Motion Planning of Concrete Pump Truck with End-Effector＇s Specified Path 免费阅读 下载全文 For motion planning of concrete pump truck( CPT) with end-effector’s hosepipe path, this paper sets up the mathematic model,including definition of its motion planning,description of its state in C space( configuration space) and its path length. An advanced rapidly-exploring random trees( RRT) algorithm is proposed, in which each tracing point dispersed from the end hosepipe path can map multi-states of CPT so as to make variety of motion path of CPT. For increasing search efficiency and motion path quality,this algorithm generates any random states of CPT in certain probability to trend to the initial state or target state mapped with the end hosepipe path,and to have the least cost between this random state and its parent state. A typical case and two special cases are analyzed in which the end hosepipe paths are reciprocating linear trajectory and planar or spatial sine curves respectively. Their results verify the feasibility and validity of the proposed algorithm.
Effect of Front Baffle Inclination Angle and Pressure Drop on Absorption Performance of a Pickup Mouth 免费阅读 下载全文 In order to improve the dust absorption performance of the reverse blowing pickup mouth, the gas-solid flow motion properties inside the reverse blowing pickup mouth were simulated by using computational fluid dynamics( CFD) software,Fluent.The results show that both the front baffle inclination angle and the pressure drop across the pickup mouth have significant impacts on dust absorption performance. As the inclination angle is increased,there is an increase in the overall and grade removal efficiency. As the front baffle inclination angle or pressure drop is increased,there is an increase in the overall and grade removal efficiencies.However,pressure drop affects energy consumption. Front baffle inclination angle and pressure drop are optimized. Optimal inclination angle and pressure drop are 105° and 2 300 Pa respectively. Sample machine is made and measured,which further verifies the appropriateness of numerical simulation and practicability of optimum strategy.
Improved Model of Start-Wave Velocity at Intersections Based on Unmanned Aerial Vehicle Data 免费阅读 下载全文 The basic parameters involved in current start-wave theoretical models such as density and velocity are difficult to obtain through traditional traffic detection devices. Thus it is hard to apply these theoretical models to the actual verification and prediction for real situation. Unmanned aerial vehicle( UAV),which can shoot aerial video and identify vehicles, roads and other objects, is introduced in this study as a new type of traffic information collection method to gather the real-time data of the necessary parameters. An improved start-wave velocity model is proposed,where the speed and density of traffic flow are converted into vehicle space headway,mean vehicle length and other auxiliary parameters which can be recognized from aerial video or other means. A UAV was used for video shooting at intersections in a flight experiment in order to verify the accuracy of the calculated start-wave velocity.The mean absolute error rate between the calculated velocity and the actual velocity is 2. 277%. Moreover, the improved start-wave velocity model showed much better accuracy than the traditional start-wave velocity model. The results indicate that the improved model is accurate enough to be used for model calibration and validation in signal timing optimization.更多还原
Opening Angle Rules of the Aerodynamic Brake Panel 免费阅读 下载全文 In order to get the relationship between aerodynamic brake effect and the opening angle,based on a high-speed train model in CFD software FLUENT,the aerodynamic force properties from brake panels with different opening angles were analyzed as well as the flow field’s variation laws. Six cases were researched,taking opening angles 45°,60°,75°,80°,85° and 90° respectively.Three-dimensional Reynolds-average Navier-Stokes equation combined with k-ε turbulence model was utilized. The control equation was discretized and solved by finite volume method.SIMPLE method was also considered to couple the pressure and velocity fields and search the numeric solutions. Conclusions can be achieved from the results which are shown as follows. When the opening angle increases from 45° to 75°,the aerodynamic forces and the central area with larger pressure increase fast,and the flow field distribution changes greatly; when the opening angle increases from75° to 90°,the aerodynamic forces and the central area with larger pressure increase slowly, and the flow field distribution changes slightly; considering train boundary and opening performance of the wind resistance brake mechanism,the opening angle should be 75°.更多还原
Analysis of the Relationship between Landuse and Non-point Source Pollution in Ashi River Basin 免费阅读 下载全文 Landuse is one of the most influential factors of non-point source pollution. Based on the three-year landuse data( 2000,2005 and 2008),Arc GIS and Fragstat were used to analyze the landuse type and the change of landscape pattern. The relationships between landuse and non-point source-total nitrogen( NPS-TN) and nonpoint source-total phosphorus( NPS-TP) were discussed with the methods of spatially statistical analysis,landscape pattern analysis and principal component analysis. The study results conveyed that agricultural land and forestland,which accounted for over 92% of the study area,were the major landuse type of Ashi River Basin.Meanwhile,the NPS pollution had close connections with landuse type and landscape pattern. When it comes to landuse type,the export risks of NPS-TN and NPS-TP were agricultural land > urban land > grassland > forestland. As for landscape pattern,NPS-TN and NPS-TP were positively related to SHDI and SHEI, while negatively connected with LPI,AI and COHESION. Therefore,the study could reach the conclusion that the more fragmented and complicated the landscape patterns were,the more serious the NPS pollution was.
