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The profiles of the edge of rectangular sheets of paper folded so as to join opposite edges were measured and compared with the profiles calculated with the theory of elasticity. I show how the calculation can be accomplished by using the aspect ratio of the loops as the only input parameter. [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]

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]

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]

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]

This paper presents a methodology to simulate the nonlinear free surface flow around an advancing ship. This methodology is based on the Moving Particle Semi-implicit (MPS) method, which is widely used to simulate the incompressible fluid flow. In this paper, the original MPS method is modified in order to analyze effectively the nonlinear free surface flow around an advancing ship. Several treatment techniques are newly proposed, and the original MPS method is modified by combining these techniques with other previous research studies. The proposed techniques include the Laplacian compensation model in the region near the body boundary, the collision model between fluid particles and wall particles, and some treatments for the opened boundary. The accuracy of the modified MPS method is verified through the numerical simulations on two benchmark problems for the performance evaluation of the particle methods and on the flows around both the wedged body and model ship. The numerical results demonstrate that the modified MPS method can be effectively applied to the simulation of nonlinear free surface flow around an advancing ship in marine engineering. [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]

In a previous paper, a calculation system for a high-accuracy, high-speed calculation of a one-dimensional (1D) Poisson equation based on the interpolation finite difference method was shown. Spatial high-order finite difference (FD) schemes, including a usual second-order accurate centered space FD scheme, are instantaneously derived on the equally spaced/unequally spaced grid points based on the definition of the Lagrange polynomial function. The upper limit of the higher order FD scheme is not theoretically limited but is studied up to the tenth order, following the previous paper. In the numerical analyses of the 1D Poisson equation published in the previous paper, the FD scheme setting method, SAPI (m), m = 2, 4, ..., 10, was defined. Due to specifying the value of m, the setting of FD schemes is uniquely defined. This concept is extended to the numerical analysis of two-dimensional Poisson equations. In this paper, we focus on Poiseuille flows passing through arbitrary cross sections as numerical calculation examples. Over regular and irregular domains, three types of FD methods—(i) forward time explicit method, (ii) time marching successive displacement method, and (iii) alternative direction implicit method—are formulated, and their characteristics of convergence and numerical calculation errors are investigated. The numerical calculation system of the 2D Poisson equation formulated in this paper enables high-accuracy and high-speed calculation by the high-order difference in an arbitrary domain. Especially in the alternative direction implicit method using the band diagonal matrix algorithm, convergence is remarkably accelerated, and high-speed calculation becomes possible. [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]

High-intensity acoustic waves existing commonly in aeronautical and aerospace vehicles manifest nonlinear propagation behaviors. Large-amplitude vibration and irregular shape of the aerospace vehicles further complicate the acoustic responses. This paper is concerned with numerical analysis of finite-amplitude acoustic responses of complex-shaped vibration objects. The time-dependent effect of the solid boundary position due to the large-amplitude vibration of the objects is considered. A set of first-order differential equations is derived to govern the finite-amplitude acoustic wave. A fourth-order dispersion-relation-preserving finite difference formulation is employed to solve the nonlinear acoustic equations on a fixed Cartesian grid. Acoustic responses of the fluid and the vibration of the complex-shaped object are coupled by considering the compatibility conditions on the fluid-solid interface. A ghost-cell sharp-interface immersed boundary method is utilized to relax the conformity requirement between the computational grid and solid boundary. Numerical filters are employed in the computational procedure to suppress numerical oscillations. The present method is validated through several numerical tests. Numerical analysis of finite-amplitude acoustic responses of a complex-shaped object is performed. The nonlinear effect of a finite-amplitude acoustic wave, the time-dependent effect of solid boundary position, and the coupling effect between them on the propagation behaviors of nonlinear acoustic waves are discussed. [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]

Nowadays, the diagnostic value of the artefactual information provided by lung ultrasound images is widely recognized by physicians. By carefully observing each individual artifact, an expert physician can derive important information on the distribution of the aerated spaces at the pleural level and, consequently, on the nature of the pulmonary disease. In this paper, a specific visual characteristic of the vertical artifacts (their length) is addressed. The impact of the acoustic properties of the interstitial medium, of the imaging parameters, and of the trap geometry on the length of the vertical artifacts is illustrated through experimental results and through the theoretical analysis of a simple model. [ABSTRACT FROM AUTHOR]

