Numerical investigation of lagrangian coherent structures in steady rotation vortex shedding control

In this paper, vortex shedding and suppression are numerically investigated as autonomous and non-autonomous dynamical systems respectively. Lagrangian coherent structures (LCSs) are used as a numerical tool to analyze these systems. These structures are ridges of Finite time Lyapunov exponent (FTLE) which act as material surfaces that are transport barriers within the flow. Initially, the utility of LCSs is explored for revealing the coherent structures of these systems. Finally, an active flow control method, steady rotation is applied to the non-autonomous dynamical system with different speed ratios to mitigate vortex shedding magnitude. This will eventually turn the system into an autonomous system. Fixed saddle points, separation profiles essentially as unstable time variant manifolds attached to cylinder wall and evolution of other unstable manifolds with variant speed ratios are analyzed with reference to LCSs. It is revealed that speed ratio of 2.1 fully suppresses the von Karman vortex street at Reynolds number of 100 and system turns into an autonomous dynamical system with fixed saddle points and time-invariant manifolds.

Demonstration of flywheel-based travelling-wave thermoacoustic engine

We report test results on a thermoacoustic engine having a piston-crank-flywheel assembly. The engine maintained steady rotation states when the heating temperature was increased more than 114°C. The rotation frequency increased with the higher heating temperature and reached 14.5 Hz when it was 296°C. The pressure versus volume diagram was created to deduce the power delivered to the piston-crank-flywheel assembly from measurements of the pressure of the working gas and the rotation angle of the flywheel.

Differential rotation in cholesteric pillars under a temperature gradient

Steady rotation is induced in cholesteric droplets dispersed in a specific liquid solvent under a temperature gradient. In this phenomenon, two rotational modes have been considered: (1) collective rotation of the local director field and (2) rigid-body rotation of the whole droplet structure. However, here we present another rotational mode induced in a pillar-shaped cholesteric droplet confined between substrates under a temperature gradient, that is, a differential rotation where the angular velocity varies as a function of the radial coordinate in the pillar. A detailed flow field analysis revealed that every pillar under a temperature gradient involves a double convection roll. These results suggested that the differential rotation in the cholesteric pillars was driven by the inhomogeneous material flow induced by a temperature gradient. The present experimental study indicates that the coupling between the flow and the director motion plays a key role in the rotation of the cholesteric droplets under the temperature gradient.

Discrete model of chain conveyor movement dynamics

Improving the reliability of structures of transport mechanisms and other elements, reducing metal content, improving performance, expanding functionality and technical capabilities is a priority area of work to improve existing and develop new machines for beet growing. The dynamic model of the chain conveyor which considers the basic movement and fluctuations of elements of the drive and a working cloth is developed in work. The model is represented by a system of discrete masses with eight degrees of freedom. The operation of chain conveyors is characterized by the presence of dynamic forces arising from the pulsating movement of the chain at a steady rotation of the drive sprocket. At the start-up site, dynamic forces from increasing the speed from zero to a certain constant value are added to these forces. Under such conditions, significant alternating dynamic loads can occur in the chain, which as a result of the accumulation of fatigue phenomena can lead to its premature destruction.

Effect of Rotational Modulation on Rayleigh – B´enard Convection in a Couple Stress Liquid

The Rayleigh-B´enard convection in a couple stress liquid with rotational modulation is studied using the linear analysis based on normal mode technique. The stability of a horizontal layer of fluid heated from below is examined when, in addition to a steady rotation, a time-periodic sinusoidal perturbation is applied. The expression for Rayleigh number and correction Rayleigh number are obtained using regular perturbation method. The expression for correction Rayleigh number is obtained as a function of frequency of modulation, Taylor number, Couple Stress parameter and Prandtl number. It is observed that rotational modulation leads to delay in onset of convection. Rotation modulation is an example of external control of internal convection.

APPLICATION OF THE APPARATUS OF BALL VECTORS IN PROBLEMS OF MECHANICS

An approach to solving problems of dynamics of distributed mechanical systems with spherical symmetry based on the use of the ball vector apparatus is demonstrated. A number of problems of the dynamics of a solid deformable body, liquid fluid, and magnetic hydrodynamics are presented, for which an analytical solution is obtained that allows us to identify qualitative features of the dynamics of the studied objects. The problem of free angular movements of a deformable body close in shape to a ball is considered. The example of almost of ball possessing cubic symmetry, body shape and almost spherical the inertia tensor in the undeformed condition, demonstrates the ability of the global movement in the body axis of steady rotation (pole). The effect is due to the fact that when a body rotates at high speed, the elastic properties play a decisive role in its dynamics. Over time, the angular velocity of the drag decreases and the movement of the body is increasingly affected by its ellipsoidplicity. The motion of an incompressible viscous fluid in the space between a rotating non-concentric sphere and an ellipsoid is studied. It is shown that the asymmetry of the flow leads to the appearance of a radial flow of the liquid. The presence of such a flow in the case of a conducting liquid is a necessary condition for generating a magnetic field. Assuming that the liquid is conductive, a study of the possibility of generating a magnetic field is carried out on the basis of the obtained flow in the framework of the kinematic approach. The smallest value of the Reynolds magnetic number is found, which creates an exponentially growing magnetic field when passing through it. The results obtained can be useful for studying the dynamics of the Earth and the planets of the Solar system and the mechanism of generating a geomagnetic field.

Study on Swing Movable Teeth Drive with External Generating Wave Mode

An external generating wave swing movable teeth drive based on sinusoidal acceleration and quintic polynomial motion has been newly developed. This drive consists of a wave generator as the input cam, a train of movable rollers which are uniformly distributed on the fixed separator, and a ring gear as the output cam. The teeth difference between the ring gear and the rollers is two. The input and output cam are engaged with the train of rollers simultaneously. The drive thus has the advantages of large gear ratio, compact structure, high torsional rigid and steady rotation, can be integrated with pulley drive to form a pulley reducer. In this paper, the motion principle is studied and the tooth profiles are derived. On this foundation, curvature of the ring gear and pressure angles of the drive are conducted. And kinematic simulation is also carried out. A physical prototype is manufactured to demonstrate the feasibility and correctness of the theoretical analysis model of the drive. This drive can be integrated with pulley drive to form a pulley reducer, which is promising for the fields needing compact structure and large transmission ratio.