THEORETICAL SUBSTANTIATION OF THE PHYSICAL MECHANISM OF ULTRASONIC CAVITATION DESTRUCTION OF MACROMOLECULES

Многообещающее направление исследований, которое потенциально может служить базой для создания эффективной технологии управления свойствами полимеров – воздействие механическими колебательными возмущениями на высокомолекулярную среду. В реальных неотверждённых полимерах механические колебательные возмущения, как правило, представляют собой кавитационно-акустическое воздействие, т.е. линейные синусоидальные колебания, создаваемые в среде, инициируют вторичное явление – кавитационные пузырьки. Пузырьки при кавитационно-акустическом воздействии периодически расширяются и схлопываются, формируя микроударные волны. Таким образом, механические колебательные возмущения имеют две составляющие – линейная синусоидальная и нелинейная ударно-волновая. Основное воздействие на структуру полимеров оказывает ударно-волновая составляющая. Для реализации данного процесса с максимальной энергетической эффективностью необходимо выявить оптимальные режимы воздействия. Для выявления оптимальных режимов воздействия в статье теоретически обоснован физический механизм разрушения макромолекул, основанный на их соударении со скоростью, превышающей критическую за счёт формирования экстремальных условий по температуре и давлению в окрестности схлопывающегося кавитационного пузырька. A promising area of research that can potentially serve as a basis for creating an effective technology for controlling the properties of polymers is the effect of mechanical oscillatory disturbances on a high–molecular medium. In real uncured polymers, mechanical oscillatory disturbances, as a rule, represent a cavitation-acoustic effect, i.e. linear sinusoidal vibrations created in the medium initiate a secondary phenomenon - cavitation bubbles. Bubbles under cavitation-acoustic action periodically expand and collapse, forming micro-shock waves. Thus, mechanical oscillatory disturbances have two components – linear sinusoidal and nonlinear shock wave. The main effect on the structure of polymers has a shock-wave component. To implement this process with maximum energy efficiency, it is necessary to identify optimal exposure modes. In order to identify optimal exposure modes, the article theoretically substantiates the physical mechanism of destruction of macromolecules based on their collision with a velocity exceeding the critical one due to the formation of extreme conditions for temperature and pressure in the vicinity of a collapsing cavitation bubble.

Nonlinear Behavior of High-Intensity Ultrasound Propagation in an Ideal Fluid

In this paper, nonlinearity associated with intense ultrasound is studied by using the one-dimensional motion of nonlinear shock wave in an ideal fluid. In nonlinear acoustics, the wave speed of different segments of a waveform is different, which causes distortion in the waveform and can result in the formation of a shock (discontinuity). Acoustic pressure of high-intensity waves causes particles in the ideal fluid to vibrate forward and backward, and this disturbance is of relatively large magnitude due to high-intensities, which leads to nonlinearity in the waveform. In this research, this vibration of fluid due to the intense ultrasonic wave is modeled as a fluid pushed by one complete cycle of piston. In a piston cycle, as it moves forward, it causes fluid particles to compress, which may lead to the formation of a shock (discontinuity). Then as the piston retracts, a forward-moving rarefaction, a smooth fan zone of continuously changing pressure, density, and velocity is generated. When the piston stops at the end of the cycle, another shock is sent forward into the medium. The variation in wave speed over the entire waveform is calculated by solving a Riemann problem. This study examined the interaction of shocks with a rarefaction. The flow field resulting from these interactions shows that the shock waves are attenuated to a Mach wave, and the pressure distribution within the flow field shows the initial wave is dissipated. The developed theory is applied to waves generated by 20 KHz, 500 KHz, and 2 MHz transducers with 50, 150, 500, and 1500 W power levels to explore the effect of frequency and power on the generation and decay of shock waves. This work enhances the understanding of the interactions of high-intensity ultrasonic waves with fluids.

Construction principle of NES shock absorber and its application in frame structure

Purpose The purpose of this paper is to describe the structure of nonlinear dampers and the dynamic equations, and nonlinear realization principles and optimize the parameters of nonlinear dampers. Using the finite element method to analyze the seismic performance of the frame structure with shock absorber. Design/methodology/approach The nonlinear shock absorber was installed in a six-storey reinforced concrete frame structure to study its seismic performance. The main structure was designed according to the eight degree seismic fortification intensity, and the time history dynamic analysis was carried out by Abaqus finite element software. EL-Centro, Taft and Wenchuan seismic record were selected to analyze the seismic response of the structure under different magnitudes and different acceleration peaks. Findings Through the principle study and parameter analysis of the nonlinear shock absorber, combined with the finite element simulation results, the shock absorption performance and shock absorption effect of the nonlinear energy sink (NES) nonlinear shock absorber are given as follows: first, the damping of the NES shock absorber is satisfied, and the linear spring stiffness and nonlinear stiffness of the shock absorber are based on the relationship k1=kn×kl2, so that the spring design length is fixed, and the linear stiffness of the shock absorber can be obtained. The nonlinear shock absorber has the characteristics of high rigidity and frequency bandwidth, so that the frequency is infinitely close to the frequency of the main structure, and when the mass of the shock absorber satisfies between 0.056 and 1, a good shock absorption effect can be obtained, and the reinforced concrete with the shock absorber is obtained. The frame structure can effectively reduce the seismic response, increase the natural vibration period of the structure and reduce the damage loss of the structure. Second, the spacer and each additional shock absorber have a small difference in shock absorption effect. After the shock absorber parameters are accurately calculated, the number of installations does not affect the shock absorption effect of the structure. Therefore, the shock absorber is properly constructed and accurately calculated. Parameters can reduce costs. Originality/value New shock absorbers reduce earthquake-induced damage to buildings.

On the Dissipative Propagation in Oppositely Charged Dusty Fluids

The dissipative propagation due to the dust viscosity of dust nonlinear shock acoustic wave in a collisionless, unmagnetised, oppositely charged viscous dusty plasma with trapped ion has been examined using parameters related to mesosphere and magnetosphere of Jupiter. The modified dissipative Korteweg de Vries–Burgers equation describes the model and solves according to different physical dissipation conditions. The physical effects of two dusty kinematic viscosity coefficients and positively charged dust grains on the shock properties are investigated.