Polymeric separators have been developed since 2010 to produce acoustophoretic separation of particles or cells in suspension with high efficiency. They rely on three-dimensional (3D) resonances of their whole structure actuated by ultrasounds. In this paper, a numerical 3D analysis is presented and validated as the only tool for optimization of these polymeric chips to perform efficient separation applications. In contrast to conventional acoustophoretic techniques based on the establishment of standing waves in the liquid phase of the channel (requiring rigid chip materials, such as silicon or glass), whole-structure resonances of the chip allow the use of materials that are acoustically soft and of low acoustic impedance, which is close to that of the liquid samples hosted. The resonance requirement is not restricted to the liquid phase in the polymeric chips, but it extends to the 3D whole structure, allowing any material. It provides significant advantages in the design and manufacture of our chips, allowing the use of low-cost materials and cheap manufacturing processes and even printing of devices. The extraordinary complexity of their multiple resonances requires theoretical approaches to optimize their acoustophoretic performance. Hence, the importance of 3D numerical analyses, which are capable of predicting the acoustic behavior of these chips, is to perform acoustophretica separation in suspensions. [ABSTRACT FROM AUTHOR]

In this paper, biomimetic spines on puffer skin were taken as the study object, and numerical simulation was used to study the effect of the spinal arrangement on drag reduction characteristics. The results showed that the drag reduction decreased with the increasing arrangement position (AP) and inflow angle (β), and the drag reduction of the average arrangement was obviously better than that of the staggered arrangement. Moreover, drag reduction increased gradually as the arrangement quantity-R/T (AQR/AQT) increased. The drag reduction increased first and then decreased with the increasing arrangement spacing-R (ASR), and the drag reduction increased as the arrangement spacing-T (AST) increased. In short, the greater the spinal quantity and spacing, the better the drag reduction effect; however, it was affected by the arrangement position, which made the drag reduction effect reduce. More notably, the optimal drag reduction reached 23.1% when the arrangement parameters were the average arrangement, β = 0°, AP = 0 mm, AQR = 11, AQT = 5, ASR = 6.5 mm, and AST = 3.5 mm. Overall, the spinal arrangement parameters can be effectively regulated until the optimal drag reduction was realized, and this work provides a valuable reference for future studies on drag reduction for engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents a numerical scheme of arbitrary order of accuracy in both space and time, based on the arbitrary high-order derivatives methodology, for transient acoustic simulations. The scheme combines the nodal discontinuous Galerkin method for the spatial discretization and the Taylor series integrator (TSI) for the time integration. The main idea of the TSI is a temporal Taylor series expansion of all unknown acoustic variables in which the time derivatives are replaced by spatial derivatives via the Cauchy-Kovalewski procedure. The computational cost for the time integration is linearly proportional to the order of accuracy. To increase the computational efficiency for simulations involving strongly varying mesh sizes or material properties, a local time-stepping (LTS) algorithm accompanying the arbitrary high-order derivatives discontinuous Galerkin (ADER-DG) scheme, which ensures correct communications between domains with different time step sizes, is proposed. A numerical stability analysis in terms of the maximum allowable time step sizes is performed. Based on numerical convergence analysis, we demonstrate that for nonuniform meshes, a consistent high-order accuracy in space and time is achieved using ADER-DG with LTS. An application to the sound propagation across a transmissive noise barrier validates the potential of the proposed method for practical problems demanding high accuracy. [ABSTRACT FROM AUTHOR]

Inertial microfluidics has been used in recent years to separate particles by size, with most efforts focusing on spiral channels with rectangular cross sections. Typically, particles of different sizes have been separated by ensuring that they occupy different equilibrium positions near the inner wall. Trapezoidal cross sections have been shown to improve separation efficiency by entraining one size of particles in Dean vortices near the outer wall and inertially focusing larger particles near the inner wall. Recently, this principle was applied to a helical channel to develop a small-footprint microfluidic device for size-based particle separation and sorting. Despite the promise of these helical devices, the effects of channel geometry and other process parameters on separation efficiency remain unexplored. In this paper, a simplified numerical model was used to estimate the effect of various geometric parameters such as channel pitch, diameter, taper angle, depth, and width on the propensity for particle separation. This study can be used to aid in the design of microfluidic devices for optimal size-based inertial particle separation. [ABSTRACT FROM AUTHOR]

