Showing papers in "Journal of Zhejiang University Science in 2014"

Interactions between engineered nanomaterials and agricultural crops: implications for food safety

Abstract: Engineered nanomaterials (ENMs) are being discharged into the environment and to agricultural fields, with unknown impacts on crop species. In this paper, we review the literature on ENMs uptake, translocation/distribution, and generational transmission in various crop species, as well as potential material trophic transfer. Previous studies reveal that ENM-exposed crops exhibit adaptive processes in response to stress, including endocytosis/endosome activities, production of antioxidant enzymes, regulation of genes related to cell division/extension and membrane transport. Some agronomic traits of crops are compromised during the adaption response, including photosynthesis, fruit yields, nutritional quality and nitrogen fixation. Cultivation of crops in ENMs-contaminated environments has unknown implications for food safety and quality. Notably, mechanisms underlying ENMs phytotoxicity and bioavailability are unclear. Additional investigations focused on developing novel techniques for in vivo identification/characterization of ENMs are critically needed. Given the abundance of uncertainty in the literature, it is clear that more research is urgently needed in the area of ENMs-crop interactions; only then can one accurately assess exposure, risk, and overall implications for food safety and also enable guidance development for the sustainable implementation of nanotechnology in agriculture and food production/manufacturing.

The state-of-the-art centrifuge modelling of geotechnical problems at HKUST

Abstract: Geotechnical centrifuge modelling is an advanced physical modelling technique for simulating and studying geotechnical problems. It provides physical data for investigating mechanisms of deformation and failure and for validating analytical and numerical methods. Due to its reliability, time and cost effectiveness, centrifuge modelling has often been the preferred experimental method for addressing complex geotechnical problems. In this ZENG Guo-xi Lecture, the kinematics, fundamental principles and principal applications of geotechnical centrifuge modelling are introduced. The use of the state-of-the-art geotechnical centrifuge at the Hong Kong University of Science and Technology (HKUST), China to investigate four types of complex geotechnical problems is reported. The four geotechnical problems include correction of building tilt, effect of tunnel collapse on an existing tunnel, excavation effect on pile capacity and liquefied flow and non-liquefied slide of loose fill slopes. By reporting major findings and new insights from these four types of centrifuge tests, it is hoped to illustrate the role of state-of-the-art geotechnical centrifuge modelling in advancing the scientific knowledge of geotechnical problems.

Emission inventory and trends of NO x for China, 2000–2020

Abstract: The rapid growth of NO x emissions in China is mainly due to intensive fossil fuel consumption. In order to control NO x emissions, a multiyear NO x emission inventory was established by a bottom-up approach for the period 2000–2010. The results showed that NO x emissions increased by 2.1 times from 11.81 million tons (Mt) in 2000 to 24.33 Mt in 2010. We found that NO x emissions had exceeded SO2 emissions in 2009 by comparison with their emission trends. We also found that the unbalanced NO x emissions in Eastern China and Western China are mainly due to the different gross regional product and industrial structure. Accounting for 70% of total energy consumption in China, coal is the largest NO x emission source among all the fossil fuels. In addition, the increased use of diesel and gasoline has spurred the increase of NO x emissions from the transportation sector. Manufacturing, electricity production, and transportation together composed about 90% of the national NO x emissions. Meanwhile, energy consumption and NO x emissions in China are predicted to be 3908.5 Mt standard coal equivalent (SCE) and 19.7 Mt in 2020 with this scenario analysis, respectively. To achieve a desired NO x reduction target, China should take strict measures to control NO x emissions, such as improvement in reduction technology, promulgation of new emission standards, and joint control by various Chinese provinces.

