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In midair haptics, ultrasound phased arrays are mainly used due to their high spatiotemporal controllability. The constraint on the presentation distance of phased arrays to form a focus can be mitigated by utilizing concave reflectors. This paper numerically examines the convergence of a surface approximated by multiple planes serving as a reflector, substituted for an ideal concave surface. A mirrored phased array produced by the planar segments forms a focus and concurrently creates interference among imaginary sources. A single-point convergence condition is derived that constrains the accuracy of the approximated reflector and the phased array size. As long as it satisfies the convergence condition, the approximated reflector can form a single focal point. Numerical simulations were conducted to confirm the validity of the convergence equation and the 5% tolerance of the segment size for the reflector deformation. An experimental campaign was also conducted and confirmed that the polyhedral reflector was able to form a single small focus by controlling the phase shift of the sound source. [ABSTRACT FROM AUTHOR]

Frequency hopping (FH) signals have been widely used to improve performance against frequency selective fading phenomenon of underwater channels. However, the channel is slowly varying in regard to changes in weather conditions, and thus the conventional FH detection transmitting signals with fixed frequency cannot guarantee good detection performance in the dynamic underwater environment. To overcome the performance degradation in slowly-varying fading dispersive channels, this paper proposes an adaptive frequency-hopping (AFH) target detection method. Compared with conventional FH detection methods, the AFH can adaptively select the optimal detection frequency based on premeasured background noise and channel frequency response measured from previous experiments. Numerical simulations and lake trials are conducted to verify the effectiveness of the AFH. The simulation results show that the AFH has better detection performance than the conventional FH. The lake trial results have also verified the validity and feasibility of AFH. Importantly, AFH also achieves a better output signal-to-noise ratio under actual noise interference. [ABSTRACT FROM AUTHOR]

Gigahertz acoustic streaming enables the synthesis of localized microjets reaching speeds of up to meters per second, offering tremendous potential for precision micromanipulation. However, theoretical and numerical investigations of acoustic streaming at these frequencies remain so far relatively scarce due to significant challenges including: (i) the inappropriateness of classical approaches, rooted in asymptotic development, for addressing high-speed streaming with flow velocities comparable to the acoustic velocity; and (ii) the numerical cost of direct numerical simulations generally considered as prohibitive. In this paper, we investigate high-frequency bulk streaming using high-order finite difference direct numerical simulations. First, we demonstrate that high-speed micrometric jets of several meters per second can only be obtained at high frequencies, due to diffraction limits. Second, we establish that the maximum jet streaming speed at a given actuation power scales with the frequency to the power of 3/2 in the low attenuation limit and linearly with the frequency for strongly attenuated waves. Last, our analysis of transient regimes reveals a dramatic reduction in the time required to reach the maximum velocity as the frequency increases (power law in –5/2), leading to characteristic time on the order of μs at gigahertz frequencies, and hence accelerations within the Mega-g range. [ABSTRACT FROM AUTHOR]

Plate-type acoustic metamaterials (PAMs) are thin structures that exhibit antiresonances with high sound transmission loss (STL) values, making PAMs a promising new technology for controlling tonal noise in the challenging low-frequency regime. A PAM consists of rigid masses periodically attached to a thin baseplate. The periodicity of PAM can be exploited in simulations, allowing to model only a single unit cell using periodic boundary conditions. This approach essentially represents the PAM as an infinite structure, but real PAM implementations will always be finite and influenced by boundary conditions. In this paper, extensive numerical simulations of different PAM configurations have been performed to study the performance of finite PAM compared to infinite PAM. The results indicate that as the number of unit cells in a finite PAM increase, the STL converges toward that of an infinite PAM. The impact of the finite PAM edge boundary conditions becomes negligible at some point. Based on the numerical results, a simple criterion is proposed to determine a priori how many unit cells are required in a finite PAM design to consider it quasi-infinite. This criterion aids in justifying unit cell models with periodic boundary conditions for efficient design optimizations in practical PAM applications. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of small disturbance on the statistical behaviors of fluid particles of the three-dimensional divergence-free hexagonal Beltrami flow from a Lagrangian point of view. Due to the butterfly-effect, numerical noise increases exponentially for chaotic dynamic systems. Thus, a powerful strategy, namely, the clean numerical simulation, is used to gain reliable/convergent trajectory in a long enough interval of time. It is found that the statistics of chaotic trajectory of fluid particles are stable in some cases, corresponding to the so-called "normal-chaos," but unstable in some cases, i.e., rather sensitive to small disturbances, corresponding to the so-called "ultra-chaos," which is a new concept proposed currently. Obviously, an ultra-chaotic trajectory of fluid particles is at a higher disorder than a normal chaotic trajectory. In theory, it is impossible to repeat any experimental/numerical results of an ultra-chaotic system even by means of statistics, but reproducibility is a corner-stone of our modern science paradigm. Hence, the wide existence or non-existence of ultra-chaos has a very important meaning. In this paper, we illustrate that the ultra-chaotic trajectories of fluid particles indeed widely exist in a hexagonal Beltrami flow field. This fact is important for deepening our understanding of chaotic dynamic systems and revealing the limitations of our paradigm of modern science. [ABSTRACT FROM AUTHOR]

In order to increase the stalling margin of a compressor under different inlet conditions, especially under inlet distortion conditions, a new coupled casing processing structure is proposed in this paper. The new structure combines the characteristics of traditional circumferential slot and axial slot casing treatments. First, based on numerical simulation results of the simplified calculation model, a control variable method is used to design the coupled casing treatment and an effective casing treatment scheme (CCTF) is obtained. Then, experiments and multistage full-channel numerical simulations are used to study the effect of CCTF on the compressor performance under uniform and distorted inlet conditions. The stability expansion effect and the mechanism of the structure under inlet distortion conditions are analyzed in detail. The results show that the jet in CCTF obstructs the main flow and causes additional mixing loss, but inhibits the expansion and crushing of the leakage vortex, thus increasing the stall margin of the compressor. Under near-stall conditions, the tail-circumferential groove provides about 64.8% of the flow rate, which improves the stability expansion capability of the casing treatment. When there is distortion at the inlet, CCTF can still effectively improve the stability. [ABSTRACT FROM AUTHOR]

