Surface Oscillations Research Articles

Study on the vertical oscillatory gas-liquid two-phase flow and heat transfer characteristics

Exploring the flow and heat transfer characteristics of oscillations will help to evaluate the dynamic behavior and safety of thermal management systems (TMS) in automobiles, ships, and aircraft. Faraday waves is a phenomenon that standing waves oscillate with half of the driving frequency under specific oscillation conditions. The current work combines both, studying the influence of oscillation parameters of Faraday waves on heat transfer since the oscillatory liquid surface and the shaking of the liquid-filled container frequently occurs in practical engineering applications. A numerical simulation on heat transfer characteristics under different vibration parameters was carried out in this study. The results demonstrate that oscillation has a promotion effect on the heat transfer coefficient. The influence of the driving frequency on heat transfer will be affected by the driving amplitude. When the driving amplitude is greater than 0.83 mm or the driving frequency is greater than 22 Hz, the waveform will change from periodic and regular to disorder and turbulence, and the heat transfer between the two-phase flow will be significantly enhanced. In the range of oscillation parameters covered in this study, increasing the driving amplitude is more effective than increasing the driving frequency for enhancing heat transfer. And when the driving amplitude is big enough, such as A = 1.03 mm, the heat transfer intensity increases to about 1.5–2 times as against A = 0.43 mm. Therefore, when considering the design of TMS, the dynamic empirical correlations proposed by this study can offer some useful guidance.

Experimental validation of saliency maps for understanding deep neural networks for weld penetration prediction

Deep neural networks (DNNs) have achieved high-level accuracy on many imaging-based penetrations to predict tasks during the welding process. However, the deep neural network decision mechanisms are often considered impenetrable leading to a lack of relevance to the welding pool behavior. To solve this problem, we build a deep learning convolutional neural network based on the reflected laser pattern image to predict the GTAW weld penetration and use the saliency map to understand the neural network. Then, we systematically analyze the relevance of saliency maps against the welding pool behavior. Experimental results show that the developed convolutional neural network model can accurately classify unpenetrated, critical penetrated, and fully penetrated with an accuracy of 98.1 %. The interpretable model for the neural network shows that the winged areas on both sides of the pattern were taken into account by the DNNs in the unpenetration, the striped area in the center of the image was highlighted in the full penetration, and the neural network focused on both the center and the sides in the critical penetration. It proves that there is a strong correlation between the welding penetration state and the pool surface oscillation information extracted by the convolutional neural network and the weld pool behavior.

Thermal impact of hybrid nanofluid due to inclined oscillatory porous surface with thermo-diffusion features

Owing to improved thermal efficiencies of hybrid nanomaterials, various applications of such tiny particles are claimed in enhancing thermal impact in heat transfer phenomenon, improving the efficiencies of solar collectors, thermal management systems and different industrial processes. Following to such motivations in mind, this research communicates the thermal impact of hybrid nanofluid with utilization of different nanoparticles due to porous infinite plate. The characterization of hybrid nanoparticles is observed with interaction of copper (Cu), aluminium oxide (Al2O3), titanium oxide (TiO2) with water base fluid The phenomenon is supported with thermal radiation phenomenon. The porous medium with uniform permeability is considered within flow regime. The onset of chemical reaction is attributed in concentration equations. The closed form solution is obtained via analytical procedure. The thermal assessment of nanoparticles in flow regime with effect of different parameters is considered. The comparative thermal observations are reported for pure nanofluid and with different nanoparticles.

The effects of the excitation pulse on flow in electromagnetic levitation experiments

Oscillating drop experiments allow the surface tension and viscosity of high temperature and highly reactive melts to be measured without an interface contacting the surface of the molten sample. Surface oscillations are induced by varying the electromagnetic field. The oscillations are measured to determine the surface tension and viscosity from the frequency and damping of the oscillations, respectively. The damping of the oscillations is, however, sensitive to the flow conditions within the melt. Recent advances have allowed transient magnetohydrodynamic models to calculate changes in the internal flow in response to variations in the magnetic field, much like those used to induce surface oscillations. These models show that the excitation pulse drives rapid acceleration within the melt. While the fluid flow may accelerate to speeds above the laminar-turbulent transition, the flow speeds are not sustained for sufficient time periods to allow turbulent flow to develop. Following the excitation pulse, the flow rapidly slows and quickly returns to the conditions present before the excitation pulse.

