带过渡深腔的动压轴承的优化设计与试验

为了提高动压轴承的承载能力和稳定性,提出一种带过渡深腔的动压轴承的新结构。由雷诺方程出发,纳入带腔动压轴承的边界条件,采用细分网格的差分算法,对轴承进行性能分析与优化设计得到带过渡腔的动压轴承的系列的特性数据和结构参数。新轴承具有承载能力大和稳定性高的特点。与普通动压轴承比较,在常用工况下,新轴承的承载能力可增大18%～98%,偏位角可由43°降低到14°,轴承稳定运转速度可提高10%～75%。在HZS-1轴承试验台上测量了轴承的油膜压力分布及偏心比。试验结果与理论分析结果具有良好的一致性。

低透气性煤层瓦斯预抽技术的探讨与实践

红阳三矿煤层埋藏深、变质程度高、瓦斯吸附性强,造成煤层透气性低,在采取开钻场先抽后采措施中,预抽时间长、提前掘送巷道增加维护工作量。针对此,提出了在工作面动压影响带采取中深孔抽放瓦斯工艺。在北一1211工作面可行性试验,结果表明,在工作面日产原煤5000t的情况下,回风流最大瓦斯浓度0.8%,一般介于0.5%～0.6%,效果显著。

Design of voltage-controlled dynamic band-pass filter based on VCA810

In order to filter signal effectively according to selective center frequency, a voltage-controlled dynamic band-pass filter with gain compensation was designed based on voltage-controlled gain wideband amplifier VCA810. The transfer function of the filter was analyzed and gain compensation voltages were given through tests; besides, a system was designed, including the gain compensation circuit and the control voltage circuit, etc. Center frequency will change from 1 kHz to 20 kHz according to control voltage on condition that bandwidth of the filter remains constant. The designed system has the advantages of simple structure, low noise, stable performance and convenient adjustment.

A resistorless CMOS bandgap reference with below 1 V output

This paper proposes a resistorless CMOS bandgap reference (BGR) circuit capable of generating a voltage less than 1V and presents a high performance start up circuit that can make the BGR circuit achieve the correct operation point at power on. The simulation with Hspice was carried out using a 0 25 μm CMOS process. The results indicate that the proposed BGR circuit can operate on a 2 2 to 3 3 V power supply and its output voltage has a variation of 11 mV at -10 to 80 ℃.

On the dissipation of negative excess porewater pressure induced by excavation in soft soil

Unloading induces negative excess porewater pressure in soil mass around a foundation pit during excavation. In this work, the dissipation rule of negative excess porewater pressure after excavation was studied. Analytical formulas for calculating the negative excess porewater pressures and the effective stresses were derived based on one-dimensional consolidation theory and Terzaghi’s effective stress principle. The influence of the dissipation of negative excess porewater pressure on earth pressure inside and outside a foundation pit and the stability of the retaining structure were analyzed through a numerical example. It was indicated that the dissipation of negative excess porewater pressure is harmful to the stability of the retaining structure and that rapid construction can make full use of the negative porewater pressure.

Statistical Analysis of Tropical Disturbances over the South China Sea During 1997-2006

Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1997 to 2006, with 54 de-veloping tropical disturbances which developed into tropical depressions and 104 non-developing tropical disturbances which never developed into tropical depressions. The development rate of tropical disturbances into tropical depressions was 34.18% in these ten years. During the period of this study, total annual numbers of tropical disturbances and developing tropical disturbances over the SCS had significant decreasing trends; however, the development rate of tropical disturbances had an insignificant increasing trend.

Evaluation of Atmospheric Circulation in the Southern Hemisphere in 20CRv2

Evaluation of the mean climate and climate variability in the Southern Hemisphere （SH） in the Twentieth Century Reanalysis data version 2 （20CRv2） is conducted and the results are compared with the NCEP/NCAR version 2 Reanalysis data （NCEPv2） and the Hadley Center sea-level pressure data （HadSLPv2）.The results show that SH polar High,SH subtropical High,upper level split jet,cross-equatorial flow,Antarctic Oscillation （AAO）,and the pattem of Pacific-South-America （PSA） has been effectively captured by 20CRv2 during 1979-2010,with an apparent zonal asymmetry of AAO in the austral winter （June-July-August,JJA）.The notable upward linear trend of AAO in the entire period of 1871-2010 is represented in both 20CRv2 and HadS1Pv2.The most remarkable discrepancy of the SH climate variability between 20CRv2 and HadSLPv2 occurred in 1897-1920 and was partly caused by such factors as the paucity of meteorological and oceanographic data in the SH to be assimilated,the handling of the specified sea-ice concentration in South Pole,and imperfect climate models.The consistency of these reanalysis data is increased with the use of a large amount of satellite observation and radiosonde data,particularly after 1979.

