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The present work aims to reveal the effect of deposition paths on transient temperature, transient stress, residual stress and residual warping in the electron beam freeform fabrication (EBF) process.

Six typical deposition paths were involved in the finite element (FE) simulations of EBF process by implementing a specially written program.

The results showed that the deposition path had a remarkable influence on heat transfer and transient temperature distribution in the scanning process, resulting in different residual stress and residual warping after cooling to room temperature. The largest and smallest temperature gradients were obtained from the zigzag and alternate-line paths, respectively. Meanwhile, the temperature gradient decreased with the increase of deposited layers. The optimum deposition path, namely, the alternate-line pattern, was determined with respect to the residual stress and residual warping.

Although some researcher revealed the importance of deposition path through FE analysis and experimental observation, their studies were usually confined within one type of deposition pattern. A complete investigation of typical deposition paths and comparison among them are still lacking in literature. To address the aforementioned gap, the present work started by extensive FE simulations of EBF process involving six representative deposition paths, namely, the alternate-line, zigzag, raster, inside-out spiral, outside-in spiral and Hilbert. For each deposition path, the transient temperature field, residual stress and residual deformation were obtained to optimize the deposition path.

The purpose of this paper is to present a novel gradient‐based iterative algorithm for the joint diagonalization of a set of real symmetric matrices. The approximate joint diagonalization of a set of matrices is an important tool for solving stochastic linear equations. As an application, reliability analysis of structures by using the stochastic finite element analysis based on the joint diagonalization approach is also introduced in this paper, and it provides useful references to practical engineers.

By starting with a least squares (LS) criterion, the authors obtain a classical nonlinear cost‐function and transfer the joint diagonalization problem into a least squares like minimization problem. A gradient method for minimizing such a cost function is derived and tested against other techniques in engineering applications.

A novel approach is presented for joint diagonalization for a set of real symmetric matrices. The new algorithm works on the numerical gradient base, and solves the problem with iterations. Demonstrated by examples, the new algorithm shows the merits of simplicity, effectiveness, and computational efficiency.

A novel algorithm for joint diagonalization of real symmetric matrices is presented in this paper. The new algorithm is based on the least squares criterion, and it iteratively searches for the optimal transformation matrix based on the gradient of the cost function, which can be computed in a closed form. Numerical examples show that the new algorithm is efficient and robust. The new algorithm is applied in conjunction with stochastic finite element methods, and very promising results are observed which match very well with the Monte Carlo method, but with higher computational efficiency. The new method is also tested in the context of structural reliability analysis. The reliability index obtained with the joint diagonalization approach is compared with the conventional Hasofer Lind algorithm, and again good agreement is achieved.

The purpose of this study is to propose a modeling method of the equivalent circuit for a new type of high-temperature superconducting partial-core transformer (HTS-PCT) made of ReBCO-coated conductors.

The modeling process is based on the “Steinmetz” equivalent circuit. The impedance components in the circuit are obtained by the calculations of the core losses and AC losses of the HTS windings by using theoretical methods. An iterative computation is also used to decide the equivalent resistances of the AC losses of the primary and secondary HTS windings. The reactance components in the circuit are calculated from the energy stored in the magnetic fields by finite element method. The validation of the modeling method is verified by experimental results

The modeling method of the equivalent circuit of HTS-PCT is valid, and an equivalent circuit for HTS-PCT is presented.

The equivalent circuit of HTS-PCT could be obtained by the suggested modeling method. Then, it is easy to analyze the characteristics of the HTS-PCT by its equivalent circuit. Moreover, the modeling method could also be useful for the design of a specific HTS-PCT.

The study proposes a modeling method of the HTS-PCT made of the second-generation HTS tapes, i.e. ReBCO-coated conductors.

This paper aims to present a method to improve the sensitive and low probabilities of false alarm of a manipulator in a human–robot interaction environment, which can improve the performance of the system owing to non-linear uncertainty in the model of the robot controller.

A novel collision detection method based on adaptive residual estimation is proposed, promoting the detection accuracy of the collision of the manipulator during operation. First, a general momentum residual estimator is designed to incorporate the non-linear factors of the manipulator (e.g. joint friction, speed and acceleration) into the residual-related uncertainty of the model. Second, model parameters are estimated through gradient correction. The residual filter is used to determine the dynamic threshold, resulting in higher detection accuracy. Finally, the performance of the residual estimation scheme is evaluated by comparing the dynamic threshold with residual in real-time experiments where a single Universal Robot 5 robot end–effector collides with the obstacle.

Experimental results demonstrate that the collision detection system can improve sensitivity and lead to low probabilities of false alarm of non-linear uncertainty in the model.

The method proposed in this article can be applied to industry and human–robot interaction area.

An adaptive collision detection method is proposed in this paper to address non-linear uncertainties of the model in industrial application.

There is not a unified modelling approach to finite element failure analysis of concrete dams. Different behaviours of a dam predicted by different fracture methods with various material constitutive models may significantly influence on the dam safety evaluation. The purpose of this paper is to present a general comparative investigation to examine whether the nonlinear responses of concrete dams obtained from different fracture modelling approaches are comparable in terms of crack propagation and failure modes.

Three fracture modelling approaches, including the extended finite element method with a cohesive law (XFEM-COH), the crack band finite element method with a plastic-damage relation (FEPD), and the Drucker-Prager (DP) elasto-plastic model, are chosen to analyse damage and cracking behaviour of concrete gravity dams under overloading conditions. The failure process and loading capacity of a dam are compared.

The numerical results indicate that the three approaches are all applicable to predict loading capacity and safety factors of gravity dams. However, both XFEM-COH and FEPD give more reasonable crack propagation and failure modes in comparison with DP. Therefore, when cracking patterns are the major concern for safety evaluation of concrete dams, it is recommended that XFEM-COH and FEPD rather than DP be used.

