322 research outputs found
Implicit Auctioning on the Kontek Cable: Third Time Lucky?
No full textCross-border capacities in Europe are currently inefficiently used. Implicit auctioning is about eliminating these cross-border trade inefficiencies by internalizing the arbitrage into the auction procedures of the Power Exchanges that are organizing trade nationally. On the Kontek Cable, implicit auctioning has been implemented without price coordination between the involved Power Exchanges. This implementation, referred to as “volume or dome coupling” as opposed to “price coupling”, has been argued to be institutionally easier to implement. The Kontek Cable experimented with three different implicit auctioning implementations whose performance we analyze empirically in this paper. We find that the third implementation is significantly outperforming the previous two implementations, but in this third implementation stakeholders partly abandoned the volume coupling approach they initially believed to be a viable alternative to price coupling.electricity, transmission, congestion management, market coupling
Vibration of Bundled Conductors Following Ice Shedding
No full textThe dynamic behavior of bundled conductors following ice shedding from one subconductor is examined numerically using the finite-element method. An existing model of ice shedding from a single conductor is improved by developing a model of spacers which connect subconductors in the span. The resulting system makes it possible to simulate vibrations following ice shedding from one span of an overhead transmission line with twin, triple, or quad bundles. Vibration characteristics are evaluated as the following parameters are varied: thickness of shed ice, distance between adjacent spacers, and number of subconductors in the bundle. Simulation results will provide information on how the amplitude of vibration and the transient dynamic forces change with the application of spacers. The maximum jump height of the ice-shedding cable, the maximum drop of the loaded cable, and the maximum cable tension are approximated as power functions of ice thickness and the distance between adjacent spacers
A cascade of autoresonances in an accelerating elevator cable system
No full textIn this project the transversal vibrations of an accelerating elevator cable system are studied, with the aim to find the resonance times, the resonance duration and the resonance amplitude. The elevator cable is modelled as an axially moving string, with length given by l(t) = l0 + 1/2 at2, with a the acceleration and t the time. The cable is sinusoidally excited at the top and fixed at the bottom. It is assumed that the axial acceleration is small compared to the transversal acceleration, that the cable mass is small compared to the car mass, and that the excitation amplitude is small compared to the length of the cable. Using these estimations, the solution for the transversal displacement u is approximated up to O(ε) with ε a small parameter. The elevator cable goes through a cascade of autoresonances: the eigenfrequencies of the cable are varying because the cable length is varying, and at several times an eigenfrequency matches the excitation frequency. These are the resonance times, and they have been found as t+ = (2/εa1l0)1/2arccos((Ωl0/χk)1/2), with t+ a measure of oscillation of t, Ω the angular excitation frequency, l0 the initial length, χk the eigenfrequency of mode k and εa1 = a. The duration of the resonances (the timescale) is shown to be O(ε-1/4) if χk≠Ωl0 and O(ε-1/6) if χk=Ωl0 (a bifurcation of the problem). The amplitude scale is thus O(ε3/4) or O(ε5/6), respectively, and solutions for the amplitude are calculated both outside and inside the resonance zone. TWN3002Applied Mathematics | Applied Physic
Nonlinear Model Reduction of Cable Slab Dynamics
No full textIn high precision motion systems, rather flexible cable slabs provide electrical power and cooling liquid to moving stages. The positioning accuracy of free floating stages is defined by the disturbances action on it. So, it is of utmost importance to accurately quantify the disturbance forces of these cables. The mathematical model of such a structure must feature geometric nonlinearities. The computational cost of such a model is often prohibitive, therefore nonlinear reduction techniques are needed. This contribution introduces a newly developed reduction technique known as the Generalized Craig Bampton (GCB) method which is an extension of the well-known Craig Bampton reduction technique, applicable to finite deformations. The GCB expressions are integrated using a two stage offline-online integration scheme which achieves near real time simulation during the online stage. The method is compared with both the fully nonlinear model and experimental results and is seen to show a good agreement with both.Engineering MechanicsPrecision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Modeling Ice Shedding Propagation on Transmission Lines with or without Interphase Spacers
No full textIce shedding propagation on a single conductor and on a circuit of three conductors in a vertical configuration where conductors are linked with interphase spacers was modeled numerically. Several concentrated loads acting along the loaded span modeled the ice, and the shedding propagation was then simulated through the removal in a defined sequence of these concentrated loads. The model determines conductor displacement and the variation of conductor tension during the vibration following ice shedding propagation; and, thus, it predicts conductor rebound height, tension peak, and to what extent the conductor clearance is reduced during vibration. Ice shedding propagation on the full-scale test line of Hydro-Quebec was considered, and the model was validated by comparing simulation results to former experimental observations. The results show that the application of spacers reduces the severity of vibration considerably, and consequently increases the conductor clearance and reduces the risk of flashover. The dynamic effects of different shedding processes were also compared. The rebound height is the greatest for a single conductor when ice detachment propagates along the conductor, but then ice falls suddenly as a big chunk. However, the consequences of sudden detachment and shedding are obtained as the most severe when conductors are linked with spacers
