双热带气旋相互作用的研究

采用无基本气流的无辐散正压模式模拟了双热带气旋的运动。应用非对称理论研究了双热带气旋的相互作用。双热带气旋中的每个热带气旋主要由通过其中心的非对称气流（即通风气流）作用而移动。这股非对称气流是由其自身的线性和非线性效应产生的非对称涡旋与其配对热带气旋形成的非对称涡旋相叠加而引起的。     

On the limiting parameters of artificial cavitation

Artificial cavitation, or ventilation, is produced by releasing gas into the liquid flow. One of the objectives of creating this multiphase flow is to reduce frictional and sometimes wave resistance of a marine vehicle completely or partially immersed in the water. Flows around surface ships moving along the water–air boundary are considered in this paper. It is favorable to achieve a negative cavitation number in the developed cavitating flow under the vessel’s bottom in order to generate additional lift. Cavities, formed in the flow, have limiting parameters that are affected by propulsion and lift-enhancing devices. Methods for calculating these influences and the results of a parametric study are reported.     

Modeling and prediction of ventilation methane emissions of U.S. longwall mines using supervised artificial neural networks

Methane emissions from a longwall ventilation system are an important indicator of how much methane a particular mine is producing and how much air should be provided to keep the methane levels under statutory limits. Knowing the amount of ventilation methane emission is also important for environmental considerations and for identifying opportunities to capture and utilize the methane for energy production.Prediction of methane emissions before mining is difficult since it depends on a number of geological, geographical, and operational factors. This study proposes a principle component analysis (PCA) and artificial neural network (ANN)-based approach to predict the ventilation methane emission rates of U.S. longwall mines.Ventilation emission data obtained from 63 longwall mines in 10 states for the years between 1985 and 2005 were combined with corresponding coalbed properties, geographical information, and longwall operation parameters. The compiled database resulted in 17 parameters that potentially impacted emissions. PCA was used to determine those variables that most influenced ventilation emissions and were considered for further predictive modeling using ANN. Different combinations of variables in the data set and network structures were used for network training and testing to achieve minimum mean square errors and high correlations between measurements and predictions. The resultant ANN model using nine main input variables was superior to multilinear and second-order non-linear models for predicting the new data. The ANN model predicted methane emissions with high accuracy. It is concluded that the model can be used as a predictive tool since it includes those factors that influence longwall ventilation emission rates.     

北京地区日最大边界层高度的气候统计特征

使用北京气象站探空观测数据和地面气温观测数据,以干绝热曲线法估算1984~2013年逐日最大边界层高度,同时计算对应的边界层平均风速和通风量。统计分析这3个边界层参量的平均特征,并利用2001~2012年的空气污染指数(API),探讨大气污染与边界层参量的关系。结果表明:(1)日最大边界层高度的30年月均值以春季和夏初(3~6月)最高,约1600 m;夏季和秋初(7~10月)次之,约1300 m;冬季(11月、12月和1月)最低,约1000~1200 m。(2)夏季,日最大边界层高度不同数值的频率大致为对称分布,峰值处于1000~1600 m范围;秋、冬季,频率分布系统性地向低值一方偏斜,600~800 m的出现频率大大增加;春季边界层高度的变化极大。(3)各季边界层平均风速以夏季为最小。(4)一年中春季通风量最大,秋季次之,冬季较低,夏季最小。(5)秋、冬季,北京中度和重污染个例(API200)集中分布于弱风、低边界层和小通风量条件,反映污染物局地累积的作用;春季污染个例半数以上以高风速、高通风量为特征,反映沙尘类外部输入性污染的作用。     

Intense reducing conditions during the last deglaciation and Heinrich events (H1, H2, H3) in sediments from the oxygen minimum zone off Goa,eastern Arabian Sea

