Abstract:Based on the Gravity Recovery and Climate Experiment （GRACE） data， this paper attempts to eliminate the gravity signals of surface processed and separate the gravity signals containing the movement characteristics of liquid outer core fluid at the core-mantle boundary from the raw data. According to the CHAOS-7 geomagnetic field model， the core geomagnetic field changes on the core-mantle boundary and the surface of the earth are reconstructed. It decomposes the gravity and magnetic signals using principal component analysis （PCA） and independent principal component analysis （ICA）， and then compares and analyzes the correlation between the two signal decomposition results. The time-varying characteristics of the third mode of the gravity field signal have good correlation with the time-varying signals of the second mode of the magnetic field signal. Meanwhile， their spatial modes reflect the obvious change characteristics of an east-west aligned “dipole” form in the low latitude area of the Pacific Ocean， corresponding to the spatial change characteristics of the second mode of the geomagnetic field in the Pacific region. After 2014， the time-varying modes of both gravity signals and the second-order conductivity of magnetic field signals exhibit the same linear and rapid change characteristics， which is also consistent with existing research results.

Abstract:It is very important to extract spatiotemporal characteristics from international aviation network and international relation network， and to analyze the association between them. The international aviation network is a kind of transportation network in the material world formed by personnel mobility and trade among countries or regions. The international relation network is a kind of social relation network in the virtual world formed by international relations such as cooperation or conflict among countries or regions. This paper， taking the countries or regions as nodes， the aviation transportation or the international relations as edges， and embedding them into geographic space， builds a geographic multiple flow network， and explores the association between them. It builds the international aviation network and the international relation network based on the airline schedule provided by OAG data and the GDELT data over the past decade. It extracts the characteristics of the two kinds of networks and explores their association based on the theories and methods of complex network and social network analysis. The research results show that both networks have scale-free properties and small world effects. The scale of the two kinds of networks shows a common trend of first increase and then decrease. The scale of the international relation network peaked in 2015 and 2016， but the counterpart of the international airport network peaked in 2020. The structures of the two kinds of networks are similar， but the similarity decreases significantly after the Russia-Ukraine conflict. There is a time lag in influence of the international relation network on the international aviation network.

Abstract:Accurate registration for forest airborne laser scanning （ALS） point clouds and terrestrial laser scanning （TLS） point clouds improves data integrity， which can better serve for forest ecological parameter retrieval. A marker-free registration method is proposed to fuse ALS point clouds and TLS point clouds based on canopy voxel features. The method achieves ALS-TLS point clouds registration with the following steps： bounding box orientation， density-height-based canopy point clouds filtering， canopy point clouds voxelization， tie feature extraction with sliding voxel templates， and transformation matrix calculation. The proposed method was validated by four datasets with different forest structure complexities， which shows that its average differences are 0.245m， 0.238m， 0.184m， and 0.020m respectively. The comparisons indicates that the proposed method outperforms its counterparts including iterative closest point algorithm， artificial matching， and the combination of the two.

Abstract:Mobile phone navigation trajectory data has a variety of traffic modes， reflecting the activities of mass crowd， which is suitable for the study of traveling patterns in different traffic modes. Based on mobile phone navigation data， the LightGBM model for traffic mode classification is first proposed to obtain the trajectories of the population in three transportation modes： walking， motorized， and non-motorized mode. Based on these three types of modes， the analysis indexes of time， space， and distance traveling patterns on weekends and weekdays are given， and an experimental analysis is conducted with the mobile phone navigation data of millions of people in Shanghai for four days. The results show that in terms of time distribution， the weekend traveling peak of the residents in Shanghai is later and shorter than that of weekdays， and traveling modes are mainly motor vehicles and walking. In terms of spatial distribution， motor vehicles are mainly concentrated in elevated areas， walking is mainly concentrated near subway stations， the guidance signs of elevated roads and subway stations are not sufficient， and there are more traffic hubs and shopping hotspots on weekends than on weekdays. In terms of distance distribution， navigation traveling distance conforms to the power-law distribution of intercepted segments， and the navigation traveling of the crowd is dominated by short and medium distances， and decays rapidly with distance growth. The research results can provide theoretical basis and technical support for urban planning and urban traffic management policy formulation.

