Showing papers in "Science China-technological Sciences in 2009"
TL;DR: In this article, a nanoparticle based planar laser scattering method (NPLS) is developed, where the nanoparticles are used as tracer, and pulseplanar laser is used as light source in NPLS; by recording images of particles in flow field with CCD, high spatiotemporal resolution supersonic flow imaging is realized.
Abstract: Due to influence of compressibility, shock wave, instabilities, and turbulence on supersonic flows, current flow visualization and imaging techniques encounter some problems in high spatiotemporal resolution and high signal-to-noise ratio (SNR) measurements. Therefore, nanoparticle based planar laser scattering method (NPLS) is developed here. The nanoparticles are used as tracer, and pulse planar laser is used as light source in NPLS; by recording images of particles in flow field with CCD, high spatiotemporal resolution supersonic flow imaging is realized. The flow-following ability of nanoparticles in supersonic flows is studied according to multiphase flow theory and calibrating experiment of oblique shock wave. The laser scattering characteristics of nanoparticles are analyzed with light scattering theory. The results of theoretical and experimental studies show that the dynamic behavior and light scattering characteristics of nanoparticles highly enhance the spatiotemporal resolution and SNR of NPLS, with which the flow field involving shock wave, expansion, Mach disk, boundary layer, sliding-line, and mixing layer can be imaged clearly at high spatiotemporal resolution.
178 citations
TL;DR: The mechanical properties of marble, limestone, and sandstone as well as the stress-strain curve, the varying characteristics of the peak strength, the peak strain and elastic modulus were studied by using the MTS810 Rock Mechanics Servo-controlled Testing System under the action of temperatures rang-ing from room temperature to 800℃ as discussed by the authors.
Abstract: The mechanical properties of marble, limestone, and sandstone as well as the stress-strain curve, the varying characteristics of the peak strength, the peak strain and elastic modulus were studied by using the MTS810 Rock Mechanics Servo-controlled Testing System under the action of temperatures rang-ing from room temperature to 800℃. Results show that (1) the peak strength and elastic modulus of marble fluctuate at the temperature from normal to 400℃; and they decrease gradually over 400℃. (2) With the rise of the temperature, the peak strength and elastic modulus of limestone show downward trend from normal temperature to 200℃; have little change from 200℃ to 600℃; and decrease sharply over 600℃. (3) The peak strength of sandstone shows a downward trend while a little change for elastic modulus at normal temperature to 200℃; and from 200℃ to 600℃, the peak strength of sandstone in-creases while a little change for elastic modulus; the peak strength and elastic modulus decrease rap-idly at the temperature over 600℃. (4) The peak strain of limestone shows little change at normal tem-perature to 600℃, however, the peak strain increases rapidly over 600℃; and for marble and sandstone, the peak strain decreases with the rise of the temperature from normal temperature to 200℃, the peak strain increases rapidly over 200℃. The result can provide valuable references for the rock engineering design at high temperature.
164 citations
TL;DR: Wang et al. as mentioned in this paper conducted a systematic investigation on the earthquake disaster to mountain tunnels and geotechnical engineering and found that the major damage of the mountain tunnels was mainly concentrated in the tunnel portals due to widespread landslides and rockfalls, and the inner part of investigated tunnels suffered moderate damages mainly due to fault displacement.
Abstract: On May 12, 2008, a strong earthquake with a magnitude of 8.0 (Ms) struck Wenchuan town, in the eastern Sichuan area of west China. Following the earthquake on May 18, the Southwest Jiaotong University organized a damage survey team and dispatched it to the affected area for the investigation into the damage and collection of information and data. This paper outlines the findings of this investigation on the earthquake disaster to mountain tunnels and geotechnical engineering. The systematic investigation, involving geological conditions, design documents, construction and maintenance records of the tunnels, has been conducted and the degree of damage to investigated tunnels has been assessed according to the width and length of cracks, the stability of the slope above the tunnel, and the condition of the groundwater inrush. The results show that the major damage of the mountain tunnels was mainly concentrated in the tunnel portals due to widespread landslides and rockfalls, and the inner part of investigated tunnels suffered moderate damages mainly due to fault displacements. It is hoped that the information shared herein could enhance the outstanding of seismic behavior of mountain tunnels and improve seismic design and construction procedures.
