202 research outputs found
Distributie van een grootschalig oppervlaktewaterproject; gescheiden of gemengd?: Case-study project Infiltratie Maaskant
No full textIn het Beleidsplan Drink- en Industriewatervoorziening is voor de waterleidingbedrijven in Nederland een toekomstbeeld geformuleerd waarin de inpassing van oppervlaktewater als bron voor de (drink-)watervoorziening in Nederland centraal staat. Hierbij wordt gesproken over een 'stabilisatie en optimalisatie' van de inzet van grondwater, hetgeen gemotiveerd wordt op basis van de verdrogingsproblematiek. Enkele waterleidingbedrijven in Nederland zijn derhalve al enige tijd bezig grootschalige projecten te realiseren waarbij de grootste zorg uitgaat naar het bereiden van goed drinkwater uit veelal verontreinigd oppervlaktewater. De grootschaligheid van deze projecten is noodzakelijk vanwege de hoge kosten die gemoeid zijn bij de geavanceerde zuiveringstechnieken die hierbij nodig zijn. Deze technieken kunnen pas rendabel gemaakt worden bij grote te behandelen volumestromen. Hoe moeten echter deze grootschalige oppervlaktewaterprojecten ingepast worden in de distributiestructuur van de veelal van oudsher uit grondwater leverende drinkwaterbedrijven? Gescheiden of gemengde levering van drinkwater uit de twee bronnen, oppervlaktewater en grondwater, is een hierbij een belangrijke optredende vraag. In het kader van deze studie is deze problematiek voor de inpassing van het Project Infiltratie Maaskant in Oost-Brabant nader onderzocht. Op basis van een aantal alternatieven die ieder getypeerd worden door kenmerken van een bepaald 'distributieprincipe' (gescheiden of gemengd), is getracht een uitspraak te doen over de gewenste structuur voor de distributie van het oppervlaktewater. Naast kosten spelen hierin kwaliteit van het (meng)produkt, leveringszekerheid, inpasbaarheid in de bestaande infrastructuur en flexibiliteit ten aanzien van de fasering een belangrijke rol. Het blijkt dat een gemengde levering verschillende voordelen heeft. Hierin speelt de optimalisatie van de grondwateronttrekkingen (zoals gesteld in het BDIV) een belangrijke rol. Deze kunnen namelijk zonder concessies te doen aan de totale jaarlijkse onttrekking een grote rol vervullen in het optimaliseren van de in te passen oppervlaktewaterzuivering. Hierbij is een sleutelrol weggelegd voor het reduceren van de piekfactoren van de levering uit het oppervlaktewater. De pieken die slechts een aantal dagen per jaar voorkomen kunnen tegen lagere kosten door het grondwatersysteem opgevangen worden. Bij de inpassing van PIM blijkt een piekfactorreductie voor de levering vanuit het oppervlaktewater van 1,72 naar gemiddeld 1,32 mogelijk te zijn. Dit heeft zowel lagere investeringskosten voor de zuivering als voor het transportsysteem tot gevolg. Globaal berekend kan hierdoor op het Project Infiltratie Maaskant 80 miljoen gulden aan investeringskosten worden bespaard. Verder blijkt het gemengd inpassen van het PIM-water gunstige gevolgen te hebben op de leveringszekerheid, op de kwaliteit, op de aansluiting bij de bestaande infrastructuur en op de flexibiliteit ten aanzien van de gefaseerde inpassing.Water ManagementCivil Engineering and Geoscience
The Randstad conurbation: a floating metropolis in the Dutch delta (co-author Paul van der Laar)
No full textThe Randstad conurbation: a floating metropolis in the Dutch delta (co-author Paul van der Laar)
The Randstad conurbation: a floating metropolis in the Dutch delta (co-author Paul van der Laar)
Eolisch sediment transport
No full textIn dit verslag is een eolisch sedimenttransport model geformuleerd en het model van De Vries geïmplementeerd en geanalyseerd. Na de afleiding van de eendimensionale advectie-diffusievergelijking vanuit de driedimensionale continuïteitsvergelijking is eerst het model van De Vries zonder diffusie onderzocht. In het model kan er onderscheid gemaakt worden tussen 3 verschillende situaties: Geen (toevoer van) sediment, Sediment-gelimiteerd en Erosie-gelimiteerd. In elke situatie zijn voor lange tijd\-schalen de toestanden van het model afgeleid vanuit de advectievergelijking. In de resultaten kwam naar boven dat de theoretische toestanden sterk overeenkwamen met de toestanden in de numerieke simulatie. Verder is het effect van numerieke diffusie van het model van De Vries geconstateerd en de grootte van dit effect afgeleid. Om het effect van numerieke diffusie te verminderen is diffusie in het model geïntroduceerd samen met het Lax-Wendroff numerieke schema. Dit schema gebruikt de gewogen upwind methode samen met de gewogen centrale Euler methode om de nauwkeurigheid van het model te verbeteren. In de resultaten is aangetoond dat numerieke diffusie kan worden gecompenseerd door het juist kiezen van dit gewicht. Uit een stabiliteitsanalyse blijkt dat de Lax-Wendorff methode een betere stabiliteitcriterium heeft dan de upwind methode. Hierdoor kan een grotere tijdstap gekozen in een numerieke simulatie. De maximale tijdstap is getest door het model te runnen met verschillende tijdstappen rondom het theoretische maximum. Uit de resultaten bleek dat het model op tijdstap die een fractie kleiner was dan de theoretische maximale tijdstap, stabiele oplossingen simuleerde. Zodra de tijdstap de maximale waarde behaalde werden de oplossingen instabiel. Door het toevoegen van diffusie aan het model is een extra voorgeschreven randvoorwaarde nodig. Door implementatie van verschillende randvoorwaarden aan het einde van het domein is gebleken dat de randvoorwaarde 'extrapoleren tweede orde' het best is. De dimensie-analyse van de advectie-diffusievergelijking wijst uit de eolischsedimenttransport gedomineerd wordt door advectief transport en het effect van diffusie verwaarloosd mag worden.Applied Mathematics | Applied Physic