The comparison of cracking behaviours of concrete dams obtained from different fracture modelling approaches is conducted. The applicability of the modelling approaches for failure analysis of concrete dams is discussed, and from the results presented in this work, it is significant to consider the suitability of the selected fracture modelling approach for dam safety evaluation.

Unmanned aerial/ground vehicles (UAV/UGV) collaboration systems are increasingly being used to perform reconnaissance and rescue missions autonomously, especially in disaster areas. The paper aims to discuss this issue.

To improve visibility, this study proposes a path-planning algorithm based on map matching. Continuous ground images are first collected aerially using the UAV vision system. Subsequently, a global map of the ground environment is created by processing the collected images using the methods of image correction, image mosaic and obstacle recognition. The local map of the ground environment is obtained using the 2D laser radar sensor of the UGV. A set of features for both global and local maps is established. Unknown values during map matching are determined via the least squares method. Based on the matched mapping, the traditional A* algorithm is used for the planning of global path in the global map, and the dynamic window method is used for adjustment of the local map.

Simulation experiments were carried out to demonstrate the effectiveness of the proposed algorithm. The experimental results show that the proposed algorithm can construct a global map of the wide environment and effectively bypass the obstacles missed by the UAV.

Prior to map matching, there is a need to extract the edge of obstacles in the global map.

This paper proposed a path planning algorithm based on map matching, yielding insights into the application of the UAV/UGV collaboration systems in disaster areas.

The characteristics of spherical robots, such as under-drive, non-holonomic constraints and strong coupling, make it difficult to establish its motion control model accurately. To improve the anti-interference performance of spherical robots in practical engineering, this paper proposes a spherical robot motion controller based on auto-disturbance rejection control (ADRC) with parameter tuning.

This paper considers the influences of the spherical shell, internal frame and pendulum on the movement of the spherical robot during the rotation to establish the multi-body dynamics model of the XK-I spherical robot. Due to the serious coupling problem of the dynamic model, the motion control state equation is constructed using linearization and decoupling. The XK-I spherical robot PSO-ADRC motion controller with parameter tuning function is designed by combining the state equation with the particle swarm optimization (PSO) algorithm. Finally, experiments are performed to evaluate the feasibility of PSO-ADRC in an actual case compared to ADRC, PSO-PID and PID.

By analyzing the required time to reach the expected value, the control stability and the fluctuation range of the standard deviation after reaching the expected value, the superiority of PSO-ADRC to ADRC, PSO-PID and PID is demonstrated in terms of the speed and anti-interference ability.

The proposed method can be applied to the robot control field.

A parameter-tuning method for auto-disturbance-rejection motion control of the spherical robot is proposed. According to the experimental results, the anti-interference ability of the spherical robot moving on uneven ground is improved. Therefore, it provides a foundation for the autonomous environmental monitoring of the spherical robot equipped with sensors.

Visual object tracking plays a significant role in intelligent robot systems. This study aims to focus on unlocking the tracking performance potential of the deep network and presenting a dynamic template update strategy for the Siamese trackers.

This paper presents a novel and efficient Siamese architecture for visual object tracking which introduces densely connected convolutional layers and a dynamic template update strategy into Siamese tracker.

The most advanced performance can be achieved by introducing densely connected convolutional neural networks that have not yet been applied to the tracking task into SiamRPN. By using the proposed architecture, the experimental results demonstrate that the performance of the proposed tracker is 5.8% (area under curve), 5.4% expected average overlap (EAO) and 3.5% (EAO) higher than the baseline on the OTB100, VOT2016 and VOT2018 data sets and achieves an excellent EAO score of 0.292 on the VOT2019 data set.

This study explores a deeper backbone network with each convolutional network layer densely connected. In response to tracking errors caused by templates that are not updated, this study proposes a dynamic template update strategy.

The purpose of this paper is to maraging 18Ni-300 steel fabricate by powder bed based selective laser melting (SLM) process. Microstructure and mechanical properties of the maraging steel part before and after heat treatment at a slow cooling rate were investigated.

The microstructure of the printed part was observed by optical microscopy and scanning electron microscopy. The phases were determined by X-ray diffraction. The surface roughness of the part was recorded by a profilometer. The tensile properties and microhardness of the parts before and after heat treatment were characterized by an electronic universal tensile testing machine and a Vickers hardness tester, respectively.

Maraging 18Ni-300 steel part comprised of the martensitic phase and a small fraction of austenite phase. After heat treatment, the volume fraction of austenite slightly increased. The surface roughness of the part was about 96 µm. The printed part was dense, but irregular pores were present. The yield strength, ultimate tensile strength (UTS), elongation and Young’s modulus of as-fabricated parts were 554.7 MPa, 1173.1 MPa, 10.9% and 128.9 GPa, respectively. The yield strength, UTS, elongation and Young’s modulus of as-treated parts were 2065 MPa, 2225 MPa, 4.2% and 142.5 GPa, respectively. The microhardness values of surface and cross-section of the as-fabricated part were 407.1 HV and 443.0 HV, respectively. After short-time heat treatment, the microhardness values of the surface and cross-section of the part were 542.7 HV and 567.3 HV, respectively. After long-time heat treatment, the microhardness values of the surface and cross-section of the part were 524.4 HV and 454.8 HV, respectively. The microhardness and tensile strength increased significantly with decreasing elongation due to the changes in phases and microstructure of the parts after heat treatment.

This work studied the effect of heat treatment at 550°C combined with a subsequent slow cooling rate on microstructure and mechanical properties of maraging 18Ni-300 steel obtained by the powder bed based SLM process.