Low Speed Conditions Research Articles

Automotive Steering System and Its Controller Design for Intelligent Vehicles

<div>With the rapid development of intelligent vehicles technology, it is extremely urgent to solve environmental pollution and energy crisis. The electric intelligent vehicles technology can accelerate the world to move towards low carbonization and intelligence. In this article, one automatic steering system and its controller are designed with this electric vehicle as the verification platform. First, based on the digital mock-up (DMU) module of the CATIA digital prototype, the motion simulation of the automatic steering system is carried out. Then, the transient dynamics and fatigue analysis module from ANSYS Workbench 16.0 software is used to simulate and analyze the transmission mechanism. After verifying the reasonable strength of the real vehicle parts, the original platform steering system is reformed. Our intelligent vehicle uses a monocular charge-coupled device (CCD) to detect road marking lines and then employs a linear two degrees of freedom (2-DOF) vehicle model to establish a preview deviation model based on the visual navigation lane lines. A vehicle lateral control method combining fuzzy logic rules, adaptive proportional-integral-derivative (PID) control strategy, and preview deviation is designed. A lateral controller is built using Simulink software for lane tracking simulation, and a good tracking effect is obtained. Finally, the results of low-speed real vehicle tests show that the vehicle can stably track the target lane line at low-speed conditions.</div>

A Novel Geometry Optimization Approach for Multi-Recess Hydrostatic Bearing Pad Operating in Static and low-Speed Conditions Using CFD Simulation

The design of a hydrostatic bearing pad is limited to simple geometry using analytical equations or one-parameter optimization based on experimental data. This study proposes and investigates a new two-parameter method for estimating optimal hydrostatic bearing pad proportions—recess area and position, using Computational Fluid Dynamics (CFD). In this study, 3D static CFD quarter model of a multi-recess hydrostatic bearing pad assuming laminar flow is used. The CFD model was calibrated based on experimentally obtained results and the literature. The recess pressure and resulting load are evaluated for a variety of recess positions and areas. Performance factors are calculated and interpolated in the MATLAB environment. Using the proposed novel two-parameter optimization, the energetic loss was reduced by 20% compared to the classical one-parameter approach. This methodology allows versatile and effective design of optimal hydrostatic bearings operating in low-speed conditions to achieve minimum energetic loss.

Research on Tunnel-Boring Machine Main Bearing Fatigue Damage and Vibration Response

Based on the damage evolution equation of bearing steel, a user subroutine was developed to simulate the fatigue damage behavior of the TBM main bearing under the condition of low speed and heavy load. In addition, the damage evolution law of the main bearing in the time domain and the space domain was studied. Then, a nonlinear spring element was introduced to simulate the interaction between the roller raceway, and the vibration response of the TBM after the main bearing damage was studied using the transient dynamic method. The research shows that the damage risk of the raceway is greater than that of the roller, and the damage risk of the main pushing raceway is greater than that of the other two raceways. The damage of the main bearing will not only lead to the increase in the peak vibration response of the TBM but also cause more frequency components of the response. By monitoring the time domain index of vibration signal, the damage degree to the main bearing can be mastered in real time, providing a reference for the maintenance of the main bearing.

The Influences of Different Parameters on the Static and Dynamic Performances of the Aerostatic Bearing

Aerostatic bearings have been widely applied to high-rotating speed machines due to their low friction and high rotational speed advantages. The geometry parameters, supply pressure and rotational speed play important roles in the static and dynamic performances of the aerostatic bearings. In this paper, the steady state and dynamic Reynolds equations are solved by the finite difference method (FDM) and used to study the static and dynamic performances of the aerostatic bearings. Then, combined with the motion equation of the rigid rotor-aerostatic bearing system, the linear stability of the aerostatic bearing is also studied. Moreover, based on the theory mentioned above, the influences of the geometry parameters (such as orifice diameter, radial clearance and eccentricity), rotational speed and supply pressure are investigated in detail. It was found that aerostatic bearing geometries, rotational speed and supply pressure had a significant effect on the steady and dynamic performances. Under the low-speed conditions and high supple pressure, the static pressure effect plays the main role in the performances of the aerostatic bearings, while on the contrary, the rotational effect plays the main role. Furthermore, a half-speed whirl may generate under certain conditions. The results also provide useful design guidelines for aerostatic bearings in high-speed machines.

