The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
Monika Ivantysynova - One of the best experts on this subject based on the ideXlab platform.
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Scaling Criteria for Axial Piston Machines Based on Thermo-Elastohydrodynamic Effects in the Tribological Interfaces
Energies, 2018Co-Authors: Lizhi Shang, Monika IvantysynovaAbstract:In lieu of reliable scaling rules, hydraulic pump and motor manufacturers pay a high monetary and temporal price for attempting to expand their production lines by scaling their existing units to other sizes. The challenge is that the lubricating interfaces, which are the key elements in determining the performance of a positive Displacement Machine, are not easily scalable. This article includes an analysis of the size-dependence of these units with regard to the significant physical phenomena describing the behavior of their three most critical lubricating interfaces. These phenomena include the non-isothermal elastohydrodynamic effects in the fluid domain, and the heat transfer and thermal elastic deflection in the solid domain. The performance change due to size variation is found to be unavoidable and explained through fundamental physics. The results are demonstrated using a numerical fluid–structure–thermal interaction model over a wide range of unit sizes. Based on the findings, a guide to scaling swashplate-type axial piston Machines such as to uphold their efficiency is proposed.
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Cyclostationary Analysis of Measured Pump Acoustic and Vibration Signals
BATH ASME 2018 Symposium on Fluid Power and Motion Control, 2018Co-Authors: Paul Kalbfleisch, Svenja Horn, Monika IvantysynovaAbstract:The stationary signal assumption is convenient as its signal processing methods are the minimum effort required to characterize periodic signals and therefore the most common. However, signals from rotating Machines have been found to naturally be characterized as cyclostationary. The existent of natural phenomenon such as, shaft imbalances, turbulent fluid flows, friction, combustion forces, and torsional vibrations create modulation effects, that can be seen in the measured signals. These observed modulations in pump noise and vibration signals are synonymous to amplitude modulations (AM), frequency modulations (FM), and potentially phase modulations in electrical systems. Having this knowledge, the fluid power noise, vibration, and harshness (NVH) researchers can draw from an enormous amount of progress made in the modern telecommunication signal processing methods of cyclostationary signals. This article introduces the basic concepts of cyclostationary signals, some of their signal processing techniques, and a simple example of analysis for a positive Displacement Machine through the cyclostationary paradigm.
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An Investigation of the Impact of Micro Surface on the Cylinder Block/Valve Plate Interface Performance
8th FPNI Ph.D Symposium on Fluid Power, 2014Co-Authors: Rene Chacon, Monika IvantysynovaAbstract:Lubricating gaps are the primary source of energy dissipation in axial piston Machines of swash plate-type. One of these lubricating gaps is designated as the cylinder block/valve plate interface, and is one of the most critical design elements for this type of positive Displacement Machine. In the past, extensive work has been done at Maha Fluid Power Research Center both to model this interface and to study the effects of micro-surface shaping on the valve plate. This paper presents a more in-depth investigation into optimizing valve plate micro-surface shaping (both by altering the number and amplitude of waves) in order to achieve a fluid film thickness that compromises between leakage and torque loss, minimizes power loss in the cylinder block/valve plate interface, and maximizes Machine efficiency.Copyright © 2014 by ASME
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an investigation of the impact of micro surface on the cylinder block valve plate interface performance
8th FPNI Ph.D Symposium on Fluid Power, 2014Co-Authors: Rene Chacon, Monika IvantysynovaAbstract:Lubricating gaps are the primary source of energy dissipation in axial piston Machines of swash plate-type. One of these lubricating gaps is designated as the cylinder block/valve plate interface, and is one of the most critical design elements for this type of positive Displacement Machine. In the past, extensive work has been done at Maha Fluid Power Research Center both to model this interface and to study the effects of micro-surface shaping on the valve plate. This paper presents a more in-depth investigation into optimizing valve plate micro-surface shaping (both by altering the number and amplitude of waves) in order to achieve a fluid film thickness that compromises between leakage and torque loss, minimizes power loss in the cylinder block/valve plate interface, and maximizes Machine efficiency.Copyright © 2014 by ASME
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The effect of cross porting on derived Displacement volume
International Journal of Fluid Power, 2014Co-Authors: Taeho Kim, Paul Kalbfleisch, Monika IvantysynovaAbstract:Derived Displacement volume (Vi) is very important for the calculation of volumetric and torque efficiency of positive Displacement Machines. A method for determining the derived Displacement volume of a unit was introduced by Toet. This method is known to be more accurate than the current ISO 8426 standard, yet still has a speed dependent error. This paper reveals the main cause of the speed dependent error found in the method by Toet for the determination of derived Displacement volume. An accurate pump model enabled the analysis of complex flow interactions inside a positive Displacement Machine. The analysis of the flows isolated the variations in derived Displacement volumes to be dependent on the design of the valve plate. A case study of two valve plates with and without cross porting verified cross porting’s influence on derived Displacement volume. Steady state measurement and the pump model simulations at low pressure differences show that the effective Displacement volumes (Ve) at different rot...