A 3D model for coupling dynamics analysis of high-speed train/track system

Abstract: A 3D dynamic model of a high-speed train coupled with a flexible ballast track is developed and is presented in this study. In this model, each vehicle is modeled as a 42 degrees of freedom multi-body system, which takes into consideration the nonlinear dynamic characteristics of the suspensions. A detailed inter-vehicle connection model including nonlinear couplers and inter-vehicle dampers, and the linear tight-lock vestibule diaphragm is established to simulate the effect of the end connections of neighboring vehicles on dynamic behavior. The track is modeled as a traditional three-layer discrete elastic support model. The rails are assumed to be Timoshenko beams supported by discrete sleepers. Each sleeper is treated as an Euler beam and the ballast bed is replaced by equivalent rigid ballast bodies. The reliability of the present model is then validated through a detailed numerical simulation comparison with the commercial software SIMPACK, with the effect of the track flexibility on the train/track interaction being analyzed simultaneously. The proposed model is finally applied to investigate the difference between dynamic performances obtained using the entire-train/track model (TTM) and the single-vehicle/track model (VTM). Several key dynamic performances, including vibration frequency response, ride comfort, and curving performance, calculated by the two types of dynamic models are compared and discussed. The numerical results show that there is a significant difference between the dynamic behaviors obtained by VTM and TTM, and that inter-vehicle connections have an important influence on the dynamic behavior of high-speed vehicles.

Key problems faced in high-speed train operation

Abstract: This paper discusses some key problems faced in high-speed train operation. These problems include: wheel tread concave wear causing the lateral oscillation of the train in operation, wheel roundness higher-order polygonal wear leading to fierce vertical vibration of wheel/rail and abnormal vibration noise of the coach interior of the train thus causing loosening and cracking of the train bogie parts, short pitch rail corrugation generation on the part of the track, fracture of cushion layer and road base fracture of the track, and increased noise inside and outside the train. At present, the mechanism of the occurrence and development of these phenomena is still not fully understood. This paper briefly reviews the related research on these problems in China and abroad, including many important recent papers and the articles published in this special issue. They make outstanding contributions to solving these problems, and include important work on train-track coupling large system theory, the relationship theory and technique of wheel/rail, and the vibration-noise reduction technology of the train.

Design criteria for sediment transport in sewers based on self-cleansing concept

Abstract: 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.

Microbial fuel cells for energy production from wastewaters: the way toward practical application *

Abstract: Much energy is stored in wastewaters. How to efficiently capture this energy is of great significance for meeting the world’s energy needs, reducing wastewater handling costs and increasing the sustainability of wastewater treatment. The microbial fuel cell (MFC) is a recently developed biotechnology for electrical energy recovery from the organic pollutants in wastewaters. MFCs hold great promise for sustainable wastewater treatment. However, at present there is still much research needed before the MFC technique can be practically applied in the real world. In this review, we analyze the opportunities and key challenges for MFCs to achieve sustainability in wastewater treatment. We especially discuss the problems and challenges for scaling up the MFC systems; this is the most critical issue for realizing the practical implementation of this technique. In order to achieve sustainability, MFCs may also be combined with other techniques to yield high effluent quality or to recover more commercial value (i.e., by producing energy-rich or high value chemicals) from wastewaters. However, research in this area is still on-going and many problems need to be settled before real-world application. Advances are required in respect of efficiency, economic feasibility, system stability, and reliability.

A 2DOF hybrid energy harvester based on combined piezoelectric and electromagnetic conversion mechanisms

Abstract: 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.

Influence of wheel polygonal wear on interior noise of high-speed trains

Abstract: This work presents a detailed investigation conducted into the relationships between wheel polygonal wear and wheel/rail noise, and the interior noise of high-speed trains through extensive experiments and numerical simulations. The field experiments include roundness measurement and characteristics analysis of the high-speed wheels in service, and analysis on the effect of re-profiling on the interior noise of the high-speed coach. The experimental analysis shows that wheel polygonal wear has a great impact on wheel/rail noise and interior noise. In the numerical simulation, the model of high-speed wheel/rail noise caused by the uneven wheel wear is developed by means of the high-speed wheel-track noise software (HWTNS). The calculation model of the interior noise of a high-speed coach is developed based on the hybrid of the finite element method and the statistic energy analysis (FE-SEA). The numerical simulation analyses the effect of the polygonal wear characteristics, such as roughness level, polygon order (or wavelength), and polygon phase, on wheel/rail noise and interior noise of a high-speed coach. The numerical results show that different polygon order with nearly the same roughness levels can cause different wheel/rail noises and interior noises. The polygon with a higher roughness level can cause a larger wheel/rail noise and a larger interior noise. The combination of different polygon phases can make a different wheel circle diameter difference due to wear, but its effect on the interior noise level is not great. This study can provide a basis for improving the criteria for high-speed wheel re-profiling of China’s high-speed trains.