The pulse forming network (PFN) has the advantages of compactness and long-pulse achievability, and is widely used in military and industrial applications. In this paper, a novel Blumlein-type PFN is investigated numerically and experimentally. Specifically, the device is composed of five Blumlein-type PFN units, which are parallelly connected in the axial direction, and the LC elements of each unit are distributed in the angular direction. Dimensions of the PFN are only Φ 560 × 345 mm2 due to the novel compact structure. Small volume is necessary in military and industrial applications, especially for some mobile platforms. Electromagnetic coupling in the structure is theoretically analyzed to improve the performance of the device. Importantly, the impedance of the structure is only 1.5 Ω, which can efficiently reduce insulation difficulty at the same power level. In order to improve the performance of the PFN, a sharpening switch is added in the circuit. Simulation results show that a 170 ns quasi-square pulse is obtained on a 1.5 Ω dummy load, and the jitter of the flap-top is only about 2%. The PFN is built and preliminarily studied in our laboratory. Quasi-square pulses with a peak voltage of 3.1 kV are obtained on a water load of 2.1 Ω. The jitter of the flap-top is ∼3.9%. Experimental results show reasonable agreement with numerical analysis. [ABSTRACT FROM AUTHOR]

Prior research has investigated resonators capable of self-tuning through the use of a sliding mass. This passive tuning mechanism can be utilized to improve vibration control; however, little is known about the nonlinear dynamic interactions between the vibrating beam and sliding mass, particularly as these apply to vibration energy harvesting applications. This paper investigates this problem by numerically and experimentally examining the response of an electromagnetic self-tuning energy harvester. We present the governing equations of this electromagnetic cantilever beam with a sliding mass using the extended Hamilton principle. These equations are then discretized using the Galerkin method and solved numerically. An experiment is carried out to validate the numerical analysis. Parametric studies are conducted to examine the effect of different system parameters on the performance of the self-tuning harvester. [ABSTRACT FROM AUTHOR]

The multi-media finite element (MME) treating the discontinuity of the conductivity within the element was proposed by authors for fast simulation of the eddy current testing (ECT) signals of a conductive crack such as a stress corrosion crack. However, in the cases when eddy current consists of a large component perpendicular to the crack surface, the simulation accuracy is sometimes not very good because of the appearance of electric charge on the crack surface. In this paper, the influences of the surface electric charge on the implementation of the numerical method and on the simulation of the ECT signals were analyzed theoretically. A series of numerical analyses were designed to investigate the scope of feasibility of the MME. The simulation accuracy of the MME for different probe orientations and crack shapes was discussed based on the analysis of the distribution of the surface charge. [ABSTRACT FROM AUTHOR]

In this paper, a coaxial electrostatic wiggler with corrugated inner and outer walls is investigated theoretically. The field distributions in this wiggler correspond to the special solution of a Laplace equation in a cylindrical coordinate system with two sinusoidal ripple boundaries. Through numerical analysis and comparison to the coaxial electrostatic wiggler with a corrugated outer wall, the results indicate that in a coaxial electrostatic wiggler with corrugated inner and outer walls, electric field undulation can be enhanced. The particle-in-cell simulation further demonstrates that the electrons can be modulated deeply. [ABSTRACT FROM AUTHOR]

In this paper, a preliminary numerical method is established to simulate the effect of nonequilibrium plasma in water vapor on the nucleation rate of condensation. In this model, the plasma drift-diffusion model is employed to describe the water vapor plasma by considering a set of simplified reaction mechanisms. A heterogeneous condensation model describes the rate of water vapor nucleation on ions. The numerical simulation results show the formation and distribution of charged particles in nonequilibrium plasma and the effect of charged particles on the nucleation rate. The results also show that the nucleation rate increases rapidly with increasing supersaturation due to the presence of nonequilibrium plasma and is significantly higher with plasma than without plasma. The process of plasma-enhanced water vapor nucleation can be simulated quantitatively by this preliminary numerical method. [ABSTRACT FROM AUTHOR]

