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In order to study the breakup and atomization mechanisms of the fuel-jet in air crossflow and realize the accurate and controllable atomization effect of fuel, this paper proposes a method by coupling the large eddy simulation method and the VOF to DPM method. The results show that the breakup and atomization of the fuel-jet are mainly caused by the Rayleigh–Taylor (R–T) unstable surface wave and the Kelvin–Helmholtz (K–H) instability. The density of fuel-particles is higher near the central region of the fuel jet trajectory, decreasing as distance from the central region increases. As the momentum ratio increases, the penetration depth of the fuel-jet column also increases, resulting in a more concentrated spatial distribution of fuel particles. Conversely, with a lower momentum ratio, the spatial distribution of fuel particles becomes more uniform. For the spatial distribution of fuel particles, a new mathematical model is established to characterize the spatial distribution boundary of fuel particles. At the same momentum ratio, the higher the air velocity, the smaller the average particle diameter. At the same Weg number, the higher the fuel-jet velocity, the higher the average particle diameter. The relative error of the average particle diameter between the experiment and numerical simulation is very small, which is 6.4%. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting faces a primary challenge in effectively capturing low-orbit vibration energy across a broad frequency range. In this paper, we present a tri-stable piezoelectric energy harvester that incorporates a dynamic amplifier (TPEH + DM), specifically designed for efficient collection of low-orbit vibration energy. The TPEH + DM comprises a piezoelectric cantilever beam connected to an innovative dynamic amplifier at its restrained end, which enhances both the rotational and lateral displacement of the piezoelectric cantilever beam simultaneously. The governing coupled differential equations of motion for the system is derived based on the Lagrange equation, and analytical expressions for its steady-state response are obtained using the multi-scale method. The influence of factors such as the mass and the stiffness ratio of the dynamic amplifier on the steady-state dynamic output characteristics of the system is investigated using the theoretical analysis and numerical simulation. The results indicate that TPEH + DM exhibits significantly improved energy harvesting performance compared to TPEH under low-orbit external excitations. The bandwidth of inter-well motion and the TPEH + DM power output may be further increased by suitably modifying the relative stiffness between the cantilever beam and the dynamic amplifier. In addition, we analyze the time-domain behavior of the system's output voltage using the ode45 solver under various external excitation frequencies and intensities. The results demonstrate that with appropriate adjustments to the mass of the tip magnet and the stiffness ratio of the dynamic amplifier, the proposed TPEH + DM system can harvest energy efficiently across a broad frequency range, even under low-orbit excitations. [ABSTRACT FROM AUTHOR]

This paper focuses on the numerical solutions of a six-compartment fractional model with Caputo derivative. In this model, we obtain non-negative and bounded solutions, equilibrium points, and the basic reproduction number and analyze the stability of disease free equilibrium point. The existence and uniqueness of the solution are proven by employing the Picard–Lindelof approach and fixed point theory. The product–integral trapezoidal rule is employed to simulate the system of FODEs (fractional ordinary differential equations). The numerical results are presented in the form of graphs for each compartment. Finally, the sensitivity of the most important parameter (β) and its impact on COVID-19 dynamics and the basic reproduction number are reported. [ABSTRACT FROM AUTHOR]

The powder mixed electrical discharge machining (PMEDM) process was simulated via finite element analysis in the current study to assess heat behavior and material removal rate. The goal of this paper is to conduct a thorough experimental and thermal examination of electrical discharge machining (EDM) in order to forecast its cutting characteristics and subsequently optimize the output variables using a response surface methodology for simulations and choosing the most suitable set of process variables related to the PMEDM process. This study's objective is to design a 2D axisymmetrical transient thermal model that might also describe the physics of material removal in a single spark PMEDM operation on a Titanium Zirconium Molybdenum (TZM) superalloy. ANSYS (version 9.1) software is used to perform transient heat transfer simulations to determine the temperature profile with the amount of material removal at different current, pulse on and off times, gap voltages, and fraction of heat that enters the specimen. The PMEDM process produced craters with a lower diameter and depth, which increased the material removal rate and enhanced the surfacing quality. Compared to the conventional EDM process, the inclusion of powder raised the heat flux given to the work material by 10%–12%. It has been determined that with the single spark modeling technique, the temperature significantly dropped in both the radial and depth directions. The computational results are compared with experimental observations for similar machining conditions, and both results agree satisfactorily. [ABSTRACT FROM AUTHOR]

Round-end aluminum alloy tube concrete columns had good durability and were very economical, but the low strength and elastic modulus of aluminum alloy led to the need for improvement in performance. This paper proposes carbon fiber reinforced plastic (CFRP) strip reinforced round-end aluminum alloy tube concrete (CREAC) columns and investigates their mechanical properties under axial compression loads. A total of eight specimens were tested, including seven CFRP reinforced specimens and one control specimen. The effects of the width, spacing, and number of layers of CFRP strips on the axial compression performance of CREAC under the same amount of CFRP were studied. The experimental results indicate that the main failure modes of the specimen are the buckling of round-end aluminum alloy tubes and the fracture of CFRP strips. The CFRP strip can significantly improve the ultimate bearing capacity of the specimen, with a maximum increase of 15.3% in the test range. When the amount of CFRP is the same, as the number of CFRP strips decreases, the bearing capacity and ductility deteriorate. Increasing the width and thickness of CFRP strips significantly improves ductility. On the basis of the validated finite element model, parameter analysis was conducted, and the calculation method for stability coefficients was fitted. A calculation method for axial compression bearing capacity suitable for CREAC was proposed, with a maximum error of less than 1% between the predicted results and experimental results. [ABSTRACT FROM AUTHOR]

