Alexandre Presas

• PhD
• Associate Professor at the UPC & Researcher at CDIF at Polytechnic University of Catalonia

Under the background of sustainable development of renewable energy, it is more and more important to recover the energy of high-pressure medium produced in the petrochemical process. In the field of petrochemicals, the multi-stage pump as turbine (PAT) has a strong economy. PAT can not only generate the high-pressure medium required in the petroch...

The widespread adoption of intermittent wind and solar energy sources disrupts the stability of power grids, necessitating frequent load rejection processes for pump-turbine. This jeopardizes the stability of pump-turbine units. To investigate the operating behavior of pump-turbine units during load rejection, this study focuses on a Francis revers...

Sediment erosion of hydraulic machinery can cause a lot of energy loss, thereby affecting their operational stability. Herein, solid–liquid two-phase flow simulations are conducted on a pump turbine using the Euler–Lagrangian model to predict the sediment-laden flow and sediment erosion. The predicted results are verified through experiments. The c...

Near-resonant flow-induced vibrations are a significant cause of fatigue damage in hydraulic impellers. The amplitude of these vibrations is limited mainly by the fluid damping, making its quantification paramount for the safety of hydraulic turbines. To study the fluid damping for low-specific-speed radial impellers, a submerged disc in still wate...

This research paper introduces advancements in hydraulic turbine condition monitoring through the implementation of vibration-based condition indicators. Conventional methods rely on vibration monitoring systems, triggering alarms or unit trips based on overall measured values at specific points. However, these methods may generate false alarms und...

This work reports on a new Kaplan turbine that experienced an unstable behaviour during its start up. The unit experienced strong sound and vibration in that phase. To identify the origin of this unstable behaviour, a set of sensors were installed within the turbine. Subsequently, tests were performed to determine the response of the different sens...

The process pump as turbine (PPAT) serves as a crucial component for recovering high-pressure energy from mediums used in chemical and refining processes. Ensuring the long-term safe and stable operation of PPAT in high-temperature and high-pressure environments is essential, with pressure pulsation being one of its most significant external charac...

Vortex breakdown in a pump sump is a complex and negative factor for the pump. Different from my previous study that focused mainly on the development process of vortex and its damage to the pump, this paper is from a new perspective that studies the energy dissipation and time–frequency characteristics induced by vortex breakdown. The tested data...

For such complex rotating machinery as hydraulic turbine, the hydraulic operation characteristics of the hydraulic turbine unit are significantly impacted by the short blade of the runner used as the splitter blade. To find the optimum position of the short blade, the study object is the 1000 MW hydraulic turbine, selects three circumferential offs...

Centrifugal pumps are essential in many industrial processes. An accurate operation diagnosis of centrifugal pumps is crucial to ensure their reliable operation and extend their useful life. In real industry applications, many centrifugal pumps lack flowmeters and accurate pressure sensors, and therefore, it is not possible to determine whether the...

The pump-turbine unit is the core equipment of pumped storage power station, and the rotor system is the key component of the pump-turbine unit. In this paper, the numerical method considering the gyro-effect and added mass effect is proposed, the effect of the added mass, gyro-effect and bearing stiffness are discussed, respectively, and a "transf...

In the XFLEX HYDRO Vogelgrun demonstrator, a run-of-river hydropower plant, the hybridization of one turbine-generator unit with a battery energy storage system is being investigated. This paper describes the integration methodology of the hybrid control algorithm without replacing the existing speed governor of the unit. Furthermore, the compariso...

Nowadays, in order to mitigate the global warming effects, there is a need of renewable energy generation for the objective of carbon neutrality. In this context, hydropower plays a key role not only because the amount of renewable energy generated but also because it is a fundamental player to ensure the stability of the electrical grid, as one of...

Cavitation is an important issue in pumped storage unit as it can compromise the safe and stable operation of the unit. The present work aims revealing the dynamic behavior of a pump-turbine runner in cavitating flow from a perspective of fluid-structure interaction. A procedure is developed to map the cavities from computation fluid dynamics simul...

Kaplan turbines are nowadays used to provide Frequency Containment Reserve (FCR) to the grid due to their fast capacity to regulate their power maintaining high efficiency. However, this continuous power regulation increases the wear and tear of the regulation system considerably. To reduce the amount of movements in the regulation servomotors, and...

