Steady-state Characteristics Research Articles

The Effect of a Linear Free Surface Boundary Condition on the Steady-State Wave-Making of Shallowly Submerged Underwater Vehicles

Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, the linearization of the free surface boundary conditions, is explored in this study by comparing the steady-state wave-making characteristics of a shallowly submerged prolate spheroid using two different simulation methods at several submergence depths and forward speeds. Hydrodynamic responses are compared between a time-domain boundary element method that makes use of a linearized free surface boundary condition and an inviscid, volume of fluid Reynolds-Averaged Navier–Stokes computational fluid dynamics code that imposes no explicit free surface boundary condition. Differences of up to 22.6%, 32.5%, and 33.3% are found in the prediction of steady state surge force, heave force, and pitch moment, respectively. The largest differences between the two simulation methods arise for motions occurring at small submergences and large wave-making velocities where linear free-surface assumptions become less valid. Nonlinearities that occur in such cases are revealed through physical artifacts such as wave steepening, wave breaking, and high-energy waves. A further examination of near-surface viscous forces reveals that the viscous drag on the vessel is depth dependent due to the changing velocity profile around the body.

Particle-in-cell modeling of electron beam generated plasma

Plasmas generated using energetic electron beams are well known for their low electron temperature (T e) and plasma potential, which makes them attractive for atomic-precision plasma processing applications such as atomic layer etch and deposition. A 2-dimensional particle-in-cell model for an electron beam-generated plasma in argon confined by a constant applied magnetic field is described in this article. Plasma production primarily occurs in the path of the beam electrons in the center of the chamber. The resulting plasma spreads out in the chamber through non-ambipolar diffusion with a short-circuiting effect allowing unequal electron and ion fluxes to different regions of the bounding conductive chamber walls. The cross-field transport of the electrons (and thus the steady-state characteristics of the plasma) are strongly impacted by the magnetic field. T e is anisotropic in the electron beam region, but low and isotropic away from the plasma production zone. The plasma density increases and the plasma becomes more confined near the region of production when the magnetic field strengthens. The magnetic field reduces both electron physical and energy transport perpendicular to the magnetic field. T e is uniform along the magnetic field lines and slowly decreases perpendicular to it. Electrons are less energetic in the sheath regions where the sheath electric field repels and confines the low-energy electrons from the bulk plasma. Even though electron and ion densities are similar in the bulk plasma due to quasi-neutrality, electron and ion fluxes on the grounded chamber walls are unequal at most locations. Electron confinement by the magnetic field weakens with increasing pressure, and the plasma spread out farther from the electron beam region.

Control strategy study for a heat pipe cooled nuclear reactor

The heat pipe cooled nuclear reactor (HPR) features simple structure, high safety, low noise, compact structure and long working time. HPR is therefore a better candidate energy source for deep space and underwater applications. Due to the unique features, the dynamics of HPR are different from conventional nuclear reactors. It is necessary to investigate the control strategy. In this study, an HPR system code HEART is coupled with 3KeyMaster to build the HPR simulation platform using the shared memory technology. Steady state and transient characteristics of HPR are obtained in the platform and analyzed. The control strategy with reactor power, heat pipe temperature and electric power controlled is proposed. The control systems are built and tuned on the simulation platform. Typical transient tests are performed to evaluate the performance of the control systems. The simulation results demonstrate that the proposed control strategy can meet control requirements on the power maneuvering and reactor startup.

Boron-Related Defects in N-Type 4H-SiC Schottky Barrier Diodes.

We report on boron-related defects in the low-doped n-type (nitrogen-doped) 4H-SiC semitransparent Schottky barrier diodes (SBDs) studied by minority carrier transient spectroscopy (MCTS). An unknown concentration of boron was introduced during chemical vapor deposition (CVD) crystal growth. Boron incorporation was found to lead to the appearance of at least two boron-related deep-level defects, namely, shallow (B) and deep boron (D-center), with concentrations as high as 1 × 1015 cm-3. Even though the boron concentration exceeded the nitrogen doping concentration by almost an order of magnitude, the steady-state electrical characteristics of the n-type 4H-SiC SBDs did not deteriorate.