When a low-voltage circuit breaker (LVCB) breaks a high current, the contact erosion caused by the arc greatly reduces the LVCB's breaking performance and service lifetime. Therefore, this paper uses AgW alloy contacts as a research object, which are commonly used for breaking high currents, and establishes a contact erosion model for an LVCB with a breaking current of 14 kA. The model considers the energy balance of a contact surface and uses a solidification and melting model and a dynamic mesh model to deal with the phase transition problem of the contact material and introduces the arc movement into this model. Using this model, the contact melting and evaporation width, erosion depth, erosion rate, and erosion mass are calculated when Ag and AgW30 and AgW70 alloys are used as contact materials. The influence of W-content on the erosion characteristics of a contact is analyzed. The results show that, although the introduction of element W significantly reduces the erosion mass, it advances the time when the melting point and boiling point are reached. The position, width, and depth of the melting pool and melting layer thickness change with the movement of the arc. In the process of contact erosion considering the movement of the arc, the introduction of W element will increase the width of the molten pool and the solidification time of the molten material. Especially when the mass percentage of element W in the contact material reached 70%, the solidification time of the molten material greatly increased, which weakened the welding resistance of the contact. [ABSTRACT FROM AUTHOR]

This paper aims at the numerical analysis of the influence of tip clearance size on the pre-stall flow features of a transonic high-speed compressor by applying the throttle model at the exit of the compressor computational domain. Steady and unsteady calculations have been performed for design, double, and triple tip clearance sizes. The transition of the stall inception type when increasing the tip clearance size and the underlying flow physics has been analyzed in detail. The results show that the stall inception type transforms from spike to modal as the size of the tip clearance changes from design to triple tip clearance. The influence of the tip clearance size on the forward spillage of the tip leakage vortex near the stall limit, which is one of the two criteria for spike stall inception, is crucial for which type of stall inception would appear. For the design clearance case, a remarkable forward spillage of the tip leakage vortex occurs near the stall limit, leading to a typical strong spike stall inception. In the condition of double clearance, the intensity of tip leakage vortex spillage was weakened because the increase in the clearance size allows more low momentum tip leakage flow to go through the clearance instead of spilling from the leading edge. Thus, a weaker spike-type inception containing the content of modal disturbances was induced. Under the triple clearance condition, the high entropy gradient interface is located inside the blade passages all the time; thus, a typical modal-type stall inception appears. [ABSTRACT FROM AUTHOR]

In this paper, we present a well-organized method to estimate the one-dimensional fractional Rayleigh–Stokes model using the construction of orthogonal Gegenbauer polynomials (GBPs) and Lagrange square interpolation to estimate the time derivative. Therefore, we design an authentic and fast numerical calculation approach based on the elaborated convergence rate recovery method. The matrix of the derivative operation of an orthogonal GBP is gained by employing the characteristic of this type of polynomial. The privilege of the numerical method is the orthogonality of the GBP and operational matrices, which reduces time computation and increases speed. Eventually, we propose three numerical examples to check the validity and numerical studies to illustrate the precision and efficiency of the new approach. [ABSTRACT FROM AUTHOR]

Pumped storage hydropower is perhaps the most reliable solution to the energy crisis, but its development and application are limited by hydraulic instability, such as S-shaped characteristics. In this paper, based on the S-shaped region pressure fluctuation test of a model pump turbine, the connection between the guide vane opening and S-shaped pressure fluctuation is established, and a guide vane opening of 28 mm is selected for numerical analysis to expand the discussion of the S-shaped pressure fluctuation characteristics to large guide vane openings. The frequency components of the vaneless space are extracted by fast Fourier transform analysis, and the rotational stall frequency is identified. Among them, the blade passage frequency and its multiplier are induced by the rotor–stator interaction, and the low-frequency component of pressure fluctuations is induced by the rotational stall and vortex rope. Based on this, the internal flow and flow rate along the S-shaped characteristic curve and their correlation with the rotational stall are analyzed. In addition, the percentage of and variation in the entropy production rate in the S-shaped region are also analyzed. [ABSTRACT FROM AUTHOR]

The interpolation finite difference method (IFDM) allows free numerical analysis of elliptic partial differential equations over arbitrary domains. Conventionally, in the finite difference method (FDM), the calculation is performed using the second-order accuracy central difference. For engineering problems, second-order accuracy calculations are often sufficient. On the other hand, much research has been carried out to improve the accuracy of numerical calculations. Although there is much research in the FDM field, the development of numerical calculations by the spectral method is decisive in improving the calculation accuracy. Numerical calculations are usually performed by double precision calculations. If double precision calculations ensure 15 significant digits in floating point computing, such numerical calculations will be the ultimate goal to reach. A numerical calculation that does not seem to have an error even though it originally has an error is defined as a virtual error-zero (VE0) calculation. In this paper, we will examine an overall picture of high-accuracy numerical calculation by the IFDM in the numerical calculation of the 1D Poisson equation. It becomes clear that a VE0 calculation is always possible in the numerical calculation method, defined as the compact interpolation finite difference scheme [(m)]. [ABSTRACT FROM AUTHOR]

