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"Falling"
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Freely falling sphere with a rigid rear-side filament
In aerodynamic and hydrodynamic devices and locomotive organisms, passive appendages have practical purposes such as drag reduction and flow control. Although these appendages also affect the dynamics of freely falling bodies, underlying principles of their functions remain elusive. We investigate experimentally the dynamics of a falling sphere with a filament appended on its rear side by varying the ratio of filament length to sphere diameter (
$l/D=0{-}3.0$
) and sphere-to-fluid density ratio (
$\\rho _s/\\rho _f= 1.06{-}1.36$
), and maintaining a similar dimensionless moment of inertia (
$I^* \\approx 0.96$
). At the Reynolds number of
$O(10^3)$
, a sphere without any filament exhibits vertical descent. However, the falling of the sphere with a filament is accompanied by periodic horizontal displacements, and the degree of zigzag motion is maximised under specific filament length. The filament induces periodic rotation of the sphere by shifting the centre of mass of the entire model and through the hydrodynamic interaction of the filament with the surrounding fluid. The rotation of the sphere increases the drag force acting on the model, reducing tangential velocity along the trajectory by 14 % compared to a plain sphere. Furthermore, the sphere rotation enhances the lift force normal to the trajectory, extending trajectory length by 5 %. These combined effects improve falling time over a certain vertical distance by 20 % compared to the plain sphere. With increasing sphere density, the effects of the filament on the falling dynamics weaken, because the offset distance between the centre of mass of the model and the geometric centre of the sphere becomes smaller.
Journal Article
Numerical investigation on the longitudinal distribution characteristics of falling film flow outside a vertical tube
In order to design the vertical falling film evaporators applied in the sewage source heat pump systems, a numerical study employing the VOF (Volume of Fluid) method has been carried out to determine the thickness and the wave behavior of falling liquid film outside a vertical tube. The effects of the annular gap, tube diameter, tube length, spray density, viscosity and surface tension are discussed. The simulation results demonstrate that spray density and the fluid viscosity are the two most influential factors affecting the film thickness. Besides, when spray density is larger than 0.100 kg/(m∙s), the film thickness decreases slightly with the increase of the flow distance. So the influence of tube length on film thickness cannot be ignored and it also should be considered in the film thickness prediction model. On the other hand, the tube diameter and the surface tension have little effect on the film thickness. It mainly have a significant impact on the wave amplitude of the liquid film at low flowrate. Besides, the annular gap provides a limited effect on the outlet section of the falling film. On the basis of the simulation results, a new correlation incorporating the tube length is developed to effectively predict the falling film thickness. Compared with the experimental data, it is found that the prediction accuracy of the correlation can be controlled within ±15%. The present research provides a theoretical basis for designing falling film evaporators.
Journal Article
Observing the unexpected enhances infants' learning and exploration
Given the overwhelming quantity of information available from the environment, how do young learners know what to learn about and what to ignore? We found that 11-month-old infants (N = 110) used violations of prior expectations as special opportunities for learning. The infants were shown events that violated expectations about object behavior or events that were nearly identical but did not violate expectations. The sight of an object that violated expectations enhanced learning and promoted information-seeking behaviors; specifically, infants learned more effectively about objects that committed violations, explored those objects more, and engaged in hypothesis-testing behaviors that reflected the particular kind of violation seen. Thus, early in life, expectancy violations offer a wedge into the problem of what to learn.
Journal Article
Reviving the lithium metal anode for high-energy batteries
Lithium-ion batteries have had a profound impact on our daily life, but inherent limitations make it difficult for Li-ion chemistries to meet the growing demands for portable electronics, electric vehicles and grid-scale energy storage. Therefore, chemistries beyond Li-ion are currently being investigated and need to be made viable for commercial applications. The use of metallic Li is one of the most favoured choices for next-generation Li batteries, especially Li–S and Li–air systems. After falling into oblivion for several decades because of safety concerns, metallic Li is now ready for a revival, thanks to the development of investigative tools and nanotechnology-based solutions. In this Review, we first summarize the current understanding on Li anodes, then highlight the recent key progress in materials design and advanced characterization techniques, and finally discuss the opportunities and possible directions for future development of Li anodes in applications.