Research and development of large-scale cryogenic air separation in China

Abstract: With the rapid growth in demand for industrial gas in steel and chemical industries, there has been significant emphasis placed on the development of China’s large-scale air separation technology. Currently, the maximum capacity of a single unit has been able to attain 120000 Nm3/h (oxygen), and the specific power consumption of 0.38 kWh/m3. This paper reviews the current state-of-the-art for large-scale cryogenic air separation systems being deployed in China. A brief introduction to the history and establishment of the large-scale cryogenic air separation industry is presented. Taking the present mainstream large-scale air separation unit operating at 60000 Nm3/h (oxygen) as an example, the technological parameters and features of the involved key equipment, including a molecular sieve adsorber, air compressor unit, plate-fin heat exchanger, turbo-expander and distillation column are described in detail. The developing 80000–120000 Nm3/h air separation processes and equipment are also introduced. A summary of the existing problems and future developments of these systems in China are discussed.

Modeling of high-speed wheel-rail rolling contact on a corrugated rail and corrugation development

Abstract: Short pitch rail corrugations were observed on a recently opened Chinese high-speed line On the basis of field measurements and observations of corrugations occurred on the high-speed line, a 3D transient rolling contact model is developed using the explicit finite element (FE) method to investigate high-speed vehicle-track interactions in the presence of rail corrugations The rotational and translational movements of the wheel are introduced as initial conditions in the model The frictional rolling contact between the wheel and the corrugated rail is solved by a penalty method based surface-to-surface contact algorithm with Coulomb’s law of friction The contact filter effect is considered automatically by the finite size of the contact patch Through specifying a time-dependent driving torque applied to the wheel axle, the tangential vehicle-track interaction on the corrugated rail is analyzed in the time domain together with the normal one at different traction levels and at rolling speeds of up to 500 km/h This analysis focuses on detailed contact solutions, such as distributions of the pressure, surface shear stress, Von Mises (V-M) stress, and frictional work The corrugation dimensions, traction level, and rolling speed are varied to investigate their influences, building a solid basis for further studying the material damage mechanisms A theory is proposed based on the simulations to explain the observed phenomenon that the corrugation gradually stabilizes The traditional multi-body approach is found to overestimate the dynamic wheel-rail interaction on a corrugated rail

Seismic response study on a multi-span cable-stayed bridge scale model under multi-support excitations. Part I: shaking table tests

Abstract: With the rapid development of bridge engineering in China, multi-span cable-stayed bridges have become one of the main structures of modern highways and railways for crossing rivers or straits In this study, a 1:100 scale model of a three-tower cable-stayed bridge was tested using a shaking table array system The mechanism associated with the seismic response of the scale model under uniform and non-uniform excitations was clarified The results from the tests indicated that: (1) the strong vibration responses of the main girder and towers under four different horizontal earthquake wave excitations were identified, and the seismic responses of the scale model were most evident under uniform Jiangxin (JX) wave excitation; (2) the seismic performances of the main girder and towers of the scale model were adversely affected by traveling wave effects, especially when the wave velocity exceeded 616 m/s, which suggests that traveling wave effects should be considered in the seismic design of multi-tower cable-stayed bridges; (3) when the peak acceleration value of the El Centro (EC) wave reached 40 m/s2, shear failure of the bearing of the middle tower first appeared This kind of shaking table tests will help to improve our understanding of dynamic performance, and will be especially useful in the design process and numerical simulation of multi-span cable-stayed bridges with large span subjected to spatially varying earthquake ground motions

Three-dimensional numerical simulation of mechanized twin stacked tunnels in soft ground

Abstract: The increase in transportation in large cities has made it necessary to construct twin tunnels at shallow depths. As far as the parallel excavation of mechanized twin tunnels is concerned, most of the cases reported in previous studies have focused on the interactions between two horizontally driven tunnels. However, less work has been devoted to the interactions between tunnels stacked over each other. The numerical investigation performed in this study has made it possible to evaluate the influence of the construction process on two stacked tunnels, using the FLAC 3D finite difference element software. The structural forces induced in each of the stacked tunnels and the displacements in the surrounding ground have been highlighted. The results of the numerical analysis indicate that new tunnel construction can have a great impact on an existing tunnel. The greatest impacts are observed when the upper tunnel is excavated first. The excavation of the upper tunnel generally leads to greater surface settlements than when the lower tunnel is excavated first. This study also shows that the normal forces induced in the lower tunnel are always greater than those developed in the upper tunnel. The normal displacements and the bending moments induced in the lower tunnel are usually smaller than those in the upper tunnel.