The high-payload transporter is a key part of the multipurpose deployer, which is important for realizing the remote handling of tokamaks. This paper presents an analysis of the key joint between the high-payload transporter and the design of the test platform. The kinematic, structural, and load characteristics of the main joints of a heavy-duty manipulator were analyzed according to the peculiarity of high precision, large length, and heavy load of the high-payload transporter. Joint No. 4 (J4) was determined to be the key joint of the high-payload transporter. The peak torque, bending moment, and shear force of J4 under working conditions and seismic conditions were determined via numerical simulations. The functions and key technical parameters of the test platform for J4 were determined according to the test analysis results and numerical simulation. The structure of the test platform was designed, and its working principle was described. [ABSTRACT FROM AUTHOR]

The frequency characteristics of the transmitted waves by the two-dimensional single-mode waveguide with a slightly rough boundary are investigated in detail. Two realizations of the waveguide with random rough boundaries are considered. Since the boundary element method based on the guided-mode extracted integral equation is employed, the boundary condition on the random rough boundary is accurately satisfied. It is found that the strong resonances with high Q-factor are created close to the cutoff frequency of the second-mode in the waveguide and they cause the small transmission (high reflection). It is shown that the Q-factors of these resonances increase with a decrease in the rms of the rough boundaries. It is shown that the rough boundary whose rms is about several thousand times smaller than the wavelength creates a strong enhanced electric field whose intensity is about several hundred times larger than that of the incident mode. [ABSTRACT FROM AUTHOR]

The commercialization of GaN-based Schottky barrier diodes in middle- and high- voltage applications still faces many challenges, in which the lack of an effective selective area p-type doping method is one of the main obstacles. This paper proposes novel vertical GaN-based Schottky diodes with trench MIS structure and an embedded p-GaN protection layer (junction-trench MIS barrier Schottky diodes, J-TMBS). The trench structure and lateral p-n junctions can be achieved by selectively etching the very thin p-GaN and then regrowing n-GaN. Therefore, the fabrication technology avoids the selective area p-type doping process, and the dry etching damage and poor sidewall regrowth interface issue, which are serious in GaN Merged pn/Schottky (MPS) diodes, can also be alleviated for the proposed J-TMBS. Compared with the optimized GaN trench MIS barrier Schottky (TMBS) diodes, the surge current capability and dielectric reliability of the proposed J-TMBS are significantly improved (the electric field of the dielectric layer and maximum lattice temperature under the surge test can be reduced by 448% and 202%, respectively). In addition, the specific on-resistance (Ron,sp) and breakdown voltage remain basically unchanged compared with TMBS. Compared with the optimized GaN MPS diodes, the proposed structure improves the specific on-resistance by 17.2% benefiting from the reduced area of the JFET region without degrading the reverse I–V characteristics and surge current capability. The proposed J-TMBS exhibits potential in practical high voltage (>600 V) application of GaN Schottky power diodes. [ABSTRACT FROM AUTHOR]

The entry of projectiles into water has been of interest to many scientists and engineers, being crucial to a wide range of engineering applications. The water entry problem is a nonlinear and unsteady phenomenon involving complicated multi-phase flow problems and fluid–solid interaction. Many scientists have been studying water entry problems in various conditions through experimental methods and numerical methods. In this paper, three-dimensional numerical simulations of the water entry problem are carried out. The multiphase flow weakly compressible smoothed particle hydrodynamics model is adopted and three-phase interaction is analyzed using pairwise force smoothed particle hydrodynamics. Dynamic boundary condition and rigid body coupling are introduced for interaction between fluid and solid. Spheres with different wetting characteristics entering water at small Reynolds numbers are investigated. Our results show good agreement with the theoretical models from previous studies into the splashing behavior of spheres. The physics of the different splashing behaviors is discussed in detail. [ABSTRACT FROM AUTHOR]

The operational stability of axial flow turbines (AFT) directly affects its safety and performance. Hence, dynamic analysis of its internal flow characteristics is essential, since its unsteady pressure characteristics are complicated. A reliable measurement approach becomes essential in order to analyze and understand the pressure fluctuation within the turbine. Dynamic pressure pulsation measurements were conducted by installing pressure sensors on the flow domain of the AFT under different operating conditions. Based on computational and experimental measurements, different unsteadiness in the flow structures resulted in various excitation signals. The excited frequencies of the stationary parts occurred at 72.50 H z 3 × f n , 145.00 H z 6 × f n , a n d 217.50 H z 9 × f n , while for the impeller, excited frequencies of 217.50 Hz (9 × fn), 435.00 Hz (18 × fn), and 652.50 Hz (27 × fn) were recorded. The rotor–stator interaction with fluid flow from the guide vane to the impeller is culpable for strong pressure pulsations. The experimental measurement shows a comprehensive agreement with numerical results. This paper focused on the analysis of pressure fluctuation in AFT combining experimental and computational methods. Moreover, an exhaustive understanding of flow characteristics of the AFT is necessary for its optimization and operational reliability. [ABSTRACT FROM AUTHOR]

