The Experts below are selected from a list of 846 Experts worldwide ranked by ideXlab platform
Seungbok Choi - One of the best experts on this subject based on the ideXlab platform.
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design and vibration control of military vehicle suspension system using magnetorheological damper and disc Spring
Smart Materials and Structures, 2013Co-Authors: Sung Hoon Ha, Minsang Seong, Seungbok ChoiAbstract:This paper proposes a new type of magnetorheological (MR) fluid based suspension system and applies it to military vehicles for vibration control. The suspension system consists of a Gas Spring, a MR damper and a safety passive damper (disc Spring). Firstly, a dynamic model of the MR damper is derived by considering the pressure drop due to the viscosity and the yield stress of the MR fluid. A dynamic model of the disc Spring is then established for its evaluation as a safety damper with respect to load and pressure. Secondly, a full military vehicle is adopted for the integration of the MR suspension system. A skyhook controller associated with a semi-active actuating condition is then designed to reduce the imposed vibration. In order to demonstrate the effectiveness of the proposed MR suspension system, a computer simulation is undertaken showing the vibration control performance of such properties as vertical displacement and pitch angle, evaluated for a bumpy road profile.
Sung Hoon Ha - One of the best experts on this subject based on the ideXlab platform.
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design and vibration control of military vehicle suspension system using magnetorheological damper and disc Spring
Smart Materials and Structures, 2013Co-Authors: Sung Hoon Ha, Minsang Seong, Seungbok ChoiAbstract:This paper proposes a new type of magnetorheological (MR) fluid based suspension system and applies it to military vehicles for vibration control. The suspension system consists of a Gas Spring, a MR damper and a safety passive damper (disc Spring). Firstly, a dynamic model of the MR damper is derived by considering the pressure drop due to the viscosity and the yield stress of the MR fluid. A dynamic model of the disc Spring is then established for its evaluation as a safety damper with respect to load and pressure. Secondly, a full military vehicle is adopted for the integration of the MR suspension system. A skyhook controller associated with a semi-active actuating condition is then designed to reduce the imposed vibration. In order to demonstrate the effectiveness of the proposed MR suspension system, a computer simulation is undertaken showing the vibration control performance of such properties as vertical displacement and pitch angle, evaluated for a bumpy road profile.
Christos N Markides - One of the best experts on this subject based on the ideXlab platform.
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An investigation of heat transfer losses in reciprocating devices
Applied Thermal Engineering, 2017Co-Authors: Caroline Willich, Christos N Markides, Alexander J. WhiteAbstract:The paper presents a detailed computational-fluid-dynamic study of the thermodynamic losses associated with heat transfer in Gas Springs. This forms part of an on-going investigation into high-efficiency compression and expansion devices for energy conversion applications. Axisymmetric calculations for simple Gas Springs with different compression ratios and using different Gases are first presented, covering Peclet numbers that range from near-isothermal to near-adiabatic conditions. These show good agreement with experimental data from the literature for pressure variations, wall heat fluxes and the so-called hysteresis loss. The integrity of the results is also supported by comparison with simplified models. In order to mimic the effect of the eddying motions generated by valve flows, non-axisymmetric computations have also been carried out for a Gas Spring with a grid (or perforated plate) of 30% open area located within the dead space. These show significantly increased hysteresis loss at high Peclet number which may be attributed to the enhanced heat transfer associated with grid-generated motions. Finally, the implications for compressor and expander performance are discussed.