Development and verification of helium–xenon mixture cooled small reaction system

Although Helium–Xenon mixture cooled small reactor has been widely concerned, there is no mature thermal calculation software that can be applied to Helium–Xenon mixture cooled small reactor in China. In this paper, a semi empirical formula used to predict the physical properties of binary inert gas mixtures is used to establish a physical property calculation model of Helium–Xenon mixture gas mixtures, and the flow and heat transfer calculation model, turbine model and compressor model are modified and improved, so as to achieve the calculation of the Brayton cycle system. The function of the original system analysis program is expanded and improved, and the simulation program for he xenon mixed gas reactor system is developed. At the same time, the closed Brayton cycle system is established by using the system analysis program developed in this paper, and the calculation results are compared with the design values. The maximum relative error is 6.9%. The steady-state operation results of the model are in good agreement with the design operation parameters, which proves the applicability of the improved simulation model. The steady-state response characteristics analysis, the introduction of positive and negative reactivity accidents and the calculation of transient conditions such as step load drop of the reactor were carried out. The overall trend is the same as the literature survey results. The results show that the system analysis program developed in this paper is suitable for the analysis of the Brayton cycle system of Helium–Xenon mixture cooled small reactor.

Experimental and analytical study on the stability of a low aspect ratio single-phase natural circulation loop coupled to a parabolic trough collector

Use of passive heat transport systems in renewable energy eliminates operator and external power requirements, thereby reducing the cost. Hence, a horizontal heater and horizontal cooler rectangular natural circulation loop (NCL) of low L/D (110) and aspect ratio (0.54) is coupled to a parabolic trough in the present work. Experimental investigations of the loop's steady state and stability characteristics were carried out at various powers corresponding to the solar irradiances using water as the heat transfer fluid. SolTrace was used to determine the heat loads at different direct normal irradiance (DNI) for the selected loop and trough dimensions. The upper threshold for stability was experimentally observed for the first time and reported here. Stability analysis carried out for different loop diameters revealed that the power at which the upper threshold of instability occurs reduces significantly with increase in loop diameter, enabling its observation in the low-pressure low temperature loop employed in the present study. Stabilizing techniques like orifice insertion and loop inclinations were also studied in detail. The results showed stability at higher heat loads (> 350 DNI), while the instability at lower heat loads can be curbed using an orifice (β = 0.5) or a loop inclination (> 4°). The small inclination can eliminate multiple steady state solutions and hence stabilizes the loop. Besides, the reduction in natural circulation flow rate with inclination is much smaller compared to the orifice making its heat transport capability higher. Additionally, the steady state results were validated with 1-D analytical model giving a good match.

Experimental and numerical simulation of shock train characteristics in an isolator with incident shocks

To better comprehend the steady-state structure and dynamic characteristics of shock train flow fields under interactions with incident shocks, wind tunnel experiments investigating the shock train flow fields in a supersonic isolator with incident shocks were conducted. High-speed schlieren visualization with multiple knife edges, surface tuft visualization, and high-frequency wall pressure measurements were used to analyze the shock train flow fields in the primary and corner regions. The understanding of the flow mechanism was enhanced based on additional three-dimensional steady numerical simulations. Flow field asymmetry was observed when the shock train interacted with parallel incident shocks. The shock train leading edge comprised a longer shock, which traversed the entire channel, and a shorter shock, with flow separation extending downstream of the longer shock. The flow downstream of the shorter shock passed through a small separation bubble before reattachment. The flow field was symmetrical when the shock train interacted with crossed incident shocks. Stronger oscillations were observed in the symmetric shock train owing to the adverse pressure gradient created by the incident shock and the inconsistent flow parameters downstream of the shock. The downstream propagation of the pressure fluctuation caused by the oscillation of the shock train leading edge was revealed based on coherence and phase analyses. The flow separation initiated further upstream in the corner region than in the primary region of the shock train flow field, and the separation flow covered a larger proportion of the flow field. These differences were enhanced by increasing the incoming Mach number.

