Stable Working Range Research Articles

Nonlinear vibration of a moving flexible printed electron web under multiphysics dynamics

Flexible electronic printing technology is a scientific technology that uses an “ink” material with conductive, dielectric, or semiconductor properties printed on a flexible web substrate to achieve precise preparation of flexible electronic devices, which are widely used in information, energy, medical, and military fields. In the preparation of the printing process of flexible printed electron webs under complex working conditions, the moving web will experience substantial unstable nonlinear dynamic behavior, such as divergence, flutter, bifurcation, and chaos. Accordingly, because of the coupling effects of the complex working conditions of the magnetic field, air and nonlinear electrostatic field forces, it is indispensable to explore the nonlinear dynamic equation of the flexible printed electron web in motion. The theory of multiphysics dynamics establishes a nonlinear vibration equation for the flexible printed electron web under multiphysics conditions. The discrete nonlinear vibration equation of state space equation was obtained by the Bubnov–Galerkin method. Utilizing the Runge–Kutta technique of the fourth-order, Poincaré maps, phase-plane diagrams, power spectra, bifurcation graphs, and time history diagrams of the moving flexible printed electron web were obtained. The influences of the velocity, electrostatic field, magnetic induction intensity, and follower force on the flexible printed electron web were analyzed. In addition, the Ansoft Maxwell finite element simulation software was used to simulate the magnetic field distribution of the moving web during roll-to-roll transmission. This paper determines the stable working range of the moving flexible printed electron web, which provides a theoretical basis for the preparation of flexible printed electronic webs.

Simulation of the effect of nonuniform fouling thickness on an axial compressor stage performance

This paper focuses on the numerical simulation of the flow status in the compressor with the condition of fouling. NASA stage 35 was considered as the object, and the commercial code ANSYS CFX was used. The deposition rate of contaminants on the surface was considered to be different along the height of the blade. A data from related study shows that the deposition rate of the contaminant on the side close to the hub is higher than the side near the shroud part. Based on the deposition law, this paper simulated the fouling of the compressor blades by changing the thickness on the blade surface. This subject only changed the thickness of the stator blade surface because of a data showing that the fouling on the stator blade surface is almost double that on the rotor blade surface. In the condition that the roughness value of the blade surface is constant, only the stable working range of the compressor is effected by the change of the surface thickness of the stator blade. There is a positive relationship between the value of compressor minimum flow rate and the value of thickness increment. After fouling the total pressure ratio and isentropic efficiency degenerated 1.59% and 3.76%, respectively.

Shift Strategy Optimization for Automatic Transmission of Heavy Trucks Based on Dynamic Programming Algorithm

The shift strategy of automatic transmission plays a vital role in the smoothness and economy of heavy-duty mining trucks. In this paper, an engine fuel consumption model, a 6 + 2 speed automatic transmission model, and a vehicle resistance model are built in MATLAB. Combined with the development of smart mining technology, the traditional two-parameter economic shift strategy is corrected based on vehicle load and road slope. The dynamic programming optimization algorithm is used to extract the best economical shift strategy under known working conditions to reduce the fuel consumption and the number of shifts. Finally, simulation experiments of the optimized shift strategy by dynamic programming in a typical mine work cycle are carried out. The simulation results show that the engine speed and output torque are maintained in a relatively stable and efficient working range by using the proposed shift strategy. Compared with the traditional two-parameter shift strategy, dynamic programming has advantages in reducing fuel consumption and shift numbers.

Influence of Tip Clearance on Flow Characteristics of Axial Compressor

This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum clearance for the stable working range. By analyzing the flow field in tip region, the role of the tip leakage flow is illustrated. In the zero-clearance model, the separation and blockage along the suction side is the main reason for rotating stall. As the tip clearance is increased to the optimum value, the separation is suppressed by the tip leakage flow. However, with the continuing increasing of the tip clearance, the scale and strength of the tip clearance vortex is increased correspondingly. When the tip clearance is larger than the optimum value, the tip clearance vortex gradually dominates the flow field in the tip region, which can increase the unsteadiness in the tip region and trigger forward spillage in stall onset.

