Jiaxin Wu, Jigang Zhang and Hongjuan Yang
This study aims to construct an evaluation system for farmers’ livelihood capital in minority areas and evaluate the impact of relocation in response to climate change on farmers’…
Abstract
Purpose
This study aims to construct an evaluation system for farmers’ livelihood capital in minority areas and evaluate the impact of relocation in response to climate change on farmers’ livelihood capital.
Design/methodology/approach
According to the characteristics of Yunnan minority areas, the livelihood capital of farmers in minority areas is divided into natural, physical, financial, social, human and cultural capital. The improved livelihood capital evaluation system measures farmers’ livelihood capital from 2015 to 2021. The net impact of relocation on farmers’ livelihood capital was separated using propensity score matching and the difference-in-difference (PSM-DID) method.
Findings
The shortage of livelihood capital makes it difficult for farmers to resist climate change, and the negative impacts of climate change further aggravate their livelihood vulnerability and reduce their livelihood capital. Relocation has dramatically increased the livelihood capital of farmers living in areas with poor natural conditions by 15.67% and has enhanced their ability to cope with climate change and realise sustainable livelihoods.
Originality/value
An improved livelihood capital evaluation system is constructed to realise the future localisation and development of livelihood capital research. The PSM-DID method was used to overcome endogeneity problems and sample selection bias of the policy evaluation methods. This study provides new ideas for academic research and policy formulation by integrating climate change, poverty governance and sustainable livelihoods.
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Gan Zhan, Zhihua Chen, Zhenyu Zhang, Jigang Zhan, Wentao Yu and Jiehao Li
This study aims to address the issue of random movement and non coordination between docking mechanisms and locking mechanisms, and proposes a comprehensive dynamic docking…
Abstract
Purpose
This study aims to address the issue of random movement and non coordination between docking mechanisms and locking mechanisms, and proposes a comprehensive dynamic docking control architecture that integrates perception, planning, and motion control.
Design/methodology/approach
Firstly, the proposed dynamic docking control architecture uses laser sensors and a charge-coupled device camera to perceive the pose of the target. The sensor data are mapped to a high-dimensional potential field space and fused to reduce interference caused by detection noise. Next, a new potential function based on multi-dimensional space is developed for docking path planning, which enables the docking mechanism based on Stewart platform to rapidly converge to the target axis of the locking mechanism, which improves the adaptability and terminal docking accuracy of the docking state. Finally, to achieve precise tracking and flexible docking in the final stage, the system combines a self-impedance controller and an impedance control algorithm based on the planned trajectory.
Findings
Extensive simulations and experiments have been conducted to validate the effectiveness of the dynamic docking system and its control architecture. The results indicate that even if the target moves randomly, the system can successfully achieve accurate, stable and flexible dynamic docking.
Originality/value
This research can provide technical guidance and reference for docking task of unmanned vehicles under the ground conditions. It can also provide ideas for space docking missions, such as space simulator docking.
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Jiawei Wang, Jinliang Liu, Guanhua Zhang and Jigang Han
Considering the “size effect” and the properties degradation of building materials on the strengthened engineering, in this paper, the technology of pasting steel plate was…
Abstract
Purpose
Considering the “size effect” and the properties degradation of building materials on the strengthened engineering, in this paper, the technology of pasting steel plate was adopted to shear strengthen a 16 m prestressed concrete hollow slab, which had serviced 20 years in cold regions. The shear properties of shear strengthen beams are analyzed.
Design/methodology/approach
Shear loading test of the shear strengthened beam and the contrast beam was conducted. Then the mechanical characteristics, failure mechanism, the mechanical response and shear capacity of shear strengthened beam and contrast beam had been discussed.
Findings
The failure mode of shear strengthened beam and contrast beam was shear compression failure, and the bond failure between concrete and prestressed reinforcement happened in both of test beams. The shear strengthening method of pasting steel plate can effectively improve the mechanical response for the shear strengthened beam. Compared with the contrast beam, the cracking load and failure shear capacity for the shear strengthened beam can be effectively increased by 12.2 and 27.6%, respectively.