Transformer-Less Soft-Switching High-Gain PWM Boost Converter With Reduced Components and Increased Effective Duty Cycle

A transformer-less soft-switching high-gain pulsewidth-modulation (PWM) converter is proposed in this article. The proposed converter is derived from a single-switch dual-inductor transformer-less boost converter by replacing the complementary diode connected to the switch with a synchronous rectifier switch. Moreover, the peak value of the reverse current of the rear-end inductor in continuous bidirectional conduction mode (CBCM) is regulated to exceed the input inductor valley current. Based on these two measures, the zero-voltage switching (ZVS) for all switches and the natural turn-off for the output diode are realized, and the effective duty cycle is enhanced. Besides, the proposed ZVS converter has the merits of fewer power components count, reduced voltage stress, and lower cost. Furthermore, the ringing issue in the original topology under light load or high input voltage conditions is eliminated. The operation principle, steady-state characteristics, dynamic model, soft-switching operation, and realization conditions are analyzed in detail, and subsequently, the parameter design method is elaborated. The proposed topology demonstrates an enhanced efficiency performance over wide operating operations with a maximum efficiency of 97.1%.

Analysis of Voltage Characteristics for Single-Phase Line Break Fault in Resonant Grounding Systems

With the rapid transition of overhead lines to covered conductors, line break fault occurs more frequently in resonant grounding systems. Line break fault, especially with earthing, requires comprehensive study. There are significant advantages for the detection of line break fault using steady-state voltage characteristics on both sides of the fault point. In this paper, a model is built for different types of single-phase line break fault in resonant grounding systems. Based on the fundamental analysis of single-phase line break fault without earthing, the single-phase line break fault with earthing at system/load side is also comprehensively studied. The neutral voltages are derived from the proposed model. The magnitudes, angles, and phase sequences of the three-phase voltages and line-to-line voltages are mathematically derived for both upstream and downstream of the fault point. The difference between single-phase line break fault and single-phase-to-earth fault is identified. The analysis is verified in the simulations. Built upon the analysis in this paper, the detection and location approaches for line break fault in resonant grounding systems can be further studied.

Sensorless Starting Control of the Brushless Synchronous Starter/Generator by Using the Main Exciter as a Quasi-Resolver at Low Speed

The main generator (MG) and the main exciter (ME) are mounted on the same shaft in the brushless synchronous starter/generator (BSSG). Besides, the internal high-frequency signals, caused by the rotating rectifier, exist in the rotor windings of ME. These mechanical and electrical features of BSSG indicate that the sensorless starting control of MG could be conducted with ME. However, the existing research of this strategy is limited to extract rotor position information from the steady-state characteristics of the rotor currents of ME and consequently has not fully exploited the potential. In this paper, a dynamic sensorless starting control method of MG by using ME as a quasi resolver is proposed. Firstly, the injection mechanism of the excitation signals in the rotor of ME and the characteristics of the induced back electromotive force (EMF) in the stator of ME in different commutation modes are analyzed to clarify the dynamic operating principle of the quasi resolver. Then, back EMF estimation based on extended state observer is presented and an envelope extraction method is proposed. According to the envelope features of the back EMF, a software-based resolver to digital conversion method is proposed. Finally, the effectiveness of this method is verified by experiments.

Transient and periodic steady-state characteristics of the local heat transfer measurement by thermal perturbation with Gaussian power density distribution

The local heat transfer coefficient measurement with temperature oscillation induced by periodic thermal perturbation – usually via a Gaussian laser beam, was investigated for the impact of the spikiness (i.e., the standard deviation) elaborated in comparison with the analytical model for dimensional analysis. The statistically more robust technique that relies on the linearity of the spatial phase distribution of the test point array was favored when the target Biot number approaches unity in terms of its order of magnitude. The preferred upper limit for thermographic scanning was discussed as the simplification of later data processing is concerned. Nonetheless, the time elapsed for an acceptable periodic steady state, which in principle leans to the higher end of the target Biot number spectrum in a log scale, indicates the benefit from the time series of pointwise temperature measurement – as in the conventional single-blow testing, where the effect of spikiness, as well as that of the location of individual test point, holds. Note that the vicinity as the target Biot number approaches unity was again observed with higher preference.

