Prediction of Room Noise Caused by Vibration of High Power Elevator Traction Machine

Total simulation from vibration of elevator motor to noise at sitting room with anti-vibration measures is confirmed in design stage. This procedure also presents decrease of acoustic noise in sitting room. In this simulation, FEM calculates wave motion, such as wave phase, interference, diffraction and natural frequency mode of sitting room wall. These procedures yield the ration between vibration of elevator motor and acoustic noise in sitting-room.

Bifurcation scenario for a two-dimensional static airfoil exhibiting trailing edge stall

We numerically investigate stalling flow around a static airfoil at high Reynolds numbers using the Reynolds-averaged Navier–Stokes equations (RANS) closed with the Spalart–Allmaras turbulence model. An arclength continuation method allows to identify three branches of steady solutions, which form a characteristic inverted S-shaped curve as the angle of attack is varied. Global stability analyses of these steady solutions reveal the existence of two unstable modes: a low-frequency mode, which is unstable for angles of attack in the stall region, and a high-frequency vortex shedding mode, which is unstable at larger angles of attack. The low-frequency stall mode bifurcates several times along the three steady solutions: there are two Hopf bifurcations, two solutions with a two-fold degenerate eigenvalue and two saddle-node bifurcations. This low-frequency mode induces a cyclic flow separation and reattachment along the airfoil. Unsteady simulations of the RANS equations confirm the existence of large-amplitude low-frequency periodic solutions that oscillate around the three steady solutions in phase space. An analysis of the periodic solutions in the phase space shows that, when decreasing the angle of attack, the low-frequency periodic solution collides with the unstable steady middle-branch solution and thus disappears via a homoclinic bifurcation of periodic orbits. Finally, a one-equation nonlinear stall model is introduced to reveal that the disappearance of the limit cycle, when increasing the angle of attack, is due to a saddle-node bifurcation of periodic orbits.

Auxetic vibration behaviours of periodic tetrahedral units with a shared edge

A very low-frequency mode supported within an auxetic structure is presented. We propose a constrained periodic framework with corner-to-corner and edge-to-edge sharing of tetrahedra and develop a kinematic model incorporating two types of linear springs to calculate the momentum term under infinitesimal transformations. The modal analysis shows that the microstructure with its two degrees of freedom has both low- and high-frequency modes under auxetic transformations. The low-frequency mode approaches zero frequency when the corresponding spring constant tends to zero. With regard to coupled eigenmodes, the stress–strain relationship of the uniaxial forced vibration covers a wide range. When excited, a very slow motion is clearly observed along with a structural expansion for almost zero values of the linear elastic modulus.

Similitudes for vibration characteristic of composite laminated plates

Similitude laws can be used to extrapolate the vibration characteristic of a small, inexpensive, and easily tested model into structural behavior for the full-size prototype. In this article, a systematic similitude approach is proposed to predict the natural frequency, mode shape, and vibration response of composite laminated plates. The emphasis of this article is to predict the vibration characteristic of composite laminated plates in an effective and convenient way. Sensitivity analysis (SA) is introduced to improve the prediction accuracy of natural frequency. For distortion similarity, the prediction accuracy is improved close to 5%. Modal assurance criterion (MAC) measures the consistency of mode shapes of the full-size prototype and scaled models. The influence of stacking sequence on mode consistency is investigated. Similitude based on virtual mode and statistical energy (SVMSE) is proposed to extrapolate the transient response of the prototype to simulate the shock environment, such as satellite–rocket separation, etc. In conclusion, the prediction accuracy of natural frequency, mode consistency, and response coincidence are considered comprehensively to extrapolate the vibration characteristic of the full-size laminated plates.

FLAT CIRCULAR SOLENOID BETWEEN MASSIVE BIFILAR COILS. ANALYSIS OF ELECTROMAGNETIC PROCESSES

An analysis and numerical estimates of induction effects in the metal of a flat circular solenoid located between the branches of an external bifilar coil in a flat inductor system excited by unidirectional currents in the bifilar windings are presented. Such a device, the design of which was first proposed earlier by the authors of this work, is of practical interest for circuits of equipment for magnetic-pulse processing of metals. The use of the considered inductor system makes it possible to minimize the influence of induction effects on electromagnetic processes in the metal of the internal inductor. Numerical estimates are obtained for the induced currents excited in the metal of the inner circular inductor placed between the outer windings of the bifilar coil. It is shown that in the low-frequency mode of acting fields, the time dependence of the excited current is a derivative of the time dependence of the exciting current and the transverse distribution of the current in the metal of the internal inductor is a linear dependence passing through the central axis of the inductor. In the high-frequency regime of acting fields, the time dependence and the radial distribution of the excited current coincide with the corresponding analogs for the exciting current, and the transverse distribution of the induced current is characteristic of a sharp surface effect, when the induced current is displaced to the boundary surfaces of the metal. It is proved that the minimum influence of the fields of the external bifilar on the electromagnetic processes in the internal inductor should be observed in the low-frequency mode, when the spatial superposition of multidirectional induced currents adds up to the zero value of the excited electromotive force of induction. The results of the analysis based on the specific calculations performed are aimed at finding the conditions for the successful technical implementation of the proposed inductor system. The creation of workable models of the proposed inductor systems and experiments to determine the real conditions for their maximum efficiency are seen as very promising in the direction of subsequent research.