Behaviour of Multiscale Progressive Damage for Different Matrix Glass Fiber Reinforced Plastics Bars 免费阅读 下载全文 The damage formation and evolution of glass fiber reinforced plastics( GFRP) bar on mechanical properties were mainly evaluated by theoretical analysis and numerical calculations which lack of test basis of damage process. The two different matrices of unsaturated polyester and vinylester GFRP bars were selected to carry out a series of macro-mesoscopic physical and mechanical tests to analyze the tensile progressive damage process on a multiscale. The formation of apparent crack,the bonding of internal components as well as the strain change were all reflected damage evolution of GFRP bar,and a certain correlation existed between them. Wherein the matrix has an obvious impact on the damage of bar,the component stress transfer effect of vinylester bar is better than unsaturated polyester from crack propagation observation and scanning electron microscopy( SEM). The cyclic loading tests quantitatively reflect the difference of damage accumulation between different matrix bars,and the failure load of bars decreases nearly 10%.
Effect of Polydimethylsilxoane Molecular of Soft Segment on Novel Urethane-Siloxane Copolymers 免费阅读 下载全文 Novel segmented urethane-siloxane copolymers were synthesized by a two-step bulk polymerization procedure using 4,4’-methylenediphenyl diisocyanate( MDI) and 1,4-butanediol( BDO)as the hard segment components and novel polypropyleneoxide polyether( PPO) blocked polydimethylsilxoane( PDMS) α,ω-dihydroxy-( PPO-PDMS-PPO) as the soft segment component,where the hard segment content was 30% by weight,and the molar ratio of NCO / OH was 1. 02. A series of urethane-siloxane copolymers were prepared from different molecular weights of α,ω-dihydroxy-( PPO-PDMS-PPO). The soft segments were different in the molecular of PDMS block segment. Chemical structure,morphology,mechanical properties,surface properties and thermal properties of thermoplastic polyurethane( TPU) were investigated by Fourier transform infrared spectroscopy( FT-IR),scanning electron microscopy and energy dispersive X-ray spectroscopy( SEM-EDX),mechanical properties( MP) test,water contact angle( WCA) test,differential scanning calorimetry( DSC),thermogravimetric analysis( TGA), respectively. According to the obtained results, the hydrophobicity of silicone modified TPU promoted,surface WCA increased from 73° to 120°. Low temperature resistant performance was improved,and the glass transition temperature decreased from- 44. 2℃ to- 120. 8℃. Thermal stability was also improved,the beginning temperature of thermal degradation increased from 281 ℃to 299 ℃.
Mixed Monotone Iterative Technique and Boundary Value Problem for a Class of Impulsive Integro-Differential Equations 免费阅读 下载全文 In this paper,the existence and uniqueness of iterative solutions to the boundary value problems for a class of first order impulsive integro-differential equations were studied. Under a new concept of upper and lower solutions, a new monotone iterative technique on the boundary value problem of integro-differential equations was proposed. The existence and uniqueness of iterative solutions and the error estimation in certain interval were obtained.An example was also given to illustrate the results.
