Empirical Study on the Impact of Rural Labor Force Flow on the Price of Agricultural Products——A Method Based on VEC Model

Based on the research introduction of domestic and foreign scholars,dynamic equilibrium between the rural labor force flow and the price of agricultural product is analyzed by VEC model,according to the data of the rural labor force flow and the price of agricultural products in the years 1990-2007.Chows breakpoint test is used to measure the stage characteristics of the impact of rural labor force flow on the price of agricultural product.Result shows that there is a long-term and stationary relationship between the flow quantity of rural labor force and the price of agricultural product.Rural labor force flow,as an exogenous force,affects the agricultural production,and further influences the price fluctuation of agricultural products.Impact of rural labor force flow on the price of agricultural product is from weak to strong,then grows gradually weaker,and reaches its peak value at the year 1998.With the development of rural society and economy and the market process,rural labor force flow endogenously affects the price of agricultural product,which has periodic characteristics.In order to achieve a dual stabilization of the rural labor force flow and the price of agricultural products,the following countermeasures are put forward:vigorously developing vocational education,increasing the support for agricultural production,and making active employment measures.

Effect of forced lamina flow on microsegregation simulated by phase field method quantitatively

The influence of supercooled melt forced lamina flow on microsegregation was investigated. The concentration distribution at solid-liquid boundary of binary alloy Ni-Cu was simulated using phase field model coupled with flow field. The microsegregation, concentration maximum value, boundary thickness of concentration near upstream dendrite and normal to flow dendrite, and downstream dendrite were studied quantitatively in the case of forced lamia flow. The simulation results show that solute field and flow field interact complexly. Compared with melt without flow, in front of upstream dendrite tip, the concentration boundary thickness is the lowest and the concentration maximum value is the smallest for melt with flow. However, in front of downstream dendrite tip, the results are just the opposite. The zone of poor Cu in upstream dendrite where is the most severely microsegregation and shrinkage cavity is wider and the concentration is lower for melt with flow than that without flow.

Phase-field modeling of dendritic growth under forced flow based on adaptive finite element method

A mathematical model combined projection algorithm with phase-field method was applied. The adaptive finite element method was adopted to solve the model based on the non-uniform grid, and the behavior of dendritic growth was simulated from undercooled nickel melt under the forced flow. The simulation results show that the asymmetry behavior of the dendritic growth is caused by the forced flow. When the flow velocity is less than the critical value, the asymmetry of dendrite is little influenced by the forced flow. Once the flow velocity reaches or exceeds the critical value, the controlling factor of dendrite growth gradually changes from thermal diffusion to convection. With the increase of the flow velocity, the deflection angle towards upstream direction of the primary dendrite stem becomes larger. The effect of the dendrite growth on the flow field of the melt is apparent. With the increase of the dendrite size, the vortex is present in the downstream regions, and the vortex region is gradually enlarged. Dendrite tips appear to remelt. In addition, the adaptive finite element method can reduce CPU running time by one order of magnitude compared with uniform grid method, and the speed-up ratio is proportional to the size of computational domain.

NUMERICAL SIMULATION OF SUCCINONITRITE DENDRITIC GROWTH IN A FORCED FLOW

Numerical simulation based on phase field method is performed to describe solidification process of pure material in a free or forced flow. The evolution of the interface is showed, and the effects of mesh grid and flow velocity on succinonitrite shape are studied. These results indicate that crystal grows into an equiaxial dendrite in a free flow and into an asymmetrical dendritic in a forced flow. With increasing flow velocity, the upstream dendritic arm tip grows faster and the downstream arm grows slower. However, the evolution of the perpendicular tip has no significant change. In addition, mesh grid has no influence on dendritic growth shape when mesh grid is above 300×300.

Simulation of faceted dendrite growth of non-isothermal alloy in forced flow by phase field method

Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.

Rural Work Force Flowing: A Unique Mode of Urbanization in China

From late l 997.we conducted a four.year study of the rural work force backflow in Anhui and Sichuan provinces.

Steady vortex force theory and slender-wing flow diagnosis

The concept vortex force in aerodynamics is sys- tematically examined based on a new steady vortex-force theory （Wu et al., Vorticity and vortex dynamics, Springer, 2006） which expresses the aerodynamic force （and moment） by the volume and boundary integrals of the Lamb vector. In this paper, the underlying physics of this theory is explored, including the general role of the Lamb vector in non- linear aerodynamics, its initial formation, and its relevance to the total-pressure non-uniformity. As a typical example, the theory is applied to the flow over a slender delta wing at a large angle of attack. The highly localized flow structures with high Lamb-vector peaks are identified in terms of their net contribution to various constituents of the total aerody-namic force. This vortex-force diagnosis sheds new light on the flow control and configuration optimization.