Originality/value
The research results can be a reference for the detection and evaluation of shear strengthened bridges, which are strengthened by pasting steel plate. Engineers can refer to the shear strengthening method in this paper to strengthen the existing bridge, which can guarantee the safety of shear strengthened bridges.
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Jiawei Wang, Yanmin Jia, Guanhua Zhang, Jigang Han and Jinliang Liu
Most existing studies are confined to model beam tests, which cannot reflect the actual strengthening effects provided by prestressed carbon-fiber-reinforced polymer (CFRP) plates…
Abstract
Purpose
Most existing studies are confined to model beam tests, which cannot reflect the actual strengthening effects provided by prestressed carbon-fiber-reinforced polymer (CFRP) plates to existing bridges. Hence, the actual capacity for strengthening existing bridges with prestressed CFRP plates is becoming an important concern for researchers. The paper aims to discuss these issues.
Design/methodology/approach
Static load tests of in-service prestressed concrete hollow slabs before and after strengthening are conducted. Based on the results of the tests, the failure characteristics, failure mechanism and bending performance of the slabs are compared and analyzed. Nonlinear finite element method is also used to calculate the flexural strength of the strengthened beams prestressed with CFRP plates.
Findings
Test results show that prestressed CFRP plate strengthening technology changes the failure mode of hollow slabs, delays the development of deflection and cracks, raises cracking and ultimate load-carrying capacity and remarkably improves mechanical behavior of the slab. In addition, the nonlinear finite element analyses are in good agreement with the test results.
Originality/value
Strengthening with prestressed CFRP plates has greater advantages compared to traditional CFRP plate strengthening technology and improves active material utilization. The presented finite element method can be applied in the flexural response calculations of strengthened beams prestressed with CFRP plates. The research results provide technical basis for maintenance and reinforcement design of existing bridges.
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Gan Zhan, Zhenyu Zhang, Zhihua Chen, Tianzhen Li, Dong Wang, Jigang Zhan and Zhengang Yan
This paper aims to focus on the spatial docking task of unmanned vehicles under ground conditions. The docking task of military unmanned vehicle application scenarios has strict…
Abstract
Purpose
This paper aims to focus on the spatial docking task of unmanned vehicles under ground conditions. The docking task of military unmanned vehicle application scenarios has strict requirements. Therefore, how to design a docking robot mechanism to achieve accurate docking between vehicles has become a challenge.
Design/methodology/approach
In this paper, first, the docking mechanism system is described, and the inverse kinematics model of the docking robot based on Stewart is established. Second, the genetic algorithm-based optimization method for multiobjective parameters of parallel mechanisms including workspace volume and mechanism flexibility is proposed to solve the problem of multiparameter optimization of parallel mechanism and realize the docking of unmanned vehicle space flexibility. The optimization results verify that the structural parameters meet the design requirements. Besides, the static and dynamic finite element analysis are carried out to verify the structural strength and dynamic performance of the docking robot according to the stiffness, strength, dead load and dynamic performance of the docking robot. Finally, taking the docking robot as the experimental platform, experiments are carried out under different working conditions, and the experimental results verify that the docking robot can achieve accurate docking tasks.
Findings
Experiments on the docking robot that the proposed design and optimization method has a good effect on structural strength and control accuracy. The experimental results verify that the docking robot mechanism can achieve accurate docking tasks, which is expected to provide technical guidance and reference for unmanned vehicles docking technology.
Originality/value
This research can provide technical guidance and reference for spatial docking task of unmanned vehicles under the ground conditions. It can also provide ideas for space docking missions, such as space simulator docking.
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Keywords
Guanhua Zhang, Jiawei Wang, Jinliang Liu, Yanmin Jia and Jigang Han
During service, cracks are caused in prestressed concrete beams owing to overload or other non-load factors. These cracks significantly affect the safety of bridge structures. The…
Abstract
Purpose
During service, cracks are caused in prestressed concrete beams owing to overload or other non-load factors. These cracks significantly affect the safety of bridge structures. The purpose of this paper is to carry out a non-linear iterative calculation for a section of a prestressed concrete beam and obtain the change in stiffness after the section cracks.
