1,720,994 research outputs found
A Neuro-Fuzzy Approach to Simulate the User Mode Choice Behaviour in a Travel Decision Framework
No full textIncreasing congestion on the main roads in urban areas pushes analysts to improve simulation of modal choice in order to obtain good estimation of the demand shares for different travel modes. In the literature, several kinds of behavioural models have been proposed in order both to evaluate the modal choice percentage in urban areas and to capture the travel behaviour by means of the estimation of some suitable parameters. However, behaviour is complex in itself and often standard models, even if sophisticated, cannot capture all the complex mechanisms underlying the user behaviour. In this paper, a neuro-fuzzy approach is proposed in order to extract the mode choice decision rules of travel users, by evaluating different sets of rules and different membership functions. Particularly, in order to determine which inputs are the most relevant in such decision process, fuzzy curves and surfaces have been taken into account. In this way, non linear effects can be considered
A Fuzzy Approach to Reduce Delays at Signalized Road Intersections
No full textIn this paper a fuzzy approach is proposed to reduce delay at isolated intersections by using as indicator the saturation degree. The starting point of the proposed approach is the use of measured traffic flows at a prefixed distance from the intersection to modify the phase length so as to reduce delay. Measured traffic flows are considered as fuzzy quantities because of their uncertainty and/or imprecision. As a consequence of the delay reduction, also environmental impacts are reduced, then the system can be identified as an ITS as it employs information and communication technologies and integrate them to obtain a more efficient transport service and reduce transport negative impacts. A test example is analyzed to show the benefits of the fuzzy controlled intersection with respect to a crispy controlled one
Modelling user mode choices by an ellipsoidal fuzzy approach
No full textAmong transport-related choices one of the most important and studied is the travel mode choice. In fact, the estimation of the travel mode percentages is crucial to forecast possible configurations of the transportation system according to suitable policies. In this work, the travel mode choice is studied by using a fuzzy approach. The underlying idea is that user travel behaviour is intrinsically uncertain and ambiguous and the user choices can be predicted only to some extent. The fuzzy approach aims at identifying the most important variables affecting user’s mode choices and predicts mode choices on the basis of fuzzy similarities approach based on ellipsoidal rules and neuro-fuzzy tuning procedure. The procedure has been tested by using a large database concerning actual mode choices outperforming other conventional fuzzy systems exploiting generalized network-based fuzzy inference
Deformable MEMS with Fringing Field: Models, Uniqueness Conditions and Membrane Profile Recovering
No full textA particular 1D II-order differential semi-linear elliptic model for electrostatic membrane MEMS devices, which is well-known in the literature, considers the amplitude of the electric field locally proportional to the membrane’s geometric curvature, which contains a term involving the fringing field according to Pelesko and Driscoll’s theory. Thus, in this paper, we will begin from this elliptical model, of which the uniqueness condition for the solution does not depend on the electromechanical properties of the membrane’s constituent material. In particular, after analyzing the model’s advantages and disadvantages, we present a new uniqueness condition for the solution depending on the properties listed above, which appears to be more important than the existence condition of the solution that is well-known in literature. Therefore, once the fringing field’s mode of action on the electrostatic force acting on the membrane is evaluated, suitable numerical techniques are used and compared to recover the membrane profile without ghost solutions and to propose an innovative criterion for selecting the membrane material, which depends on the electrical operative parameters and vice-versa. Finally, the possible industrial uses of the studied device are evaluated
A 2D membrane MEMS device model with fringing field: Curvature-dependent electrostatic field and optimal control
No full textAn important problem in membrane micro-electric-mechanical-system (MEMS) modeling is the fringing-field phenomenon, of which the main effect consists of force-line deformation of electrostatic field E near the edges of the plates, producing the anomalous deformation of the membrane when external voltage V is applied. In the framework of a 2D circular membrane MEMS, representing the fringing-field effect depending on |u|2 with the u profile of the membrane, and since strong E produces strong deformation of the membrane, we consider |E| proportional to the mean curvature of the membrane, obtaining a new nonlinear second-order differential model without explicit singularities. In this paper, the main purpose was the analytical study of this model, obtaining an algebraic condition ensuring the existence of at least one solution for it that depends on both the electromechanical properties of the material constituting the membrane and the positive parameter δ that weighs the terms |u|2. However, even if the the study of the model did not ensure the uniqueness of the solution, it made it possible to achieve the goal of finding a stable equilibrium position. Moreover, a range of admissible values of V were obtained in order, on the one hand, to win the mechanical inertia of the membrane and, on the other hand, to ensure that the membrane did not touch the upper disk of the device. Lastly, some optimal control conditions based on the variation of potential energy are presented and discussed