Dual-wavelength reflectance-ratio method for emissivity-free temperature measurements applied to electromagnetically levitated liquid Ni

The applicability of the dual-wavelength reflectance-ratio (DWR) method to emissivity-free radiation thermometry of electromagnetically levitated high-temperature liquid metals was investigated. To establish the measurement technique, the DWR method was applied to liquid Ni levitated in a static magnetic field, which suppresses the surface oscillation and the translational motion. In a previous study, temperature of the levitated liquid metals measured by DWR showed deviations of about 95 K to 175 K from the temperature measured by a calibrated pyrometer. Since this discrepancy could be attributed to the imperfect contribution of the auxiliary light, the effect of the optical setup of the auxiliary light on the temperature measurement was investigated in this study. By using a reflecting collimator for the auxiliary optical system and adopting the radiance ratio determined considering the geometrical arrangement of the measurement system, the difference between temperature of liquid Ni kept near its melting temperature (𝑇𝑚 = 1728 K) measured using DWR and the temperature measured by a pyrometer calibrated using the melting point of Ni was 12 K on average and the standard deviation in the temperature measurement was 25 K (𝑛 = 5).

Directional virtual time-to-contact: A new measure for investigating temporal, spatial, and control aspects of postural balance control

Virtual time-to-contact (VTC) is a promising approach for investigating postural balance control. However, current VTC calculation approaches are limited as they (1) cannot be used to evaluate directional components of balance, and (2) only assess a single, temporal aspect of balance control. This study introduces a new approach for VTC calculation, namely directional VTC, expanding VTC to assess temporal, spatial, and control aspects of balance. Three case studies were conducted across varying populations and conditions as a proof-of-concept of the presented method. The first study examined quiet stance on a firm surface in people with Parkinson’s disease (PD; n = 10) in comparison to their healthy peers (n = 10). The second and third studies assessed balance control of healthy individuals under challenging environments. Ten healthy individuals participated in standing tasks on compliant ground surfaces, while another ten on oscillatory ground surfaces, all simulated by a dual-axis robotic platform. Preliminary results not only provided a closer look at balance control with multiple aspects, including temporal, spatial, and control aspects, but also showed how different aspects of balance changed due to neurological diseases (Case Study I) or challenging standing grounds (Case Studies II and III). This study advances our understanding of posture biomechanics and its clinical applications.

Resonant Oscillations within Multiple Moonpools for a Fixed Rectangular Vessel

_ We present experimental results of resonant free surface oscillations within three circular moonpools arranged in tandem at forward, central, and aft positions of a fixed rectangular vessel in head waves. The piston mode resonance frequency is primarily captured, which decreases with the increase in the vessel draft. The aim is to study the effect of body diffraction on the free surface amplitude and phase of the oscillating water columns at the three locations. The results indicate that, in general, the forward moonpool has the highest response amplitude, whereas the relative amplitudes of the central and aft moonpools depend on the wave frequency. It is observed that the nondimensional response amplitude increases nonlinearly with decreasing wave steepness close to the resonance frequency, while the effect diminishes at lower wave frequencies. The oscillation phase differences between the moonpools show effects of wave-body interaction, a phenomenon dependent on the vessel draft and wave frequency. Finally, the study includes a comparison of the responses at the three moonpool locations between multiple and single configurations. Introduction A moonpool is a vertical opening through the ship deck and open to the sea at the bottom, which is installed in vessels specialized in certain offshore operations. Resonant water column oscillations are encountered in moonpools (Aalbers 1984) due to vessel operations in waves. On the other hand, oscillating water columns (OWCs) have been extensively researched, primarily due to their potential for ocean wave energy conversion (Evans 1978; Heath 2012; Falcão & Henriques 2016). Now, considering design perspectives, the focus of the studies on water column resonance in waves depends on the specific marine application. For example, wave energy converters would require maximized OWC responses for efficient energy capture (Evans & Porter 1995; Morris-Thomas et al. 2007), while large free surface oscillations within moonpools of drillships have adverse effects on the vessel dynamics (Fakuda 1977).