Based on the magnetic field configuration of the Chinese First Quasi-axisymmetric Stellarator (CFQS) device, three types of orbits such as the passing orbit, blocked trapped orbit, and localized trapped orbit are simulated using the Boris algorithm. Also, the orbital topology, orbit transition, and loss characteristics of these particles under different initial conditions are studied in this paper. It is found that there exists a transition from blocked trapped orbits to localized trapped orbits due to small continuous helical ripples. This phenomenon is analyzed as follows: we define the angle between the particle drift velocity ( v → D ) and the radial direction ( ρ ^ ) as β. If the blocked-localized transition appears in the region where β > 9 0 ○ , the localized particles will return to the blocked particles and be constrained. However, if the blocked-localized transition happens in the region where β < 9 0 ○ , localized particles will drift out of the last closed flux surface and be lost. The simulation results show that the loss of localized particles in the CFQS is mainly located in some specific regions within the vicinity of the toroidal angle φ = 0 ○ , 18 0 ○ and the poloidal angle θ = 9 0 ○ . [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to investigate the solution of general reaction–diffusion glycolysis system numerically. Glycolysis model demonstrates the positive solution as the unknown variables show concentration of chemical substances. Three numerical methods are used to solve glycolysis model. Two methods are well-known finite difference (FD) schemes and one is proposed FD scheme. The proposed scheme is explicit in nature. The main feature of the proposed FD scheme is to preserve the property of positivity retained by the glycolysis model. Results are compared with forward Euler explicit scheme and Crank Nicolson implicit scheme. All the attributes are verified by simulations. [ABSTRACT FROM AUTHOR]

Among the methods of the numerical analysis of the physical phenomena of the continuum, the finite difference method (FDM) is the first examined method and has been established as a full numerical calculation system over the regular domain. However, there is a general perception that generality in numerical calculations cannot be expected over complex irregular domains. As using the FDM, the development of computational methods that are applicable over any irregular domain is considered to be a very important contemporary problem. In the FDM, there is a marked characteristic that the theory developed by the (spatial) one-dimensional (1D) problem is naturally applied to the 2D and 3D problems. The calculation method is called the interpolation FDM (IFDM). In this paper, attention is paid to 1D Laplace and Poisson equations, and the whole image of the IFDM using the algebraic polynomial interpolation method (APIM), the IFDM-APIM, is described. Based on the Lagrange interpolation function, the spatial difference schemes from 2nd order to 10th order including odd order are calculated and defined instantaneously over equally/unequally spaced grid points, then, high-order accurate and high-speed computations become possible. [ABSTRACT FROM AUTHOR]

The present paper presents a mathematical probe for incompressible steady two-dimensional flow of Williamson fluid along an exponentially stretching cylinder. Derived PDEs for this work are changed into ODEs by adopting right transformations. Then numerical procedure is carried out by Shooting Technique in accordance with the RK-Method of order six. The influence of the Reynold's number and Weissenberg's numbers on the velocity profile is analyzed, and the variation in skin friction coefficient is explored. The results are elaborated upon through graphs and tables. The validity of the results is presented by comparing them with the previous works. [ABSTRACT FROM AUTHOR]

In this paper, the momentum and heat transfer between charged particles and neutral particles in a needle-to-plane dielectric barrier discharge reactor with Ar as the working gas are simulated. In this simulation, the heat transfer from ions to the neutral atom is described by the interaction term between ions and atoms. Detailed discharge reaction mechanisms are considered in the simulation including metastable atom. The Navier-Stokes equation is solved in combination with the Poisson equation and the charged particles drift-diffusion equations. The interrelation between the gas discharge and the gas flow characteristics are preliminary revealed. In particular, when the streamer strikes the cathode, the maximum gas temperature can reach 1026 K, and the high temperature area is concentrated in a confined space around the needle cathode tip with a thickness of 0.01 mm and a diameter of 0.1 mm. Then, the temperature change decreases to 400 K in 1 μs. Induced by the discharge, the pressure perturbation of the gas can exceed 6×104 Pa at 1.1 μs, and an expanding wave is created. The propagation velocity of the expanding wave is close to the sound velocity. The forward velocity decreases from approximately 120 m/s at 1.1 μs to 5.5 m/s at 4.4 μs. The inverted velocity remains at approximately 5 m/s. The number density for the neutral particles has a minimum value, which is approximately 8×1024 m-3, in the sheath as well as changes in the expanding wave propagation in the plasma bulk. [ABSTRACT FROM AUTHOR]