Two sediment cores, ABP-32/GC-01R and ABP-32/GC-03 were collected at a water depth of 642 m and 1086 m off Goa from the present day Oxygen Minimum Zone (OMZ) of eastern Arabian Sea (EAS) cover time span of last 18 ka and 32 ka respectively were analysed for multi-proxy redox-sensitive elements to understand the variation in the redox conditions and factors responsible for its development.Redox-sensitive elements concentration and their normalized ratios (Mn/Al, U/Th, Mo/Al and Ce/Ce*) suggest that sediment core ABP-32/GC-01R is under more reducing conditions due to its location within the centre of OMZ compared to core ABP-32/GC-03 which is at the base of OMZ. Sediments from the EAS are of non-euxinic environments where dissolved sulfide is present but restricted to the sediment pore-waters. Lack of significant correlation (r=< 0.1) of organic carbon with U and Mo suggest that productivity may not have control on the development of reducing conditions. The lowest Mn/Al ratio, strong negative Ce/Ce* anomaly and remarkable enrichment of U/Th and Mo/Al ratios during the last deglaciation, and Heinrich events (H1, H2, H3) indicate intense reducing conditions probably due to poor ventilation by oxygen depleted bottom waters from Subantarctic Mode Waters (SAMW) - Antarctic Intermediate waters (AAIW). There is a distinct lathanide fractionation in the sediment cores where, La_(n)/Yb_(n) ratio is <1, ≈1 and >1 during the last 10 ka (Holocene), 14–10 ka (includes-Younger Dryas and Bǿlling-Allerǿd), 18–14 ka (last deglaciation) and Heinrich events suggesting less reducing, terrigenous dominated and intense reducing condition respectively.     

含瓦斯气体地质条件下的泥水盾构施工

根据在含有瓦斯气体地质下施工的经验和教训,通过对所采取措施的分析,提出在含瓦斯气体地层中掘进施工合理建议。要求必须加强瓦斯气体检测,采取高稠度密封油脂用量、双液浆背填、加强通风等各种有效封堵措施保证施工安全。     

CO and CO2 emissions from spontaneous heating of coal under different ventilation rates

Carbon monoxide (CO) and carbon dioxide (CO₂) emissions during a spontaneous heating event in a coal mine are important gases to monitor for detecting the spontaneous heating at an early stage. However, in underground coal mines, the CO and CO₂ concentrations and their related fire ratios may be affected by mine ventilation. In this study, CO and CO₂ emissions from spontaneous heating of a U.S. coal sample were evaluated in an isothermal oven under different airflow ventilation rates ranging from 100 to 500 cm³/min. Laboratory experiments were conducted at oven temperatures of 70, 90, and 100 °C. The temperature at the center of the coal sample was continually monitored, while the CO, CO₂, and oxygen (O₂) concentrations of the exit gas were continually measured. The results indicate that CO was generated immediately after the airflow passed through the coal, while CO₂ was generated in a late phase. The amounts of CO generated under different airflow rates were approximately the same at the initial temperature of 70 °C, while the amounts of CO generated increased significantly as the airflow rates and initial temperatures increased. The ratio of CO/CO₂ was found to be independent of airflow rate and initial temperature, approaching a constant value of 0.2 quickly if there was no thermal runaway. The value tended to decrease when a thermal runaway took place. The CO/O₂ deficiency ratio was dependent on both airflow rates and the initial temperature. The experimental results are in qualitative agreement with some large-scale test and field monitoring results.     

Analysis of Carbon Dioxide Variations in the Atmosphere of Srednja Bijambarska Cave,Bosnia and Herzegovina

