Table of Content

20 November 2022, Volume 58 Issue 6

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Dynamic Analysis of Touchdown Impact for the Landing Gear of Reusable Launch Vehicle and Experimental Evidence

YUAN Han, WANG Xiaojun, ZHANG Hongjian, MOU Yu, WANG Lei, WANG Chen

2022, 58(6):  977-988.  DOI: 10.13209/j.0479-8023.2022.084

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In order to describe the lateral vibration of the landing gear caused by landing of launch vehicle, an equivalent model for the excitation of landing impact is proposed. In this model, the excitation is equivalent to the superposition of impact excitation and steady excitation. Secondly, the bending vibration modes of the landing gear are established by the assumed mode method, where the coupling term of the longitudinal deformation caused by transverse deformation is included in the expression of bending vibration. The dynamic response, excited by the landing impact, is solved by the mode superposition method, so as to obtain a semi-analytical solution for the problem. The real product experiments of vertical landing impact show that the proposed model is able to accurately describe the lateral vibration and maximum moment of the landing gear. Finally, we analyze how the parameters of the configuration and strength of materials affect the landing gear using the proposed model. The result can guide the parameter design of the landing gear in the engineering implementation.

Theoretical Analysis on the High Enthalpy Radiation Particle Laden Compressible Flow

LI Tingting, LIU Pengxin, YUAN Xianxu, ZHOU Qiang, LI Qing

2022, 58(6):  989-998.  DOI: 10.13209/j.0479-8023.2022.039

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The theoretical equations of particle laden compressible flow by taking into account of heat radiation and convection were derived. It is found that, the heat exchange between dispersed phase and carried fluid phase is proportional to square of Mach number. In extreme high temperature environment, the convective heat transfer between two phases is one way, which means that the isothermal particle transfers the heat into the fluid, but the fluid can not cool down the radiation-heated particle via convection. In addition, the effect of shrinking core on the particle dynamics was investigated. The shrinking core effect modifies the Stokes number of particle, therefore the time evolution of unsteady velocity of particle from rest to terminal state in a uniform flow was altered.

Second Harmonic Generation of Surface Plasmon Polaritons in a Plasmonic Waveguide

ZHANG Tongzhou, XU Yi, GAO Baowei, ZHANG Jiasen

2022, 58(6):  999-1006.  DOI: 10.13209/j.0479-8023.2022.085

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Second harmonics generation in plasmon waveguides has been difficult due to the large phase mismatch, and waveguides designed to solve the problem are hard to fabricate and haven’t been experimentally realized. By combining monolayer molybdenum disulfide (MoS₂) and plane waveguide, we realized the plasmon-to-plasmon second harmonic generation in waveguide and studied the features of MoS₂-Ag structures in second harmonics generation, which paves the way to practical second harmonics generation in plasmon waveguides.

Design Methodology of SHA2 Hardware Accelerator

MA Zhangang, LI Tingting, CAO Xixin

2022, 58(6):  1007-1014.  DOI: 10.13209/j.0479-8023.2022.086

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In view of difficulty of SHA2 hardware acceleration, a novel performance-improving scheme of SHA2 hardware accelerator is put forth with the following techniques adopted. 1) Using 4K bits Ping-Pong buffer storing padded message block, the Message Padding Unit and Hash Calculation Unit can work in parallel as two stages of two-stage pipeline. 2) In Hash Calculation Unit, computations which have no dependency on iterative computation are extracted from two folded rounds of hash transformation as pre-computation unit and can work concurrently with post-computation unit in the form of two-stage pipeline rather than pseudo-pipeline which was proposed in the previous researches. 3) 3:2/4:2 compressors without carry chain and fast adders are adopted in pre-computation unit and post-computation unit to shorten critical path greatly. The proposed scheme also supports double hash computation which directs digest result of source data to the entry of hash iteration unit to obtain final result of double hash of SHA2, improving the performance of SHA2 hardware accelerator.

A Hardware Accelerator for SSD Object Detection Algorithm Based on FPGA

XIE Hao, CAO Jian, LI Pu, ZHAO Xiongbo, ZHANG Xing

2022, 58(6):  1015-1022.  DOI: 10.13209/j.0479-8023.2022.096

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A hardware accelerator of object detection algorithm based on FPGA is designed to accelerate the computation of SSD object detection algorithm. Loop tiling and loop unrolling are used to optimize the loops of convolution and pooling, and can be re-configurated in any parallelism. In order to reduce data transmission time, feature maps are reorganized based on AXI, without any hardware resource overhead. After implementing the hardware accelerator to Xilinx ZCU development board, it can accelerate SSD at a performance of 534.72 GOPS, and the inference time is 113.81 ms.