Optimized Cooperative Control of Error Port-Controlled Hamiltonian and Adaptive Backstepping Sliding Mode for a Multi-Joint Industrial Robot

Robot joints driven by permanent magnet synchronous motors (PMSM) often cannot have both superior accuracy and rapidity when they track target signals. The robot joints have fine dynamic characteristics and poor steady-state characteristics when the signal controller is used, or they have fine steady-state characteristics and poor dynamic characteristics when the energy controller is used. It is hard to make robot joints that have both superior dynamic and steady-state characteristics at once using a single control method. In order to solve this problem, the strategy of optimized cooperative control is proposed. First, an error port-controlled Hamiltonian (EPCH) energy controller and an adaptive backstepping sliding mode (ABSM) signal controller are designed. Second, an optimized cooperative control coefficient based on the position error of a robot joint is designed; this enables the system to switch smoothly between the EPCH energy controller and ABSM signal controller. Next, the strategy of optimized cooperative control is designed. In this way, robot systems can combine the advantages of the EPCH energy controller and the ABSM signal controller. Finally, simulation results demonstrate that using the strategy of optimized cooperative control gives robot joints outstanding control performance in terms of tracking accuracy and response rapidity.

Correlation of Volumetric Vaporsorption and Vapor Sensing Phenomenon of Flower-Like MoS2-Based Sensor

An innovative approach is reported with an aim to effectively correlate room temperature alcohol vapor (methanol, ethanol, and 2-propanol) sensing performance of flower-like MoS2 sphere-based devices with the corresponding vacuum volumetric vaporsorption study. Hydrothermally derived flower-like MoS2 sphere-based resistive devices were tested to detect the above species and the steady-state characteristics of the sensor (response magnitude and baseline drift) were directly and effectively correlated with the corresponding physisorption measurements carried out using Quantachrome Autosorb iQ. Response magnitude of the sensing layers having different porosity and effective surface area was duly predicted from the volume of adsorbed vapor species on the respective surfaces. Moreover, the baseline drift of the sensors was directly correlated with the amount of target species that remain chemisorbed. Considering rising and falling (transient characteristics) edges of the dynamic response curve, it was found that response time is predominantly governed by the physisorption phenomena, while the recovery is determined by both the mechanism (physidesorption and chemidesorption), though later having relatively lower influence. The highest response magnitude ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 77%) was achieved for sensor originated from the highest deposition time (24 h) toward methanol. It was duly correlated with its highest Brunauer–Emmett–Teller (BET) surface area (10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula> /g) as well as its highest methanol adsorption at room temperature (116 cm3/g) among the lot. The highest baseline drift ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12^{\circ }{)}$ </tex-math></inline-formula> of 24-h deposited device was explained in the light of the highest open-loop gap (30 cm3/g).

Effect of lubricant inertia on steady-state characteristics of textured hydrodynamic journal bearing

PurposeThis paper aims to investigate the effects of inertia of the lubricant on the performance parameters of journal bearings textured with spherical-shaped textures.Design/methodology/approachThe lubricant is assumed to be Newtonian, and the flow is considered laminar. Considering the lubricant inertia effects, the modified Reynolds equation is discretized using the finite difference method and solved with the Gauss–Seidel successive over-relaxation scheme using the progressive mesh densification method.FindingsThe results from this numerical study indicate that the lubricant inertia improves textured journal bearing performance characteristics significantly. The improvement is more significant in the case of heavily loaded bearings. Furthermore, it is observed that protruded texturing in journal bearings shows better results compared to dimple textured journal bearings.Originality/valueUnderstanding the effect of lubricant inertia is essential for efficiently designing textured journal bearings. Thus, the results shown here would be helpful for the researchers and the bearing designers.