Abstract:This paper reviews the site selection methods on the issues of the asteroid sample return missions， and expounds the process of selecting the final sampling area L08-E1 and Nightingale area from the primary candidate sampling areas in Hayabusa2 of Japan and the OSIRIS-REx sample return missions of the US. The analysis method of engineering and scientific value factors involved in sampling site selection and the selection process of other asteroid attachment missions are introduced. Thebasic methods of each site selection factor for the previous steroid sample return missions is expounded， the comparative relationship between the sampling site selection of Hayabusa2 and OSIRIS-REx is discussed from the perspective of probe load， site selection process， methods and results， the reference significance of the existing asteroid sampling site selection method for China’s asteroid sample return site mission is proposed combining the asteroid exploration mission planning， and the future work to the site selection scheme of the asteroid sample return missions is forecasted.

Abstract:Effective management of river channels is a prerequisite for maintaining the healthy ecological condition of river channels. An ontology-based method for storing multi-source river health data is proposed to address the problems of cross-sector management， inefficient storage， and semantic information ignored in river health data. An ontology model of river health domain is constructed， and a storage method of river health data based on Neo4j graph database is designed. Taking the river in Baoshan District， Shanghai as an example， a river health visualization prototype system is developed， which successfully achieves the storage and query of river health ontology data in concepts， relations， attributes and instances. A comparison test of the query efficiency of two different ontology storage methods is designed to validate the effectiveness and feasibility of the method proposed in this paper.

Abstract:Although the remote sensing information extraction technology is constantly being innovated， there are still huge bottlenecks in terms of intelligence， precision， and practicality. Therefore， it is necessary to conduct a comprehensive summary and discussion on the development topic of remote sensing intelligent computing and information extraction. From the four levels of “mechanism-scale-data-intelligence”， this paper gradually discusses the development and fusion of remote sensing information extraction and quantitative inversion paths， the different processing unit modes based on pixels and object-oriented， the spatial-temporal spectral data fusion， the intelligent factors of remote sensing interpretation. It proposes a future-oriented remote sensing intelligent computing architecture which is driven by two-way “data acquisition knowledge” and “knowledge-guided data”， and integrates remote sensing big data and geoscience knowledge maps， trying to promote the transition of remote sensing science from classics to modernization.

Abstract:In view of the wellbore stability of drilling in methane hydrate-bearing sediments， an analytical model in unsteady state is established considering hydrate dissociation， heat conduction， and fully fluid-solid coupling.And analytical solutions for seepage， temperature and mechanical fields with time and polar radius during overbalanced and underbalanced drilling are obtained. The analytical solutions are in good agreement with the numerical results under the same conditions and compared with the partial hydraulic-mechanical coupling results. The key parameters affecting wellbore stability， such as drilling fluid pressure， and the elastic modulus reduction caused by hydrate dissociation， are analyzed. The results show that compared with partial hydraulic-mechanical coupling results， if the influence of volume deformation of solid on seepage is considered， the pore pressure decreases （increases） while stresses increase （decrease） and radial displacement decreases during overbalanced （underbalanced） drilling. The most dangerous position for the formation is at the wellbore wall and a too high or too low drilling fluid pressure will lead to wellbore instability. The deterioration of formation in mechanical properties caused by hydrate dissociation will reduce the safest drilling fluid pressure. The reduction of formation stiffness caused by hydrate dissociation is very easy to induce wellbore instability and the wellbore instability can usually be caused by reducing the elastic modulus in the dissociated region by 50% during overbalanced drilling.

Abstract:The internal reinforcement technology is an effective method to control the deformation of shield segmental linings and local joints. The commonly used reinforcement technology is to add steel plates or other structures in a tunnel， but it has the defects of covering the lining surface after reinforcement， which is not conducive to the observation of lining diseases. Assembled reinforced structures were proposed in this paper， and positive and negative bending tests were conducted to study the mechanical properties of the segmental joints with and without the assembled reinforced structures. The experimental results show that the assembled reinforced structures have a certain reinforcement effect on the segmental joints bearing positive and negative bending moments. After the joints open， the assembled reinforced structures bear the load together with the bolts， limit the opening of the joints， and improve the bearing capacity of the joints. However， the reinforcement effect of the assembled reinforced structure on the joint bearing negative bending moment is limited and less obvious than that on the joint bearing positive bending moment. The main reason for this is that the structure is installed on the inner arc surface of the joint， which can effectively control the opening of the inner arc surface of the joint， but the opening restriction effect of the outer arc surface of the joint is small. In addition， the concrete around the connection positions between the assembled reinforced structures and the segments are damaged. The connection is critical for the reinforcement effect of the assembled reinforced structures， which， thus， needs to be further optimized.