149 citations
TL;DR: The fundamental principles of anti-adhesion and anti-resistance of soil animals are interpreted by reviewing the current status in this research field and summarizing the work of the research group at Jilin University of China in the past decades.
Abstract: The theoretical studies of bionics of machinery have great scientific significance, and the development of bionic machines has large practical values in the field of engineering and technology. Through the rigorous selection process of evolution, the survived living organisms have successfully developed outstanding abilities to adapt to their surroundings and to reproduce their offspring. In this review, we interpreted the fundamental principles of anti-adhesion and anti-resistance of soil animals by reviewing the current status in this research field and summarizing the work of the research group at Jilin University of China in the past decades. The principles and technologies used in morphology bionics, electric-osmosis bionics, flexibility bionics, configuration bionics and coupling bionics were examined. Finally, the applications of the engineering bionics and their extensive prospects were introduced.
96 citations
TL;DR: In this paper, a set pair analysis method (SPAM) is proposed for water resources system assessment, which takes fuzzy property of threshold values for grade standards into full account and avoid determining the discrepancy uncertainty coefficient i or i 1, i2, i3,... in SPA.
Abstract: Most traditional assessment methods, which have complicated mathematic formulas, are difficult for calculation and application in water resources system assessment. A new approach to water resources system assessment, the set pair analysis method (SPAM), has been proposed based on the principle of set pair analysis (SPA). The basic ideals and steps of SPAM are discussed. The proposed method can take fuzzy property of threshold values for grade standards into full account and avoid determining the discrepancy uncertainty coefficient i or i1, i2, i3, ... in SPA. The presented method is simple in concept, convenient to calculate and feasible for application. Two case studies of water resources assessment have been made. The results show that the proposed method is satisfactory.
96 citations
TL;DR: In this paper, the authors analyzed the distribution of geohazards triggered by the Wenchuan earthquake by using means of GIS technology and the conclusions are as follows: (1) the earthquake gehazards showed the feature of zonal distribution along the earthquake fault zone and linear distribution along rivers; (2) the distribution had a marked hanging wall effect, for the development density of gehoazards in the hanging wall of earthquake fault Zone was obviously higher than that in the foot wall and the width of strong development zone in a hanging wall was about 10 km;
Abstract: As the Wenchuan Earthquake was of high magnitude and shallow seismic focus, it caused great damage and serious geohazards. By the field investigation and the interpretation of remote-sensing information after the earthquake and by using means of GIS technology, the distribution of geohazards triggered by the earthquake are analyzed and the conclusions are as follows: (1) The earthquake geohazards showed the feature of zonal distribution along the earthquake fault zone and linear distribution along the rivers; (2) the distribution of earthquake geohazards had a marked hanging wall effect, for the development density of geohazards in the hanging wall of earthquake fault zone was obviously higher than that in the foot wall and the width of strong development zone in the hanging wall was about 10 km; (3) the topographical slope was a main factor which controlled the development of earthquake geohazards and a vast majority of hazards were distributed on the slopes of 20° to 50°; (4) the earthquake geohazards had a corresponding relationship with the elevation and micro-landform, for most hazards happened in the river valleys and canyon sections below the elevation of 1500 to 2000 m, particularly in the upper segment of canyon sections (namely, the turning point from the dale to the canyon). Thin ridge, isolated or full-face space mountains were most sensitive to the seismic wave, and had a striking amplifying effect. In these areas, collapses and landslides were most likely to develop; (5) the study also showed that different lithologies determined the types of geohazards, and usually, landslides occurred in soft rocks, while collapses occurred in hard rocks.
