Study on the Influence of Piloti on Mean Radiant Temperature in Residential Blocks by 3-D Unsteady State Heat Balance Radiation Calculation

Piloti is commonly used in tropical and subtropical climate zones to get high wind velocity and create shadowed areas in order to optimize the living environment of residential blocks,but there are few studies to reveal the influence of piloti on the radiant environment of residential blocks systematically. Taking the city of Guangzhou as an example,using 3-D Unsteady State Heat Balance Radiation Calculation Method,this paper shows that the mean radiant temperature( MRT) under piloti area increases with the increase of piloti ratio,and especially when piloti ratio is equal to 100%,the MRT increase trend becomes sharp. The MRT of exposed area decreases with the increase of piloti ratio,especially when piloti ratio reaches 100%,the decrease trend of MRT becomes sharp,which offers the reference for the study on piloti design in subtropical climate zones and further research on living environment by CFD simulation in residential blocks.

Unsteady state precipitation of M_(23)C_(6)carbides during thermal cycling in reduced activation steel manufactured by laser melting deposition

The temperature field distribution and thermal history of Fe-9Cr2WVTa reduced activation steel prepared by laser melting deposition(LMD)have been calculated with Gaussian and Ring laser beams,and the nucleation and growth behaviors of M_(23)C_(6)precipitates in the 1st,7th and 19th layers have been calculated using the modified classical nucleation theory and Svoboda Fischer Fratzl Kozeschnik model.The energy distribution shows W-shape with Ring laser beam while it shows V-shape with Gaussian laser beam,which results in the more uniform M_(23)C_(6)size in the same layer with Ring laser beam.Precipitates in the bottom(i.e.,the 1st layer)have the minimum size and the size increases with the layer number with Gaussian and Ring laser beams.The temperature history,the instantaneous nucleation rate and the size evolution of M_(23)C_(6)have been systematically discussed.The results indicate that the nucleation,growth and re-dissolution of precipitates in reduced activation steel depend on the amount of energy absorbed in the thermal cycle during LMD.The continuous accumulation of energy during the thermal cycle leads to larger M_(23)C_(6)at the top area.The unsteady state precipitation dynamics of M_(23)C_(6)carbides during thermal cycling are consistent with the simulation results.

Unsteady-State Grinding Technology (II) Experimental Studies of Grinding Forces and Force Ratio

As is known to all, grinding force is one of the most important parameters to evaluate the whole process of grinding. Generally, the grinding force is resolved to three component forces, namely, normal grinding force F n, tangential grinding force F t and a component force acting along the direction of longitudinal feed which is usually neglected because of insignificance. The normal grinding force F n has influence upon surface deformation and roughness of workpiece, while the tangential grinding force F t mainly affect power consumption and service life of grinding wheel. In order to study deep into the process of the unsteady state grinding, we set up a measurement system to monitor the change of grinding force during the course of grinding and try to find some difference in the change of grinding force between the steady state grinding and unsteady state grinding. In the test, the normal and tangential grinding forces, F n and F t were measured by using a set of equipments including sensor, amplifier, oscilloscope and computer monitor. From the results, we can conclude that: 1) In the unsteady state grinding process, the values of the grinding forces are much lower than those of the steady state grinding process and the grinding force ratio showed a nonlinear fluctuation. 2) The tendency of the grinding forces in the process of the unsteady state grinding proved the existence of the cutting and micro-cutting actions. 3) Because the grinding force signals of the unsteady state grinding are much weaker than those of the steady state grinding, to obtain accurate value of the grinding forces, wave filtering is needed to be done. The whole process to filter the perturbation wave can be separated into three steps in order, changing the grinding force signals from analog signals into digital signals, FFT (fast Fourier transform) treatment to the digital signals, and IFFT(inversion fast Fourier transform) treatment to the digital signals after spectrum limitation.

