This paper presents an experimental investigation into the shear behavior of reinforced ultra-high toughness cementitious composite (UHTCC) beams through flexural tests under a point loading, where UHTCC shows tension strain-hardening and multiple cracking characteristics. The varied parameters include shear-span ratios of about 2.06, 3.08, and 4.11, and web reinforcement ratios of 0%, 0.25%, 0.37%, and 0.55%. The experimental results reveal that reinforced UHTCC (RUHTCC) beams have superior shear resistance compared with reinforced concrete (RC) beams and show stable crack propagation and multiple cracking behaviors in shear. The use of UHTCC as the matrix of beams can serve as a replacement for minimum web reinforcement. A small amount of stirrups used in RUHTCC slender beams results in a more ductile flexure-shear or even flexural failure. However, the use of stirrups in both short beams and RUHTCC slender beams brings little improvement in ultimate shear strength, and thus no shear synergy between UHTCC and stirrups is obtained. A tied-arch model and a truss model can be used to represent the shear mechanism of RUHTCC short and slender beams, respectively. UHTCC web subjected to tension can be considered as inclined tension web members in a truss model for RUHTCC slender beams.

This study is focused on the impact of thermal stratification on interflow travel time. A quantitative relation between buoyancy frequency and interflow travel time is theoretically derived based on the Bernoulli principle of energy conservation. Experiments and numerical simulations are carried out to validate the applicability of the proposed relation. For experiments, interflow movement is successfully detected in a small-depth water tank by releasing a denser flow into a temperature stratification environment. For numerical simulations, a vertical 2D renormalization group (RNG) k-( model is developed to simulate the interflow. The results both of the experiments and of the numerical simulations verify our proposed theory. The derived analytic relation is useful for the prediction of contaminant travel time in reservoirs and in assisting pollution control.

Fin arrangement, which can cause temperature to be distributed non-uniformly and decrease heat exchange efficiency, can also affect fluid flow and distribution in different channels of a plate-fin heat exchanger. To reduce fluid maldistribution, the fluid flow and distribution should be investigated systematically. However, there is as yet no research reported on the fin arrangement effect. We investigated fluid flow and heat transfer at the inlet of a plate-fin heat exchanger by numerical calculation combined with simulation analysis. We simulated the fluid flow under seven kinds of fin arrangement, and analyzed the effects. The distribution of fluid parameters in four monitor positions among three sections was examined when the inlet flow velocity was 1 m/s with an inlet structure arranged with different numbers of fins. Denser fin arrangements among inlet, diversion, and heat exchange sections all intensify the turbulence at the outlet. With increase of arrangement density, the fluid flow direction will be changed and the fluid distribution inside the exchanger will be intensified to equalize the fluid temperature in different channels of the same layer. Furthermore, the effects of 18 combinations of fins in different sections on fluid flow were studied. Fin arrangements in different sections have more significant effect on turbulence than flow velocity and pressure; in comparison with the inlet and heat exchange sections, the diversion section has a significant effect on turbulence at the outlet of the heat exchanger.

This study employs the least square support vector machine (LSSVM) for the prediction of pullout capacity of small ground anchor. LSSVM is firmly based on the theory of statistical learning and uses regression technique. In LSSVM, Vapnik and Lerner (1963)’s ε-insensitive loss function was replaced by a cost function which corresponded to a form of ridge regression. The input parameters of LSSVM were equivalent anchor diameter, anchor embedment depth, average cone tip resistance, average cone sleeve friction, and installation technique. Using 83 out the available 119 in-situ test datasets, an LSSVM regression model was developed. The goodness of the model was tested using the remaining 36 data points. The developed LSSVM also gave an error bar of predicted data. A sensitivity analysis was conducted to determine the effect of each input parameter. The results were compared with the artificial neural network (ANN) model. Overall, LSSVM was shown to perform well.

The air-conditioning system in a large commercial or high-rise building is a complex multi-variable system influenced by many factors. The energy saving potential from the optimal operation and control of heating, ventilating, and air-conditioning (HVAC) systems can be large, even when they are properly designed. The ultimate goal of optimization is to use the minimum amount of energy needed to improve system efficiency while meeting comfort requirements. In this study, a multi-zone variable air volume (VAV) and variable water volume (VWV) air-conditioning system is developed. The steady state modes and dynamic models of the HVAC subsystems are constructed. Optimal control based on large scale system theory for system-level energy-saving of HVAC is introduced. Control strategies such as proportional-integral-derivative (PID) controller (gearshift integral PID and self-tuning PID) and iterative learning control (ILC) are studied in the platform to improve the dynamic characteristics. The system performance is improved. An 18.2% energy saving is achieved with the integration of ILC and sequential quadratic programming based on a steady-state hierarchical optimization control scheme.

In this study, eight fly ash samples and three bottom ash samples from different areas are collected for analysis of their physicochemical properties and emission content of dioxin precursors and metals. Their surface characteristics, their effects on dioxin precursors, and important aspects of the compositions of residual ash (fly ash and bottom ash) are investigated. Poly-chlorobenzenes (PCBzs) in the fly ash of a fluidized bed incinerator (FBI) are 7.35 to 357.94 µg/kg, and in that of a fire grate incinerator (FGI) are 6.74 to 96.52 µg/kg. The concentrations in bottom ash are the same (i.e., 2.23 to 2.99 µg/kg) regardless of the furnace type. The concentrations of polycyclic aromatic hydrocarbons (PAHs) in FGI fly ash samples (0.293 to 1.783 mg/kg) are less than these in samples from FBIs (1.820 to 38.012 mg/kg). Low boiling point PAHs (mainly 2- and 3-ringed PAHs) and high boiling point PCBzs (mainly H_xCB and P_eCBz) are the major constituents of residual ash. Different distributions of PCBzs and PAHs are mainly dictated by the incineration characteristics of FBI and FGI. Al and Fe, as non-toxic “light metals” are the major constituents of the residual ash, and Ni and Zn as non-toxic heavy metals play important roles in the total heavy metal. Cu, Pb, and Cr are the three major toxic heavy metals. The correlation of the metals and the dioxin precursors is discussed and distinguished.

During mode-locked ultrafast laser experiments, we find that semiconductor saturable absorber mirrors (SESAMs) from the same manufacturing process may, from batch to batch, show different working ranges: pure Q-switching, Q-switched mode-locking, and continuous wave (CW) mode-locking. This is because, in high-volume wafer-scale fabrication, there is typically an estimated 1% error for high-quality molecular beam epitaxy (MBE) growth, which introduces a variation in the parameters of an individual SESAM. In this paper, we will analyze how that 1% error in layer thickness influences the behaviour of SESAMs in three different structures: resonant SESAM, anti-resonant SESAM, and enhanced SESAM. Furthermore, the characteristics of the SESAM will affect the mode-locking dynamic behavior of ultrafast solid state lasers. In the worst case, a SESAM with a fabrication error may prevent the laser cavity from mode-locking. Proper laser cavity design can help to reduce the impact of SESAM fabrication errors on laser performance and maintain the laser in the CW mode-locking range.