On boundary damping to reduce the rain–wind oscillations of an inclined cable with small bending stiffness
No full textIn this paper, a model will be derived to describe the rain–wind-induced oscillations of an inclined cable. Water rivulets running along the cable and aerodynamics forces acting on the cable are taken into account to describe these oscillations. A boundary damper is assumed to be present near the lower endpoint of the cable. For a linearly formulated initial-boundary value problem for a tensioned beam equation describing the in-plane transversal oscillations of the cable, the effectiveness of this damper is determined by using a two-timescales perturbation method. It is shown how mode interactions play an important role in the dynamic behaviour of the cable system. Some resonant and non-resonant cases have been studied in detail.Mathematical Physic
Real-time numerical modeling of subsea cable dynamics – Visualized in Augmented Reality
No full textThere lies an opportunity for significant cost savings in the installation of subsea cables in offshore wind farms which is why the current work proposes a state-of-the-art method for monitoring the cable during installation. The proposed method enables offshore crew to look through the water with the use of augmented reality. To this end a real-time numerical model of the subsea cable dynamics is developed. The model is created in programming language C# and visualization in augmented reality is done using the game-engine Unity. This development environment is uncommon for engineering and scientific purposes and has been selected based on its ability to visualize model results in augmented reality, its extensive graphics library, its capability to process real-time in- and outputs and its free availability. Relevant physics are analyzed on contribution to global cable geometry and tension for the case of shallow water cable laying, resulting in an equation of motion which is sufficiently accurate for representing the physical phenomena occurring during cable lay. An assessment of the measurements required by the model during operation is made. The main challenge of modeling in real-time is that the average model time step is limited by available computational power, in turn limiting the axial stiffness range which can be modeled without the occurrence of numerical instability. Discretization is done using a lumped mass method. It is shown that cable dynamics can be modeled in real-time using an explicit method and that overcoming the associated limitation on axial stiffness does not lead to inaccurate results. The developed numerical solution is verified using OrcaFlex, which is typical software for dynamic analysis of offshore marine systems. An augmented reality interface is developed, including color codes indicating the structural state of the cable. The current work enables the visualization of the real-time model in augmented reality. Potential legal issues related to the implementation of augmented reality during offshore cable lay are outlined during a collaboration with Tilburg University. Successful practical implementation of the proposed innovation is associated with promising opportunities
Investigation of the dynamic behavior of a cable-harnessed structure
No full textTo obtain predictive modeling of a spacecraft, the author investigates the effects of adding cables to a simple structure with the goal of developing an understanding of how cables interacting with a structure. In this research, the author presents predictive and accurate modeling of a cable-harnessed structure by means of the Spectral Element Method (SEM). A double beam model is used to emulate a cable-harnessed structure. SEM modeling can define the location and the number of connections between the two beams in a convenient fashion. The proposed modeling is applied and compared with the conventional FEM. The modeling approach was compared to and validated by measurement data. The validated modeling was implemented to investigate the effect of the number of connections, of the spring stiffness of interconnections, and of mass portion of an attached cable. Damping has an important role in structural design because it reduces the dynamic response, thereby avoiding excessive deflection or stress, fatigue loads, and settling times. Experimental results with some specimens indicate a clear change of damping on the main structure with the inclusion of cable dynamics. The author investigated the modification of the damping of the host structure induced by various attached cables. The identification of a damping matrix is performed using measured data. The effect of the flexibility of a cable harness on damping is observed through experiments with various types of cables. The effect of the number of connections on damping is also investigated by changing the number of connections. Moreover, to overcome the sensitivity to noise in measured data of damping matrix identification approach, various methods are compared with a simulated lumped model and real test results. An improved damping matrix identification approach is proposed and can generate the unique damping matrix over the full frequency range of interest.Ph. D
Modelling Cable and Pipe Failures from Excavation Works
