IOP Conference Series: Earth and Environmental Science
Refurbishment and upgrading of ageing hydropower plants contribute to increase of renewable energ... more Refurbishment and upgrading of ageing hydropower plants contribute to increase of renewable energy share in modern electrical grid systems. The potential increase of discharge and flexibility of load variation may result in much higher dynamic loads on both refurbished and non-refurbished plant components during transient operating events. First, water hammer control strategies are outlined including operational scenarios, surge control devices, redesign of the pipeline components, or limitation of operating conditions. Water hammer models and solutions are briefly discussed in the light of their capability, availability and uncertainty. The core of the paper is devoted to investigations of water hammer effects in a high-head hydropower plant Piva, Montenegro which is currently in the final phase of refurbishment. The flow-passage system of the Piva HPP is comprised of the intake structure, followed by three parallel penstocks each with Francis type water turbine at the downstream e...
Several comparative studies in this work were carried out with the help of the method of characte... more Several comparative studies in this work were carried out with the help of the method of characteristics. This numerical method is the most effective for solving a system of partial equations (hyperbolic type) describing a complex problem associated with the water hammer phenomenon. The numerical tests have been performed for the selected constant value of the introduced dimensionless water hammer number. The presented comparisons showed that the unsteady flows without column separation are analogous in various hydraulic systems when the value of this number has been preserved. Besides, cavitating flows with such a constant value of this number were also tested. These studies indicated the existence of another dimensionless number which was called a cavitation number. Maintaining the fixed values of both dimensionless numbers guaranteed similarity of flows in different examined systems in which cavitation occurred.
Frequency analysis of hydraulic vibrations has been applied using a transfer matrix and impedance... more Frequency analysis of hydraulic vibrations has been applied using a transfer matrix and impedance method. The computer program is given for the self-excited and forced vibrations, together with an example of self-excited vibrations in hydropower plant. The study indicates that frequency analysis makes possible detailed determination of elements which are the source of vibration and can be either eliminated or altered. The reliability of the method has been confirmed by experimental results in situ.
Double-regulated vertical axial water turbine with conical distributor, which is worldwide known ... more Double-regulated vertical axial water turbine with conical distributor, which is worldwide known as a Saxo-type turbine, is the main subject of this paper. Due to continuous research, development and improvement, advanced and compact structure, simplified civil construction works, reliability, ecological design and versatile applicability, the turbine became very recognizable product of company Litostroj Power, with over 30 successfully commissioned units in North American and Canadian market mainly. Authors see the Saxo turbine as one of the most interesting and suitable solutions for small and medium size hydro power plants. This paper aims to draw attention on this unique and interesting turbine design especially because experiences show that hydro power plant investors are somehow conservative and they mainly prefer and trust in more conventional turbine types i.e. Kaplan turbines and tubular turbines. The paper enlightens important design, hydraulic, economic and operation adva...
This paper deals with the behaviour of a hydraulic turbomachine during transients (water hammer) ... more This paper deals with the behaviour of a hydraulic turbomachine during transients (water hammer) in piping systems. A brief description of the method of characteristics and the fundamentals of transient cavitating pipe flow are given. The hydraulic turbomachine is treated as a boundary condition within the staggered grid of the method of characteristics. Case studies for a sudden load rejection of two 34-MW Francis turbines and a centrifugal pump rundown are presented. There is good agreement between the computational and the field-test results for both cases.
Valves are an indispensable element of every pipeline system (water supply, hydro power plant etc... more Valves are an indispensable element of every pipeline system (water supply, hydro power plant etc.), and their control is of great importance for the proper functioning of the system. Ball, butterfly, globe, and needle valves are usually used as flow control valves in pressurized pipe systems. Closing the valve can lead to an increase/decrease of the pressure, or water hammer, which can cause significant problems in the system in case this pressure is not maintained within prescribed limits. Depending on the generated transient events and on the installed surge protection devices, extreme pressures may compromise the pipe system safety, operation, and performance. An adequate closing law and closing time may lead to lower maximum and higher minimum pressures and increase system safety. The aim of this paper is experimental investigation of the influence of actuator pressure (the valve closure is controlled by the valve actuator) on electro-pneumatically operated valve (EPV) closure ...
