Misalignment can significantly impact the force transmission in bevel gears. The thermal expansion of the shaft can impact the stiffness of the transmission system which further influences the misalignment. The effect of the thermal expansion of the shaft on the misalignment is given by a relationship between the thermal expansion and the bearing stiffness and shaft system deformation. A non-linear finite element model is built to model a bevel gear transmission system with the thermal expansion to calculate the bevel gear misalignment. The results show that the thermal expansion reduces the bevel gear misalignment with higher working temperatures giving greater thermal expansion effects. The results describe how to use the expansion effect for bevel gear rating and design.

A decomposition strategy based on substructuring is developed for optimizing complex discrete structures with a large number of design variables and a collaborative architecture is used as the solver. A large structure is decomposed into several small substructures with no overlap, where each substructure corresponds to a discipline. The variables, objectives and constraints in the original problem are assigned to the separate disciplines. Only one finite element analysis of the complete structure is performed at the system level during each iteration with optimization and finite element analyses of the substructures at the discipline levels. Coupled state variables are passed from the system level to the disciplines as constants. The coupled state variables are updated after each finite element analysis of the complete structure at the system level to coordinate the differences in the coupled state variables among disciplines. Thus, a complex structural optimization problem is decomposed into several parallel, self-governed subproblems. The results of numerical examples demonstrate that this cooperative optimization method requires less evaluations of the complete structure and is able to obtain better results with better stability than optimizing the complete structure as a whole.

A two-speed, automatic mechanical transmission (AMT) is developed for electric vehicles with a planetary gear system, a centrifugal clutch and a belt brake. The transmission shifts seamlessly between the two gears to eliminate the power interruption problem during gear shifting in conventional AMT. The electric vehicle driveline is modeled to get the optimal control method using dynamic programming and convex optimization. The optimal control variables and optimal control system minimize vehicle jerk and frictional losses. A normal sectional control method is also used during gear shifting for comparison in simulations. The simulations indicate that the optimal control method significantly improves the gear shift comfort while maintaining the dynamic performance as well as vehicle acceleration with decreases of frictional losses in the clutch and brake.

The response characteristics of linear sweep voltammetry (LSV) were used to develop an equivalent circuit model of a proton exchange membrane (PEM) fuel cell to distinguish the various electrochemical processes, including hydrogen desorption on the platinum, charging of the double-layer capacitance, electron internal short circuits and hydrogen crossover. This model eliminated the effect of the scan rate on the LSV results so that the hydrogen crossover current and membrane electronic resistance could be measured. A galvanostatic method was also used to measure the hydrogen crossover current and the electronic resistance. Measurements on a single cell with an active area of 34 cm² with the LSV method show that the hydrogen crossover current is 1.19 mA·cm^-2 and the electronic resistance is 479 Ω·cm² while the galvanostatic measurements give the hydrogen crossover current of 1.25 mA·cm^-2 and the electronic resistance of 413 Ω·cm². This model can be used to analyze various electrochemical measurements in PEM fuel cells with the two methods giving complementary measurements for various PEM fuel cell processes.

Urea is produced in a tower with falling liquid droplets to enhance the evaporation and drying of the urea particles. The physical process has a liquid column feeding an atomizer. This study analyzes the effect of the nozzle diameter, liquid velocity and air flow velocity on the urea maximum drop diameter. A model is developed to predict the critical heights of the liquid column and the maximum drop diameter. The model predictions agree well with the experimental data, indicating its ability to predict the maximum drop diameter. The atomizer nozzle diameter and the tangential velocity at the orifice strongly influence the drop size, while the liquid velocity at the orifice has little impact on the maximum drop diameter. The air flow velocity in the tower also affects the maximum drop diameter when the air flow velocity is greater than 1.5 m·s^-1, but the effect is very small for the air flow velocity less than 1.5 m·s^-1. Thus, the maximum drop diameter can be increased by increasing the atomizer nozzle diameter and the tangential velocity at the orifice. Secondary breakup will occur with large drops falling in the tower during cooling and solidification. The critical Weber number gives the maximum drop diameter of urea in the tower for granulation processing about 4 mm.

A numerical method is developed based on the conservation equations for multicomponent reacting systems to better predict char particle combustion. The advantage of this method is that many physical and chemical processes occurring in the char particle boundary layer are described in detail with less CPU time, which improves the studies of the char combustion mechanism. This method can also be used to simulate real situations with relatively simple flow patterns, like the char particle combustion in a drop tube furnace (DTF). Four chars are combusted in a DTF with their final conversions measured. The predicted char conversions compare well with the measured data to validate this method. As the ambient temperature increases, the char combustion rate becomes faster and the O₂ concentration decreases while the CO and CO₂ amounts strongly increase in the char particle boundary layer.

