The Experts below are selected from a list of 438 Experts worldwide ranked by ideXlab platform
Abgottspon Hubert - One of the best experts on this subject based on the ideXlab platform.
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Short-term hydro scheduling of a variable speed pumped storage hydropower plant considering head loss in a shared penstock
IoP, 2019Co-Authors: Kong Jiehong, Skjelbred, Hans Ivar, Abgottspon HubertAbstract:In this paper we present in detail how to handle the nonlinear and state-dependent elements in the power consumption function (PCF) of a variable speed pump (VP). The function is formulated by piecewise linear approximations with dynamically specified breakpoints. In the proposed method, the head variation resulting from the change in the water level of the upstream and downstream reservoirs and head loss caused by the friction of water on the penstock wall are both considered. Furthermore, we put forward a heuristic to incorporate the head loss in a penstock shared by multiple VPs in a short-term hydro scheduling tool used for daily operation in the real world. The case study is taken from the Limmern pumped storage hydropower plant with 4×250 MW reversible Francis pump-turbines with variable speed technology. Each penstock is shared by two of the four units. The numerical results demonstrate that the appropriate formulation of the PCF and the accurate representation of the head loss in a shared penstock are crucial for obtaining realistic and optimal scheduling for VPs
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Short-term hydro scheduling of a variable speed pumped storage hydropower plant considering head loss in a shared penstock
'IOP Publishing', 2019Co-Authors: Kong Jiehong, Skjelbred, Hans Ivar, Abgottspon HubertAbstract:In this paper we present in detail how to handle the nonlinear and state-dependent elements in the power consumption function (PCF) of a variable speed pump (VP). The function is formulated by piecewise linear approximations with dynamically specified breakpoints. In the proposed method, the head variation resulting from the change in the water level of the upstream and downstream reservoirs and head loss caused by the friction of water on the penstock wall are both considered. Furthermore, we put forward a heuristic to incorporate the head loss in a penstock shared by multiple VPs in a short-term hydro scheduling tool used for daily operation in the real world. The case study is taken from the Limmern pumped storage hydropower plant with 4×250 MW reversible Francis pump-turbines with variable speed technology. Each penstock is shared by two of the four units. The numerical results demonstrate that the appropriate formulation of the PCF and the accurate representation of the head loss in a shared penstock are crucial for obtaining realistic and optimal scheduling for VPs.Short-term hydro scheduling of a variable speed pumped storage hydropower plant considering head loss in a shared penstockpublishedVersio
Anton Schleiss - One of the best experts on this subject based on the ideXlab platform.
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stress intensity factor for single edge and buried cracks at longitudinal butt welded joints of steel Penstocks and liners
ECF21, 2016Co-Authors: Alexandre Jean Pachoud, Pedro Manso, Anton SchleissAbstract:Steel Penstocks and steel-lined pressure tunnels and shafts are the high pressure part of the waterway system which connects reservoirs to hydropower plants. The development of volatile renewable energies such as solar and wind induces harsher dynamic water pressures in Penstocks and pressure shafts, particularly for pumped-storage power plants which are used to balance the electricity grid. The development of high-strength steels has allowed thinner and therefore more economic liners. Nevertheless, welded high-strength steels do not provide higher fatigue resistance and are more sensitive to hydrogen-induced cracking. In this context, the fracture mechanics assessment of fatigue life of steel Penstocks becomes a major concern for new and existing power plants under severe and hasher operation conditions. In order to estimate fatigue life using fracture mechanics approach, the stress intensity factors (SIFs) must be known. Some formulas are available in literature for cracks in plated steel structures, cylinders and welds. However, most of them have restricted ranges of applications, and the influence of some parameters is not clarified. No specific methodology exists to estimate SIFs at longitudinal butt welded joints of steel Penstocks and steel liners. In this study, a systematic parametric study of SIFs for single-edge and buried cracks at longitudinal butt welded joints is performed by means of Finite Element Analysis (FEA) over geometrical ranges of steel Penstocks. Weld parameters such as internal radius, thickness, ovality, roof-topping, linear misalignment, weld reinforcement, weld length and weld notch angle are considered. The FEA includes large-deflection effects. Results are compared with published results and commonly used formulas for SIFs of cracks in plated structures and welds. This study provides designers with new insights regarding fracture mechanics approach for fatigue life estimation of steel Penstocks and steel liners.