93 citations
TL;DR: Tangjiashan Barrier Lake is one of the largest barrier lakes caused by the Wenchuan Earthquake as mentioned in this paper, and its risk analysis, emergency plan and effect of the emergency plan are introduced in this paper.
Abstract: Tangjiashan Barrier Lake is one of the largest barrier lakes caused by the Wenchuan Earthquake. Its risk analysis, emergency plan and effect of the emergency plan are introduced in this paper. The dam height of Tangjiashan Barrier Dam is about 105 m, and the reservoir storage capacity is 3.2×108 m3. When the dam broke the flood peak were estimated to be larger than 48000 m3/s, which might cause a enormous disaster to the downstream cities and residents. A discharge channel with 13 m deep and 8 m wide was drug, so that the water may flow out of the lake before the dam breaks. As a result, the drainage and risk mitigation project are successful. During the drainage process, the flood peak was about 6500 m3/s, and about 1.6×108 m3 of water was drained off and the residual reservoir capacity was only 8.97×107 m3. A new channel with average width 100 m was formed, which can bear floods of 200 years frequency. The successful experience and the collected data can be used to deal with the similar natural disasters in future.
84 citations
TL;DR: This paper systematically presents the methodology based on the screw theory for the first time and analyzes six representative puzzling mechanisms, and interprets the essential reason for validity of the methodology.
Abstract: It is well known that the traditional Grubler-Kutzbach formula fails to calculate the mobility of some classical mechanisms or many modern parallel robots, and this situation seriously hampers mechanical innovation. To seek an efficient and universal method for mobility calculation has been a heated topic in the sphere of mechanism. The modified Grubler-Kutzbach criterion proposed by us achieved success in calculating the mobility of a lot of highly complicated mechanisms, especially the mobility of all recent parallel mechanisms listed by Gogu, and the Bennett mechanism known for its particular difficulty. With wide applications of the criterion, a systematic methodology has recently formed. This paper systematically presents the methodology based on the screw theory for the first time and analyzes six representative puzzling mechanisms. In addition, the methodology is convenient for judgment of the instantaneous or full-cycle mobility, and has become an effective and general method of great scientific value and practical significance. In the first half, this paper introduces the basic screw theory, then it presents the effective methodology formed within this decade. The second half of this paper presents how to apply the methodology by analyzing the mobility of several puzzling mechanisms. Finally, this paper contrasts and analyzes some different methods and interprets the essential reason for validity of our methodology.
78 citations
TL;DR: In this paper, a proactive roadbed-cooling approach was developed and used to lower the ground temperature in order to maintain a perennially frozen subgrade in Qinghai-Tibet Railway.
Abstract: Under global warming scenarios, the passive method of simply increasing the thermal resistance by raising the embankment height and using insulating materials has been proven ineffective in warm and ice-rich permafrost areas and therefore could not be used in the Qinghai-Tibet Railway engineering Instead, a proactive “cooled-roadbed” approach was developed and used to lower the ground temperature in order to maintain a perennially frozen subgrade The concept that local and site-specific factors play an important role in the occurrence and disappearance of permafrost has helped us to devise a number of measures to cool down the roadbed For example, we adjust and control heat transfer by using different embankment configurations and fill materials The Qinghai-Tibet Railway project demonstrates that a series of proactive roadbed-cooling methods can be used to lower the temperature of permafrost beneath the embankment and to stabilize the roadbed These methods include solar radiation control using shading boards, heat convection control using ventilation ducts, thermosyphons, air-cooled embankments, and heat conduction control using “thermal semi-conductor” materials, as well as combinations of above mentioned three control measures This roadbed-cooling approach provides not only a solution for engineering construction in sensitive permafrost areas but also a countermeasure against possible global warming
73 citations
TL;DR: The extended finite element method (XFEM) is a new numerical method for modeling discontinuity as discussed by the authors, which is used for concrete hydraulic fracturing by XFEM, and it has been successfully applied for hydraulic fracture analysis.