In the current energy market, hydraulic turbines are increasingly demanded to work in Frequency containment reserve (FCR) mode to compensate the constant frequency fluctuations in the electrical grid. To do so, hydraulic turbines change their generating power continuously which implies to regulate the flow rate. Kaplan turbines are double regulated...

Overload instability is a self-excited phenomenon that occurs in Francis turbines working over the Best Efficiency Point. It provokes huge power swings and pressure fluctuations in the hydraulic circuit. One particular issue is that this phenomenon appears suddenly and just before its onset the machine can operate in a very stable manner. In this s...

The natural frequencies of a turbine can be calculated from numerical methods. By comparing these natural frequencies with excitation sources, one can know the danger of a resonance and a possible failure in a component of the turbine. Therefore, it is often very important to have an accurate numerical model of the turbine to determine these natura...

In order to satisfy the power demand in the electrical grid, hydraulic turbine units frequently work under off-design operation conditions and pass through transient events. These operation conditions can lead to high vibration amplitudes in the turbine runners, decreasing their useful life, and in some cases to premature failures. To determine and...

To prevent lifetime shortening and premature failure in turbine runners, it is of paramount importance to analyse and understand its dynamic response and determine the factors that affect it. In this paper, the dynamic response of a Kaplan runner is analysed in air by numerical and experimental methods. First, to start the analysis of Kaplan runner...

Lead-cooled fast reactor (LFR) is an important reactor type of the Generation IV nuclear energy, and the main coolant pump (MCP) is the only and most critical power equipment in primary circuit of LFR. The shutdown idling performance of the MCP, is one of the most important safety indicators in the event of a station blackout accident. When the mot...

Bulb turbine units are one of the most installed turbines in run-of river projects with relatively low head. In order to enlarge the useful life of these turbines and avoid fatigue problems and cracks, it is of paramount importance to understand and determine the most relevant parameters and their influence on the dynamic response of the structure....

Solar power installations are increasing every year due to the decarbonization policy established around the world. Photovoltaic (PV) systems and specifically one-axis solar trackers are the most used type of installations in solar power plants. Those solar trackers are slender structures installed in open-air areas sometimes subjected to high spee...

To cope with the intermittent power supply of the new renewable energies and demand fluctuations, Francis turbines are required to operate more and more in an extended operating range, far away from the design point. With this operating behavior, it is very complex to interpret the trend of vibration parameters typically used in Condition Monitorin...

Motive: External vibration excitation might be key to many novel non-surgical interventions for pathologies in the musculoskeletal system and in other parts of the human organism. Lack of understanding about vibration patterns, their controllability, and reproducibility are three limitations of ongoing research. This study establishes a bovine vib...

One of the most critical operating conditions in hydraulic turbines is the start-up transient. This may be characterized by the presence of several resonances, which increase the vibration and stress levels on the runners. At present, its study is of interest due to the more frequent starts and stops of the turbines in the last years. The present s...

The assessment of the remaining useful life due to fatigue in Francis turbine runners implies complex measurements with strain gauges that have to be installed in a submerged and rotating structure, which is excited with high pressure pulsations and strong turbulent flows. Furthermore, the conditioning, storage and transmission of these signals to...

With the current demand of flexibility to hydraulic turbines, these are working under off-design conditions more than ever. Under these conditions different complex hydraulic phenomena appear, especially in Francis turbines, affecting the machine stability as well as reducing the useful life of its components. Hence, it is desirable to detect in re...

With the increasing entrance of wind and solar power for the generation of electricity, more flexibility is demanded to hydropower plants. More flexibility means that hydro turbines have to increase the operating range between minimum and maximum power. In Francis turbines the maximum power is limited by the appearance of a strong hydraulic excitat...

[This corrects the article DOI: 10.1371/journal.pone.0245768.].

The development of treatment strategies for improving secondary stability at the bone-implant interface is a challenge. Porous implants are one solution for improving long-term implant stability, but the osteoconduction process of implants into the bone can be slow. Strain-driven osteogenesis from the mechanostat theory offers insight into pathways...

Nowadays, one of the major mechanical issues of hydraulic turbines and particularly Francis turbines are the failures produced by fatigue. Due to the massive entrance of new renewable energies such as wind or solar, hydraulic turbines have to withstand off-design conditions and multiple transients, which greatly increase the risk of fatigue failure...

We investigate the power densities which are obtainable locally in a vibration bioreactor. These reactor systems are of great relevance for research about oncological or antibacterial therapies. Our focus lies on the local liquid pressure caused by resonance vibration in the fluid contained by the reactor’s petri dish. We use for the excitation one...