No full textCables and pipes are critical infrastructure systems (CISs) which are mostly located in the very crowded subsurface. Especially in urban areas, a typical road includes five to ten infrastructure systems which are all owned and managed by different entities. The CISs are spatially interdependent as these are highly interconnected due to the close spatial proximity. Despite the critical function of cables and pipes, over 30,000 cable and pipe failures from excavation works are reported in the Netherlands yearly. Multiple studies have been conducted to reduce the risk of excavation damage. These studies have mainly focused on the impact side. Remarkable as from an extensive cooperation between the network operators and other stakeholders, a guideline (CROW500) was formed that seeks to prevent cable and pipe damage from excavation works.The objective of this thesis is to develop a model to accurately predict cable and pipe failures from excavation works, considering spatial interdependencies. The associated research question is: “What method can predict the influence of spatial interdependencies on the probability of failure from excavation works on the cables and pipes of subsurface utility operators?”Predictive analyses are frequently used for enhanced decision making by subsurface utility operators, whereby cable and pipe failures, having large impact in this sector, are relatively rare. This thesis explores the possibilities of modelling rare event data within the subsurface utility industry, through which specific situations, such as failures from excavation works, can be considered. A case study within Evides Water Company was conducted whereby 107,000 non-failures and 180 failures from excavation works were collected. In terms of statistical techniques, alternative models to logistic regression and Bayesian logistic are considered. Two approaches, involving weighting and synthetic minority oversampling have been examined to compensate the imbalanced classifiers in the data set. Balancing is done by over-, under sampling, as well as by weighting, which aim to increase the accuracy of the models. At algorithm level, under sampling and weighting combined were tested and found to improve the balanced accuracy to 0.66 with 0.38 of the failures predicted. At data level, over and under sampling by SMOTE resulted in 0.58 of failures predicted and a balanced accuracy of 0.61. These results proved that logistic regression for network operators can predict failures in specific situations with reasonable accuracy.Civil Engineering | Construction Management and Engineerin
Transportation of Cable Suspended Load using Unmanned Aerial Vehicles: A Real-time Model Predictive Control approach
No full textUnmanned Aerial Vehicles (UAV) have received an increasing amount of attention recently with many applications being actively investigated across the globe, and several related open research questions being actively pursued. Possible applications include search and rescue, disaster relief, environmental monitoring and surveillance, transportation, and construction. Transportation of cable suspended payloads using Unmanned Aerial Vehicles is one such application which is the topic of this research. Autonomous transportation of objects using UAV can contribute to the safe and reliable supply of food and medicine in remote or disaster-affected areas and even in commercial delivery of goods. The state-of-the-art approaches towards the slung load transportation either develop non-linear feedback control laws to stabilize the system to a predefined trajectory or employ open loop off-line trajectory planning schemes to generate optimal control inputs to the system. Most of these techniques often rely on availability of an accurate model of the system backed up with simulation results. Very few results exist which target experimental validation of the proposed method. Based on the findings of the previously conducted literature survey, it appears that the application of closed loop on-line trajectory generation and control schemes to transport a slung payload in swing free manner remains unanswered. The work in this thesis sets off to answer the research questions in this direction and address the issues that come along with experimental validation. Model Predictive Control (MPC) is a promising framework, which provides the means to tackle both the trajectory generation problem and the feedback control problem in an unified manner. As a result, it forms the most important component of this thesis. Specific research problem that is addressed in this thesis is to transport a cable suspended load using quadrotor from one point to another, while minimizing the swing through the use of Linear Time Invariant MPC techniques. A non-linear dynamic model for the quadrotor-slung load system is obtained and the structure within the system dynamics is exploited to decide the control strategy. Two different MPC formulations viz. MPC with integral action and MPC with delta-u formulation are simulated and compared to Linear Quadratic control with integral action which acts as a benchmark controller. Backed with simulation results, it is shown through experimental validation that it is possible to control the swing of cable suspended load using linear control techniques. MPC being an computationally expensive task, state-of-the-art fast optimization solvers such as FORCES PRO is used to achieve on-line implementation of MPC for the quadrotor-slung load system. To this end, a new software framework for implementation of MPC is developed which establishes a wireless link with the quadrotor resulting in a real-time networked control loop.Systems and ControlDelft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
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