Direct observation of bunching of elementary steps on protein crystals under forced flow conditions

Bunching of elementary steps by solution flow is still not yet clarified for protein crystals. Hence, in this study, we observed elementary steps on crystal surfaces of model protein hen egg-white lysozyme （HEWL） under forced flow conditions, by our advanced optical microscopy. We found that in the case of a HEWL solution of 99.99% purity, forced flow changed bunched steps into elementary ones （debunching） on tetragonal HEWL crystals. In contrast, in the case of a HEWL solution of 98.5% purity, forced flow significantly induced bunching of elementary steps. These results indicate that in the case of HEWL crystals, the mass transfer of impurities is more significantly enhanced by forced solution flow than that of solute HEWL molecules. We also showed that forced flow induced the incorporation of microcrystals into a mother crystal and the subsequent formation of screw dislocations and spiral growth hillocks.

Characteristics of debris flow impact on a double-row slit dam

To accurately predict impact loads can ensure the safe operation of debris flow control projects.The instantaneous impact process is usually considered in the calculation of the debris flow impact force;however,the redistribution of an impact load after structural regulation is unclear.In this study we deduced the theoretical calculation of a debris flow impact on a double-row slit dam,and carried out a verification experiment on the debris flow impact.The calculation model considers the influence of the debris flow properties,dam arrangement and pile material.The results show that the impact force of the debris flow is obviously affected by the bulk density.When the bulk density is 21 kg/m^(3),the maximum impact force on the pile dam is 1.15 times that when the bulk density is 15 kg/m^(3),but the time it takes for the debris flow to pass through the dam body is reduced by 60%.The larger the relative pile spacing,the more sufficient the flow space and the lower the maximum impact force.The maximum impact force of relative pile spacing of 0.8 is 12%less than that of elative pile spacing of 0.5.The horizontal distribution of the impact force in the mud depth range is parabolic.The maximum impact force on the centre pier is 1.3 times that of a side pier,and the maximum impact force on the dam body appears at the top of the mud depth range.From the vertical distribution of the impact force,the maximum impact force at the highest mud mark is approximately 70%of that of the bottom.With the increase in the relative pile spacing,the longitudinal maximum impact force distribution first decreases and then increases.

Analysis and Calibration of Internal Flow Force of EjectorPowered Engine Simulator System in Wind Tunnels

The ejector-powered engine simulator(EPES)system is an important piece of equipment in conducting an influence test of the intake and jet flow in low-speed wind tunnels.In this work,through the analysis of the structure and principle of EPES,three parts of the internal flow force were obtained,namely,the additional resistance before the inlet,the internal flow force in the inlet and the thrust produced by the ejector.On the assumption of one-dimensional isentropic adiabatic flow,the theoretical formulae for calculating the forces were derived according to the measured total pressure,static pressure and total temperature of the internal flow section.Subsequently,a calibration tank was used to calibrate the EPES system.On the basis of the characteristics of the EPES system,the process and method of its calibration were designed in detail,and the model installation interface of the calibration tank was reformed.By applying this method,the repeatability accuracy of the inlet flow rate calibration coefficient was less than0.05%,whereas that of the exhaust flow rate and velocity was less than 0.1%.Upon the application of the calibration coefficients to the correction of the wind tunnel experiment data,the results showed good agreement with the numerical simulation results in terms of regularity and magnitude before stall,which validates the reasonableness and feasibility of the calibration method.Analysis of the calibration data also demonstrated the consistency in the variation law and trend between the theoretical calculation and actual measurement of internal flow force,further reflecting the rationality and feasibility of the theoretical calculation.Nevertheless,the numerical difference was large and further widened with a higher ejection flow rate mainly because of the accuracy of flow measurement and the inhomogeneity of internal flow.The thrust deflection angle of EPES is an important factor in correcting this issue.In particular,the thrust deflection angle becomes larger with small ejection flow and becomes smaller with an increase in flow rate,essentially exhibiting a general change of less than 10°.