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A two-phase single-reciprocating-piston heat conversion engine: Non-linear dynamic modelling
Applied Energy, 2017Co-Authors: Christoph J.w. Kirmse, Aly I. Taleb, Oyeniyi A. Oyewunmi, Andrew J. Haslam, Christos N MarkidesAbstract:A non-linear dynamic framework is presented for the modelling of a novel two-phase heat engine termed ‘Up-THERM’, which features a single solid moving-part (piston). When applied across the device, a constant temperature difference between an external (low- to medium-grade) heat source and an external heat sink is converted into sustained and persistent oscillations of pressure and volumetric fluid displacement. These oscillations are transformed in a load arrangement into a unidirectional flow from which power is extracted by a hydraulic motor. The Up-THERM engine is modelled using a system of first-order differential equations that describe the dominant thermal/fluid processes in each component of the device. For certain components where the deviations from a linear approximation are non-negligible (Gas Spring in the displacer cylinder, check valves and piston valve, and heat exchangers), a non-linear description is employed. A comparison between the linear and non-linear descriptions of the Gas Spring at the top of the displacer cylinder reveals that the non-linear description results in more realistic predictions of the oscillation frequency compared to experimental data from a similar device. Furthermore, the shape of the temperature profile over the heat-exchanger surfaces is modelled as following a hyperbolic tangent function, based on findings from an experimental investigation. Following the validation of these important device components, a parametric study is performed on the Up-THERM engine model with the aforementioned non-linear component descriptions, aimed at investigating the effects of important geometric parameters and of the heat-source temperature on key performance indicators, namely the oscillation frequency, power output and exergy efficiency of the engine. The results indicate that the geometric design of the displacer cylinder, including the height of the Gas Spring at the top of the cylinder, and the heat-source temperature have the most significant influence on the performance of the engine. A maximum exergy efficiency of 2.8% and a maximum power output of 175W are observed at the proposed operating temperature of 450°C for a nominal Up-THERM design (based on the physical dimensions of a device prototype and water as the working fluid; the role of the working fluid is explored in follow-up paper Ref. [1]) but with shorter displacer cylinder Gas-Spring lengths relative to a nominal design. The results and insight can assist the further development of this technology, in particular as a prime mover in combined heat and power applications.
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Experimental Analysis of Loss Mechanisms in a Gas Spring
Volume 2: ASME 2016 Energy Storage Forum, 2016Co-Authors: Paul Sapin, Drazen Fabris, Alexander J. White, Aly I. Taleb, Christos N MarkidesAbstract:Copyright © 2016 by ASME. Reciprocating-piston compressors and expanders are promising solutions to achieve higher overall efficiencies in various energy storage solutions. This article presents an experimental study of the exergetic losses in a Gas Spring. Considering a valveless piston-cylinder system allows us to focus on the thermodynamic losses due to thermal-energy exchange processes in reciprocating components. To differentiate this latter loss mechanism from mass leakages or frictional dissipation, three bulk parameters are measured. Pressure and volume are respectively measured with a pressure transducer and a rotary sensor. The Gas temperature is estimated by measuring the Time-Of-Flight (TOF) of an ultrasonic pulse signal across the Gas chamber. This technique has the advantage of being fast and non-invasive. The measurement of three bulk parameters allows us to calculate the work as well as the heat losses throughout a cycle. The thermodynamic loss is also measured for different rotational speeds. The results are in good agreement with previous experimental studies and can be employed to validate CFD or analytical studies currently under development.
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The Influence of Real Gas Effects on Thermally Induced Losses in Reciprocating Piston-Cylinder Systems
12th International Conference on Heat Transfer Fluid Mechanics and Thermodynamics, 2016Co-Authors: Aly Taleb, C Barfuss, Paul Sapin, Caroline Willich, A.j. White, Drazen Fabris, Christos N MarkidesAbstract:The efficiency of expanders is of prime importance for various clean energy technologies. Once mechanical losses (e.g. through valves) are minimized, losses due to unsteady heat exchange be-tween the working fluid and the solid walls of the containing device can become the dominant loss mechanism. In this device, Gas Spring devices are investigated numerically in order to fo-cus explicitly on the thermodynamic losses that arise due to this unsteady heat transfer. The specific aim of this study is to in-vestigate the behaviour of real Gases in Gas Springs and compare this to that of ideal Gases in order to attain a better understand-ing of the impact of real Gas effects on the thermally losses in reciprocating piston expanders and compressors. A CFD-model of a Gas Spring is developed in OpenFOAM. Three different Gas models are compared: an ideal Gas model with constant ther-modynamic and transport properties; an ideal Gas model with temperature-dependent properties; and a real Gas model using the Peng-Robinson equation of state with temperature and pressure-dependent properties. Results indicate that, for simple, mono-and diatomic Gases like helium or nitrogen, there is a negligible difference in the pressure and temperature oscillations over a cy-cle between the ideal and real Gas models. However, when look-ing at a heavier (organic) molecule such as propane, the ideal Gas model tends to overestimate the temperature and pressure com-pared to the real Gas model, especially if no temperature depen-dency of thermodynamic properties is taken into account. Ad-ditionally, the ideal Gas model (both alternatives) underestimates the thermally induced loss compared to the real Gas model for heavier Gases. Real Gas effects must be taken into account in or-der to predict accurately the thermally induced loss when using heavy molecules in such devices.