The Connection between the Sea Surface Height Anomaly Preceding the Indian Ocean Dipole and Summer Rainfall in China

The sea surface height anomaly(SSHA) signals leading the fall Indian Ocean Dipole(IOD) are investigated. The results suggest that, prior to the IOD by one year, a positive SSHA emerges over the western-central tropical Pacific(WCTP), which peaks during winter(January-February-March, JFM), persists into late spring and early summer(April-May-June, AMJ), and becomes weakened later on. An SSHA index, referred as to SSHA_WCTP, is defined as the averaged SSHA over the WCTP during JFM. The index is not only significantly positively correlated with the following-fall(September-October-November, SON) IOD index, but also is higher than the autocorrelation of the IOD index crossing the two different seasons. The connection of SSHA_ WCTP with following-summer rainfall in China is then explored. The results suggest that higher(lower) SSHA_ WCTP corresponds to increased(reduced) rainfall over southern coastal China, along with suppressed(increased) rainfall over the middle–lower reaches of the Yangtze River, North China, and the Xinjiang region of northwestern China. Mechanistically, following the preceding-winter higher(lower) SSHA_WCTP, the South Asia High and the Western Pacific Subtropical High are weakened(intensified), which results in the East Asian summer monsoon weakening(intensifying). Finally, the connection between SSHA_WCTP and El Ni?o-Southern Oscillation(ENSO) is analyzed. Despite a significant correlation, SSHA_WCTP is more closely connected with summer rainfall. This implies that the SSHA_WCTP index in the preceding winter is a more effective predictor of summer rainfall in comparison with ENSO.

An interdecadal change of tropical cyclone activity in the South China Sea in the early 1990s

Tropical cyclone （TC） genesis in the South China Sea （SCS） during 1979-2008 underwent a decadal variation around 1993. A total of 55 TCs formed in the SCS from May to September during 1994- 2008, about twice that during 1979-1993 （27）. During the TC peak season （July-September, JAS）, there were 43 TCs fi＇om 1994-2008, but only 17 during 1979-1993. For July in particular, 13 TCs formed from 1994-2008, but there were none during 1979-1993. The change in TC number is associated with changes of key environmental conditions in atmosphere and ocean. Compared to 1979-1993, the subtropical high was significantly weaker and was displaced more eastward during 1994-2008. In the former period, a stronger subtropical high induced downward flow, inhibiting TC formation. In the latter period, vertical wind shear and outgoing longwave radiation all weakened. Mid-level （850-500 hPa） humidity, and relative vorticity were higher. Sea surface temperature and upper layer heat content were also higher in the area. All these factors favor TC genesis during the latter period. The decadal change of TC genesis led to more landfalling TCs in Southern China during the period 1994-2008, which contributed to an abrupt increase in regional rainfall.

Research on Ground Movement Laws for Strip Mining Under Thick Alluvium

With the discrete element method, the simulation and analysis of a series of numerical models were made. This research revealed ground movement laws for strip mining under thick alluvium and gave calculation formulae for the maximum ground subsidence and horizontal movement as a function of basement rock thickness and mining width, thus providing sound evidence for future strip mining under thick alluvium.

The Cold Vortex Circulation over Northeastern China and Regional Rainstorm Events

In this study,regional rainstorm events (RREs) in northeastern China associated with the activity of the Northeastern China Cold Vortex (NCCV) were investigated on a medium-range time scale.The RREs occurring in northeastern China could be categorized into three groups according to the distribution of heavy rainfall.The largest cluster is characterized by the rainstorm events that occur on the northwestern side of the Changbai Mountains along a southwest-northeast axis.These events occur most frequently during the post-meiyu period.The authors place particular emphasis on the RREs that belong to the largest cluster and are closely associated with the activity of the NCCV.These RREs were preconditioned by the transportation of substantial amounts of water vapor to which the anomalous western Pacific subtropical high (WPSH) contributed.The attendant anomalous WPSH was primarily driven by the anomalous transient eddy feedback forcing the nearby East Asian jet.The development of the NCCV circulation was concurrent with the RREs and acted as their primary causative factor.A perspective based on low-frequency dynamics indicates that Rossby wave packets emanated from the blocking-type circulation over northeastern Asia led to the development of the NCCV activity.

Giant magnetoimpedance effect in stress-joule-heated Co-based amorphous ribbons

Co-based Co63Fe4B22.4Si5.6Nb5 amorphous ribbons with a width of 150 μm and a thickness of 50 μm were prepared by single-roller melt-spinning process.The giant magneto-impedance(GMI) effect of the stress-joule-heated ribbons under applied tensile stress ranging from 37 to 148 MPa was investigated.Experimental results show that the spectra of GMI ratio vs.external direct current(dc) field(Hex) of the samples changes dramatically with annealing tension() and driving frequency.The single-peak(SP) GMI curve with maximum GMI ratio of 260% and magnetic field sensitivity of 52%/Oe was obtained in the sample applied tensile stress of 74 MPa at frequency of 3.6 MHz.A three-peak behaviour appeared in the samples under σ of 111 and 148 MPa.The uncommon three-peak behaviour was attributed to several factors,which effectively originated from the balance between domain-wall movement and magnetization rotation.