In the present work, indirect noises generated by compositional disturbances in a non-isotropic convergent nozzle are studied using Large Eddy Simulations (LESs). An in-house compressible LES code, Boundary Fitted Flow Integrator-LESc, is utilized to simulate the noise generation in the system. A non-reflective outlet boundary condition is used to eliminate numerical reflections and to ensure the reproduction of the operating conditions in the experiments. The experiments are designed to feature two configurations with different injection positions, which enable the separation of direct and indirect noises. Different operating conditions are investigated, including different injection gases and air mass flow rates. This present paper compares computational results with the experimental measurements. The results revealed that the processes of direct and indirect noise generation are successfully reproduced in the LES, with the noise magnitudes in good agreement with those in the measurements. Injection of gases with smaller (He) and larger (CO2) molar masses compared to air is found to generate negative and positive indirect noises, respectively, in the LES, which is consistent with the experimental findings. The effect of different air mass flow rates is also investigated and discussed, and the direct noise and indirect noise amplitudes are both found to be closely related to the air mass flow rate. [ABSTRACT FROM AUTHOR]

Asymmetric layout gate station projects are prevalent in gate station engineering. When multiple pump units operate within such projects, the inflow patterns of the pump devices at different stations exhibit significant variations. Notably, edge pump units often display adverse operating characteristics, including vibration. This study aims to elucidate the hydraulic behavior of edge pump units in asymmetric layout gate station projects using numerical simulation methods. We validate the reliability of our numerical calculations through physical model tests. Specifically, we investigate the flow pressure pulsation characteristics of the axial flow pump device within the edge pump unit under various switching schemes employed in the gate station project. The results show that pressure fluctuations in axial flow pump devices exhibit distinct time-frequency characteristics based on different flow rates. An increase in flow rate results in a sharp rise in pressure fluctuation amplitudes within the axial flow pump device of the edge pump unit. During symmetric operation, the peak pressure fluctuations of the axial flow pump device are significantly smaller than those observed during asymmetric operation. This suggests that the edge pump unit operates more stably and experiences fewer pressure fluctuations under symmetric conditions. Optimizing the operation of edge pump units ensures stability and prolongs the service life of gate station projects. [ABSTRACT FROM AUTHOR]

A turbine flowmeter for sensing the water supply in an ice-making system of a refrigerator requires high sensitivity to the flow rate. This research aims to develop a comprehensive performance evaluation technique by constructing an experimental setup and establishing a numerical technique to simulate the rotational motion of the impeller in response to the injection of water into the flowmeter. An experimental rig was built to secure the measurement accuracy according to the fluid temperature and pressure changes and verify the reliability under various flow conditions from low to high. A numerical method based on the six-degree of freedom method was used to confirm its validity, which is different from a moving reference frame, which numerically analyzes the rotational speed of the turbine by backtracking the rotational speed to correspond to the flow conditions by giving it a constant rotational speed. By simulating water injection into the flowmeter, generating kinetic energy in the impeller according to the flow rate, and subsequently rotating the impeller due to the generated torque, the numerical analysis cost was reduced, allowing direct numerical analysis of the impeller's acceleration motion. The results were evaluated in terms of angular velocity and pulse signal, and the applicability and reliability of the numerical technique were verified by comparing the numerical results with experimental results. The aerodynamic performance of the impeller was analyzed to understand the phenomena as the impeller rotates. The results of this study can be utilized to conduct future research to improve the performance of flow meters, thus proving its value as a preliminary study. [ABSTRACT FROM AUTHOR]

The quantitative research on swelling properties of bentonite considering the influence of salt ions under the effect of hydrothermo-mechanical coupling is relatively weak. Based on a calculation model for the swelling characteristics of bentonite from a fractal perspective, this work proposes a novel coupled multifield control equation for unsaturated bentonite considering the influence of salt ions. The numericalization of the coupling control equation was completed by secondary development of a numerical analysis platform. The new theoretical model's dependability and validity were validated by comparing it to experimental data. The evolution of the related-field quantities under the multifield coupled effect in salt-bearing environments was obtained, and the effect of salt ion concentration was analyzed. The calculation showed that the temperature of bentonite changed periodically with changing ambient temperature. Temperature gradient induces migratory movement of water from high to low temperature regions. The hollow axisymmetric soil sample gradually saturated from outside to inside with increasing water injection rate at the outer cylindrical surface. The swelling pressure of bentonite will increase with an increase in water content, whereas the presence of salt ions weakened the swelling behavior. Temperature and relative humidity were less affected by salt ion concentration. [ABSTRACT FROM AUTHOR]

To propose a method for testing the dynamic change rate of the throat diameter based on the characteristics of the jet noise field, this study measured the effect of the size variation of the throat diameter on the jet noise during engine nozzle operation. Steady-state flow field simulation and transient noise simulation based on the Ffowcs Williams–Hawkings equation were carried out using large-eddy simulation for nozzles with different sizes of the throat diameter. The jet noise's sound pressure level (SPL) is discussed and analyzed. By performing a Fourier transform on the noise signal obtained from the simulation, the influence rule of throat diameter size on the magnitude and frequency characteristics of jet noise is analyzed. The results show that the jet noise signal mainly manifests in the low-frequency region. With a gradual increase in frequency, the corresponding amplitude will first increase and then decrease. The effect of the change in the nozzle throat size on the structure of the jet wave system is more prominent; with the increase in the throat diameter, the SPL of the jet noise tends to increase, and the peak frequency of the SPL tends to decrease. The size of the nozzle throat diameter affects the change in the main frequency of the noise, which decreases as the nozzle throat diameter becomes larger. [ABSTRACT FROM AUTHOR]