Torben Ole Andersen - One of the best experts on this subject based on the ideXlab platform.
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Feedback Control of Pulse-Density-Modulated Digital Displacement Transmission Using a Continuous Approximation
IEEE-ASME Transactions on Mechatronics, 2020Co-Authors: Niels Henrik Pedersen, Per Johansen, Torben Ole AndersenAbstract:Feedback control of digital Displacement Machines is complicated due to the nonsmooth digital behavior. Full-stroke operated digital Displacement Machines are characterized by delivering a discrete volumetric output based on the ratio of activated cylinder chambers. The binary input decision (active or inactive) is made discretely with an update rate proportional to the speed of the Machine. For a digital fluid power transmission with two digital Displacement Machines with varying and different speeds and which dynamics greatly influence each other through the pressurized fluid line, the control task is further complicated. To overcome this problem, this article presents a continuous approximation of a pulse-density-modulated digital Displacement Machine, which allows for dynamic analysis and control design. This article shows that linear feedback control theory is adequate to show stability if the number of cylinders, Displacement throughput, and rotational speed of the Machine are sufficiently high. Additionally, the excitation frequencies must be sufficiently low to not excite the discrete behavior. An optimal state feedback controller is synthesized and tested in a nonlinear simulation model, which represents the physical digital hydraulic transmission. Simulation results shows great tracking performance similar to a transmission with ideal fluid power Machines, but with noticeable fluctuations due to the digital Machine characteristics.
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Analysis of Requirements for Valve Accuracy and Repeatability in High Efficiency Digital Displacement Motors
BATH ASME 2018 Symposium on Fluid Power and Motion Control, 2018Co-Authors: Sondre Nordås, Morten Kjeld Ebbesen, Torben Ole AndersenAbstract:Traditional variable Displacement piston Machines achieve high efficiency when operating at high Displacements, but struggle with poor efficiency at low Displacements. The pistons are connected to high pressure and low pressure in conjunction with the output shaft position and the Displacement is changed by changing the piston stroke, resulting in almost constant friction, leakage, and compressibility losses independent of Displacement. In digital Displacement Machines, the rotary valve is replaced by two fast switching on/off valves connected to every cylinder. By controlling the fast switching on/off valves, the cylinders can be controlled individually and friction, leakage and compressibility losses can be minimized resulting in high efficiency even at low Displacements. Previous studies have shown that high efficiency digital Displacement Machines require fast switching valves with high flow capacity and optimal valve timing strategy. When the digital Displacement motor is to start, stop or be controlled at low speeds, the on/off valves must be able to open against high pressure difference. When opening the valves actively, the valve timing has to be conducted properly to minimize valve throttling losses and flow and pressure peaks. First, this paper shortly describes a previously developed method to estimate valve characteristics like transition time and flow capacity for a digital Displacement Machine. Then the paper presents a novel method of describing the required valve accuracy and repeatability to keep the valve throttling losses low and Machine efficiency high.