Abstract: The extended finite element method (XFEM) is a new numerical method for modeling discontinuity. Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally, the method is verified by two examples and the advantages of the XFEM for hydraulic fracturing analysis are displayed.
73 citations
TL;DR: Wang et al. as mentioned in this paper investigated the effect of the cohesive strength of filling of cohesive homogeneous earth dams on breach formation and found that when the strength is smaller, the breach process becomes faster, and the peak outflow, the final width and depth of breach become bigger.
Abstract: In consideration of the range of clay content of Chinese earth dams, the world’s highest prototype tests have been made to research on the effects of cohesive strength of filling of cohesive homogeneous earth dam on breach formation. Three breach mechanisms were presented, they were the source-tracing erosion of dam body with the form of “multilevel headcut”, “two-helix flow” erosion of dam crest and collapse of breach sidewalls due to instability. It can be concluded that the cohesive strength of filling of earth dam has great effect on breach formation. When the cohesive strength is bigger, the breach process becomes slower, and the peak outflow and the final width and depth of breach become smaller. The main character of the breach formation is head cutting and dumping collapse. When the cohesive strength is smaller, the breach process becomes faster, and the peak outflow, the final width and depth of breach become bigger. The main character of the breach formation is single level head cutting and shearing collapse.
TL;DR: In this paper, a new type of ultra-lightweight metallic lattice structure (named as the X-type structure) was reported, which was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure with top and bottom facesheets to form sandwich panels.
Abstract: A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density.
TL;DR: In this article, a nonlinear model was presented for analysis of damage-cracking behavior in arch dams during strong earthquakes using different seismic input mechanisms, including a plastic-damage model for cyclic loading of concrete considering strain softening and a contact boundary model of contraction joint opening.
Abstract: In this study, a nonlinear model is presented for analysis of damage-cracking behavior in arch dams during strong earthquakes using different seismic input mechanisms. The nonlinear system includes a plastic-damage model for cyclic loading of concrete considering strain softening and a contact boundary model of contraction joint opening. Two different earthquake input mechanisms are used for comparison, including massless foundation input model and viscous-spring boundary model considering radiation damping due to infinite canyon. The results demonstrate that effects of seismic input mechanism and radiation damping on nonlinear response and damage-cracking of the dam are significant. Compared with the results of using massless foundation input model, the damage-cracking region and contraction joint opening are substantially reduced when using viscous-spring boundary model to take into account radiation damping. However, if the damping ratio of the dam is artificially increased to about 10%–15% for massless foundation input model, the joint opening and damage-cracking of the dam are comparable to the results obtained from the viscous-spring boundary model.
TL;DR: Wang et al. as discussed by the authors reviewed the development of traditional lime-based bond in ancient times and found that the application of organic materials in inorganic mortar was a sharp-cut characteristic during the developing process of construction gelled materials in ancient China.
Abstract: The development of traditional lime-based bond in ancient times was reviewed in this paper. It was proved by a lot of historical data that the application of organic materials in inorganic mortar was a sharp-cut characteristic during the developing process of construction gelled materials in ancient China. The important role sticky rice mortar ever played and the historical significance were revealed. Due to the excellent performance, such as high adhesive strength, good toughness, water-proof and so on, traditional mortar represented by sticky rice mortar should be one of the greatest technological contributions of the day in the world. Modern technology was employed in the study of the sticky rice lime mortar and the researching results of our laboratory and some researchers, including the composition and the mechanism of solidification, were also presented. It was found that the sticky rice acted as a matrix of bio-mineralization which affected the microstructure of the calcium carbonate crystal and there was cooperation between sticky rice and calcite produced during the solidifying of the sticky rice mortar, which maybe lead to the excellent performance of the mortar. Because of excellent performance and importance in science, sticky rice mortar can be regarded as one of the greatest inventions in construction history of China. Relative research of sticky mortar will be of importance for the exploring of ancient momentous invention and the repairing of ancient construction.