In the impinging region of opposing jets, strong mixing and significant energy dissipation are observed, but the mixing parameters invariably change with the opposed impinging strength (OIS). In this paper, the ratio of the turbulent kinetic energy (TKE) intensity at the theoretical impinging point to the nozzle exit is defined as the opposed impinging strength. To examine the mixing properties of opposed impinging jets (OIJs) in a limited field under various OIS, a renormalization group k-ε turbulence model is employed to calculate three-dimensional OIJs under various OIS. The nozzle exit diameter is set to 0.6 m, and the inlet velocity is between 0.08 and 8 m/s, so the simulations are performed at Re between 4.8 × 104 and 4.8 × 106. This work focuses on the radial and vertical jets produced after impinging as well as the distribution of the TKE, flow field, and vortices. A thorough investigation reveals that although the OIS of the jets is primarily determined by the degree of jet development, it increases with the Reynolds number. A low OIS results in less mixing in the surrounding water and relatively unconstrained jet generation; however, it also results in limited energy extraction from the fluid. Once the OIS is high, there is more mixing in the surrounding water, and more energy is also lost during impinging. The distribution of vortices in the vortex field is not only influenced by the OIS but is also very closely related to the scale of the limited mixing field. [ABSTRACT FROM AUTHOR]

Multiple-gated junctionless transistors (JLTs) with an extremely simple structure and bulk-conduction-based operation could overcome fundamental problems with respect to short-channel effects for sub-3-nm technology nodes. In this paper, the performance of a tri-gate JLT with an electrostatically highly doped channel is demonstrated through numerical simulation. Unique characteristics previously reported in fabricated JLTs were exhibited by the tri-gate transistors with an additional bottom-gate bias (Vgb = 50 V), which induced an effectively highly doped state of the channel. The results of this study show the feasibility of producing impurity scattering-free JLTs for next-generation technology nodes. [ABSTRACT FROM AUTHOR]

Helmholtz resonator (HR) is widely used in various fields, but the classic HR usually should satisfy the acoustically compact condition, which limits the application range of the classic HR. This paper investigates analytically and numerically the acoustic performance of a HR in which the length of the neck is not limited under the acoustically compact conditions. An analytical model is developed for accurately and quickly predicting resonant frequencies and transmission loss of the Helmholtz resonator with an extended neck (HREN), and numerical simulations have been performed to validate the developed analytical model. Both the analytical and numerical studies reveal that the HREN has multiple resonant frequencies, and a method is developed for approximate and fast calculation of the multiple resonant frequencies. [ABSTRACT FROM AUTHOR]

Solid composite propellants often contain metal particles, such as aluminum particles, and the internal flow field in a solid rocket motor is a typical gas–solid two-phase flow field. In this study, to address the problem of the erosion of particles on the wall during the working process of an engine, a particle erosion model was established based on the interaction mechanism between the particles and the wall. From the perspective of particle dynamics, the interaction mechanism between the moving particles and the wall was analyzed. The force of the particles on the wall surface was obtained, and a formula for solving the particle erosion rate was deduced by using the strength theory and the energy conservation principle. It was combined with Hertz's contact theory to analyze the factors influencing the erosion rate. In this paper, the particle erosion experiments revealed not only the relationship between erosion rate and erosion angle but also the correlativity between erosion rate and particle concentration. In addition, the experimental results are consistent with the deduced results, which proves the reliability of the model established in this paper. The multiphysics simulation program Rocstar, developed by the Center for Simulation of Advanced Rockets at the University of Illinois, was used to perform a numerical simulation of the two-phase flow in the Jet Propulsion Laboratory nozzle. The results agreed well with the literature and the experimental data. The feasibility and accuracy of the calculation of the gas-phase and two-phase flow fields of the solid rocket motor nozzle were confirmed, laying the foundation for the numerical simulation of the entire process of the full flow field of the engine. [ABSTRACT FROM AUTHOR]

Multi-tandem fuel tanks have a complex structure, low flow rate between tanks, and, unlike single-fuel tanks, uneven pressure distribution, which makes their fuel supply and pressurization difficult to control. This paper uses a volume-of-fluid model based on the finite-volume method to track the fuel motion in different states of a flight vehicle and obtains the liquid-surface sloshing and the liquid flow in the connecting pipe. The model uses the dynamic meshing technique combined with the pressure at the solid wall to track the motion of the one-way stop valve diaphragm in the connecting pipe, thereby better predicting the fuel transfer in the connecting pipe. The calculation covers the whole process of flight vehicle erection, standby, flight, pumping, and pressurization and provides the distribution of pressure in different fuel tanks and the fuel flow characteristics in the connecting pipe. The calculation results are consistent with the experimental results, which verifies the accuracy of the model. By calculating different working cases, the results show that the different states of the flight vehicle strongly affect the sloshing of the liquid in the fuel tank, the pressure distribution, and the opening and closing of the valves. The maximum mass flow rate through the three valves, pressure at the bottom of the tank, and pressure at the pumping port all increase after the pressurization in the fuel tank. The flow of fuel between different tanks can be increased by changing the structure of the connecting pipe, which affects the pressure at different locations in the tank and at the pumping port. [ABSTRACT FROM AUTHOR]

