基于质量流模型的关联多工序制造过程加工质量研究

为了提升智能车间工件加工质量的合格率,考虑到相邻工序间的加工质量传递的影响,提出一种基于质量流模型的关联多工序制造过程加工质量分析模型。根据工件加工流程建立多工序制造过程质量流模型,识别出影响制造过程质量的瓶颈工序;根据制造过程参数提出了加工质量修改建议;通过某智能车间零部件工作缸的生产过程进行验证,由该模型计算出的工件加工合格率与历史数据相比,相对误差为0.35%。实验表明,该模型可以反映实际生产制造的过程,验证了模型的实用性。

Influence of feature size of micro-scale channel on ink flow characteristics

Under the micro-scale condition,feature size of the channel is one of the main factors influencing the fluid flow characteristics. In printing process,ink thickness in the extrusion zone formed by two ink rollers may reach micron scale. Compared with macroscopic fluid,the velocity field and the pressure field of fluid may change when the feature size of fluid channel reaches micron scale. In order to control printing quality,it is necessary to research the influence of feature size on ink flow characteristics in micro scale. This paper analyzes it in theory,and then numerical simulation of an ink flow model with different feature sizes is carried out in no slip condition. The influence of the feature size on the ink flow characteristics and the wall shear force are obtained. Besides,the ink flow model with different feature sizes is simulated numerically in slip condition,and the influence of feature size on ink flow characteristics is obtained. Finally,by comparing and analyzing the above results,it can be concluded that both the ink velocity and pressure at the inlet of the extrusion zone are inversely proportional to the feature sizes whether in slip condition or not. And the ink velocity in slip condition is larger than that without slip,the pressure at the inlet of the extrusion zone is less than that in no slip condition. Within the micro-scale range,the ink velocity difference between the two conditions cannot be ignored. Therefore,it is necessary to consider slip when analyzing the influence of feature size of micro-scale channel on ink flow characteristics.

A Reynolds mass flux model for gas separation process simulation:Ⅱ.Application to adsorption on activated carbon in a packed column

Simulations of adsorption process using the Reynolds mass flux model described in Part I of these serial articles are presented. The object of the simulation is the methylene chloride adsorption in a packed column(0.041 m id,packed with spherical activated carbon up to a length of 0.2 m). With the Reynolds mass flux model,breakthrough/regeneration curves, concentration and temperature as well as the velocity distributions can be obtained. The simulated results are compared with the experimental data reported in the literature and satisfactory agreement is found both in breakthrough/regeneration curves and temperature curves. Moreover,the anisotropic turbulent mass diffusion is characterized and discussed.

Mathematical model for coupled reactive flow and solute transport during heap bioleaching of copper sulfide

Based on the momentum and mass conservation equations, a comprehensive model of heap bioleaching process is developed to investigate the interaction between chemical reactions, solution flow, gas flow, and solute transport within the leaching system. The governing equations are solved numerically using the COMSOL Multiphysics software for the coupled reactive flow and solute transport at micro-scale, meso-scale and macro-scale levels. At or near the surface of ore particle, the acid concentration is relatively higher than that in the central area, while the concentration gradient decreases after 72 d of leaching. The flow simulation between ore particles by combining X-ray CT technology shows that the highest velocity in narrow pore reaches 0.375 m/s. The air velocity within the dump shows that the velocity near the top and side surface is relatively high, which leads to the high oxygen concentration in that area. The coupled heat transfer and liquid flow process shows that the solution can act as an effective remover from the heap, dropping the highest temperature from 60 to 38 ℃. The reagent transfer coupled with solution flow is also analyzed. The results obtained allow us to obtain a better understanding of the fundamental physical phenomenon of the bioleaching process.