Dynamic Performance Analysis of the Coupling Shaft System in a Carpet Tufting Machine Utilizing the Transfer Matrix Method 免费阅读 下载全文 The dynamic performance of the coupling shaft system in a carpet tufting machine is the most critical factor affecting the carpet tufting machine’s efficiency,and the product quality of the tufted carpet. To determine how to avoid resonance produced by the coupling shaft system’s vibration during the weaving process,the dynamic performance of a coupling shaft system in a carpet tufting machine was analyzed. Focusing on a DHGN801D-400 carpet tufting machine,a dynamic model of coupling shaft system was established by utilizing transfer matrix methodology. On the basis of this model,the natural frequencies and mode shapes of the coupling shaft system were obtained through simulations. The correctness of the theoretical model and the dynamic performance of the coupling shaft system were validated by experiments. The first order natural frequency of the coupling shaft system was close to 600 r / min. A conclusion can thus be drawn that operating the carpet tufting machine near this speed should be avoided as much as possible.
Simulation and Experimental Study of Dynamic Characteristics of a Pneumatic Actuator in Air Splicer 免费阅读 下载全文 Splicing process parameters determined by dynamic characteristic of pneumatic actuator in air splicer have a significant influence on the performance of spliced yarn. Both gas thermodynamic and pneumatic actuator dynamic models, which were solved by the Runge-Kutta algorithm, were established to analyze the relationship among structural parameters of a pneumatic actuator and splicing process parameters such as splicing duration and gas consumption. Additionally,a visualization test bench to observe the dynamics of the pneumatic actuator and a mass flow measurement system to track splicing duration and gas consumption were designed. Comparisons between experimental data and simulation results show that the mathematical model accurately accounts for the dynamic characteristics of the pneumatic actuator,and consequently predicts splicing process parameters, which provides a theoretical foundation for the design optimization of air splicer.
Morphology,Bending Property and Secondary Structure Estimation of Dog Hair 免费阅读 下载全文 The morphology, bending property and secondary structure estimation of dog hair were investigated by scanning electron microscope( SEM),fiber compression bending analyzer,fiber frictional coefficient tester and Fourier transform infrared spectroscopy( FTIR). The SEM micrograph of hair indicated guard hair( GH),intermediate hair( IH) and underhair( UH) from dog hair fibers displayed considerable differences in the diameter,length,scale shape and medulla. In addition,the bending property of fibers were related to the diameter of fibers and the percentage and structure of medulla. The UH had the greatest frictional coefficient,while the guard hair had the largest bending rigidity in three kinds of hairs. The analysis of amide I region implied that there was an apparent variety in the secondary structure of hairs,mainly the percentage of α-helix and β-pleated sheet and β-turn structure. The X-ray diffraction results showed that the crystallinity of the UH was the lowest in the three kinds of fibers. The tensile behaviors of dog hair also indicated that the increase of β-pleated and β-turn structure caused the increase of the breaking strength.
Experimental Research on Grinding Surface-Quality of Dental Zirconia 免费阅读 下载全文 The properties and cutting performance of Y2O3-stabilized tetragonal zirconia polycrystal（ Y-TZP） used widely for dental restoration have been introduced. The surface roughness of denture made by the ceramics plays an important role in product quality. In order to enhance the surface quality of denture processing,the effect of grinding parameters such as spindle speed,feed rate and the depth of cut with different levels on denture surface roughness were deeply studied to look for reasonable grinding parameters. The experiment was arranged in the orthogonal method. A new dental bur used only for dentistry was employed to carry out the experiment in a high accuracy machining center which was developed by Nanjing University of Aeronautics and Astronautics. The experimental results demonstrated that the depth of cut was the major parameter on surface roughness. With scanning electron microscope（ SEM）,it was found that the ceramics debris and its surfaces damage were mainly affected by depth of cut. The surface formation mechanism of zirconia ceramics was revealed by the morphology of machined surface. The topographies of the grinded ceramics surfaces demonstrated that zirconia ceramics was removed by its brittle fracture and plastic deformation. The plastic deformation region at grinded ceramic surface was larger with the smaller grinding depth.Finally, an example for grinding molar crown using zirconia ceramics was provided. After processing,the surface morphology of the molar crown was measured. The results showed that its quality was high and met the requirements of dental restoration. The research results of this paper provide useful and theoretical basis for denture processing.