Simulation Study of Fuel Concentration Field in Common-rail Diesel Engine Combustion Chamber under Plateau Environment

China has the largest plateau in the world, with an average altitude of 2000m-4500m. Due to the decrease of atmospheric pressure and temperature, the decrease of air density and the decrease of water boiling point, resulting in a decrease in power, economy, low temperature starting and cooling, soot emissions and other performance, soot emissions increase, the diesel engine can not accord with the requirements of plateau areas in the plateau area. Fuel concentration field of diesel engine has important influence on its dynamics, economy and emissions. The paper uses numerical simulation to study the fuel concentration field of combustion chamber in the plateau environment of CA6DL2-35E3R common-rail diesel engine. The results show that altitude has great impact on fuel concentration field of combustion chamber, and fuel concentration field increases with the increase of altitude, and compared with high speed condition, more fuel is distributed at the bottom and top of the combustion chamber under low speed condition.

The effects of geometry parameters on the aerodynamic performance of CFJ airfoil used by a STOL transport

With the purpose of investigating the effects of geometry parameters of CFJ (Coflow jet) device on the aerodynamic characteristics of the supercritical bacj airfoil used by a STOL transport, we have carried out a computational analysis of CFJ airfoil with different values of injection slot size and location under the low-speed condition. The results show that the lift coefficient decreases gradually with decreasing stall angle, when the injection slot size is increased. When α=8°, with increasing injection slot size, the velocity of blowing jet decreases with decreasing power consumption and increasing aerodynamic effectiveness. Further, with the injection slot shifted towards the downstream direction, the α value corresponding to the maximum effective lift-drag-ratio increases with increasing maximum lift coefficient.

Simulation and Optimization for Position Servo Control System of Switched Reluctance Motor

Switched reluctance motors are widely used in household appliances, textile machines, electric vehicles, and other fields due to their simple structure, low cost, high reliability, high efficiency, large starting torque, and wide speed regulation range. With the continuous expansion of the application field of SRM, higher requirements are put forward for the design of the motor position servo control system. The control system should be highly accurate and easy to deploy and have strong anti-interference. Based on the traditional switched reluctance motor control method, this paper designs a feedforward control position loop and applies CVC control at low-speed conditions to optimize the accuracy, anti-interference, and torque ripple characteristics of position servo control. The simulation results prove that the design results of the servo control system are correct and effective.

Correction of the IRD Influence for Paleo‐Current Flow Speed Reconstructions in Hemipelagic Sediments

AbstractReconstructions of past changes in deep‐sea current intensities are needed to understand ocean‐climate interactions in the past. The mean size of the sortable silt fraction (10–63 μm, ) is one of the most used proxies in this domain. However, in polar and subpolar environments under relatively low flow speed conditions, the presence of Ice‐Rafted Detritus (IRD) may alter the record and thus bias the interpretation of paleo‐current strength changes. In this paper, we examine the influence of IRD on the record of three sedimentary cores from the subpolar North Atlantic and the Antarctic margin. The influence of unsorted IRD on records is clearly established. To remove this IRD influence on grain‐size distributions (GSDs), we propose a new method based on End‐Member Analysis approach, and for which a MATLAB script is made available. This method characterizes the GSD of the unsorted IRD input, allowing it to be isolated and discarded, and the current sensitive variability to be robustly identified. The method therefore allows the recalculation of a modified sediment GSD free of unsorted IRD influence and the construction of modified and sortable silt percentage (the % of the 10–63 μm in the total <63 μm fraction) records. The application of the method to the three studied cores shows that (a) the unsorted IRD component is correctly removed from the grain‐size signal and (b) the new record is consistent with the XRF‐based ln(Zr/Rb) grain‐size proxy.

Feature Recognition on Friction Induced Vibration of Water-Lubricated Bearing under Low Speed and Heavy Load

Under low speed and heavy load operating conditions, the marine water-lubricated bearing (WLB) is often in a mixed lubrication state. This leads to abnormal friction-induced vibrations and noise in underwater vehicles. An empirical mode decomposition (EMD) based method for identifying friction-induced vibration characteristics of WLB was proposed, and friction-induced vibration experiments of WLB were carried out. The results showed that the specific pressure and lubricant temperature significantly affected friction-induced vibrations while the cooling water flow hardly had an effect. Studying the monotonicity of the eigenvalues of IMF energy, time-domain standard deviation, bias angle, and center of gravity frequency can visualize the trend of the bearing friction-induced vibration signals. Among them, the critical point of friction-induced vibrations could be analyzed by the inflection point of IMF energy, standard deviation, bias angle, and the sudden increase of the center of gravity frequency. The study results were valuable for revealing the friction-induced vibration mechanism of WLB and providing an important reference for design optimization.