Improved risk management in infrastructural construction projects: Improved accuracy and precision within the risk reserve, based on the project's risk profile determined through the unique character of infrastructural projects
No full textCivil Engineering | Construction Management and Engineerin
The dynamic response of a wind turbine blade to downwind tower shadow
No full textThe quest for affordable renewable energy causes the need for bigger and more efficient wind turbines. To counter the problem of possible collisions between the growing turbine blades and the tower support structure, downwind turbines might be a solution. For this configuration, blade flexibility no longer forms a problem and besides that passive yaw systems can be applied. However, the fatigue lifetime of the turbine components might significantly decrease due to tower shadow effects. This thesis aims to decrease the uncertainty in the difference between downwind turbines and the conventional upwind turbines. An aeroelastic blade model is constructed using a finite element model of the NREL 5MW turbine blade. This model is subsequently converted to a downwind model including a wake behind the tower structure that temporarily slows down the inflowing wind on the blade when the blade is in the tower shadow area. This wake description follows from a literature review and should be valid for the flow conditions around the turbine. History dependency of the aerodynamic forces on the blades is included in the model using the Küssner function. A comparison in tower wake effects is done using simulations of upwind and downwind turbine blades which result in the blade motions caused by the tower shadow disturbance. From these motions also the root moments are deduced over time as well as the angle of attack variations for the different blade elements. A comparison with other software confirms the order of magnitude of the blade position in equilibrium and a check for dynamic stall issues is done to show the possible influence on the blade lift after the tower shadow disturbance. The root moment variations are used as a fatigue indicator using rainflow analysis. Concluding from this, wind velocities near cut-out speed for downwind turbines cause the biggest wake effects. The static blade deflections and root moments are at the highest for rated wind speed at upwind turbines. Compared to upwind turbines, the downwind turbines are prone to higher wake effects and therefore increased fatigue damage. The overturning root moment and flapwise deflection variations for downwind turbine blade have shown to be up to 88 % and 100 % higher compared to those for upwind turbines respectively
Maintenance Offshore Wind: Feasibility study into alternative lifting systems for offshore wind turbine maintenance operations
No full textIn the transition from a fossil fuel driven economy to renewable solutions, the activities in offshore wind energy are growing. Operation and maintenance costs of offshore wind turbines are high, therefore alternative methods should be developed to reduce these costs. The replacement of heavy components, like a gearbox or a generator, is a frequently occurring operation that can be improved.Currently the replacement of these components is performed by a jack-up crane vessel which has two downsides: (1) long mobilization time and (2) high operational costs. The development of systems that can replace heavy components can contribute to reduce the maintenance costs of offshore wind turbines.Therefore in the first part of this thesis, developments and techniques were investigated which can do so. It was observed that different types of solutions are already available for onshore maintenance purposes like the crane developed by Liftra and the Gamesa flexifit. Furthermore new concepts are being developed by the wind turbine manufacturer Vestas and Anson, a Chinese crane builder. These developments are addressing the problem of reducing the maintenance costs, but still two important downsides are present: (1) insufficient lifting capacity for gearbox replacement and (2) most systems are designed to be used on specific turbines. The current developments and available techniques were studied to generate concepts that can address these shortcomings. This resulted in a promising solution where a relatively small crane is installed on the wind turbine tower from a floating vessel. A great advantage over currently used method is that no specialised maintenance vessel is required for a gearbox replacement and thereby costs and time can be saved. This crane is attached to the tower structure by use of a clamping mechanism and is kept in position by generating frictional force. To