Design/methodology/approach
The existing stress of prestressed reinforcement was measured by performing a boring stress release test on two pieces of an in-service 16 m prestressed concrete hollow plate. Considering the non-linear effects of materials, the calculation model of the loss in the flexural stiffness of the prestressed concrete beam was established based on the existing prestress. The accuracy of the non-linear calculation method and the results obtained for the section were verified by conducting a bending destruction test on two pieces of the 16 m prestressed concrete hollow plate in the same batch and by utilising the measured strain and displacement data on the concrete at the top edge of the midspan section under all load levels.
Findings
The flexural stiffness of the section decreases rapidly at first and then gradually, and structural rigidity is sensitive to the initial cracking of the beam. The method for calculating the loss in the flexural stiffness of the section established with the existing stress of prestressed reinforcement as a parameter is accurate and feasible. It realizes the possibility of assessing the loss in the rigidity of a prestressed concrete structure by adopting the existing stress of prestressed reinforcement as a parameter.
Originality/value
A method for quickly determining the loss in the stiffness of structures using existing prestress is established. By employing this method, engineers can rapidly determine whether a bridge is dangerous or not without performing a loading test. Thus, this method not only ensures the safety of human life, but also reduces the cost of testing.
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Qin Qin, Jigang Huang, Jin Yao and Wenxiang Gao
Scanning projection-based stereolithography (SPSL) is a powerful technology for additive manufacturing with high resolution as well as large building area. However, the surface…
Abstract
Purpose
Scanning projection-based stereolithography (SPSL) is a powerful technology for additive manufacturing with high resolution as well as large building area. However, the surface quality of stitching boundary in an SPSL system has been rarely studied, and no positive settlement was proposed to address the poor stitching quality. This paper aims to propose an approach of multi-pass scanning and a compensation algorithm for multi-pass scanning process to address the issue of poor stitching quality in SPSL systems.
Design/methodology/approach
The process of multi-pass scanning is realized by scanning regions repeatedly, and the regions can be cured simultaneously because of the very short repeat exposure time and very fast scanning. Then, the poor stitching quality caused by the non-simultaneous curing can be eliminated. Also, a compensation algorithm is designed for multi-pass scanning to reduce the stitching errors. The validity of multi-pass scanning is verified by curing depth test, while the performance of multi-pass scanning as well as proposed compensation algorithm is demonstrated by comparing with that of a previous SPSL system.
Findings
The results lead to a conclusion that multi-pass scanning with its compensation algorithm is an effective approach to improve the stitching quality of an SPSL system.
Practical implications
This study can provide advice for researchers to achieve the satisfactory surface finish with SPSL technology.
Originality/value
The authors proposed a process of multi-pass scanning as well as a compensation algorithm for SPSL additive manufacturing (system to improve the stitching quality, which has rarely been studied in previous work.
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Xiaowei Shao, Mingxuan Song, Jihe Wang, Dexin Zhang and Junli Chen
The purpose of this paper is to present a method to achieve small satellite formation keeping operations by using the differential lift and drag to control the drift caused by J2…
Abstract
Purpose
The purpose of this paper is to present a method to achieve small satellite formation keeping operations by using the differential lift and drag to control the drift caused by J2 perturbation in circular or near-circular low earth orbits (LEOs).
Design/methodology/approach
Each spacecraft is equipped with five large flat plates, which can be controlled to generate differential accelerations. The aerodynamic lift and drag acting on a flat plate is calculated by the kinetic theory. To maintain the formation within tracking error bounds in the presence of J2 perturbation, a nonlinear Lyapunov-based feedback control law is designed.
Findings
Simulation results demonstrate that the proposed method is efficient for the satellite formation keeping and better accuracy advantage in comparison with classical approaches via the fixed maximum differential aerodynamic acceleration.
Research limitations/implications
Because the aerodynamic force will reduce drastically as the orbital altitude increases, the formation keeping control strategy for small satellites presented in this paper should be limited to the scenarios when satellites are in LEO.
Practical implications
The formation keeping control method in this paper can be applied to solve satellite formation keeping problem for small satellites in LEO.
Originality/value
This paper proposes a Lyapunov control strategy for satellite formation keeping considering both lift and drag forces, and simulation results show better performance with high accuracy under J2 perturbation.