Ensuring the uniformity of oscillations of a flat membrane by sources of ultrasonic impact

The article presents the results of studies aimed at ensuring the uniformity of vibrations of a flat membrane by sources of ultrasonic exposure. The relevance of the conducted research lies in the fact that for the effective implementation of physical and physicochemical processes in thin liquid films, it is necessary to ensure the maximum uniformity of the effect over the entire surface area of the spreading film. The main problem is that today there are no ultrasound emitters that are able to form a uniform distribution of vibrations over the entire impact plane and thereby ensure the uniformity of the technological process. The vibration concentrators and reciprocating working tools that currently exist are distinguished by a limited radiation surface. This is due to the fact that attempts to increase the area of the radiating surface lead to the need to use multipackage piezoelectric transducers. However, in this case, it is not possible to ensure the in-phase oscillations of each packet (due to wave processes inside the emitter material) and, therefore, for large surface areas, the oscillations turn out to be inhomogeneous or have a small amplitude. The authors propose a mathematical model that will allow optimizing the location of the emitters to ensure maximum uniformity of oscillations of a flat surface. The proposed model makes it possible to identify the optimal configurations of radiators, which provide the smallest dispersion of the oscillation amplitude of the free surface (on which there are no fixed radiators).

Investigation of spontaneous capillary flow and heat transfer characteristics in parallel microchannels based on phase-field model

• The mechanism of liquid surface oscillation in capillary flow is revealed. • Effect of channel structure on capillary flow and heat transfer is discussed. • A novel heat sink based on parallel capillary microchannels is constructed. • Non-circular heat sink obtains better capillary flow and heat transfer performance. Passive heat dissipation based on capillary flow has excellent applications in the thermal management of electronic devices and spacecraft due to its advantages of spontaneity and high stability. However, the conflicting relationship between capillary pressure and permeability in conventional sintered capillary wick severely limits its heat dissipation limit, and the complex and tortuous flow path is the key limiting factor. In this study, a novel close-packed capillary microchannel is constructed to provide an unobstructed flow path, and based on the phase-field model, the capillary flow and heat transfer characteristics of capillary microchannels with different structures are investigated. First, for the single channel, the oscillatory mechanism of phase interface in the initial stage of capillary flow, which has received little attention before, is revealed, which is mainly caused by the reconstruction of the advancing meniscus. This provides more nuanced insights into the initiating mechanism of capillary flow. In the noncircular channel, due to the change in curvature of the liquid surface at the acute angle and the expansion of the adsorption layer on the wall surface, the capillary velocity and heat transfer capacity improve compared to circular channels of equal hydraulic diameter. In addition, the effects of channel diameter and wettability on capillary flow and heat transfer are discussed. Capillary microchannels with better wettability and larger diameter achieve better capillary flow and heat transfer capabilities. On this basis, the parallel capillary microchannels inside the block are analyzed, and the non-circular channels achieve a higher capillary velocity while ensuring capillary pressure. Furthermore, the design of the noncircular section obtains a smaller thermal resistance and greater heat transfer efficiency, where the triangular microchannels show the best results. For the same hydraulic diameter and total block area, the performance decreases continuously as the inner angle of the channel increases. These results provide new ideas and a theoretical basis for designing high-performance passive heat sinks based on capillary flow.