This study introduces an innovative asymmetric tri-stable piezoelectric vibration energy harvester (ATPVEH) augmented with an elastic base (EB), aimed at optimizing energy capture from low-orbit vibrations. This design incorporates a uniquely configured asymmetric tri-stable piezoelectric cantilever beam, positioned within a U-shaped block that is further enhanced by an elastic base. A strategically placed spring (kf)–mass (Mf) system, situated between the U-shaped block and the constrained end of the beam, significantly boosts the vertical displacement of the beam during vibrational events. We developed a dynamic model for the ATPVEH+EB utilizing Lagrange's equations, exploring the impact of various factors—including the asymmetry of the potential well, the stiffness of the elastic base, the mass of the spring–mass system, and the load resistance—on the system's nonlinear dynamic responses. Our findings indicate that the ATPVEH+EB facilitates more efficient energy harvesting from low-orbit vibrations, demonstrating dual response peaks across its operational frequency spectrum. Notably, the displacement and output voltage amplitudes of the ATPVEH+EB can be enhanced by increasing mf or decreasing kb, whereas the peak output power transitions toward a lower frequency range as the load resistance escalates. Both theoretical analyses and numerical simulations corroborate the ATPVEH+EB's superior performance in harvesting energy within low-orbit vibrational environments. [ABSTRACT FROM AUTHOR]

In this study, the transmission frequency dependence of the random waveguide, which is the waveguide having a randomly corrugated boundary, on waveguide length is investigated using an accurate numerical method. While resonances in the low-frequency region are caused by the interference among the dominant modes, those in the high-frequency region are caused by the mode conversion from the dominant mode to the second mode. Furthermore, their characteristics have not been investigated in detail. Numerical analysis shows that the resonant frequencies in the high-frequency region are nearly independent of the length of the random waveguide within the numerical error. It indicates that random waveguides can be regarded as a stack of independent resonators in high-frequency regions. [ABSTRACT FROM AUTHOR]

This research explores the solution of the time-fractional Newell–Whitehead–Segel equation using two separate methods: the optimal auxiliary function method and a new iterative method. The Newell–Whitehead–Segel equation holds significance in modeling nonlinear systems, particularly in delineating stripe patterns within two-dimensional systems. Employing the Caputo fractional derivative operator, we address two case study problems pertaining to this equation through our proposed methods. Comparative analysis between the numerical results obtained from our techniques and an exact solution reveals a strong alignment. Graphs and tables illustrate this alignment, showcasing the effectiveness of our methods. Notably, as the fractional orders vary, the results achieved at different fractional orders are compared, highlighting their convergence toward the exact solution as the fractional order approaches an integer. Demonstrating both interest and simplicity, our proposed methods exhibit high accuracy in resolving diverse nonlinear fractional order partial differential equations. [ABSTRACT FROM AUTHOR]

An efficient technique was used to model corona discharges without incorporating flux corrections. A position-state separation (POSS) technique was employed to solve the convection-dominated continuity equations prevalent in designing efficient corona discharges. The suggested approach utilizes an Eulerian scheme to solve the convective acceleration, diffusion, and response subproblems. The exceptional performance of POSS in terms of computing cost, resilience, and resolution is demonstrated by a series of numerical tests in various dimensions and coordinate systems. MATLAB was used to run four tests, namely, the square test, Davies test, general advection-diffusion test, and corona test. The average error in POSS was calculated as 0.06, which is much lower than the error in FEM-FCT (0.2677) and FVM-MUSCL (0.2650) algorithms. A 1 mm thick peak of space charge was formed around the anode after 1.2 ns. For an outer radius of 2 cm, ripples in ionizing waves were seen at t = 5000 ns. All the ionizing peaks were produced at around 0.5 cm away from the anode. [ABSTRACT FROM AUTHOR]

The authors of this study numerically analyze the characteristics of impingement of supercooled large droplets on the surface of the rotating hood of an aircraft. We use the secondary development function of Fluent software to first compare the prevalent models of impinging supercooled large droplets and then develop a modified model to numerically simulate their characteristics of impingement on the surface of a rotating hood in order to examine the effects of the diameter of the droplets, the speed of rotation, and the corresponding velocity of inflow on them. The results showed that the efficiency of the loss of mass of the droplets caused by their splashing and rebounding was low on the top of the cone, while the efficiency of local droplet collection was the highest. The efficiency of mass loss quickly increased, while that of droplet collection sharply decreased in the area of transition from the top to the side. The efficiencies of mass loss and droplet collection were nearly constant on the side of the cone, while that of the latter decreased to zero on the tail of the cone. When the median volumetric diameter of the droplets was increased from 79 to 250 μm, the efficiency of the loss of mass increased by about 15% on the side of the cone, but that of local droplet collection changed only slightly. The efficiency of the loss of mass decreased by about 20%, while that of local droplet collection increased by about 2.6% on the top of the cone under this condition. When the speed of rotation was increased from 1200 to 4300 r/min and the corresponding velocity of inflow was increased from 30 to 140 m/s, the efficiency of mass loss increased by about 15% on the side of the cone, while that of local droplet collection changed little. The efficiency of mass loss on the top of the cone decreased by about 37.5%, while that of local droplet collection increased by about 8% in this case. [ABSTRACT FROM AUTHOR]

