ISEP - Departamento de Engenharia Eletrotécnica
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- 2-echelon lastmile delivery with lockers and occasional couriersPublication . Santos, André Gustavo dos; Viana, Ana; Pedroso, João PedroWe propose a new approach for the lastmile delivery problem where, besides serving as collecting points of orders for customers, parcel lockers are also used as transshipment nodes in a 2-echelon delivery system. Moreover, we consider that a customer (occasional courier) visiting a locker may accept a compensation to make a delivery to another customer on their regular traveling path. The proposed shared use of the locker facilities – by customers that prefer to self-pick up their orders, and also as a transfer deposit for customers that prefer home delivery – will contribute to better usage of an already available storage capacity. Furthermore, the use of occasional couriers (OCs) brings an extra layer of flexibility to the delivery process and may positively contribute to achieving some environmental goals: although non-consolidation of deliveries may, at first sight, seem negative, by only considering OCs that would go to the locker independently of making or not a delivery on their way home, and their selection being constrained by a maximum detour, the carbon footprint can be potentially reduced when compared to that of dedicated vehicles. We present a mixed-integer linear programming formulation for the problem that integrates three delivery options – depot to locker, depot to locker followed by final delivery by a professional fleet, and depot to locker followed by final delivery by an OC. Furthermore, to assess the impact of OCs’ no show on the delivery process, we extend the formulation to re-schedule the delivery of previous undelivered parcels, and analyze the impact of different no-show rates. Thorough computational experiments show that the use of OCs has a positive impact both on the delivery cost and on the total distance traveled by the dedicated fleets. Experiments also show that the negative impact of no-shows may be reduced by using lockers with higher capacities.
- 2022 - O contexto atual das ITED/ITURPublication . Duarte, Jorge Manuel FerreiraNo ano de 2005, começou a obrigatoriedade de qualquer edifício ter uma infraestrutura ITED (Infraestrutura de Telecomunicações em Edifícios), quer seja na sua construção ou reconstrução. O ponto principal na elaboração do manual na sua primeira edição era de juntar a rede de pares de cobre com a rede de cabo coaxial e de fibra ótica. Por outro, dotar a nível de infraestruturas, mais concretamente a rede tubagens, para a entrada de vários operadores aos clientes, de forma que as infraestruturas não fossem o problema. Notar que, um dos objetivos principais, era que houvesse livre concorrência entre operadores e não houvesse barreiras físicas no fornecimento de serviços aos seus clientes.
- Absolutely stable difference scheme for a general class of singular perturbation problemsPublication . El-Zahar, Essam R.; Alotaibi, A. M.; Ebaid, Abdelhalim; Baleanu, Dumitru; Machado, J. A. Tenreiro; Hamed, Y. S.This paper presents an absolutely stable noniterative difference scheme for solving a general class of singular perturbation problems having left, right, internal, or twin boundary layers. The original two-point second-order singular perturbation problem is approximated by a first-order delay differential equation with a variable deviating argument. This delay differential equation is transformed into a three-term difference equation that can be solved using the Thomas algorithm. The uniqueness and stability analysis are discussed, showing that the method is absolutely stable. An optimal estimate for the deviating argument is obtained to take advantage of the second-order accuracy of the central finite difference method in addition to the absolute stability property. Several problems having left, right, interior, or twin boundary layers are considered to validate and illustrate the method. The numerical results confirm that the deviating argument can stabilize the unstable discretized differential equation and that the new approach is effective in solving the considered class of singular perturbation problems.
- Accessing complexity from genome informationPublication . Machado, J. A. TenreiroThis paper studies the information content of the chromosomes of 24 species. In a first phase, a scheme inspired in dynamical system state space representation is developed. For each chromosome the state space dynamical evolution is shed into a two dimensional chart. The plots are then analyzed and characterized in the perspective of fractal dimension. This information is integrated in two measures of the species’ complexity addressing its average and variability. The results are in close accordance with phylogenetics pointing quantitative aspects of the species’ genomic complexity.
- Active Replication: Towards a Truly SRAM-based FPGA On-Line Concurrent TestingPublication . Gericota, Manuel G.; Alves, Gustavo R.; Silva, Miguel L.; Ferreira, J. M. MartinsThe reusing of the same hardware resources to implement speed-critical algorithms, without interrupting system operation, is one of the main reasons for the increasing use of reconfigurable computing platforms, employing complex SRAM-based FPGAs. However, new semiconductor manufacturing technologies increase the probability of lifetime operation failures, requiring new on-line testing / fault-tolerance methods able to improve the dependability of the systems where they are included. The Active Replication technique presented in this paper consists of a set of procedures that enables the implementation of a truly non-intrusive structural on-line concurrent testing approach, detecting and avoiding permanent faults and correcting errors due to transient faults. In relation to a previous technique proposed by the authors as part of the DRAFT FPGA concurrent test methodology, the Active Replication technique extends the range of circuits that can be replicated, by introducing a novel method with very low silicon overhead.