Abstract:In order to analyze the dynamic deviatoric stress distribution law and calculate the settlement of elastic-plastic foundation by high-speed train load， a 2.5D FEM（finite element model） for elastic-plastic foundation under high-speed train load was derived. The high-speed train load was simplified to quasi-static train load and the modified train load including random excitation force. The distribution of dynamic deviatoric stress in the elastoplastic foundation at two kinds of loads was comparativly calculated. The settlement of homogeneous elastoplastic foundation was calculated by the cumulative plastic strain model of soft clay at cyclic loading. The results show that the dynamic deviatoric stress in the elastoplastic foundation is distributed in a saddle shape， and the maximum value appears in the soil near the edge of the foundation bed. When the train speed is less than the Rayleigh wave speed of the soil， the attenuation curve of the dynamic deviatoric stress in the foundation is smooth. When the train speed is close to or greater than the Rayleigh wave speed of the soil， the dynamic deviatoric stress exhibits a fluctuating attenuation under the influence of the Mach effect. The dynamic deviatoric stress distribution is more consistent with the actual situation at modified train load. The foundation settlement is relatively fast at the initial stage of high-speed rail operation， and the settlement rate gradually stabilizes. When calculating the ground settlement caused by the high-speed rail operation， the influence of train speed and random excitation force should be considered at the same time.

Abstract:To evaluate and calibrate the maximum crack width formulas for flexural concrete members reinforced with fiber-reinforced polymer （FRP） bars in current design standards， available literature on crack width tests of FRP reinforced concrete （RC） flexural members was extensively surveyed. After applying multiple filtering criteria， a database including 111 FRP-RC flexural members was developed. Then， the database was used to evaluate the accuracy of the crack width provisions from three design guidelines by comparing the tested widths with predictions. It was determined that GB 50608—2010 highly underestimated the maximum crack width， especially for the GFRP-RC and BFRP-RC members. In contrast， CJJ/T 280—2018 was more predictive than the other guidelines， while ACI 440.1R-15 provided conservative predictions. Based on this database， modifications were made to the non-uniform strain coefficient formula for tensile FRP bars in GB 50608—2010 by introducing an elastic modulus ratio E_f /E_s. Furthermore， the bond-dependent coefficients in the three design guidelines were calibrated to account for the effect of surface treatment.

Abstract:Based on flume experiment and numerical simulation， a refined study on 3D flow induced by a reef-type submerged breakwater was conduced to observe the turbulence performance and hydrodynamic characteristics in uniform inflow. Particle image velocimetry （PIV） is experimentally employed to successfully capture the three-dimensional vortex structure inside and outside the reef and a continuous vortex structure with transverse symmetry in the time-average flow field， which reveals the ambient water exchange mechanism promoted by perforation of reef-type breakwaters. Further， a 3D numerical model with the same specifications of the PIV experiment is built using the finite volume method. An evaluation of the most frequently typically used four turbulence models， i.e. standard k-ε， renormalization group k-ε， realizable k-ε and large eddy simulation （LES）， on the flow field in vicinity of the perforated reef-type breakwater reef is presented. The results show that the inner flow separation predicted by LES is the most accurate due to the advantage of LES for directly solving the large eddy in the Navior-Stokes equation. However， the computational efficiency of the model is the lowest. The velocity and vortex structure near the reef block captured by realizable k-ε approximates the PIV flow visualization， and the computational efficiency is the highest， which is the most suitable turbulence model for the limited computed hardware equipment.

Abstract:A new deflection index， total deflection ratio（R_TD）， was proposed for v oid identification，whose theoretical characteristics were analyzed. To investigate the applicability of R_TD in void identification of airport rigid pavement， finite element models were built using Abaqus. The influences of pavement structure parameters， joint load transfer capacity and void parameters on deflection indexes were analyzed. The results show that， compared with the deflection ratio and intercept， R_TD has a higher correlation with pavement structure parameters， and a relatively accurate criterion can be established based on the higher correlation. In addition， R_TD is sensitive to void parameters and can avoid the coupling effect of joint load transfer capacity and void beneath slab. Overall， R_TD is more applicable in the void detecting of airport rigid pavement.

Abstract:Driving distraction is a common abnormal behavior which seriously disturbs the safety and stability of traffic flow. Because the vehicle has a large degree of freedom in the longitudinal car-following（CF） driving context， most of the distracted driving behaviors exist in the CF driving context. Therefore， it is of great significance to deeply understand the characteristics of the distracted CF， and accurately describe the distracted CF behavior. This paper classified and modeled distracted the CF behavior based on behavioral characteristics and explored the adaptability of CF models in different states using model calibration methods. First， a large number of distracted CF samples were extracted based on the naturalistic driving data of Shanghai which spaned more than 3 years， and the distracted CF events were preliminarily classified into five kinds based on the stimulus-response framework of driving behavior. Then， the adaptabilities of four existing classical CF models （GHR， Gipps， IDM， and Wiedemann） on distracted CF behavior were compared， and the classification of distracted CF was optimized according to the results of the model adaptability using five-fold cross-validation. As a result， three types of distracted CF behavior （numbness reaction， overreaction， and delay reaction） were determined. Finally， two modeling strategies for the distracted CF behavior were discussed （AIDM and TDIDM）. The results show that rational calibration of the IDM model can accurately describe different types of distracted CF behavior.