Journal Article
A two-phase sharp-interface numerical model of falling film thermal desalination in a vertical channel
A two-dimensional, sharp-interface two-phase laminar flow numerical model for evaporation from a salt-water falling liquid film with a co-current humid air flow on the interior of a parallel plate vertical channel is presented. The elliptic governing equations in both phases are solved simultaneously in an implicit, fully coupled approach using an in-house Fortran code. The liquid-gas interface is tracked precisely on an automatically adjusted non-orthogonal structured mesh. The basis of the evaporation model is validated for pure water falling film evaporation. A parametric study of evaporation from a salt-water falling film is presented. The study varies the inlet salinity of the film, the inlet liquid Reynolds number, the wall heat flux, and the air relative humidity. The effects of these variations on quantities such as the evaporation rate, the axial velocity, the salinity in the film, and the temperature are presented. The results demonstrate the capablity of the new model to predict the details of falling film thermal desalination.
Journal Article
Study on influence of missile-target intersection parameters on damaged steel plate of blast-fragmentation warhead
In order to study the damage effect of blast-killing warhead on steel target at different falling velocities and falling angles, AUTODYN-3D software was used to numerically simulate the damage of blast-killing warhead on steel target at different falling velocitis and falling angles using SPH algorithm. The results show that the hole shape of the target plate is quadrilateral when the falling angle is 0°, the hole shape of the target plate is round when the falling angle is 90°, the hole shape of the target plate is circular and fan-shaped when the falling angle is 30° and 60°. At the same falling angle, the hole area of the target plate increases with the increase of falling velocities. At the same falling velocities, the hole area of the target plate increases first and then decreases with the increase of falling angle.
Journal Article
Research on Confidence Analysis Method of Lightning Strike Accidents on Distribution Lines
Currently, lightning is the main cause of power system faults. Due to insufficient equipment and technology, low insulation level, the distribution network being the main part of power outages, and the complex causes of distribution network faults, it is difficult to determine whether each fault in the distribution network is caused by lightning strikes. In this paper, the concept of lightning strike confidence, i.e., the possibility of a line lightning strike fault caused by falling lightning, is proposed, and a lightning strike confidence analysis is performed for a 10 kV distribution line in the mountainous region of South China to determine the possibility of a line lightning strike fault caused by falling lightning based on the lightning locating system data of the distribution line at the moment of the fault. First, the calculation method of the lightning strike confidence is derived; then the distribution law of the distribution line lightning strike confidence, the influence of the ground tilt direction, and ground tilt angle on the distribution line lightning strike confidence are analyzed; finally, the distribution line lightning strike confidence is analyzed by an example.
Journal Article
Association Between Gait Lower Limb Intra and Interlimb Coordination and Fear of Falling and Falling History in Older Adults
Aging often leads to a decline in intersegmental coordination, particularly in the lower limbs, which can negatively impact gait stability and symmetry. While fear of falling (FoF) and a history of falls (HoF) increase fall risk in older adults, their relationship with intra- and intersegmental coordination during gait remains understudied. This cross-sectional observational study involved 60 participants aged 60 and older. The three-dimensional range of motion of lower limb joints during gait was assessed using an optoelectronic system. Intra- and intersegmental coordination were evaluated via the Continuous Relative Phase (CRP) variable, including its mean, standard deviation, and coefficient of variation. The results showed that the HoF and FoF groups had higher mean CRP values in the left hip-knee (HOF, p = 0.004) and hip-ankle (FOF, p = 0.030) in the sagittal plane, as well as higher standard deviation values in the left knee-ankle (HOF, p = 0.006) and right hip-ankle (HOF, p = 0.004). Inter-segmental coordination differences were also observed, with higher mean CRP values between the knee joints in the sagittal plane (HOF, p = 0.046) and lower mean and standard deviation values between the ankle joints (FOF, p = 0.048 and p = 0.038, respectively). This study concludes that fear of falling and history of falling are significantly associated with altered intra- and intersegmental coordination in older adults, which may contribute to fall risk. Understanding these altered coordination patterns is crucial, as it underscores the therapeutic significance of targeting these changes, which could lead to interventions aimed at improving gait stability and reducing fall risk in elderly individuals.
Journal Article