The improvement of transonic compressor performance by the self-circulating casing treatment

The performance curve of the compressor is limited by the surge boundary, so it is of great significance to increase the stable working range of the compressor. The self-circulating casing treatment is an effective way to improve the stable working range of the compressor. In this paper, the study of the influence of the injector position of the self-circulating casing treatment on the transonic axial flow compressor rotor performance is carried out by using the numerical simulation. The influence mechanism of the injector position on the enhancing stability effect of the self-circulating casing treatment is revealed. It is found that the self-circulating casing treatment can reduce the blade tip blockage by restraining the blade tip clearance leakage flow and changing the trajectory of the tip clearance leakage vortex, thus delaying the deterioration of the rotor tip flow field and improving the rotor stability. When the injector position of the self-circulating casing treatment moves from the upstream of the leading edge of the blade tip to the trailing edge of the blade tip, the enhancing stability effect of the self-circulating casing treatment increases first and then decreases. But the high-velocity jet from the injector of the self-circulating casing treatment aggravates the mixing loss of the rotor tip flow field, so that the rotor efficiency slightly decreases after using the self-circulating casing treatment.

Theoretical model and experiment of the hybrid Maglev vehicle employing high temperature superconducting magnetic levitation and permanent magnetic levitation

The Maglev vehicle, widely considered as a promising transportation type, has distinct characteristics, such as high speed, environmental protection, non-contact operation and distributed load and so on. According to the principle of magnetic levitation technology, it can be divided into four types: Permanent magnet levitation (PML), electromagnetic levitation (EML), electrodynamic levitation (EDL) and superconducting magnetic levitation (SML). Among four Maglev technologies, both the SML with high temperature superconducting (HTS) bulks and the PML with conventional permanent magnets belong to the passive levitation mechanisms, and both of them need permanent magnet track. Due to the strong magnetic properties of permanent magnet materials, the load capacity of the PML can reach 3−6 t/m, but requires additional guidance controls, while the SML with the unique HTS flux-pinning effect can realize self-stable levitation with little active control. Therefore, considering the different levitation characteristics of the SML and the PML above the permanent magnet track, their potential hybrid application can achieve a larger load capacity and a bigger levitation gap at the same time. In the paper, a new SML-PML hybrid Maglev method and the corresponding theoretical models are proposed. Firstly, simulation models of the PML module and the SML module were built by finite element software. The simulation results show the different levitation performances of the two Maglev components. As to the SML module, it vertically behaves as the levitation force within the levitation height of 10−15 mm, and always achieves passive stable along the lateral direction. As to the PML module, the levitation force is relatively bigger at the calculated height of 20−60 mm, but the lateral force increases as the levitation height decrease and increases with the lateral displacement. It implies that the SML guidance capability should cover the PML lateral force at first. Hence, according to the Earnshaw theorem, the load capacity in typical working cases of the hybrid Maglev system was predicted from the simulation data. Considering the further lateral stability and the comprehensive levitation force utilization, the optimal passive stable working range and the lateral reversible range were discussed, which provide the theoretical basis for the design of the hybrid Maglev vehicle prototype. Then, based on the real magnet tracks of the HTS Maglev ring test line, the “Super-Maglev”, in our group, a new manned hybrid Maglev vehicle prototype employing the PML and the SML modules was manufactured for carrying one passenger. In the designed two-layer Maglev frame, the linear bearings composed of the linear guide rails and the sliders are employed for vertical decoupling to guarantee the position difference of the SML and PML modules. At the same time, the lateral coupling keeps rigid since the lateral unbalance is covered by the SML module. This easy and feasible mechanical coupling way enhances the matching complementarity of the lateral recoverability of the two Maglev components. Compared with the “Super-Maglev” performance under the same working condition, the load capacity of the hybrid Maglev vehicle was increased by 17% and the cost input was lower compared with the price of one single on-board HTS bulk. Finally, static loading experiments and dynamic characteristics tests verified that the hybrid Maglev vehicle has the advantages of strong load capacity, simple structure and low cost. This work provides a new technical scheme for future Maglev transportation applications.

Effectiveness of Variable Rotor Blades Technique&Variable Stator Vanes Technique in AdjustingAxial-flow Compressor

Multi-stage Axial-flow compressor is the main driver of continuous transonic wind tunnel and it usually has ultra-wide operating range. High performance wind tunnel generally requires its multi-stage axial-flow compressor has high economic performance and stability in its ultra-wide operating range. The combination of variable compressor rotational speed and variable geometry technique, variable rotor blades technique (VRBT) and variable stator vanes technique (VSVT), has been widely adopted in extending the stable working range with high efficiency of multi-stage axial-flow wind tunnel compressor. Adjusting Effectiveness was defined in this paper to quantify the effectiveness of VRBT and VSVT in extending stable and high aerodynamic efficiency operating range of wind tunnel axial-flow compressor under various operating conditions. The results show that the adjusting effectiveness of VRBT and VSVTis a function of reaction degree, flow coefficient, loading coefficient and the amount of loading coefficient change.