Solution Properties of a New Dynamic Model for MEMS with Parallel Plates in the Presence of Fringing Field
No full textIn this paper, starting from a well-known nonlinear hyperbolic integro-differential model of the fourth order describing the dynamic behavior of an electrostatic MEMS with a parallel plate, the authors propose an upgrade of it by formulating an additive term due to the effects produced by the fringing field and satisfying the Pelesko–Driscoll theory, which, as is well known, has strong experimental confirmation. Exploiting the theory of hyperbolic equations in Hilbert spaces, and also utilizing Campanato’s Near Operator Theory (and subsequent applications), results of existence and regularity of the solution are proved and discussed particularly usefully in anticipation of the development of numerical approaches for recovering the profile of the deformable plate for a wide range of applications
An Inhomogeneous Model for Laser Welding of Industrial Interest
Full text linkAn innovative non-homogeneous dynamic model is presented for the recovery of temperature during the industrial laser welding process of Al-Si (Formula presented.) alloy plates. It considers that, metallurgically, during welding, the alloy melts with the presence of solid/liquid phases until total melt is achieved, and afterwards it resolidifies with the reverse process. Further, a polynomial substitute thermal capacity of the alloy is chosen based on experimental evidence so that the volumetric solid-state fraction is identifiable. Moreover, to the usual radiative/convective boundary conditions, the contribution due to the positioning of the plates on the workbench is considered (endowing the model with Cauchy–Stefan–Boltzmann boundary conditions). Having verified the well-posedness of the problem, a Galerkin-FEM approach is implemented to recover the temperature maps, obtained by modeling the laser heat sources with formulations depending on the laser sliding speed. The results achieved show good adherence to the experimental evidence, opening up interesting future scenarios for technology transfer
Curvature Dependent Electrostatic Field in the Deformable MEMS Device: Stability and Optimal Control
No full textThe recovery of the membrane profile of an electrostatic micro-electro-mechanical system (MEMS) device is an important issue because, when applying an external voltage, the membrane deforms with the consequent risk of touching the upper plate of the device (a condition that should be avoided). Then, during the deformation of the membrane, it is useful to know if this movement admits stable equilibrium configurations. In such a context, our present work analyze the behavior of an electrostatic 1D membrane MEMS device when an external electric voltage is applied. In particular, starting from a well-known second-order elliptical semi-linear di erential model, obtained considering the electrostatic field inside the device proportional to the curvature of the membrane, the only possible equilibrium position is obtained, and its stability is analyzed. Moreover, considering that the membrane has an inertia in moving and taking into account that it must not touch the upper plate of the device, the range of possible values of the applied external voltage is obtained, which accounted for these two particular operating conditions. Finally, some calculations about the variation of potential energy have identified optimal control conditions
A 2D non-linear second-order differential model for electrostatic circular membrane MEMS devices: A result of existence and uniqueness
No full textIn the framework of 2D circular membrane Micro-Electric-Mechanical-Systems (MEMS), a new non-linear second-order differential model with singularity in the steady-state case is presented in this paper. In particular, starting from the fact that the electric field magnitude is locally proportional to the curvature of the membrane, the problem is formalized in terms of the mean curvature. Then, a result of the existence of at least one solution is achieved. Finally, two different approaches prove that the uniqueness of the solutions is not ensured
Upgrading urban traffic flow by a demand-responsive fuzzy-based traffic lights model
No full textA fuzzy model is proposed here to speed up traffic flows and reduce delay at road-signalized intersections by using real-time measures and traffic lights adaptation. The proposed demand-responsive control approach combines fixed-duration cycle and fuzzy calculus to reduce the overall delay without giving too much penalty to traffic streams. The traffic lights signal modification is based on the concept of “intersection saturation degree” that identifies the intersection performances. The numerical results of the proposed fuzzy approach confirm its better performances with respect to the other traditional control approaches
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