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A review of wave celerity in frictionless and axisymmetrical steel-lined pressure tunnels
Journal of Fluids and Structures, 2011Co-Authors: Fadi Hachem, Anton SchleissAbstract:Generally applicable approaches for estimating the‘‘quasi-static’’, which means without fluid–structure interaction and frequency-dependent water-hammer wave speed in steel-lined pressure tunnels are analyzed. The external constraints and assumptions of these approaches are discussed in detail. The reformulated formulas are then compared to commonly used expressions. Some special cases of wave speed calculation such as unlined pressure tunnels and open-air Penstocks are investigated. The quasi-static wave speed is significantly influenced by the state of the back fill concrete and the near-field rock zone (crackedoruncracked). In the case when the set wo layers are cracked, the quasi-static wave speed is over estimated in between 1% and 8%compared to uncracked concrete and near field rocklayers. Depending on the stiff ness of steel liner and penstock, the fluid–structure interaction leads to significant difference in wave speeds values. Compared to the quasi-staticcase, the fluid–structure interaction approach, applied to steel-lined tunnels, results up to 13%higher wave speed values in the high-frequency range (higher than 600Hz)and up to 150% lower values for frequencies between 150 and 300 Hz in the considered test case.
Kong Jiehong - One of the best experts on this subject based on the ideXlab platform.
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Short-term hydro scheduling of a variable speed pumped storage hydropower plant considering head loss in a shared penstock
IoP, 2019Co-Authors: Kong Jiehong, Skjelbred, Hans Ivar, Abgottspon HubertAbstract:In this paper we present in detail how to handle the nonlinear and state-dependent elements in the power consumption function (PCF) of a variable speed pump (VP). The function is formulated by piecewise linear approximations with dynamically specified breakpoints. In the proposed method, the head variation resulting from the change in the water level of the upstream and downstream reservoirs and head loss caused by the friction of water on the penstock wall are both considered. Furthermore, we put forward a heuristic to incorporate the head loss in a penstock shared by multiple VPs in a short-term hydro scheduling tool used for daily operation in the real world. The case study is taken from the Limmern pumped storage hydropower plant with 4×250 MW reversible Francis pump-turbines with variable speed technology. Each penstock is shared by two of the four units. The numerical results demonstrate that the appropriate formulation of the PCF and the accurate representation of the head loss in a shared penstock are crucial for obtaining realistic and optimal scheduling for VPs
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Short-term hydro scheduling of a variable speed pumped storage hydropower plant considering head loss in a shared penstock
'IOP Publishing', 2019Co-Authors: Kong Jiehong, Skjelbred, Hans Ivar, Abgottspon HubertAbstract:In this paper we present in detail how to handle the nonlinear and state-dependent elements in the power consumption function (PCF) of a variable speed pump (VP). The function is formulated by piecewise linear approximations with dynamically specified breakpoints. In the proposed method, the head variation resulting from the change in the water level of the upstream and downstream reservoirs and head loss caused by the friction of water on the penstock wall are both considered. Furthermore, we put forward a heuristic to incorporate the head loss in a penstock shared by multiple VPs in a short-term hydro scheduling tool used for daily operation in the real world. The case study is taken from the Limmern pumped storage hydropower plant with 4×250 MW reversible Francis pump-turbines with variable speed technology. Each penstock is shared by two of the four units. The numerical results demonstrate that the appropriate formulation of the PCF and the accurate representation of the head loss in a shared penstock are crucial for obtaining realistic and optimal scheduling for VPs.Short-term hydro scheduling of a variable speed pumped storage hydropower plant considering head loss in a shared penstockpublishedVersio
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Dynamic incorporation of nonlinearity into MILP formulation for short-term hydro scheduling