Influence of injection mode on the combustion characteristics of slight temperature rise combustion in gas turbine combustor with cavity

Interstage turbine combustors can be used to improve the thrust-to-weight ratio of gas turbines, but their operating conditions and technical requirements are obviously different from those of traditional gas turbine combustors. A typical feature of these combustors is the slight temperature rise combustion under the high velocity conditions of combustor inlets. In this study, a new type of interstage turbine combustor with high performance was proposed, and the influence of the injection mode on the combustion characteristics was investigated. Seven combustion modes with a trapped-vortex combustion zone and preheated fuel nozzles were designed. The effects of the average temperature of the combustion zone (changed by the air injection mode) and the combustion-zone temperature distribution (changed by the combustion-zone configuration) on the combustion characteristics, including the stable combustion boundary, the combustion efficiency, and the temperature distribution, were studied experimentally and numerically. The results showed that high-efficiency combustion in a wide, stable working range was achieved. The new combustor had a shorter length than the conventional combustor and had a wider lean blowout boundary compared to the same type of combustor. Based on the results, the optimal combustor configuration that could be used for practical applications in high-efficiency gas turbines was determined.

Unified discrete‐map modelling and dynamical behaviour analysis of current mode controlled tri‐state dc–dc converters

Through analysing the operating principle of current mode controlled (CMC) tri-state dc-dc converters, the inductor current borders are obtained and a unified discrete-map model of CMC tri-state dc-dc converters with ramp compensation is established. According to this model, the dynamical behaviour of the tri-state dc-dc converters is analysed by utilising bifurcation diagram. In addition, the boundary equation of tri-state dc-dc converters from stable pseudo-continuous conduction mode (PCCM) period-1 state to unstable state is derived. The expressions of the minimum slope of ramp compensation for the converter shifting from unstable state to stable PCCM period-1 state are also obtained. Meanwhile, the operating regions are divided effectively by the boundary equation. The research results indicate that border collision bifurcation could occur when the circuit parameters vary, including a bifurcation from one periodic orbit to another periodic orbit, such as period-1 to period-2 or period-2 to period-4 and so on, or a bifurcation from a period orbit to chaotic orbit. By using ramp compensation, the stable working range of the CMC tri-state dc-dc converter could be broadened. Finally, an experimental circuit is built and the experiment results verify the theoretical analysis.

Research on Performance Optimization of Multi-Stage Centrifugal Fan

The optimization of fan performance under changed conditions has important significance for the practical application of the fan. In view of the low efficiency of the original fan, the stable working flow span of the flow pressure curve is narrow, and it is difficult to meet the performance requirement after the working point change. Without changing the radial and axial dimensions of the fan, the performance of the original fan is optimized so that it increases from the total pressure 16153pa to 17271pa when operating flow 1900m3/h, meets the optimized target of total pressure 17000pa, the performance increases by 6.9%, and makes the stable working range of its pressure curve widen.

Effect of swirl field on the fuel concentration distribution and combustion characteristics in gas turbine combustor with cavity

The development of modern energy technology made more demands for the performance of the gas turbine, and more attention was paid to the engine's stability, efficiency and cleanliness. The technical level of combustor played an important role in the engine's efficiency and emissions issues. In order to broaden the stable working range and reduce emissions of the combustor, the fuel concentration distribution and combustion characteristics of trapped vortex combustor was numerically and experimentally analyzed in this study. The influences of swirl field and fuel injection mode were studied, and the research was conducted under the non-reaction condition and the reaction condition, respectively. Based on the numerical simulation results of fuel concentration distribution, a new type of trapped vortex combustor with centrifugal nozzles was designed, and the combustion characteristics of the combustor were experimentally evaluated. The results showed that a vertical double vortex structure could be formed in the cavity under various conditions. The air velocity of cavity inlet, the spray cone angle, and Sauter mean diameter of kerosene droplets had different effects on the liquid and gaseous fuel concentrations. High efficiency and low emissions combustion could be achieved, which was beneficial to improve gas turbine efficiency and reduce pollution emissions.