This paper analyzed colloidal characteristics of a bimodal distribution emulsion system using bulk rheological and numerical approaches. The experiment measured simple shear to confirm emulsion shear thinning and viscosity tendencies. Numerical models employed the multi-component lattice Boltzmann method to express interfacial tension, surfactant movement, and viscosity of liquid phases. Numerical models were helpful to implement interactions between two or more varied-sized liquid droplets, since they express droplet deformation and interaction forces and can also provide rheological analysis, whereas shear flow experiments cannot. In monodisperse systems (i.e., uniform droplet size), larger droplets decrease emulsion relative viscosity. However, mixture viscosity for bimodal systems (small droplets mixed with large droplets) was lower than that for the monodisperse system. The reduced viscosity was related to increased droplet deformability and decreased shear stress at the droplet surface. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical simulation and experimental test of a multi-element focused air-coupled transducer. The experimental structure of each transducer element comprises 1-3 connectivity piezo-composite stacking with two matching layers to overcome the enormous impedance mismatch between the piezo-composite disc and air. The numerical simulation is carried out using the circular-piston radiation model, and the experimental results for the acoustic field agree well with the simulation results. Furthermore, surface microcracks are detected successfully using a C-scan system involving the designed multi-element focused air-coupled transducer. The results show that the designed multi-element focused air-coupled transducer offers excellent focusing ability and is beneficial for detecting surface microcracks. [ABSTRACT FROM AUTHOR]

The average specific forced radiation wave impedance of a finite rectangular panel is of importance for the prediction of both sound insulation and sound absorption. In 1982, Thomasson published numerical calculations of the average specific forced radiation wave impedance of a square of side length 2e for wave number k in half octave steps of ke from 0.25 to 64. Thomasson's calculations were for the case when the forced bending wave number kb was less than or equal to k. Thomasson also published approximate formulas for values of ke above and below the published results. This paper combines Thomasson's high and low frequency formulas and compares this combined formula with Thomasson's numerical calculations. The real part of the approximate formula is between 0.7 dB higher and -1 dB lower than the numerical calculations. The imaginary part of the approximate formula is between 2.3 dB higher and -2.6dB lower than the numerical calculations. This paper also gives approximate formulas for the case when kb is greater than or equal to k. The differences are between 0.8 and -1.2 dB for the imaginary part and between 6.2 and - 2.4 dB for the real part. [ABSTRACT FROM AUTHOR]

A novel type of electromagnetic inductive valve has been developed for the gas injector of the planar pulsed inductive plasma thruster. However, due to the complex operation process of the valve, the design work and the performance prediction can only be accomplished by experimentation. This paper explains a two dimensional model applied to predict the valve performance. The electromagnetic and mechanical aspects which dominate the valve operation process are treated as two weakly coupled problems. The equivalent circuit method is applied to analyze the electromagnetic problem where the valve is represented by a series of sub-conductors. The Lorentz force is calculated and introduced into the mechanical problem as an analytical load. Simulation and experimental validations are implemented in a prototype valve. Compared results from experiments convince that the present model can be used to predict the valve dynamic performances with satisfying accuracy. Moreover, the detailed insight with respect to the development of magnetic flux density, induced current, Lorentz force and velocity of the diaphragm is presented to better understand the valve operation process. The results indicate that the effective acceleration of the diaphragm occurs in the initial phase of valve opening. Only the diaphragm obtains enough kinetic energy during the first half cycle of the coil current, can the valve be fully opened. [ABSTRACT FROM AUTHOR]

This paper performs numerical investigations on the interaction of shock wave with an ellipsoidal bubble in liquid medium. The governing equations, including the conservative Euler equations and the non-conservative transport equation of the liquid volume fraction, are discretized based on the finite volume method. A tangent of hyperbola for interface capturing (THINC) interface reconstruction scheme is employed for the phasic densities and the liquid volume fraction to maintain the interface sharpness. The major-axis (z-axis) of the bubble is parallel to the incident planar shock wave. Different collapse behaviors are observed for two ellipsoidal geometries, named as the disk-like bubble and rugby-like one. Different collapse patterns of an initial ellipsoidal bubble are presented and the manifestation is that the transverse jets pierce the bubble differently, classified as along the centerline, off-centerline along the circumferential direction or along the meridian line if the aspect ratio is varied. For the disk-like bubble, it presents the strongest collapsing process under certain eccentricity, characterized by the highest water hammer pressure under the same incident shock strength. The second sheeting jet is an important factor that leads to the collapse of the remaining bubbles pierced by the first transverse jet. [ABSTRACT FROM AUTHOR]

