A common approach for modeling the dynamic behavior of distributed parameter systems is the approximation through finite-segmentmodels. These models are able to accurately predict the dynamic behavior of the system g...
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A common approach for modeling the dynamic behavior of distributed parameter systems is the approximation through finite-segmentmodels. These models are able to accurately predict the dynamic behavior of the system given that "adequate" segments are included in the model. Frequency-based methodologies can be used to address the complexity of such models. The purpose of the current work is to address the complexity of distributed parameter using the previously developed activity metric. More specifically the complexity of an Euler-Bernoulli beam model is considered. Bond graph models of this system already exist in the literature and the objective is to identify the necessary complexity (number of segments). A new modeling procedure is proposed for this type of systems where the model starts from simple and the number of segments is increased until an activity based criterion is satisfied. An illustrative example is provided to demonstrate the effectiveness of this methodology. (C) 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
Background In robot-assisted minimally invasive surgery (MIS), knot-tying is an important but challenging task for surgeons when performing surgery by manipulating a master-slave robot system. Knot-tying in the conven...
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Background In robot-assisted minimally invasive surgery (MIS), knot-tying is an important but challenging task for surgeons when performing surgery by manipulating a master-slave robot system. Knot-tying in the conventional way is restricted by a confined workspace, which may cause the suture loop to be unstable and make knot-tying difficult and time-consuming in robot-assisted MIS. Methods A knot-tying approach named 'bending-twisting knot-tying' (BTKT) has been developed for robot-assisted surgery systems operating in a confined workspace. The non-linear deformation of sutures during knot-tying is qualitatively described using knot theory. The length ratio of a knot (LoK) and the feasible coefficient (Fc) are introduced to evaluate the quality of BTKT knots. Simulations and experiments are performed based on finitesegment dynamic models and the MicroHand Surgical system, respectively, to describe the dynamic behaviours of the knots. Sensitive parameters, including the length of a suture (L), the distance between two ends (d) and the angle between tangents of the two ends (a) are analysed based on the model. Results For a terylene suture, the length of the suture L and the distance between the two ends d should satisfy 1.12d <= L <= 14.4d. When L and a are constant, the smaller d is, the larger are LoK and Fc relative to different sutures. A knot of high quality can be tied with a small alpha. Conclusions Simulation and experimental results show that BTKT requires a smaller workspace and can form more stable loops compared to conventional methods. Copyright (C) 2008 John Wiley & Sons, Ltd.
A novel unified theory for distortion analysis of thin-walled hollow section has been proposed based on the Hellinger-Reissner variational principle to account for distortional shear deformation effects. Based on the ...
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A novel unified theory for distortion analysis of thin-walled hollow section has been proposed based on the Hellinger-Reissner variational principle to account for distortional shear deformation effects. Based on the proposed theory, a finite segment model has been developed and the method for determining the distortion functions of the cross-section has been proposed. The rationality of approaches for determining distortional shear stress has been analysed and it is concluded that Bredt's pure distortion does not exist in the single-cell hollow section. Comparisons and analyses have been performed between the proposed theoretical model and the existing four groups of theories in distortion analysis of thin-walled hollow section. Effectsof distortional warping shear stress on the shear deformation has been investigated and the results indicate that the distortional shear deformation effect results in a decrease of the distortional warping stresses and shear stresses but an increase of the transverse bending stresses. The numerical study indicates that the distortional shear deformation effects can be ignored and the first derivative of the distortion angle can be employed as the distortional warping function for the conventional hollow sections of bridge structures.
Axially functionally graded (AFG) beams, with variable coefficients in the governing equation, are a novel class of composites structures that have continuous variations in material properties from one component to an...
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Axially functionally graded (AFG) beams, with variable coefficients in the governing equation, are a novel class of composites structures that have continuous variations in material properties from one component to another. In this paper, the asymptotic development method (ADM) is utilized to investigate the free vibration of uniform AFG beams with different boundary conditions. By decomposing the variable flexural stiffness and mass per unit length into reference invariant parts and variant parts, perturbation theory is introduced to obtain an approximate formula of the natural frequencies of the uniform AFG beams. The numerical results of the proposed method are confirmed by comparing the obtained results with those obtained via finite element analysis and the published literature results, the comparison reveals the proposed method yields an accurate estimate of the first three order natural frequencies of the AFG beam. Moreover, the influences of the gradient parameter and support conditions on the first three natural frequencies are discussed. The proposed analytical method is simple and efficient and can be used to conveniently analyze uniform AFG beams with arbitrary changes in the material properties along the axial direction.
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