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A Framework for the Analysis of Thermal Losses in Reciprocating Compressors and Expanders
Heat Transfer Engineering, 2014Co-Authors: Richard Mathie, Christos N Markides, Alexander J. WhiteAbstract:This article presents a framework that describes formally the underlying unsteady and conjugate heat transfer processes that are undergone in thermodynamic systems, along with results from its application to the characterization of thermodynamic losses due to irreversible heat transfer during reciprocating compression and expansion processes in a Gas Spring. Specifically, a heat transfer model is proposed that solves the one-dimensional unsteady heat conduction equation in the solid simultaneously with the first law in the Gas phase, with an imposed heat transfer coefficient taken from suitable experiments in Gas Springs. Even at low volumetric compression ratios (of 2.5), notable effects of unsteady heat transfer to the solid walls are revealed, with thermally induced thermodynamic cycle (work) losses of up to 14% (relative to the work input/output in equivalent adiabatic and reversible compression/expansion processes) at intermediate Peclet numbers (i.e., normalized frequencies) when unfavorable solid a...
Frank Rinderknecht - One of the best experts on this subject based on the ideXlab platform.
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free piston linear generator and the development of a solid lubrication system
Journal of Energy Resources Technology-transactions of The Asme, 2018Co-Authors: Roman Virsik, Frank Rinderknecht, Horst E FriedrichAbstract:The free piston linear generator is a new electromechanical generator. It converts chemical energy into electrical energy by means of a combustion process, a linear generator and a Gas Spring. Thereby the technology aims to have better properties than other electromechanical generators. Therefore this publication deals with the explanation of the concept, the characteristics of a free piston linear generator and one of the challenges in the development. In order to use a port scavenging the emission issue is the challenge and has to be solved. One possible solution is the use of solid lubricants to substitute motor oil. The development methodology and one aspect of the development will be explained.
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a high efficient energy converter for a hybrid vehicle concept Gas Spring focused
2012Co-Authors: Florian Kock, Frank RinderknechtAbstract:Abstract: This publication deals with the concept, the explanation, the development and the actual measurement results of a free-piston linear generator (FPLG) with the focus on the Gas Spring. The free-piston linear generator is able to convert chemical energy into electrical energy by using a combustion process. In this publication the function and the characteristics of the free-piston linear generator will be explained first. Then the surrounding system and its effects on the FPLG are explained. This is important to understand the effect of every subsystem to the FPLG. In the next step the development based of the three base components, the Gas Spring [7], the linear generator [4] and the combustion [6] will be explained. Each chapter includes actual measurement results generated on a purpose-built test bench. At the end of the publication the current situation of the FPLG development and the further steps are represented.
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investigation of a high efficient free piston linear generator with variable stroke and variable compression ratio a new approach for free piston engines
World Electric Vehicle Journal, 2007Co-Authors: Markus Graef, Sven-erik Pohl, Peter Treffinger, Frank RinderknechtAbstract:Chemical energy can be converted to electricity with very high efficiencies by means of a free piston linear generator allowing a variable stroke and a variable compression ratio. Therefore online-downsizing in part-load is possible by reducing the stroke. As a result throttling, wall and friction losses are reduced. The paper describes the concept of the free piston linear generator, which is well suited for the HCCI-combustion process. It is expected that emissions and the fuel-consumption can be noticeable reduced. Calculations based on the NEDC indicate significant fuel savings for a mid-class car. Because of the non-existing mechanical coupling, cylinder cut-off can be realized very easily reducing the consumption of high power cars especially in urban drive cycles. The components linear generator and the Gas Spring have been built up and tested successfully. Examinations of the combustion process have begun on a fully variable electromagnetic valve-train test stand. A sophisticated adaptive control scheme is presented providing solid controls for the free-piston system. The paper describes the current status of the hardware development.