Determination of the relationship between electromagnetic power absorption and temperature distributions inside highly heterogeneous biological samples based on numerical methods is essential in biomedical engineering (e.g. microwave thermal ablation in clinic). In this paper, the gradient expression is examined and analyzed in detail, as how the gradient operators can be discretized is the only real difficulty to the solution of bio-heat equation for highly inhomogeneous model utilizing implicit scheme. [ABSTRACT FROM AUTHOR]

Noise mapping in large and dense urban areas is computationally challenging, if not impossible, with the use of conventional numerical techniques. Recently, promising results have shown the potential of energy-based models to compete with conventional numerical techniques. In this paper, a hybrid full-wave/diffusion propagation model is proposed to address some of the flaws of the traditional diffusion model. The full-wave model is used for predicting sound propagation (i) near the source, where interactions between waves are important, and (ii) outside the cluttered environment, where free-field-like conditions apply. The diffusion model is used in regions where diffusion conditions are met. [ABSTRACT FROM AUTHOR]

This paper investigates the incompressible fractional MHD Maxwell fluid due to a power function accelerating plate with the first order slip, and the numerical analysis on the flow and heat transfer of fractional Maxwell fluid has been done. Moreover the deformation motion of fluid micelle is simply analyzed. Nonlinear velocity equation are formulated with multi-term time fractional derivatives in the boundary layer governing equations, and convective heat transfer boundary condition and viscous dissipation are both taken into consideration. A newly finite difference scheme with L1-algorithm of governing equations are constructed, whose convergence is confirmed by the comparison with analytical solution. Numerical solutions for velocity and temperature show the effects of pertinent parameters on flow and heat transfer of fractional Maxwell fluid. It reveals that the fractional derivative weakens the effects of motion and heat conduction. The larger the Nusselt number is, the greater the heat transfer capacity of fluid becomes, and the temperature gradient at the wall becomes more significantly. The lower Reynolds number enhances the viscosity of the fluid because it is the ratio of the viscous force and the inertia force, which resists the flow and heat transfer. [ABSTRACT FROM AUTHOR]

Joint-free (RE)Ba2Cu3Ox (REBCO) coil based on ‘wind-and-flip’ technique has been developed to generate a persistent magnetic field without power supply. This paper is to study the magnetization characteristics of the joint-free REBCO coil by field cooling, in order to trap higher field. A joint-free pancake coil is wound by REBCO tapes and the field cooling magnetization test is performed on it. An approximate numerical model based on H-formulation is built for this coil to analyze its magnetization behavior, which is validated by the experimental results Analysis show that a persistent direct current is induced in the coil during the field cooling operation, which generates the trapped field. The induced current of the joint-free coil shows an intrinsic non-uniform distribution among turns. Increasing the magnetization field and critical current of REBCO conductors can considerably increase the trapped field. But the trapping factor (the rate of trapped field to background magnetization field) reaches a maximum value (60 % for the test coil). This maximum value is an intrinsic characteristics for a fabricated coil, which only depends on the coil’s geometry structure. With a same usage of REBCO tapes, the trapping factor can be improved significantly by optimizing the coil structure to multiple pancakes, and it can approach 100 %. [ABSTRACT FROM AUTHOR]

The long relative propagation delays between the underwater acoustic channels poses a challenge to the detection of the multiple-input multiple-output signals but also gives a chance for a better space-time signal processing scheme. This paper proposes a detection ordering scheme for the layered space-time detection with the successive interference cancellation (SIC) algorithm, where the channel relative delays leading asynchronous arrival of the layered signals are utilized to arrange the detection order that is quite important for a SIC detection. This delay-based ordering is demonstrated as an optimal one for minimizing the detection error probability via the geometrically based model of the SIC detection. The complexity and calculation of the ordering procedure are significantly decreased by means of the delay estimations of the sub-channels. An iterative layered spacetime detector combining the delay-base ordered SIC algorithm with the iterative block decision feedback equalizer is employed, where the iterative equalizer is utilized for the cancellation of the multipath interference and the asynchronous arrival interference. Numerical results show that up to 4 dB performance gain obtained by the delay-based ordered SIC detection for a 2×2 MIMO system. [ABSTRACT FROM AUTHOR]