Maximum pressure is one of the key factors that affect jet scouring. Previous studies have focused on the attenuation characteristics of the submerged jet, but there are few studies on the influence of the nappe shape on the pressure of the plunge pool. In this paper, a combination of numerical simulation and physical experiments was used to determine the influence on the maximum pressure of the vertical rectangular submerged jet with different aspect ratios (1, 3, 5, 8, 11.25, 15, and 20), incident flow velocity, and water depth on the plunge pool bottom. The hydraulic diameter, D, of the entering interface was proposed to measure the degree of dispersion of the nappe, based on which an empirical formula for the maximum pressure on the plunge pool bottom was obtained. By applying the formula to other shapes of jets (rhombuses, triangles, circles, ellipses, etc.), higher precision calculation results were also obtained, and the formula calculation results were in good agreement with the test results of the existing literature. [ABSTRACT FROM AUTHOR]

Plasma jet normally operates in a regime of positive or negative streamers. Different propagating behaviors have been investigated for positive streamers. However, there are few studies on negative streamers. In this paper, a two-dimensional fluid model is used to simulate the behavior of a negative streamer encountered with a cloud of positive ions. Simulation results indicate that the negative streamer behaves like a free streamer when the ion cloud has a low charge density. After initiation near the needle tip, the streamer propagates along the axis, passes through the ion cloud, and finally reaches the anode vicinity along a straight line. When the streamer reaches the ion cloud, its head radius (R0) is investigated as a function of parameters, including the voltage amplitude and the gap width, as well as the charge density, axial position, and spatial size of the ion cloud. At a given moment, electric field strength and electron density near the streamer head increase with increasing charge density of the ion cloud. In the case of a high charge-density ion cloud, after a primary streamer propagates some distance along the axis, a positive secondary streamer, and a negative secondary streamer start to propagate from the cloud to the cathode and the anode, respectively. [ABSTRACT FROM AUTHOR]

A number of one-dimensional models have been developed to inform the design of piezoelectric transducers. The majority of these models are in the frequency domain. In this paper, we develop a one-dimensional time-domain model for the mechanical response of a piezoelectric layer. Secondary effects, resulting from feedback between the acoustic and electric variables, are included in the model. Our approach utilizes Green's function for the Helmholtz equation with radiation boundary conditions and the methods of complex analysis. The model predictions are validated by comparison with a finite-difference time-domain numerical simulation of the governing acoustic equations in and outside the layer. This time-domain model enables efficient calculation of the secondary piezoelectric action effects and provides the mechanical response to an arbitrary electrical source. [ABSTRACT FROM AUTHOR]

This paper presents the results of intensive investigations of electromagnetic interference caused primarily by closely arranged antennas within subwavelength distance; potential applications involve the principle of scattering cancellation. A cloaked planar monopole antenna (CPMA) is newly proposed in this work. The performance of the CPMA is compared with that of a bare planar monopole antenna. Numerical simulations with the two antenna types were conducted, and various configurations with the potential for practical applications in the industrial and defense sectors were tested. [ABSTRACT FROM AUTHOR]

Target direction-of-arrival (DOA) estimation is often difficult in the presence of strong interference—especially when the target DOA is very close to the interference DOA—since the strong interference signal can mask the weak target signal and make the DOA estimation hard. To address this problem, an efficient sparse method for DOA estimation is proposed in this paper, in which the effect of strong interference on the target DOA estimation is significantly reduced. An on-grid version of the grid evolution technique is then developed to nonuniformly refine the grid, thereby reducing the computational complexity while retaining reasonable accuracy. Numerical simulations and experimental results demonstrate that, compared to state-of-art methods, the proposed method achieves higher efficiency and better DOA estimation performance in the presence of strong interference. [ABSTRACT FROM AUTHOR]

This document is a retraction notice from AIP Advances regarding four manuscripts that have been retracted due to evidence of manipulation in the publication and peer review processes. The editors of AIP Advances have determined that critical steps in the peer review process were manipulated, including the return of identical reviewer reports and author-suggested reviewers requesting revisions to add citations to unrelated works by the authors. As a result, the validity of these papers has been called into question and they are considered potentially unreliable. The authors maintain that the data support the validity of the papers, but the editors believe that the issues with the peer review process undermine confidence in their validity. [Extracted from the article]

This paper proposes a method to reduce the computational cost of the spectral division method that synthesizes moving sources. The proposed method consists of two approximations: that of the secondary source driving function and that of the trajectory of the moving sources. Combining these two approximations simplifies the integral calculations that traditionally appear in the driving functions, replacing them with a correction of the frequency magnitude and phase of the source signals. Numerical simulations and subjective experiments show that the computational cost can be reduced by a factor of 50–100 compared to the conventional method without significantly affecting the synthesized sound field and the sense of localization. [ABSTRACT FROM AUTHOR]

Personal Sound Zone (PSZ) allows listeners to enjoy their individual sound without being disturbed by sound from other zones. Acoustic contrast, signal distortion, and array effort are the most frequently used metrics for measuring the performance of a PSZ system. However, usually, the three metrics cannot be optimized at the same time. A trade-off between the three metrics has to be made when designing a PSZ system. In this paper, two generalized methods based on multi-objective optimization are proposed for dealing with all possible trade-off problems between the three metrics in PSZ. Optimality analysis of the two proposed methods is taken, and the relationship between the two proposed methods is investigated. Numerical simulations are presented to validate the efficacy and flexibility of the two proposed methods. [ABSTRACT FROM AUTHOR]

This paper studies the thermal conduction of Frenkel–Kontorva (FK)-ϕ4 lattices with the finite number of atoms under a periodic force. Through numerical simulations, we find that in the thermal conduction of non-linear lattices, external periodic signals can act in conjunction with noise to create stochastic resonance behaviors and that some adjustable dynamical parameters, such as the onsite potential of the FK and ϕ4 lattices, the amplitude and frequency of external periodic signals, can regulate heat flux. Our study results can provide a sufficient theoretical basis for the fabrication of thermal devices and the control and utilization of thermal energy. [ABSTRACT FROM AUTHOR]