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Event-driven control of a speed varying digital Displacement Machine
ASME BATH 2017 Symposium on Fluid Power and Motion Control, 2017Co-Authors: Niels Henrik Pedersen, Per Johansen, Torben Ole AndersenAbstract:The design and analysis of feedback controllers for digital Displacement Machines requires a control oriented model. The Displacement throughput of a full stroke operated Machine is altered on a stroke-by-stroke basis at fixed rotation angles. In the case of a fixed speed operation, it may be treated as a Discrete Linear Time Invariant control problem with synchronous sampling rate. To make synchronous linear control theory applicable for a variable speed digital Displacement Machine, a method based on event-driven control is presented. Using this method, the time domain differential equations are converted into the spatial (position) domain to obtain a constant sampling rate and thus allowing for use of classical control theory. The method is applied to a down scaled digital fluid power motor, where the motor speed is controlled at varying references under varying pressure and load torque conditions. The controller synthesis is carried out as a discrete optimal deterministic problem with full state feedback. Based on a linear analysis of the feedback control system, stability is proven in a pre-specified operation region. Simulation of a non-linear evaluation model with the controller implemented shows great performance, both with respect to tracking and disturbance rejection.
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State of the Art Review on Theoretical Tribology of Fluid Power Displacement Machines
9th FPNI Ph.D. Symposium on Fluid Power, 2016Co-Authors: Remzija Cerimagic, Per Johansen, Torben Ole Andersen, Henrik C. PedersenAbstract:Over the past 20 years an increasing focus on efficiency and reliability in fluid power Displacement Machines has provided an incentive to study loss and wear mechanisms. One example is the hydrostatic fluid power transmission systems for wind and wave energy applications. The loss and wear mechanisms are mainly attributed to the tribological interfaces in fluid power Machines. Consequently, optimization of efficiency and reliability of fluid power Machines imply consideration of tribological interface design. The majority of the work done by researchers and engineers on the study of loss and wear mechanisms in the lubricating gaps in fluid power Machines is confined to simulation models, as experimental treatments of these mechanisms are very difficult. This means, that a complete verification of the theoretical work is difficult. The aim of this paper is a state of the art review on the theoretical work for the design and optimization of fluid power Displacement Machines, and also the work done to validate the theoretical models. This review is not a complete historical account, but aim to describe current trends in fluid power Displacement Machine tribology. The review considers the rheological models used in the theoretical approaches, the modeling of elastohydrodynamic effects, the modeling of thermal effects, and finally the experimental validation of the theoretical models.
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LQR Feedback Control Development for Wind Turbines Featuring a Digital Fluid Power Transmission System
9th FPNI Ph.D. Symposium on Fluid Power, 2016Co-Authors: Niels Henrik Pedersen, Per Johansen, Torben Ole AndersenAbstract:Research within digital fluid power (DFP) transmissions is receiving an increased attention as an alternative to conventional transmission technologies. The use of DFP Displacement Machines entails a need for applicable control algorithms. However, the design and analysis of controllers for such digital systems are complicated by its non-smooth behavior. In this paper a control design approach for a digital Displacement Machine® is proposed and a performance analysis of a wind turbine using a DFP transmission is presented. The performance evaluation is based on a dynamic model of the transmission with a DFP motor, which has been combined with the NREL 5-MW reference wind turbine model. A classical variable speed control strategy for wind speeds below rated is proposed for the turbine, where the pump Displacement is fixed and the digital motor Displacement is varied for pressure control. The digital motor control strategy consists of a full stroke operation strategy, where a Delta-Sigma pulse density modulator is used to determine the chamber activation sequence. In the LQR-control design approach, the discrete behavior of the motor and Delta-Sigma modulator is described by a discrete linear time invariant model. Using full-field flow wind profiles as input, the design approach and control performance is verified by simulation in the dynamic model of the wind turbine featuring the DFP transmission. Additionally, the performance is compared to that of the conventional NREL reference turbine, transmission and controller.
Per Johansen - One of the best experts on this subject based on the ideXlab platform.
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Feedback Control of Pulse-Density-Modulated Digital Displacement Transmission Using a Continuous Approximation
IEEE-ASME Transactions on Mechatronics, 2020Co-Authors: Niels Henrik Pedersen, Per Johansen, Torben Ole AndersenAbstract:Feedback control of digital Displacement Machines is complicated due to the nonsmooth digital behavior. Full-stroke operated digital Displacement Machines are characterized by delivering a discrete volumetric output based on the ratio of activated cylinder chambers. The binary input decision (active or inactive) is made discretely with an update rate proportional to the speed of the Machine. For a digital fluid power transmission with two digital Displacement Machines with varying and different speeds and which dynamics greatly influence each other through the pressurized fluid line, the control task is further complicated. To overcome this problem, this article presents a continuous approximation of a pulse-density-modulated digital Displacement Machine, which allows for dynamic analysis and control design. This article shows that linear feedback control theory is adequate to show stability if the number of cylinders, Displacement throughput, and rotational speed of the Machine are sufficiently high. Additionally, the excitation frequencies must be sufficiently low to not excite the discrete behavior. An optimal state feedback controller is synthesized and tested in a nonlinear simulation model, which represents the physical digital hydraulic transmission. Simulation results shows great tracking performance similar to a transmission with ideal fluid power Machines, but with noticeable fluctuations due to the digital Machine characteristics.