Random amplified polymorphic DNA reveals that TiO2 nanoparticles are genotoxic to Cucurbita pepo

Abstract: Titanium dioxide nanoparticles (TiO2 NPs) are used in cosmetics, sunscreens, paints, and toothpaste, among other applications. These NPs are very stable and can be transported and dispersed in wastewater and biosolids. Animal species have shown negative reactions to TiO2 NPs. However, little is known about their toxicity in plants, specifically the possibility of gen- otoxic effects. In this study, we used a random amplified polymorphic DNA (RAPD) technique to study the genotoxic effects of TiO2 NPs on hydroponically cultivated zucchini (Cucurbita pepo) plants. Seeds were allowed to germinate for 7 d and plants were selected at random for individual and population studies. Four plants were selected for the individual study and 18 for the popu- lation study. RAPD profiles of TiO2 NPs treated plants showed differences in band intensity, loss of bands, or appearance of new bands, compared to untreated plants. To the authors' knowledge, this is the first report of the genotoxic potential of TiO2 NPs in zucchini.

Measurements and analysis of track irregularities on high speed maglev lines

Abstract: Track irregularities have an obvious effect on the running stability and ride quality of maglev trains traveling at high speeds. We developed a measurement principle and data processing method which were applied to the high speed maglev line operating. The method, which includes partial filtering, integration, resampling of signal, and a low pass Butterworth filter, was used to calculate the irregularities of the maglev line. The spectra of the sample space were evaluated. A 7-parameter power spectrum density (PSD) function of line irregularities was fitted, based on the measured data. Analysis of the results showed that the maglev stator plane irregularities were better than conventional railway vertical rail irregularities when the wavelength was 5–100 m, and worse when the wavelength was 1–5 m. The PSD of maglev guidance plane irregularities was similar to that of cross level GRSHL (German railway spectra of high irregularity) when the wavelength was 10–100 m. The irregularities were clearly worse than cross level rail irregularities in a conventional railway when the wavelength was 1–10 m. This suggests that short-wavelength track irregularities of a maglev line caused by deviation and inclination of the stator plane should be minimized by strictly controlling the machining error of functional components during construction and maintenance.

Significance of physicochemical and uptake kinetics in controlling the toxicity of metallic nanomaterials to aquatic organisms

Abstract: With the extensive applications of metallic-based nanomaterials (MNs), concerns are growing of their potential impact on aquatic organisms. Unlike traditional metal pollutants, MNs have different surface properties and compositions, which may modify their impact on aquatic environments as well as their bioavailability to aquatic organisms. Kinetic processes of MNs, such as dissolution, stabilization, aggregation, and sedimentation, are important in determining their bioavailability and subse- quent toxicity to aquatic organisms. Among all of the physicochemical kinetics, the dissolution of MNs attracts the most attention, due to their potential toxicity generated by dissolved ions. This review summarizes the dissolution behavior of three common MNs, i.e., ZnO nanoparticles (ZnO-NPs), Ag nanoparticles (Ag-NPs), and TiO2 nanoparticles (TiO2-NPs), in toxicological studies. A kinetic model was developed to evaluate the contribution of dissolved ion on the total MN accumulation. Finally, toxicological data of the MNs to algae, zooplankton, and fish are summarized and interpreted based on their kinetics. Different dissolution rates were observed for ZnO-NPs, Ag-NPs, and TiO2-NPs, and their solubility also varied during different toxicological studies, leading to a variable but increasing waterborne ion concentration during exposure. The bioavailability of these MNs and corresponding ions also varied for different aquatic organisms (e.g., algae, zooplankton, and fish). Specifically, the MNs appeared to be more bioavailable to daphnids, rendering a minor contribution of ion during short-term exposure. Generally, dissolved ion contributed partially to toxicity of ZnO-NPs and Ag-NPs, while the toxicity of TiO2-NPs was mainly due to the generated reactive oxygen species (ROS). Additionally, the role of dissolved ion in both MN bioaccumulation and toxicity intensified during chronic ex- posure as a result of dissolution, thus it is critical to monitor the dissolution of MNs in toxicological studies. This review empha- sizes the importance of integrating physicochemical kinetics and uptake kinetics in evaluating the bioavailability and toxicity of both MNs and dissolved ions.