The multiple signal classification (MUSIC) type method has been widely used to detect point-like scatterers embedded in a homogeneous background medium. This paper extends the MUSIC-type method to the detection of point-like scatterers that are embedded in an inhomogeneous background. Although the background Green’s function at each test point is not directly available in inhomogeneous background scenario, this paper proposes an approach, based on the finite element method, to simultaneously obtain the Green’s function at all test points. Numerical simulations illustrate the efficacy of the proposed theory and algorithm presented in this paper, and some interesting observations, which are absent in homogeneous background scenario, are highlighted and discussed. [ABSTRACT FROM AUTHOR]

This paper is devoted to the rigorous obtention of the energy balance in porous materials. The wave propagation in the porous media is described by Biot-Allard’s {u,U} and {u,P} formulations. The paper derives the expressions for stored kinetic and strain energies together with dissipated energies. It is shown that, in the case of mixed formulations, these expressions do not correspond to the real and imaginary parts of the variational formulations. A quantitative convergence analysis of finite element scheme is then undertaken with the help of these indicators. It is shown that the order of convergence of these indicators for linear finite-element is one and that they are then well fitted to check the validity of finite-element models. [ABSTRACT FROM AUTHOR]

The ultrasonic wave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation. [ABSTRACT FROM AUTHOR]

Acoustical-based imaging techniques have found merit in determining the behavior of vibrating structures. These techniques are commonly used in numerous applications to obtain detailed noise source information and energy distributions on source surfaces. Source reconstructions using near-field acoustical holography (NAH) are reliant upon accurate measurement of the pressure field at the hologram surface. For complex acoustic fields this requires fine spatial resolution and therefore demands large microphone arrays. In this paper, an interpolation method is developed for obtaining the complex pressure field at the hologram surface from pressure and velocity measurements. Because particle velocity measurements provide directional information, a more accurate characterization of the pressure field with fewer measurement locations is obtained. The processing technique presented does not relate directly to the holographic reconstruction itself. However, the interpolation scheme presented serves as a preprocessing step before a NAH algorithm is applied. The presentation and validation of the interpolation scheme is the major focus of the paper. An analytical comparison of NAH reconstructions from traditional pressure measurements to reconstructions using the preprocessed pressure and velocity measurements is presented. A vibrating plate and cylinder are considered as test cases to validate the analytical results. [ABSTRACT FROM AUTHOR]

The skewness of the first time derivative of a pressure waveform, or derivative skewness, has been used previously to describe the presence of shock-like content in jet and rocket noise. Despite its use, a quantitative understanding of derivative skewness values has been lacking. In this paper, the derivative skewness for nonlinearly propagating waves is investigated using analytical, numerical, and experimental methods. Analytical expressions for the derivative skewness of an initially sinusoidal plane wave are developed and, along with numerical data, are used to describe its behavior in the preshock, sawtooth, and old-age regions. Analyses of common measurement issues show that the derivative skewness is relatively sensitive to the effects of a smaller sampling rate, but less sensitive to the presence of additive noise. In addition, the derivative skewness of nonlinearly propagating noise is found to reach greater values over a shorter length scale relative to sinusoidal signals. A minimum sampling rate is recommended for sinusoidal signals to accurately estimate derivative skewness values up to five, which serves as an approximate threshold indicating significant shock formation. [ABSTRACT FROM AUTHOR]

The complex frequency shifted perfectly matched layer (CFS-PML) can improve the absorbing performance of PML for nearly grazing incident waves. However, traditional PML and CFS-PML are based on first-order wave equations; thus, they are not suitable for second-order wave equation. In this paper, an implementation of CFSPML for second-order wave equation is presented using auxiliary differential equations. This method is free of both convolution calculations and third-order temporal derivatives. As an unsplit CFS-PML, it can reduce the nearly grazing incidence. Numerical experiments show that it has better absorption than typical PML implementations based on second-order wave equation. [ABSTRACT FROM AUTHOR]

This paper presents an empirical linear equation to predict peak pressure level of anthropogenic impulsive signals based on its correlation with the sound exposure level. The regression coefficients are shown to be weakly dependent on the environmental characteristics but governed by the source type and parameters. The equation can be applied to values of the sound exposure level predicted with a numerical model, which provides a significant improvement in the prediction of the peak pressure level. Part I presents the analysis for airgun arrays signals, and Part II considers the application of the empirical equation to offshore impact piling noise. [ABSTRACT FROM AUTHOR]