BECKHOFF多通道技术在汽车纵梁生产线上的运用

随着现代汽车工业的发展,汽车生产制造技术对新工艺新技术提出了更高要求。本文基于BECKHOFF双通道技术,对加工设备的动作工艺进行改进,可切实有效地实现各轴运转的无缝对接,进一步缩短生产周期,增加企业竞争力。     

An improved method for predicting discharge of homogeneous compound channels based on energy concept

Accurate estimation of flow discharge in a compound river channel is increasingly important in river management and hydro-environment design. In this paper, a new model is developed to improve the prediction of flow based on Energy Concept Method (ECM) and Weighted Divided Channel Method (WDCM) along with the apparent shear stress at the interface between main channel and floodplain. The new model is compared with a wide range of our experimental data and the data available in the literature. The 27 datasets used include homogenous symmetric channels (22 datasets) and asymmetric channels (5 datasets) with various aspect ratios [channel total width (B) at bankfull / main channel bottom (b) =1.5–15.8], and bed slopes (S_o = 4.3 × 10⁻⁴–1.3 × 10⁻²). It was found that the new model has significantly improved the accuracy of flow prediction compared with the traditional Divided Channel Method (DCM), and has also considerably better results than the ECM and WDCM methods against all the datasets, particularly for relatively low flow depths of floodplain where the flow discharges are most difficult to predict correctly. The new model predicts the total discharge well for both symmetric and asymmetric channels, within an averaged relative error of about 5%.     

Explicit solution for normal depth of parabolic section of open channels

To obtain the normal depth of parabolic section of open channels, multiple known parameters were incorporated into a comprehensive one by transforming basic equations, and a concept of the non-dimensional normal depth was introduced. The normal depth equations were simplified into a non-dimensional iterative formula that was proved to have a high velocity of convergence. By analyzing the comprehensive parameter and dimensionless normal depth under condition of usually adopted sizes of parabolic channels and through establishing their relationship, the iterative initial value of normal depth was obtained. The normal depth of parabolic channels was acquired by substituting the initial value into the iteration formula. The error analysis was made and a case study was provided as an application example. The case study showed that the iteration formula was very simple, convenient and precise for determining the normal depth of parabolic channels with the maximum relative error of normal depth being less than 0.34% when the ratio of width to depth was between 0.2 and 20.     

Residence time distribution and oxygen transfer in a novel constructed soil filter

BACKGROUND: The constructed soil filter (CSF), also known as soil biotechnology is a system for water renovation, which makes use of formulated media, culture of soil micro‐ and macro‐organisms, additives and plantation to purify water and wastewater. The process gives benefits in terms of applicability across very small to large scale, natural aeration, absence of moving parts, no biological sludge generation, odor free green aesthetic ambience. RESULTS: Residence time distribution (RTD) studies were carried out using laboratory scale CSF. Pulse potassium bromide tracer tests were carried out to determine RTD, and the Peclet number found to be 9–13 for a 2 m bed, and 2–3 for a 0.30 m bed with oxygen transfer of 0.08 h^?1. CONCLUSION: The two‐channel dispersion model for flow behavior shows a good fit to the experimental data, indicating a reactor Peclet number 9–13 for a 2 m bed and 2–3 for a 0.3m bed. Oxygen transfer studies carried out using various methods gave an oxygen transfer coefficient of about 0.08 h^?1. Wastewater purification studies indicate overall COD removal rate of around 50 mg L^?1 h^?1, suggesting that highly aerobic conditions are prevalent in the CSF system. Copyright © 2009 Society of Chemical Industry     

Variable antenna‐space shift keying for high spectral efficiency in exponentially correlated channels

In space shift keying (SSK), all information bits are transmitted by antenna indices rather than transmitting symbols. To obtain high spectral efficiency, exponentially increasing number of antennas is used, which is generally not practical. Less number of antennas can only be possible by using more than one active antenna, such as generalized SSK, but this type of solutions result in excessive degradation in bit error ratio in correlated channels. In this study, variable number of active antennas for each codeword is proposed and called variable antenna‐SSK. First of all, pairwise error probability is obtained for variable number of antennas in the case of correlated channels. Then, to reduce the correlation effect, a novel antenna codeword construction method that minimizes the pairwise error probability is introduced for exponentially correlated channels. Codeword sets are obtained for k = 3 and 8 bits/s/Hz for 7 and 13 transmit antennas. Simulation results show that variable antenna‐SSK gets better performance according to its counterparts with increasing effect of correlation. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a cross-section based streamflow routing package for MODFLOW