A numerical study of the effects of roller paths on dimensional precision in die-less spinning of sheet metal

Abstract: Die-less spinning eliminates the dependence upon the mandrel of traditional spinning, but bringing about comparatively poor dimensional accuracy which needs to be improved. In this paper, roller paths in the first pass of die-less spinning, including concave, convex, linear and combined ones are parameterized according to the degree of bending and their effects on dimensional precision (thickness variation and shape deviation) have been studied by using experiments of finite element (FE) analysis. The effects of roller paths on thickness variation, shape deviation, tool forces, and stress and strain variations have been analyzed numerically. The results showed that for concave roller paths, the thickness variation is not very sensitive to the degree of bending, while a low degree of bending of the roller path can result in a low shape deviation. For convex roller paths, a low degree of bending leads to both low thickness reduction and low shape deviation. Further research shows that a combined roller path with convex-concave curve could contribute a low shape deviation, while an inverse combined roller path gives better thickness precision.

High temperature mechanical performance and micro interfacial adhesive failure of textile reinforced concrete thin-plate

Abstract: The mechanical performance of textile reinforced concrete (TRC) thin-plate under high temperature conditions was investigated using three-point bending tests. The influence of polypropylene (PP) fiber addition on the out-of-plane load capacity of TRC thin-plate after high temperature treatment was also studied. The results showed that the thermostability of TRC thin-plate with textile impregnated with epoxy resin was not good, but that the out-of-plane load capacity of TRC thin-plate after high temperature treatment could be improved by increasing the plate thickness or the textile distribution rate. Under normal temperature and a high temperature of 120 °C, the out-of-plane load capacity of specimens could be increased and cracks better distributed by mixing the TRC with PP fiber. However, the out-of-plane load capacity of TRC thin-plate under a continuous high temperature of 200 °C was not much affected by the addition of PP fiber. The result of a microcosmic scanning electron microscope (SEM) test showed that the main reason for the interfacial adhesive failure between the textile and the original concrete substrate was the degradation of the epoxy resin under high temperature.

Investigation into external noise of a high-speed train at different speeds

Abstract: This paper presents a detailed discussion of the experimental analysis of the external noise produced by a Chinese high-speed train traveling at different speeds. Based on the delay and sum beam-forming method, a microphone array with 78 microphones was used to measure the external noise produced by the train moving at speeds of up to 390 km/h. The experiment and its analysis showed that the main noise produced by the train originates in three areas: the wheel/rail system (or bogies), the pantograph, and the inter-coach gaps of the train. The frequency characteristics and sound exposure level (SEL) of these main sources were analyzed for different speeds. In the range of 5000 Hz, the SELs of the three main noise sources are clearly identified. Along the vertical height of the train, as seen from the rail head, the maximum noise levels always occur in the wheel/rail area. At different measurement field points, the predominant noise components of the total noise have different frequencies that vary with the train speed. Furthermore, at the measurement points, the rolling noise has a greater contribution to the total noise than the aerodynamic noise. The experimental results and their corresponding analysis are very useful for the control and reduction of the external noise produced by high-speed trains.

Interval multiobjective optimization of structures based on radial basis function, interval analysis, and NSGA-II

Abstract: 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.

Phytotoxicity of silver nanoparticles to cucumber (Cucumis sativus) and wheat (Triticum aestivum)

Abstract: The increasing release of silver (Ag) nanoparticles (NPs) into the environment highlights the importance of exploring the interactions between Ag NPs and plants, which are the basis of most ecosystems. In this study, two plant species, Cucumis sativus L. (cucumber) and Triticum aestivum L. (wheat) were exposed to Ag NPs and Ag+ (added as AgNO3) at the germination and vegetative growth stages. Above certain concentrations, Ag NPs and Ag+ were toxic to the two plants. However, stimulatory effects were observed on root elongation for the cucumbers that were exposed to Ag NPs at concentrations below 200 mg/L, and Ag+ at concentrations below 5 mg/L. The two plants were more susceptible to the toxicity of Ag NPs at the vegetative growth stage than the germination stage. Ag was accumulated in the roots and was subsequently translocated to the shoots after the exposure to Ag NPs. To assess the role of released Ag+, we measured the dissolution of Ag NPs in exposure solutions. About 0.03% and 0.01% of Ag NPs were dissolved into a hydroponic solution at the germination stage for cucumber and wheat, respectively; while 0.17% and 0.06% at the vegetative period for cucumber and wheat, respectively. Cysteine, a strong chelating ligand of Ag+, could completely eliminate the effects of Ag NPs on cucumber and wheat, suggesting that the phytotoxicity of Ag NPs was possibly caused by the release of Ag+.