A new numerical solution of transient flow simulations in viscoelastic pipes is presented, examin... more A new numerical solution of transient flow simulations in viscoelastic pipes is presented, examined, and compared with traditional solutions and experimental results. Here the viscoelastic behaviour of the pipe wall is modelled explicitly and the wall shear stress implicitly. The new solution will be able to facilitate a better understanding of the unsteady flow behaviour in a plastic pipe in water supply systems. It will also contribute to lowering the computational costs of such systems and improving the accuracy of viscoelastic pipe diagnosis such as leak detection in the future.
IOP Conference Series: Earth and Environmental Science, 2019
This paper presents recent experimental results of pressure measurements during filling and empty... more This paper presents recent experimental results of pressure measurements during filling and emptying of a relatively small-scale pipeline at the University of Montenegro. Experimental setup for investigation of water hammer and its special effects (unsteady friction, cavitation, column separation, trapped air, fluid-structure interaction - FSI), and pipeline filling and emptying is installed at the Faculty of Mechanical Engineering. It consists of an upstream end high-pressurized tank, horizontal steel pipeline (total length: 55.37 m, inner diameter: 18 mm, pipe wall thickness: 2 mm), four valve units positioned along the pipeline including the end points, and a downstream end outflow tank. The setup was upgraded in 2018 with the installation of new piezoresistive pressure transducers and pipe displacement sensors as well as additional electro-pneumatically operated ball valve at the upstream end of the pipeline. The filling of an initially empty pipeline is performed by a sudden op...
IOP Conference Series: Materials Science and Engineering, 2019
The work presents two modified cavitation models for the simulation of transient flow in pressure... more The work presents two modified cavitation models for the simulation of transient flow in pressure plastic pipes. The first model is a discrete bubble cavitation model, the prototype of which was presented by Shu, and the second one is the Adamkowski model. In the latter model, the problem encountered in the classical model (DVCM -discrete vapour cavitation model) related to artificial damping of pulsation, which results from approximate timing of cavity opening and collapse. In both models, the corrected efficient calculation of Zielke convolution integral was used to simulate the unsteady wall shear stresses. The numerical results from the two models agree well with the results of measurement in the literature.
Transient vaporous cavitating pipe flow occurs when the pressure drops to the liquid vapour press... more Transient vaporous cavitating pipe flow occurs when the pressure drops to the liquid vapour pressure. A brief description of the method of characteristics, and fundamentals of unsteady pipe flow friction and transient cavitating pipe flow are given. The main objective of this paper is to present a novel discrete gas cavity model (DGCM) with consideration of unsteady friction effects. Numerical results are compared with the results from laboratory measurements. Inclusion of unsteady friction into DGCM significantly improves numerical results.
Prehodni parni kavitacijski tok v cevi vzbudi padec tlaka na parni tlak kapljevine. Podan je kratek oris metode karakteristik, temu slede osnove nestalnega kapljevinskega trenja in prehodnega kavitacijskega toka v cevi. Glavni cilj tega prispevka je predstavitev novega plinskega kavitacijskega modela (DGCM) z upoštevanjem vplivov nestalnega trenja. Rezultati izračuna so primerjani z rezultati meritev v laboratoriju. Upoštevanje nestalnega trenja v DGCM da bolj točne računske rezultate.