An iRAM-based Light-Weight Cryptographic Algorithm Implementation Scheme against Physical Memory Disclosure Attacks

LI Yanchu, JING Jiwu, LEI Lingguang, WANG Yuewu, WANG Pingjian

2022, 58(6):  1023-1034.  DOI: 10.13209/j.0479-8023.2022.095

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An iRAM-based light-weight secure cryptographic algorithm implementation scheme is proposed, which can execute multiple cryptographic algorithms concurrently without affecting the iRAM-assisted functions of the system. The scheme restricts the sensitive data in the cryptographic algorithm implementation to a single loadable segment, separates the non-sensitive data from this segment, and modifies the loading procedure of the trusted applications to allocate only the segment containing sensitive data to the iRAM space. It can minimize the occupation of iRAM by cryptographic operations. A series of representative cryptographic algorithms are implemented on the real device. The experimental results show that the performance overhead of all cryptographic algorithms is less than 4.3%, and each algorithm’s demand for iRAM is less than 4.5 KB, saving more than 78% compared with existing schemes, which supports the deployment of the scheme on all mainstream platforms.

Design and Implementation of Object Detection Acceleration Module Based on an ARM+FPGA Heterogeneous Platform

LI Fang, CAO Jian, LI Pu, XIE Hao, ZHAO Xiongbo, WANG Yuan, ZHANG Xing

2022, 58(6):  1035-1041.  DOI: 10.13209/j.0479-8023.2022.089

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Object detection algorithms based on deep learning use big models are difficult to be deployed at the edge. Taking YOLO (you only look once) object detection algorithm as an example, an acceleration module based on an ARM+FPGA heterogeneous platform is proposed. The FPGA chip accelerates the forward process of the compressed model while ARM is responsible for process scheduling. Experiment results show that the peak performance of the system reaches 425.8 GOP/s under 200 MHz working frequency. The system on a Xilinx ZCU102 board achieves a frame rate at 30.3 fps, while the power consumption is 3.56 W. It is also configurable.

Three Dimensional Dynamic Simulation Method of Toxic Gas Leakage Accident Based on CALPUFF Model: A Case Study of Kaixian Blowout Accident 

ZHANG Rongqian, LI Mei, YANG Dong’ou, LIU Hui

2022, 58(6):  1042-1054.  DOI: 10.13209/j.0479-8023.2022.094

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Aiming at the problems in the current emergency management GIS systems integrated with atmospheric dispersion models, such as low spatio-temporal resolution and without 3D terrain, a set of three-dimensional gas diffusion simulation methods was proposed based on the CALPUFF model. The three-dimensional spatio-temporal distribution data of the gas diffusion concentration was obtained through multi-layer calculations, and the Marching Cubes visualization technology was used to read and display the data, achieving the dynamic gas diffusion effect in three-dimensional space. “12·23” Kaixian blowout accident was used as a case study and the simulation was carried out to compare with the actual situation in two and three dimensions. The results show that the three-dimensional calculation based on CALPUFF model has higher accuracy of the magnitude and spatial distribution of gas concentration, and the three dimensional spatio-temporal dynamic simulation has high resolution and reconstruction efficiency, achieving a good visual effect. It can better express the gas leakage process and diffusion pattern and provide an important auxiliary decision-making means for emergency management.

3D Forward Simulation of Marine Natural Gas Hydrate Production Monitoring with the Downhole Controlled-Source Electromagnetic System

LIU Ying, HE Tao, ZHANG Yi

2022, 58(6):  1055-1068.  DOI: 10.13209/j.0479-8023.2022.090

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In order to know well the range and degree of gas hydrate dissociation during the large-scale exploitation of marine natural gas hydrate, the finite element software COMSOL is used to simulate the electromagnetic monitoring of the natural gas hydrate exploitation through the downhole controlled-source electromagnetic (CSEM) method. By constructing the 3D formation model containing the high-resistivity hydrate reservoir layer, the comparison between the downhole vertical source and the conventional towed horizontal source indicates that the former has advantages on the electric field responses for small source-receiver offsets required for monitoring. Then, the influence of vertical source monitoring system parameters, such as metal casing, vertical source depth, emission frequency, observation errors and noises, on the seafloor electric field responses are analyzed. The simulation results show that the metal casing, vertical source depth and emission frequency have significant influences on the seafloor electric field responses, and especially for the existence of metal casing, the vertical source should be placed below the hydrate reservoir and the low frequency such as 1 Hz of emission electrical current should be considered. The observation errors and noises of the monitoring system would not significantly affect the performance of the monitoring system with metal casing under the condition of small offsets. When the production range of the hydrate reservoir increases, the downhole vertical source monitoring system ensures that seafloor receivers can detect the electric field changes caused by hydrate exploitation and effectively identify the lateral boundary of production area. Hence, it is feasible to use the downhole CSEM method to monitor the dynamic reservoir process during marine hydrate exploitation. 