Forest trees as a natural metamaterial for surface wave attenuation in stratified soils

Forest trees have been shown to act as a natural metamaterial to attenuate elastic waves. However, the existing studies assumed that forest trees are located on homogeneous soils and did not consider the soil stratification that widely exists in natural strata. This study investigates the forest trees as a natural metamaterial to manipulate the propagation of elastic waves in stratified soils. A semi-analytical method is proposed to calculate the dynamic responses of a layered half-space coupled with arbitrary number of trees. A close-form Green’s function for a harmonic line load on a layered half-space is derived by the thin layer method, and subsequently used to determine the multiple scattered wavefield induced by forest trees as surface oscillators. The attenuation performance of forest trees on stratified soils is systematically investigated. Trees with a graded array of heights can provide a wide attenuation zone at frequencies below 80 Hz. Since the higher surface wave modes in a layered half-space can propagate forward without being affected by trees, the attenuation efficiency of trees on stratified soils is significantly lower than that of trees on corresponding homogeneous soils. The performance uncertainty induced by the randomness of the height, sizes, and spacing of trees is subsequently investigated through a Monte Carlo simulation. The forest trees can still obtain a significant attenuation efficiency at frequencies below 80 Hz even the randomness of tree properties being considered. The randomness in height and radius leads to significant uncertainty in attenuation performance, while the randomness in spacing results in reasonable uncertainty.

Resonant Acoustic Rheometry to Measure Coagulation Kinetics in Hemophilia A and Healthy Plasma: A Novel Viscoelastic Method.

Compared with conventional coagulation tests and factor-specific assays, viscoelastic hemostatic assays (VHAs) can provide a more thorough evaluation of clot formation and lysis but have several limitations including clot deformation. In this proof-of-concept study, we test a noncontact technique, termed resonant acoustic rheometry (RAR), for measuring the kinetics of human plasma coagulation. Specifically, RAR utilizes a dual-mode ultrasound technique to induce and detect surface oscillation of blood samples without direct physical contact and measures the resonant frequency of the surface oscillation over time, which is reflective of the viscoelasticity of the sample. Analysis of RAR results of normal plasma allowed defining a set of parameters for quantifying coagulation. RAR detected a flat-line tracing of resonant frequency in hemophilia A plasma that was corrected with the addition of tissue factor. Our RAR results captured the kinetics of plasma coagulation and the newly defined RAR parameters correlated with increasing tissue factor concentration in both healthy and hemophilia A plasma. These findings demonstrate the feasibility of RAR as a novel approach for VHA, providing the foundation for future studies to compare RAR parameters to conventional coagulation tests, factor-specific assays, and VHA parameters.

Обработка резьбы инструментом с осевым колебанием резьбообразующих профилей

A method for planetary thread rolling with a prefabricated tool with oscillation of the thread-forming surfaces is proposed. It indicates the possibility of obtaining a thread in an aluminum alloy AMg6M with a profile corresponding to the profile of a metric thread. An experimental design of a prefabricated tool with the possibility of angular adjustment of two disks has been developed. The influence of the disk displacement angle relative to each other on the force during planetary thread rolling and the microhardness of its lateral sides was carried out. The value of the disc offset angle is set, which provides the minimum force during rolling. A comparison was made of the microhardness of thread flanks obtained by thread milling and planetary rolling using disks without oscillation and with oscillation of thread forming surfaces. The research results could be useful for designers in the design of deforming thread forming tools and for technologists in the assess process of the possibility of using planetary thread rolling.

Effect of pulsed laser energy on grain morphology and texture characteristics of stainless steel fabricated by laser-PTA additive manufacturing

This study proposes a pulse laser-assisted plasma transfer arc (Laser-PTA) additive manufacturing process. By using this process, the tensile strength and elongation of stainless steel are increased by 11.3% and 21.59% respectively. Using electron backscatter diffraction (EBSD) technique to study the microstructure and texture characteristics of the deposited layers. Further, the mechanism of the pulsed laser energy regulating the microstructure is revealed. The experimental results showed that the continuous growth of coarse columnar crystals in multi-layers deposition structures can be blocked by pulsed laser energy. Compared with the PTA process, the grain size of the multi-layers deposition structure obtained by the laser-PTA process is smaller, and the trend of preferred orientation is weakened. Moreover, increasing the laser pulse power can make this effect more significant. The result of texture analysis showed that the improvement of mechanical properties of laser-PTA samples is the result of grain refinement in deposition layers, inhibition of preferred orientation, and increase of volume fraction of high angle grain boundaries. The surface oscillation and thermal convection in the molten pool break the growth of columnar dendrites, destroy the original temperature gradient and affect the growth morphology and orientation of grains, which is the main mechanism to improve the process of laser-PTA additive manufacturing.

