As a new coming technique in the gas flow measure area, Ultrasonic flowmeters (USF) are just becoming the most favorite selection, special for the nature gas transport project. Due to the accuracy, stability, no pressure loses, wide measure range, and low cost, the Ultrasonic flowmeters just show its competitions.
USF can be used to measure the gas and liquid both, there are same theories: Ultrasonic flow meters determine the fluid velocity by transmitting pulse stream upwards and downwards and measuring the transit times. The times are used in calculating the sound and flow velocity of the fluid. When ultrasonic wave transits at the stand and moving media, according the fix coordinates (such as the meter body), the sound speed is different, and the diff is a function of the media's moving velocity. So we can get the media's velocity by measure the time of flight of the wave. Then get the flow rate. The USF's usage for liquid flow measure is developed for a long time, and got excellent success. But the usage for gas is just beginning for almost ten years, and the technique is grasped just by several companies.
Because the complexity of measurement environment, the gas flow measure application will encounter more factors causing errors: the changes in velocity profiles due to installation effect and wall roughness, the pressure flaps in the pipes, ultrasonic noise produced by the regulator etc. In order to overcome those defects, the technique of fluid mechanics simulation and digital signal processing are applied to research on the flow characteristics and Laguerre filter based adaptive methods.
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Due to the great demands made on newly developed systems the importance of the integration of mechanics, electronics and informatics in mechatronic systems is ever increasing.
This thesis describes the development of mechatronic systems considering as example clamping systems for 3D-laser welding and milling process. For the accurate accomplishment of the laser welding operation three-dimensionally shaped pieces of sheet metal must be located in position. The occurring sheet clamping forces during laser welding are determined. Different physical effects for the power transmission onto the sheet metal are investigated. Furthermore several concepts are presented for the positioning of hydraulic cylinders without position measurement systems, and new types of hydraulic components are introduced. In the second part of this thesis the development of autonomous clamping systems for milling process is presented. The necessary hydraulic components are introduced as well as the accumulator and the controller. The communication between the clamping system and the machine control is realised by radio transmission. Further on an autonomous hydraulic power supply is presented which meets the requirements of the industry concerning robust and simple design.
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Aim of this PhD thesis is the development of the 1D simulation model of the lubrication circuit for a diesel ICE; the math model being faithful following some experimental validation. The model represents an useful tool for the design of the lubricating pump, whose capacity has both to fulfil the exact requirements of oil consumers during all operating conditions and to avoid unnecessary pressurising of the hydraulic network. A single overhead camshaft diesel engine of a medium size passenger car has been analysed and the pressure-flow rate requirements of oil consumers have been investigated. The main oil consumers are nozzles providing an appropriate flow rate to the piston undercrown for cooling and lubricating cylinders and the crankshaft journal bearings.
A rig for testing piston cooling jets has been assessed and the simulation model has been developed matching the experimental results.
The simulation model of the entire network has been built-up in the AMESimTM environment and predicts the flow rate demand and the pressure level within the circuit as functions of the engine speed and oil pan temperature.
Simulation outcomes brought to evidence the mainly laminar flow regime within the network. Furthermore, simulation has showed that fluid resistance of the lubrication circuit reduces with the engine speed. The reasons of the fluid resistance variation are (1) the increase of drag flow within journal bearings and pressure supplying connection rod bearings and (2) the lowering of oil film mean viscosity. Therefore, if the lubrication circuit should be lumped to represent the load for simulation purposes or if a test rig for lubricating pumps has to be developed, it is necessary to consider a laminar restrictor whose section increases with engine speed.
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The thesis is embedded within the field of aeroservoelasticity. A sophisticated robust controller design method for regulation of weakly damped aeroelastic wing structures using the primary flight controls is presented. Moreover, the impact of underlying system architectures, the performance of the actuation system, its robustness as well as selected failure cases are considered. The investigation of the system structure interaction comprises detailed models based on physical representatives, non-linear simulation and real hydraulic actuation systems within an integrated aeroservoelastic hardware-in-the-loop simulation.
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The industry - and especially the mining industry - asks nowadays for energy efficient on/off-valves. This request can no longer be fulfilled by the usually used solenoid valves due to the fact that their potential seems to be exhausted. Thus, a piezoelectric on/off pilot valve for mining application has been developed in this dissertation. This valve allows for a reduction in power consumption of the factor 2.5 compared to usual solenoid pilot valves.
