空调横导风条注塑模具设计

针对结构复杂的空调横导风条的成型工艺特点,确定了注塑模具的整体设计方案,材料选用丙烯腈-丁二烯-苯乙烯塑料(ABS)。采用UG软件对产品进行建模,设计分型面在塑件的最大轮廓处,并设计了模架的浇注系统、顶出机构、整体嵌入式型腔和型芯、抽芯机构、冷却系统等机构。塑件结构复杂,为薄壁长条形,两端和中间有肋板,并附有圆孔和卡扣,两侧圆柱卡扣采用斜导柱抽芯机构成型,侧壁圆孔采用斜顶抽芯机构成型,并计算了抽芯距离及抽拔力。模具选用1模2腔侧浇口的型腔布局形式,通过分析,确定了浇口位置,浇口形式为潜水进胶,确保外观面无浇口痕迹。设置了23根推杆和拉料杆、4斜顶杆,每个塑件采用8推杆和2斜顶杆顶出,实现了浇注凝料的自动脱模。实践证明,模具结构布局合理,运行安全可靠,成型质量稳定。

矿井风网调节方案的可行性

本文从技术、经济、安全等方面讨论风网自身的特性,将控制位置由按需分风网扩展到自然分风网,在理论与实践上均有重要意义。在通风设计中,求出的许多方案优劣参杂,甚至含有难以应用的方案,若能事先筛掉不可行方案,则可在设计计算中节省大量的时间与人力,也为决策提供方便。

具有补风装置的排油烟系统的射流速度对污染物的控制

厨房是室内空间的一部分,是室内污染物散发的主要来源。为了降低污染物的含量,笔者通过AIRPAK软件模拟厨房内的流场,在排风口下风加入补风条缝,当条缝进行补风时污染源的四周会形成空气幕墙,通过调节改变速度速度控制污染物的扩散。

几个PC-1500机程序介绍

我院编制了煤矿设计各专业有关的几个PC-1500袖珍计算机BASIC语言程序,现介绍如下:1.复杂通风网路计算程序该程序采用H.Cross迭代法,对原始输入数据进行压缩处理,使输入数据减少到最低限度.对任意的复杂通风网路,只要输入网路的风道个数、回路个数、各风道的初始风量和风阻值;在回路中有风机时,还需输入风机的额定负压,再输入各回路的风道号.

硬汉归来——试驾北京汽车BJ40

儿时对国产车的记忆,除了大红旗、老上海以外,还有一位身披‘军装"吃苦耐劳的硬汉——北京吉普212。提起"212",大家首先能想到的就是正义凌然的军人形象,虽然"212"在我们印象中并不完美,但它却成为那个年代最为亮丽的一条风景线。随着时代的发展,"212"逐渐淡出了人们的视线,可人们抹不去的是对那个年代的一份纪惦。在去年底北京汽车BJ40正式上市,全新的外观与动力让它成为性能SUV里的新军,但不变的是它继续延续了北京吉普212的优良传统,但能否继续书写辉煌还须拭目以待。外观:硬汉外型霸气外露北京汽车BJ40采用双色车身设计。

FORTY-EIGHT CASES OF ACUTE GOUTY ARTHRITIS TREATED COMPREHENSIVELY WITH ELECTROACUPUNCTURE AND WARMING MOXIBUSTION

Objective To probe into the effects on acute gouty arthritis treated comprehensively with electroacupuncture (EA) and warming moxibustion. Methods 70 cases were randomized into treatment group (48 cases), in which the EA+warming moxibustion was applied; and controlled group (22 cases), in which, colchicine was prescribed for oral administration. Results The statistical outcomes after 1 course treatment in treatment group: 28 cases were cured (58.33%), 18 cases improved (37.50%) and the total effective rate was 95.83%. In controlled group: 12 cases (54.55%) were cured, 8 cases improved (36.36%) and the total effective rate was 90.91%. The therapeutic effects of two groups were basically consistent, without significant different (P>0.05). But, concerning to side effect, there was no any toxic side effects in the group treated with EA+warming moxibustion, and the occurrence rate in the group treated with colchicine was 40.91%. Conclusion Electroacupuncture+warming moxibustion achieves good therapeutic effects without any side effects.