The health condition of hydraulic turbines is one of the most critical factors for the operation safety and financial benefits of a hydro power plant. After the massive entrance of intermittent renewable energies, hydropower units have to regulate their output much more frequently for the balancing of the power grid. Under these conditions, the com...

Hydropower is nowadays essential for balancing the electrical grid providing flexibility and fast response. The role of hydraulic turbines has changed from working at their Best Efficiency Point (BEP) to work in the whole operating range when demanded. Francis turbines working at off-design conditions suffer from dynamic problems that affect the us...

Because of the addition of stochastic supply to the power grid introduced by new renewable energies, hydropower is required to respond rapidly to the fluctuation between power demand and supply. Consequently, hydropower units must work under extreme off-design conditions, where the machines are more prone to suffer from damages and shorter useful l...

Worldwide electricity generation is featured by the growth of intermittent renewable energies. In this context, hydropower plays a fundamental role because it provides flexibility to the power grid and ensures its stability. The new grid requirements have led hydropower units to working under a wider range of loads and with more start/stop sequence...

Post-operative therapy for joint replacement is often performed to optimize bone volume and bone-implant contact. Methods, such as pulsed therapeutic ultrasound, have been shown to be a valuable addition to regular physiotherapy to increase bone regeneration. To evaluate the efficacy of kilohertz-frequency (kHz) resonant stimuli to additively manuf...

A large crack was discovered on one blade of a Kaplan turbine prototype after the inspection of the machine. In order to know the origin of the crack, a failure analysis was previously carried out (Zhang et al., 2019). To know the modal behaviour of cracked structures is of interest in order to detect the crack while in operation. For this purpose,...

Tidal energy systems and specifically tidal barrages are renewable energy systems, that use the potential energy of tides to produce electricity. Actually, there are few tidal power stations operating, although recent studies show the potentiality of installing new units in a recent future due to the constant improvement of the technology related....

The dynamic behavior of Francis runners is of interest in the hydraulic machinery field since it is one of the most used type of hydraulic turbines for electricity generation. To evaluate the dynamic behavior of Francis runners, their natural frequencies have been studied extensively in the past. However, mode-shapes and damping ratios associated t...

Nowadays, hydropower is demanded to provide flexibility and fast response into the electrical grid in order to compensate the non-constant electricity generation of other renewable sources. Hydraulic turbines are therefore demanded to work under off-design conditions more frequently, where different complex hydraulic phenomena appear, affecting the...

Determining the natural frequencies and mode shapes of rotating turbomachinery components from both rotating and stationary reference frames is of paramount importance to avoid resonance problems that could affect the normal operation of the machine, or even cause critical damages in these components. Due to their similarity to real engineering cas...

Reactive power shortage is one of the current issues that endanger the stability of the power grid systems. Some massive blackouts have been experienced in the past years due to the unbalance of reactive power. One of the solutions to provide the necessary reactive power to the grid is to operate generators as motors and supply or absorb reactive p...

An effective condition monitoring is essential to increase the availability of Pelton turbines and to avoid unexpected damage. The main challenge consists in determining the deformations and the stresses in the runner while in operation. To do so, it is essential to understand the dynamic response of the machine, and especially of the runner. Moreo...

Erosive cavitation in hydraulic turbines affects severely the runner structure, increasing maintenance costs and reducing the remaining useful life of the component. Actual vibro-acoustic techniques used to detect this kind of cavitation in hydraulic turbines are based on analysing high-frequency vibrations in different parts of the unit. Particula...

Francis turbines are increasingly demanded to work at part load in order to satisfy the electricity generation demand and to compensate the non-constant generation of other renewable sources such as wind or solar. At part load, Francis turbines present complex flow patterns dominated by cavitation and especially by the draft tube vortex rope. The v...

At present, hydropower plants play an important role because of their flexibility in the generation of electricity. Today, the required operating range of turbine units is expected to extend to deep part load. At part load the draft tube vortex rope is generated and, in some cases, can produce large pressure pulsations limiting the operation of the...

Oscillating water column (OWC) axial impulse turbines permit the conversion of wave energy into electrical power. Unlike other hydropower units with a mature and well established technology, such turbines have been recently developed, there are still few prototypes operating and therefore there is a large space for optimizing its design. Many recen...