TL;DR: In this paper, the authors reformulate the DDA as a mixed complementary problem (MiCP) and then choose the path Newton method (PNM) to solve the problem.
Abstract: The contact between blocks is treated by the open-close iteration in the conventional discontinuous deformation analysis (DDA), which needs to introduce spurious springs between two blocks in contact and to assume the normal stiffness and the tangential stiffness (the penalty factors). Unreasonable values of stiffness would result in numerical problems. To avoid the penalty factors and the open-close iteration, we reformulate the DDA as a mixed complementary problem (MiCP) and then choose the path Newton method (PNM) to solve the problem. Some examples including those originally designed by Shi are reanalyzed, which proves feasibility of the proposed procedure.
TL;DR: In this article, the authors investigated the bending behavior of a functionally graded composite beam crack-controlled by UHTCC (abbreviated as UHTC-FGC beam) and established a theoretical calculation model to evaluate the results of four-point bending experiment on long composite beams without web reinforcement.
Abstract: Based on the concept of functionally graded concrete, UHTCC (ultrahigh toughness cementitious composites) material with excellent crack-controlling ability is strategically substituted for part of the concrete, which surrounds the main longitudinal reinforcement in a reinforced concrete member. Investigations on bending behavior of such a functionally graded composite beam crack-controlled by UHTCC (abbreviated as UHTCC-FGC beam) have been carried out. After establishing a theoretical calculation model, the paper discusses the results of four-point bending experiment on long composite beams without web reinforcement, and validates the theoretical formulae through experimental results of UHTCC-FGC beams with different thicknesses of UHTCC layer. Besides improving bearing capacity and saving steel reinforcements, the results indicate that UHTCC-FGC beams can also effectively control the deformation and enhance the ductility of members. At last, the optimal thickness of UHTCC layer in UHTCC-FGC beams has been confirmed, which can not only save materials and improve mechanical performance of members, but also be very effective in preventing corrosion-induced damage and enhancing the durability of members by controlling crack width below 0.05 mm under service conditions.
TL;DR: Based on the conceptual summarization of the supersaturated total dissolved gas (TDG) production process, the TDG prediction model for high-dam projects, in which the ski-jump energy dissipation is adopted, is developed in this paper.
Abstract: The supersaturated total dissolved gas (TDG) generated during high dam spills may cause gas bubble disease for fish and ultimately endanger their existence. As more and more high-dam hydropower projects have been constructed in China, the environmental assessment of the supersaturated TDG is becoming more and more important. It is of great importance for quantitative impact assessment of the supersaturated TDG of high dams and for the construction of ecological friendly high-dam hydropower projects. Based on the conceptual summarization of the TDG production process, the TDG prediction model for high-dam projects, in which the ski-jump energy dissipation is adopted, is developed in the paper. The model is validated by field data and employed in the TDG prediction of a high-dam hydropower project to be built in southwest China.
TL;DR: This paper is an attempt to optimally design a novel spatial three-degree-of-freedom (3-DOF) parallel robot by using the concept of motion/force transmission, and three indices are defined.
Abstract: Optimal design is one of the most important issues in robots. Since the very beginning, the concepts of the Jacobian matrix, manipulability and condition number, which are used successfully in the field of serial robots, have been applied to parallel robots. Unlike serial robots, parallel robots are good for motion/force transmission. Their performance evaluation and design should be correspondingly different. This paper is an attempt to optimally design a novel spatial three-degree-of-freedom (3-DOF) parallel robot by using the concept of motion/force transmission. Accordingly, three indices are defined. The suggested indices are independent of any coordinate frame and could be applied to the analysis and design of a parallel robot whose singularities can be identified wholly by using the relative angle between the output and adjacent links, and by using the relative angle between the input and adjacent links.
TL;DR: In this article, the bifurcations and chaotic dynamics of a simply supported symmetric cross-ply composite laminated piezoelectric rectangular plate are studied for the first time.