A numerical model was developed to investigate the tar production during pyrolysis of a single coal particle. The model was based on the fragmentation and diffusion (FD) coal pyrolysis model and considered the secondary reactions and diffusion inside the coal particle. The model was validated by pyrolysis experiments in a drop-tube furnace and then used to investigate the influences of the final temperature, heating rate and particle diameter. The results show that the competition between the secondary reactions and tar diffusion greatly influences the tar production. Increases of the final temperature and the heating rate improve both the tar secondary reactions and the diffusion while increasing the particle diameter improves the tar secondary reactions and hinders the diffusion. The final tar yield decreases with increasing final temperature, increasing heating rate and increasing particle diameter.

Installation and calibration difficulties restrict the use of circular gratings to improve the precision of practical high-precise inductosyn-based angular measurement systems through angle-error sampling and compensation. The study analyzes appropriate solutions of sparse error sampling and compensation methods for this problem. The error characteristics of inductosyn-based angular measurement systems are analyzed to compensate for the subdivision error caused by the existing zero-point error and other subdivision errors to get the overall zero-point error with a prism. An error compensation method is then given using sparse sampling data. Tests show that the precision of an angular measurement system is improved by this method from a peak to peak error of 11.7″ to 2.9″. The method accurately identifies the zero-point error and provides full-range error compensation with sparse sampling data for an inductosyn-based angular measurement system.

Residual austenite content in steel strongly influences the mechanical properties and thermal stability of the materials. Eddy current testing method is used to determine the residual austenite content in the steel since the relative permeability of the austenite phase, which is indicated by eddy current tests, is much smaller than that of the ferromagnetic phases. A finite element analysis method is used to simulate eddy current tests with samples having different relative permeabilities. The results show that the output signal of the alternating current (AC) bridge corresponds well with the relative permeability. The amplitude and phase of the output signal can be used as feature variables, which both having good linear correlation with the relative permeability that after processing. The residual austenite content can then be determined using the relationship between the austenite content and the relative permeability.

Lift-off affects the signal in eddy current testing. A circuit designed to reduce the lift-off effect adjusts the reference voltage based on an analysis of the influence of the lift-off effect on the probe coil voltage. A dephasing and amplification circuit is used to decouple the phase and amplitude to separate the phase and amplitude adjustments to improve the reference voltage adjustment efficiency. A test specimen is designed to validate the feasibility of the method. Tests indicate that the defect signal amplitude with this method is 20 times larger than the signal from the lift-off effect. The influence of lift- off effect on the defect signal can then be ignored with this circuit.

The drawback of the conventional sliding mode observer (SMO) when used for disturbance estimation is that it leads to nonzero estimation errors for a time-varying disturbance and chattering. A repetitive SMO (R-SMO) is developed for a repetitive linear motor system where periodic and non-periodic disturbances exist at the same time, which overcomes the drawback of the conventional SMO. The R-SMO incorporates the internal mode of the periodic disturbance to achieve asymptotic convergence to the periodic disturbance. The switching term then only needs to estimate the non-periodic disturbance which significantly reduces the chattering. The R-SMO is shown to be asymptotically convergent. Tests show that the R-SMO well estimates the disturbances of a linear motor system, improves the tracking accuracy after feedforward compensation and is superior to the conventional SMO in terms of convergence accuracy and chattering. Extensions to systems with multiple periodic disturbances and non-repetitive systems are discussed.

Flexure-based mechanisms are widely used in industry as highly precise micro-motion mechanisms. This paper presents a compliance calculation method for planar flexure-based mechanisms. The compliance of flexure hinges is used to relate the deformations to the loads on flexure member with the end-effector motion obtained using the virtual work principle. Then, a matrix method is used to derive concise compliance equations for serial and parallel flexure mechanisms. The compliance and the relationship between the compliance terms and variable geometric parameters are analyzed for three typical flexure-based mechanisms. The model results compare well with finite element method (FEM) predictions with a maximum difference of 7% and an average difference of 3%. This method provides theoretical and technical support for the design and optimization of flexure-based mechanisms.

A constrained implicit equation is developed to enhance the robustness and precision of perspective contour extraction for cylinders. The contour curve fitting problem is converted to a nonlinear optimization problem containing nonlinear constraints by a linear approximation. The problem is then solved with a rough estimate of the curve parameters and the noisy points filtered to find reasonable points based on the rough estimate of the curve parameters. This constrained problem is then converted to an unconstrained problem using the penalty function method to find the solution. This method takes advantage of the constraint between the lines and the ellipse to give better anti-noise performance for perspective cylinder contour extraction than separate methods using lines or ellipses. Tests of synthetic and real images show that this method effectively improves perspective contour curve fitting for cylinders.