In the author's previous work, we introduced an open-source accelerated computational fluid dynamics code for scientific computations using a graphics processing unit system (OpenCFD-SCU). This code offers significantly improved computation speed and can be applied to challenging direct numerical simulation (DNS) problems. This paper presents several high-resolution cases using OpenCFD-SCU: (1) a 24° compression ramp at Mach 2.9, where the length of the ramp is 200 mm and the mesh number is 7.68 × 109; (2) a 34° compression ramp at Mach 6 with a mesh number of 9.3 × 109; (3) a cold-wall flat plate at Mach 10 with a friction Reynolds number of 1550 and mesh number of 4.5 × 109; (4) a blunt cone with a 1 mm head radius and 0° attack angle at Mach 10, where the mesh number is 24 × 109; and (5) a lifting-body model at Mach 6 with a mesh number of 11.1 × 109. Compared with DNS studies of compressible wall-bound turbulent flow under similar conditions, these cases have larger computational domains, finer resolutions, or higher Reynolds numbers, demonstrating the simulation capability of OpenCFD-SCU and broadening the scope of DNS applications. We have conducted preliminary analyses of these cases and have established an open-access database to store these data. The source code of OpenCFD-SCU can be accessed at http://developer.hpccube.com/codes/danggl/opencfd-scu.git; this website also contains detailed database descriptions and data acquisition methods. [ABSTRACT FROM AUTHOR]

In this paper, the performance of silicon carbide (SiC) light-triggered thyristor (LTT) with a p-type NiO emitter region is analyzed through numerical simulation. The conductivity modulation in SiC LTT is significantly enhanced with the help of high injection efficiency of holes in NiO/SiC heterojunction. The injected hole density at the surface of the p− long base is increased by ∼21.2 times and the corresponding specific on-state resistance (Ron,sp) is only 36.7 mΩ cm2, which is reduced by about 29%. Moreover, hole-injection enhancement by NiO/SiC heterojunction also exhibits excellent potential in improving the dynamic characteristics of SiC LTTs. The simulation results indicate that the turn-on time of SiC LTT can be reduced by ∼57.76% when triggered by 1.0 W/cm2 ultraviolet light. Furthermore, energy dissipations of SiC LTT during the turn-on and turn-off processes can be reduced by 91.4% and 21.9%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a far-field enhanced-resolution underwater ultrasonic imaging on the basis of a single-slit structured planar focusing lens. The iterative angular spectrum approach was employed to optimize the planar focusing lens from a designated focal pattern, characterized by focal length and full width at half maxima. Numerical simulations and experimental investigations were conducted on different target objects. Compared to the conventional method, both results showed that the performance of far-field ultrasonic imaging was comprehensively enhanced with the proposed planar focusing lens, in terms of resolving capability, working distance, operational bandwidth, and robustness. The single-slit structured planar focusing lens is cost effective and easy to fabricate, which would greatly benefit ultrasonic imaging and drive new applications of ultrasound in various scenarios. [ABSTRACT FROM AUTHOR]

Toroidal droplets are inherently unstable in viscous oils; they either shrink to a single drop or break into several spherical droplets due to Rayleigh–Plateau instability. In this paper, the breakup dynamics of toroidal droplets in immiscible viscous oils have been numerically investigated. A two-dimensional model combined level-set method is proposed. Numerical results reveal that the initial aspect ratios, interfacial tensions, and outer liquid viscosities play important roles in determining the breakup dynamics of toroidal droplets. The initial aspect ratios dominate the number of split droplets, which is consistent with a linearly scaling law n = 0.57 R0/a0. By considering key factors of interfacial tension in this process, it is found that interfacial tension is crucial in the initial morphology of the toroidal droplet and helps to retard the unstable breakup dynamics. Interestingly, reducing the interfacial tension stabilizes it against breakup. We further study the effect of viscosity on the breakup dynamics. The surrounding viscous oils contribute to stabilizing the interfacial-tension-driven instabilities and extending the breakup time. Thus, for a toroidal droplet in high viscosity oils and a sufficiently low interfacial tension system, the unstable breakup dynamics could be delayed. Our findings provide a novel fundamental understanding of toroidal droplets and are beneficial to applications involving the manipulation of toroidal droplets. [ABSTRACT FROM AUTHOR]

One of the techniques to improve the underwater acoustic stealth performance of ships is to use the wide-spectrum characteristics of chaotic signals to weaken the line spectrum of radiated underwater acoustic signals. To modulate the signal in an expected way, this paper proposes a criterion for constructing a bidirectionally coupled system based on the original system, which enables the response system and the drive system to achieve generalized chaotic synchronization with the desired manifold and gives a method to determine the reliable interval of coupling coefficients. The simplified criterion is suitable for constructing a unidirectionally coupled system. Taking the Chen system and Chua's circuit as examples, the reliable interval of coupling coefficient is deduced by using the proposed criterion. Bidirectionally coupled chaotic systems are constructed for the desired linear manifold and nonlinear manifold, and the validity of the construction method and the criterion is verified by numerical simulation. [ABSTRACT FROM AUTHOR]

Underwater platforms provide long-term detection of undersea targets. In this paper, we propose a method for the estimation of target motion parameters by submerged static acoustic detection equipment. The proposed method is based on the Radon transform of modeling the target moving in a uniform straight line. The heading angle, the time to the closest point of approach (CPA), and the ratio of velocity to the horizontal range of the target at the CPA to the sensor are obtained by applying the generalized Radon transform (GRT) to bearing–time records. The velocity of the target is determined by applying the GRT to the line-spectrum–time records. Furthermore, the motion trajectory of the target with respect to the detection equipment can be calculated from the above parameters. To validate the feasibility and performance of the proposed method, computer simulations and sea trials based on a fixed single vector measurement system were analyzed in this paper. The results suggest that the proposed method can accurately estimate the motion parameters and can calculate the trajectory of the moving vessel along a straight line at constant velocity. [ABSTRACT FROM AUTHOR]

