Search Results (19)

This study presents a novel numerical framework that elucidates the critical, yet previously underexplored, role of Marangoni vortex dynamics in determining the final surface quality during the laser polishing of Ti6Al4V (TC4). TC4 titanium alloy is widely used in aerospace, biomedicine, and other high-precision applications due to its excellent specific strength, corrosion resistance, and biocompatibility. However, its surface quality directly affects the fatigue life and service performance of parts, and traditional polishing methods suffer from low efficiency and high pollution. As a non-contact, controllable surface treatment technology, nanosecond laser polishing has demonstrated unique advantages in balancing processing efficiency and surface quality. This study systematically discussed the influence of key process parameters (spot overlap rate, laser power, and scanning times) on the nanosecond laser polishing of TC4 titanium alloy. It revealed the internal physical mechanism by analyzing the temperature and velocity fields and vortex dynamics during molten-pool evolution. It is found that the polishing effect is determined by the process parameters, which adjust the thermal–fluid coupling physical field (temperature distribution, melt flow, and vortex structure) in the molten pool. There is an optimal combination of parameters (spot overlap rate of 79%, laser power of 0.8 W, scanning speed of 5 m/min, scanning 3 times) that can place the molten pool in an optimal dynamic balance state and achieve effective flatness. The experimental results show that, under this parameter, the surface roughness of the specimen with an initial roughness of 1.223 μm is reduced by about 32%. The research further clarified the mechanism by which the initial roughness of the base metal influences the molten pool: the greater the initial roughness, the more pronounced the “peak shaving and valley filling” effect. Under the same parameters, the improvement rate of the specimen with the initial roughness of 1.623 μm could reach about 40%. This study not only establishes the optimized process window but also reveals the essential relationship between “process parameters–bath behavior–surface quality” from the level of the physical field of the molten pool. The findings provide a practical guideline for parameter optimization, directly applicable to the high-precision laser finishing of critical titanium components in the aerospace and biomedical industries. Full article

Cables in cable-supported bridges are critical structural components with exceptional tensile capacity, and their assessment is essential for the safety of both the cables themselves and the entire bridge. Microwave radar, a non-contact and efficient measurement technique, has emerged as a promising tool for bridge cable evaluation. This study demonstrates the deployment of microwave radar on bridge decks to efficiently measure the displacements of multiple cables, enabling coverage of all cables while effectively eliminating low-frequency components caused by deck deformation and radar motion using the LOWESS method. The measured cable displacements can be directly used to characterize vibrations, particularly for detecting vortex-induced vibrations (VIVs), without the need for numerical integration of accelerations. Furthermore, microwave radar is applied to free-decay testing for cable damping evaluation, providing an improved signal-to-noise ratio and eliminating the need for sensors installed via elevated platforms, thereby enhancing the reliability of damping assessments. The effectiveness of these approaches is validated through field testing on two cable-stayed bridges. Full article

The combustion diagnostics of rotating detonation engines (RDE) based on excited-state hydroxyl radical (OH*) chemiluminescence imaging is an important method used to characterize combustion flow fields. Overcoming the limitations of imaging devices to achieve nanosecond-scale temporal resolution is crucial for observing the propagation of high-frequency detonation waves. In this work, a nanosecond-scale imaging system with an ultra-high spatiotemporal resolution was designed and constructed. The system employs four near ultraviolet (NUV)-visible ICMOS, equipped with a high-gain, dual-microchannel plate (MCP) architecture fabricated using a new atomic layer deposition (ALD) process. The system has a maximum electronic gain of 10⁷, a minimum integration time of 3 ns, a minimum interval time 4 ns, and an imaging resolution of 1608 × 1104 pixels. Using this system, high-spatiotemporal-resolution visualization experiments were conducted on RDE, fueled by H₂–oxygen-enriched air and NH₃–H₂–oxygen-enriched air. The results enable the observation of the detonation wave structure, the cellular structure, and the propagation velocity. In combination with optical flow analysis, the images reveal vortex structures embedded within the cellular structure. For NH₃-H₂ mixed fuel, the results indicate that detonation wave propagation is more unstable than in H₂ combustion, with a larger bright gray area covering both the detonation wave and the product region. The experimental results demonstrate that high spatiotemporal OH* imaging enables non-contact, full-field measurements, providing valuable data for elucidating RDE combustion mechanisms, guiding model design, and supporting NH₃ combustion applications. Full article