CFD modeling of methane distribution at a continuous miner face with various curtain setback distances

Knowledge of the airflow patterns and methane distributions at a continuous miner face under different ventilation conditions can minimize the risks of explosion and injury to miners by accurately forecasting potentially hazardous face methane levels. This study focused on validating a series of computational fluid dynamics(CFD) models using full-scale ventilation gallery data that assessed how curtain setback distance impacted airflow patterns and methane distributions at an empty mining face(no continuous miner present). Three CFD models of face ventilation with 4.6, 7.6 and 10.7 m(15, 25, and 35 ft) blowing curtain setback distances were constructed and validated with experimental data collected in a full-scale ventilation test facility. Good agreement was obtained between the CFD simulation results and this data.Detailed airflow and methane distribution information are provided. Elevated methane zones at the working faces were identified with the three curtain setback distances. Visualization of the setback distance impact on the face methane distribution was performed by utilizing the post-processing capability of the CFD software.

The Survival Probability in Generalized Poisson Risk Model

In this paper we generalize the aggregated premium income process from a constant rate process to a poisson process for the classical compound Poinsson risk model,then for the generalized model and the classical compound poisson risk model ,we respectively get its survival probability in finite time period in case of exponential claim amounts.

Predicting Siltation in Entrance Channel Based on Wind Conditions

The siltation induced by wind waves in an entrance channel is one of the prime factors influencing the operation efficiency of a port. It is necessary to predict the siltation accurately for dredging and ship operation passing through the entrance of the port. However, it is difficult to apply the traditional method to predicting entrance siltation because of its complex computational procedure and lacking the data of ocean dynamic elements in the specified sea area. From the view of energy conservation, a direct relationship between wind conditions and sediment deposition can be founded. On the basis of the above methodology, an empirical formula expressed by wind conditions for forecasting the siltation in the entrance channel is set up. The wind conditions are easily obtained from the local meteorological stations or weather maps, so the formula established in this paper is more convenient and practical than the traditional method. A case study is provided, in which the emopirical formula is calibrated and verified utilizing the measured wind and siltation conditions in the entrance channel of the port. Comparisons between computed values and measured data show satisfactory aqreement.

基于空气动力学分析的A柱结构优化设计

以汽车实际开发过程中为了降低风阻系数和风噪大小,通过对车身外造型进行外流场CFD分析,提出A柱造型的局部优化方向,然后再通过对车身A柱结构的不同分件形式、安装固定方式的可行性对比分析,选择最佳可实施的方案,通过在A柱与前风挡之间增加卡接的前风窗装饰条的方式实现A柱造型的局部优化来提升整车性能,降低风阻系数和风噪大小。

Human evacuation affected by smoke movement in mine fires

The objective of this work is to investigate the influence of smoke movement during mine fires on miner evacuation behaviors. A three-dimensional computational fluid dynamics method was conducted to reconstruct the lane- way conveyor belt fire scenes under two ventilating conditions. The parameters, including temperature-time histories, soot density, carbon monoxide and heat release rate, were simulated to characterize the mine fires at various ventilating speeds. A miner evacuation model affected by fire smoke movement was advanced to describe the miner evacuation behaviors, which can be divided into three stages. Based on the evacuation model coupled with the mine fire smoke movement, the available safety evacuation time for miners involved in coal mine fire located in different sites was estimated. Two evacuation patterns were advanced according to the ventilating speeds combined with the model of miner evacuation behaviors. The results show that the miners located between the inlet-air end and the air door in lane 1 should be evacuated to the inlet-air end and other miners involved in coal mine fire could choose the air door as the escaping destination, when the ventilation speed is greater than 3 m/s. Accordingly, the research can be used as references for the mine safety administration authorities to design the safety evacuation.