Large eddy simulations and Ffowcs Williams–Hawkings acoustic analogy methods have been adopted to simulate the flow-induced noise for variable cross-section pipelines under variable flow velocity conditions in this paper, and the main influencing factors of flow-induced noise are analyzed numerically, including the flow velocity and variable diameter angle. Results manifested that the flow field distribution, sound source characteristics, and frequency spectrum characteristics of the sound pressure level (SPL) at different flow velocities follow similar trends. The average acoustic source intensity increases gradually with the increase in flow velocity. The maximum of the acoustic source intensity is located near the outlet of the variable diameter angle due to the vortex effect. The flow-induced noise in variable cross-section pipelines is mainly low-frequency noise, and its energy is mainly concentrated below 200 Hz according to the frequency spectrum characteristics. Additionally, the SPL increases with the increase in flow velocity. Compared with v = 1 m/s, the SPL at v = 2 m/s and v = 3 m/s increases by 9.4% and 22.1%, respectively. In addition, there is an approximate linearly increasing relationship between the SPL and the variable diameter angle. The minimum of the SPL appears at φ = 15.2°, and the maximum appears at φ = 25.7° at different flow velocities, which is up to 70.18 dB. Briefly, the flow-induced noise characteristics, including the average acoustic source intensity, the SPL, and the frequency spectra, are revealed in this paper. This provides a theoretical basis for the optimization of variable cross-section piping systems and the investigation of flow-induced noise control techniques. [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]

Air gap thickness significantly affects the detonation reliability of explosive trains. This paper mainly studies the detonation reliability of explosive trains with a micro-sized air gap. First, the detonation process of the JO-9C mild detonation cord initiating the 1.7 g/cm3 JO-11C booster is simulated by the AUTODYN software, and the critical air gap thickness is obtained between 0.32 and 0.40 mm. Second, a test device for explosive trains with adjustable air gap thickness is designed based on the numerical simulation results, and the adjustable step length of the air gap thickness is 0.0625 mm. Finally, a small sample evaluation method that does not depend on the standard deviation of the sensitivity distribution is proposed, and only 86 test samples are needed to verify the detonation reliability of 0.9999 at 0.1 mm air gap thickness. The test device designed and the small sample evaluation method proposed can be referred to for the detonation reliability evaluation of explosive trains with a micro-sized air gap. [ABSTRACT FROM AUTHOR]

The internal flow of hydrodynamic retarder is a three-dimensional, complex, viscous, and unstable gas–liquid two-phase flow. The importance of numerical simulation of a hydrodynamic retarder has been paid attention to, but the research on the two-phase flow pattern of the retarder is rarely. Flow pattern diagnosis plays an important role in the study of two-phase flow because the premise of establishing the mathematical model of the two-phase flow is to accurately determine the flow structure of the flow system. Based on the numerical simulation and experimental research, this study found the corresponding relationship between the two-phase flow distribution inside the hydrodynamic retarder and the filling rate (expressed as "q"). The result shows that, when q = 0.1–0.2, the liquid in the working chamber is less. Under the action of centrifugal force, the liquid mainly gets distributed in the outer ring of the circulating circle, forming a laminar flow. When q = 0.3–0.4, the flow pattern of the gas–liquid two-phase flow changes from the laminar flow to slug flow. When q = 0.5–0.9, with a further increase in the filling ratio, the flow becomes a dispersed bubble flow. This paper provides an effective method for the analysis and identification of the two-phase flow pattern of a hydrodynamic retarder. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of a periodic suction-blowing excitation on the aerodynamic sound generated by a laminar flow past a square cylinder using the direct numerical simulation approach. The periodic suction-blowing excitation has been prescribed on the top and bottom surfaces of the square cylinder. The proper orthogonal mode decomposition (POD) technique has been used to find information about important modes associated with disturbance pressure fields. The POD technique separated the contribution of the dominant lift dipole equivalent sources and the drag dipole equivalent sources to the disturbance pressure field for the no-excitation case. The POD technique also revealed that the periodic suction-blowing excitation introduced an additional monopole equivalent sound source and a drag dipole equivalent sound source due to periodic enhancement and reduction of the body's effective cross-sectional area. Modifications in the sound field due to changes in excitation amplitude, forcing frequency, and the phase delay between the excitation and vortex shedding process have been studied in detail. Although no significant changes in the flow field were noticed due to a small amplitude of excitation, the directivity of the sound field was significantly altered. The sound fields have been classified into five distinct zones for different periodic suction-blowing excitation frequencies. The beats of sounds were noted when the forcing frequency of excitation and the Strouhal frequency associated with vortex shedding were sufficiently close. It is observed that the in-phase excitation in which either blowing or suction is applied on both surfaces of a cylinder at a particular instant introduces a significant bias in the sound field directivity. The interaction between the lift dipole equivalent sources due to vortex shedding and the monopole and the drag dipole equivalent sources due to excitation introduces a bias in the sound field directivity. As a result, a dominant sound field is observed either in the top-left or in the bottom-left parts of the domain. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on rotating detonations in a hollow combustor with the slit-orifice nozzle. The experimental results reveal that the propagation speed of detonation waves increases with the rise of mass flow rates and is greater than the Chapman–Jouguet detonation speed (VC−J). Furthermore, numerical simulations of rotating detonation in a non-premixed three-dimensional cylindrical combustor have been conducted based on a multispecies reacting code. The influence of two mixing schemes—that is, slit-orifice and coaxial injector—on detonation waves are studied to determine whether the characteristics of detonation waves tend toward high-frequency combustion instability due to changes in the mixing scheme. It is found that the slit-orifice scheme's detonation speed, pressure, and temperature are significantly higher than those of the coaxial injector scheme. In particular, the detonation speed of the former reaches 124% of the VC−J, while that of the latter is only 80.5% of the theoretical value. The numerical results reveal that the low-speed detonation is caused by the deterioration of the hydrogen (H2)/air mixing conditions. Moreover, the flow-field structures of two mixing schemes were comparable, both containing transverse detonation waves, oblique shocks, contact surfaces, and wedge-shaped reactant regions. Furthermore, the Rayleigh index analysis showed that the unsteady heat release was in phase with the pressure fluctuations, amplifying the pressure. Therefore, it is suggested that high-frequency combustion instability may be a manifestation of rotating detonation waves under poor mixing conditions. [ABSTRACT FROM AUTHOR]

