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1 – 10 of 20Jiandong Wei, Manyu Guan, Qi Cao and Ruibin Wang
The purpose of this paper is to analyze the cable-supported bridges more efficiently by building the finite element model with the spatial combined cable element.
Abstract
Purpose
The purpose of this paper is to analyze the cable-supported bridges more efficiently by building the finite element model with the spatial combined cable element.
Design/methodology/approach
The spatial combined cable element with rigid arms and elastic segments was derived. By using the analytical solution of the elastic catenary to establish the flexibility matrix at the end of the cable segment and adding it to the flexibility matrix at the ends of the two elastic segments, the flexibility matrix at the end of the cable body is obtained. Then the stiffness matrix of the cable body is established and the end force vector of cable body is given. Using the displacement transformation relationship between the two ends of the rigid arm, the stiffness matrix of the combined cable element is derived. By assigning zero to the length of the elastic segment(s) or/and the rigid arm(s), many subdivisions of the combined cable element can be obtained, even the elastic catenary element.
Findings
The examples in this field and specially designed examples proved the correctness of the proposed spatial combined cable element.
Originality/value
The combined cable element proposed in this study can be used for the design and analysis of cable-stayed bridges. Case studies show that it is able to simulate cable accurately and could also be used to simulate the suspenders in arch bridges as well in suspension bridges.
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Alberto Cardona and Alfredo Huespe
Presents an implementation of continuation methods in the context of a code for flexible multibody systems analysis. These systems are characterized by the simultaneous presence…
Abstract
Presents an implementation of continuation methods in the context of a code for flexible multibody systems analysis. These systems are characterized by the simultaneous presence of elastic deformation terms and rigid constraints. In our formulation, the latter terms are introduced by an augmented Lagrangian technique, resulting in the presence of Lagrange multipliers in the set of unknowns, together with displacement and rotation associated terms. Essential aspects for a successful implementation are discussed: e.g. the selection of an appropriate metric for computing the path following constraint, a flexible description of control parameters which accounts for conservative and nonconservative loads, imposed displacements and imposed temperatures (dilatation effects), and the inclusion of second order derivatives of rigid constraints in the Jacobian. A large set of examples is presented, with the objective of evaluating the numerical effectiveness of the implemented schemes.
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Tianlei Wang, Fei Ding and Zhenxing Sun
Stiffness adjusting ability is essential for soft robotic arms to perform complex tasks. A soft state enables dexterous operation and safe interaction, while a rigid state enables…
Abstract
Purpose
Stiffness adjusting ability is essential for soft robotic arms to perform complex tasks. A soft state enables dexterous operation and safe interaction, while a rigid state enables large force output or heavy weight carrying. However, making a compact integration of soft actuators with powerful stiffness adjusting mechanisms is challenging. This study aims to develop a piston-like particle jamming mechanism for enhanced stiffness adjustment of a soft robotic arm.
Design/methodology/approach
The arm has two pairs of differential tendons for spatial bending, and a jamming core consists of four jamming units with particles sealed inside braided tubes for stiffness adjustment. The jamming core is pushed and pulled smoothly along the tendons by a piston, which is then driven by a motor and a ball screw mechanism.
Findings
The tip displacement of the arm under 150 N jamming force and no more than 0.3 kg load is minimal. The maximum stiffening ratio measured in the experiment under 150 N jamming force is up to 6–25 depends on the bending direction and added load of the arm, which is superior to most of the vacuum powered jamming method.
Originality/value
The proposed robotic arm makes an innovative compact integration of tendon-driven robotic arm and motor-driven piston-like particle jamming mechanism. The jamming force is much larger compared to conventional vacuum-powered systems and results in a superior stiffening ability.
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The work involved in solving certain fixed‐fixed arch problems can be considerably reduced by adopting the clastic centre method.
The work involved in solving certain fixed‐fixed arch problems can be considerably reduced by adopting the classic centre method.