To obtain improved thermal performance of flat plate solar collectors, the effect of square and rectangular riser tubes of a flat plate collector (FPC) were numerically investigated and compared with circular riser tube FPC in the present study. For this purpose, a three-dimensional numerical model for FPC collectors has been developed and simulated in CFD software ANSYS FLUENT. Transient thermal performance analysis is carried out to find out the optimum geometrical configuration of the FPC riser tube. The numerical results indicated that using the square-shaped riser tube in FPC improves the collector's useful heat exchange rate as well as thermal efficiency as compared to the use of circular and rectangular riser tubes. There is a maximum 8.1% higher heat exchange rate of the collector with a square riser tube than a circular riser tube under the same operating conditions. The average efficiency of the collector with the circular tube is 65.95%, whereas the square tube has the highest efficiency of 70.44%. However, the pressure drops through the square and rectangular riser geometry are higher than the circular tube. By making a balance between enhanced heat exchange rate and increased pressure drop, the performance evaluation criterion was evaluated and the square-shaped riser tube having the highest value of 2.65 is better than the other configurations. The results clearly indicate that the collector's performance is notably influenced by the shape of the riser tube, with a square shape yielding superior performance. [ABSTRACT FROM AUTHOR]

Zika virus infection is a vastly transmitted disease among humans. It was carried worldwide by international travelers. In 2016, Zika virus infection was present in more than 20 countries and territories in America. Thousands of cases were diagnosed in Cabo Verde, western Africa. Fifty-seven regions suffered from Zika virus in 2020, and the World Health Organization reported more than one hundred thousand cases worldwide. In this work, the modeling and transmission dynamics of Zika virus are studied dynamically and numerically. Positivity, boundedness, reproduction number, equilibria, and local stability are part of the numerical analysis. New nonstandard numerical techniques are examined for the said model. The primary purpose is to maintain the continuous model's behavior and dynamical properties. The proposed nonstandard finite approximation is studied according to the consistency and local stability of the solutions. Some numerical examples clearly show the improvement of the new schemes compared to other well-known methods. [ABSTRACT FROM AUTHOR]

To ensure the safe and stable operation of wind turbines, it is essential that the blades have sufficient bending stiffness to prevent excessive deflection and tower impact. A method combining static loading test and numerical analysis is proposed to solve the problem of identifying the cross-sectional bending stiffness of actual blades. Two working conditions, namely multi-point static test and single-point static calibration, are considered. A mathematical model of a cantilever beam with an initial small curvature and variable cross section is established. By fitting the deflection measurement data obtained from the static loading test, the deflection differential equation is solved by the finite difference method to obtain expressions for the cross-sectional bending stiffness under large and small deflection. The analysis results of several blade models show that the bending stiffness identification error for most blade sections is less than 10%, confirming the effectiveness of this method. This provides a practical and theoretical basis for the design, analysis, and refinement of test parameters for large-scale blades. [ABSTRACT FROM AUTHOR]

It is generally believed that thrombus formation does not occur in the left ventricle (LV) because of the high speed of blood flow. However, the LV has complex internal structures such as trabeculae carneae (TC) and papillary muscles (PM) on its inner wall, which may cause blood stagnation resulting in thrombus formation. In this study, the effects of the TC, PM, and torsional motion on the hemodynamics in the LV were investigated by computational fluid dynamics (CFD) analyses. An LV model was reconstructed from magnetic resonance imaging, and the shape was modified to mimic TC and PM. Then, the CFD analyses of blood flow were performed using several different combinations of TC, PM, and torsional motion. As the results, the presence of TC decreased the time-averaged wall shear stress and increased the relative residence time (RRT) of a blood stagnation index at the apex of the LV model. The TC-induced blood stagnation was also confirmed by a transportation analysis of the passive scalar. These hemodynamic changes were attributed to the fact that TC blocked the large vortex structures generated during the diastole, thus preventing them from reaching the apex. Moreover, the PM only affected the hemodynamics in its immediate vicinity, and torsional motion caused irregular changes to the RRT level and distribution at the apex. Therefore, the complex internal structures and torsional motion of the LV could cause blood stagnation. [ABSTRACT FROM AUTHOR]

In this study, we investigate a single server architecture in which the customer service system is not aware of the length of the line that was sent to them. Thus, the system-controlling equations here become what are known as the vacation differential equations. Here, we argue specifically that this vacation is what is causing the oscillations in the performance measurements of the system. The symbolic structure of the differential equation of the non-Markovian queuing problem is introduced in this study. A procedure of maintenance work is included in this model in terms of the vacation stage to support this minimal non-interrupted service system. The findings offer a thorough analysis of the system that enables it to operate more profitably even if it is interrupted by any associated activities. The supplemental variable method solves the queuing problem caused by the aforementioned subsequent outcomes. Estimates are made for the queue size, server idle time, use, and probability generating factors for each operating method. Numerical analysis was performed on specific examples using mathematical software. This strategy is perfectly acceptable because it is regularly employed and makes use of a statistical demarcation method. The graphical representation of this perspective provides precise calculations of the apparent constraints. [ABSTRACT FROM AUTHOR]

The propagation of nonplanar (cylindrical or spherical) Gardner solitons (GSs) in a plasma system containing nonthermally distributed heavy ions, light ions, q nonextensive distributed electrons, and arbitrarily charged dusts is studied theoretically and numerically. The modified Gardner equation is derived using the reductive perturbation method. The basic properties (amplitude, polarity, speed, and so on) of nonplanar dust-acoustic Gardner solitons (DA GSs) are analyzed numerically. Numerical analysis shows that the properties of the DA GSs in cylindrical and spherical geometry differ from those in planar geometry. The findings of the present study considerably contribute to space plasma and laboratory plasma. [ABSTRACT FROM AUTHOR]