Dynamic Characteristics of Tracked Vehicle Power Train Considering Road Random Torsional Excitation 免费阅读 下载全文 The road random torsional excitation is one type of torque rooted from the road roughness and vehicle drive system. This paper aims to study how the road random torsional excitation affects the dynamic characteristics of vehicle power train. The method of simulating the random torsional excitation of tracked vehicle is explored at first. Secondly,the road random torsional excitations under different road roughness,vehicle speeds and pre-tensions are obtained. Thirdly,the dynamic analysis model of tracked vehicle power train is constructed with the consideration of the road random torsional excitation. Eventually,the influences of this excitation on output torque,bearing support force,vibration acceleration and dynamic shear stress of transmission shafts are intensively studied.The research conclusions are helpful to correct and refine the present virtual prototype of tracked vehicle power train.
Antimicrobial M aterials： Synthesis of Reactive 5,5-Dimethylhydantoin Derivative and Application in Cellulose with Dyeing Process 免费阅读 下载全文 The efficient and regenerable antibacterial properties of Nhalamines make them an ideal candidate for parapretion of antimicrobial textiles. In this study,a 5,5-dimethylhydantoin-based reactive N-halamine precursor, 4-( 4-( 3-( 3-hydroxypropyl)-5,5-dimethylhydantoin)-6-chloro-1,3,5-triazinylamino)-benzenesulfonate( HTB), was synthesized and characterized by ~1H-NMR. The synthesized compound was coated to cotton fabrics via reactive dye dyeing process. The coated cotton showed excellent antimicrobial activities against S. aureus( Gram-positive) and E. coli O157: H7( Gram-negative) with short contact times after exposing to diluted household bleach. The treatment method used in this study has a small effect on the tensile strength of cotton fabrics. The durability and regenerability of the chlorinated cotton samples were tested.Although the chlorine content decreased towards washing and storage,almost all of the initial oxidative chlorine levels could be regained after rechlorination.
Protective Performance of Fiberglass Fabrics Coated by Silicone Resin Mixed with Nature Filler Powders 免费阅读 下载全文 The coated fiberglass fabric was prepared to protect personnel and equipment from sparks, heat, and molten metals during hot work projects. Ferric oxide powder 2%,mica powder6%,wollastonite powder 4%,and white carbon black 8% were added in the phenyl methyl silicone to prepare the composite silicone solution. The french chalk and coupling agent can effectively solve the deposition of fillers in the coating solution. Compared with the original fiberglass fabric,heat resistance of the coated fabric under high temperature was greatly improved, and the temperature limitation in short period was higher than 900℃. Horizontal flammability tests showed that the coated fabric was non-combustible with no melting and no fragments. The temperature for long period usage of coated fabric was lower than 500 ℃. Welding drop test showed that the coating could prevent the molten metals,sparks and heat from transferring in the fabric. Test for toxic gas release showed that the toxic gases such as HCN,SO2,HCl,and HF were not detected,only CO（ 100 mg / m3） and NO（ 12 mg /m3） were detected,and their concentrations were far lower than the limitation values CO（ 4 375 mg / m3） and NO（ 134 mg /m3）. The breaking strength of coated fabric was almost twice the strength of the original fabric,and the coated surface had good water and oil repellency.
