This study analyzes the dynamic characteristics of a three-speed uninterrupted powertrain automatic mechanical transmission (AMT) for an electric bus. The AMT structure reduces the power interruption during shifting. A Lagrange equation is developed for the three-speed uninterrupted powertrain AMT that includes the target vehicle performance characteristics. The model is solved in MATLAB/Simulink to compare the performance characteristics of the target vehicle with this three-speed uninterrupted powertrain AMT and without a transmission with simulations of the entire acceleration and deceleration ranges of the target vehicle. The model predicts the clutch and brake torque curves during shifting and predicts the drive motor input torque and final output torque. The dynamic equations are also used to verify the feasibility of power recovery during shifting. The results show that the three-speed uninterrupted powertrain AMT improves the vehicle dynamics of electric buses and maintains power during shifting.
A three-dimensional fluid-structure interaction (FSI) finite element model of a twin gas-chamber hydraulic damper was used to study the high-speed damping characteristics of the damper. The numerical results agreed well with experimental data. The damping characteristics were analyzed for various initial gas chamber volumes and initial pressures with comparisons with a single gas-chamber hydraulic damper. A single pressurized gas sub-chamber in the compression chamber of a monotube hydraulic damper results in more oil cavitation during the compression stroke. The twin gas-chamber hydraulic damper overcomes this problem but still has delayed reverse damping in both the compression and extension strokes. This problem can be reduced by using smaller gas chambers with higher initial gas pressures. The time delay ratio of the damping force reverse increases with increasing piston vibration frequency. The damping force reverse delay ratio in the compression stroke decreases with increasing piston vibration frequency (2.5~15 Hz) for the same vibration displacement, but this ratio in the extension stroke first increases (2.5~10 Hz) and then decreases (10~15 Hz) with increasing frequency. These characteristics are important when designing twin gas-chamber hydraulic dampers.
Drum brakes are a key safety component in heavy commercial vehicles, so they need accurate failure characteristic models. Drum cracking is the most common failure mechanism for drum brakes. This paper presents a coupled temperature-stress model for drum brakes that can obtain the dynamic stress curves for accelerated fatigue working conditions. Then, this paper fitted the relationship between the stress and strain of the material on the inner drum surface at high temperatures and used the former dynamic stress curves as the fatigue load. The Manson-Coffin-Basquin model was then used to predict the failure life of each point on the inner surface. This drum brake lifetime prediction method was then verified against accelerated fatigue test results. This model can include the effects of the load fluctuations on the drum during use, as well as the effect of the material performance degradation at high temperatures. This model is useful for optimizing engineering designs of drum brakes.
The influence of thermal error on machine tool processing accuracy was analyzed for a computer numerical control (CNC) horizontal lathe. Thermal error data was recorded using an infrared thermal imager, a displacement sensor and a temperature sensor to establish a thermal error model and a thermal error compensation system. Infrared thermal images and correlation analyses were used to optimize the locations of key temperature measurement points. Then, a linear regression thermal error model was developed for the main lathe axis in the radial direction (X direction). Tests show that the linear regression model is robust and suitable for thermal error modelling of the lathe. The linear regression model was then used to develop a thermal error compensation system based on a Siemens 828D CNC system and an S7-300PLC (programmable logic controller). Tests show that the radial thermal error of the shaft is reduced from the original 10 μm to less than 5 μm with the accuracy improved by more than 50%.
The voltage and current signals and arc images during arc ignition of tungsten inert gas - metal inert gas (TIG-MIG) hybrid welding were recorded using a data acquisition system and a high-speed camera. The data was used to study the effects of electrode polarity of the TIG welding and the MIG welding and the shielding gas type for the MIG welding on the arc ignition of TIG arc-assisted MIG welding. MIG welding with direct current electrode positive is necessary for TIG arc-assisted MIG welding to achieve non-contact arc ignition through an elongated discharge channel. TIG welding with direct current electrode negative or positive only affects the ease of non-contact arc ignition for TIG arc-assisted MIG welding. MIG welding achieves non-contact arc ignition because the electrons in the outer layer of the TIG arc move towards the end of the MIG welding wire where they collide with neutral particles in the surrounding shielding gas which ionizes some of them and generates many positively and negatively charged particles. The gap conductivity then significantly increases and the gap breaks down at low voltage. MIG welding with pure Ar shielding gas more easily achieves non-contact arc ignition than with Ar + 1% O2 (volume fraction) or Ar + 15% CO2 (volume fraction).
Lower limb exoskeletons can help paraplegic patients walk through rehabilitation. Powered exoskeletons do not require much muscle strength in the affected limbs, but the drive motors are rather large and heavy. Unpowered energy-storage exoskeletons do not require motors, but require more patient muscle strength which may cause fatigue during continuous use. This paper describes a clutched elastic actuator based on a ratchet mechanism that can be used as the hip joint driver for a lower limb of an exoskeleton. Patients rely on their upper limb and trunk muscles and crutches to slowly transfer the center of gravity during the support phase. The motor then stores energy during this motion in a torsional spring. During the swing phase, the torsional spring then quickly releases energy to help the patient step forward and complete a gait cycle. This paper presents a model for the driver during the support phase (spring energy storage) and the swing phase (spring energy release). The angular acceleration and deceleration are selected to minimize the peak power. Simulations show that the clutched elastic actuator significantly reduces the average power and the peak power compared with a motor and gearbox driving the patient's hip joint. Therefore, the system can have small low torque, low power motors to reduce the size and weight of the actuators and the entire exoskeleton.