A novel steady-state corona characteristics simulation approach for a sharp rod-type static discharger based on the corona zone range iteration of electrode boundary

This paper presents a simulation approach to solve the steady-state corona model of a rod-type static discharger with a sharp tip. Based on the requirement of charge density distribution on the corona boundary, a novel iteration calculation method is proposed to automatically solve the corona zone range of the electrode boundary that cannot be predetermined for a sharp electrode. Moreover, a recursive calculation strategy that uses the corona convergence solution of some high-voltage parameters as the initial solution is employed to improve the computational stability and efficiency in scanning simulations with different voltage and wind speed parameters. Through the simulation and verification of a typical rod-type static discharger, we observed that the convergence is fast for the boundary range iteration, and the recursive calculation strategy is also effective. In addition, the volt–ampere characteristics and inception voltage obtained using the simulation were in good agreement with the measurement. Through simulation of a static discharger applied in a typical longitudinal wind field environment, we observed that the proposed approach is still effective at wind speeds up to hundreds of m/s.

Research on the vibration characteristics of an embedded elastic metamaterial plate

For a class of embedded elastic metamaterial plate, a general vibration analysis process is given based on the idea of equivalent analysis, which combines the equivalent medium theory and the classical thin plate vibration theory. The embedded elastic metamaterial plate is treated as an equivalent homogeneous plate with abnormal effective medium parameters by using the equivalent medium theory, and then the natural vibration characteristics and steady-state vibration characteristics are investigated. The results show that the semi-analytic form of the vibration analysis process is effective, which can obtain the vibration characteristics of such heterogeneous and complex structures quickly and accurately within the medium and low frequency regions. The results also reveal the plate’s anomalous behaviors that are quite different from the traditional homogeneous plates. For the natural vibration, there exists no natural frequency in the band gap and they can be formed only in the pass band. These modes tend to gather gradually when approaching the initial frequency of the band gap, and the closer to the lower band edge of the band gap, the smaller the distance between natural frequencies and the greater the modal density. Additionally, the modes of the corresponding orders before and after the band gap are identical on the macro level but completely different on the unit-cell level. For the steady-state vibration, there is no resonance peak in the band gap, the resonance peaks are distributed denser and denser when approaching the initial frequency of the band gap, and the distribution of the displacement field at corresponding order of resonance peaks before and after the band gap is also similar on the macro level. This work not only facilitates the design and analysis of elastic metamaterial plate structures, but also deepens the understanding of their extraordinary vibration characteristics and expands the design space of mode characteristics.

Tribological Properties of Glass Bead-Filled Polyamide 12 Composite Manufactured by Selective Laser Sintering.

To enhance the properties of polyamide 12 (PA12/Nylon 12) manufactured by the selective laser sintering (SLS) process, micron-sized glass beads are used as a filler, and the resulting composite is known as glass bead-filled PA12 (PA 3200 GF). Despite PA 3200 GF basically being a tribological-grade powder, very little has been reported on the tribological properties of laser-sintered objects based on this powder. As the properties of SLS objects are orientation-dependent, this study is devoted to investigating the friction and wear characteristics of the PA 3200 GF composite sliding against the steel disc in the dry-sliding mode. The test specimens were aligned in the SLS build chamber along five different orientations (X-axis, Y-axis, Z-axis, XY-plane, and YZ-plane). Additionally, the interface temperature and the friction-induced noise were measured. The pin-shaped specimens were examined using a pin-on-disc tribo-tester for 45 min to investigate the steady-state tribological characteristics of the composite material. The results revealed that the orientation of build layers relative to the sliding plane was a ruling parameter that determined the dominant wear pattern and the wear rate. Accordingly, where build layers were parallel or inclined to the sliding plane, abrasive wear predominated, and wear rate became 48% higher than that of specimens with perpendicular build layers, for which adhesive wear predominated. Interestingly, a noticeable synchronous variation of adhesion and friction-induced noise was observed. Taken together, the results from this study can efficiently serve the goals of fabricating SLS-functional parts with customized tribological properties.