Multifunctional carbon/epoxy composites with power transmission capabilities

This study evaluates the power transmission of multifunctional composites with embedded conductors. The electrical conductors were constructed by braiding copper strands with Para-aramid fibers into a tape configuration, then placing these tapes within carbon/epoxy prepregs to create a multifunctional structure. Experiments were performed on these multifunctional composites under tensile loading conditions. During experimentation, the conductive tapes were incorporated within an electrical bridge to record their resistance change as a function of mechanical strain. The Digital Image Correlation (DIC) technique was used to obtain in-plane displacements and strains as a function of time. In addition, low-speed flight condition experiments with an airfoil shape composite system were carried out in a wind tunnel to study the temperature performance of these structures while under high currents. Computational models were then created to expand the experimental efforts and evaluate the system’s multiscale performance. Experimental results show that the mechanical load on the conductive tape is mainly carried by the Para-aramid yarns, leading to a relatively consistent electrical performance and airflow over the wind foil providing efficient power transmission. Lastly, the computational models showed consistency in the electrical/mechanical results and established a framework for analyzing multi-functional structures (MFS).

Experimental and numerical study on the mixed lubrication performances of a new bearing

The traditional water-lubricated bearings are difficult to form effective lubricating film under extreme low-speed and heavy-duty conditions, resulting in the low-load, high-resistance, high-vibration and high-noise shortcomings. The deep-physical mechanisms are not clear. The paper investigates the mixed lubrication performances and critical characteristics for water-lubricated bearings under extreme conditions. A novel multi-field coupling lubrication model is proposed. The functional mapping relationships among lubrication performances, the critical characteristics and the influencing factors are developed. The rotor dynamic models considering surface micro-topography are built. The variation mechanisms of the dynamic behaviors are revealed. The theoretical analysis is consistent with experiment, which proves the model and algorithm’s correctness. The academic value of the paper is expected to achieve a novel breakthrough in formation of effective hydrodynamic film under extreme severe conditions for such bearings.

Structural health dynamic monitoring for gear transmission based on guided waves

The rotating machinery has a wide range of applications in many fields. The gear transmission system is one of the key structures of rotating machinery. Once the failure occurs to the gear system, it will destroy the equipment itself and lead the whole industrial production to break. Thus, it is necessary to directly monitor the health condition of the gear system under static and running working conditions. Guided waves method is a technology which has been widely used in the field of structural health monitoring. In this paper, guided waves technology is innovatively applied to the condition monitoring of gear system, which realizes the gear structure direct monitoring for low speed rotating machinery. The piezoelectric transducers integrated with the SMART Layer were placed near the gear mesh region for the direct health monitoring. The feasibility was verified by the guided waves monitoring experiments in a fixed-axis spur gear transmission system. The tooth wear and gear crack were monitored by guided waves under a single working condition. In addition, the stability verification experiment of guided waves was also performed under various low-speed working conditions. To characterize the propagation of gear faults, considering the characteristics of guided waves, a modified health indicator extraction methodology is proposed based on permutation entropy. The results indicated that the guided waves technology has fantastic potential applications in gear transmission system dynamic direct health monitoring.

Attitude Control of Vehicle Based on Series Active Suspensions

When vehicles with traditional passive suspension systems are driving in complex terrain, large swing and vibrations of the car body make passengers and goods uncomfortable and unstable, even at very low-speed conditions. Considering the actual need for intelligent resource exploration in the sustainable economy, visual-based perception and localization systems of unmanned vehicles still cannot handle the sensor noise coursed by large body motions. In order to improve the stability and safety of vehicles in complex terrain, an attitude control system is proposed for mainly eliminating the external body motions of the vehicle by using series active suspensions. A model predictive control method considered the differences between the simulated and real vehicle, and the performance restrictions of actuators are used to design the attitude controller for reducing the heaving, pitching, and rolling motions of the vehicle. After simulations and real car tests, the results show that the proposed attitude controller can significantly improve the attitude stability of vehicles in harsh terrain.

