Forced Resonance Oscillations Research Articles

Experimental research of cable tension tuning of a scaled model of cable stayed bridge

The paper describes the idea and the algorithms of a method for reducing the resonant vibration of the cables in a footbridge. The method relies on change of the static tension in chosen cables of the footbridge. The changes in static tension are introduced when resonance vibration occurs. The paper delineates empirical research employed to experimentally verify the numerical prediction. It has been demonstrated that it is possible to select some stay cables in which applicable change in static tension force value ensures amplitude reduction of forced resonance oscillations of any cable of the whole system. The choice of cables and the magnitude of tension change in them were based on the sensitivity analysis of an eigenproblem formulated in accordance with second order theory. The experimental research was designed to demonstrate practical effectiveness of amplitude reduction of stay cable resonant vibration method. A physical laboratory model of the footbridge was built in compliance with dimensional analysis on a scale of 1:10. Operational Modal Analysis (OMA) method was applied to identifying modal characteristic of a footbridge model.

Forced Resonant Oscillations as a Response to Periodic Winds in a Stratified Reservoir

The response of the Sau reservoir to a wind field characterized by having marked periodicities of 12 h and 24 h has been studied. Measurements of temperature, with a thermistor string, and currents, with an acoustic Doppler current meter, show that the reservoir also responds with the same water periodicities. During certain times of the stratified period, some of the natural oscillation modes of the reservoir are close to these forcing wind periods. In particular, in mid-July the vertical Mode V2 is close to 12 h and in mid- to end of September the vertical Mode V3 is close to 24 h. In these situations, these modes are selected out of the spectrum of possible internal waves and the reservoir behaves as a forced oscillator in resonance with the wind. The structure and the period of these vertical modes have been elucidated by using the 3D model ELCOM. Both modes are affected by the Earth's rotation at the widest part of the reservoir.

Loss of superfluidity in a Bose–Einstein condensate via forced resonant oscillations

We predict the loss of superfluidity in a Bose–Einstein condensate in an axially symmetric harmonic trap alone during resonant collective oscillations via a classical dynamical transition. The forced resonant oscillation can be initiated by (a) periodic modulation of the atomic scattering length with a frequency that equals twice the radial trapping frequency or multiples thereof, or by (b) periodic modulation of the radial trapping potential with a frequency that equals the radial trapping frequency or multiples thereof. Suggestion for future experiment is made.

Natural aging and dynamic mechanical properties of polymer matrices

The influence of natural six-month aging at 293 K of two kinds of epoxy resins with different network density on their dynamical properties was studied. All the samples were examined by forced resonance oscillations at a frequency of 200 Hz in the range of 120–520 K. The components of the complex Young's modulus E′, E″, tan δ, and low-frequency velocity of sound were measured. The basic temperature transitions including Tg and the network density ν were determined from the experimental data. It was established that after aging of epoxy resins cured by the cross-linking agent meta-phenylenediamine their network density ν decreased (“cold” degradation). By using the cross-linking agent 2,6-diaminopyridine, ν and Tg increased. An attempt is made to explain the nature of this phenomenon.

Effects of ionizing radiation on the viscoelasticity of glassy polyethylene terephthalate films

Abstract The viscoelastic properties of Gamma-ray irradiated polyethylene terephthalate (PET) sheets, extruded in the glassy state, were measured by a method of forced resonance oscillations. Density variations due to γ-irradiation with different doses were found suitable to describe changes of the cross-linking rate. The dynamic Young's modulus of PET-films showed a decrease within the dose range 200-500 kGy which has anomalous behaviour related to the glass transition (alpha-relaxation) by γ-irradiation to a rubberlike state at a dose of 200 kGy. The low frequency velocity of sound showed no correlation with the density of irradiated PET-films.

The asymptotic solution of linearized problems on the natural and forced resonance oscillations of a medium of low viscosity

For the linearized problems of the natural and forced resonance oscillations of a medium of low viscosity, written in dimensionless form, the asymptotic behaviour of the solution with respect to a small parameter (proportional to the coefficient of viscosity) is found. This behaviour reflects the boundary-layer nature of the solution.

Hysteresis and Heating in Vulcanized Rubber

Abstract Laboratory tests for evaluating energy losses due to hysteresis are analyzed. The importance of taking into consideration the thermal conductivity and cooling conditions of the rubber sample for the evaluation of heating due to hysteresis losses at temperature equilibrium is discussed. Two new test methods, based on forced resonance oscillations, are described, in which the rubber samples are deformed respectively in shear and in tension at frequencies of 20 to 200 cycles per second, with dynamic shear strain of 0.02 to 0.4 and dynamic tension strain of 1 to 5 per cent, and at a temperature of 20 to 110° C. Experimental results obtained with natural rubber and GR-S gum and tread stocks are presented. The hysteresis losses in gum stocks are found to follow the quadratic law versus dynamic shear strain, and the dynamic modulus G is found to be independent of shear strain. With tread stock the hysteresis losses are lower than would be the case with the quadratic law versus dynamic shear deformation, and the dynamic modulus G decreases with increasing dynamic shear strain. Neither the hysteresis losses nor the modulus depend on the shape or size of the specimen. The modulus is found to be independent of frequency, while the hysteresis losses are found to increase proportionally with frequency. As an application of the test method, results are presented of the effect of the quality and quantity of various types of carbon black on hysteresis heating of GR-S stocks.