It is challenging to simulate stream-aquifer interactions for the wide channel streams with the existing stream routing packages of MODFLOW. To overcome this limitation, a Cross-Section streamflow Routing (CSR) package is developed to simulate the streamflow and the interaction between streams and aquifers for the stream with a width larger than the MODFLOW grid size. In the CSR package, streams are divided into stream segments which are formed by two consecutive cross-sections. A cross-section is described by a number of streambed points that determine the geometry and hydraulic properties of the streambed. The stream water depth and streamflow at the cross-sections are related by the Single Channel method, the Divided Channel method, a data table or a power function. A rapid algorithm is used to compute the submerged area of the MODFLOW grid. The streambed conductance of a grid cell is computed based on its submerged area, streambed hydraulic conductivity and thickness. Stream-aquifer seepage is subsequently estimated as the product of the streambed conductance and difference between the stream stage and groundwater hydraulic head. Stream-aquifer seepage is treated as lateral flow in the streamflow routing computation with the Muskingum-Cunge method or mass conservation method. A hypothetical problem is established to test the capabilities of the CSR package with steady- and transient-state models. The results compare favorably with the SFR2 package and the HEC-RAS model. However, significant difference in flood wave attenuation is observed between the CSR package and the SFR2 package. It proves that the CSR package is capable of simulating the variation of stream-aquifer interactions in both space and time efficiently. The CSR package represents a certain improvement over previous MODFLOW streamflow packages by providing the efficient cross-section based computation and the unique capability of simulating streambed heterogeneity in longitudinal and transverse directions.     

Approach to designing bribery-free and coercion-free electronic voting scheme

Electronic voting has been in development for more than 20 years, during which it has produced outstanding results both in theory and in practice. However, bribery and coercion remain an open problem, as there is still no suitable manner to prevent or fight them. Publications emphasizing practicality has not been able to achieve effective protection, probably due to their overtly simple protection method, while publications emphasizing theories are difficult to put into practice due to the complicated protection method devised by them. Thus, how to design a scheme that can flawlessly prevent problems of bribery and coercion as well as put into practice easily becomes a significant issue. In this paper, we suggest that designers apply two indispensable design components, invisible channel and biometrics receipts, to design a prevention e-voting scheme, and also to introduce several feasible technology to help with its implementation. Followingly, a prevention electronic voting scheme that matches our ideal is proposed. We expect this study to arouse the interest of more researchers regarding the subject.     

A wind-tunnel study of flow distortion at a meteorological sensor on top of the BT Tower, London, UK

High quality wind measurements in cities are needed for numerous applications including wind engineering. Such data-sets are rare and measurement platforms may not be optimal for meteorological observations. Two years' wind data were collected on the BT Tower, London, UK, showing an upward deflection on average for all wind directions. Wind tunnel simulations were performed to investigate flow distortion around two scale models of the Tower. Using a 1:160 scale model it was shown that the Tower causes a small deflection (ca. 0.5°) compared to the lattice on top on which the instruments were placed (ca. 0-4°). These deflections may have been underestimated due to wind tunnel blockage. Using a 1:40 model, the observed flow pattern was consistent with streamwise vortex pairs shed from the upstream lattice edge. Correction factors were derived for different wind directions and reduced deflection in the full-scale data-set by <3°. Instrumental tilt caused a sinusoidal variation in deflection of ca. 2°. The residual deflection (ca. 3°) was attributed to the Tower itself. Correction of the wind-speeds was small (average 1%) therefore it was deduced that flow distortion does not significantly affect the measured wind-speeds and the wind climate statistics are reliable.     

A study on port plug distortion caused by narrow gap combined GTAW & SMAW and Electron Beam Welding

A study of port plug distortion resulting from narrow gap combined GTAW & SMAW and Electron Beam Welding was carried out. Thermomechanical finite element analysis of port plug becomes virtually impossible because of the requirement of huge number of nodes and elements. Hence an analysis method based on the concept of inherent strain was used in this work. The computational time required was about 40-50 min only in a Core (TM) 2 Duo, 2.66 GHz computer with 2 GB RAM, which otherwise was not possible with other conventional computation techniques. As was expected the overall distortion due to EB welding was found to be less compared to that of narrow gap GTAW & SMAW.     

邻近建筑物暗挖地铁风道施工方案研究

针对北京地铁十号线呼家楼站风道施工情况,对风道施工方案和邻近建筑物的保护措施进行了详细的研究,监测结果表明所采用施工方案是合理的,确保了邻近建筑物的安全和地铁风道施工的安全。