Leading-edge (LE) serrations on owls' outermost remiges play a crucial role in the silent flight of owls. While the aeroacoustic characteristics of LE serrations have been widely studied using single feathers/airfoils, how they affect feather–feather (feather slots) interactions during flight remains unclear. Here, we present a numerical analysis of the effects of owl-inspired LE serrations on the aeroacoustics of tandem wing models. Large-eddy simulations and Ffowcs Williams–Hawkings analogy are combined to resolve the flow and acoustic fields around the tandem wings. The results demonstrate that serration-induced aeroacoustics are closely associated with the gap distance (D) between fore and hind wings. At a low AoA of 5°, as D increases, the LE serrations on the fore wing initially reduce the far-field sound pressures (D < 0.22c) by passively altering the laminar–turbulent transition on upper wing surfaces but turn out to increase the sound pressures remarkedly when D > 0.22c due to the flow instability induced at the hind wing LE. However, at a high AoA of 15°, the fore wing serrations enable robust sound reductions for all gap distances by mitigating the flow instabilities in the vicinity of the fore wing trailing edge and hind wing LE. Furthermore, the combination of LE serrations on fore and hind wings is verified to be capable of bringing nonlinear synergetic effects on the suppression of flow fluctuations and noise, which can inspire innovative biomimetic designs for low-noise multirotor drones and wind turbines. [ABSTRACT FROM AUTHOR]

In this study, a zero-dimensional numerical simulation of the atmospheric pressure plasma (APP) interface with a liquid solution was performed. By assuming that the solution reaction is dependent on the injection of radicals and electrons, we were able to obtain a single short APP discharge with the liquid solution. This study can predict excitation temperature, electron temperature, and population densities of species and result in optimum conditions for a chemical reaction for the synthesis of nanoparticles or other applications of the reaction between APP and liquid surface. This work aims to explain the effect of pH values on the synthesis of gold nanoparticles compared with experimental results. We found that the effect of pH value is expected to impact the generation of gold nanoparticles. Therefore, a high pH value is suitable for generating gold atoms for nano-synthesis. The fundamental plasma properties, such as population density, electron temperature, excitation temperature, and gas temperature, and chemical reaction process were studied. The simulation results were consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

In this work, we report spectra-dependent energy harvesting by optimizing the photon management of an indoor photovoltaic device while taking into consideration the degradation of electrical transport characteristics caused by the nano-photonic structures. For the test case of a CdTe-based photovoltaic device, it has been shown that although the incorporation of dielectric-filled nanoholes in the absorber layer can enhance light absorption by about 40%, the optical-to-electrical conversion efficiency of the device is significantly diminished because of the degradation of the electrical transport characteristics. Instead, the best performance metrics are obtained when the nanostructures are incorporated in the window layer of the device alone. A finite difference time domain based numerical analysis, coupled with Poisson's equation and continuity equation, shows that by controlling the areal density of the optimized structure in direct correlation with spectral characteristics of the illuminating light source, it is possible to maximize the overall power conversion efficiency of the indoor photovoltaic device. In the case of commercial white light-emitting diodes (LEDs), large arealdensities of holes are found to be more conducive for harvesting energy from cool-white LEDs, whereas smaller areal densities of holes provide better performances for illumination under warm-glow white LEDs. [ABSTRACT FROM AUTHOR]

Mode tracking based on correlation is a common method to achieve reasonable mode ordering in characteristic mode analysis (CMA). However, it is time-consuming to traverse the correlation calculation with all frequency points. For this reason, it is proposed to use information entropy in determining the frequency points of mode swapping in advance, which effectively improves the computational efficiency of CMA. Meanwhile, it is pointed out that for higher-order modes or electrically large structures, pseudo-degenerate modes are prone to appear, which results in mode swapping. In a large frequency range, the reactance property of a mode can be reversed, causing a change in the physical meaning of the mode. Therefore, CMA is best performed in the frequency range adapted to the structure size. Numerical analysis examples show the feasibility of this mode tracking method and confirm the rationality of mode performance analysis. [ABSTRACT FROM AUTHOR]

Air-coupled ultrasonic transducers based on novel piezoelectrets with extremely small acoustic impedance have some distinctive advantages including no coupling agent, flexibility, and eco-friendliness, compared to conventional ultrasonic transducers. Such advantages make them unique in the applications of nondestructive testing. In this study, a focused air-coupled ultrasonic transducer featuring a sphere-shaped transduction surface is designed by introducing flexible irradiated cross-linked polypropylene (IXPP) films. The characteristic of focusing is evaluated by numerical and experimental analysis. The results show that, by bending the IXPP film into a sphere, the ultrasonic energy can be concentrated to a certain small area to achieve better sensitivity and higher resolution. Furthermore, the IXPP focusing transducer has an obvious focusing effect when the opening radius D of the transducer is increased. Meanwhile, with the reducing radius R of the spherical surface and increasing frequency f of excitation, the value of the deviation coefficient α can be made smaller so that the transducer designed in this way can obtain a better focusing effect. [ABSTRACT FROM AUTHOR]

