In this thesis the numerical simulation of the non-isothermal turbulent flow is applied as a tool to investigate the flow in the atmospheric boundary layer. There are a variety of phenomena that influence the atmospheric flow. To take them into account, the whole set of the three-dimensional, time dependent conservation equations defined for mass, momentum, energy and scalar quantities, must be solved. Atmospheric flow and dispersion modelling is closely connected with the environment protection and safety. The attention is focused on the numerical prediction of velocity and concentration field in micro-scales. The possibilities of general computational fluid dynamics (CFD) codes application are investigated and the practical problems are solved, including the accidental release of gaseous pollutant in the complex terrain obtained from the geographical information database (GIS).
The PhD-thesis deals with hydraulic supply systems for continuously variable chain drives in automotive applications. Only continuously variable transmissions provide the opportunity to adjust the transmissions ratio independently from the engine speed to the cars driving condition (speed). Continuously chain or metal belt drives transmissions therefore provide the best driveline efficiency. Due to the fact, that the torque is transmitted by friction a especially designed clamping system is needed. This system normally uses hydraulic elements because of their high power density. To provide the necessary oil flow a hydraulic supply system is needed.
After a short description of the conventional constant flow clamping and supply system (introduced by P.I.V.-Reimers) modifications to improve the efficiency for the use in a hybrid car and a tractor are shown. By using quasistatic simulations with MATLAB/SIMULINK it is shown that up to 0,3 l/100 km fuel (diesel) can be saved in the FTP 72 test cycle when the constant flow hydraulic supply system for the chain variator is optimized in the hybrid car and the energy consumption is reduced to a minimum. A mechanically driven system with an electronically open loop flow controlled vane pump with variable displacement therefore pro-vides the best effort. For the use in the Hybrid car an additionally supply system with a speed controlled purely electrically driven gear pump is necessary. The static and dynamic system performance was measured and simulated using MATLAB/SIMULINK. The maximum efficiency of both supply systems is 72 % at an oil flow of 8 l/min and a system pressure of 45 to 55 bar. The dynamic behaviour was tested by measuring the systems response on an step increase of the desired oil flow from 5 l/min up to 8l/min. At a relatively high system pressure of 50 bar the purely electrically system reaches the new set value after a delay of 45 ms, in the same test the mechanically driven system with an open loop flow controlled vane pump takes 60 ms at a system pressure of 30 bar. The dynamic performance therefore is quite sufficient for the use in automotive applications. Simulations of the transmissions clamping system show that the lowest possible hydraulic energy consumption can be achieved by a new flow and pressure controlled clamping system for the CVT without any throttle losses. Therefore a first approach of the corresponding hydraulic supply system is presented and tested theoretically using dynamic simulations.
In this study, a soft actuator, made of silicone rubber and driven with compressed air, has been developed. This actuator has the essential flexibility owing to compressed air and the elasticity of silicone rubber. Paying attention to these features, it is applied to an in-pipe mobile robot and a soft robot hand. In the in-pipe mobile robot, it can travel in various types of pipes with diameter changing at a joint and with an arbitrary sectional shape. In the robot hand, it can grasp unshaped or flexible objects without any complicated control algorithm. The validity of soft actuator has been confirmed through some experiments.
Hydraulic circuits are characterized by high power density. Therefore, the tribological systems of the components are considerably stressed by friction and wear. Modern coating processes like PVD (Physical Vapour Deposition), Plasma Diffusion and Thermal Spraying enable sufficient wear protection. Moreover, frictional characteristics of the surfaces are improved with suitable coating materials.
In this publication, the tribological properties of coatings are investigated and compared to standard materials. At first, results concerning friction and wear from basic investigations with simplified specimen are presented. Then, coated piston guides and piston rods in hydraulic cylinders and coated pistons and valve plates in axial piston pumps are investigated. The results indicate, that especially the wear resistance of the components is decisively increased by coatings. It is shown which coating processes and which coating materials are best suited for specific applications.
In the design of automobiles, occupant and pedestrian safety are important design issues. If a vehicle were to be involved in a collision or near-collision, it would be desirable, if the on-board systems could detect impact or potential impact, handle safety through deployment of various safety systems, and steer away from impact. For this, an impact study to find the location and magnitude of impact and damage identification is relevant. Two different scenarios are discussed: 1) Non-damaging impact -- the severity of impact is considered to be limited as not to cause structural damage; 2) Damaging impact -- the impact is severe enough to cause structural damage.
For non-damaging impacts, a generalized dynamic methodology is developed based on the Mindlin Plate Theory, the Rayleigh-Ritz energy approach, and the Hamilton principle. This procedure is demonstrated for a simply-supported rectangular plate for static and impact loads, with point and area contacts. The forward model results (predicting strains for known forces) are compared with FEA and known analytical solutions and are found to be in good agreement. An algorithm using deconvolution for identifying the impact location and magnitude for a set of known strains (inverse model) is developed and compared to a forward model study. The known impact force history in the forward model and the output from the inverse algorithm compared favorably.