THE DDTCI SWITCH ALGORITHM FOR ABR TRAFFIC CONTROL IN ATM NETWORKS

For the issue of flow control for Available Bit Rate (ABR) traffic in ATM network,a new improved Explicit Rate (ER) algorithm named Dynamic Double Threshold Congestion Indication (DDTCI) algorithm is presented based on the Explicit Forward Congestion Indication (EFCI) Current Cell Rate (CCR) algorithm and Relative Rate (RR) algorithm. Different from the early ER algorithm, both the high-level and the low-level threshold is dynamically changing according to the state of the bottleneck node. We determinate the congestion state with the information of the two dynamic threshold, and control the cell rate of the source by feed back mechanism. Except for the well performance in both link utilization and fairness in distribution of available bandwidth, the improved algorithm can alleviate the fluctuation of sending rate dramatically. The mechanism is modeled by a fluid model, and the useful expressions are derived.Simulation results show up our conclusion.

A Reynolds mass flux model for gas separation process simulation:Ⅰ. Modeling and validation

Separation process undertaken in packed columns often displays anisotropic turbulent mass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux(RMF) model.With the RMF model, the concentration and temperature as well as the velocity distributions can be simulated numerically. The modeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation,while the modeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and momentum transfer equations, so that the Boussinesq postulate and the isotropic assumption are abandoned. To validate the presented RMF model, simulation is carried out for CO2 absorption into aqueous Na OH solutions in a packed column(0.1 m id, packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are compared with the experimental data and satisfactory agreement is found both in concentration and temperature distributions. The sequel Part II extends the model application to the simulation of an unsteady state adsorption process in a packed column.

A Simple Lumped Mass Model to Describe Velocity of Granular Flows in a Large Flume

This paper presents a lumped mass model to describe the run-out and velocity of a series of large flume tests,which was carried out to investigate some propagation mechanisms involved in rapid,dry,dense granular flows and energy transformation when the flows encountered obstacles and reoriented their movement directions.Comparisons between predicted and measured results show that the trend of predicted velocities was basically matched with that of measured ones.Careful scrutiny of test videos reveals that subsequent particles with a higher velocity collided with slowed fronts to make them accelerate. However,this simple model cannot reflect collisions between particles because it treated released materials as a rigid block.Thus,the predicted velocity was somewhat lower than the measured velocity in most cases.When the flow changed its direction due to the variation in slope inclination,the model predicted a decrease in velocity.The predicted decrease in velocity was less than the measured one within a reasonable range of 10% or less.For some cases in which a convexity was introduced,the model also predicted the same trend of velocities as measured in the tests.The velocity increased greatly after the materials took a ballistic trajectory from the vertex of the convexity,and reduced dramatically when they finally made contact with the base of the lower slope.The difference between prediced and measured decrease in velocity was estimated to be about 5% due to the landing.Therefore,the simple lumped mass model based on the energy approach could roughly predict the run-out and velocity of granular flows,although it neglected internal deformation,intergranular collision and friction.

Experimental investigation on solar-flue gas chimney

Flue gases exhausted from thermal power plants contain more than 50% of the fuel thermal energy. In the present work, experimental investigation was carried out to study the utilization of thermal energy in flue gases to enhance the performance of modified solar chimney consisting of Savonius wind rotor. A modified solar chimney model was designed and fabricated to carry out experimental measurement. The model consists of thermal energy conversion unit; Savonius wind rotor and a chimney. The thermal energy in the flue gas transfers to the air particles in the air channel across the absorber plate and results in upward air stream due to the buoyancy effect. With an 9 absorber area of 2.36 re＇and flue gas mass flow rate of0.18 kg/s, air velocity＇ of 4.1 m/s was achieved at the top of the thermal unit. Increasing the mass flow rate of the flue gas to 0.24 kg/s enhances the air velocity to be 4.6 m/s. The results have demonstrated the possibility＇ of utilizing the thermal energy in the waste flue gas to enhance the performance of a solar chimney and facilitate the continuous operation during the absence of the sun.