Unsteady-state Grinding Technology (III) Studies on the Surface Quality

In conventional grinding theory, the chief removed mode of ceramic coprocessor by diamond tools was brittle removal. In order to perform the plastic removal or ductility processing of engineering ceramics the high degree of accuracy and high rigidity grinner must be using micro grain size diamond grinding wheel to direct the processing of micron below rank depth to prevent form the occurring of the brittle processing zone. This will resulted in the high expense of grinding. The expense of grinding could even reach the 80% of the total manufacture cost of the ceramic part. Ultra-precision grinding for advanced ceramics has been achieved by the unsteady-state grinding technique. In this paper, we mainly deals with observing and analyzing the surface quality of the silicon nitride ground by pink fused alumina wheel in different grinding parameters. To optimize the grinding parameters in the process of the unsteady-state grinding, the experiments of X-ray diffraction, energy spectrum analysis, SEM observation and roughness measurement were performed. The results show that: 1. In the process of unsteady state grinding, high line speed (rotational speed) of the grind wheel can improve the roughness of the silicon nitride apparently. It was also evident that the larger the grain mesh size, the better the surface quality. 2. There exists an optimum combination of grinding conditions such as grinding wheel speed, rotational speed of the workpiece, feed rate between the grinding wheel and the workpiece, grinding times and cutting coolant. The surface quality of the silicon nitride can be up to the standard of mirror finishing. 3. By analyzing the finished surface with X-ray diffraction and energy spectrum, the existence of some new phases including titanium and alumina was proved. 4. By utilizing the unsteady state grinding technique, the surface roughness of Ra ≤ 0.030 μm can be achieved by grinding the silicon nitride with the pink fused alumina wheel in low cost. Based on the unsteady-state grinding technique, this paper put forward a new processing method which by utilizing aluminum oxide grinding wheel to perform burnishing process and impudent the low surface roughness processing of engineering ceramic, the Ra is about 0.01 μm. Furthermore, the working efficiency of this method is high, and the process cost is low, so it is a prospective processing method.

Unsteady-State Grinding Technology (I) Theoretical Generalization and Research on Grinding Mechanism

In conventional grinding theory, it is obvious that there must be a very high hardness difference between grains of the grinding wheel and workpieces. The best grinding wheels are those giving the lowest "natural limiting surface roughness" while cutting at appreciable plunge velocities. With the development of new materials and new machining processes, conventional theories of grinding techniques are no longer suitable to explain many phenomena in the course of grinding procedures. In dealing with precision or ultra-precision grinding processes of advanced ceramics, many results of experiments and practical production have shown that grinding with super hard materials wheels is not the only method to machine advanced ceramics. This paper is intended to propose a new grinding theory named as unsteady-state grinding technique evolved from some phenomena that can not be explained by conventional grinding theory. Unsteady-state grinding technique means the technique which can make the surface roughness of the materials, especially hard and brittle, be up to the standard of ultra-precision machining by utilizing common wheels characteristic of inferior self-sharpening and wear-resistance. In the process of machining, the common wheel need to be redressed about 3～5 times and the time between two redressings is about 3～5 minutes. As a validation of the new grinding technology, experimental work was performed to prove the existence of the unsteady state in the process of ultra-precision grinding with common abrasive wheel-pink fused alumina wheel. From the results of the observation of the wheel topography, the whole grinding process in unsteady state was separated into three stages namely cutting by grains peaks, micro-cutting by micro edges of the broken grains and rubbing without material removal, which is different from conventional grinding theory. For the difference of hardness between grinding wheel and workpiece material is not so apparent, some people have doubts about whether the cutting especially micro-cutting actions exist in the process of unsteady state grinding. By utilizing the common abrasive wheel newly redressed to grind the finished surface of silicon nitride glut and comparing the finished surface with the damaged surface in SEM pattern and surface roughness, the existence of cutting and micro- cutting actions in the unsteady state grinding process was confirmed.

Sensitivity Numerical Analysis of Human Body Exergy Balance under an Unsteady-State Thermal Environment —Behavioral Adaptation Induced by Undesirable Cold Storage by Building Envelope in Winter

We analyzed the relationships between the human body exergy balance and behavioral adaptations induced by undesirable cold storage by a building envelope under an unsteady-state thermal environment in winter. The complex interaction of the warm exergy production by shivering, lifting of the shell ratio, and reduction of the blood flow rate was considered to constitute the physiological adaptation necessary for maintaining the constant core temperature, which was an important aspect in living organisms. In the case of intermittent use room, it was suggested that better thermal comfort and desirable behavioral adaptations, which decreased the consumption of fossil fuels, could be achieved if interior wooden cladding was used in constructions with building envelopes that had a comparatively large heat capacity, or in cases of wooden constructions in which the building envelope heat capacity was comparatively small.

