The critical penetration condition is an essential component of studies on the mechanism of sink vortex formation. However, the condition and its transition process are unknown. To address this issue, we constructed a Rankine-vortex-based fluid mechanic model, and proposed a Helmholtz-equation-based solution method to acquire the critical penetration condition. The two-phase mass suction-extraction mechanism of the Ekman boundary layer was discussed. Numerical results show that the critical penetration condition is dependent on the initial velocity components; if the initial disturbances are enhanced, the suction-extraction height and Ekman layer thickness increase. A particle image velocimetry (PIV)-based observation experimental platform was developed, and the effectiveness of the proposed method was verified. The vortex core boundary was observed first, so the radius of the vortex core could be acquired precisely.

An efficient mixing process is very important for the engineering implementation of an airbreathing propulsion system. The air and injectant should be mixed sufficiently before entering the combustor. Two new wall-mounted cavity configurations were proposed to enhance the mixing process in a conventional transverse injection flow field. Their flow field properties were compared with those of a system with only transverse injection ports. Grid independency analysis was used to choose a suitable grid scale, and the mixing efficiencies at four cross-sectional planes (namely x=20, 40, 60, and 80 mm, which are just downstream of the jet orifice) were compared for the configurations considered in this study. The results showed that hydrogen penetrated deeper when a cavity was mounted upstream of the transverse injection ports. This is beneficial to the mixing process in supersonic flows. The mixing efficiency of the configuration with the wall-mounted cavity was better than that of the conventional physical model, and the mixing efficiency of the proposed novel physical model I (98.71% at x=20 mm) was the highest of all. In the case with only transverse injection ports, the vortex was broken up by the strong interaction between the shear layer over the cavity and the jet.

A cable dome is a form of cable-strut tensegrity structure, which is popular for long span membrane roof structures. However, there is an opportunity for its major development for a wider range of applications if rigid roof cable dome structures can be achieved. In this paper, we propose the tensile beam-cable dome (TBCD), a new type of space structure based on the features of the cable dome. By changing the ridge cables to hinged tensile beams, a structure can easily be covered with a rigid roof. We introduce its configuration and mechanical characteristics, and put forward four categories of this structure with hinges set at different locations on the tensile beams. In addition to achieving the aims of tow-lifting and tensioning construction, the integral tow-lifting method is presented for TBCD, and the nonlinear dynamic finite element method (NDFEM) of form-finding analysis is introduced for the overall construction analysis. For integral tow-lifting construction, the mechanism hinges should be set at the middle of the tensile beams to make the tensile beam grid into a mechanism system. Through construction analysis of seven mechanism hinge distribution modes, the modes with mechanism hinges set only on the middle or inner tensile beams were optimal.

This paper pertains to case drain pressure limitation for axial piston swashplate pumps used in open-loop circuits. The critical case drain pressure for pumps of this type is considered from the oil film perspective of the slipper/swashplate pair: (1) height of the lubricating oil film, (2) supporting stiffness, and (3) location of the centroid of the equivalent hydrodynamic lifting force. A dynamic lubricating oil film simulation model is established to determine the critical case drain pressure for which the slipper cannot remain in a stable state. Based on the simulation results, the worst condition occurs at the point when the height of the lubricating oil film is the maximum, the supporting stiffness is the minimum, and the distance between the centroid of the equivalent hydrodynamic lifting force and the bottom center of the slipper is the maximum. The slipper is stable only when the difference between the case drain pressure and the suction pressure is within a reasonable range. Subsequently, a design criterion is put forward to specify the reasonable case drain pressure, and this is validated by experimental results.

This study of bed-load transport was undertaken on the basis of laboratory data in two states, i.e., limit of deposition and deposited bed, by using new design criteria, whereby, compared to earlier similar studies, fewer parameters were considered, yet with almost the same or in some cases an even greater level of accuracy. The modified criterion in the new design for transport in the limit of deposition was using only three dimensionless parameters, i.e., Froude number, volumetric concentration of sediment, and relative size of the grain. But the new design criterion applied to the deposited bed case used four dimensionless parameters, i.e., three parameters used for the preliminary case besides the relative thickness of sedimentation. Compared with other known relationships in sediment transport, the produced equations introduced here yield better results than previous studies. With the lessened number of parameters, the results are much easier to obtain.

To improve the multiple performance indices of practical engineering structures under uncertainties, an interval constrained multiobjective optimization model was constructed with structural performance indices included in objectives and constraints being functions of the interval uncertain parameters. An algorithm integrating radial basis function (RBF), interval analysis, and non-dominated sorting genetic algorithm (NSGA-II) was put forward to locate the Pareto-optimal solutions to the interval multiobjective optimization model. A series of RBFs were constructed based on the Latin hypercube experimental design (LHED) and finite element analysis (FEA), which were then integrated with interval analysis to compute the interval bounds of the objective and constraint functions under the fluctuation of uncertain parameters. Then the fitness of every individual during the NSGA-II-based optimization could be obtained. The case study on the optimization of the mechanical performance of a press slider with uncertain material properties demonstrated the feasibility and validity of the proposed methodology.