Face Recognition Based on Adaptive Sparse Coefficient 免费阅读 下载全文 Recently,robust sparse coding achieves high recognition rates on face recognition( FR),even when dealing with occluded images. However,robust sparse coding is that the coefficients are guaranteed global sparse when solving the sparse coefficients. In this paper,the coefficient vector is divided into multiple regions. Then,the elements in the object region are enabled to approximate global maximum by adding two constraint conditions( the maximal element of coefficient vector is in the object region; the sum of elements in the object region is the maximum value among all regions),which makes the distribution of sparse coefficient adapt to different classes of testing images. The efficacy of the proposed approach is verified on publicly available databases( i. e.,AR and Extended Yale B).Furthermore, the proposed method still can achieve a good performance when the training samples are limited.
Numerical Simulation Investigation of the Impact of Simplified Architectural Canopy Models on the Distribution of Flow Filed 免费阅读 下载全文 A series of simulations of air flow through three kinds of2 D vegetation canopies along with different canopy morphology have been conducted by computational fluid dynamics( CFD). Two different turbulent closure models have been used, including standard k-ε turbulent model and RNG k-ε turbulent model with or without source / sink terms,respectively,for the purpose of wind energy applications. In this study,the complicated morphology of3 D vegetation canopy is simplified to three types of 2D simplified canopy model analyzed by the main parameter leaf area index( LAI). Effects of branches and leaves on airflow are also modelled by introducing circles into the 2D simplified canopy model with or without source / sink terms by adding drag force terms in the momentum and turbulent energy equations in porous sub-domains.The main model parameters of source / sink terms are identified thanks to experimental data obtained by direct wind tunnel measurements of the air flow speeds through a branch of Osmanthus fragrans. Moreover,three different canopy shapes of the vegetation canopy are introduced into the simulation. The predictive skills of single-and two-equation( k-ε) models with or without source / sink to compute profiles of mean velocity( u),turbulent kinetic energy( TKE),TKE dissipation rate( ε) and turbulent intensity( I) are compared against datasets collected from other works and field measurements. In conclusion, it is demonstrated that vegetation canopy model 1 using RNG or standard k-ε turbulent model with source / sink terms proves to be a physically accurate and numerically robust method. The method which is better than other two vegetation canopy models is recommended for future use in simulating turbulent flows within and above the canopy in 3D in more details.
Application of Monodisperse Thermo-Responsive Composite Microgels with Core-Shell Structure Based on [email protected] Bimetallic Nanorod as Core in Surface Enhanced Raman Spectroscopy Substrate 免费阅读 下载全文 The monodisperse [email protected] bimetallic nanorod is encapsulated by crosslinked poly( N-isopropylacrylamide)( PNIPAM) to produce thermo-responsive composite microgel with well-defined core-shell structure( Au@ Ag NR@ PNIPAM microgel)by seed-precipitation polymerization method using butenoic acid modified Au @ Ag NRs as seeds. When the temperature of the aqueous medium increases from 20℃ to 50℃,the localized surface plasmon resonance( LSPR) band of the entrapped Au @ Ag NR is pronouncedly red-shifted because of the decreased spatial distances between them as a result of shrinkage of the microgels,leading to their plasmonic coupling. The temperature tunable plasmonic coupling is demonstrated by temperature dependence of the surface enhanced Raman spectroscopy( SERS) signal of 1-naphthol in aqueous solution. Different from static plasmonic coupling modes from nanostructured assembly or array system of noble metals,the proposed plasmonic coupling can be dynamically controlled by environmental temperature. Therefore, the thermo responsive hybrid microgels have potential applications in mobile LSPR or SERS microsensors for living tissues or cells.
Estimating the Shareholder＇s Terminal Payoff in Insurer＇s Solvency Ratio Model under Fractional Market 免费阅读 下载全文 The insurer’s solvency ratio model in a class of fractional Black-Scholes markets is studied. In this market,the price of assets follows a Wick-It stochastic differential equation,which is driven by the fractional Brownian motion. The market coefficients of market model are deterministic functions. By the stochastic calculus of the fractional Brownian motion and the pricing formula of European call option for the fractional Brownian motion,the explicit formula for the expected present value of shareholder’s terminal payoff is given. The model extends the existing results.
