Large components with thick walls have slow cooling rates during tempering. Improper tempering parameters can cause temper brittlement in CrMoV steels. The effect of tempering cooling rate on the toughness of bainite welds is investigated for thick circular components. Slow tempering cooling rates reduce the weld toughness. Multi-layer, multi-pass welds experience layered brittle fracture, which illustrates that slow tempering cooling rates affect only local welds with the greatest toughness reduction in the heat affected zone (HAZ) between the layers. Auger electron spectroscopy (AES) analyses show that the segregation of C, O and Ni along the prior austenite grain boundaries is associated with the toughness reduction.

This study uses 9%Cr parent metal containing boron and 2.25%Cr weld metal to study the influence of long-term aging at elevated temperature on the carbon migration between the parent metal and weld metal. The size and number of precipitates in the carbon-enriched zone increase after long-term aging, but the precipitates in the carbon-denuded zone change little, which increases the differences in the mechanical properties between the carbon-enriched and carbon-denuded zones. Finite element analyses indicate that the carbon-denuded zone is damaged first by bearing loads with the damage increasing with long-term aging. Transmission electron microscope (TEM) pictures show that the precipitates at the grain boundaries of the heat affected zone in the 9%Cr parent metal change little, but precipitates inside the grains become coarse after long-term aging. Boron is responsible for the changes of the precipitates at grain boundaries and inside the grains, because the boron tends to segregate at the grain boundaries, which slows coarsening of the precipitates by occupying vacancies around the precipitates.

Weak zones in welded joints due to low cycle fatigue can affect the safety of welded steam turbine rotors. This study analyzes the low cycle fatigue strength of welded 25Cr2Ni2MoV refractory steel steam turbine rotor joints. The strains in the weak zones of the welded joints are modeled statistically. The reason for the weak zone shift is studied using hardness tests and finite element analyses. The experimental results show that cracks develop in the weld and in tempered regions of the heat affected zone. The weak zone shifts from the weld to tempered regions with decreasing strain. With large strains, the plastic strain concentrates in the weld while with low strains, the weld stays in the elastic range. The large hardness gradient in the tempered region with sandwich construction increases the strain concentration.

Scattered point pattern matching is an important issue in computer vision and pattern recognition, which is widely used for target recognition, medical and remote sensing image registration, and position and pose measurements. This paper describes an algorithm for use in an explosive ordnance disposal robot for when the target object is partial exposed. A simulated annealing-particle swarm optimization (SA-PSO) algorithm based on particle density distribution changes for scattered point pattern matching is developed. The algorithm is more accurate and faster than previous algorithms. The fitness function is constructed from a series of scattered points collected from the local surface of a rotated object. Accurate surface fitting and pose parameters are found using coordinate transforms. The factors that affect the accuracy and applicability are discussed in detail. Tests show that this method is accurate and efficient, with less points needed and less sensitivity to point errors compared with the traditional least squares method.

Electromagnetic suspension (EMS) systems are unstable open-loop, strongly nonlinear systems. The suspension accuracy of EMS systems for machine tools is improved by integrating the feedback linearization method with a disturbance observer (DOB) to precisely linearize the EMS system. The feedback linearization error is analyzed and modeled in this paper. The DOB is then designed to compensate for the feedback linearization error. This study indicates that the DOB effectively compensates for the feedback linearization error to give precise linearization of EMS systems. Tests illustrate that the EMS feed system gives precise linearization and the platform suspension accuracy is greatly improved to micron scale accuracy.

Bearingless induction motors always suffer from the influence of rotor resistance variations. An adaptive online rotor resistance identification method is developed here based on an observer of the suspension force commands. This study analyzes the influence of the rotor resistance variation on the air-gap flux identification. Real-time online identification of the rotor resistance is based on observations of the suspension force commands, which utilizes the principle that the suspension force commands are sensitive to the air-gap flux in the torque windings. Tests of a bearingless induction motor show that the peak-peak displacements of the rotor are reduced by 60% by this adaptive online rotor resistance identification method.

