magnet will be mounted to the tip of an electromagnetic shaker such that the motion of the magnet relative to the structure will cause a time changing field and the formation of eddy currents. The actuator will be demonstrated to be beneficial due to its ability to apply actuation forces without contacting the structure. This study will show that the non-contact nature of the system eliminates mass loading and added stiffness which are downfalls of traditional excitation techniques. Additionally, it will be shown that the use of a non-contact device preserves the mode shapes of the structure, whereas a stinger results in distortions due to the added constraint. Using this concept, a model of the actuation system will be developed, allowing the beams response to be simulated. The actuation system will then be used to excite a cantilever beam to obtain the modal parameters without contacting the structure. The novel non-contact actuation system developed in this paper provides a new method performing vibration testing of on lightweight or flexible structures while preserving their dynamics.     

水下噪声及其控制技术进展和展望

本文主要介绍近年来船舶行业水下噪声研究进展情况，包括水下噪声形成机理和预报；水下噪声控制技术；水下噪声近代测量分析技术，并提出对水下噪声研究工作的展望。     

工作机械相对振动的研究

本文对工作机械的相对振动进行了理论和实验研究。分析了相对振动的激励和合成原理,提出了工件和工具同相振动和异相振动、同相域以及相对振动放大因子等概念。在此基础上指出了减小相对振动的途径,以作为设计和改造工作机械的参考。     

The theoretical research of the medium effect on the vibrational spectrum and the energy of intramolecular coordination O → Si in (benzoyloxymethyl)trifluorosilane molecule

The characteristics of (benzoyloxymethyl)trifluorosilane C₆H₅C(O)OCH₂SiF₃ containing a five-membered heterocycle closed by intramolecular coordination O → Si bond (Ia) and its most stable acyclic isomer (Ib) have been calculated by HF, MP2(Full) non-empirical methods, and DFT(B3LYP) using 6-311G(d) and 6-311 + G(2d,p) basis sets. The (C₈H₁₈, C₆H₆, (C₄H₉)₂O, CHCl₃, (CH₂)₄O, CH₂Cl₂, CH₃CN) medium effect on the energy and structural characteristics, dipole moments, and vibrational spectra of Ia and Ib isomers was calculated by the DFT(B3LYP)/6-311 + G(2d,p) method in the Onsager SCRF model approximation. The DFT(B3LYP)/6-311 + G(2d,p) calculation reasonably reproduces the medium effect on coordination energy, geometry, dipole moments, and band frequencies in the vibrational spectrum of Ia.     

Quasi-localized vibrations and phonon damping in glasses

There is ample evidence both from computer simulation and experiments that the structural disorder characterizing glasses and amorphous materials leads to quasi-localized vibrations (QLVs). The effect of these modes on low temperature properties such as heat capacity and conduction or tunnelling can be calculated in the framework of the soft potential model. Recently it has been shown that this concept can be extended to describe the boson peak (BP). By interaction, the density of states of the QLVs is changed to a characteristic shape corresponding to the boson peak in inelastic scattering. The QLVs interact with the sound waves and dampen them. We show that resonant scattering between QLVs and sound waves can describe the strong damping observed experimentally.     

Vibration analysis of truncated conical shells subjected to flowing fluid

A method to predict the dynamic behaviour of anisotropic truncated conical shells conveying fluid is presented in this paper. It is a combination of finite element method and classical shell theory. The displacement functions are derived from exact solutions of Sanders’ shell equilibrium equations of conical shells. The velocity potential, Bernoulli’s equation and impermeability condition have been applied to the shell–fluid interface to obtain an explicit expression for fluid pressure which yields three forces (inertial, centrifugal, Coriolis) of the moving fluid. To the best of the authors’ knowledge, this paper reports the first comparison made between two works which deal with conical shells subjected to internal flowing fluid effects. The results obtained by this method for conical shells with various boundary condition and geometries, in vacuum, fully-filled and when subjected to flowing fluid were compared with those of other experimental and numerical investigations and good agreement was obtained.     

一种双臂型低温导热带的性能研究

详细介绍了低温导热带的设计特点。从理论上分析了低温导热带的冷量传输性能和减振特性,得到通过利用高导热率材料可以有效地减小导热温差和降温时间。通过实验验证了低温导热带与制冷机和高温超导滤波器的耦合实验,耦合温差为2.5K。实验结果和理论值基本吻合,分析了造成温差的原因。根据实验结果,提出了新的改进和实施方案。     

Analysis of the Solvability of Linear Vibration Models

In this article we consider a general linear vibration problem in variational form. Models for the vibration of systems of elastic bodies can be written in this form. We show how properties of the damping term determines the time differentiability of the solution and establish classes of permissible initial conditions. The proofs are based on a direct link between the variational form and an abstract differential equation.     

A new sinusoidal shear deformation theory for bending,buckling, and vibration of functionally graded plates

A new sinusoidal shear deformation theory is developed for bending, buckling, and vibration of functionally graded plates. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. Unlike the conventional sinusoidal shear deformation theory, the proposed sinusoidal shear deformation theory contains only four unknowns and has strong similarities with classical plate theory in many aspects such as equations of motion, boundary conditions, and stress resultant expressions. The material properties of plate are assumed to vary according to power law distribution of the volume fraction of the constituents. Equations of motion are derived from the Hamilton’s principle. The closed-form solutions of simply supported plates are obtained and the results are compared with those of first-order shear deformation theory and higher-order shear deformation theory. It can be concluded that the proposed theory is accurate and efficient in predicting the bending, buckling, and vibration responses of functionally graded plates.