A study on the design of a hybrid policy for carbon abatement

A necessary way to mitigate global warming is carbon reduction, which the international community is now actively promoting. China has committed a target goal for carbon reduction to the international society, and has devoted a great effort toward researching the impact of related policies. Carbon taxation and carbon trading are the two main mechanisms to advocate carbon abatement, which many countries have been using. Each of these two mechanisms possesses advantages and disadvantages, and an appropriate combination of them can make best use of their advantages while bypassing their disadvantages, creating a superior mechanism. In our opinion, the main differences between these two mechanisms are that carbon taxation has a lower institution cost(consisting of the related infrastructural investment and the regulation cost,etc), and is easier to operate, but lacks the flexibility in response to variations of market conditions. However, this flexibility is just the origin of risk, which increases the difficulty for firms in their decision of carbon abatement and is an indirect way to incentivize carbon abatement, compared to carbon trading, which has a more direct effect in carbon reduction. Based on the above observation, we present a hybrid mechanism of carbon abatement, which is an organized combination of carbon taxation and carbon trading. It consists of two parts: first, the carbon taxation, which has a progressive tax rate, second, the carbon trading. Small firms will only pay the carbon tax, while large firms, will first need to get the initial carbon emission quotas by some way, and then trade it in the carbon market if necessary. For firms with extra emissions,they will receive a punishment according to a high carbon tax rate. This hybrid policy considers the equity between different firms in carbon emission rights as well as the efficiency of the mechanism while decreasing the risk level for firms in the carbon emission decision, making it superior to the two previous policies. We also analyze the feasibility of this hybrid policy in China,address some important issues in the implementation of this hybrid policy in China and present the relevant suggestions. The discussion in this paper can serve as a reference to the government in the decision of carbon policies.

Short Sellers Are Indeed Sophisticated Traders!

Current literature shows that short sellers earn positive returns on their trades and that the superior performance of short sellers is due to their better analytic skills. In this paper, we investigate, if it is possible for a short seller to make profits even if he does not have insider information or is not sophisticated. We use a one period model and assume that stock price follows a random walk with a positive drift to show that the＇ expected return for an uninformed short seller is always negative and his risks are always greater than the risks of a stock buyer. Hence a short seller would not trade unless he has superior trading skills and/or information. We also show that the market conditions when the stock＇s dividend yield is greater than the risk free rate gives the shortsellers advantage over stock buyers.

Analysis on air-leakage law of goal in condition of ascending mining for top-coal caving

Using the Jisan Coalmine's top-coal caving for the 3down coal seam with ascending mining as the project background, the air-leakage characteristics of the goaf wasanalyzed. Through data fitting of the in situ observation, the models of gas seepage, diffusion and air-leakage in the goaf were established in ascending mining. The ComputationFluid Dynamics software Fluent was used to simulate the air-leakage law of the goaf. Theresults of the numerical simulation provide a basis for the use of the technology of ventilation and fire prevention in the working face of an ascending mining, which ensures thesafety in production in the working face of the top-coal caving for 3_down coal seam in theJisan Coalmine.

External Weather Data Assimilation to Simulate Wind and Temperature Fields in the Region of Gualeguaych~, Argentina

This work shows the comparison between the results of wind and temperature simulation and data weather measurements in low layers near Gualeguaychfi City, Argentine, for 12 h in January 1, 2011. The model ARPS （advanced regional prediction system） with two options in the boundary conditions is used. In such conditions, wave-radiating open （radiative） with relaxation to the initial state were used while otherwise used absorbing boundary conditions data forced from MBLM （meso-scale boundary layer model） operational forecasters used by the National Weather Office. The results of both simulations are compared with data measured by three weather stations located around of the Uruguay River. As both simulations are initialized using the same data, there is a better agreement between the values obtained by forcing the boundary conditions for which are using ＂radiative＂ boundary conditions after 2 h physical time from the start of the simulation.

Control of Grid Side Converter under Unbalance Voltage Conditions for Variable Speed Wind Turbine

This paper proposes the control of a grid side converter under unbalance voltage conditions for wind turbine system. The control technique is designed to operate under unbalance voltage by independent control between positive and negative components. The converter will regulate the DC link voltage at the specific value （650 V）. To verify an operation of the proposed control, the simulation is conducted by MATLAB/SIMULINK program. The experiments are conducted on a 5 kW system composed of wind turbine simulator, machine side converter and the propose grid side converter for operation under unbalance voltage. By comparing the simulation experimentation results, it can be shown that the proposed control can be continuously operating through an extremely sag voltage without damage. Moreover the proposed control can deliver power to the grid and regulate DC link voltage under unbalance voltage.