The results of one year’s monitoring in Srednja Bijambarska Cave (Bosnia and Herzegovina) are presented and discussed. Temporal variations of the carbon dioxide (CO₂) concentration are controlled by the switching between two ventilation regimes driven by outside temperature changes. A regression model with a simple perfectly mixed volume applied to a cave sector (“Music hall”) resulted in an estimate of ventilation rates between 0.02 h⁻¹ and 0.54 h⁻¹. Carbon dioxide input per plan surface unit is estimated by the model at around 50 × 10⁻⁶ mh⁻¹ during the winter season and up to more than 1000 × 10⁻⁶ mh⁻¹ during the first temperature falls at the end of summer (0.62 μmoles m⁻² s⁻¹ and 12.40 μmoles m⁻² s⁻¹ for normal conditions respectively). These values have been found to be related to the cave ventilation rate and dependent on the availability of CO₂ in the surrounding environment. For airflow close to zero the values of CO₂ input per plan surface have a range in the order of magnitude of a few units × 10⁻⁶ mh⁻¹. Based on two experiments, the anthropogenic contribution from cave visitors has been calculated, at between 0.35 l_CO2 min⁻¹ person⁻¹ and 0.45 l_CO2min⁻¹person⁻¹.     

Assessing bottom water anoxia within the Late Devonian Woodford Shale in the Arkoma Basin,southern Oklahoma

Comparing the concentration of molybdenum (Mo) (ppm) and total organic carbon (TOC) (wt%) within sediments allows interpretation of the relative degrees of bottom water restriction within the geologic record. The Woodford Shale is interpreted as transgressive systems tract (TST) grading into highstand systems tract (HST). The lowermost Woodford preserves a Mo-TOC signal that is consistent with a restricted basin that periodically received influxes of water consistent with rising sea levels flowing into restricted sub-basins that became isolated by localized conditions. The middle Woodford preserves a signal that indicates an increased ventilation at the sediment-water interface persisting until the maximum flooding surface. The presence of phosphate nodules in the uppermost Woodford suggests sufficient oxygen to retain the Mo in solution and indicates active upwelling and circulation with the Paleotethys.It is also possible to document changing ventilation patterns, non-destructively, within a basin by utilizing changing trends in redox-sensitive trace metals (Mo, Ni, and Cu) and an approximation of the degree of pyritization (aDOP) based on an idealized formula for pyrite (FeS₂). This chemofacies approach produces a qualitatively similar interpretation to the changing Mo-TOC signal and can evaluate lateral trends in bottom water ventilation where destructive sampling is not permitted. Distal regions preserve the greatest degree of bottom water ventilation. Proximal regions preserve highly variable conditions with more restricted conditions being common in the lowermost Woodford Shale and ventilation improving upsection.Interpreting changing levels of bottom water anoxia enable greater degrees of precision in targeting potential hydrocarbon resources. Furthermore, this information improves our understanding of the changing environmental conditions of the Woodford Shale. The Framvaren Fjord is a reasonable modern analog for bottom water restriction in the lowermost portion of the Woodford Shale. The Cariaco Basin is a good modern analog for bottom water restriction in the middle and uppermost Woodford Shale.     

Flow of winter-transformed Pacific water into the Western Arctic

The dynamics of the flow of dense water through Barrow Canyon is investigated using data from a hydrographic survey in summer 2002. The focus is on the winter-transformed Bering water—the highest volumetric mode of winter water in the Chukchi Sea—which drains northward through the canyon in spring and summer. The transport of this water mass during the time of the survey was 0.2–0.3 Sv. As the layer flowed from the head of the canyon to the mouth, it sank, decelerated, and stretched. Strong cyclonic relative vorticity was generated on the seaward side of the jet, which compensated for the stretching. This adjustment was incomplete, however, in that it did not extend across the entire current, possibly because of internal mixing due to shear instabilities. The resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation. Multiple eddies of winter-transformed Bering water were observed along the Chukchi–Beaufort shelfbreak. Those to the west of Barrow Canyon were in the process of being spawned by the eastward-flowing shelfbreak current emanating from Herald Canyon, while the single eddy observed to the east originated from the Barrow Canyon outflow. It is argued that such an eddy formation is a major source of the ubiquitous cold-core anti-cyclones observed historically throughout the Canada Basin. Implications for the ventilation of the upper halocline of the Western Arctic are discussed.