External Illumination Enables Coaxial Sensing of Surface and Subsurface Molten Pool Geometry in LPBF

Laser powder bed fusion (LPBF) attracts the attention of high-end manufacturing sectors for its capability of depositing free-form components with elevated mechanical properties. However, due to the intrinsic nature of the feedstock material and the interaction with the laser beam, the process is prone to defect formation and manufacturing inaccuracies. Therefore, the development of a monitoring architecture capable of measuring the geometrical features of the process tool (i.e., the melt pool generated by the laser-material interaction) is of paramount importance. This information may then be exploited to evaluate process stability. In this work, a high-speed camera was implemented coaxially in the optical chain of an LPBF system to extrapolate the geometrical features of the molten pool surface and its oscillatory behaviour, with elevated spatial and temporal resolution. A secondary light source was tested in both coaxial and off-axis configuration to dominate process emission and assess optimal illumination conditions for extracting the molten pool’s geometrical features. Preliminary results showed that the off-axis configuration of the illumination light enabled direct measurement of the molten pool surface geometry. A newly developed image processing algorithm based on illuminated images obtained via the coaxial observation frame was employed to provide automated identification of the melt pool geometry. Moreover, bright reflections of the external illumination over the melt surface could be clearly observed and used to characterise the oscillatory motion of the molten material. This information may therefore be taken as an indirect indicator of the molten pool penetration depth, hence providing information regarding the subsurface geometry. A successive experimental investigation showed the capability of the monitoring architecture to resolve the molten pool’s length, width and area with elevated acquisition frequency. Molten pool surface oscillations in the kHz range could be correlated to the penetration depth while the molten pool width measured via the high-speed imaging setup corresponded to the track width of the depositions. Hence, the methodological approach for the concurrent measurement of the molten pool’s geometry in three spatial dimensions was demonstrated and may be used to track the stability of LPBF depositions.

Analysis of Potential Fluctuation in Flow

Understanding the physics of flow instabilities is important for processes in a wide range of engineering applications. Flow instabilities occur at the interfaces between moving fluids. Potential fluctuations are generated at the interfaces between two moving fluids based on the relationship of continuity. Theoretical analysis demonstrated that, in flow instabilities, potential fluctuation exhibits a potential oscillatory wave surface concurrently in the temporal and spatial dimensions. Potential fluctuations already internally exist in flow before flow instabilities begin to develop; these potential fluctuations greatly affect the formation of interpenetrating structures after forces act on the interfaces. Experimental studies supported the theoretical study: Experiments visualizing condensation flows using refrigerant in one smooth tube and one three-dimensional enhanced tube were conducted to show the development of potential fluctuation in spatial dimensions, and an experiment with cooling tower fouling in seven helically ridged tubes and one smooth tube were conducted to show the development of potential fluctuation in the temporal dimension. Both experimental studies confirmed that potential fluctuation was determined by the densities and velocities of the two fluids in the instability as indicated by the relationship of continuity. In addition, the results of numerical simulation in the literature qualitatively confirm the theoretical study. This paper is a first attempt to provide a comprehensive analysis of the potential fluctuation in flow.