Anisotropic Zoning and Dynamic Mechanism of Upper Mantle beneath South China Block

LIN Yuting, YU Yong, CHEN Yongshun

2022, 58(6):  1069-1076.  DOI: 10.13209/j.0479-8023.2022.091

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Analyzing the broadband portable seismic stations deployed in South China Block (SCB), the SKS wave splitting method is used to study the anisotropy of the upper mantle beneath the region. The results show that the SKS wave splitting parameters in SCB vary significantly from west to east. In Sichuan Basin (SB) where the cratonic lithosphere remains relatively intact, splits of SKS wave are not obvious, reflecting that the lithosphere here is thick and undeformed. In the fold belt system at the eastern margin of the SB, fast polarization directions of the SKS wave splitting are mostly in NNE direction with about 1 s splitting delay times, indicating that the thick lithosphere has undergone deformation and the anisotropy owing to the deformation has been frozen in the lithosphere. In the eastern part of the SCB, the fast polarization directions are mainly ENE and splitting delay times are about 1 s. The anisotropy in this area mainly attributes to flow of the asthenosphere coinciding with the mantle-wedge flow. Finally, many Null splitting results are observed in the transition zone of the eastern margin of the SB with 200 km width, which may be caused by the complicated geological tectonic events it has been suffered.

Investigation on Urban Heat Island Intensity Model of the Residential District in Mid & High-Density Cities

LIU Yan, LI Qi, YANG Liu, ZHANG Tengyue, LIU Jiaping

2022, 58(6):  1077-1090.  DOI: 10.13209/j.0479-8023.2022.092

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Based on the physical process of the urban heat island (UHI) effect, the Urban Heat Island Intensity Model is established by solving the energy balance equation with the analytic method, which provides a basic model for further research on the correction of outdoor calculating parameters considering the impact of UHI. This model includes two parts: the urban surface energy balance calculation module and the urban canopy energy balance calculation module. At the same time, the Global (UHI) Data Set and the observation data in Xi’an, Birmingham, Madison, and Basel are used to verify the model. The validation results show that the urban under-lying surface energy balance calculation module has high calculation accuracy in both rural and urban areas (rural: RMSE<1℃; urban: RMSE<3.2℃); the calculation accuracy of the urban canopy energy balance calculation module is high (RMSE<1.5℃), which is similar to that of the same type of models, and the modelled data has a high consistency with the observation data. The observation data is used to verify the rationality of retaining only the first-order term in the construction of the urban heat island intensity model (RMSE<0.7℃). The sensitivity analysis results show that the sensitivity of urban underlying surface parameters are affected by climatic conditions; the wind speed is the most sensitive parameter in meteorological data. 

Environmental Quality Mineralogical Analysis of Trace Metals in Urban Mangrove Surface Sediments

GUAN Chunya, LI Ruili, WANG Qian, GUO Wenxiao, SHEN Xiaoxue

2022, 58(6):  1091-1100.  DOI: 10.13209/j.0479-8023.2022.101

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Mineral composition and trace metal elements content of mangrove surface sediments were measured in Futian, Baguang, Shajing and Xixiang district in Shenzhen city. The mineralogical evaluation system was used to explore the relationship between mineral composition and trace metal enrichment. The results showed that the mineral composition of surface sediments of Shenzhen urban mangrove was mainly clay minerals and quartz and there were variation among sample sites. The trace metal pollution in Shajing mangrove was the most serious, followed by Xixiang mangrove and Futian mangrove, and Baguang mangrove was the least serious. The enrichment of trace metal was affected by human activities. The enrichment of trace metals was related to the mineral composition of sediments. Gypsum and clay minerals had stronger trace metal enrichment ability.

Evaluation and Impact Factors of Spatial Supply and Demand of Public Sports Facilities in Shenzhen

WU Jiansheng, QIAN Yun, WANG Hongliang, ZHU Huizhen, WANG Han

2022, 58(6):  1101-1110.  DOI: 10.13209/j.0479-8023.2022.088

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From the perspective of 10-minute fitness circle, points of interest (POI), mobile signal data and other data were employed in this research. The accessibility of public sports facilities was measured with network analysis in GIS and Gini coefficient was used to analyze the equity of the supply and demand matching degree of public sports facilities in Shenzhen. The influencing factors of spatial supply and demand of public sports facilities were explored by geographical detectors. The results showed that, first, the overall accessibility of public sports facilities in Shenzhen was relatively high, which basically met the requirements of 10-minute fitness circle. Second, the distribution of public sports facilities was relatively fair. The distribution of facilities in different streets of the same municipal district was highly fair while the equity between municipal districts could be further improved. Third, the relationship between supply and demand in Yantian, Pingshan, Dapeng District was well-matched while sports facilities in the subdistrict at the junction of Futian District and Luohu District were centralized distributed, which set a limitation to the ability of service. Finally, land price was the most important factor affecting the spatial supply-demand relationship of public sports facilities in Shenzhen, followed by the density of road network and the number of bus stops. The total population and the proportion of man-made surface also had a certain impact on the supply and demand relationship.

