Artificial ground freezing of underground mines in cold regions using thermosyphons with air insulation

Current practice of underground artificial ground freezing(AGF)typically involves huge refrigeration systems of large economic and environmental costs.In this study,a novel AGF technique is proposed deploying available cold wind in cold regions.This is achieved by a static heat transfer device called thermosyphon equipped with an air insulation layer.A refrigeration unit can be optionally integrated to meet additional cooling requirements.The introduction of air insulation isolates the thermosyphon from ground zones where freezing is not needed,resulting in:(1)steering the cooling resources(cold wind or refrigeration)towards zones of interest;and(2)minimizing refrigeration load.This design is demonstrated using well-validated mathematical models from our previous work based on two-phase enthalpy method of the ground coupled with a thermal resistance network for the thermosyphon.Two Canadian mines are considered:the Cigar Lake Mine and the Giant Mine.The results show that our proposed design can speed the freezing time by 30%at the Giant Mine and by two months at the Cigar Lake Mine.Further,a cooling load of 2.4 GWh can be saved at the Cigar Lake Mine.Overall,this study provides mining practitioners with sustainable solutions of underground AGF.

Changes and spatial patterns of the differences between ground and air temperature over the Qinghai-Xizang Plateau

The difference between ground soil and air temperature （Ts-Ta） was studied by using the data of ground and air temperature of 99 stations over the Qinghai-Xizang （Tibet） Plateau from 1960 to 2000,and its spatial distribution and time changing tendency have been diagnosed by principal component analysis and power spectral analysis methods. The results show that the values of （Ts-Ta） are the maximum in June and the minimum in December. The first three loading eigenvectors, which reflect the main spatially anomalous structure of （Ts-Ta） over the Qinghai-Xizang Plateau, contain the contrary changing pattern between the northwestern and the southeastern regions, the pattern response of the sea level elevation and the geography, and the pattern response of the distribution of the permafrost. There are four patterns of time evolution including the patterns of monotonous increasing or decreasing trends, the basic stability pattern and the parabola pattern with the minimum value. （Ts-Ta） has a periodic variation about 2 years. According to the spatial distribution of the third loading eigenvectors of （Ts-Ta） over the Qinghai-Xizang Plateau in cold season, the permafrost response region and the seasonal frozen ground response region are identified.

A Bilevel Programming Approach for Optimization of Airport Ground Movement

This paper proposes an optimization model for the airport ground movement problem(GMP)based on bilevel programming to address taxi conflicts on the airport ground and to improve the operating safety and efficiency.To solve GMP,an iterative heuristic algorithm is designed.Instead of separately investigating each problem,this model simultaneously coordinates and optimizes the aircraft routing and scheduling.A simulation test is conducted on Nanjing Lukou International Airport(NKG)and the results show that the bilevel programming model can clearly outperform the widely used first-come-first-service(FCFS)scheduling scheme in terms of aircraft operational time under the precondition of none conflict.The research effort demonstrates that with the reduced operating cost and the improved overall efficiency,the proposed model can assist operations of the airports that are facing increasing traffic demand and working at almost maximum capacity.

An Air Route Planning Model of Unmanned Aerial Vehicles Under Constraints of Ground Safety

With the rapid growth of the number and flight time of unmanned aerial vehicles(UAVs),safety accidents caused by UAVs flight risk is increasing gradually.Safe air route planning is an effective means to reduce the operational risk of UAVs at the strategic level.The optimal air route planning model based on ground risk assessment is presented by considering the safety cost of UAV air route.Through the rasterization of the ground surface under the air route,the safety factor of each grid is defined with the probability of fatality on the ground per flight hour as the quantitative index.The air route safety cost function is constructed based on the safety factor of each grid.Then,the total cost function considering both air route safety and flight distance is established.The expected function of the ant colony algorithm is rebuilt and used as the algorithm to plan the air routes.The effectiveness of the new air route planning model is verified through the logistical distribution scenario on urban airspace.The results indicate that the new air route planning model considering safety factor can greatly improve the overall safety of air route under small increase of the total flight time.