DETERMINATION OF THE FEATURES OF THE SHAPE AND VIBRATION FREQUENCY OF TURBINE BLADES ON DIGITAL MODELS

A digital solid model of a turbine blade with a mounting shelf has been developed in SolidWorks. The description of complex surfaces is made using spline functions. The method of computer simulation using SolidWorks Simulation was used to study the distribution of natural oscillations of the blade depending on the method of its fixing during machining. The spectra of natural oscillations of the blade in the sound range have been obtained and analyzed. The form of natural vibrations of complex surfaces is also analyzed. For the correct choice of processing parameters during machining, it is necessary to take into account both the conditions for fixing the part in the fixture and the natural frequency of the part. It is noted that an equally important parameter is the form of oscillations of a thin surface at the studied frequencies. It is noted that in the future it is possible to solve these problems through computer simulation.

Mathematical Models of Transonic Flatter of Aerody-namic Control Surfaces of Supersonic Aircraft

In the article, the joint analysis of the Bernoulli equations for compressed gas, variations of the supersonic flow parameters of the Prandtl-Meyer expansion fan and the hypothesis of aerofoil dynamic curvature were used to develop a linear and a nonlinear mathematical models describing the occurrence of transonic flutter of aerodynamic control surfaces of supersonic aircraft. The analysis of the obtained mathematical models confirms a theoretical possibility of the occurrence of transonic flutter of aerodynamic control surfaces of supersonic aircraft that is due to the peculiarities of the interaction of shock waves with the angular velocity of elastic bending oscillations of aerodynamic control surfaces.

Couple stress Darcy–Forchheimer nanofluid flow by a stretchable surface with nonuniform heat source and suction/injection effects

The thermal enhancement of industrial and engineering processes with interaction of nanofluids is exclusively important and presents applications in extrusion systems, heat transfer devices, electronic chips, chemical reactions, nuclear processes, etc. Owing to such motivated significance of nanofluids, the aim of this investigation is to present the heat and mass transfer phenomenon in the Couple stress nanofluid flow containing the microorganism due to oscillatory stretched surface. Additionally, the Darcy–Forchheimer applications, nonuniform heat source and nonlinear thermal radiation effects are considered. The modification in the concentration equation is done by activation energy. The independent variables in the defined flow system are decreased via suitable variables. The computation is simulated using the homotopy analysis method. It is noticed that the magnitude of velocity periodically decreases for larger values of suction parameter and inertia coefficient. The presence of an external heat source parameter enhanced the temperature profile. Moreover, the increment in the suction parameter improves the heat and mass transfer rate.

Three-dimensional Langevin dynamics of N atom scattering from N-covered Ag(1 1 1)

We analyzed the dynamics of N atom scattering from N -covered Ag(1 1 1), using the generalized Langevin oscillator (GLO) method and a three-dimensional neural network potential energy surface. Two values for the mass of the surface oscillator were considered in the GLO model to account for the energy exchange with the surface, i.e., that of Ag and that of N. For these mass values different trends were found for the dependence of the ratio of the average final divided by the average initial translational energy on the scattering angle. Using the nitrogen mass gives a trend closer to the experimental results for the dependence of the energy of the in-plane scattered atoms on the scattering angle, but worse agreement with experiment for the angular distribution of the in-plane scattered atoms. Two different algorithms are applied to integrate the stochastic equations of motion in the presence of energy dissipation. Our calculations show that a trivially extended Bulirsch-Stoer algorithm is more efficient than an algorithm based on a Langevin Liouville operator splitting technique, in that it yields the same results with a much larger time step.

Study of Free Oscillations of Bays in the Northwestern Part of Posyet Bay

To study the specific features of free surface oscillations in the northwestern part of Posyet Bay (the Sea of Japan), a series of experimental works using an installation with a laser meter for measuring hydrosphere pressure variations were carried out in 2012 and 2014. In the course of the joint analysis, measurement results for oscillations with periods of 10–30 min and the results of calculations using a numerical model of shallow water with a difference approximation on an irregular triangular space grid, datasets of the space–time parameters for the resonance oscillations of the studied water area were obtained. The results of the numerical simulations confirm the manifestation of the resonance properties of Novgorodskaya, Expedicii, and Reyd Pallada Bays water areas on the oscillations singled out during the experimental studies. The positions of the peaks on the model resonance curves are consistent with the positions of the clearly pronounced peaks of the energy spectrum in the field data.