An investigation of flow characteristics in slope siphon drains

Abstract: This paper presents a study of flow characteristics in high-lift siphon drains A laboratory test was conducted to investigate the effects of hose diameter and flow velocity on siphon drainage Three types of water flow were observed and analyzed The experimental results show that the flow characteristics of siphon drainage are significantly influenced by the hose diameter Water flows in the form of a wall pressing flow in a large diameter siphon hose (eg, larger than 50 mm) under low flow velocity, which leads to discontinuous siphon drainage However, water flows in the form of an integral slug flow in a small diameter siphon hose (eg, smaller than 40 mm) under low flow velocity, which leads to continuous siphon drainage Based on experimental observations, a thermodynamic derivation of the threshold of siphon hose diameter for continuous siphon drainage was analytically conducted In slope engineering, a 36 mm polyurethane (PU) hose is recommended for siphon drainage

Effect of the inclination angle on the transient performance of a phase change material-based heat sink under pulsed heat loads

Abstract: The transient performance of a phase change material (PCM)-based heat sink may be affected by its inclination angle because natural convection usually occurs and dominates melting during the operation of the heat sink. An experimental setup was designed and used in this study that allows for the alternation of the inclination angle of the heat sink. The inclination angle was varied from 0° to 90° at increments of 15°, while two pulsed heat loads (20 and 40 W) were adopted. 1-hexadecanol of a nominal melting temperature of 49 C was selected as the PCM. The transient performance of the heat sink was characterized by the temperature variations at the center of the heat spreader under various conditions. The results showed that the transient perfor- mance of the heat sink is able to be improved by simply increasing its inclination angle which then facilitates the natural convec- tion during melting. However, the variation in the performance is not a monotonous function of the inclination angle. Although the time-averaged thermal resistances of the heat sink were shown to be only marginally lowered, the maximum operation times may be greatly extended under the given thermal conditions. For a heat load of 40 W and the maximum allowable temperature of 75 °C, the operation time of the heat sink is extended by up to nearly 67% at an inclination angle of 75° when compared to that of the horizontal case. Based on the cases tested, the optimal inclination angle was found to lie between 60° and 75°.

Working characteristics of concrete-cored deep cement mixing piles under embankments

Abstract: The concrete-cored deep cement mixing (DCM) pile is a new kind of composite pile created by inserting a precast core pile into the DCM column socket and has only been used in a few expressway projects to date. In this paper, full scale field tests of composite foundations reinforced by both concrete-cored DCM piles and by conventional DCM columns under embankments were conducted in northeast of Nanjing Surrounding Expressway (NS-N Expressway), China. With the installation of settlement plates, multipoint settlement gauges, inclinometers, piezometers, pressure transducers, and steel stress meters, the results of plate load tests and long-term monitoring, including ultimate bearing capacity, total settlement, settlement along depth, lateral movement, loading sharing ratio, vertical stress of precast core pile, and excess pore pressure were presented. Based on field test results, the reinforcement effects of composite foundations reinforced by concrete-cored DCM piles and conventional DCM columns were compared. The load transfer characteristics of concrete-cored DCM piles under embankments were also discussed. The test results show that the foundation treatment effect of concrete-cored DCM pile is better than that of the conventional DCM column. Compared to the conventional DCM column, the upper load borne by concrete-cored DCM pile is higher, while the excess pore pressure in concrete-cored DCM pile composite foundation is lower than that in conventional DCM column composite foundation. Under embankment, negative friction occurs at the upper section of concrete-cored DCM pile.