This paper presents a torque distribution method for an individual-wheel drive vehicle, in which each wheel is controlled individually by its own electric motor. The terminal sliding mode technique is employed for the motion control so as to track the desired vehicle motion obtained by interpreting the driver's commands. Thus, finite-time convergence of the system's dynamic errors can be achieved on the terminal sliding manifolds, as compared to the well-used linear sliding surface. By considering nonlinear constraints of the tire adhesive limits, a simple yet effective distribution strategy is introduced to allocate the motion control efforts to each of the four wheels. Through the use of a high-fidelity CarSim full-vehicle model, vehicle stability and handling performance of the proposed controller is evaluated in both open-and closed-loop simulations.

Motor vehicles are the major source of urban air pollution. The abatement of air pollutant emissions is an urgent task for environmental protection. This paper simulated the abatement for carbon monoxide (CO), volatile organic compounds (VOCs), nitrogen oxides (NO x ), and particular matter (PM) emissions from vehicles under four scenarios in the year 2015 in Hangzhou, China. It was found that the emissions of CO, VOCs, NO x , and PM from vehicles were 440.551, 23.079, 44.255, and 6.532 kt/a in 2010 in Hangzhou, respectively. The vehicle population will increase to over 1.2 million with a 60.7% growth rate until 2015 (estimated). Based on the scenario analysis, it was found that eliminating substandard vehicles and upgrading vehicle’s standards could help reduce CO and VOCs effectively, while the expected abatement of NO x and PM would be offset by the rapid increase in the vehicle numbers. It was also found that integrated measurements, including eliminating substandard vehicles, upgrading vehicle standards, supplying low sulfur oil, and introducing alternative fuel vehicles could simultaneously reduce the four key pollutants. These integrated policies make it possible to reduce 250.197, 10.270, 1.791, and 0.335 kt/a CO, VOCs, NO x , and PM with 56.79%, 44.50%, 4.05%, and 5.14% decrease rates in 2015, respectively, when compared to those in 2010.

This paper presents a two-degree-of-freedom (2DOF) hybrid piezoelectric-electromagnetic energy harvester (P-EMEH). Such a 2DOF system is designed to achieve two close resonant frequencies. The combined piezoelectric-electromagnetic conversion mechanism is exploited to further improve the total power output of the system in comparison to a stand-alone piezoelectric or electromagnetic conversion mechanism. First, a mathematical model for the 2DOF hybrid P-EMEH is established. Subsequently, the maximal power output of the 2DOF hybrid P-EMEH is compared both experimentally and theoretically with those from the 1DOF piezoelectric energy harvester (PEH), 1DOF electromagnetic energy harvester (EMEH), 2DOF PEH, and 2DOF EMEH. Based on the validated mathematical model, the effect of the effective electromechanical coupling coefficients (EMCC) on the maximal power outputs from various harvester configurations is analyzed. The results indicate that for the 2DOF hybrid P-EMEH, although the increase of the power output from one electromechanical transducer will lead to the decrease of the power output from the other, the overall performance of the system is improved in weak and medium coupling regimes by increasing electromechanical coupling. In weak and medium coupling scenarios, the hybrid energy harvester configuration is advantageous over conventional 1DOF or 2DOF harvester configurations with a stand-alone conversion mechanism.

Understanding the dispersion and aggregation of carbon nanotubes (CNTs) in the aqueous environment are critical for the fate, bioavailability, and the environment and health risk assessment of them because the better suspended CNTs display a higher mobility and could transfer to a longer distance in the environment to possibly pose greater ecological and environmental risks. In this study, we have found that bulk single-walled carbon nanotubes (SWCNTs) could not be dispersed and stably suspended in water and sodium dodecylbenzene sulfonate (SDBS) solution by shaking at 140 r/min, although they could be stably suspended in SDBS solution by sonication. Even through sonication, SWCNTs suspended in SDBS solution do not remain stable at the presence of environmentally relevant cations (e.g., Na + , K + , Ca 2+ , and Mg 2+ ) after dilution. These observations suggest that SWCNTs will not travel long distances in significant concentrations in the natural environment to pose great ecological and environmental risks. We also observed that the re-aggregation of suspended SWCNTs in the presence of cations was dependent on the SDBS concen- tration rather than the SWCNT concentration in the suspension. Both SDBS and sonication play important roles in the dispersion of SWCNTs, with sonication breaking down large aggregates of SWCNTs, while SDBS adsorbed on the SWCNTs inhibits the coagulation and aggregation by steric/electrostatic repulsion to maintain the stability of the suspension in water.