Abstract:This paper first constructs a vitality index based on mobile phone signaling data to measure the crowd travel intensity and scope in site service area. Based on the matching degree of ridership and vitality， 77 rail stations in suburban Shanghai are divided into three groups： high vitality and high ridership， high vitality and low ridership， and low vitality and low ridership， accounting for 38%， 18% and 44% respectively. The multinominal Logit model is developed with multi-dimensional attributes， such as development intensity of station service area and service level of the rail. The results show that compared with rail stations whose vitality and ridership are both high， rail stations with a high vitality but a low ridership are mainly distributed on the lines that do not directly pass through the main urban area， and it is more necessary to strengthen the service level of the rail and reduce crowd dependence on cars to improve rail ridership. Rail stations with a low vitality and a low ridership are mainly distributed in outer suburbs with a low development density and strengthening the development level of the site service area is the key to improve vitality and ridership. This paper provides a novel research perspective for the synergistic development of ridership and vitality of suburban rail sites in large cities.

Abstract:Based on the uneven distribution of refrigerant flow， a thermal-hydraulic simulation mode for the external heat exchanger of heat pumps in electric vehicles was built， and it is found that the overall performance of the layout of single-pass as well as 4-pass is in an inferior position. Compared with that of the 2-pass configuration， the heat transfer capacity of the single-pass configuration is decreases by 25.3% in summer and 23.3% in winter wet conditions， respectively. The difference between the heat transfer capacities of the configurations of 4-pass， 3-pass， and 2-pass is insignificant. The refrigerant side pressure drops of the structures of 4-pass and 3-pass are 2.5~2.8 and 1.8~2.5 times those of the structure of 2-pass， respectively. The experimental results of the system show that， under various operating conditions， the coefficient of performance （COP） of the heat pump system with the 2-pass external heat exchanger is higher than that of the heat pump system with the 3-pass external heat exchanger. Under wet operating conditions in winter， the heating capacity and COP of the system with the 2-pass external heat exchanger are increased by 6.4% and 9.4%， respectively， compared to those of the system with the 3-pass external heat exchanger. It is concluded that the 2-pass structure is more suitable for the external heat exchanger of heat pumps in electric vehicles.

Abstract:The splashing dynamics of a water droplet impacting a water film was experimentally investigated by a high-speed camera. The splashing limit， the size distribution of secondary droplets， and the velocity of secondary droplets were analyzed. The results show that within the range of the experimental parameters， the splashing occurs when the Weber number increases. The dimensionless parameter K （K=We·Oh^-0.4） could be used to describe the splashing limit. When K > 2 100， splashing phenomenon happens. In addition， with the increase of the K number， both the dimensionless secondary droplet diameter and the dimensionless velocity of secondary droplets increase. The effect of dimensionless film thickness on the diameter distribution of secondary droplets is not significant. However， the average dimensionless velocity of secondary droplets produced by crown splashing decreases with the increment of dimensionless film thickness.

Abstract:The detailed composition， propagation characteristics， and sources of waves from South Atlantic Ocean to Gulf of Guinea remain an unsolved problem. The temporal and spatial distribution of waves from South Atlantic to Gulf of Guinea in winter were simulated by constructing a two-layer nested wave model based on SWAN （Simulating WAves Nearshore）. The results suggest that the significant wave height decreases from high latitude （south of 30 ° S） to low latitude （north of 30 °S） in South Atlantic. There exists a close correlation between wave propagation direction and wind field in high latitude， but a significant distinction in low latitude. The distribution of swell is highly correlated with the mixed waves， and accounts for a large proportion of the mixed wave in South Atlantic， especially in the low latitude area with a low wind speed. There exists a stable S-SW swell system from the middle of South Atlantic to the Gulf of Guinea， and the simulated two-dimensional spectra shows concentrated swell wave energy in narrow directional distribution. The Gulf of Guinea is obviously swell dominated during the simulation period. The simulation study indicates that the swell system in maximum significant wave height event of the Gulf of Guinea during simulation period could be traced back to the strong wind and waves in the Roaring Forties in South Atlantic about 6.5 days ago.