Effect of the first two wheelset bending modes on wheel-rail contact behavior

Abstract: The objective of this paper is to develop a new wheel–rail contact model, which is suitable for considering the effect of wheelset bending deformation on wheel–rail contact behavior at high speeds. Dummies of the two rigid half wheelsets are introduced to describe the spacial positions of the wheels of the deformed wheelset. In modeling the flexible wheelset, the first two wheelset bending modes are considered. Based on the modal synthesis method, these mode values of the wheelset axle are used to solve the motion equations of the flexible wheelset axle modeled as an Euler–Bernoulli beam. The wheel is assumed to be rigid and always perpendicular to the deformed axle at the wheel center. In the vehicle model, two bogies and one car body are modeled as lumped masses. Spring–damper elements are adopted to model the primary and secondary suspension systems. The ballasted track is modeled as a triple-layer discrete elastic supported model. Two high-speed vehicle–track models, one considering rigid wheelset models and the other considering flexible wheelset models, are used to analyze the differences of the numerical results of the two models in both frequency and time domains. In the simulation, a random high-speed railway track irregularity is used as wheel–rail excitations. Wheel–rail forces are calculated and analyzed in the time and frequency domains. The results clarify that this new contact model can characterize very well the influence of the first two bending modes of the wheelset on contact behavior.

Measurement and characterization of engineered titanium dioxide nanoparticles in the environment

Abstract: Titanium dioxide nanoparticles (TiO2-NPs) are common components used in sunscreens, cosmetics, industrial applications, and many other products Concerning their high production and widespread applications, characterization and quantification of TiO2-NPs in various matrixes is a topic of great interest for researchers studying their potential environmental and health impacts Validated and easily applicable analytical tools are required to develop and implement regulatory frameworks and an appropriate risk assessment for engineered nanoparticles (ENPs) Herein, we provide a critical review of the current knowledge available on world-wide production and measured environmental concentrations as well as on available techniques to measure and characterize these ENPs in the environment

An efficient adaptive finite element method algorithm with mass conservation for analysis of liquid face seals

Abstract: To improve lubrication effect and seal performance, complicated geometrical hydrodynamic grooves or patterns are often processed on end faces of liquid lubricated mechanical seals. These structures can lead to difficulties in precisely estimating the seal performance. In this study, an efficient adaptive finite element method (FEM) algorithm with mass conservation was presented, in which a streamline upwind/Petrov-Galerkin (SUPG) weighted residual FEM and a fast iteration algorithm were applied to solve the lubrication equations (Reynolds equation). A mesh adaptation technique was utilized to refine the computation domain based on a residual posterior error estimator. Validation, applicability, and efficiency were verified by comparison among different algorithms and by case studies on seals’ faces with different groove structures. The study investigated the influence of the order of shape function and the mesh number on the leakage balance. Mesh refinement occurred mainly in cavitation zones when cavitation happened, otherwise it occurred in regions with a high pressure gradient. Numerical experiments verified that the proposed algorithm is a fast, effective, and accurate method to simulate lubrication problems in the engineering field apart from end face seals.

Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation

Abstract: To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient ω and a softening modulus coefficient α were introduced to take into account the stiffness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Mohr-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model’s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength parameters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confining pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.

Study on the safety of operating high-speed railway vehicles subjected to crosswinds

Abstract: A coupled vehicle-track dynamic model is put forward for use in investigating the safety effects of crosswinds on the operation of a high-speed railway vehicle. In this model, the vehicle is modeled as a nonlinear multi-body system, and the ballasted track is modeled as a three-layer discrete elastic support system. The steady aerodynamic forces caused by crosswinds are modeled as ramp-shaped external forces being exerted on the vehicle body. This model was used in a numerical analysis of the dynamic response and dynamic derailment mechanisms of high-speed vehicles subjected to strong crosswinds. The effects of the crosswind speeds, crosswind attack angle, and vehicle speed on the operational safety of the vehicle were examined. The operational safety boundaries of a high-speed vehicle subjected to crosswinds were determined. The numerical results obtained indicate that crosswinds at attack angles of 75° to 90° with respect to the forward direction of the vehicle have a great influence on the safety of operating high-speed railway vehicles. The wheelset unloading limit, which determines the position of the warning boundary dividing the safe operating area and the warning area, is the most conservative, i.e., the safest, criterion to use in assessing the high-speed operational safety of vehicles in crosswinds.

A terminal sliding mode based torque distribution control for an individual-wheel-drive vehicle

Abstract: 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