A landslide is a kind of geological disaster, which seriously threatens the production and lives of people around it. In collapsible loess areas, landslides occur more frequently. There are many cracks at the edge of the loess platform. This paper studies the relationship between the characteristics of cracks at the edge of the platform and the stability of the loess platform slope through numerical simulation. It is found that some cracks will eventually form a through sliding surface and form a landslide, while some cracks are relatively safe for the time being. According to the calculation results, the statistical formula is obtained to reveal the relationship between them, which is helpful to predict the loess platform landslide according to the cracks at the edge of the tableland in the future. [ABSTRACT FROM AUTHOR]

Metasurfaces have shown excellent ability in manipulating light fields. However, the intrinsic chromatic aberration impairs the quality of their broadband operation, which is a serious problem restricting the application of metadevices, especially metalenses. In this paper, a polarization-independent broadband achromatic metalens composed of engineered structures that have spatially varying gradient sizes is devised to focus the light over the mid-infrared region from 3 to 5 µm. The proposed dielectric metalens is constructed by an array of meta-units with a hollowed square pillar. By tuning its structural parameters, the optical response of the meta-unit turns out to be broadband achromatic, insensitive to the polarization state, and of high efficiency. Numerical simulation results show that the designed metalens can significantly suppress chromatic aberrations over a broad mid-infrared and hold a focusing efficiency of nearly 75%. Our work is beneficial to improving the mid-infrared broadband imaging quality and detection efficiency. [ABSTRACT FROM AUTHOR]

In order to address the problem of dust pollution at the transfer point of the coal transportation system, this paper carries out a numerical simulation on the dust diffusion law of the coal transportation system. The simulation results show that the dust concentration at the three openings in the transshipment point is the highest, and the farther away from the transshipment point, the lower the dust concentration. Depending on the simulation results, a pneumatic spray dust reduction scheme can be proposed by performing a field experiment. Based on the controlling variable experiments and existing studies, the parameters of pneumatic spray can be stated in the following way: the flowing rate should be laid out at 0.7 l/min, with its air velocity being 25 m/s and the working pressure being 0.6 MPa. The entire spray scheme can be verified through the computer simulation process. Thus, it can be calculated and determined that the spray scheme should be installed with four nozzles at the anterior end of the lower belt guide trough, with one nozzle at the back end and two nozzles at the upper belt feeding point. Eventually, the scheme has to be validated by the field experiments. Thus, the consequences of the on-spot experiment and test show that the scheme we have suggested is in a position to reduce the dust concentration effectively in the entire area of the transshipment point, bringing about the dust reduction rate over 90%. [ABSTRACT FROM AUTHOR]

The large time step scheme, which is commonly used in hydrodynamic numerical simulation, adopts the multielement reconstruction method in order to improve both the computational efficiency and accuracy; however, this results in numerical oscillation and calculation divergence. Therefore, it is necessary to develop methods to suppress the occurrence of numerical oscillation near the discontinuities. The numerical oscillation that is induced can be suppressed by using the random choice method (RCM) with the van der Corput random number sequence. In order to optimize the suppression performance, error analysis has been carried out in this paper for the calculation results from the RCM with the popular van der Corput random sequence combinations for selecting the optimal sequence combination. In order to further eliminate any short-wave numerical oscillations near the discontinuities, a method that combines the RCM with a nonlinear filter, which often used in aeroacoustic calculations, has been proposed in this paper to suppress short-wave oscillations. Specifically, the RCM and the nonlinear filter method were sequentially implemented in order to process the calculation results at each time step. The results showed that this method had a good suppression effect on the numerical oscillations near the discontinuities, which was demonstrated by the numerical experiments. [ABSTRACT FROM AUTHOR]

This paper proposes an approach to reconstruct the time-dependent forces acting on a vibrating structure from pressure measurements. In the approach, the pressures measured in the near field of the structure are related to the exciting forces at the reconstruction points by the transfer functions determined in an experimental way, whereupon the time-dependent forces can be reconstructed with these pressures as inputs. In the reconstruction process, an additional regularization with a mixed lp,q-norm term is introduced to resolve the ill-posed inverse problem, which is able to take advantage of the prior knowledge of space and time characteristics of the forces. A numerical simulation of reconstructing the time-dependent forces acting on a plate and two experiments of reconstructing the impact forces acting on a semi-cylindrical shell and an elliptically shaped structure are carried out. The results demonstrate the feasibility of the proposed approach for reconstructing the forces in both temporal and spatial domains from pressure measurements. The proposed approach provides a non-contact and real-time way to identify the locations of forces and reconstruct their time histories, which can be further used to reveal the mechanical cause of the radiated noise. [ABSTRACT FROM AUTHOR]

Nucleate boiling is an essential heat exchange method in industry. Due to the complicated mechanisms of the boiling process, prediction of its heat transfer performance has always been challenging. Studying the growth and heat transfer characteristics of a single bubble is of great significance for understanding the internal mechanisms of nucleate boiling. In this paper, single bubble growth in saturated pool boiling was numerically studied. The microlayer evaporation at the bubble base was calculated and added to the simulation via UDFs. The effects of contact angle, wall superheat, and microlayer initial thickness distribution were investigated. The results show that a thinner microlayer has a greater evaporation rate, resulting in an increased bubble growth rate and departure diameter. The bubble growth rate, departure time, and departure diameter increase with the increase in the contact angle and wall superheat. As the wall superheat increases, there is a competition between microlayer evaporation and phase interface evaporation, which ultimately leads to an extremum of the total contribution of microlayer evaporation to bubble growth. The heat transferred by microlayer evaporation accounts for at least 67.3% and up to 83.6% of the bubble's latent heat at departure, indicating that microlayer evaporation has a significant impact on bubble growth. [ABSTRACT FROM AUTHOR]