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investigation of a high efficient free piston linear generator with variable stroke and variable compression ratio
2006Co-Authors: Markus Graf, Peter Treffinger, Sven-erik Pohl, Frank RinderknechtAbstract:Chemical energy can be converted to electricity with very high efficiencies by means of a free piston linear generator, which allows a variable stoke and a variable compression ratio.Therefore online-downsizing in part-load is possible by reducing the stroke. As a result throttling, wall and friction losses are reduced The paper describes the concept of the free piston linear generator, which is also well suited for the HCCI-combustion process. Emissions and the consumption can be noticeable reduced. Calculations based on the NEDC indicate significat fuel savings for a compact car. Because of the non-existing mechanical coupling, cylinder cut-off can be practised very easily reducing the consumption of high power cars especially in urban drive cycles. The components linear generator and the Gas Spring have been built up and tested successfully. Examinations of the combustion process have begun on a fully variable electromagnetic valve-train test stand. The examinations contain the Gas exchange in two-stroke mode and the influence of the variable stoke and compression ratio on the combustion process. A sophisticated adaptive control scheme is presented which controls the whole system. The paper gives the actual status of the hardware development.
Shin-ichiroh Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Development of gait training system powered by pneumatic actuator like human musculoskeletal system
2011 IEEE International Conference on Rehabilitation Robotics, 2011Co-Authors: Shin-ichiroh Yamamoto, Yoshiyuki Shibata, Shingo Imai, Tatsuya Nobutomo, Tasuku MiyoshiAbstract:The purpose of this study was to develop a body weight support gait training system for stroke and spinal cord injury (SCI) patient. This system consists of an orthosis powered by pneumatic McKibben actuators and a piece of equipment of body weight support. The attachment of powered orthosis can be fit to individual subjects with different body size. This powered orthosis is driven by pneumatic McKibben actuators arranged as a pair of agonistic and antagonistic bi-articular muscle models and two pairs of agonistic and antagonistic mono-articular muscle models like the human musculoskeletal system. The body weight support equipment suspends the subject's body in a wire harness, with the body weight is supported continuously by a counterweight. The powered orthosis is attached to the body weight support equipment by a parallel linkage, and its movement of powered orthosis is limited at the sagittal plane. The weight of the powered orthosis is compensated by a parallel linkage with a Gas-Spring. In this paper, we report the detailed mechanics of this body weight support gait training system and the results of several experiments for evaluating the system.
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Development of body weight support gait training system using antagonistic bi-articular muscle model
2010 Annual International Conference of the IEEE Engineering in Medicine and Biology, 2010Co-Authors: Yoshiyuki Shibata, Shingo Imai, Tatsuya Nobutomo, Tasuku Miyoshi, Shin-ichiroh YamamotoAbstract:The purpose of this study is to develop a body weight support gait training system for stroke and spinal cord injury. This system consists of a powered orthosis, treadmill and equipment of body weight support. Attachment of the powered orthosis is able to fit subject who has difference of body size. This powered orthosis is driven by pneumatic McKibben actuator. Actuators are arranged as pair of antagonistic bi-articular muscle model and two pairs of antagonistic mono-articular muscle model like human musculoskeletal system. Part of the equipment of body weight support suspend subject by wire harness, and body weight of subject is supported continuously by counter weight. The powered orthosis is attached equipment of body weight support by parallel linkage, and movement of the powered orthosis is limited at sagittal plane. Weight of the powered orthosis is compensated by parallel linkage with Gas-Spring. In this study, we developed system that has orthosis powered by pneumatic McKibben actuators and equipment of body weight support. We report detail of our developed body weight support gait training system.