The use of modern manufacturing technology together with numerical stress and flow simulation allowed the development and the realisation of a working prototype during the course of the research work. Two facts are of fundamental importance for the function of the overall system "piezo valve" in this context. Firstly, the development of a temperature compensation for the piezo actuator, which neutralises the thermal contraction of the actuator over the whole temperature range of the valve. Secondly, the development of a valve stage which takes into account the very small displacement of a piezo actuator, and still ensures the hydraulic performance asked for.
The valve developed during this research work is able to provide working pressures higher than asked for after the switching of the valve in a reproducible manner. The functional prototype produced a pressure level of 128 bar, even surpassing the flow rate of out of the shelf solenoid valves. The sealing system ensures internal and external tightness, both static and dynamic. The use of piezoelectric actuators to realise an on/off pilot valve with CAN bus interface as described in this dissertation pushed the state-of-the-art of mining technology further on. Thus, a far reaching flexibilisation of mining equipment regarding the composition of the control equipment is possible in the near future.
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Modeling and analysis using Finite Element Method (FEM) have not been applied so far for the prediction of servovalve characteristics, which can be characterized as a coupled problem encompassing Fluid-Structure Interaction (FSI).
The objective of the present research work is to develop a design methodology to study the dynamics of the FSI of jet pipe EHSV with built-in mechanical feedback using FEM. The FSI is established by modeling the mechanical parts, fluid filled cavities and the interaction between the two domains. The mechanical parts of the jet pipe EHSV are modeled with general-purpose finite elements like beam, shell, and solid elements while the fluid filled cavities with special-purpose hydrostatic fluid elements. The pressure and flow variations in the fluid cavities of the servovalve are functions of jet pipe and spool positions and these are implemented using external subroutines. These subroutines are active throughout the analysis to capture the instantaneous jet pipe and spool positions. The FE analysis is carried out to study the steady-state valve operation, flow gain and load flow analysis of servovalve-actuator system. The velocity of spool and piston obtained through the FE simulation matches well with the theoretically obtained results. Thus the FE model using fluid cavities and fluid links created to establish the FSI of servovalve-actuator system is adequate.
An experimental setup has been designed and fabricated to test the stiffness of critical components of jet pipe EHSV- feedback spring assembly and flexure tube. The stiffness values obtained from experiments agree well with the values obtained from FE simulation.
The FE analysis is extended to study the response of critical components - feedback spring assembly, jet pipe assembly and actuator to determine the individual resonant frequencies. The frequency responses of the servovalve and the servovalve-actuator system have been carried out with and without the FSI. Estimated the operating bandwidth and phase lag of the servovalve and servovalve-actuator system. The obtained results compare well with the data of commercially available devices.
Also a simplified empirical model of jet pipe EHSV is developed and simulated using MATLAB with the various parameters obtained from the FE model. The simulation results agree well with the FE simulation results verifying the correctness of the detailed FE model with FSI included.
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Nowadays, the environmental and comfortable performances of machinery are becoming increasingly the focus of attention and a crucial force to promote the development of engineering and science. For sure, the fluid power technology should follow this development direction, in which the noise control is one of key fundamental research subjects. The flow-induced vibration fields are the source of noise in essence. At present, the deep understanding of the hydraulic valve noise based on investigating into the flow is still lack, mainly because of the complicated flow in the small size internal flow passage of hydraulic valves.
In this thesis, Computational fluid dynamic (CFD), theoretical analysis and extensive experimental approaches including the pressure distribution measurement, the visualization of cavitating flow and the external sound noise frequency analysis were used to investigate the noise characteristics of the grooves in spool valve. A new test rig used to measure the pressure distribution in groove has been proposed, thus the mechanism of the noise differences related to the different grooves can be investigated. It was found that both the grooves with a passage of same cross-section areas and the grooves with large sloping angel can be used to reduce the cavitation noise levels effectively because these two type groove configurations can increase the pressure distribution in groove. Another interesting result is that the steady flow force in spool valve consisting of groove changes with the shift of the flow direction on the groove pass. In the converging flow direction, the value of the flow force is small, and furthermore its direction tends to open the valve in middle range of valve openings. An interpretation was proposed that the bubble growth process is determined mainly by the pressure distribution in grooves and the bubble maximum size just before collapse is the most important factor to the sound noise level. The research results presented in this thesis have showed the importance in both practice and theory for the improvement of the low-noise performance of the grooves in hydraulic valve.