Control valves in nuclear systems operate under high-pressure differentials generating intense transient fluid forces that induce destructive structural vibrations, risking resonance and the valve stem fracture. In this study, computational fluid dynamics (CFD) was employed to characterize the internal flow dynamics of the valve, supported by experiment validation of the fluid model. To account for nonlinear structural effects such as contact and damping, a coupled fluid–structure interaction approach incorporating nonlinear perturbation analysis was applied to evaluate the dynamic response of the valve core assembly under fluid excitation. The results indicate that flow separation, re-circulation, and vortex shedding within the throttling region are primary contributors to structural vibrations. A comparative analysis of stability coefficients, modal damping ratios, and logarithmic decrements under different valve openings revealed that the valve core assembly remains relatively stable overall. However, critical stability risks were identified in the lower-order modal frequency range at 50% and 70% openings. Notably, at a 70% opening, the first-order modal frequency of the valve core assembly closely aligns with the frequency of fluid excitation, indicating a potential for critical resonance. This research provides important insights for evaluating and enhancing the vibration stability and operational safety of control valves under complex flow conditions. Full article

In this study, we propose a novel approach for dynamic micro-vibration measurement based on an interferometric system utilizing a fractional optical vortex (FOV) beam as the reference and a Gaussian beam as the measurement path. The reflected Gaussian beam encodes the vibration information of the target, which is extracted by analyzing the rotational behavior of the petal-like interference pattern formed through coaxial interference with the FOV beam. When the topological charge (TC) of the FOV beam is less than or equal to one, a single-petal structure is generated, significantly reducing the complexity of angular tracking compared to traditional multi-petals OAM-based methods. Moreover, using a Gaussian beam as the measurement path mitigates spatial distortions during propagation, enhancing the overall robustness and accuracy. We systematically investigate the effects of TC, CCD frame rate, and interference contrast on measurement performance. Experimental results demonstrate that the proposed method achieves high angular resolution with a minimum angle deviation of 18.2 nm under optimal TC conditions. The system exhibits strong tolerance to environmental disturbances, making it well-suited for applications requiring non-contact, nanometer-scale vibration sensing, such as structural health monitoring, precision metrology, and advanced optical diagnostics. Full article

In this paper, the detached eddy simulation (DES) method is used to calculate the aerodynamic characteristics of NACA0015 airfoil by combining the Riemann approximate solution HLLC (Harten–Lax–van Leer Contact) with the high-order weighted essentially non-oscillatory (WENO) scheme and the weighted compact nonlinear scheme (WCNS), respectively. By comparing the calculation results of the two different numerical schemes with the wind tunnel test results, it is found that both numerical schemes can accurately calculate the aerodynamic parameters at small angles of attack. However, in the range of near-stall angle (in the range of 10–15°), the calculation results of various numerical schemes have a certain degree of deviation. The calculation results of the fifth-order WCNS and the fifth-order WENO scheme are closer to the experimental values. The fifth-order WCNS predicts the stall angle of attack more accurately than the fifth-order WENO scheme. The calculation accuracy of the fifth-order WCNS is better than that of the fifth-order WENO scheme under the post-stall condition (where the angle of attack is greater than 15°). By comparing the vorticity contours calculated by different numerical schemes, it is found that the numerical dissipation of the fifth-order accuracy is smaller than that of the third-order accuracy, and the vortex capture ability is stronger. WCNS captures the small vortex structure that the WENO scheme does not. Full article

The spiral case plays a role in providing stable and uniform water flow in the pump-turbine unit, and the overall structure with the surrounding concrete is an important foundation for the safe and stable operation of the unit and power plant. In order to clarify the comprehensive bearing capacity of preloading steel spiral case under pump operating conditions, this study is based on the theory of the fluid–structure coupling and contact model and uses ANSYS CFX 2021 R1 and mechanical to analyze the flow fluctuation characteristics and dynamic structural response of a preloading steel spiral case and surrounding concrete under different preloading pressures in the intermediate head pump condition. The results indicate that the main frequency of pressure fluctuations inside the main frequency ($1 f_n$) of pressure fluctuations inside the spiral case is influenced by the unstable flow. The contact state between the preloading steel spiral case and concrete is closely related to the relative magnitude of preloading pressure and hydraulic pressure. Higher preloading pressure can lead to an increase in initial preloading clearance, resulting in a decrease in contact area. The vortex motion inside the spiral case is the main factor affecting the distribution of deformation. The rotor–stator interaction also has a certain impact on the vibration of the spiral case structure, even though the influence of rotor–stator interaction on pressure fluctuation inside the spiral case is already small. The monitoring points where the maximum values of static stress and dynamic stress are located are different. Increasing the preloading pressure value does not always guarantee the safety of concrete structures, as the sticking contact area in early contact transfers most of the stress of the spiral case, resulting in significant stress concentration. Under the working conditions of this study, the concrete in contact with the inner edge and nose vane is subjected to excessive loads. Therefore, it is necessary to reinforce the structure with steel bars or other methods to improve its tensile strength. A minimum preloading pressure value of 3.2 MPa is beneficial for reducing the risk of concrete cracking. The research results can provide a deeper understanding of the behavior of preloading steel spiral cases under pump conditions and guide optimization design. Full article