Numerical Simulation of a Courtyard under Different Ground Thermal Conditions and Flow Patterns 免费阅读 下载全文 The impact of thermal conditions of the ground on ventilation in the interior courtyard and rooms of enclosed building is very important to improve the air quality in courtyard. The computational fluid dynamics( CFD) model was used to investigate the flow field of a certain courtyard and analyze the static differential pressure between the two sides of the vent and ventilation conditions of the courtyard. The results indicate that thermal effects not only changed the air flow pattern of the interior courtyard but also obviously increased the flow velocity of the upper space of the courtyard. For the most of courtyard rooms,the absolute value of static differential pressure increases as the thermal intensity of the ground increases. In all wind directions,the air exchange rate of the courtyard increases with the higher thermal intensity of the ground which makes a greater influence on the increasing of the ventilation rate of the roof opening than that on the gate opening.
Energy Efficient Relay Positioning and Power Allocation for One-Way N-Relay Channel 免费阅读 下载全文 Two end-users which have symmetric traffic requirements in terms of data rate are considered. They exchange information in Rayleigh flat-fading channels and multiple serial half-duplex relay nodes are employed to extend the communication coverage and assist the bidirectional communication between them using the analog network coding( ANC) protocol. With the objective of minimizing the sum transmit energy at the required data rate c,the optimal relay positioning and power allocation problem is firstly investigated and then the sub-optimal solutions for a two-relay channel are proposed,due to no close-form optimal solution. Furthermore,a sub-optimal scheme of relay positioning and power allocation,called equal-distance equal-transmit-power( EDEP) for an arbitrary Nrelay channel,N > 1 is proposed. Simulation results demonstrate a consistence with our proposed scheme.
Genetic Diversity Analysis on Rep-PCR Genomic Fingerprinting and 16S rDNA Sequences of Desulfurization Bacteria 免费阅读 下载全文 In order to reduce deleterious effect on environment,human health and facilities caused by original sulfides, more attention should be paid to biodesulfurization studying for fossil fuels. In this work, eight isolates were characterized by several DNA-based methods such as BOX element polymerase chain reaction( BOX-PCR), enterobacterial repetitive intergenic consensus( ERIC)-PCR and random amplification of polymorphic DNA( RAPD)-PCR. The desulfurization performance was determined by micro-coulometric method,Gibb’s assay and barium sulfate test. It was found out that ERIC-PCR displays a much higher inter-strain heterogeneity compared with using BOX. The length of the primer didnot play the most important role in bacterial classification. The combination of the analysis of repetitive-sequence-based polymerase chain reaction ngerprinting and 16 S r DNA was able to provide more effective way in the separation and identification of bacteria.According to the analysis of 16 S r DNA,the more efficient desulfurization strain should belong to Klebsiella variicola.
Experimental Study on Performance of Supercritical CO_2 Heat Exchanger with Four Different Inner Tubes 免费阅读 下载全文 The experiment was conducted to investigate the heat transfer performance of supercritical CO2 in a casing heat exchanger by comparing their heat transfer,entropy production unit number,non-dimensional entropy production rate and field synergy factor.The results show that both heat transfer and entropy production unit number in four tubes decrease with water temperature increasing.Heat transfer and entropy production unit number in multiple tubes（ i. e.,triple straight tube and double helix tube） is higher than their single counterparts; the non-dimensional entropy production rate increases with water temperature. Non-dimensional entropy production rate of triple straight tube and double helix tube is far below the single tube. Field synergy factor of double helix tube is much higher than that of the triple straight tube under the same condition. Further experiment was carried out in double helix tube,under various CO2 pressure and inlet water temperature,the results are analyzed and reported in this paper.
Condensing Effect of Suction Slot in Compact-Siro Spinning on Fiber Strands 免费阅读 下载全文 Compact-siro spinning is a new kind of spinning technique which combines compact spinning and siro spinning,and widely put into practice. Based on the airflow data in the condensing zone,it builds the geometrical model of fiber strands,and then the trajectory of single fiber can be got. The difference of trajectory and compact effect of fibers strands is also analyzed in the condensing zone of three different suction slots. By comparing with the data of three different suction slots,it selects the compact-siro spinning suction device whose yarn has the best overall performance. The theory analysis gives foundation and explanation for experiment,and also provides theoretical basis for optimizing the properties of compactsiro yarn in production practice.