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Now, with energy resources being consumed increasingly to be exhausted and environment pollution being serious gradually, wind power is paid great attention to by more and more countries as renewable resource and pollution-free energy resource. The technology also becomes research hotspot of many scholars.
In the thesis, the variable-speed constant-frequency pitch-controlled theoretical basis is put forward by research of wind turbine aerodynamic characteristics and is proved rationally by model emulation. Based on the domestic element and process level, the electro-hydraulic proportional pitch-controlled actuator is designed according to the characteristics such as rapidity, energy conservation and security. The pitch-controlled wind turbine semi-physical simulation test-bed is formed, with the pitch-controlled actuator, load device and control being real and the other components of the wind turbine being substituted by emulational models. The semi-physical simulation test-bed equals to the real pitch-control wind turbine. In the test-bed, the control performances can satisfy all the demands under the condition of starting up, lower the rate wind speed, above the rate wind speed, parking, normal stop, and emergency stop. Because of the great nonlinearity of wind turbine, the traditional PID control effect is not very perfect. The model predictive control is adapted for pitch control. Support vector regression algorithm is used to identify wind turbine nonlinear system. Because the differential circuit is used in the electro-hydraulic proportional pitch-controlled system, the model of feathering is different from that of backpaddling. Therefore, the two models are switched in the predictive control course. Considering that torque impact has greatly effect on the life length of gearbox, the torque load limited constraint condition is added to predictive control. Then, when wind speed is up the rated speed, the generator power is kept more steadily around the rated speed and the pitch load fluctuation is lower than that by adopting the traditional PID control.
The individual pith control by electromotor is also another good power control method. The actuator is designed in the thesis. The control strategy is to combine fuzzy control with the weight number that is mainly decided by the acceleration and the blade azimuth angle. The simulation result indicates that when the wind speed is higher than the rated speed, the pitch load fluctuation is greatly reduced and the output power is kept around the rated speed.
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Future mechatronic systems of mobile working machinery have special requirements to satisfy functional safety. Therefore a safety-aligned development concept, consisting of process model, methods and tools, was worked out, which describes the required measures from synthesis to validation of mechatronic systems. A typical tractor/implement-combination was used as testing object, where automation strategies in terms of complete headland management or autonomous process-automation ("Implement Guided Tractor Control") above the state of the art were implemented. Due to parallels in system architecture, available technologies and dynamic working circumstances, the selected application is exemplary for mobile working machinery. This thesis describes generally the process model of the development concept. After choice of safety-appropriate system architecture suitable, partly enhanced methods are introduced and assigned to each development step. Therefore the specified maximum risk level for the corresponding system is decision criterion. Advantages of a continuous model-based approach are shown. One striking example is the development and implementation of a safety-aligned dispensation of hydraulic resources. Problems of conventional "Load Sensing"-systems are identified in field tests and a new electronic alternative concept is introduced and validated. Furthermore test results document validation of the overall experimental vehicle automatics, which had been worked out according the development concept, and allow generalization of the results for the whole area of mobile working machinery.
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Recently, in order to overcome the major disadvantage of oil hydraulic systems such as their potential fire hazard and environmental pollution, a new way of thinking on fluid power control technology has begun with the concept of using tap water as a working fluid.
One of the most important components in constitution of water hydraulic systems is flow or pressure control valve. Water hydraulic servo valve and proportional control valve have already been developed. Due to their high performance characteristic, these are very useful in many cases of water hydraulic application, but their price level is very high and serious attention for the maintenance must be given at the time of use. Accordingly, the flow or pressure control using high-speed solenoid valve controlled by PWM control method could be a good solution for these problems.
This dissertation is concerned with the development of a novel water hydraulic high-speed solenoid valve with a two-stage mechanism. By virtue of the two-stage mechanism and proposed particular design, which use the leakage flow through the clearance between the main poppet and sleeve as internal pilot flow, it is possible for the developed valve to have unique features, such as no internal leakage, fast switching, large rated flow, high rated pressure. Furthermore, in order to improve the problems related to practical use of the developed valve such as large flow fluctuation and noise, the method for using proportional poppet as the main valve as well as setting the maximum opening area of the pilot valve as the main valve does not reach to the stroke end is proposed. Through the application of proposed method, it is identified that considerable amount of the flow fluctuation is reduced and approximately 3[dB] of sound pressure level is reduced in comparison with the water hydraulic two-stage high speed solenoid valve which uses ordinary poppet.