The iron-based superconductors (IBSs) of the recently discovered 1144 class, unlike many other IBSs, display superconductivity in their stoichiometric form and are intrinsically hole doped. The effects of chemical substitutions with electron donors are thus particularly interesting to investigate. Here, we study the effect of Co substitution in the Fe site of ${\mathrm{CaKFe}}_4$${\mathrm{As}}_4$ single crystals on the critical temperature, on the energy gaps, and on the superfluid density by using transport, point-contact Andreev-reflection spectroscopy (PCARS), and London penetration depth measurements. The pristine compound ($T_{\mathrm{c}}\simeq 36$ K) shows two isotropic gaps whose amplitudes (${\Delta }_1$ = 1.4–3.9 meV and ${\Delta }_2$ = 5.2–8.5 meV) are perfectly compatible with those reported in the literature. Upon Co doping (up to ≈7% Co), $T_{\mathrm{c}}$ decreases down to ≃20 K, the spin-vortex-crystal order appears, and the low-temperature superfluid density is gradually suppressed. PCARS and London penetration depth measurements perfectly agree in demonstrating that the nodeless multigap structure is robust upon Co doping, while the gap amplitudes decrease as a function of $T_{\mathrm{c}}$ in a linear way with almost constant values of the gap ratios $2{\Delta }_i/k_{\mathrm{B}}{T}_{\mathrm{c}}$. Full article

During the preparation of high dilutions, repeated external vibration (shaking) is used. We hypothesized that it was the vibration treatment, and not the negligible content of the initial substance, that underlies the activity of highly diluted preparations. In order to test this, the vibration was separated from the dilution process. After vibrating two tubes together on a vortex mixer (one containing water and the other the initial substance) the electrical conductivity and radio frequency radiation intensity of water differed from the unvibrated control, and the ability to exert a modifying effect on the target solution appeared, as assessed using ELISA and terahertz spectroscopy, appeared. Thus, the properties of the neutral carrier (water) changed after non-contact exposure to the initial substance. We have named this process ‘crossing’ and its products ‘aqueous iterations of the initial substance’. Several aqueous iterations with different physical properties were obtained, some of which have a modifying effect and others cause various chemical (catalytic) and biological (antiviral) effects similar to those of the initial substance. This indicates that during crossing, substances enter into post-vibration supramolecular interactions. At the nanoscale level, aqueous iterations and the initial substance are structurally symmetrical, which allows us to assume that the preservation of the symmetry of substances subjected to vibration treatment is the basis of the post-vibration interaction phenomenon. Full article

In certain precision work scenarios, underwater robots require the ability to adhere to surfaces in order to perform tasks effectively. An efficient and stable suction device plays a pivotal role in the functionality of such underwater robots. The vortex suction cup, distinguished by its uncomplicated design, high suction efficiency, and capability for non-contact adhesion, holds significant promise for integration into underwater robotic systems. This paper presents a novel design for a vortex suction cup and investigates its suction force and torque when encountering surfaces with varying curvature radii using Computational Fluid Dynamics (CFD) simulations and experimental testing. These findings offer valuable insights for the development of robots capable of adapting to underwater structures of different dimensions. Results from both experiments and simulations indicate that reducing the curvature radius of the adhered surface results in a decrease in suction force and an increase in torque exerted on the suction cup. As the adhered surface transitions from flat to a curvature radius of 150 mm, the adhesion force of our proposed vortex suction cup decreases by approximately 10%, while the torque increases by approximately 20% to 30%. Consequently, the adhesion efficiency of the suction cup decreases by about 25% to 30%. Full article

This study presents a comprehensive exploration centred on the morphology and surface structure of bladeless wind turbines (BWTs) aimed at optimizing their wind energy harvesting capability. Unlike conventional wind technology where vortex-induced vibration (VIV) is seen as problematic due to aeroelastic resonance, this effect becomes advantageous in BWT energy harvesters, devoid of frictional contact or gears. The primary objective of this study is to develop an optimal BWT design for maximizing energy output. Specifically, this study delves into optimizing the energy performance of these VIV wind energy harvesters, investigating how the geometry (shape and roughness) influences their operating range, known as Lock-In range. The results demonstrate how variations in geometry (convergent, straight, or divergent) can shift the Lock-In range to different Reynolds numbers (Re), modelled by the equation: Re (max Lock-In) = 0.30 α + 4.06. Furthermore, this study highlights the minimal impact of roughness within the considered test conditions. Full article