Abstract: The bifurcations and chaotic dynamics of a simply supported symmetric cross-ply composite laminated piezoelectric rectangular plate are studied for the first time, which are simultaneously forced by the transverse, in-plane excitations and the excitation loaded by piezoelectric layers. Based on the Reddy’s third-order shear deformation plate theory, the nonlinear governing equations of motion for the composite laminated piezoelectric rectangular plate are derived by using the Hamilton’s principle. The Galerkin’s approach is used to discretize partial differential governing equations to a two-degreeof-freedom nonlinear system under combined the parametric and external excitations. The method of multiple scales is employed to obtain the four-dimensional averaged equation. Numerical method is utilized to find the periodic and chaotic responses of the composite laminated piezoelectric rectangular plate. The numerical results indicate the existence of the periodic and chaotic responses in the averaged equation. The influence of the transverse, in-plane and piezoelectric excitations on the bifurcations and chaotic behaviors of the composite laminated piezoelectric rectangular plate is investigated numerically.
TL;DR: The entransy dissipation extremum principle provides new warranty and criterion for optimization of heat transfer as discussed by the authors, which provides some guidelines for some relevant thermal design problems, and the method presented in this paper can be used to optimize the model constructal geometry.
Abstract: The entransy dissipation extremum principle provides new warranty and criterion for optimization of heat transfer. For two cases (body with heat generation and body heated externally) of a solid conducting wall with an open cavity, a dimensionless equivalent thermal resistance based on entransy dissipation definition was taken as the optimization objective to optimize the model constructal geometry. Numerical results validated the necessity and feasibility of the presented method. Comparisons of the numerical results based on minimization of dimensionless maximum thermal resistance and minimization of dimensionless equivalent thermal resistance, respectively, showed that there was no obvious difference between the two results when the volume fraction Φ occupied by cavity was small, but the difference between the two results increased with the increases of Φ and the body aspect ratio H/L for any model. The optimal cavities for bodies heated externally were more slender than those for bodies with heat generation. Heat origin had obvious effect on the global performance of heat transfer. The entransy dissipation of body heated externally increased 2―3 times than that of body with heat generation, indicating that the global performance of heat transfer weakened. The method presented herein provides some guidelines for some relevant thermal design problems.
TL;DR: In this paper, the potential impacts and power outputs of a barrage across the Severn Estuary were assessed using an unstructured grid, high-resolution, model being developed and applied to the estuary to assess the implications of each of five shortlisted proposed schemes on the hydrodynamic, geomorphologic, flood risk and faecal indicator organism changes within the EE.
Abstract: Details are given herein of the current main proposals for tidal energy provision from the Severn Estuary, in the UK, with particular emphasis being focused on the Severn Barrage project, as originally promoted by the Severn Tidal Power Group. In particular, emphasis has focused on assessing the potential hydro-environmental impacts and power outputs of a barrage across the estuary, with an unstructured grid, high resolution, model being developed and applied to the estuary to assess the implications of each of five shortlisted proposed schemes on the hydrodynamic, geomorphologic, flood risk and faecal indicator organism changes within the estuary. An outline is given of recent research on power refinements to the model to assess the options for power generation. The results show that the Severn Barrage has the potential to reduce the tidal currents in a highly dynamic estuary. This leads to the reduction of suspended sediment loads (particularly upstream of the barrage), an increase of light penetration within the water column and, potentially, an increase in the benthic bio-diversity and the level of aquatic life in the estuary. The results also show that the Severn Barrage will reduce markedly the risk of flooding upstream of the barrage and to a lesser extent downstream of the structure. In contrast the alternative options have far less impact on flood risk changes. In addition to the Severn Barrage some results are shown herein for a typical lagoon option, namely the Fleming Lagoon.
TL;DR: In this paper, the basic concepts related to biological coupling are introduced from the bionic viewpoint, and the general modes of biological coupling studies are analyzed and the prospects of multi-coupling bionics are predicted.