Comparison of Aerodynamic Loss of a Gas Turbine Vane with Various Trailing Edge Cooling Schemes

In this study, a comparison of aerodynamic loss of gas turbine vane with various trailing edge configurations was experimentally performed. For the trailing edge, three cooling schemes (the cutback slot, the central injection slot, and the pressure side hole) and three levels of trailing edge diameter (7.5, 10.0, and 12.5% of the throat width, respectively) were considered. The total pressure loss was measured in a five-vane linear cascade at the low-speed mainstream condition (20 m/s) using a Kiel probe and a two-axis traversing device. The measurement region was constrained to the near mid-span region, and the measurement step size was 1 mm. The results showed that the distribution of the total pressure loss was strongly affected by cooling schemes. The vane with the pressure side hole showed a similar distribution to that of the baseline in which a cooling scheme was not applied. It was also shown that the total pressure loss increased as the trailing edge diameter increased regardless of the cooling schemes. Except for the cutback slot cases, there was an inflection point at which the tendency of the area-averaged total pressure loss to the blowing ratio was changed. Through the present study, correlation equations for each cooling scheme were derived against the trailing edge diameter and the blowing ratio.

A Trajectory Compensation Method Considering the Car-Following Behavior for Data Missing of Millimeter-Wave Radar in Roadside Detection Applications.

Concerning roadside traffic detection applications, and to address the millimeter-wave radar's missing data problem caused by target occlusion or the absence of features in low-speed conditions, this paper proposes a trajectory compensation method regarding car-following behavior. Referring to the installation scheme of the detector, a coordinate transformation method is presented to unify the radar spatial coordinates with the road coordinates. Considering the driver's car-following behavior, the optimal velocity model (OV), full velocity difference model (FVD), and the full velocity difference and acceleration (FVDA) model are applied for tracking the vehicle's trajectory related to the movement of the vehicle ahead. Finally, a data compensation scheme is presented. Taking actual trajectory data as samples, the proposed methods are verifiably useful for compensating for missing data and reconstructing target trajectories. Statistical results of different missing data trajectories demonstrate the rationality of the application of car-following models for the missing data compensation, and the FVDA model performs well compared with the OV and FVD models.

Investigation of high-speed deep well pump performance with different outlet setting angle of space diffuser

As one of the important equipment for pumping groundwater, how to improve the operation performance of deep well pump has been a research hotspot. At present, most of the deep well pump hydraulic design research mainly focuses on the low speed condition, and there is still a lack of systematic research on the internal flow theory and design method of the high speed deep well pump. In this paper, numerical simulation is used to investigate the performance change law of high speed deep well pump under different space diffuser blade outlet setting angles, and the performance test of the design scheme model is used to verify the accuracy of numerical simulation. The hydraulic loss inside the space diffuser and the velocity moment at the outlet are quantitatively analyzed. The results shown that the outlet setting angle of 90° is a relatively optimal solution. Under the designed outlet setting angle, the hydraulic loss in the first-stage space diffuser decreases with the increase of the flow rate, and the average hydraulic loss in the space diffuser at all levels fluctuates between 16% and 20%. With the increase of the number of stages, the velocity moment at the outlet of the space diffuser also increases gradually, and the change trend of the velocity moment at the outlet of the first-stage space diffuser under different outlet setting angles is relatively consistent. This research can provide reference for the optimal design and application of high speed deep well pump.

Effects of a simplified drilling protocol at 50 rpm on heat generation under water-free conditions: an in vitro study.

In recent years, guided implant surgery has been widely used for the convenience of patients and surgeons. Further streamlining the surgical procedure would make implant surgery more convenient. Low-speed water-free conditions are often used in guided implant surgery. Therefore, in this study, we attempted to confirm once again whether drilling was safe at a low speed without water. The main purpose of this study was to evaluate whether a simplified drilling protocol that omits some intermediate steps in the drilling process was safe from the viewpoint of heat generation. D1 density artificial bone blocks were drilled under 50 rpm, 10 N·cm water-free conditions, and the surface temperature was measured using a digital infrared camera. First, drilling was performed with the sequential drilling method, which is the most widely used technique. Second, for each drill diameter, the temperature change was measured while performing simplified drilling with omission of the previous 1, 2, or 3 steps. In sequential drilling, the heat generated during drilling at all diameters was less than the critical temperature of osteonecrosis (47°C) except for the ⌀2 drill. Statistical significance was observed in all groups when comparing sequential and simplified drilling in the ⌀3.2, ⌀3.8, and ⌀4.3 drills (P<0.001). However, in the simplified drilling procedures, the temperature was below the osteonecrosis threshold temperature (47°C) except for the ⌀4.3 drill with the omission of the previous 3 steps (⌀3.0, ⌀3.2, and ⌀3.8). In general, drilling under low-speed, water-free conditions has shown stable results in terms of heat generation. Simplified drilling showed statistically significantly greater heat generation than sequential drilling. However, most of the diameters and omitted steps seem to be clinically acceptable, so it will be useful if an appropriate selection is made according to the patient's clinical condition.