Recent changes in ground surface thermal regimes in the context of air temperature warming over the Heihe River Basin, China

Changes in ground surface thermal regimes play a vital role in surface and subsurface hydrology, ecosystem diversity and productivity, and global thermal, water and carbon budgets as well as climate change. Estimating spring, summer, autumn and winter air temperatures and mean annual air temperature（MAAT） from 1960 through 2008 over the Heihe River Basin reveals a statistically significant trend of 0.31 °C/decade, 0.28 °C/decade, 0.37 °C/decade, 0.50 °C/decade, and 0.37 °C /decade, respectively. The averaged time series of mean annual ground surface temperature（MAGST） and maximum annual ground surface temperature（MaxAGST） for 1972–2006 over the basin indicates a statistically significant trend of 0.58 °C/decade and 1.27 °C/decade, respectively. The minimum annual ground surface temperature（MinAGST） in the same period remains unchanged as a whole. Estimating surface freezing/thawing index as well as the ratio of freezing index to thawing index（RFT） in the period between 1959 and 2006 over the basin indicates a statistically significant trend of-42.5 °C-day/decade, 85.4 °C-day/decade and-0.018/decade, respectively.

^7Be content and its seasonal variation in the ground air around Hangzhou area

Twice investigations around Hangzhou area show that ^7Be content average in the ground air is 5.9mBq.m^-3.The content of ^7Be is the highest in autumn-winter period reaching about 7.7mBq.m^-3,the next is in spring about 6.2mBq.m^-3.then is in the early summer about 5.7mBq.m^-3,close to the annual average level;and the lowest in a year is in summer-autumm period with a value about 3.8mBq.m^-3.Exhibited is a decreasing trend from autumn-winter period to summer-autumn of the next year,which is negatively correlated with the variation of the seasonal rainfall in Hangzhou area.But this trend is different from that reported by UNSCEAR:it is the highest in spring and the lowest in the late autumn,which is based only on ^7Be falling down from the stratosphere.However,the present investigation shows that the seasonal rainfall is the main factor influencing the variation tend of ^7Be content in the air.

AIR GROUND RANGING OF AIRBORNE RADAR USING WAVELET TRANSFORM

A new method of air ground ranging of airborne radar based on wavelet transform was proposed. The wavelet domain noise excision was applied as a post processing tool to reduce the white Gaussian noise appearing in the radar echo. The wavelet approach overcomes the drawbacks of the traditional ranging method, thus considerably improving the accuracy and speed of air ground ranging. The whole algorithm was performed in frequency domain. It can take full advantage of the radar’s former hardware resource, such as FFT high speed processor. The simulation results demonstrate the validity of our new approach.

A Variational Method for the Fuse-Warhead Coordination Design of an Air-Faced Missile

This paper presents a variational method for the fuse-warhead coordination design of an air-faced missile, which takes the distribution density of fragments for a variable and the totalprobability of kill of single missile against an air-target for an objective function.

Henry’s Equilibrium Partitioning between Ground Water and Soil Air: Predictions versus Observations

Humans spend 64% - 94% of their time indoors;therefore, indoor air quality is very important for potential exposure to volatile organic compounds (VOC). The source of VOC in the subsurface may come from accidental or intentional releases, leaking landfills or leaking underground and above-ground storage tanks. Once these contaminants are present near or beneath buildings, they may move as a vapour through soil gas and enter the building. A large number of vapour intrusion (VI) algorithms have been published in peer-reviewed publications that link indoor VOC concentrations to the contamination of soils. These models typically include phase partitioning calculations of VOC based on Henry’s law to estimate the concentration of a particular contaminant in soil gas. This paper presents the results from a series of laboratory experiments concerning the use of the Henry’s Law constant for the calculation of toluene concentrations in equilibrium between ground water and soil air. A series of column experiments were conducted with various toluene concentrations in artificial (ground) water to contrast the predicted and observed (soil) air concentrations. The experiments which exclude soil material show a toluene fugacity behaviour roughly in line with Henry’s law whereas the experiments which include soil material result in equilibrium soil concentrations which were around one order-of-magnitude lower than was expected from a Henry Law-based estimation. It is concluded that for toluene inclusion of Henry’s Law in VI algorithms does not provide an adequate description of volatilisation in soils and may lead to an overestimation of health risk. Instead, a model based on a simple description of the relevant intermolecular interactions could be explored.

Ground Rupturing Due to Entrapped Air/Gas in the Unconfined Zone

The sudden and large oscillation of pressure of compressed air/gas entrapped in porous medium due to the changes in the actual pore-fluid pressure, during recharge of water following intense rainfall after a prolonged period of dryness such that the rainfall intensity exceeding infiltration capacity, leads to the generation of hydo-tremors. These hydro-tremors cause ground rupturing, subsidence, developments of cracks in the building, etc. A theoretical model has been presented to estimate the successive values of compressed air/gas pressures due to the successive development of actual pore-fluid pressures and effective stresses during recharge of water of the unconfined zone during the onset of the summer monsoon of 2008 in the northern parts of India.