generate this force, hydraulic cylinders are pressing the pads (contact surfaces of the clamp) against the tower structure. For the applicability of this concept it is of major importance that the structural integrity of the tower is maintained, while sufficient frictional force is generated to avoid the crane from slipping down during lifting operations. Therefore, in the second part of this thesis a feasibility study is done on the application of this clamping mechanism on wind turbine towers. By use of finite element modelling a workable contact surface configuration of this clamping mechanism was found. The following four variables were studied: (1) elasticity of the contact layer, (2) number of pads used, (3) width and (4) height of the pads. The latter three relate to the contact surface area and the elasticity of the contact layer influences the distribution of the forces from the clamp to the tower structure. Investigating these variables, it was concluded that; the proposed solution should have a contact layer where the elasticity modulus is higher than 1200 Mpa. By adding more pads, the loading capacity increases. However, it also results in a more complex structure and therefore it is advised to reduce the number of pads and instead widen them. Considering this trade off, a four pad configuration is selected to determine the required width and height of the pad. For this set-up it is advised to use a pad width of eighty degrees and pad height of three meter to meet the requirement of replacing the gearbox, the heaviest component of the wind turbine powertrain. Furthermore, to assure this clamping mechanism works on towers of different dimensions (i.e. diameter and wall thickness combinations), the loading capacity was determined for a variety of tower dimensions. By doing so, insights are gathered on the application of this clamping mechanism on different turbines. To make the data useful for further application, tables are included which indicate the loading capacity for investigated wind turbine towers. Offshore and Dredging Engineerin
Optimization of the efficiency of tandem solar cellsusing simulated annealing
No full textIn this thesis, a simulated annealing algorithm is implemented to optimize the efficiency of a tandem solar cell. The efficiency of a tandem solar cell is approximated by the current of the tandem solar cell. This current is determined by the simulation program GenPro4. Firstly, the general concepts of simulated annealing is described. After understanding these concepts, a simulated annealing algorithm is implemented for our specific problem. This algorithm includes the handling of discrete variables which describe the structure of the solar cell. The results contain multiple variants of the newly implemented simulated annealing algorithm, which differ in the used temperature schedule. Finally, a conclusion is made that a temperature schedule with a slower convergence gives the best results. However, one should consider a slightly faster convergence whenever there is a need to reduce the computational time. Moreover, one should write their own implementation of a simulated annealing algorithm when dealing with discrete variables, thus not use the provided function of MATLAB.Applied Mathematic
Definition and Response Validation of a Simplified Aero-Servo-Elastic Wind Turbine Model
No full textCurrently, the foundation design of offshore wind turbines is based on a simple cantilever beam model with a mass representing the rotor and nacelle, or by making use of wind turbine simulation software such as Bladed, which are built for rotor design. The simple models are unrealistic since the dynamic interaction between the aerodynamic loads, hydrodynamic loads, control system and the structure is not included which leads to a lack of understanding of the behavior of the structure and possibly a poor design. The simulation software models, on the other hand, require input that the wind turbine designing party is not willing to provide, are computationally expensive, and since these are 'black box' models, give no insight into the system. In between these methods, there is currently unoccupied room for a hybrid model which includes relatively advanced rotor aerodynamics but remains computationally inexpensive while providing good insight into the behavior of the system.This thesis aims to define such a model based on modification of models present in literature and validate it by comparing its behavior to commercial wind turbine design software. First, a model of only the rotor with a rigid frictionless drivetrain shaft and blade pitch control system (the model restricts itself to the above rated regime) is considered and validated by comparison with Bladed. The blades of the rotor are assumed to be identical and rigid, the flow is assumed to be attached and the wind velocity field is uniform and has only one directional component. The effect of the use of different wake models is tested and it is concluded that for a step wind input the equilibrium wake model is most suited, while for a turbulent wind input the dynamic wake model is the best option. Simplification of the model results in the conclusion that the lift and drag coefficients can be