Runoff control and non-point source pollution reduction in a sponge reconstruction community in a rainy city were studied using online monitoring and model simulations of a typical community in the sponge city pilot area. The rainfall-runoff volume and the suspended solid (SS) concentration were monitored continually at the two outlets from the community. A storm water management model (SWMM) was used to simulate the runoff control and non-point source pollution reduction in the sponge city design. Then, the model parameters were calibrated and validated against a natural rainfall event during the monitoring period. The results showed that all of the Nash-Sutcliffe efficiency coefficients were greater than 0.71, which ensured the model accuracy. Finally, the model was used to evaluate the effect of total runoff control and non-point source pollution reduction for 2 scenarios "before" and "after" the sponge city construction. The results showed that the sponge city construction helped control the runoff volume and reduce the non-point source pollution. After the sponge city construction, the total annual runoff rate was 52.9% of the total rainfall, the annual runoff was reduced by 28.0%, and the pollutant load was reduced by 66.3%. Overall, the runoff rate exceeded 70% for 81 rainfall events. Extreme rainfall events and the rainfall characteristics for each rainfall event have varying degrees of influence on the rainfall control rates. The average rainfall control rate in this study area in 2009 was 86.5%. The average rainfall control rates were 79.9% for light storms and 88.2% for severe storms. The rainfall amount and the preceding dry period strongly influenced the runoff control capacity. The average rainfall control rates were 98.1% for a light rainfall (< 15 mm), 73.8% for a moderate rainfall (10~25 mm) and 52.9% for a heavy rainfall (> 25 mm). For rainfall events after dry periods of 6 days or more (15 events in total), the rainfall runoff control rate exceeded 90%. The rainfall duration and average rainfall intensity had little effect on the rainfall runoff control rate.
Domestic and international urban rail transit noise evaluation standards and regulations were investigated to develop a noise evaluation method with indexes and thresholds for urban rail transit underground station platforms in China. This comparison evaluates the similarities and differences in the evaluation methods, evaluation indexes and thresholds. The platform noise and vibrations at a typical underground station are measured during operating hours to identify the noise and vibration distributions at different locations on the platform. The results show that the noise levels are significantly greater at both ends of the platform than in the middle and that current noise evaluation methods do not accurately reflect the feelings of passengers at both ends of the platform. Thus, the noise levels at both ends should be considered when evaluating platform noise levels. The maximum A-weighted sound pressure at both ends of the platform is 88.4-90.4 dB(A) which annoys the passengers when superimposed on the platform vibrations. Thus, the maximum A-weighted sound pressure is recommended to serve as an auxiliary evaluation index. Field tests show that the equivalent continuous A-weighted sound pressure for 1 hour is 75.3-79.4 dB(A), which is higher than the environmental noise threshold along the railway line used in the current norms. This will impact passengers staying on the platform for a long time or staff working on the platform.
Uranium is the key fuel component in nuclear power plants. However, the possibility of uranium and its compounds entering the water supply can seriously harm the environment and human health. Therefore, the analysis and treatment of uranium in water have attracted much attention. This paper describes the main methods, the latest research progress and existing problems related to uranium separation and enrichment from water starting from uranium analyses of laboratory water to the treatment of uranium-bearing water in the environment. Finally, the advantages and disadvantages of uranium separation and enrichment methods in water and their applications are summarized.
Increased urbanization, high-density urban populations and large urban areas have increased the importance of urban security planning. The People's Republic of China has established the Ministry of Emergency Management to study urban emergency management systems. This study reviewed urban emergency management systems in the United States, the United Kingdom, and Japan to identify three types of urban emergency management mechanism models and the corresponding emergency management models. Multi-agent simulations were then used to simulate these three emergency management mechanisms and evaluate their efficiencies. The results show that the "integrated" mechanism gives more reasonable task assignments and function divisions while the "communication" mechanism is more fluid and provides more orderly communications and decision-making.
Research on 3-D face recognition has made great progress in recent years. 3-D face recognition is more effective than 2-D face recognition. Its main feature is the use of 3-D shape data for recognition. The 3-D face recognition methods are categorized into three types based on the source of the 3-D shape data with methods based on 2-D color images, high quality 3-D scanning data, and low quality RGB-D images. This study reviews these methods and discusses their advantages and disadvantages. This paper then reviews the use of deep learning methods for 3-D face recognition. Besides, 3-D and 2-D face data fusion methods are reviewed for bi-modal face recognition. The commonly used 3-D face databases are also summarized. Finally, the main difficulties and future development trends of 3-D face recognition are discussed.