In this present study, we propose a method for exposing biological cells to mechanical vibration. The motive for our research was to design a bioreactor prototype in which in-depth in vitro studies about the influence of vibration on cells and their metabolism can be performed. The therapy of cancer or antibacterial measures are applications of int...

The overarching goal of the gathering was to define a concept for technology design research in Giessen to improve patient outcomes through the design of assistive technology that assists both patients and surgeons. The emerging field of regenerative rehabilitation where trauma patients are treated by methods of regenerative medicine promises grea...

When discussing potential resonances in hydraulic turbine runners, cavitation effects are usually neglected. Nevertheless, recent studies have experimentally proved, that large cavitation volumes in the proximity of flexible simple structures, such as hydrofoils, greatly modify their natural frequencies. In this paper, we analyze a resonance case i...

Submerged systems are found in many engineering, biological, and medicinal applications. For such systems, due to the particular environmental conditions and working medium, the research on the mechanical and structural properties at every scale (from macroscopic to nanoscopic), and the control of the system dynamics and induced effects become very...

The ability of hydropower to adapt the electricity generation to the demand is necessary to integrate wind and solar energy into the electrical grid. Nowadays, hydropower turbines are required to work under harsher operating conditions and an advanced condition monitoring to detect damage is crucial. In this paper the methodology to improve the con...

Hydropower plants are of paramount importance for the integration of intermittent renewable energy sources in the power grid. In order to match the energy generated and consumed, Large hydraulic turbines have to work under off-design conditions, which may lead to dangerous unstable operating points involving the hydraulic, mechanical and electrical...

One of the main causes of damage in hydraulic turbines is cavitation. While not all cavitation appearing in a turbine is of a destructive type, erosive cavitation can severely affect the structure, thus increasing maintenance costs and reducing the remaining useful life of the machine. Of all types of cavitation, the maximum erosion occurs when clo...

Linear elastic fracture mechanics (LEFM) approaches are seldom used to analyze fatigue problems in hydraulic turbomachinery, where extremely simplified fatigue models are normally considered. In one of the largest Kaplan hydraulic turbines in the world, the piston rod, which is an important load transfer component, was found broken twice at the sam...

Nowadays, hydropower plays an essential role in the energy market. Due to their fast response and regulation capacity, hydraulic turbines operate at off-design conditions with a high number of starts and stops. In this situation, dynamic loads and stresses over the structure are high, registering some failures over time, especially in the runner. T...

Due to the increasing share of new renewable energies like wind and solar in the generation of electricity the need for power regulation and energy storage is becoming of paramount importance. One of the systems to store huge amounts of energy is pumped storage using reversible hydropower units. The machines used in these power plants are pump-turb...

Hydropower plays a key role in the actual energy market due to its fast response and regulation capacity. In that way, hydraulic turbines are increasingly demanded to work at off-design conditions, where complex flow patterns and cavitation appear, especially in Francis turbines. The draft tube cavitation surge is a hydraulic phenomenon that appear...

Nowadays, hydropower plays an essential role in the energy market. Due to its fast response [...]

Nowadays, hydropower plants are of paramount importance for the integration of intermittent renewable energy sources in the power grid. [...]

Abstract

In this paper, an uncommon failure of a Pelton turbine has been analyzed. After the monitoring system detected a sudden increase in the vibration levels, the turbine was inspected. The inspection showed that a fragment of one bucket broke off during operation. Moreover there were several buckets with cracks, always located in the same side of the b...

The fast change in new renewable energy is affecting directly the required operating range of hydropower plants. According to the present demand of electricity, it is necessary to generate different levels of power. Because of its ease to regulate and its huge storage capacity of energy, hydropower is the unique energy source that can adapt to the...

Francis turbines operate in many cases out of its best efficiency point, in order to regulate their output power according to the instantaneous energy demand of the grid. Therefore, it is of paramount importance to analyse and determine the unstable operating points for these kind of units. In the framework of the HYPERBOLE project (FP7-ENERGY-2013...

Experimental tests in prototype are necessary to understand the dynamic behaviour of the machine during different operating points. Hydraulic phenomena as well as its effect on the structure need to be studied in order to avoid instabilities during operation and to extend the life-time of the different components. For this purpose, a complete exper...

Studying the dynamic response of Francis turbine runners is of paramount importance in order to avoid resonance problems during operating conditions. For this purpose, the natural frequencies as well as their associated mode-shapes and damping ratios of the runner have to be determined. In this paper, an Experimental Modal Analysis (EMA) of the run...