In order to implement sensor integration, the sensor gain factor and parameters that affect smart sensor performance are also investigated using a Taguchi method. Gain factors obtained using FEA and experimental work are used in both forward and inverse models.
In the case of a damaging impact, forward dynamic analyses for undamaged and damaged plates are performed for a known set of forces. Analyses are carried out for nine different damage locations on a simply supported plate and six different damage sizes (0.01% to 10%). Changes in frequency and mode shape assist in assessing damage severity.
This work, using distributed smart systems is useful for impact identification and damage assessment in a structure. Future application of this approach is envisioned in the area of automobile and passenger safety.
Ideal hydraulic force models have been used in active suspension studies for decades, but few studies have investigated hydraulic effects, which are the core of system force generation. This thesis details the mathematical modelling and controller design of a quarter car active suspension test rig. An emphasis is placed on the hydraulic modelling and unknown parameters in the model were experimentally identified. A new approach was used to identify the system by the transformation of the quarter car model to one-DOF and two-DOF models. This reduced the model complexity and allowed the parameters to be identified from a series of transfer functions linking vehicle parts and the hydraulic models. Non-linear gain compensation was designed to aid the linearised modelling. Simulation and experimental results were then compared. It is shown that the hydraulic component model is crucial to formulate accurate active control schemes. Full-state feedback controls were realised by pole-assignment (PA) and linear quadratic optimal method (LQ). Simulation results suggest that even though the performance of active suspension designed by the PA is superior to that of the optimum passive suspension, it still possesses a design constraint similar to the passive system, in which the optimum design is a compromise between the natural frequency and transmissibility effects. With a different design concept, the LQ provides a better solution because the method effectively shifts the dominant natural frequency to a very low frequency range. This allows the damping rate to be increased to its critical value with the smallest effect on the transmissibility. Experimental results reveal that the identified model with the LQ controller may be used to predict the dynamic responses of the actual system within certain ranges of design parameters because of a considerable difference between the initial condition of the test rig and the linearised operating design.
The axial piston pumps and motors are required to be operated in a higher-pressure area from the viewpoints of energy saving and of high power density. This thesis deals two types of axial piston pump and motor, i.e., swash plate type and bent axis type. The two types of pump and motor have two common sliding parts. One of the sliding parts is between piston and cylinder, the other is between rotor and valve plate. The method of theoretical analysis considering the interaction between the motion of the sliding elements and the lubrication characteristics is presented, the validity of the theory is confirmed by experiments and some suggestions for design are also proposed.
In this thesis a concept for semi-active aircraft landing gear systems controlled by fuzzy-logic is developed and the potential improvements on the landing gear and aircraft dynamics are investigated. It is shown that by semi-active landing gear systems the maximum structural loads induced by the touchdown impact can be significantly reduced and the passenger comfort on the rough runways can be considerably improved.
Streamline coordinate systems are effective on solving the flow inside the channel with curved solid walls and the flow with free surfaces. In the streamline coordinate systems used in this dissertation, one coordinate is taken along a streamline and the other coor-dinate is taken orthogonal with streamlines. The flow is assumed to be viscous, incompressible and steady. The governing equations are derived using a method of metric coefficient. In this dissertation, a new numerical method is developed to solve the governing equations. The flow in a poppet valve and the jet from a coaxial pipe are analyzed, and the validity of this method is confirmed by comparing the obtained results with previous experimental results. This method especially useful for computing the flow force acting on the walls of channel.
Smart materials such as piezoceramics are being widely used as actuators and sensors in micro-positioning and active control applications. However, a major limitation of actuators made of piezoceramics is the non-linearity arising due to hysteresis, particularly under high electric fields. It is desirable to have a methodology to predict the effects of hysteresis for these actuators.
The problem is even more challenging for new classes of piezoceramic smart material actuator. These actuators are complex, elasto-ceramic structures embedded in a wide variety of material matrices. Hysteresis modeling via first principles is virtually impossible for such actuators. Hence, phenomenological approaches are of great interest. The main objective of this dissertation is to investigate the application of the Preisach approach, which is a popular phenomenological model, to predict the hysteresis effects in state of the art piezoceramic actuator systems.
Preisach models have been successfully used in the past to predict hysteresis in ferromagnetic system. However, in order to successfully predict the hysteresis for a piezoceramic actuator system, the model, its identification and implementation must take into account the differences in the hysteretic behavior of ferromagnetic and piezoceramic materials. In this research, a modified geomet-ric interpretation and numerical implementation method has been developed to describe the phenomenon of the piezoceramic hysteresis. A new type of dynamic Preisach model has also been proposed by introducing the dependence of the Preisach function on the input variation rate. Finally, in order to simplify and generalize the identification process, a new approach, Wavelet identification for Preisach model, is presented in this dissertation.
The level of performance of the new approaches has been tested by comparing the experimental results to those predicted by the models. The results of this comparison show that the improved Presisach model can be successfully used to predict the hysteresis response of peizoceramic actuator systems.
