Review of Single Bubble Motion Characteristics Rising in Viscoelastic Liquids

The emphasis of this review is to discuss three peculiar phenomena of bubbles rising in viscoelastic fluids, namely, the formation of a cusp, negative wake, and velocity jump discontinuity, and to highlight the possible future directions of the subject. The mechanism and influencing factors of these three peculiar phenomena have been discussed in detail in this review. The evolution of the bubble shape is mainly related to the viscoelasticity of the fluid. However, the mechanisms of the two-dimensional cusp, tip-streaming, “blade-edge” tip, “fish-bone” tip, and the phenomenon of the tail breaking into two different threads, in some special viscoelastic fluids, are not understood clearly. The origin of the negative wake behind the bubbles rising in a viscoelastic fluid can be attributed to the synergistic effect of the liquid-phase viscoelasticity, and the bubbles are large enough; thus, leading to a very long relaxation time taken by the viscoelastic stresses. For the phenomenon of bubble velocity jump discontinuity, viscoelasticity is the most critical factor, and the cusp of the bubbles and the surface modifications play only ancillary roles. It has also been observed that a negative wake does not cause velocity jump discontinuity.

Prediction of Jumping Distance Using Run-Up Velocity and Age for Female Long Jumpers

It is the flight distance which is approximately ninety percent of jump distance in long jump. On the other hand, there are many biomechanical factors that determine the flight distance and horizontal velocity is considered to be the most effective factor. The aim of this study was to create a jump distance estimation model based on run-up velocity that can practically be used by trainers. The research data was included 858 valid trials of 156 female Turkish long jumpers (ages: 17.8±3.4 years). According to the correlation results of the current study; a nonlinear regression model was used between the variables found to have the highest correlation (age, last 10 meter run-up velocity, jump distance). According to this model, 79.10% of the jump distance can be estimated with the variables of age and run-up velocity in the last ten meters. Developed to be used for female long jumpers at a broad performance level, this model may make it possible to make technical evaluations about whether the velocity, technique and strength of a female long jumper are stable. Keywords: long jump, velocity, age, prediction model

FEATURES OF HEAT TRANSFER IN A FLAT POROUS MICROCHANNEL WITH THE SECOND ORDER SLIP BOUNDARY CONDITIONS

The results of the study of heat transfer under forced convection in a flat porous microchannel taking into account the boundary conditions of slippage of the first and second order are considered. The simulation showed that with decreasing porosity the flow velocity in the central part of the microchannel and the slipping velocity on the wall decrease due to the increase in hydrodynamic resistance. Taking into account the influence of the boundary conditions of the second order shows that the magnitude of the velocity jump on the wall varies depending on the value of the parameter A2. The jump decreases with a positive value of A2, with a negative value - increases in comparison with the case A2 = 0 (first order boundary conditions). Qualitatively similar effects of porosity and second-order boundary conditions were also observed with respect to temperature profiles. The results of the calculation of the relative Nusselt number showed that the decrease in porosity contributes to the intensification of heat transfer. The dynamics of the change in the heat transfer coefficient with an increase in the Knudsen number indicates that an increase in the Prandtl number also leads to an improvement in the thermal interaction of the flow with the channel wall. The analysis of taking into account the boundary conditions of the second order showed that at small values of the Prandtl number (Pr ≤ 1) the influence of the parameter A2 was not observed. At A2 < 0 the effects of the boundary conditions of the second order lead to an increase in the relative Nusselt number, whereas at A2> 0 the value of the normalized Nusselt number decreases in comparison with the case A2 = 0 (boundary conditions of the first order).

Vertical velocity fields along the Eastern Mediterranean coast as revealed by late Holocene sea-level markers

&lt;p&gt;Vertical movements of the solid surface reflect crustal deformation and mantle deep related phenomena. For Holocene times, coastlines displaced from the present mean sea level are often used, combined with past relative sea levels (RSL) prediction models, to clue the vertical deformational field.&amp;#160;&lt;br&gt;Along the coast from south-western Turkey until Israel and Cyprus, a certain amount of good quality data is already published, leaving only a gap where data are absent along the Central Anatolian Plateau (CAP) coast. Based on new field observations along with this sector, between Adalia and Adana (Mersin, southern Turkey), together with AMS 14C dating, the gap is filled, allowing to describe an overall frame made by vertical differential movements along the Eastern Mediterranean coast.&amp;#160;&lt;br&gt;Most recent Glacial Isostatic Adjustments (GIA) models have been used to remove the glacio-hydro isostatic component of the RSL. Different solutions from ICE-6G(VM5a) and ICE-7G(VM7) models (developed by W.R. Peltier and co-workers, Toronto University), as also a solution from the GIA model progressively developed by K. Lambeck and collaborators at the Australian National University, have been applied on 201 middle-to-late Holocene markers of RSL. Both GIA models have been implemented within the numerical Sea level Equation solver SELEN4.&lt;br&gt;Tectonic velocity has been therefore calculated. Starting from southwestern Turkey, subsidence has been found within the range between -0.91 mm/yr and -2.15 mm/yr confirming values from previous works. Velocities from the new markers along the CAP coast are positive ranging between 1.01 and 1.65 mm/yr. These two first blocks are separated by a sharp velocity contact, occurring along the complex fault zone of the Isparta Angle. Such values for the CAP margin were expected as recently published papers report high vertical velocities for a Middle to Late Pleistocene uplift event. Moving to the east, velocities are also positive, within 0.3-0.6 mm/yr, along the coast between the Hatay Gulf and southern Lebanon. The spiked profile of the Lebanese sector is likely due to co-seismic deformations along the Lebanese Restraining Bend faults (LRB). To the south, the Israeli coast is instead showing stability according to some unique RSL markers named&amp;#160;piscinae&amp;#160;while other markers indicate slow subsidence. Hence another velocity jump of at least 0.5 mm/yr is recognizable between Israel and Lebanon: it is probably associated with already known brittle structures. In northern Cyprus, the only Holocene sea-level marker confirms the almost zero vertical velocity values already obtained for the MIS 5e marine terrace. Therefore, a vertical velocity jump occurs between stable Cyprus and the uplifting CAP southern margin, although they are placed on the same overriding plate of the subduction system. High-angle normal faults at the northern margin of the Adana-Cilicia Basin could explain these different vertical velocity fields.&amp;#160;&lt;br&gt;These results depict a complex frame of wide independently moving crustal blocks where kinematic separation occurs along well-known regional fault zones. Driving causes of the block movements could be related either to regional tectonics, as it probably is for the LRB coast, or to mantle dynamics, for the uplifting Turkish sector where deeper processes should be considered.&amp;#160;&lt;/p&gt;