Health Assessment of the Baitiao-Fu River Based on Ecological Integrity and Social Service Functions

XI Haojun, YUAN Yibin, ZAN Xiaohui, LI Tianhong

2022, 58(6):  1111-1120.  DOI: 10.13209/j.0479-8023.2022.104

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The Baitiao-Fu River, a typical tributary of Jinjiang River in Chengdu City of China, was selected to perform the health assessment based on ecological integrity and social service functions. Therein, 16 specific indicators from three aspects including habitat characteristics, biological community and social service were selected to establish a river health assessment system for meeting the needs of river ecosystem integrity and human services. Field investigation, remote sensing and GIS, environmental DNA, and statistical method were used to quantify these indicators, and the comprehensive assessment method was applied to four river segments to calculate the river health assessment index (RHI). The results showed that all RHIs of these tributaries ranged from 3.23 to 3.82, suggesting the sub-healthy level. The river health status was generally good in the upper reaches, whereas that was relatively poor in the middle and lower reaches, which presented strong spatial heterogeneity, and reflected that the health of river system might be affected by human activities. The results provide a scientific basis for the sustainable management of rivers in Chengdu Plain, and contribute a method for health assessment of river ecosystems affected by human activities.

Research and Practice of Village Classification Facing the Demand of Spatial Management and Control: A Case Study of Wuqing District, Tianjin

DAI Linlin, YU Xuan, LÜ Jinmei

2022, 58(6):  1121-1129.  DOI: 10.13209/j.0479-8023.2022.103

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In the past practice of village classification, the problem of not being closely connected with spatial management and control requirements is common, which largely affects the effectiveness of planning up and down transmission. Based on the principle of practicability, the study explored how to connect village classification with spatial management and control requirements step by step. On this basis, combined with the evaluation results of village development potential and multiple rounds of upper and lower linkage organization methods, the village type pedigree and classification path that takes into account the actual management and control needs and the development demands of the villagers was formed. And the study conducted an empirical study on 622 villages in Wuqing District, Tianjin City as examples.

Simulation of Urban Evapotranspiration Considering Vegetation Coverage

CHEN Zhi, HUANG Ying, DING Jinshan, SHI Zhe, QIU Guoyu, YAN Chunhua

2022, 58(6):  1130-1140.  DOI: 10.13209/j.0479-8023.2022.097

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Based on half-hourly data collected from eddy covariance systems, an urban evapotranspiration estimation model was built using random forest model, which introduced the source area information-vegetation coverage as input variables. Vegetation coverage were obtained by combining footprint modeling and land remote sensing data. The simulation results were used to fill the missing values and explore the major control factors of the evapotranspiration during both dry and wet seasons in Shenzhen, China. The results show that compared with the traditional RF and MDS model, urban evapotranspiration could be simulated with better accuracy considering vegetation coverage, R²=0.73, RMSE=20.5 W/m², MAE=13.3 W/m², pbias=0.8%. For the estimation of relatively high evapotranspiration in wet seasons, RF performs significantly better than MDS model. MDS model under-estimates by 12.4% while RF only by 4.7%. During wet seasons of Shenzhen, vegetation coverage is the major control factor of evapotranspiration. In dry seasons, temperature, net radiation, saturated water vapor pressure deficit are the major control factors.

Review of Atmospheric Moist Convection Categories and Triggering Mechanism of Deep Moist Convection

ZHENG Yongguang, CHEN Jiong

2022, 58(6):  1141-1152.  DOI: 10.13209/j.0479-8023.2022.093

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The definitions and characteristics of different types of atmospheric moist convection and severe convective weather are summarized. The research advances and outlook of the triggering mechanism of deep moist convection (DMC) are focused on. The organizational forms of atmospheric shallow moist convective cumulus similar to Bernard convection depend on the intensity of vertical wind shear in the planetary boundary layer. According to different classification standards, DMC can be divided into surface-based convection and elevated convection, or ordinary thunderstorms and severe convective storms. The definition of severe convective weather has been presented somewhat arbitrarily, and the thresholds of such type of weather are different in different nations, but it certainly has the characteristic of extreme and is prone to disaster. The difficulty of exhaustively monitoring the detailed type and intensity of such weather still exists. The triggering mechanism of surface-based convection is actually in the planetary boundary layer, which is complex and diverse. Many DMC events are triggered as the result of convergence line interaction or the interaction of different mechanisms. In the future, it is necessary to strengthen the measurement ability of the boundary layer, to conduct in-depth studies on the climatological characteristics and mechanism of DMC trigger, and to improve the ability of fine data assimilation and numerical simulation of boundary layer processes.