'Elsevier BV', 2019Co-Authors: Skjelbred, Hans Ivar, Kong Jiehong, Fosso, Olav BAbstract:Optimization tools are widely used for solving the short-term hydro scheduling (STHS) problem in a cascaded hydro system. In a mixed integer linear programming (MILP)-based formulation, the nonlinear and non-convex hydropower production function (HPF) is represented by piecewise linear approximation. However, instead of using a set of predefined curves with static breakpoints or a preprocessing phase to define the complete relationship between the power output, the net head, and the water discharge, this paper proposes a novel method in which the breakpoints in the linearization are determined dynamically, taking into account the time-varying head effect, intake loss, penstock loss, tailrace loss, and head-dependent turbine efficiency. Only one binary variable is needed to indicate the on/off status and power generation of a unit per period. Furthermore, there are few studies available on how to represent the HPF precisely for the hydraulic system where Penstocks are shared by multiple generating units. In this paper, we investigate three heuristics to explicitly incorporate the nonlinear and state-dependent power loss in shared Penstocks into the STHS problem. The method and heuristics have been implemented in an operational STHS tool used by many hydropower producers in Nordic countries. We use a simple hydro system to illustrate the method and heuristics and a real hydro system in Northern Norway to study calculation efficiency and solution quality. The numerical results indicate that the proposed method can precisely represent the head-dependent and nonlinear operating characteristics of the generating units. The accurate modeling of a system with multi-level shared penstock configurations is crucial for obtaining the optimal unit commitment. The heuristics can effectively handle the power loss in shared penstock in various operating conditions. © 2019 Elsevier Lt
Shi He Qin - One of the best experts on this subject based on the ideXlab platform.
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influence of concrete tension softening properties on the steel liner reinforced concrete penstock
Applied Mechanics and Materials, 2013Co-Authors: Shi He QinAbstract:In combination with the practice of a large hydropower station, concrete damaged plasticity model is introduced into the steel-liner reinforced concrete penstock for the nonlinear analysis, the damage distribution rules of the surrounding concrete and the stresses of the steels are furtherly studied under the different tension softening characteristic curves, the conclusions can provide the reference for damage assessment of the surrounding concrete and the optimization allocation of the reinforcement for the penstock.
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nonlinear fem analysis of the steel liner reinforced concrete penstock considering softening effect
Applied Mechanics and Materials, 2012Co-Authors: Shi He QinAbstract:In combination with the practice of a hydropower station steel-liner reinforced concrete penstock, the finite element model is established to analyze bearing characteristics of the penstock. In the paper, cracking behaviors of the surrounding concrete as well as stresses of the steel liner and reinforcement under normal water pressure are intensively studied based on the model test. The results can provide the basis for the safety operation of the steel-liner reinforced concrete penstock.
Aydogan Ozdamar - One of the best experts on this subject based on the ideXlab platform.
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numerical and experimental investigation of optimum surge tank forms in hydroelectric power plants
Renewable Energy, 2013Co-Authors: Tarik Efe Kendir, Aydogan OzdamarAbstract:Abstract Load changes occurring in water turbines often result in pressure waves at hydroelectric power plants. Load reduction or the sudden closure of the turbines causes high pressures to build on the penstock similarly to a water hammer. This pressure can cause damage to components of the power plant. Surge tanks are used to prevent these problems. For two power plants operating at similar flow rates, diameters and lengths of the Penstocks, and diameters and lengths of the tunnels, the surge tank with a smaller volume is the most economically viable. The purpose of this study is to obtain an optimised surge tank configuration to reduce the cost of a hydropower plant in the future. Two methods were used for determining the optimum tank form: characteristic and finite difference methods (for the rigid and elastic method/approach). In addition, frictional losses and velocity loads inside the pipes and surge tanks were examined for different surge tank configurations in this study. In this paper, economically optimised surge tanks used for hydroelectric power plants were investigated. For this purpose, four basic surge-tank systems were numerically investigated. A 2° inclined straight V-type surge tank was found to be the most optimum configuration. Both rigid and elastic water column calculation methods were used for this study. Following this approach, an experimental model of a hydroelectric power plant with an optimised surge tank was created based on the model. This experimental model and prototype were numerically investigated. Finally, the results were compared and were found to be in agreement.