Abstract: The phenomena that biological functions originate from biological coupling are the important biological foundation of multiple bionics and the significant discoveries in the bionic fields. In this paper, the basic concepts related to biological coupling are introduced from the bionic viewpoint. Constitution, classification and characteristic rules of biological coupling are illuminated, the general modes of biological coupling studies are analyzed, and the prospects of multi-coupling bionics are predicted.
TL;DR: In this paper, both sensitivity-based method and simulation method are used to analyze the streamflow response to climate variability and human activities in the upper catchment of the Yellow River Basin (UYRB) in a study.
Abstract: Both sensitivity-based method and simulation method are used to analyze the streamflow response to climate variability and human activities in the upper catchment of the Yellow River Basin (UYRB) in this study. The separation regime of effects from climate variability and human activities is investigated. Results show that the changes of streamflow are more sensitive to precipitation than potential evapotranspiration (PET). Effect of climate variability on streamflow estimated using the sensitivity-based method is weak in the upper catchment of Jimai station, and strong in the upper catchment of Lanzhou station, where the climate effects accounted for about 50% of total streamflow changes. Effects of human activities on streamflow accounted for about 40% in the UYRB, with weaker effects in the upper catchment of Tangnaihai station than those in the upper catchment of Lanzhou station. Both climate variability and human activities are main factors to affect the changes of streamflow in the UYRB.
TL;DR: In this paper, a cradle-to-gate life cycle assessment was conducted to calculate the greenhouse gas (GHG) emissions, such as CO2, CH4, CF4 and C2F6 emissions, based on statistic data of Chinese aluminum industry of the year 2003.
Abstract: A cradle-to-gate life cycle assessment was conducted in this paper to calculate the greenhouse gas (GHG) emissions, such as CO2, CH4, CF4 and C2F6 emissions, based on statistic data of Chinese aluminum industry of the year 2003. The results showed that the GHG emissions for 1 t primary aluminum production was 21.6 t CO2 equivalent which is 70% higher than that of worldwide average level of the year 2000. The main contributors of emission were the alumina refining and aluminum smelting process accounting for 72% and 22% in accumulative emission, respectively. According to the development and application of new process technologies for primary aluminum production and the ‘target of energy-saving and emissions-reducing’ of Chinese government, the reduction potential of the GHG emissions for alumina and aluminum production were estimated. The results indicated that China aluminum industry would achieve the target of reducing about 25% GHG emissions by the end of 2010.
TL;DR: In this paper, the authors discussed the distribution optimization of the limited high conductivity material with the simulated annealing algorithm to homogenize the temperature field in a two-dimensional heat conduction problem.
Abstract: The homogenization of temperature field and temperature gradient field are very important for many devices, systems and equipments, such as satellites and electronic devices. This paper discusses the distribution optimization of the limited high conductivity material with the simulated annealing algorithm to homogenize the temperature field in a two-dimensional heat conduction problem. At the same time, the temperature gradient field is homogenized with the bionic optimization method. The results show that the two optimization targets are consistent to some extent, while the bionic optimization method could save much computing time. In addition, there are threshold values for the amount of high conductivity material and the ratio of the high conductivity to the low conductivity beyond which further increasing these values brings very little improvement on the homogenization of temperature field and temperature gradient field.
TL;DR: In this article, a two-stage heated tube system with cracked products collection/analysis was used and it can achieve a fuel temperature range of 700-1100 K, a pressure range of 3.5-4.5 MPa and a residence time of approximately 0.5 -1.3 s.