Abstract
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In a jet‐propelled aircraft, take‐off and landing is facilitated by arranging laterally disposed jet‐propulsion units 7, 7a for pivotal movement about transverse axes and by the…
Abstract
In a jet‐propelled aircraft, take‐off and landing is facilitated by arranging laterally disposed jet‐propulsion units 7, 7a for pivotal movement about transverse axes and by the provision of adjustable deflectors 48, 48a, 49, 49a in the jet nozzle of an engine (not shown) mounted in the fuselage. A pilot‐controlled lever 26 controls through a circuit 27 an electromagnetic valve 28 connected to a hydraulic valve 29 controlling through pipes 30, 30a jacks 18, 18a which rotate the engines 7, 7a respectively. A branch circuit 31 from circuit 27 controls a device (not shown) for operating the deflectors 48–49a. The power output of engines 7 and 7a may be controlled by levers 32, 32a connected through control lines 33, 33a to throttle valves (not shown). The elevator, aileron and rudder controls are conventionally operated from the control column 40 and rudder pedals 37 and servo‐control mechanisms such as electrically operated jacks 45, 46 and 47 are inserted in the control rods 38, 41, 43 and 43a respectively. The deflectors 48, 48a are controlled by an electrically operated jack 51 connected to the rudder control rod 38. Similarly, deflectors 49, 49a are controlled by a jack 55 connected to the elevator control rod 41. For the purpose of automatic stabilization the jacks 51 and 55 are further controlled respectively by amplifiers 50 and 56 which receive signals from gyro references 52, 57 and devices 53, 58 responsive to aircraft speed. Lateral stabilization is obtained by connecting the aileron control rods 43, 43a and the throttle valves for engines 7 and 7a to jacks 63, 63a energized from amplifiers 64, 64a supplied with signals from a gyro reference 65 and an aircraft‐speed responsive device 66. A take‐off platform, FIG. 1a (not shown) is described consisting of a fixed base member and an inclinable platform, operated by a cable winch from a horizontal position in which the aircraft is run on to the platform to an inclined position appropriate for take‐off. Ducts are provided in alignment with engines 7 and 7a when in their vertical positions so that exhaust gases may be re‐directed on to the under‐surfaces of the aircraft wings. A warning lamp placed on the ground in view of the pilot is switched off by a cable connected to the aircraft to give the pilot an indication of height in order that he may rotate with safety, the engines 7 and 7a into their forward‐propulsion positions.
Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National…
Abstract
Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.
D.F.H. Wolfe, S.W. Wijesoma and R.J. Richards
Tasks in automated manufacturing and assembly increasingly involve robot operations guided by vision systems. The traditional “look‐and‐move” approach to linking machine vision…
Abstract
Tasks in automated manufacturing and assembly increasingly involve robot operations guided by vision systems. The traditional “look‐and‐move” approach to linking machine vision systems and robot manipulators which is generally used in these operations relies heavily on accurate camera to real‐world calibration processes and on highly accurate robot arms with well‐known kinematics. As a consequence, the cost of robot automation has not been justifiable in many applications. This article describes a novel real‐time vision control strategy giving “eye‐to‐hand co‐ordination” which offers good performance even in the presence of significant vision system miscalibrations and kinematic model parametric errors. This strategy offers the potential for low cost vision‐guided robots.
V.O. Gamarra‐Rosado, G. Fernández, J.C. Grieco, M. Armada and N. Aliane
States that control is of the essence in cybernetics. Summarizes the dynamic equations for a flexible one‐link manipulator moving in the horizontal plane. Employs the finite…
Abstract
States that control is of the essence in cybernetics. Summarizes the dynamic equations for a flexible one‐link manipulator moving in the horizontal plane. Employs the finite element method, based on elementary beam theory, during the process of formulation. Develops and instruments a one‐link flexible manipulator in order to control its vibration modes. Uses a simple second‐order vibration model which permits vibrations on the rod to be estimated using the hub angle. The validation of the dynamic model and the structural analysis of the flexible manipulator is reached using proper infrared cameras and active light sources for determining actual positions of objects in space. Shows that the performance of the control is satisfactory, even under perturbation action.
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