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Due to growing product requirements of the market hydrostatic systems have to perform a steadily growing number of functions. At the same time they have to be highly reliable while remaining on a low price level. Although it seems to be sensible to approach development problems of such complex products systematically, the generally acknowledgement design methodology VDI-guideline 2221 is far from being used on a desirable level. Furthermore in most businesses does neither a systematic documentation nor a further use of projecting knowledge of previous development projects take place because adequate documentation methods and tools are lacking or there is simply little to no time allowed for these tasks.
In this thesis a web based projecting tool for hydrostatic systems has been developed and prototypically implemented. This makes it possible for the often distributed working project teams to work on a common, phase overlapping development platform. The generally digital information processing is based on a product reference model especially developed for hydrostatics from this specific product models can be deduced.
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The supplement of information on the component's condition is important for complex automation systems at any time. This improves safety, can be used to schedule maintenance and helps to avoid breakdowns. To pay off in reduced costs, the online condition monitoring system itself has to be reliable in its predictions and must be easily useable with low additional investments needed. This thesis describes the development of condition monitoring functions for electrohydraulic linear drives, which actually lack functions to supply information on the component's condition. The work is based on the idea that signals and data, being available on electrohydraulic drives for the purpose of digital control, can be additionally used for peripheral condition-monitoring. No additional sensors are necessary.
For verification purpose fault test rigs are used. Increased friction, leakage and spool wear are simulated at the test stand. Parameters are identified correctly and changes in parameters can be observed.
The computational effort for model-based fault detection with linear and non-linear parameter estimation is calculated for multiple processor types and presented in detail. The implementation and integration into the peripheral control concept is studied by means of programs on PC, microcontroller and an real-time system together with a control task.
The investigated algorithms provide an early detection of progressive faults and simultaneously help to recover the causes for failures. For microcontrollers and DSPs in the controls of electrohydraulic linear drives with different sensor configurations, this thesis provides experiences with a variety of condition monitoring functions.
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This thesis addresses the position control problem of manipulator robots with hydraulic drives. These robots have a great potential of application in the construction industry, agricultural equipment, transport and material handling equipment, mining equipment, manufacture, siderurgy, metallurgy, aviation, navy and others industry fields, it due to advantages of the high relationship torque/dimension and the flexibility of installation of their actuators. However, there are many difficulties to reach precise response in hydraulic actuators. Telling about these difficulties, we can point the dynamics less damping, the dead zone of control valves, the friction in the actuator's sealing, the obtainment of the system parameters and the strong coupling between the non linear dynamics of actuators and the mechanic arm in hydraulic robots. In the survey of state of the art of the hydraulically actuated manipulators, the few technical literatures about control of hydraulic robots don't tell about all of these difficulties. So, a non linear model of 5º order is developed to the hydraulic robot considering the dynamic friction based in microdeformation of the roughness in the surfaces of contact. Observing the dynamic behavior of the pressure in the valves gaps, a methodology to identify and compensate the dead zone in proportional directional valves is proposed. Based in the robot model, a strategy of cascade control is used, allowing a division into two subsystems: the mechanical subsystem and the hydraulic one. The cascade controller is adequate in the implementation of control techniques to compensate the dynamic difficulties of each subsystem, it allows the direct compensation of the friction in the mechanical subsystem and the utilization of a centralized control scheme to take into account the dynamic coupling. The stability analysis of the complete system in closed loop with the cascade controller and friction observer was made through the Lyapunov direct method. The prototype of hydraulic robot was built for experimental implementation of the control algorithms developed in this thesis. Theoretical and experimental results show the validity and the features of the proposed cascade controller.
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In a hydraulic system using standard hydraulic actuators, the compound control of displacement and thrust is not easy and complicated control technique is required. In such a hydraulic system, high-performance servo valve, displacement and force sensors are necessary. As a result, the system becomes very complicated, and the size and cost becomes relatively large and high.
In this research, a novel hydraulic actuator is developed to realize simplicity and miniaturization of the usually complicated hydraulic system, in which compound control of displacement and thrust is required. This actuator is a kind of compact hydraulic cylinder system, which consists of a stepping motor, a control valve with a spool and a slide sleeve, a hydraulic cylinder and built-in mechanical feedback mechanisms, without any servo valve or force sensors. The mechanical feedback mechanisms are incorporated to have displacement and pressure feedback functions so that compound control can be accomplished. And the slide sleeve is supported by the springs on both sides, so that the actuator has mechanical flexibility and compliance control function.