Designing a Biomimetic Ornithopter Capable of Sustained and Controlled Flight

We describe the design of four ornithopters ranging in wing span from 10 cm to 40 cm, and in weight from 5 g to 45 g. The controllability and power supply are two major considerations, so we compare the efficiency and characteristics between different types of subsystems such as gearbox and tail shape. Our current omithopter is radio-controlled with inbuilt visual sensing and capable of takeoff and landing. We also concentrate on its wing efficiency based on design inspired by a real insect wing and consider that aspects of insect flight such as delayed stall and wake capture are essential at such small size. Most importantly, the advance ratio, controlled either by enlarging the wing beat amplitude or raising the wing beat frequency, is the most significant factor in an ornithopter which mimics an insect.

Effect of Different Blood Cycle Modeson Mass Transfer of Artificial Kidney

Based on the one-dimensional and unsteady-state Krogh model, this paper investigates mass transfer of artificial kidney under three blood cycle modes during the course of hemodialysis. The variations of the permeable solute clearance with increasing time and the dialysis time with increasing blood flux are simulated in detail,and then one optimal blood cycle mode is acquired. The results are very important to improve the clinical dialysis efficiency of artificial kidney.

A model for coupling reservoir inflow and wellbore flow in fishbone wells

A coupling model is proposed in this paper by using the Green Function and Newman＇s product principle, and the solution method is provided here as well. This model can be used to describe the reservoir inflow and wellbore flow for fishbone wells in an unsteady flow or pseudo-steady flow state. A case study indicates that the bottom hole pressure declines quickly in the unsteady flow period which is very short. The pressure drop per unit time remains unchanged under the pseudo-steady flow conditions. The distribution of flow rate along the main wellbore shows a wave shape under the unsteady flow condition, and the flow rate distribution in each branch is similar. The flow rate distribution along the main wellbore is irregular ＂U＂ shaped under the pseudo-steady flow condition, and the space-symmetrical branches have the same flow distribution pattern. In the initial production period, the flow rate increases significantly as the length of branches and the angle between branches and the main wellbore increase. As the production continues, the length and angle of branches have only a slight effect on the flow in fishbone wells.

Calculation of Temperature Fields of Electric Locomotive Wheels during Emergency Braking on Tangent Track at a Speed of 200 km/h

According to the heat transfer theory, an unsteady state heat transfer model of electric locomotive wheels during emergency braking on tangent track at a speed of 200 km/h has been established in this paper. The explicit finite difference method is used in the numerical calculation of temperature fields of wheels. From the calculation results, the determination of braking distance and the material choice of brake shoes are discussed.

A FINITE ELEMENT AND BOUNDARY ELEMENT METHOD OF NUMERICAL SIMULATION OF TWO DIMENSIONAL AND TWO PHASE FLOW

In this paper, an efficient finite element and boundary element method is presented for a two dimensional and two phase flow model with satisfactory results. So another method for solving reservoir simulation of two dimensional and two Phase flow is developed.

A Brief Review on Aerodynamic Performance of Wingtip Slots and Research Prospect

Wingtip slots,where the outer primary feathers of birds split and spread vertically,are regarded as an evolved favorable feature that could effectively improve their aerodynamic performance.They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design.This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots.Following a review of previous wingtip slot research,four imperfections are put forward:vacancies in research content,inconsistencies in research conclusions,limitations of early research methods,and shortage of the aerodynamic mechanism analysis.On this basis,further explorations and expansion of the influence factors for steady state are needed;more attention should be poured into the application of flow field integration method to decompose drag,and evaluation of variation in induced drag seems a more rational choice.Geometric and kinematic parameters of wingtip slot structure in the unsteady state,as well as the flexibility of wingtips,should be taken into account.As for the aerodynamic mechanism of wingtip slots,the emphasis can be placed on the study of the formation,development,and evolution of wingtip vortices on slotted wings.Besides,some research strategies and feasibility analyses are proposed for each part of the research.

Activation in the initial stage of oxygen permeation in SrCo_(0.9)Ta_(0.1)O_(3-δ)

Mixed conducting perovskite oxide SrCo_（0.9）Ta_（0.1）O_（3-δ）（SCT） is synthesized by solid-state reaction method.The activation in the initial stage of oxygen permeation through the SCT membrane is investigated.The results show that the activation in the initial stage of oxygen permeation has activate-memory,the first activation can only help to reduce active time of the next cycles,but it is helpless to increase the final oxygen permeation flux.XRD characterization shows that the imperfect perovskite phase structure is gradually improved and the crystal lattice has made some self-adjustment under the permeation conditions,therefore,the oxygen permeation flux of SCT disk membrane increases gradually and till it reaches a steady state.