Air-Ground Temperature Coupling: Analysis by Means of Thermal Orbits

Long-term measurements of air, near-surface (soil) and ground temperatures that were collected between 1994 and 2013 at the drill site of the Geothermal Climate Change Observatory (Prague) were analyzed to understand the relationship between these variables and to reveal the mechanisms of heat transport at the land-atmosphere boundary layer. The 2D Thermal Orbit (TO) method was applied to detect regularities that were hidden in noisy and highly variable temperature time series. The results showed that the temperatures at shallow depths were affected by surface air temperature (SAT) variations on seasonal and annual time scales and could be regarded as an accurate proxy for low frequency temperature variations at the Earth’s surface. Only low-frequency/ high-amplitude surface temperature variations penetrate into the subsurface because of strong damping and the filtering effect of the ground surface. The borehole temperatures have good potential to capture temperature variations (periodicities) over long time scales that cannot be detected in the SAT series themselves because of the interference of higher frequency noise. The TO technique is a useful and powerful tool to quickly obtain diagnostics of the presence of long periodicities in borehole temperature time series.

Channel Modeling for Air-to-Ground Wireless Communication

In this paper, we discuss several large-scale fading models for different enviromnents. The COST231-Hata model is adapted for air-to-ground modeling. We propose two criteria for air-to- ground channel modelling based on test data derived from field testing in Beijing. We develop a new propagation model that is more suitable for air-to-ground communication that previous models. We focus on improving this propagation model using the field test data.

Self-organizing strategy design and validation forintegrated air-ground detection swarm

A self-organized integrated air-ground detection swarmis tentatively applied to achieve reentry vehicle landing detection,such as searching and rescuing a manned spaceship. The detectionswarm consists of multiple unmanned aerial vehicles （UAVs）and unmanned ground vehicles （UGVs）. The UAVs can accessa detected object quickly for high mobility, while the UGVs cancomprehensively investigate the object due to the variety of carriedequipment. In addition, the integrated air-ground detectionswarm is capable of detecting from the ground and the air simultaneously.To accomplish the coordination of the UGVs andUAVs, they are all regarded as individuals of the artificial swarm.Those individuals make control decisions independently of othersbased on the self-organizing strategy. The overall requirements forthe detection swarm are analyzed, and the theoretical model ofthe self-organizing strategy based on a combined individual andenvironmental virtual function is established. The numerical investigationproves that the self-organizing strategy is suitable andscalable to control the detection swarm. To further inspect the engineeringreliability, an experiment set is established in laboratory,and the experimental demonstration shows that the self-organizingstrategy drives the detection swarm forming a close range and multiangularsurveillance configuration of a landing spot.

Soil Nature Effect Investigation on the Ground-to-Air Heat Exchanger for the Passive Cooling of Rooms

The building sector consumes much energy either for cooling or heating and is associated to greenhouse gas emissions. To meet energy and environmental challenges, the use of ground-to-air heat exchangers for preheating and cooling buildings has recently received considerable attention. They provide substantial energy savings and contribute to the improvement of thermal comfort in buildings. For these systems, the ground temperature plays the main role. The present work aims to investigate numerically the influence of the nature of soil on the thermal behavior of the ground-to-air heat exchanger used for building passive cooling. We have taken into account in this work the influence of the soil nature by considering three types of dry soil: clay soil, sandy-clay soil and sandy soil. The mixed convection equations governing the heat transfers in the earth-to-air heat exchanger have been presented and discretized using the finite difference method with an Alternate Direction Implicit (ADI) scheme. The resulting algebraic equations are then solved using the algorithm of Thomas combined with an iterative Gauss-Seidel procedure. The results show that the flow is dominated by forced convection. The examination of the sensitivity of the model to the type of soil shows that the distributions of contours of streamlines, isotherms, isovalues of moisture are less affected by the variations of the nature of soil through the variation of the diffusivity of the soil. However, it is observed that the temperature values obtained for the clay soil are higher while the sandy soil shows lower temperature values. The values of the ground-to-air heat exchanger efficiency are only slightly influenced by the nature of the soil. Nevertheless, we note a slightly better efficiency for the sandy soil than for the sandy-clayey silt and clayey soils. This result shows that a sandy soil would be more suitable for geothermal system installations.