- Adaptive Controller for Systems of Fractional Dynamics Based on Robust Fixed Point TransformationsPublication . Tar, J. K.; Rudas, I. J.; Bitó, J. F.; Tenreiro Machado, J. A.; Kozlowski, K.In this paper a discrete time approximation of Caputo’s fractional order derivatives is used for modeling the dynamic behavior of hypothetical fractional order systems the appropriate responses of which that can directly be manipulated by some physical agents are some fractional order time-derivatives of their state variables. A possible generalization of the concept of “initial conditions” of the integer order systems is proposed as “preceding history” for fractional order ones. It is shown that the number of the independent data characteristic to the “preceding history” can be made independent of the order of derivation. It is shown that the discrete time approximation proposed makes it possible to interpret the order of derivation in a higher range than in the case of the original integral form of Caputo’s definition. By providing a simple analysis of the so obtained time-sequences it is shown that by manipulating the order of differentiation in this model both dissipative and unstable behavior can be modeled. The dissipative casecorresponds to the presence of unmodeled internal degrees of freedom that are dynamically coupled to the directly controlled ones but cannot directly be controlled. The unstable case seems to be appropriate for modeling the behavior of systems coupled to some directly unmodeled exciting environment. For this purpose very simple mathematical estimations can be applied. The paradigm controlled is a fractional order Φ6 type Van der Pol oscillator that already obtained certain attention in the literature. It is shown that the simple fixed point transformations based adaptive control elaborated for integer order systems can be applied without any modification for fractional order ones.
- Adaptive nonlinear vibration control based on causal time-invariant green functions and on a novel branch of soft computingPublication . Tar, József K.; Rudas, Imre J.; Bitó, János F.; Tenreiro Machado, J. A.In this paper a simple nonlinear, adaptive approach inspired by the fractional derivatives based CRONE control is presented for vibration damping. Its key idea is replacement of the fractional derivatives with the mathematically less restricted concept of time-invariant Green functions. Instead of the traditional PID feedback terms it applies positive definite weighted moving average of the square of the error plus a nonlinear term making the error converge to zero. In this way simple kinematic design of the desired damping becomes possible. The adaptive part of the controller guarantees the realization of this kinematic design without making it necessary to the designer to have an accurate and complete dynamic model of the system to be controlled or to design sophisticated linear controller. The applicability of the approach is illustrated via simulations for a paradigm consisting of a pair of coupled damper linear oscillators under external excitation. One of the oscillators is not modeled by the controller. The adaptive loop successively maps the observed system behavior to the desired one without exerting any effort to identify the reasons of the differences. The approach was found be useful for solving vibration damping problems with unmodeled and uncontrolled internal degrees of freedom.
- Adaptive nonlinear vibration damping inspired by the concept of fractional derivativesPublication . Tar, József K.; Rudas, Imre J.; Bitó, János F.; Tenreiro Machado, J. A.In this paper a simple nonlinear, adaptive approach inspired by the CRONE method is presented for vibration control. It replaces the fractional derivatives with time-invariant Green functions. Being completed by a nonlinear feedback term it makes the positive definite weighted moving average of the square of the error converge to zero in the kinematic design of the desired damping the realization of which is guaranteed by the controller's adaptive nature. The burden of designing a sophisticated linear controller is evaded. The applicability of the approach is illustrated via simulations for a damped linear oscillator under external excitation at its resonance frequency. The adaptive loop simply successively maps the observed system behavior to the desired one without exerting any effort to identify the reasons of the differences. It is expected to be useful for solving even more complicated vibration damping problems with unmodeled and uncontrolled internal degrees of freedom.
- Adaptive reduction of the order of derivation in the control of a hydraulic differential cylinderPublication . Tar, József K.; Bitó, János F.; Rudas, Imre J.; Tenreiro Machado, J. A.Servo valve controlled hydraulic differential cylinders are non-linear, strongly coupled multivariable electromechanical tools applicable for driving e.g. manipulators. When the piston has finite but considerable velocity with respect to the cylinder the system’s behavior can be “linearized” because the viscous friction i.e. the main source of disturbance is smooth function of this velocity and causes linear damping. When this velocity is in the vicinity of zero the effect of adhesion is the dominating disturbance force that abruptly changes direction depending on the sign of this velocity. Furthermore, at zero relative velocity adhesion can compensate arbitrary forces within certain limits keeping the piston fixed. In the paper a concise application of the Stribeck model of friction and adhesion is reported in an adaptive control in which varying fractional order derivatives are used to reduce the hectic behavior of friction in the case of “critical” trajectories that asymptotically converge to a fixed position and zero velocity. Simulation results made by INRIA’s Scilab are presented. It is concluded that the combined application of the two adaptive techniques reported accurate control can be achieved without knowing the accurate model of the piston-cylinder system.
- Adaptive tackling of the swinging problem for a 2 DOF crane – payload systemPublication . Tar, József K.; Rudas, Imre J.; Bitó, János F.; Machado, J. A. Tenreiro; Kozłowski, Krzysztof R.The control of a crane carrying its payload by an elastic string corresponds to a task in which precise, indirect control of a subsystem dynamically coupled to a directly controllable subsystem is needed. This task is interesting since the coupled degree of freedom has little damping and it is apt to keep swinging accordingly. The traditional approaches apply the input shaping technology to assist the human operator responsible for the manipulation task. In the present paper a novel adaptive approach applying fixed point transformations based iterations having local basin of attraction is proposed to simultaneously tackle the problems originating from the imprecise dynamic model available for the system to be controlled and the swinging problem, too. The most important phenomenological properties of this approach are also discussed. The control considers the 4th time-derivative of the trajectory of the payload. The operation of the proposed control is illustrated via simulation results.