evaluated for the mean wind velocity and chosen to be time independent without having any significant effect, while the induction factor cannot be chosen to be time independent without it significantly affecting the behavior of the model. The aerodynamic torque is linearized with respect to wind velocity, rotational rotor velocity, pitch angle and induction factor, which results in an acceptable approximation while the operating conditions are within reasonable proximity of the chosen mean operation state. Afterwards, a tower structure and flexible drivetrain shaft are added to the model, which again is validated by using Bladed. Frequency domain analysis shows that the tower motions of both the model and Bladed are similar, thus validating the model. The aerodynamic excitation is linearized with respect to wind velocity, structural motion, rotational rotor velocity, pitch angle and induction factor and applied to the model including a tower structure and flexible drivetrain shaft. Lastly, it is concluded that after simplification of the model and linearization of the aerodynamic excitation the model results in a good approximation of the wind turbine simulation software.Offshore and Dredging Engineerin
The Interplay between the Contract Type and the Management of Cost Groups: Exploring the relationship between the contract type and the management of cost groups in Dutch national infrastructure projects
No full textConstruction projects are argued to be the most complex of all production undertakings (Baccarini, 1996). Williams (2002, 2005) states that the complexity of these projects is a contributing factor to project failures, such as cost overrun, which are commonly seen in infrastructure project (Cantarelli, Molin, Van Wee, & Flyvbjerg, 2012). As one of the first Morris & Hough (1988) describe that cost overruns are common and that many projects appear as failures, while Flyvbjerg et al. (2003) agrees with Morris & Hough, by stating that this is a long-lasting problem since cost estimates have not improved and cost escalations have not decreased in the past 70 years. However, between the 1990s and 2000s, western governments were reassessed and more tasks were privatized (England & Ward, 2007; Pollit & van Thiel, 2007). Governments expected that private contractors would be able to innovate more, deliver quicker, reduce costs, and operate more efficient (Savas, 2000) resulting in integrated contract types. This research aims to provide insight into the relationship between the contract type and the management of cost groups, in Dutch national infrastructure projects in order to improve cost management. To provide an answer to the main research question, a literature study has been performed followed by a statistical analysis of 68 infrastructure projects with contract types including, RAW (n=24), E&C (n=22), and D&B(M) (n=22). Combined with the expectations of the expert panel this study concludes that there is no relation between the contract types RAW, E&C, and D&B(M) and the cost management of Dutch national infrastructure projects. However, it has been observed that project members of a contractor overestimate the relationship that D&B(M) projects should have higher cost overruns. This study concludes that the cost performance, of cost groups other than engineering, differ insignificantly and marginally small between contract types with varying design responsibilities. Moreover, the expert panel assumes that more information leads to less uncertainty and risks resulting in less cost overruns. Which is a common reasoning as stated in the GWW market analysis performed by McKinsey. However, this study concludes that the unavailability of information depending on the moment of contracting does not have an influence on the uncertainty of the cost performance nor the cost performance itself. Therefore, this study does not believe that the “two-phase-process” as proposed by McKinsey will contribute to less uncertainty about the cost performance. Instead, this study illustrates that Dura Vermeer confidently applies percentages to estimate relatively small, often process-related indirect cost groups which on average incur a cost overrun. Therefore, both the client and contractor should improve the process of constructing large complex infrastructure projects in order to improve the cost performance.Civil Engineering | Construction Management and Engineerin
Multi-Machine Scheduling Lower Bounds Using Decision Diagrams
No full textWe investigate the use of relaxed decision diagrams for obtaining lower bounds on multi-machine scheduling problems. The type of scheduling problem we consider models a railway service site where maintenance jobs are performed, but is sufficiently general to potentially have wider applicability.We find that our decision diagram formulation is able to give decent lower bounds in short time. Our implementation is competitive with lower bounds given by existing solvers, and is superior when due times are small and have small variance. Further, we find that our model greatly improves upon a naive extension of the state of the art for single-machine scheduling [23].Computer Science | Software Technolog
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