Low-speed finite element frontal impact analysis on aluminum alloy bumper made of 6063-T6

In this research, a low-speed impact numerical simulation has been performed on a 6063-T6 Aluminum alloy bumper welded by MIEA technique using ANSYS® LS-DYNA® Workbench™ 19.2, according to the requirements of the Federal Motor Vehicle Safety Standards and Regulations. For the numerical simulation, mechanical properties were obtained from quasi-static tensile tests in 6063-T6 aluminum alloy joints, these joints were manufactured using the MIEA (modified indirect electric arc) technique and a MIG welding process and post-weld heat treatment (PWHT). For the numerical impact simulation, the following parameters have been used: mass of the impactor of 1000 kg, speed of the impactor 4 km/hr and material of the impactor AISI 4130 steel. The simulation study showed that aluminum alloy joints used in bumper beam has excellent mechanical strength under low-speed impact conditions. Among the mechanical properties that have been recovered due to PWHT are the following: it was possible to harden the fusion zone, that is, there was an increase in hardness values from 80 HV0.1 to 98 HV0.1, the heat affected zone was eliminated, obtaining hardness values of approximately 110 HV0.1, a recovery in yield strength (59%) was observed, that is, in welding condition (170 MPa) and welding condition plus PWHT (270 MPa). In terms of tensile strength, a recovery (42%) was observed, going from welding condition (214 MPa) and welding condition plus PWHT (304 MPa). Tensile strength also had an increase ranging from 214 MPa to 304 MPa. This represents an increase of 42 pct. Finally, the simulation showed that the welding zone on the bumper has very good resistance to low speed impact since no permanent deformations were observed, that is, after the impact the bumper returns to its initial position.

Real-World Pipe-Out Emissions from Gasoline Direct Injection Passenger Cars

The analysis of real-world emissions is necessary to reduce the emissions of vehicles during on-road driving. In this paper, the matrix of gasoline direct injection passenger cars is applied to analyze the real-world emissions. The results show that high acceleration and high speed conditions are major conditions for the particulate number emissions, and the particulate number emissions are positively correlated with torque and throttle opening. The catalyst temperature and saturation are important factors that affect nitrogen oxide emission. The nitrogen oxide emissions of low speed and low torque conditions cannot be ignored in real-world driving. The carbon dioxide emissions are positively correlated with acceleration, torque and throttle opening. Once the vehicles are in the acceleration condition, the carbon dioxide emissions increase rapidly. The vehicles with higher average emission factors are more susceptible to driving behaviors, and the differences in the emission factors are more obvious, leading to an increase in the difficulty of emission control.

A Review on Up-to-Date Gearbox Technologies and Maintenance of Tidal Current Energy Converters

This paper presents a review-based comparative study of state-of-the-art technologies, technical challenges and research barriers, and development trends of gearboxes used in tidal current energy converters (TCECs). Currently, the development of commercial projects using TCECs is still in the demonstration phase. While many drivetrain designs and configurations of TCECs inherit from those of wind turbines, different operational constraints, e.g., high-torque and low-speed conditions, make TCECs potentially suffer from high failure rates in harsh deep-sea environments. Evidence of these potentially high failure rates highlights the need for adopting the most resilient drivetrain options with a high degree of maintainability. The gearbox option is a critical issue that needs to be addressed for the choice of the drivetrain configuration due to its longest downtime per failure among all drivetrain components of TCECs. The main purpose of this study is to review current gearbox technologies of TCECs with advantages and disadvantages as well as to identify future technical challenges and research barriers. Gearbox maintenance is also a focal point in this study. We present a discussion of the operation phase to highlight operational maintenance methods currently used in the tidal energy industry. This study will, therefore, address the critical issue by proposing a review-based gearbox option comparison and discussing potential solutions to reduce operation and maintenance costs of gearboxes of TCECs.