In this dissertation, the explanation of the working principle for compound control was conducted, and the basic characteristics of this actuator were investigated theoretically, and the static and dynamic characteristics were tested experimentally. An orifice adjustment method was introduced to improve the dynamic performance for compound control, and then its effectiveness was confirmed by simulation study and experiments. In addition, the compliance control method by adjusting the system-spring-constant virtually was proposed. And the theoretical analysis and the preliminary experiments showed its effectiveness. Finally, as an application, experiment of grasping and lifting a ball was conducted. It was confirmed that the actuator can be used for the control of displacement, thrust and compliance.
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The knowledge of the ageing mechanism of ecologically compatible hydraulic oils is of great importance to the improvement of their oxidation stability.
Therefore, in this research work, a comprehensive investigation on the ageing mechanism of trimethylolpropane-tri-oleate (TMPO) was carried out by means of chemical analysis.
Firstly, the ageing mechanism of TMPO and the influences of metal catalysts and additives were studied with a Rotary Bomb Test apparatus in laboratory tests. The results show that the main ageing mechanism of TMPO involves free radical reactions. The catalytic action of metals takes effect by metal ions. On the one side, the metal ions can accelerate free radical reactions. On the other side, they can co-ordinate with free radicals at higher temperatures and produce complexes, whose formation decelerates the oil ageing. Added phenol antioxidants acting as radical scavengers can obviously improve the oxidation stability of oils. In addition, Vitamin C and its derivatives exhibit a great synergism with them.
Further, the ageing behaviour of TMPO in bench tests was compared with the expected results deduced from the laboratory tests. The investigation shows that the viscosity and the acid value of oils can be used as characteristic indicators to evaluate the ageing levels of oils in the bench tests. The combination of laboratory tests and bench tests is valuable to understand the real ageing mechanism in practical use. Finally, tendencies towards effective antioxidants-systems were concerned to greatly improve the oxidation stability of ecologically compatible hydraulic oils.
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By H. Murrenhoff
Publisher: Shaker, Aachen
Edited by National Fluid Power Association
Publisher: OMNIPRESS, Madison, Wisconsin, USA
Edited by Y. Lu, Q. Wang and W. Li
Publisher: International Academic Publishers, Beijing, China
By Noah D. Manring
Publisher: John Wiley & Sons
It has been 38 years since Herbert Merritt wrote and published his classical work, "Hydraulic Control Systems". Since Merritt first published his book in 1967, other texts have appeared in the literature, but none have managed to displace his volume as it sets forth general principles and a more rigorous development of the fluid power science. Even so, Merritt's text has carried with it a significant deficiency that has made its use in the academic world somewhat cumbersome; viz., the classic text contains no pedagogical resources which ought to include homework and example problems. Furthermore, 38 years of textual stagnation has dated the book and modern updates have been needed for some time. It is with great appreciation for Herbert Merritt that this updated text is being offered.
As previously noted, this present work has been written to remedy the pedagogical deficiencies of Merritt's text and to make updates where they are needed. To address the teaching needs, a preliminary section has been added to the book in which fundamental concepts of fluid mechanics and system dynamics are reviewed. Furthermore, each chapter has been concluded with a section of homework problems that may be used to exercise the student and to assist the instructor. Scattered throughout the chapters are example problems noted as Case Studies. These case studies are aimed at illustrating points within the text, and at showing the student how to implement and use the equations. Technical updates have also been added as research over the past thirty years has advanced the state of the art in this field. In particular, a more thorough analysis of transient fluid flow-forces has been added to the section on valves; and poppet valves, which were omitted from Merritt's text, have now been included. In the area of pumps, a discussion of flow ripple has been introduced for both gear pumps and axial-piston pumps. Also, an updated analysis of the pump control problem has been added for swash-plate type machines. For hydraulic system design, a methodology suggested by Richard Burton at the University of Saskatchewan has been used throughout the text. This methodology begins the analysis at the load point of the system and works its way backward to the ultimate power source. For each hydraulic control system that is discussed in the text, control objectives of position, velocity, and effort are illustrated using reduced order models and PID controllers.
Though the efforts of this current work are well-intended, undoubtedly readers will find deficiencies that will need to be addressed at some time. With a bit of history in mind, the author welcomes future updates of this work and only pleads with the critic not to wait for 38 years.