Intelligent Dynamic Test System for Vehicle Engine Based on 5G Internet of Things

With the development of the automobile industry, the improvement of the reliability test level and the intelligent fault diagnosis level of the engine, as the heart component of the automobile and the assembly with the highest failure rate, becomes more and more important. In a context where technology is being upgraded, the development of intelligent automotive engine inspection system based on IoT thinking is set to become the major trend in the future. The objective of this article would be to have better knowledge about smart car engine system in the 5G IoT era. It is also through the study, a dynamic testing and characterization of the engine. The performance of the automobile engine, especially the dynamic performance, is further optimized. In this article, we focus on the PUMAOPEN test system of AVL and the system under test, the state management of the test process, and the intelligent transformation of key components. The results show that: studies and analyses the dynamic working conditions of intelligent vehicles on the Internet of Things, and compares the dynamic working conditions with the steady working conditions from qualitative to quantitative. By analyzing the influence of throttle opening change rate and speed change rate on dynamic performance and engine dynamic torque estimation, the fast sensing and response-ability in the engine testing process is improved. When the engine is accelerated by the experimental method presented in this article, and when the throttle opening is more than 30% and the engine speed varies at 100 and 200 rpm/s, the output value of the torque is higher than the output value of the steady-state torque or has little difference with the output value of the steady-state torque, and tends to be stable. In deceleration performance, the dynamic output torque of the engine is asymmetric. And it will deviate from the steady-state output torque, showing different dynamic response characteristics in different working sections. Throttle delay, overshoot characteristics, mechanical inertia, inflation coefficient, air–fuel ratio, and ignition advance angle when engine speed changes sharply will make engine dynamic characteristics deviate from steady-state characteristics.

Electromagnetic Performance Prediction of an Induction Machine Using an Improved Permeance-Based Equivalent Circuit Model Considering the Frequency and B–H Curve Dependent Core Loss Branches

Equivalent circuit models (ECMs) are extensively used in the prediction of steady-state performance characteristics of electric machines due to its simplicity and ease of implementation. In this article, permeance-based ECM is developed and improved by incorporating the machine's nonlinearities, and magnetic saturation. A recursive core loss model as a function of air gap voltage, considering <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B–H</i> hysteresis, eddy current, excess loss coefficients, and Steinmetz factor is developed to improve the accuracy of the electromagnetic performance prediction. Furthermore, an adaptive restart genetic algorithm is used to improve the accuracy of the coefficients and Steinmetz factor prediction over a wide range of frequencies and flux densities for both the stator and rotor. Moreover, skin effect is incorporated in the eddy current core loss to accurately consider the impact of varying frequencies and loadings. Finally, the proposed permeance-based ECM's calculated torque, core loss, and efficiency are experimentally validated using a prototyped squirrel–cage traction induction machine at various speeds and loading conditions. Toward net-zero carbon emissions, transportation electrification is a significant step requiring high–speed traction motors for electric vehicle application. Therefore, an accurate ECM is proposed that can successfully capture the frequency-dependent effects in the prediction of core loss, torque, and efficiency.

Short-Circuit Protection for Resonant Switched-Capacitor Converter

Short-circuit protection is critical and indispensable for resonant switched-capacitor converter (RSCC) to improve the reliability. Based on comparison of frequency control, duty ratio control and traditional variable frequency variable duty ration control (VFVDC-I), a novel variable frequency variable duty ratio control (VFVDC-II) is proposed for RSCC to suppress the short-circuit current. By analyzing the operation principle and short-circuit mechanism, the RSCC steady-state characteristics as well as the soft switching conditions under four methods are discussed. Then, the resonant characteristics of four methods are compared through state trajectory analysis. At last, the experiments are carried out to verify the correctness of theoretical analysis and feasibility of proposal method. The experimental results demonstrate that the proposed VFVDC-II avoids the voltage oscillation caused by narrow pulse and achieves the shortest transient response and the lowest peak resonant current at short circuit. Moreover, zero voltage switching is realized during turning on, which helps reduce the switching loss.