Galerkin–Ivanov transformation for nonsmooth modeling of vibro-impacts in continuous structures

This work deals with the modeling of nonsmooth vibro-impact motion of a continuous structure against a rigid distributed obstacle. Galerkin’s approach is used to approximate the solutions of the governing partial differential equations of the structure, which results in a system of ordinary differential equations. When these ordinary differential equations are subjected to unilateral constraints and velocity jump conditions, one must use an event detection algorithm to calculate the time of impact accurately. Event detection in the presence of multiple simultaneous impacts is a computationally demanding task. Ivanov (Ivanov A 1993 “Analytical methods in the theory of vibro-impact systems”. Journal of Applied Mathematics and Mechanics 57(2): pp. 221–236.) proposed a nonsmooth transformation for a vibro-impacting multi-degree-of-freedom system subjected to a single unilateral constraint. This transformation eliminates the unilateral constraints from the problem and, therefore, no event detection is required during numerical integration. This nonsmooth transformation leads to sign function nonlinearities in the equations of motion. However, they can be easily accounted for during numerical integration. Ivanov used his transformation to make analytical calculations for the stability and bifurcations of vibro-impacting motions; however, he did not explore its application for simulating distributed collisions in spatially continuous structures. We adopt Ivanov’s transformation to deal with multiple unilateral constraints in spatially continuous structures. Also, imposing the velocity jump conditions exactly in the modal coordinates is nontrivial and challenging. Therefore, in this work, we use a modal-physical transformation to convert the system from modal to physical coordinates on a spatially discretized grid. We then apply Ivanov’s transformation on the physical system to simulate the vibro-impact motion of the structure. The developed method is demonstrated by modeling the distributed collision of a nonlinear string against a rigid distributed surface. For validation, we compare our results with the well-known penalty approach.

The Influence of Surfactants, Dynamic and Thermal Factors on Liquid Convection after a Droplet Fall on Another Drop

The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection is considered. The particle motion is realized by a complex curvilinear trajectory. The fall of droplet with and without surfactant additives is considered. Estimates of the influence of the thermal factor (thermocapillary forces) and the dynamic factor (inertia forces) on convection are given. The scientific novelty of the work is the investigation of the simultaneous influence of several factors that is carried out for the first time. It is shown that in the presence of a temperature jump for the time of about 0.01–0.1 s thermocapillary convection leads to a 7–8 times increase in the mass transfer rate in drop. The relative influence of inertial forces is found to be no more than 5%. The fall of drops with surfactant additives (water + surfactant) reduces the velocity jump inside the sessile drop 2–4 times, compared with the water drop without surfactant. Thermocapillary convection leads to the formation of a stable vortex in the drop. The dynamic factor and surfactant additive lead to the vortex breakdown into many small vortices, which results in the suppression of convection. The obtained results are of great scientific and practical importance for heat transfer enhancement and for the control of heating and evaporation rates.

Acceleration Compensation for Estimation of Along-Track Velocity of Ground Moving Target from Single-Channel SAR SLC Data

Across-track acceleration is a major source of estimation error of along-track velocity in synthetic-aperture radar (SAR) ground moving-target indication (GMTI). This paper presents the theory and a method of compensating across-track acceleration to improve the accuracy of along-track velocity estimated from single-channel SAR single-look complex data. A unique feature of the proposed method is the utilisation of phase derivatives in the Doppler frequency domain, which is effective for azimuth-compressed signals. The performance of the method was evaluated through experimental data acquired by TerraSAR-X and speed-controlled and measured vehicles. The application results demonstrate a notable improvement in along-track velocity estimates. The amount of along-track velocity correction is particularly significant when a target has irregular motion with a low signal-to-clutter ratio. A discontinuous velocity jump rather than a constant acceleration was also observed and verified through comparison between actual data and simulations. By applying this method, the capability of single-channel SAR GMTI could be substantially improved in terms of accuracy of velocity, and moving direction. However, the method is effective only if the correlation between the actual Doppler phase derivatives and a model derived from the residual Doppler rate is sufficiently high. The proposed method will be applied to X-band SAR systems of KOMPSAT-5 and -6.