This paper proposes a binaural-centered mode-matching (BCMM) method that performs sound field reproduction with two reproduction points, one at each ear. A sound field reproduced by higher-order Ambisonics converges to the target field around a sweet spot whose size is inversely proportional to the frequency when the truncated order of the spherical harmonic expansion is constant. By contrast, BCMM translates the spherical harmonic coefficients on the basis of the addition theorem to realize two reproduction points at both ear positions. The BCMM method thereby avoids degradation of reproduction due to a smaller sweet spot at higher frequencies, as occurs with the conventional method, and thereby, leads to an accurate reproduction at higher frequencies. A comparison of numerical simulations of the binaural signals obtained when rendering with BCMM and conventional methods shows that, compared with the conventional method, the BCMM method improves the reproduction accuracy. [ABSTRACT FROM AUTHOR]

The laser-triggered vacuum switch (LTVS) is a type of high-voltage closing switch with broad application prospects in pulsed-power technology. Research into the triggering process of the LTVS is not only helpful to understand the triggering mechanism of the LTVS but also beneficial to the optimization of the LTVS. In this paper, the triggering process and the delay time of a LTVS with a Ti–KCl mixture target was analyzed theoretically. A numerical simulation was performed to describe the laser-target ablation process and the expansion dynamics of the initial plasma. The simulation results were compared with the experimental results. It is clear that the triggering process and delay time strongly depend on the laser intensity. As the laser intensity rises, the velocity of initial plasma increases, resulting in a shorter delay time of the LTVS. Increasing the gap voltage can also shorten the delay time. [ABSTRACT FROM AUTHOR]

This study is aimed at predicting the characteristics of vibration and sound radiation of violins and understanding the relationships among the properties of its wood, vibration, and sound radiation. Numerical simulations of the vibration mode of a violin body are performed, and the sound radiated by it are analyzed using the finite element method. The geometry of a real violin is scanned using a micro-computed tomography scanner, and the orthotropic properties of spruce and maple, such as Young's modulus, rigidity modulus, and Poisson's ratio, are set as the parameters of the numerical simulation. The main vibration modes, such as A0 and center bout rotation, and the acoustic pressure level around the violin body are calculated. This paper describes the influence of the density and longitudinal stiffness on the eigenfrequencies and sound radiation. [ABSTRACT FROM AUTHOR]

Due to the extremely complex changes in marine environmental factors and frequent changes in the actual load current of the submarine cable, it is necessary to analyze and study the mechanical and thermal characteristics of the high-voltage submarine cable system under different conditions to ensure the reliability of the power transmission performance of the submarine cable. In this paper, the finite element model is adopted to study the physical parameters of the submarine cable, taking burial depth, ambient temperature, and current as dependent variables. Some of the parameters related to the environment refer to the ocean currents near Zhoushan, and the model bases on the actual current and temperature data of the 500 kV AC submarine cable. The results show that in order to increase the load capacity of the submarine cable and reduce the thermal strain of the submarine cable, the heat dissipation of the submarine current should be increased, so the buried depth should be appropriately reduced. After the ambient temperature rises, in order to reduce the loss of electric energy and cable deformation, the carrying current should be reduced moderately. The research carried out a simulation based on the actual physical parameters of each layer of the submarine cable and predicted the changes in the submarine cable in Zhoushan with different current carrying capacity in different seasons, so it has reference significance in actual engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents an analytical investigation of the drain current model for symmetric short channel InGaAs gate-all-around (GAA) MOSFETs valid from depletion to strong inversion using a continuous expression. The development of the core model is facilitated by the solution of the quasi-2D Poisson equation in the doped channel, accounting for interface trap defects and fixed oxide charges. Correction to short channel effects such as threshold voltage roll-off, drain induced barrier lowering, and subthreshold slope degradation is later introduced, complemented with channel length modulation, velocity saturation, and mobility degradation from surface roughness, leading to accurate mobile charge density for electrostatic capacitance–voltage and transport characterization. The effect of physical process parameters such as fin width, oxide thickness, and channel length scaling is thoroughly investigated in both on and off states of the transistor. The robustness of the model is reflected by the precise match with published experimental reports in the literature. An Ron of 1160 Ω μm is obtained from output characteristics and a switching efficiency improvement of 2.5 times is estimated by incorporating a high-κ dielectric into the GAA transistor. Numerical 3D simulations from TCAD corroborate the validity of the proposed model in all regions of operation. [ABSTRACT FROM AUTHOR]

Waterbomb structures are origami-inspired deformable structural components used in new types of robots. They have a unique radially deployable ability that enables robots to better adapt to their environment. In this paper, we propose a series of new waterbomb structures with square, rectangle, and parallelogram base units. Through quasi-static axial and radial compression experiments and numerical simulations, we prove that the parallelogram waterbomb structure has a twist displacement mode along the axial direction. Compared with the square waterbomb structure, the proposed optimal design of the parallelogram waterbomb structure reduces the critical axial buckling load-to-weight ratio by 55.4% and increases the radial stiffness-to-weight ratio by 67.6%. The significant increase in the radial stiffness-to-weight ratio of the waterbomb structure and decrease in the critical axial buckling load-to-weight ratio make the proposed origami pattern attractive for practical robotics applications. [ABSTRACT FROM AUTHOR]