Temperature rise of He Ⅱ forced flow and its negative Joule-Thomson effect

The temperature rise of He Ⅱ transfer system due to the negative Joule-Thomson(JT)effect is one of the major problems in the He Ⅱ forced flow system design.Negative Joule-Thomson effect of the He Ⅱ forced flow was analyzed and calculated in this paper.The temperature rise due to the heat leak along the transfer pipeline was calculated by the simplified equation and was modified by considering the negative Joule-Thomson effect.The modified results were compared with the temperature rise obtained by non-linear differential equations with consideration of the pressure gradient.The results show that the pressure gradient has strong effect on the temperature distribution.The modified results are in good agreement with the values calculated by the complicated equation,which verifies the effectiveness of the simplified equation in calculating the temperature rise when the negative JT effect of He Ⅱ is known.

A Novel Method for Determining the Void Fraction in Gas-Liquid Multi-Phase Systems Using a Dynamic Conductivity Probe

Conventional conductivity methods for measuring the void fraction in gas-liquid multiphase systems are typically affected by accuracy problems due to the presence of fluid flow and salinity.This study presents a novel approach for determining the void fraction based on a reciprocating dynamic conductivity probe used to measure the liquid film thickness under forced annular-flow conditions.The measurement system comprises a cyclone,a conductivity probe,a probe reciprocating device,and a data acquisition and processing system.This method ensures that the flow pattern is adjusted to a forced annular flow,thereby minimizing the influence of complex and variable gas-liquid flow patterns on the measurement results;Moreover,it determines the liquid film thickness solely according to circuit connectivity rather than specific conductivity values,thereby mitigating the impact of salinity.The reliability of the measurement system is demonstrated through laboratory experiments.The experimental results indicate that,in a range of gas phase superficial velocities 5–20 m/s and liquid phase superficial velocities 0.079–0.48 m/s,the maximum measurement deviation for the void fraction is 4.23%.

Flow field simulation and establishment for mathematical models of flow area of spool valve with sloping U-shape notch machined by different methods

Precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke was derived. The computational fluid dynamics was used to analyze the flow features of the sloping U-shape notch on the spool, such as mass flow rates, flow coefficients, effiux angles and steady state flow forces under different operating conditions. At last, the reliability of the mathematical model of the flow area for the sloping U-shape notch orifice on the spool was demonstrated by the comparison between the orifice area curve derived and the corresponding experimental data provided by the test. It is presented that the bottom arc of sloping U-shape notch （ABU） should not be omitted when it is required to accurately calculate the orifice area of ABU. Although the theoretical flow area of plain bottom sloping U-shape notch （PBU） is larger than that of ABU at the same opening, the simulated mass flow and experimental flow area of ABU are both larger than these of PBU at the same opening, while the simulated flow force of PBU is larger than that of ABU at the same opening. Therefore, it should be prior to adapt the ABU when designing the spool with proportional character.

Numerical Simulation and Experimental Study of the Effects of Disposal Space on the Flow Field Around the Combined Three-Tube Reefs

The artificial reefs placed on the seabed with different layouts and disposal spaces will produce variational flow field. The intensity and scale of the combined three-tube artificial reefs with different layouts at five Reynolds numbers（Re） are numerically investigated by use of the RNG k-ε turbulent model and SIMPLEC algorithm. A stationary no-slip boundary condition is used on the models and the bottoms, and the free surface is treated as a ＂moving wall＂ with zero shear force and the same velocity with inflow. In order to validate the simulation results, a particle image velocimetry（PIV） experiment is carried out to analyze the flow field. The numerical simulation results are consistent with the data obtained from experiment. The corresponding errors are all below 20%. Based on the validation, the effects of disposal space on flow field are simulated and analyzed. According to the simulation, in a parallel combination, a better artificial reef effect is obtained when the disposal space between two parallel reefs is 1.0L（L is the length of the combined three-tube reef model）. In a vertical combination, when the disposal space between two vertical reefs is 1.0L to 2.0L, the artificial reef effect is better.