Two-dimensional and three-dimensional computational fluid dynamics studies of a spherical bubble impacted by a supersonic shock wave (Mach 1.25) have been performed to fully understand the complex process involved in shock–bubble interaction (SBI). The unsteady Reynolds-averaged Navier–Stokes computational approach with a coupled level set and volume of fluid method has been employed in the present study. The predicted velocities of refracted wave, transmitted wave, upstream interface, downstream interface, jet, and vortex ring agree very well with the relevant available experimental data. The predicted non-dimensional bubble and vortex velocities are also in much better agreement with the experiment data than values computed from a simple model of shock-induced Rayleigh–Taylor instability (the Richtmyer–Meshkov instability). Comprehensive flow visualization has been presented and analyzed to elucidate the SBI process from the beginning of bubble compression (continuous reflection and refraction of the acoustic wave fronts as well as the location of the incident, refracted and transmitted waves at the bubble compression stage) up to the formation of vortex rings as well as the production and distribution of vorticity. Furthermore, it is demonstrated that turbulence is generated with some small flow structures formed and more intensive mixing, i.e., turbulent mixing of helium with air starts to develop at the later stage of SBI. [ABSTRACT FROM AUTHOR]

The improved delayed detached eddy simulation is adopted in the present study to investigate the influence of the train length on its aerodynamic performance. The low y+ wall treatment and the cubic constitutive relation are adopted to resolve the viscous flows and model the anisotropic turbulence within the boundary layer. The analysis implied that the distribution region and intensity of velocity fluctuation are strengthened, resulting in a larger turbulence kinetic energy distribution and a higher boundary layer thickness as the train length increases. A reduction in the streamwise velocity and the negative pressure with the increasing train length on the tail train is observed, resulting in lower drag and lift coefficients. As the length of the train increases, both the mean and instantaneous slipstream velocities are increased. The boundary layer thickness and the skin friction coefficient are compared with flat plate theory, reduced-scale, and full-scale experiments, proving the ability of numerical simulation to model the boundary layer velocity profile and skin friction coefficient distribution correctly. The wake structures are identified by the Spectral Proper Orthogonal Decomposition method, the dominant mode frequency decreases, and the wavelength becomes larger as the length of the train becomes longer due to the thickening boundary layer. [ABSTRACT FROM AUTHOR]

In order to analyze the pressure pulsation characteristics of a single-conduit vertical submersible axial-flow pump device under bidirectional operation, the unsteady numerical simulation of the pump device was carried out based on computational fluid dynamics. The pressure pulsation coefficient and fast Fourier transform were used to analyze the pulsation of each monitoring point in the time–frequency domain. The results show that the pressure pulsation at different positions of the pump device is mainly affected by the impeller rotation, and the amplitude is large at the blade frequency and its harmonic frequency. In the positive operation, the main frequency of pressure pulsation at each monitoring point at the inlet of the impeller is three times the rotating frequency, and in the reverse operation, the main frequency of pressure pulsation at each monitoring point is 0.5 times the rotating frequency. The amplitude of pressure pulsation at each monitoring point at the inlet of the impeller is less than that of the positive operation, while the amplitude of pressure pulsation at the outlet of the impeller and the guide vane is larger than that of the positive operation. In the positive and reverse operation, the axial force of the impeller is significantly affected by the inlet velocity, and the amplitude of the axial force is small in the rotation period. The axial force increases with the increase of flow rate. The radial force of the impeller is significantly affected by the inflow flow pattern. The radial force changes obviously in the rotation period, and the radial force does not change regularly with the flow rate. The radial force of the impeller under reverse operation is 7.75 times that under positive operation. [ABSTRACT FROM AUTHOR]

Large-area solar cells are more susceptible to imperfect surfaces, such as edges or cracks. Numerical two-dimensional methods are developed and applied to study the effects of the imperfect surface in solar cells. The two-dimensional effects investigated in this work reveal the lateral conduction of solar cells, which causes inconsistent potentials and a deviation of photocurrent. The mask effects from distributed series resistance on luminescence techniques, such as photoluminescence and electroluminescence, are also explored. Lateral conduction hides the information of the real distribution of defects, and numerical methods are applied to eliminate the effect. In multijunction solar cells, lateral conduction in the interlayer leads to the complementarity between the luminescence of top and bottom cells. Furthermore, the distributed series resistance also causes a knee in the I–V curves, resulting in a decrease in the efficiency of the cell. The research in this work demonstrates that different categories of defects show different influences on solar cells, and the effect is more obvious on the open-circuit voltage rather than the short-circuit current. The study of distributed series resistance and lateral conduction in this work not only gives an explanation of experimental data but also provides instructions for the developments of large-area solar cells. [ABSTRACT FROM AUTHOR]

Aerosol particles are one of the main routes of transmission of COVID-19. Mobile air purifiers are used to reduce the risk of infection indoors. We focus on an air purifier that generates a defined volumetric air flow through a highly efficient filter material. We investigate the transport of aerosol particles from an infected dummy equipped with an aerosol generator to receiving thermal dummies. For analysis, we use up to 12 particle sensors to monitor the particle concentration with high spatial resolution. Based on the measurement data, a computational fluid dynamics (CFD) model is set up and validated. The experimental and numerical methods are used to investigate how the risk of infection suggested by the particle exposure in an exemplary lecture hall can be reduced by a clever choice of orientation of the air purifier. It turns out that obstructing the outlet stream of the air purifier may be particularly advantageous. The particle concentration at the head height deviates by 13% for variations of the location and orientation. At an air change per hour of 5, the cumulated PM1 mass at the head level was reduced by 75%, independently of the location of the infected dummy, compared to the "natural decay" case, showing that filtration is an effective means of reducing aerosol particle concentrations. Finally, CFD simulation was used to monitor the particle fates. The steady simulation results fit quite well with the experimental findings and provide additional information about the particle path and for assessing the comfort level due to air flow. [ABSTRACT FROM AUTHOR]