Abstract: Thermal cracking of China No.3 aviation kerosene was studied experimentally and analytically under supercritical conditions relevant to regenerative cooling system for Mach-6 scramjet applications. A two-stage heated tube system with cracked products collection/analysis was used and it can achieve a fuel temperature range of 700-1100 K, a pressure range of 3.5-4.5 MPa and a residence time of approximately 0.5-1.3 s. Compositions of the cracked gaseous products and mass flow rate of the kerosene flow at varied temperatures and pressures were obtained experimentally. A one-step lumped model was developed with the cracked mixtures grouped into three categories: unreacted kerosene, gaseous products and residuals including liquid products and carbon deposits. Based on the model, fuel conversion on the mass basis, the reaction rate and the residence time were estimated as functions of temperature. Meanwhile, a sonic nozzle was used for the control of the mass flow rate of the cracked kerosene, and correlation of the mass flow rate gives a good agreement with the measurements.
TL;DR: In this article, a numerical simulation of water flow over the stepped spillway is conducted using Mixture multiphase flow model, in which different turbulence models are chosen to enclose the controlling equations.
Abstract: Numerical simulation of water flow over the stepped spillway is conducted using Mixture multiphase flow model. Different turbulence models are chosen to enclose the controlling equations. The turbulence models investigated are realizable k-ɛ model, SST k-ω model, v2-f model and LES model. The computational results by the four turbulence models are compared with experimental ones in the following aspects: mean velocity, the spanwise vorticity and the growth of the turbulent boundary layer thickness in the streamwise direction. It is found from the comparison that the realizable k-ɛ model, in which the rotation tensor is included, shows good performance for simulation of flows involving rotation, boundary layer and recirculation. The realizable k-ɛ model is the most efficient in simulating flow over stepped spillways. Further, the characteristics of water flow on the stepped spillway are studied in terms of the mean velocity profile normal to the pseudo-bottom and the pressure field on the steps based on the simulation results using realizable k-ɛ model.
TL;DR: In this paper, the nonlinear free transverse vibrations of a nano-beam on simple supports are investigated based on nonlocal elasticity theory and the governing equation is proposed by considering geometric nonlinearity due to finite stretching of the beam.
Abstract: The nonlinear free transverse vibrations of a nano-beam on simple supports are investigated based on nonlocal elasticity theory. The governing equation is proposed by considering geometric nonlinearity due to finite stretching of the beam. The method of multiple scales is applied to the governing equation to evaluate the nonlinear natural frequencies. Numerical examples are presented to demonstrate the analytical results and highlight the contributions of the nonlinear term and nonlocal effect.
TL;DR: In this paper, the authors investigated the pool boiling characteristics at the thermal interface with TiO2 nanotube arrays (TNTAs) and showed that the TNTAs interface can enhance the swimming pool boiling heat transfer compared to the pure Ti metal plate.
Abstract: Surface with TiO2 nanotube arrays (TNTAs) is superhydrophilic and of great specific area. This paper investigates the pool boiling characteristics at the thermal interface with TNTAs. The results show that the TNTAs interface can enhance the pool boiling heat transfer compared to the pure Ti metal plate. The bubbles formed at the initial nucleation state are very small and released in higher frequency. The pool boiling heat transfer enhancement at the TNTAs interface may be attributed to the high density of nucleate site, high intrinsic heating area of nanotubes layer, superhydrophilicity and the vertically oriented nanotube structure.
TL;DR: In this article, the authors make theoretical research on construction quality real-time monitoring and system integration of core rockfill dam, and propose implementation method and integrated solution of construction QoT monitoring and realtime monitoring of the core rock fill dam construction process.
Abstract: With the enlargement of core rockfill dam construction scale and the improvement of construction mechanization level, the traditional manual construction quality control method is now difficult to meet the quality and safety demands of modern dam construction, so automatic and real-time dam construction quality monitoring with high-techs is urgently needed. The paper makes theoretical research on construction quality real-time monitoring and system integration of core rockfill dam, proposes implementation method and integrated solution of construction quality real-time monitoring of core rockfill dam construction process, realizes refining, all-whether, entire-process and real-time control and analysis on key links of dam construction, and introduces the application of the construction quality real-time monitoring and system integration technology to a practical core rockfill dam project.