This paper presents the modeling, simulation and re lated validation of water column separation i... more This paper presents the modeling, simulation and re lated validation of water column separation in hydr aulic systems. First, the modeling of hydraulic components using e lectrical analogy is introduced. This modeling is b ased on finite difference method with a centered scheme in space a nd L x scheme for discharge applied to momentum and co tinuity equations in case of a pipe filled with fluid. The resulting set of ordinary differential equations ca n be represented as a Tshaped electrical equivalent scheme. The possible t hermodynamic damping of fluid and pipe material is also introduced and the equivalent scheme is adapted consequently. The time domain numerical integration of the equati on set is performed using Runge-Kutta fourth order method. Th en, the model of water column separation is present d. This model assumes an initial free gas content homogeneo usly distributed leading to a wave speed in pipe wi th liquid – free gas mixture which is strongly pressure dependent. T h...
The effects of interference of pressure waves in simple piping systems were studied. A freeware c... more The effects of interference of pressure waves in simple piping systems were studied. A freeware computer code Allievi developed at the University of Valencia was used to simulate dynamic waveforms in simple and complex networks. The tests were carried out according to three scenarios. No pressure increases significantly exceeding the Joukowsky pressure in simple cases were noticed. When the effects of the simultaneous closing of three valves located at the three pressure reservoirs with pipes of the same diameter connected at "Y" junction were tested, it was shown that wave interference (between primary and reflected waves) is influenced strongly by the length of the analyzed pipes. Additionally, when a change of diameter was assumed at the "Y" junction, secondary waves appear, which are responsible for increased pressure in this type of the system (even when the lengths of the lines are identical). Water supply pipe systems are subject to cyclical loads and wave...
IOP Conference Series: Earth and Environmental Science
Refurbishment and upgrading of ageing hydropower plants contribute to increase of renewable energ... more Refurbishment and upgrading of ageing hydropower plants contribute to increase of renewable energy share in modern electrical grid systems. The potential increase of discharge and flexibility of load variation may result in much higher dynamic loads on both refurbished and non-refurbished plant components during transient operating events. First, water hammer control strategies are outlined including operational scenarios, surge control devices, redesign of the pipeline components, or limitation of operating conditions. Water hammer models and solutions are briefly discussed in the light of their capability, availability and uncertainty. The core of the paper is devoted to investigations of water hammer effects in a high-head hydropower plant Piva, Montenegro which is currently in the final phase of refurbishment. The flow-passage system of the Piva HPP is comprised of the intake structure, followed by three parallel penstocks each with Francis type water turbine at the downstream e...
Several comparative studies in this work were carried out with the help of the method of characte... more Several comparative studies in this work were carried out with the help of the method of characteristics. This numerical method is the most effective for solving a system of partial equations (hyperbolic type) describing a complex problem associated with the water hammer phenomenon. The numerical tests have been performed for the selected constant value of the introduced dimensionless water hammer number. The presented comparisons showed that the unsteady flows without column separation are analogous in various hydraulic systems when the value of this number has been preserved. Besides, cavitating flows with such a constant value of this number were also tested. These studies indicated the existence of another dimensionless number which was called a cavitation number. Maintaining the fixed values of both dimensionless numbers guaranteed similarity of flows in different examined systems in which cavitation occurred.
Frequency analysis of hydraulic vibrations has been applied using a transfer matrix and impedance... more Frequency analysis of hydraulic vibrations has been applied using a transfer matrix and impedance method. The computer program is given for the self-excited and forced vibrations, together with an example of self-excited vibrations in hydropower plant. The study indicates that frequency analysis makes possible detailed determination of elements which are the source of vibration and can be either eliminated or altered. The reliability of the method has been confirmed by experimental results in situ.
Double-regulated vertical axial water turbine with conical distributor, which is worldwide known ... more Double-regulated vertical axial water turbine with conical distributor, which is worldwide known as a Saxo-type turbine, is the main subject of this paper. Due to continuous research, development and improvement, advanced and compact structure, simplified civil construction works, reliability, ecological design and versatile applicability, the turbine became very recognizable product of company Litostroj Power, with over 30 successfully commissioned units in North American and Canadian market mainly. Authors see the Saxo turbine as one of the most interesting and suitable solutions for small and medium size hydro power plants. This paper aims to draw attention on this unique and interesting turbine design especially because experiences show that hydro power plant investors are somehow conservative and they mainly prefer and trust in more conventional turbine types i.e. Kaplan turbines and tubular turbines. The paper enlightens important design, hydraulic, economic and operation adva...