Modified Saint-Venant equations for flow simulation in tidal rivers

Flow in tidal rivers periodically propagates upstream or downstream under tidal influence. Hydrodynamic models based on the Saint-Venant equations （the SVN model） are extensively used to model tidal rivers. A force-corrected term expressed as the combination of flow velocity and the change rate of the tidal fevel was developed to represent tidal effects in the SVN model. A momentum equation incorporating with the corrected term was derived based on Newton＇s second law. By combing the modified momentum equation with the continuity equation, an improved SVN model for tidal rivers （the ISVN model） was constructed. The simulation of a tidal reach of the Qiantang River shows that the ISVN model performs better than the SVN model. It indicates that the corrected force derived for tidal effects is reasonable; the ISVN model provides an appropriate enhancement of the SVN model for flow simulation of tidal rivers.

EFFECT OF LIQUID FLOW ON PRIMARY ARM SPACING OF CONSTRAINED COLUMNAR CRYSTALS

An experimental apparatus,which has a convection generator and an aid-heater,is developed for the study of the effect of stable laminar liquid flow on the directional solidification process by the use of transparent alloy SCN-2wt-% Ace.The flow is perpendicular to primary arms. By in-situ observation and photographing at different specific moments,it has been found that such a flow can cause a great change in primary spacings of constrained columnar crystals:for cells,the spacings become smaller;but for dendrites,they become larger.The former is mainly due to the tilted growth of upstreamside branches,while the latter is mainly due to the coup- ling effect of liquid flow with solutal field around dendrite tips.The faster the liquid flows,the further smaller the cell spacing and the further larger the dendrite spacing.

NUMERICAL SIMULATION ANALYSIS OF EXTERNAL FLOW FIELD OF WAGON-SHAPED CAR AT THE MOMENT OF PASSING

In the course of studying on aerodynamic change and its effect on steering stability and controllability of an automobile in passing, because of multi interaction streams, it is difficult to use traditional methods, such as wind tunnel test and road test. If the passing process of an automobile is divided into many time segments, so as to avoid the use of moving mesh which takes large calculation resource and CPU processing time in calculating, the segments are simulated with computational fluid dynamics （CFD） method, then the approximate computational results about external flow field will be obtained. On the basis of the idea, the change of external flow field of wagon-shaped car at the moment of passing is simulated through solving three-dimensional, steady and uncompressible N-S equations with finite volume method. Numerical simulation analysis of side force coefficient, stream lines, body surface pressure distribution of wagon-shaped car are presented and a preliminary discussion of aerodynamic characteristics of correlative situations is obtained. Finally, the C3 -x/l curve of side force coefficient（C3） of car following relative distance （x/l） between cars is obtained. By comparison, the curve is coincident well with the experimental data, which shows creditability of numerical simulation methods presented.

Analysis of dynamic features in intersecting pedestrian flows

This paper focuses on the simulation analysis of stripe formation and dynamic features of intersecting pedestrian flows.The intersecting flows consist of two streams of pedestrians and each pedestrian stream has a desired walking direction.The model adopted in the simulations is the social force model, which can reproduce the self-organization phenomena successfully. Three scenarios of different cross angles are established. The simulations confirm the empirical observations that there is a stripe formation when two streams of pedestrians intersect and the direction of the stripes is perpendicular to the sum of the directional vectors of the two streams. It can be concluded from the numerical simulation results that smaller cross angle results in higher mean speed and lower level of speed fluctuation. Moreover, the detailed pictures of pedestrians＇ moving behavior at intersections are given as well.

Numerical Investigation of Submarine Hydrodynamics and Flow Field in Steady Turn

This paper presents numerical simulations of viscous flow past a submarine model in steady turn by solving the Reynolds-Averaged Navier-Stokes Equations（RANSE） for incompressible, steady flows. The rotating coordinate system was adopted to deal with the rotation problem. The Coriolis force and centrifugal force due to the computation in a bodyfixed rotating frame of reference were treated explicitly and added to momentum equations as source terms. Furthermore, velocities of entrances were coded to give the correct magnitude and direction needed. Two turbulence closure models（TCMs）, the RNG k-ε model with wall functions and curvature correction and the Shear Stress Transport（SST） k-ω model without the use of wall functions, but with curvature correction and low-Re correction were introduced, respectively. Take DARPA SUBOFF model as the test case, a series of drift angle varying between 0° and 16° at a Reynolds number of 6.53×10^6 undergoing rotating arm test simulations were conducted. The computed forces and moment as a function of drift angle during the steady turn are mostly in close agreement with available experimental data. Though the difference between the pressure coefficients around the hull form was observed, they always show the same trend. It was demonstrated that using sufficiently fine grids and advanced turbulence models will lead to accurate prediction of the flow field as well as the forces and moments on the hull.