COMPUTER SIMULATION OF METHANE MIGRATION IN LONGWALL PANELS WITH DESCENSIONAL VENTLIATION

It is important to study the methane transport phenomenon in a longwall panel under descensional ventilation conditions. In this paper the gob area is divided into a number of nodes to represent the rectangular percolating elements. The connections between nodes (elements) become branches,so that a network can be formed. Using the mechanics of porous media fluid flow, the mathematical model of air and gas flows has been established. Based on the existing ground pressure theories,the porosity of the inhomogeneous porous media in the gob can be given. In computer simulation it is considered that air pressure and temperature are functions of position ; air density, viscosity, and natural ventilation pressure are functions of temperature,pressure and methane concentration,and the resistance varies with air density and viscosity. Finally,the calculation results are given to show the differences between ascensional and descensional ventilation methods.

Characteristics of the convective bursts and their relationship with the rapid intensification of Super Typhoon Maria(2018)

For Super Typhoon Maria(2018),the multi-intensity change stages are identified and reproduced by numerical simulation.It is rather difficult to perform a perfect simulation for such a repeatedly reinforced typhoon during its long life-cycle and remote path.In this study,the rapid intensification(RI)episode is focused on to investigate the convective burst(CB)characteristics and the relationship between the CBs and the RI of Maria.For Typhoon Maria,1)the spatial pattern of the inner-core CBs in distinct shear-relative quadrants,instead of the overall inner-core CBs frequently used in previous studies,presents cyclonic rotation from downshear to upshear quadrants during RI,producing a higher efficiency for tropical cyclone(TC)spinup,which accelerates the RI process.2)Dual meanings/relationships exist between CBs and RI for Maria,in contrast to the previous argument that CBs might be an indicator or a precursor to RI.The sudden growth of CBs prior to RI provides a precursor for the upcoming RI.Additionally,the appearance of the CB peak soon after RI indicates RI could lead to more intensive deep convections.The overlap of CBs with high inertial stability inside the radius of maximum wind plays a significant role in the RI of TCs.3)The synoptic attributions to CBs are also explored for the entire troposphere,fitting in the bottom-up thinking of convection growth.The CBs might be associated with high convective available potential energy in the boundary layer,a strengthening of the deep-layer secondary circulation,and an enhanced upper-level eddy momentum flux convergence.

Value-at-Risk Approach to Currency Crises： A Brazilian Example With the Central Bank and Currency Based Assets＊

This paper uses a Value at Risk （VaR） approach to evaluate a country financial vulnerability, by analyzing the risk exposure of its Central Bank, as if their assets are subject to market risk. The Brazilian currency exchange swaps contracts （USS/Brazilian Reais） are submitted to a delta-normal VaR method, in order to evaluate the market risk of each swaps series, by modeling the variance of the daily returns, from August 1999 to January 2003. All daily returns series exhibited heteroscedasticity in the conditional variance and sudden changes in the unconditional variance. The points of changes of the unconditional variance were determined through the Iterative Cumulative Sum of Squares （ICSS） algorithm, and the conditional variance was modeled with Markov-Switching-Generalized Autoregressive Conditional Heteroscedasticity （SWGARCH） in order to capture heteroscedasticity and regime change. The results lead to two main conclusions： First, a VaR model must incorporate heteroscedasticity and regime switching in order to describe the variance of the tested series, submitted to brisk changes of economic and political scenarios. Second, a volatility-based VaR do not necessarily generate forward-looking indicators, but rather coincident indicators of possible financial vulnerabilities. The future research will evolve towards evaluating the effects of the Basel III recommendations as if they could be applied to this crisis period.

Wind Shear Investigation for Site-Specific Wind Turbine Performance Assessment

The wind energy assessment studies are generally performed referring to neutral stability conditions for the atmosphere; this is considered a good hypothesis because neutral conditions characterize the high wind situations. However the increasing size of modem multi megawatt wind turbines allows to produce energy even in low wind regimes and non-neutral conditions can involve significant production period. In such situations the variations of the vertical wind shear can affect the energy production in a sensible way and it could be fundamental to investigate how atmospheric stability and orography can affect the wind profile and the power conversion. In this paper meso-scale numerical data, CFD modeling and remote sensed wind data were used in order to analyze such behavior and to understand how wind shear influences the energy content and the discussion about how to adjust the power curve to the site specific conditions.