This paper presents an approach on stability analysis of cable-driven parallel robots (CDPRs) considering cable mass based on cable tensions and stiffness matrix condition numbers. A cable model is introduced considering the effect of cable mass. A stiffness model is established based on the cable model. Then, the stiffness matrix condition numbers are presented. Furthermore, the stability of CDPRs is discussed. Numerical simulations show that the stability is better in the center and at the top of the whole workspace than in other places, which agrees well with theoretical predictions. The mixed evaluation stability indices considering cable mass and neglecting cable mass are, respectively, compared. The results show that cable mass is not negligible when evaluating accurately the stability of a cable-driven parallel robot. [ABSTRACT FROM AUTHOR]

As effective representations of complex systems, complex networks have attracted scholarly attention for their many practical applications. They also represent a new tool for time series analysis. In order to characterize the underlying dynamic features, the structure of transformed networks should be encoded with the systematic evolution information that always hides behind the time series data. Thus, the way of mapping segments of the time series into nodes of the network is particularly crucial, but it is liable to be unstable under noise and missing values. In this paper, we propose a coarse-graining based on statistics of segments (CBS) founded complex network method, which can make it immune to interference to a certain degree. The time series is divided into many segments by a slide window, of which the width is determined by the multi-scale entropy of the data. We use a multi-dimensional symbol to represent the motion state of every segment. Due to the utilization of the distribution information of the fragments' numerical characteristics, the coarse-graining process is self-adaptive to some extent. The complex network is then established based on the adjacent relations of the symbolic sequence. With our method, the differences in the network measurements between the periodic and chaotic motion is easily observable. Furthermore, we investigated the robustness of CBS by adding noise and missing values. We found that CBS is still valid, even with strong noise and 15% missing values, and simulation shows that it is more robust than the VG and LS approaches. By mapping a time series into a complex network, we provide a new tool for understanding the dynamic evolution mechanism of a complex system. This method has been applied in various fields, such as physics, engineering, medicine and economics. However, the interference of noise may greatly affects the reliability of judgment, which is based on the structures of transformed networks. An insufficient robustness is mostly to blame for the transformation from a time series to a symbolic sequence. In this paper, we suggest a new approach to the coarse-graining process which is self-adaptive for threshold choosing. Simulations show that even with strong disturbances, our network structure is easily distinguishable under different dynamic mechanisms. [ABSTRACT FROM AUTHOR]

To realize multi-band mode conversion in a high-power microwave incoherent power combination system, a tri-band conversion system (at X-, Ku-, and Ka-bands) is proposed in this paper. The tri-band conversion system mainly consists of three parts: a dual-band multiplexer, a circular waveguide with a 90° bend, and a tri-band mode converter. To investigate the mode coupling characteristics in the system, every part is carefully analyzed and verified. Numerical and simulation results show that the final conversion efficiencies of the conversion system are 98.9% [coaxial transverse electromagnetic (TEM) mode–coaxial TE11 mode at 10.16 GHz], 99.1% (coaxial TEM mode–coaxial TE11 mode at 14.45 GHz), and 99.6% (circular TM01–circular TE11 at 30.5 GHz). Meanwhile, its maximum power handling capacities reached 1.5 GW, 957.6 MW, and 726.2 MW. The good agreement between theoretical analyses and simulation results demonstrates that the proposed tri-band system is feasible in high-power microwave applications. [ABSTRACT FROM AUTHOR]

This paper presents a method to characterize the effective properties of inertial acoustic metamaterial unit cells for underwater operation. The method is manifested by a fast and reliable parameter retrieval procedure utilizing both numerical simulations and measurements. The effectiveness of the method was proved to be self-consistent by a metamaterial unit cell composed of aluminum honeycomb panels with soft rubber spacers. Simulated results agree well with the measured responses of this metamaterial in a water-filled resonator tube. A sub-unity density ratio and an anisotropic mass density are simultaneously achieved by the metamaterial unit cell, making it useful in implementations of transformation acoustics. The metamaterial, together with the approach for its characterization, are expected to be useful for underwater acoustic devices. [ABSTRACT FROM AUTHOR]

For the study of the double wave configuration for the dynamic power cable of a Floating Offshore Wind Turbine (FOWT) in shallow water, this paper presented a comparison of the hydrostatic and hydrodynamic performance between a lazy wave and a double wave configuration. The double wave shape's parametric presentation was first developed based on an extension of a previous parametric lazy wave shape. An aero-hydro-servo-elastic integrated model fully coupling the FOWT and the dynamic power cable was then proposed in the SIMO/RIFLEX code for numerical simulation. Subsequently, the strain-cycle curve and the rain flow counting method were employed to estimate the copper conductor's fatigue damage. The bending moment was proved to provide the major fatigue contribution. The results showed that the double wave offered superior performance than the lazy wave. The second arc of the double wave configuration was proved critical for suffering high curvature, tension, and fatigue damage. A lower position and less hogged wave arc were suggested for the determination of the double wave shape. [ABSTRACT FROM AUTHOR]

The hot-spot temperature of a dry-type air-core reactor is a crucial factor that determines the service life of the reactor. Although the environment elevation has a significant influence on the reactor's heat dissipation performance and hot-spot temperature, studies seldom focus on the temperature distribution for different altitude scenarios. To this end, this paper proposes a temperature field simulation model with multi-parameter coupling constraints based on the laminar–turbulent flow state. The calculation of the temperature field with the hot-spot temperature at different altitudes is finally achieved. The simulation results show that the hot-spot is located at 6.3% from the top of the sixth encapsulated-winding. It also shows that the hot-spot temperature of the reactor increases by 5 K–11 K with the altitude ascending by 1 km. Moreover, the hot-spot temperature of the reactor exceeds the temperature index at an altitude of 3.25 km, which will result in a shortened service life. Fiber Bragg grating temperature sensors are embedded in encapsulated-windings to detect the temperature for verifying the validity of the temperature field model, which could provide critical temperature rise evaluation rules for the operation safety of the dry-type air-core reactor. [ABSTRACT FROM AUTHOR]