Multi-ram forging is the main production process for large-diameter valves. However, premature cracking at the root of the punch and plastic deformation at the top of the punch are the main problems in the forging process with the punches often having short service lives. This study analyzes the forging process, especially the irregular metal flow that creates offset loading forces on the punch, which leads to punch failures. The low thermal resistance causes the plastic deformation at the top of the punch. This analysis optimizes the metal flow during the forging through die optimization to reduce the stress concentrations at the punch root by changing the joint between the punch and the press. The FGH96 super alloy is used to improve the deformation resistance at high temperatures. Optimization of the fillet radius in the mold and smoothing of the punch surface reduce the stress concentration at the joint to effectively reduce cracking. The stresses at the top of the punch are below the yield strength with the FGH96 super alloy so plastic deformation does not occur at the top of the punch. A horizontal punch made to forge a 3 inch (7.62 cm) valve body works very well with no cracks or deformation at the punch top for 100 cycles. The punch service life is then much longer.

In time difference of arrival (TDOA)/frequency difference of arrival (FDOA) passive location systems used in micro/ nano-satellite formations, improving the location accuracy usually requires a large increase in data transmissions, which severely reduces the system efficiency due to the narrow data link bandwidth of the satellites. A TDOA/FDOA estimation method is developed based on sub-sampling transmissions without increasing the data transmissions, which significantly improves the FDOA accuracy by a time expansion while maintaining the TDOA estimation accuracy. The TDOA accuracy is analyzed and the maximum sub-sampling rate is derived. Simulations show that for wideband signals, the location accuracy of this method is improved more than 6 fold over that of the compressed sensing method for the same data transmission.

Satellite data transmission systems need high coding gains, multiple rates and high reliability channel coding. A low complexity, high speed encoder is designed for low-density parity-check (LDPC) codes, which reduces the hardware size and improves the encoding speed and reliability. The system reuses hardware resources for codes of various rates and lengths and uses a low-storage architecture and a partially triple-modular-redundant design scheme. Field programmable gate array (FPGA) synthesized results show that the encoder integrates 28 codes with aerospace reinforcement and a maximum encoding speed of 3.2 Gb/s in a Xilinx XC2V3000 FPGA chip. The flip-flop, look-up table (LUT) and RAM costs of the encoder are 24.5%, 34.4% and 11.1% less than that for the traditional scheme. This encoder design scheme will improve satellite data transmission systems.

The high fuel temperature rise at the shut-off operating condition in a reheat fuel centrifugal pump is addressed by cooling the impeller by fuel flowing through a by-pass from the pump inlet. The ejection-cooling is analyzed using the Reynolds average Navier-Strokes (RANS) method with the shear stress transport (SST) turbulence model and the Rayleigh-Plesset cavitation model. The results show that the ejection-cooling design can reduce the high fuel temperature rise at the shut-off condition. The power consumption and the friction heat are both reduced in the reheat fuel centrifugal pump with the ejection-cooling device because of the vapor core region in the impeller central zone which reduces the fuel temperature rise.

The photon counting detection model and the multi-scattering photon propagation model were used to investigate the effects of atmosphere visibility on the path loss and delay spread of an ultraviolet scattering channel with a vertical transmitter-receiver and the achievable data rate with on-off keying (OOK) modulation. Simulations show that, at a given communication range, the delay spread increases with improving atmosphere visibility. When the communication range is set, there is a best visibility where the minimum path loss occurs and this best visibility increases with increasing communication range. For a given communication range, there are a best visibility and an optimum baud rate that maximize the achievable data rate. With large communication ranges, the best visibility increases while the optimum baud rate and the corresponding maximum achievable data rate decrease.

Photon counting detectors (PCDs) are important in spectral X-ray imaging and computed tomography (CT) systems. Various PCD energy calibration methods have been developed but have many limitations because of the influences of the pulse pileup, charge sharing and other physical effects. This paper describes a calibration method using only one monochromatic source. An iterative technique is used to fully analyze the data to determine the energy for various thresholds. The method gives good results with fewer tests than other calibration methods. The charge sharing effect is implicitly corrected, which is an important factor in the calibration of small pixel detectors. This method is quite universal and can be used to calibrate other PCDs.

Some stocks in the stock market share the common characteristics of low prices, high turnover rates, and high historical highest daily returns. These all imply strong speculative investments, so these stocks are referred to as lottery-type stocks. Some investors are very speculative and prefer to invest in lottery-type stocks. Analyses of an individual investor trading data set show that: 1) Individual investors significantly over-weight lottery-type stocks in their investment portfolios with 14% lottery-type stocks compared to the average market portfolio of 9%. 2) Young, male, less experienced investors using high turnover rates and investors from western China prefer lottery-type stocks. 3) During bull markets, investors have stronger speculative tendencies.