This paper deals with the behaviour of a hydraulic turbomachine during transients (water hammer) ... more This paper deals with the behaviour of a hydraulic turbomachine during transients (water hammer) in piping systems. A brief description of the method of characteristics and the fundamentals of transient cavitating pipe flow are given. The hydraulic turbomachine is treated as a boundary condition within the staggered grid of the method of characteristics. Case studies for a sudden load rejection of two 34-MW Francis turbines and a centrifugal pump rundown are presented. There is good agreement between the computational and the field-test results for both cases.
Valves are an indispensable element of every pipeline system (water supply, hydro power plant etc... more Valves are an indispensable element of every pipeline system (water supply, hydro power plant etc.), and their control is of great importance for the proper functioning of the system. Ball, butterfly, globe, and needle valves are usually used as flow control valves in pressurized pipe systems. Closing the valve can lead to an increase/decrease of the pressure, or water hammer, which can cause significant problems in the system in case this pressure is not maintained within prescribed limits. Depending on the generated transient events and on the installed surge protection devices, extreme pressures may compromise the pipe system safety, operation, and performance. An adequate closing law and closing time may lead to lower maximum and higher minimum pressures and increase system safety. The aim of this paper is experimental investigation of the influence of actuator pressure (the valve closure is controlled by the valve actuator) on electro-pneumatically operated valve (EPV) closure ...
A new numerical solution of transient flow simulations in viscoelastic pipes is presented, examin... more A new numerical solution of transient flow simulations in viscoelastic pipes is presented, examined, and compared with traditional solutions and experimental results. Here the viscoelastic behaviour of the pipe wall is modelled explicitly and the wall shear stress implicitly. The new solution will be able to facilitate a better understanding of the unsteady flow behaviour in a plastic pipe in water supply systems. It will also contribute to lowering the computational costs of such systems and improving the accuracy of viscoelastic pipe diagnosis such as leak detection in the future.
IOP Conference Series: Earth and Environmental Science, 2019
This paper presents recent experimental results of pressure measurements during filling and empty... more This paper presents recent experimental results of pressure measurements during filling and emptying of a relatively small-scale pipeline at the University of Montenegro. Experimental setup for investigation of water hammer and its special effects (unsteady friction, cavitation, column separation, trapped air, fluid-structure interaction - FSI), and pipeline filling and emptying is installed at the Faculty of Mechanical Engineering. It consists of an upstream end high-pressurized tank, horizontal steel pipeline (total length: 55.37 m, inner diameter: 18 mm, pipe wall thickness: 2 mm), four valve units positioned along the pipeline including the end points, and a downstream end outflow tank. The setup was upgraded in 2018 with the installation of new piezoresistive pressure transducers and pipe displacement sensors as well as additional electro-pneumatically operated ball valve at the upstream end of the pipeline. The filling of an initially empty pipeline is performed by a sudden op...
IOP Conference Series: Materials Science and Engineering, 2019
The work presents two modified cavitation models for the simulation of transient flow in pressure... more The work presents two modified cavitation models for the simulation of transient flow in pressure plastic pipes. The first model is a discrete bubble cavitation model, the prototype of which was presented by Shu, and the second one is the Adamkowski model. In the latter model, the problem encountered in the classical model (DVCM -discrete vapour cavitation model) related to artificial damping of pulsation, which results from approximate timing of cavity opening and collapse. In both models, the corrected efficient calculation of Zielke convolution integral was used to simulate the unsteady wall shear stresses. The numerical results from the two models agree well with the results of measurement in the literature.