Nonlinear dynamical behaviors of a moving membrane under external excitation

In this paper, the nonlinear vibration characteristics of a moving printing membrane under external excitation are studied. Based on the Von Karman nonlinear plate theory, the nonlinear vibration equation of the axial motion membrane under the external excitation is deduced. The Galerkin’s method is used to discretize the vibration differential equations of the membrane, and then the state equation of the system is obtained. The state equation of the system is numerically solved by the fourth-order Runge–Kutta method. The relationship between the nonlinear vibration characteristics and the amplitude of external excitation, damping coefficient, and aspect ratio of the printing membrane is analyzed by using the time histories, phase-plane portraits, Poincare maps, and bifurcation diagrams. Chaotic intervals and the stable working range of the moving membrane are obtained. This study provides a theoretical basis for predicting and controlling the stability of the membrane.

Micro-UFO (Untethered Floating Object): A Highly Accurate Microrobot Manipulation Technique.

A new microrobot manipulation technique with high precision (nano level) positional accuracy to move in a liquid environment with diamagnetic levitation is presented. Untethered manipulation of microrobots by means of externally applied magnetic forces has been emerging as a promising field of research, particularly due to its potential for medical and biological applications. The purpose of the presented method is to eliminate friction force between the surface of the substrate and microrobot. In an effort to achieve high accuracy motion, required magnetic force for the levitation of the microrobot was determined by finite element method (FEM) simulations in COMSOL (version 5.3, COMSOL Inc., Stockholm, Sweden) and verified by experimental results. According to position of the lifter magnet, the levitation height of the microrobot in the liquid was found analytically, and compared with the experimental results head-to-head. The stable working range of the microrobot is between 30 µm to 330 µm, and it was confirmed in both simulations and experimental results. It can follow the given trajectory with high accuracy (<1 µm error avg.) at varied speeds and levitation heights. Due to the nano-level positioning accuracy, desired locomotion can be achieved in pre-specified trajectories (sinusoidal or circular). During its locomotion, phase difference between lifter magnet and carrier magnet has been observed, and relation with drag force effect has been discussed. Without using strong electromagnets or bulky permanent magnets, our manipulation approach can move the microrobot in three dimensions in a liquid environment.

Titanium Disulfide Coated Carbon Nanotube Hybrid Electrodes Enable High Energy Density Symmetric Pseudocapacitors

While electrochemical supercapacitors often show high power density and long operation lifetimes, they are plagued by limited energy density. Pseudocapacitive materials, in contrast, operate by fast surface redox reactions and are shown to enhance energy storage of supercapacitors. Furthermore, several reported systems exhibit high capacitance but restricted electrochemical voltage windows, usually no more than 1 V in aqueous electrolytes. Here, it is demonstrated that vertically aligned carbon nanotubes (VACNTs) with uniformly coated, pseudocapacitive titanium disulfide (TiS2 ) composite electrodes can extend the stable working range to over 3 V to achieve a high capacitance of 195 F g-1 in an Li-rich electrolyte. A symmetric cell demonstrates an energy density of 60.9 Wh kg-1 -the highest among symmetric pseudocapacitors using metal oxides, conducting polymers, 2D transition metal carbides (MXene), and other transition metal dichalcogenides. Nanostructures prepared by an atomic layer deposition/sulfurization process facilitate ion transportation and surface reactions to result in a high power density of 1250 W kg-1 with stable operation over 10 000 cycles. A flexible solid-state supercapacitor prepared by transferring the TiS2 -VACNT composite film onto Kapton tape is demonstrated to power a 2.2 V light emitting diode (LED) for 1 min.

Experimental investigation of an active control casing treatment of centrifugal compressors

This paper presents an experimental investigation of stability enhancement of a centrifugal compressor using an Active Control Casing Treatment (ACCT) system. In order to evaluate the effect of ACCT structure on the stability enhancement of centrifugal compressor, experiments were performed at different rotational speeds and various numbers of injection holes and mass flow of injected air by means of the centrifugal compressor test rig with a maximum rotational speed of 15,000rpm. The experimental results show that the stable working range of centrifugal compressor was extended by 32.73% with injection of 4.5% of design mass flow at an operating speed of 10,586rpm and by utilizing ACCT with 4 holes. It was found that the enhancement ability increases with the decrease in rotating speed and the injection of 4.5% of design mass flow. The pressure ration of the centrifugal compressor with ACCT was increased due to added momentum of injection air. The pressure ratio of the centrifugal compressor with 16 holes ACCT could be increased by about 1.72% at different mass flow of air injection when the rotational speed was 10,586rpm.