Effect of Phase Change Materials on the Thermal Protective Performance of the Multi-layered Fabrics Examined by TPP Tester under Flash Fire 免费阅读 下载全文 Cotton fabrics treated with phase change materials( PCMs)were used in multi-layered fabrics of the fire fighter protective clothing to study its effect on thermal protection. The thermal protective performance( TPP) of the multi-layered fabrics was measured by a TPP tester under flash fire. Results showed that the utilization of the PCM fabrics improved the thermal protective performance of the multi-layered fabrics. The fabric with a PCM add on of 41. 9% increased the thermal protection by 50. 6% and reduced the time to reach a second degree burn by 8. 4 s compared with the reference fabrics( without PCMs). The employment of the PCM fabrics also reduced the blackened areas on the inner layers. The PCM fabrics with higher PCM melting temperature could bring higher thermal protective performance.
Effect of Rotating Speed Fluctuation on External Hydraculic Performance of a Vane Pump 免费阅读 下载全文 The rotating speed fluctuation for turbomachinery is a common problem, which will cause severe destruction for equipments and basis when the fluctuation is very strong. In this paper,in order to study the transient response characteristics of a radial vane pump subjected to slight( 5%) and strong( 20%)fluctuating rotational speeds, the variation characteristics of the external hydraulic performances are numerically predicted by means of computational fluid dynamics( CFD) technology. The results manifest that the responses of head and flow rate are different relative to the fluctuating characteristics of rotational speed. The response of the former is very satisfied in synchronism,while that of the latter is hysteretic. Meanwhile,it is found that the variation tendencies of the static pressures at the inlet and outlet of the pump are completely opposite, while the response characteristics of the dynamic pressures at the inlet and outlet are nearly identical.Subsequently,in order to further reveal the transient behavior during the instantaneous operating periods,two non-dimensional parameters are employed to deeply analyze it. The result shows that the variation tendencies of these two parameters are also approximately opposite.Moreover,the quasi-steady assumption is not able to be used to accurately assess the transient flow during transient operating periods. The comparison results show that the transient behavior does not show obvious distinctions between slight and strong fluctuating rotating speeds.
Numerical Analysis of the Hydrodynamic Lubrication of Micro-grooved Friction Pair 免费阅读 下载全文 A growing interest is given to the hydrodynamic lubricated friction pair with surface textured. Because of its relatively simple processing methods and low manufacturing costs,micro-groove has become the most valuable form of surface texture,and definitely has broad application prospects in mechanical engineering. Based on numerical simulation,the present study aims to examine the effects of surface forms and cross-section types of micro-groove on the hydrodynamic lubrication performance,and to find out the optimal structural parameter for designing logical micro-grooves. Different surface form and cross-section types are designed to maximize the texture hydrodynamic effect. The average pressure of such microgrooved surface is evaluated in detail,and the variation trends with changes of the length of micro-groove,lp,or the depth,hp,are discussed. The theoretical results show that micro-grooves with rational design contribute to the improvement of hydrodynamic lubrication performance of friction pair largely. For a specific micro-grooved friction pair,the optimal surface form and crosssection type make the lubrication performance best.
Composition of the Value of Tourism Creative Products under the Influence of Regional Culture 免费阅读 下载全文 With the analysis of the influence of regional culture on the value of tourism creative products,the characteristics of the value of tourism creative products were studied,and the impact of regional culture on the composition and realization of the value was summarized. Thus, the general law of the influence of external factors on the product value could be drawn. Characteristics of the value of tourism creative products is contrasted to analyze the requirement motivation of consumers and to seek the ways of realization for products value with the influence of regional culture.The mathematical evaluation model was employed for evidence.Based on the model,the influencing factors of the value of different types of creative products were explored, which would provide theories and enlightenment for the co-creation and appreciation of creative products in the future.