铁路地质灾害勘察识别与监测预警

地质灾害对铁路建设、安全运营构成了极大威胁,“天空地”一体化综合勘察技术有效解决了地质灾害勘察识别难题。“天”基多源立体卫星遥感技术实现艰险复杂山区地质灾害的大范围精准判识,长时序InSAR与高精度GPS实现高陡岸坡的稳定性监测分析;“空”基真实感大场景、机载倾斜摄影和机载LiDAR扫描技术实现高植被覆盖区隐蔽性地质灾害判识;“地”基三维立体勘探技术获取岩土体结构、属性、参数;共同构建沟谷山地灾害链风险评价方案,为建设工程合理选址和工程设置提供依据。介绍地质灾害监测预警的方法、内容、技术和预警模型,对监测预警技术发展方向进行展望。

空气舵抖振载荷地面模拟试验技术研究

固体火箭的空气舵在挂机飞行中受到抖振载荷作用,出现了异常偏转现象,需要通过地面试验排查原因,并开展抖振载荷适应性考核。由于传统的试验方法未能复现故障,本文提出了一种新的抖振载荷地面模拟试验新技术,通过挂机飞行舵面实测数据计算舵面抖振载荷,并基于优化算法完成地面模拟试验条件制定,通过多激振器联合激励方法来完成抖振载荷加载。该试验技术在地面试验中成功实现了产品故障复现,大幅提高试验考核的真实性,该研究结果可以推广应用到其它舵产品气动载荷地面考核中。

面向6G全域融合的智能接入关键技术综述

针对空天地一体化接入网络,该文在总结相关研究的基础上,阐述了未来空天地一体化接入架构的关键技术,分析了空口技术、多址技术、干扰分析、计算技术和人工智能(AI)技术等几个重点方向的研究进展,提出了多种接入形式并存的灵活性网络架构。针对6G全域融合网络接入的重点研究问题,结合用户的服务质量需求,构建了一体化AI赋能架构,提出了大规模混合多址接入及弹性资源适配策略。基于网络架构立体化、网络协同传输、一体化网络资源管理、未来空天地接入技术以及网络协同计算等未来重点研究方向进行了讨论和展望。

面向密集场景的空天地网络资源分配算法

空天地网络具有覆盖范围大、吞吐量高、弹性强等优点。该文针对大量用户并发接入、网络负载不均衡所引发的网络拥塞、服务质量恶化等问题,提出一种面向密集场景的资源分配算法。首先以用户需求为中心,根据不同类型用户任务的偏好来构建用户效用函数,然后基于匹配博弈的网络选择算法和结合对偶上升法的功率控制算法来实现负载均衡,优化资源分配方案。实验表明,相较于传统策略,所提策略整体用户接入率至少提高35%,时延和吞吐量方面性能提升超过50%;在密集场景下,能更有效地均衡负载,提升网络性能。

卫星遥感水利应用进展与展望

监测感知数据是构建数字孪生水利体系的基础,卫星遥感是重要的监测感知手段。随着我国航天事业的蓬勃发展,依托国家科技重大专项、国家重点研发计划等科研项目开展技术攻关,以及国家防汛抗旱指挥系统工程等重大项目的推广应用,水利部构建了“采存算用全自主、遥感处理全链条、主要业务全覆盖、应用服务全贯通”的卫星遥感水利应用技术体系。卫星遥感技术在数字孪生水利数据底板建设、流域防洪、水资源管理与调配、河湖管理、水土保持、水利工程监测监管等业务工作中得到了广泛应用,发挥了显著成效。未来将从持续拓展卫星遥感影像资源、深度融合人工智能技术、强化“天空地”协同监测融合应用等方面,推动卫星遥感水利应用,赋能水利业务。

空地协同通信感知一体化系统的轨迹与资源分配联合优化

该文研究空地协同通信感知一体化系统,其中无人车(UGV)基站和无人机(UAV)中继集群组成空地协同网络,为用户提供通信服务,同时对目标区域进行探测感知。在更加准确的莱斯衰落信道模型下,研究联合优化无人机集群的通信感知关联、发射功率和飞行轨迹以及无人车基站的发射功率和行进轨迹,在目标区域感知频率和有效感知功率阈值的约束下,最大化用户最小平均通信速率。为了解决变量高度耦合且非凸的整数优化问题,首先利用块坐标下降法将原问题分解成4个子问题;接着引入松弛变量并将整数约束转化为惩罚项,然后证明莱斯信道下的有效感知功率是关于轨迹变量和松弛变量凸复合函数的联合凸函数;再利用连续凸优化法处理非凸项,并提出一种双层迭代算法高效求解次优解。仿真结果表明,与几种基准方案相比,所提优化算法在相同感知性能下,提高了用户最小平均通信速率,更好地实现了通信与感知性能之间的权衡,并具有良好的收敛性。