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Optimal control of a wind turbine with digital fluid power transmission
Nonlinear Dynamics, 2018Co-Authors: Niels H. Pedersen, Per Johansen, Torben O. AndersenAbstract:Digital fluid power (DFP) technology may lead to a paradigm shift in large-scale transmission systems in, e.g., wind and wave energy. Therefore, the development of applicable control algorithms is of major importance, but is complicated by the non-smooth behavior of the DFP Displacement Machines. The power throughput of a full stroke operated digital Displacement Machine is quantized by the number of pressure chambers. The dynamics of each pressure chamber may be described by highly nonlinear continuous differential equations, whereas the input is discretely updated and binary (active or inactive). This paper contributes with a feedback control strategy for a digital Displacement Machine, where the binary inputs are handled by a pulse density modulator. The paper presents a linearization method of handling the many nonlinearities and thereby enabling the use of Discrete Linear Time Invariant (DLTI) control theory. The control strategy is validated for control of a digital fluid power wind turbine transmission, where both a deterministic and a stochastic optimal controllers are synthesized. The study is based on the NREL 5-MW reference wind turbine, where its model is combined with a nonlinear model of the DFP transmission and full-field flow wind profiles are used for a realistic performance evaluation scenario. By simulation, it is found that the performance of the optimal controllers using the DFP transmission is similar to that of the NREL controller using a conventional transmission.
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Event-driven control of a speed varying digital Displacement Machine
ASME BATH 2017 Symposium on Fluid Power and Motion Control, 2017Co-Authors: Niels Henrik Pedersen, Per Johansen, Torben Ole AndersenAbstract:The design and analysis of feedback controllers for digital Displacement Machines requires a control oriented model. The Displacement throughput of a full stroke operated Machine is altered on a stroke-by-stroke basis at fixed rotation angles. In the case of a fixed speed operation, it may be treated as a Discrete Linear Time Invariant control problem with synchronous sampling rate. To make synchronous linear control theory applicable for a variable speed digital Displacement Machine, a method based on event-driven control is presented. Using this method, the time domain differential equations are converted into the spatial (position) domain to obtain a constant sampling rate and thus allowing for use of classical control theory. The method is applied to a down scaled digital fluid power motor, where the motor speed is controlled at varying references under varying pressure and load torque conditions. The controller synthesis is carried out as a discrete optimal deterministic problem with full state feedback. Based on a linear analysis of the feedback control system, stability is proven in a pre-specified operation region. Simulation of a non-linear evaluation model with the controller implemented shows great performance, both with respect to tracking and disturbance rejection.
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State of the Art Review on Theoretical Tribology of Fluid Power Displacement Machines
9th FPNI Ph.D. Symposium on Fluid Power, 2016Co-Authors: Remzija Cerimagic, Per Johansen, Torben Ole Andersen, Henrik C. PedersenAbstract:Over the past 20 years an increasing focus on efficiency and reliability in fluid power Displacement Machines has provided an incentive to study loss and wear mechanisms. One example is the hydrostatic fluid power transmission systems for wind and wave energy applications. The loss and wear mechanisms are mainly attributed to the tribological interfaces in fluid power Machines. Consequently, optimization of efficiency and reliability of fluid power Machines imply consideration of tribological interface design. The majority of the work done by researchers and engineers on the study of loss and wear mechanisms in the lubricating gaps in fluid power Machines is confined to simulation models, as experimental treatments of these mechanisms are very difficult. This means, that a complete verification of the theoretical work is difficult. The aim of this paper is a state of the art review on the theoretical work for the design and optimization of fluid power Displacement Machines, and also the work done to validate the theoretical models. This review is not a complete historical account, but aim to describe current trends in fluid power Displacement Machine tribology. The review considers the rheological models used in the theoretical approaches, the modeling of elastohydrodynamic effects, the modeling of thermal effects, and finally the experimental validation of the theoretical models.