Transient vaporous cavitating pipe flow occurs when the pressure drops to the liquid vapour press... more Transient vaporous cavitating pipe flow occurs when the pressure drops to the liquid vapour pressure. A brief description of the method of characteristics, and fundamentals of unsteady pipe flow friction and transient cavitating pipe flow are given. The main objective of this paper is to present a novel discrete gas cavity model (DGCM) with consideration of unsteady friction effects. Numerical results are compared with the results from laboratory measurements. Inclusion of unsteady friction into DGCM significantly improves numerical results.
Prehodni parni kavitacijski tok v cevi vzbudi padec tlaka na parni tlak kapljevine. Podan je kratek oris metode karakteristik, temu slede osnove nestalnega kapljevinskega trenja in prehodnega kavitacijskega toka v cevi. Glavni cilj tega prispevka je predstavitev novega plinskega kavitacijskega modela (DGCM) z upoštevanjem vplivov nestalnega trenja. Rezultati izračuna so primerjani z rezultati meritev v laboratoriju. Upoštevanje nestalnega trenja v DGCM da bolj točne računske rezultate.
This paper presents the modeling, simulation and re lated validation of water column separation i... more This paper presents the modeling, simulation and re lated validation of water column separation in hydr aulic systems. First, the modeling of hydraulic components using e lectrical analogy is introduced. This modeling is b ased on finite difference method with a centered scheme in space a nd L x scheme for discharge applied to momentum and co tinuity equations in case of a pipe filled with fluid. The resulting set of ordinary differential equations ca n be represented as a Tshaped electrical equivalent scheme. The possible t hermodynamic damping of fluid and pipe material is also introduced and the equivalent scheme is adapted consequently. The time domain numerical integration of the equati on set is performed using Runge-Kutta fourth order method. Th en, the model of water column separation is present d. This model assumes an initial free gas content homogeneo usly distributed leading to a wave speed in pipe wi th liquid – free gas mixture which is strongly pressure dependent. T h...
The effects of interference of pressure waves in simple piping systems were studied. A freeware c... more The effects of interference of pressure waves in simple piping systems were studied. A freeware computer code Allievi developed at the University of Valencia was used to simulate dynamic waveforms in simple and complex networks. The tests were carried out according to three scenarios. No pressure increases significantly exceeding the Joukowsky pressure in simple cases were noticed. When the effects of the simultaneous closing of three valves located at the three pressure reservoirs with pipes of the same diameter connected at "Y" junction were tested, it was shown that wave interference (between primary and reflected waves) is influenced strongly by the length of the analyzed pipes. Additionally, when a change of diameter was assumed at the "Y" junction, secondary waves appear, which are responsible for increased pressure in this type of the system (even when the lengths of the lines are identical). Water supply pipe systems are subject to cyclical loads and wave...
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Papers by Anton Bergant
Prehodni parni kavitacijski tok v cevi vzbudi padec tlaka na parni tlak kapljevine. Podan je kratek oris metode karakteristik, temu slede osnove nestalnega kapljevinskega trenja in prehodnega kavitacijskega toka v cevi. Glavni cilj tega prispevka je predstavitev novega plinskega kavitacijskega modela (DGCM) z upoštevanjem vplivov nestalnega trenja. Rezultati izračuna so primerjani z rezultati meritev v laboratoriju. Upoštevanje nestalnega trenja v DGCM da bolj točne računske rezultate.
Prehodni parni kavitacijski tok v cevi vzbudi padec tlaka na parni tlak kapljevine. Podan je kratek oris metode karakteristik, temu slede osnove nestalnega kapljevinskega trenja in prehodnega kavitacijskega toka v cevi. Glavni cilj tega prispevka je predstavitev novega plinskega kavitacijskega modela (DGCM) z upoštevanjem vplivov nestalnega trenja. Rezultati izračuna so primerjani z rezultati meritev v laboratoriju. Upoštevanje nestalnega trenja v DGCM da bolj točne računske rezultate.