Bifurcation and chaos in high-frequency peak current mode Buck converter**Project supported by the National Natural Science Foundation of China (Grant No. 61376029), the Fundamental Research Funds for the Central Universities, China, and the College Graduate Research and Innovation Program of Jiangsu Province, China (Grant No. SJLX15_0092).

Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode (CCM) are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in iL–vC plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that, with the increase of reference current Iref, the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding Iref decreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller.

Regulating Effect of Asymmetrical Impeller on the Flow Distributions of Double-sided Centrifugal Compressor

AbstractTo achieve the rebalance of flow distributions of double-sided impellers, a method of improving the radius of rear impeller is presented in this paper. It is found that the flow distributions of front and rear impeller can be adjusted effectively by increasing the radius of rear impeller, thus improves the balance of flow distributions of front and rear impeller. Meanwhile, the working conversion mode process of double-sided centrifugal compressor is also changed. Further analysis shows that the flowrates of blade channels in front impeller are mainly influenced by the circumferential distributions of static pressure in the volute. But the flowrates of rear impeller blade channels are influenced by the outlet flow field of bent duct besides the effects of static pressure distributions in the volute. In the airflow interaction area downstream, the flowrate of blade channel is obviously smaller. By increasing the radius of rear impeller, the work capacity of rear impeller is enhanced, the working mode conversion process from parallel working mode of double-sided impeller to the single impeller working mode is delayed, and the stable working range of double-sided compressor is broadened.

Optical driven electromechanical transistor based on tunneling effect

A new electromechanical transistor based on an optical driven vibrational ring structure has been postulated. In the device, optical power excites the ring structure to vibrate, which acts as the shuttle transporting electrons from one electrode to the other forming the transistor. The electrical current of the transistor is adjusted by the optical power. Coupled opto-electro-mechanical simulation has been performed. It is shown from the dynamic analysis that the stable working range of the transistor is much wider than that of the optical wave inside the cavity, i.e., the optical resonance enters nonperiodic states while the mechanical vibration of the ring is still periodic.

A Numerical Study on the Effect of Bleed System on Starting Ability and Flow Performance of Rampressor Inlet

A unique supersonic compressor rotor with high pressure ratio, termed the Rampressor, is presented by Ramgen Power Systems, Inc., (RPS). Based on the models of Rampressor inlet, the inlet flow field with bleed system is numerically studied. Validation of the employed computational fluid dynamics (CFD) scheme is provided through test cases. The effects of boundary layer bleed location and bleed amount on Rampressor rotor inlet start and flow performance are analyzed. The results indicate that the boundary layer bleed has a significant effect for start and flow performance of Rampressor inlet. Boundary layer bleed technique has been applied to eliminate the emerging flow separation zone for enhancing Rampressor rotor inlet performance and enlarging its stable working range. The starting ability and flow performance of Rampressor inlet are efficiently improved by bleeding system, but the improvement effect is different for Rampressor inlet with different bleed location. Along the position of bleeding system moves forward, the range of Rampressor inlet normal work rotation speed is enlarged. The flow performance of Rampressor inlet improves obviously with the increment of bleed flow rate, and exit stability of Rampressor inlet enhances. And in the same back pressure work condition of Rampressor inlet, bleed system has been shown to be effective that exit stability of Rampressor inlet ameliorates, but the loss of compressed air from the bleed system has a negative effect on overall Rampressor inlet efficiency.

Influence of Dihedral Stacking on The Performance of An Axial Fan

This paper presents the effect of positive dihedral (lean) on the aerodynamic performance of a low speed axial fan. The blade profiles of the reference (base) fan are stacked on a radial line at the centre of gravity of each profile. The stacking line of the fan with the dihedral, along which the blade profiles are shifted in the direction perpendicular to the chordline, makes an angle of 45 in the radial direction. The performances of the both fans are investigated by means of ANSYS CFX commercial CFD software and are validated by experiments. Both of the computational and the experimental results show that positive dihedral removes the unstable operation region of the fan. Moreover, the total pressure rise and the total-to-total efficiency are increased at low flowrates. The detailed investigation shows that the induced radial velocity in the outward direction may be the reason of the positive effect of the dihedral at low flowrates. As a result, dihedral stacking extends the stable working range of the fan by removing the unstable region.