Due to their long-lived nature, vortex rings are highly promising for the non-contact transportation of colloidal microparticles. However, because of the high complexity of the structures, their description using rigorous, closed-form mathematical expressions is challenging, particularly in the presence of strongly inhomogeneous colloidal suspensions. In this work, we comprehensively study this phenomenon, placing special emphasis on a quantitative description of the ability of vortex rings to move the particles suspended in a liquid over distances significantly exceeding the ring’s dimensions. Moreover, within the study, we present straightforward analytical approximations extracted by using the fitting of the experimental and numerical simulation observations that reveal the dynamics of vortex rings transporting the microparticles. It includes both the dependence of the concentration on the distance traveled by the vortex ring and coefficients describing the evolution of vortex ring shape in time, which were not presented in the literature before. It turns out that despite the fact that 2D modeling is a simplification of the full 3D problem solution and is unable to capture some of the minor effects of real behavior, it has demonstrated a good consistency with the results obtained via experiments regarding the process of particles transportation. Full article

This work theoretically studies the capability of using vortex tubes to provide the necessary heating and cooling energies required by a typical direct-contact membrane distillation (MD) process. The vortex tube generates a temperature separation that can supply the membrane distillation process with sufficiently hot feed and cold permeate with a temperature difference as large as 70 °C. Several structures integrating vortex tubes and MD with and without heat recovery and cascading are proposed and their respective performances are assessed and compared. A maximum distillate production of 38.5 kg/h was obtained at an inlet air pressure of 9 bar, cold air mass ratio of 0.7, and air-to-water mass ratio of 9. The corresponding energy consumption was found to be 25.9 kWh/m³. The production rate can be increased up to 75.2 kg/h and the specific energy consumption can be reduced to 13.3 kWh/m³ when three MD stages were connected in series using the same single vortex tube at the same operating conditions. It is found that the cold fraction plays an important role in the balance between heating and cooling operations. In addition, cold fraction values smaller than 0.7 should be avoided to prevent water from freezing inside the membrane. Full article

The evolution of the falling drop substance transfer in a target fluid at rest was traced by high-speed video techniques. Two flow modes were studied: slow intrusive flow, when the KE of the drop was comparable or less than the available potential energy (APSE), and a fast impact flow, at a relatively high drop contact velocity. For the substance transfer visualization, a drop of alizarin ink solution at various concentrations was used. The use of transparent partially colored fluid allows tracing the drop matter motion in the bulk and on the fluid free surface. The traditional side and frontal view of flow patterns were registered and analyzed. In both flow modes, the substance of the drop partially remained on the free surface and partially went into the target fluid bulk, where it was distributed non-uniformly. In the intrusive mode, the drop substance partially remained on the surface, while the main mass of the drop flowed into the thickness of the target fluid, forming the lenticular colored domain. The intrusion was gradually transformed into an annular vortex. In the impact mode, the drop broke up into individual fibers during the coalescence, creating linear and reticular structures on the surface of the cavity and the crown. The flow patterns composed of individual fibers were rapidly rebuilt as the flow evolved and the splash emerged and decayed. The sizes of cavities and colored fluid domains were compared in different flow regimes as well. The total energy transfer and transformation impact on the flow structure formation and dynamics was revealed. Full article

Due to the special structure of double-half inner rings, four-point contact ball bearings are prone to uneven forces in the inner raceway during movement, which affects the dynamic performance of the rolling element and cage, and even leads to cage sliding. Dynamic performance of the cage is an important factor affecting the working stability of bearings. In this paper, in order to grasp the operation law of the cage so as to guide the application of four-point contact ball bearings, the dynamic model of four-point contact ball bearings is established by the secondary development of Automatic Dynamic Analysis of Mechanical Systems (ADAMS). The dynamic performance of the cage is analyzed and evaluated with the indexes of vortex radius ratio and vortex velocity deviation ratio of the cage centroid trajectory. The results show the following: the cage stability increases and then decreases to a certain degree with rotating speed-rise; it increases and then decreases with the increase in the pure axial load; under a combination of axial and radial load, the cage moves more smoothly with smaller radial force. Rotating speed has little effect on cage stability, while radial force has a great influence on cage stability, followed by axial load. In order to verify the simulation results, a test bench for rolling bearing cages is developed, and the accuracy of the simulation results is verified by the test results. Full article