Traditional direct simulation Monte Carlo (DSMC) models using rectangular elements inevitably have errors when dealing with complex computational domain boundaries. Unstructured grids are able to adapt to any complex geometric shape but are rarely applied because of the highly disordered topological structure, complex calculations and low execution efficiency. This paper describes a particle trajectory tracking algorithm based on an unstructured Delaunay triangle mesh. The computational domain is divided into various rectangular regions with only a small number of triangular elements with the particle trajectory tracking achieved by first searching the rectangular regions and then the triangular elements. The algorithm is used in a two-dimensional DSMC program with the results comparing well with results in the literature. The DSMC program is then used to predict the flow field in a showerhead aperture with argon as the neutral reference gas with an inlet pressure of 200 Pa and an inlet temperature of 300 K. The results show that the radial velocity and temperature distributions are less affected by the showerhead aperture than by the radial pressure distribution. Increasing the showerhead aperture improves the radial velocity and temperature distribution uniformity, while decreasing the showerhead aperture improves the radial pressure distribution uniformity.

Lane control systems automatically keep a vehicle in its lane to improve driving safety. Such systems need to adapt to the driver's characteristics and should reduce unnecessary intervention. A small deviation model of the human-vehicle system is formulated for on-line prediction of the future vehicle trajectory with an assistance control strategy based on model predictive control (MPC). A corrective steering angle is computed by solving a quadratic programming problem. The nominal trajectory is predicted using the current vehicle information. Then, a deviation model is obtained by successively linearizing the human-vehicle system around the nominal prediction trajectory. A cost function and I/O constraints are designed according to a performance index. Simulations and real world tests show that this approach is able to avoid unintended lane departures while adapting to the driver's driving patterns and avoiding unnecessary intervention.

Driving behavior plays an important role in fuel consumption and safe driving. Thus, driving behavior recognition can improve driving safety and optimize energy use. This study presents a steering and lane-changing behavior recognition system based on the vehicle status obtained from a steering wheel angle sensor. A support vector machine linear classifier is then used to analyze the vehicle body transfer angle and maximum steering angle given by a moving direction vector model. Lagrange number multiplication and quadratic programming are used in an optimal classifier for recognizing steering and lane-changing behavior. Real vehicle tests show that this methodology has 98% accuracy for steering and lane-changing behavior recognition. This system can be integrated into a warning and control system to improve driving safety.

The flow field and reaction processes in a coal hydrogasifier reactor were modeled using a three-dimensional numerical model of Rockwell's 6 t/d entrained flow coal hydrogasifier using the hydropyrolysis kinetic model developed by Johnson and Tran as well as tar hydrocracking reactions. The numerical predictions were in good agreement with experimental results for the 6 t/d hydrogasifier. The simulations show that the flow field in the hydrogasifier can be categorized into a cross-flow impinging region, a jet-reflux flow region, and a plug flow region. The primary devolatilization reactions are complete immediately after the rapid mixing of the hot hydrogen and coal particles. The methane is mainly produced in the cross-flow impinging region and jet-reflux region. Most of the lower hydrogasifier has plug flow. Small particles are heated and lose weight faster in the cross-flow impinging region and jet-reflux flow region, while in the plug flow region, the particle size has minor effect on the particle temperature and mass history.

Supercritical CO₂ storage in saline aquifers results in a density gradient which causes dispersion and sedimentation due to CO₂ dissolving in the brine during the CO₂ migration. This density gradient plays a significant role in promoting the geological storage capacity, reducing pressures on the caprock, and reducing the CO₂ leakage risk. This paper describes numerical investigations of the influence of key parameters such as the salinity, temperature, and pressure on the amount of CO₂ dissolved in brine per unit volume over time. The results show that, for the same permeability and porous structure of the saline aquifer, a higher salinity leads to weak fingering with small amounts of dissolved CO₂. Higher temperatures contribute to strong fingering and small amounts of dissolved CO₂. Higher pressures also produce fingering with large amounts of dissolved CO₂.

A one-dimensional optimization design system based on iSIGHT was used to optimize the matching of a diffuser with a centrifugal impeller. The system was then used to optimize the geometry and matching characteristics of a low pressure stage centrifugal compressor for a MW size gas turbine. The results show that the diffuser and impeller are not well matched in the original design. The diameter ratio of the vaneless diffuser is too large, resulting in low efficiencies throughout the entire stage. The one-dimensional optimization results are used to redefine the diffuser geometry to improve the performance. The vaneless diffuser outlet diameter is reduced and the original single stage diffuser is replaced by a tandem vane diffuser. The optimization significantly improves the performance of the entire stage. The pressure ratio is increased by about 4% and the efficiency is increased by about 2%.