This study was attempted to solve the problems associated with a swash plate axial piston motor when it operates at low speed and start. To measure the performance of the motor at low speed a special test method 'low speed test' was used. High friction of the bearing elements in the motor caused the mechanical and volumetric loss at low speed. The shares of mechanical and volumetric loss from different bearing elements are identified with the methods of measures and analyses, so that the improvement potential of the bearing elements can be appraised accurately.
By use of new materials such as PVD- coating friction can be reduced. A piston-cylinder test bench was used to choose the proper PVD- coatings. The piston and valve plate were coated with different materials by means of PVD and some combination showed improvements of the mechanical efficiency. With design changes of the swash plate the volumetric efficiency can be improved. By means of a new designed construction valve plate it was possible to increase the start torque of the motor. A novel motor which combines the advantages of bent axis and swash plate motor with a joint was designed, constructed and researched.
Edited by: A. Esposito
648 pages
Publisher: Prentice Hall
ISBN 0130102253
This study places emphasis on understanding how fluid power systems operate and on their practical applications. A basic background in the field of fluid power is provided, allowing students to understand the design, analysis, operation and maintenance of fluid power systems.
Edited by: M. E. Meadows and T. M. Walski
316 pages
Publisher: Haestad Press
ISBN 0965758060
With over 100,000 users in more than 160 countires, Haestad Methods is the world's leading provider of hydraulic and hydrologic computer modeling applications. Haestad Methods also leads the way in providing the practical resources necessary for understanding the rapidly advancing role of computer technology in civil engineering with IACET-certified and PDRES-accredited continuing education workshops, the Online RFP database CivilProjects.com, and Haestad Press - computer-aided water modeling publications.
Edited by: K. Mobley
360 pages
Publisher: Butterworth-Heinemann
ISBN 0750671742
A specialist in industrial power plant dynamics provides plant managers, maintenance managers, operators, and trainees with an introduction to fluid power in industrial plants. The volume is divided into two sections covering hydraulics and pneumatics. In both sections, the subject matter ranges from basic principles and elements of the system through maintenance and troubleshooting.
Edited by: F. D. Norvelle
285 pages
Publisher: Prentice Hall College Div.
ISBN 0137163592
This book provides readers with a very broad introduction to the basic concepts of electrohydraulics control systems specifically, and motion control in general. It includes both the mechanical and electrical aspects of the various types of valves, and methods of controlling them.
Other chapter topics include reviews of basic fluid power and electricity, sensors, programmable logic controllers, and robotics. This book serves as a solid foundation upon which to build and apply more specialized knowledge. For technicians involved in the industry-an industry which desperately needs this type of background.
Edited by: J. Ruan
281 pages
Publisher: Zhejiang University Press
ISBN 7 308 02117 3/TP 237
First Published in January 2000
The book includes nine chapters. Chapter 2 is a summary of fundamentals of compressible and incompressible fluid mechanics relating to fluid power control. In Chapter 3, the concept of valve-mechanism is introduced and the operation principle and characteristics for the various hydraulic and pneumatic valves are analyzed and discussed. Chapter 4 and 5 are the theory for constructing various types of 2-stage valves (called 2D valves) using linear and rotary motions of a single spool. The advantages of 2D valves, such as dirt-tolerance, very small pilot leakage and high level for both static and dynamic performance are demonstrated through experiments and simulations. In Chapter 6, 7 and 8, a new method for continual control of stepper motor is introduced. The continual control of stepper motor is undertaken by a one-chip computer system and inside "tracking:" algorithm. In this way, the dynamic response of the digital valves is greatly promoted. The hysteresis, repetitive error of the digital valves is reduced to 1/N (N is stepper number corresponding to full stroke of the spool) times of conventional servo/proportional valve, since the stepper motor operating under continual mode can be regarded as a N-polar proportional magnet. Besides, A digital "fragment" signal produced by the tracking algorithm acts as a dither and is beneficial to the reducing frictional force of the spool. The dynamic response of continual control and the design for soft/hard ware of the digital valve controller are presented. Chapter 9 is about application of digital valve in hydraulic (pneumatic) digital control system and software design. Several examples are given.
Edited by: N. Vasiliu
795 pages
Publisher: S.C. Editura TECHNICA S.A.
Language: Romanian
ISBN 973-31-1316-6
Fluid Mechanics And Its Practical Applications is a wide, important and interesting theoretical and technical field, which can be treated in some different manners. The authors of this book regarded the above field in close connection with many other scientific and technical fields, trying to create a global image of the realistic mathematical modelling, numerical simulation, experimental identification, and performance tests.
This volume contains the results of a systematic research on the steady-state behaviour, and the transients occurring in the hydro-static transmissions, trying to draw a straight line between theory and practice. The analysis, synthesis and design cover the fixed and variable displacement pumps and motors (piston, vane and gear), pressure and flow valves, electrohydraulic amplifiers, hydraulic and electrohydraulic servomechanisms, hydraulic and electrohydraulic servopumps and servomotors. Most of the theoretical treatments are presented in a practical manner, starting from the needs of the designers.