Heat Transfer Optimization for Air-Mist Cooling between a Stack of Parallel Plates

A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between the plates based on the development of the boundary layers for small and large separation distances,and for dilute mist conditions.Simulation results show the optimal separation distance to be strongly dependent on the liquid-to-air mass flow rate loading ratio,and reach a limit for a critical loading.For these dilute spray conditions,complete evaporation of the droplets takes place.Simulation results also show the optimal separation distance decreases with the increase in the mist flow rate.The proposed theoretical model shall lead to a better understanding of the design of fins spacing in heat exchangers where multiphase spray cooling is used.

Sand flux and wind profiles in the saltation layer above a rounded dune top

The near-bed airflow and the movement of sand dune sediments by wind are fundamental dune geomorphological processes.This research measured the wind profiles and sand mass flux on the rounded top of a transverse dune at the southern edge of the Tengger Desert to examine how to best predict the vertical profile of sand flux.This work also tested the accuracy of previously developed models in predicting the apparent roughness length during saltation.Results show that mass flux vertical distribution over the dune top is underestimated by an exponential function,overestimated by a power function,but closely matches the predictions made using the LgstcDoseRsp function.Given suitable values ofα,βandγaccording to the grain size composition,S?rensen equation with the peaked shape of the mass transport curve will well predict the dimensionless mass flux qg/ρu*3against dimensionless shear velocity u*/u*t.The modified Charnock model works best of the previously published models tested,with an R2of 0.783 in predicting the enhanced roughness over the moving sand surface,as opposed to an R2of0.758 for the Owen model and an R2of 0.547 for the Raupach model.For the rounded dune top in this study,C m=0.446±0.016.

A mass-conservative average flow model based on finite element method for complex textured surfaces

A mass-conservative average flow model based on the finite element method(FEM) is introduced to predict the performances of textured surfaces applied in mechanical seals or thrust bearings.In this model,the Jakobsson-Floberg-Olsson(JFO) boundary conditions are applied to the average flow model for ensuring the mass-conservative law.Moreover,the non-uniform triangular grid is utilized,which can deal with the problem of complex geometric shapes.By adopting the modeling techniques,the model proposed here is capable of dealing with complex textured surfaces.The algorithm is proved correct by the numerical experiment.In addition,the model is employed to gain further insight into the influences of the dimples with different shapes and orientations on smooth and rough surfaces on the load-carrying capacity.

Experimental investigation of vortex-induced vibrations of long free spans near seabed

There are many experimental studies dedicated to determining the effect of the proximity of a plane boundary on the vortex-induced vibration (VIV) of submarine pipeline spans, but they all only concerned the first mode VIV motion of the pipe. In this paper, a pipe model, 16 mm in diameter, 2.6 m in length and with a mass ratio (mass/displaced mass) of 4.30, was tested in a current tank. The reduced velocity was in the range of 0-16.7 and gap ratios at the pipe ends were 4.0, 6.0 and 8.0. The response of the model was measured using optical fiber strain gauges. Results of response amplitude and frequency were presented and the transition from the first dominant mode to the second one was shown. In the tests, it was found that the response amplitude experienced a continuous transition between the two modes, but the dramatic increase in the response frequency appeared with the shift in dominant mode from the first mode to the second one as the flow velocity increased. As the gap ratio decreased, the shift in the dominant mode took place at a higher reduced velocity.

Spatial distribution of 10m firn temperature in the Antarctic Ice Sheet

A database of Antarctic 10 m firn temperature was constructed using available borehole temperature measurements with data quality control to extend knowledge of Antarctic climate. Slopes from a high-resolution digital elevation model and the main ice divide were used to delineate main drainage sectors across Antarctica. In each drainage sector, a quantitative relationship between temperature and latitude, longitude and altitude was established using available tim temperature data. Quantitative relationships incorporating other factors affecting Antarctic air temperature such as atmospheric circulation and small-scale to- pography were used to derive a 10-km resolution grid map of surface temperature. The resulting temperature patterns presented a reasonable depiction of both large and small-scale variations in Antarctic 10 m firn temperature. This map is useful for many spatial variation studies, Antarctic ice sheet models, and comparison with satellite-derived temperature data and outputs of atmospheric general circulation models.