EX draconis: using eclipses to separate outside-in and inside-out outbursts

ABSTRACT We present a study of the eclipses in the accreting white dwarf EX draconis (EX Dra) during TESS Cycles 14 and 15. During both of the two outbursts present in this data set, the eclipses undergo a hysteretic loop in eclipse-depth/out-of-eclipse-flux space. In each case, the direction in which the loops are executed strongly suggests an outburst that is triggered near the inner edge of the accretion disc and propagates outwards. This in turn suggests that the outbursts in EX Dra are ‘inside out’ outbursts; events predicted by previous hydrodynamic studies of dwarf nova accretion discs and confirmed spectroscopically in a number of other accreting white dwarf systems. We therefore propose that the direction of the loop executed in eclipse-depth/out-of-eclipse flux space be used as a test to phenomenologically distinguish between ‘inside out’ and ‘outside in’ outbursts in other eclipsing dwarf novae; a reliable and purely photometric test to differentiate between these phenomena.

Methods for estimating hysteretic behavior and vibration responses of a timing belt tensioner

An automatic tensioner that consists of a torsional spring and friction damping elements is widely used in belt drive system. The relation of the applied torque versus the imposed angle of tensioner during loading and unloading processes is described as a hysteretic loop. An analytical model is established for estimating the hysteretic behavior of a tensioner, and measurements for hysteretic loop in quasi-static and dynamic excitation are carried out to validate the analytical model. Taking one engine timing belt drive system as a studying example, the method and the procedure for estimating vibration responses of the nonlinear tensioner are given. An iterative algorithm for predicting the accurate equivalent viscous damping of tensioner is carried out in analyzing a belt drive system. The vibration responses of tensioner are validated by the measurement of timing belt drive system. The developed method presented in this article is useful for predicting the hysteretic behavior of tensioner, vibration responses, and the parameters optimization of a belt drive system.

THE MODIFIED MOHR – COULOMB AND DRUCKER – PRAGER MODELS. INFLUENCE OF ECCENTRICITY ON HYSTERESIS LOOP AND ENERGY LOSS

The eccentricity parameters appearing in the modified Mohr-Coulomb and Drucker-Prager models are studied. The influence of the eccentricity on shape and size of the hysteretic loop and plastic dissipation energy are analyzed. Both kinematic and force loadings are considered.

The lateral force hysteretic characteristic of a pitching slender body without and with synthetic jet control

The lateral hysteretic characteristic generated by asymmetric vortical flow behind the tangent-ogive cylinder is investigated without and with micro synthetic jet control, when the slender body undergoes a large amplitude pitching motion. Experiments are conducted in a low speed wind tunnel of Nanjing University of Aeronautics and Astronautics at a Reynolds number of 46000. The change rule of the instantaneous pressure distribution reflects the aerodynamic characteristic of the whole model. The data of temporal flow file are acquired using particle image velocimetry locked-phase method and present the asymmetric vortices evolution. Results show that asymmetric vortices still exist in the leeward of the slender body during the dynamic pitching motion. However, the asymmetric degree of the vortices distribution, swirling strength and breakdown location are different which is greater in the downward pitching than in the upward pitching, which leads to the lateral force hysteretic phenomenon. In addition, the hysteretic loop expands as the reduced frequency increased. It is an effective method of the flow control that uses micro synthetic jet alternative blow to control the lateral force in the dynamic pitching motion. Furthermore, the lateral force, the pressure distribution and the hysteretic loop shape are changed continuously as the duty cycle of the control signal increased. For the duty cycle of 50%, the vortices distribution, the swirling strength and breakdown location tend to be symmetrical, so the lateral force decreases significantly and the hysteretic loop is eliminated.

Deformation of a concrete matrix subject to a cyclic freeze–thaw process

With cyclic freeze–thaw process, the strain hysteretic loop of concrete matrix is raised upwards indicating that residual strain occurs, which proves that the damage is continuously accumulated and an irreversible deterioration process is generated.

Dynamic Properties of Silicate-Grouted Sand at Low Stress Level

The creep behaviors of silicate-grouted sandy soil were investigated. A series of haversine creep tests with three frequencies (0.01 Hz, 0.05 Hz, and 0.1 Hz) were carried out to evaluate the dynamic properties (complex modulus and phase angle) of materials at low stress level. The stress-strain relationship for the sinusoidal test was plotted as an elliptical hysteretic loop. The complex modulus |G*(ω)| and the phase angle δ were determined from the hysteretic loop at a given frequency ω. While the complex modulus |G*(ω)| of the tested material increased, the complex compliance |J*(ω)| and the phase angle δ decreased with frequency ω within the tested frequency range.