The acid dew point in flue gases must be accurately predicted to avoid fouling and corrosion of the heating surfaces and improve the boiler thermal efficiency. Operating experience in many power plants has shown that current models over-predict the acid dew point. Two devices are built to measure the acid dew points for different conditions. Two models are then developed to predict the acid dew point based on thermodynamic correlations between the acid dew point and key factors in the system. Then, the flue gas acid dew points predicted by the models and from previous studies are compared to the experimental data. The results show that the plug-measuring device measurements are more sensitive to variations of the water vapor in the flue gas than the extraction-measuring device measurements.

In turbulent gas-biomass particle combustion, the turbulent fluctuations of the gas velocity affect the particle motion. However, the effects of the turbulent fluctuations of the gas temperature on the particle instantaneous temperature need to be further explored. The instantaneous temperature variations of biomass particles in a hot gas with fluctuating temperatures are analyzed numerically in this study. The results show that the particle temperatures will fluctuate with the gas temperature. The amplitudes of particle temperature fluctuations are affected by the intensity of the gas temperature fluctuations. Increases in the gas temperature fluctuations lead to increases in the particle temperature fluctuations. Increased particle Reynolds numbers enhance the heat transfer between the particles and the gas. As a result, the particle temperature relaxation time decreases, so the particle temperature responds faster to the gas temperature fluctuations and the particle temperature fluctuations increase.

Because of earth gravity, liquid fuel tanks cannot be fixed on air-bearing tables to simulate satellite movements in space. This paper describes the use of fly wheels to simulate the sloshing liquid torques for ground simulations. A liquid sloshing model is used to compute the sloshing torques with fly wheels then designed to output the same torques in real time for satellite sloshing liquid simulations. Simulations show that the influences of sampling time, delay, and external moments are well simulated and that an equivalent treatment of the fly wheel dynamics equations can simplify the computations of the fly wheels' angular velocity and the gyro force analysis.

The sub-mechanism of toluene oxidation was identified using path and sensitivity analyses. A chemical kinetics mechanism for a four-component gasoline surrogate fuel made of iso-octane/n-heptane/ethanol/toluene includes 75 species and 305 elementary reactions. The validated results show that the mechanism gives good agreement with experimental data for the pure fuel ignition delay time, laminar flame speed, and chemical structure predictions. The model also predicts the ignition delay time of multi-component gasoline surrogate fuels in the specified pressure and temperature range and reproduces the auto-ignition characteristics of different research octane number (RON) gasoline fuels. Since this chemical kinetics model has few species and few reactions, the mechanism can be used in multidimensional, computational fluid dynamics (CFD) simulations of the gasoline combustion.

Large floating roof tanks usually contain a large amount of flammable liquids which can lead to catastrophes. This study analyzes accident scenarios based on 88 large external floating roof tank accident case analyses. Fire dynamics simulator (FDS) is used to compute the heat flux distribution under a rim seal fire, a full surface fire, and a bund fire. The personal vulnerability model is then used to calculate the individual risk based on the heat fluxes. The effect of wind on the risk distribution is discussed and the safety distances for firefighters are identified. The results provide useful reference for firefighting.

This study analyzes the location assignments for outbound containers in terminals to reduce the container re-handling during loading operations. Previous studies assumed that the container arrival probability for each weight group remained unchanged during the entire receiving process, which is not true in practice. This study adjusts the probability that the remaining containers have not yet arrived at the terminal. A constrained dynamic programming model is then constructed for this problem. Small-instances can be directly optimized by the dynamic programming model. Large-instances are solved with a two-stage heuristic algorithm. The first stage develops a heuristic to generate the precedence of the stacking patterns for each container weight group. The second stage uses a heuristic algorithm based on the rolling strategy. Numerical calculations show that the dynamic programming method for small-instances and the two-stage heuristic algorithm for large-instances both significantly improve the solution quality and reduce the container re-handling.