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LQR Feedback Control Development for Wind Turbines Featuring a Digital Fluid Power Transmission System
9th FPNI Ph.D. Symposium on Fluid Power, 2016Co-Authors: Niels Henrik Pedersen, Per Johansen, Torben Ole AndersenAbstract:Research within digital fluid power (DFP) transmissions is receiving an increased attention as an alternative to conventional transmission technologies. The use of DFP Displacement Machines entails a need for applicable control algorithms. However, the design and analysis of controllers for such digital systems are complicated by its non-smooth behavior. In this paper a control design approach for a digital Displacement Machine® is proposed and a performance analysis of a wind turbine using a DFP transmission is presented. The performance evaluation is based on a dynamic model of the transmission with a DFP motor, which has been combined with the NREL 5-MW reference wind turbine model. A classical variable speed control strategy for wind speeds below rated is proposed for the turbine, where the pump Displacement is fixed and the digital motor Displacement is varied for pressure control. The digital motor control strategy consists of a full stroke operation strategy, where a Delta-Sigma pulse density modulator is used to determine the chamber activation sequence. In the LQR-control design approach, the discrete behavior of the motor and Delta-Sigma modulator is described by a discrete linear time invariant model. Using full-field flow wind profiles as input, the design approach and control performance is verified by simulation in the dynamic model of the wind turbine featuring the DFP transmission. Additionally, the performance is compared to that of the conventional NREL reference turbine, transmission and controller.
Jan Vierendeels - One of the best experts on this subject based on the ideXlab platform.
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Development of a thermodynamic low order model for a twin screw expander with emphasis on pulsations in the inlet pipe
Applied Thermal Engineering, 2016Co-Authors: Iva Papes, Joris Degroote, Jan VierendeelsAbstract:A twin screw expander is a positive Displacement Machine used in various applications of waste heat recovery. The performance of this Machine is influenced by internal leakages, gas pulsations formed in the inlet pipe and the properties of the refrigerant. In this paper a multi-chamber mathematical model of a twin screw expander is presented to predict its performance. From the mass and energy conservation laws, differential equations are derived which are then solved together with the appropriate Equation of State (EoS) in the instantaneous control volumes. In order to calculate the mass flow rates through leakage paths more accurately, flow coefficients used in the converging nozzle model were derived from 3D Computational Fluid Dynamic (CFD) calculation. Due to high gas pulsation levels at the inlet port, a coupling with a 3D CFD inlet pipe model is introduced in order to better predict throttling losses. The maximal deviation between predictions by the developed model and 3D CFD calculations of the complete Machine is around 5% for the mass flow rate and the power output.
Torben O. Andersen - One of the best experts on this subject based on the ideXlab platform.
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Optimal control of a wind turbine with digital fluid power transmission
Nonlinear Dynamics, 2018Co-Authors: Niels H. Pedersen, Per Johansen, Torben O. AndersenAbstract:Digital fluid power (DFP) technology may lead to a paradigm shift in large-scale transmission systems in, e.g., wind and wave energy. Therefore, the development of applicable control algorithms is of major importance, but is complicated by the non-smooth behavior of the DFP Displacement Machines. The power throughput of a full stroke operated digital Displacement Machine is quantized by the number of pressure chambers. The dynamics of each pressure chamber may be described by highly nonlinear continuous differential equations, whereas the input is discretely updated and binary (active or inactive). This paper contributes with a feedback control strategy for a digital Displacement Machine, where the binary inputs are handled by a pulse density modulator. The paper presents a linearization method of handling the many nonlinearities and thereby enabling the use of Discrete Linear Time Invariant (DLTI) control theory. The control strategy is validated for control of a digital fluid power wind turbine transmission, where both a deterministic and a stochastic optimal controllers are synthesized. The study is based on the NREL 5-MW reference wind turbine, where its model is combined with a nonlinear model of the DFP transmission and full-field flow wind profiles are used for a realistic performance evaluation scenario. By simulation, it is found that the performance of the optimal controllers using the DFP transmission is similar to that of the NREL controller using a conventional transmission.