Large water waves in reservoirs, lakes, bays and oceans may be generated by landslides, shore instabilities, snow avalanches, glacier and rock falls. For Alpine lakes impulse waves are particularly significant, due to steep shores, narrow reservoir geometries, possible large slide masses and high impact velocities. The resulting impulse waves can cause disaster due to run-up along the shore-line and overtopping of dams. The complexity of the phenomena posed formidable challenges to physical model experiments that encompassed laboratory set-up, measurement techniques and data analysis. The verified scaling law was based on the generalized Froude similitude. The granular rockslide impact experiments were conducted in a rectangular prismatic water wave channel. The slide impact characteristics were controlled by means of a novel pneumatic landslide generator, which allowed exact reproduction and independent variation of single dynamic slide parameters within a broad spectrum. The following four relevant parameters governing the wave generation were analyzed: granular slide mass, slide impact velocity, stillwater depth and slide thickness. The slope angle a = 45°, the slide granulate density rg =2.64 t/m3 and the grain diameter were not altered. State-of-the-art laser measurement techniques such as digital particle image velocimetry (PIV) and laser distance sensors (LDS) were applied to the decisive initial phase. The wave generation was characterized by an extremely unsteady three phase flow consisting of the slide granulate, water and air entrained into the flow. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into the kinematics of the wave generation process. Differential estimates such as vorticity, divergence, elongational and shear strain were extracted from the velocity vector fields. The fundamental assumption of irrotational flow in the Laplace equation was confirmed experimentally. At high impact velocities flow separation occurred on the slide shoulder resulting in a hydrodynamic impact crater, whereas at low impact velocities no flow detachment was observed. The hydrodynamic impact craters may be distinguished into outward and backward collapsing impact craters. The maximum crater volume, which corresponds to the water displacement volume, exceeded the landslide volume by up to an order of magnitude. The water displacement caused by the landslide generated the first wave crest and the collapse of the air cavity followed by a run-up along the slide ramp issued the second wave crest. The extracted water displacement curves may replace the complex wave generation process in numerical models. The recorded wave profiles were extremely unsteady and non-linear. Four wave types were determined: weakly non-linear oscillatory wave, non-linear transition wave, solitary-like wave and dissipative transient bore. Most of the generated impulse waves were located in the intermediate water depth wave regime. Nevertheless the propagation velocity of the leading wave crest closely followed the theoretical approximations for a solitary wave. Between 5 and 50% of the kinetic slide impact energy propagated outward in the impulse wave train. The main wave characteristics were related to the landslide parameters driving the whole wave generation process. The subaqueous slide run-out, the water displacement and the main wave characteristics were all described by multiple regressions of the following three dimensionless quantities: the slide Froude number, the relative slide volume and the relative slide thickness. The slide Froude number was identified as the dominant parameter. The obtained predictive equations allow a rapid assessment of the threats posed by a possible event. A detailed investigation, however, would require a full numerical simulation including the lake bathymetry and the surrounding topography. The physical model results were compared to the giant rockslide generated impulse wave which struck the shores of the Lituya Bay, Alaska, in 1958. The measurements obtained in the physical model were in agreement with the insitu data.
This thesis presents the development of new continuous electrohydraulic control concepts for central hydrostatic power control units (PCUs). The new PCU concepts involve a control chain with a servovalve and a rotational motor on the one hand and a secondary controlled variable displacement motor system on the other. Two different drive and control structure versions are presented for each concept. With the aid of modified PCU test units, the dynamic response in both the time and the frequency range is investigated theoretically and experimentally, with dynamic simulation models verified in laboratory experiments. System optimizations are essentially realized with regard to the starting, cruising and positioning response, as well as the power flow, and show, among other things, that the PCU concept with secondary control permits not only considerable potential power savings, but also safe operation of the high lift system through active and passive safety measures.
This thesis demonstrates the tribologically positive effect of a systematic contouring of sealing and bearing gaps in hydrostatic machines, instancing the piston cylinder assembly of swash plate type axial piston machines. Such geometry variations of the piston are only in orders of some micrometers, but nevertheless have a strong effect on the operating behaviour. Against the background of proceeding development in the area of production engineering, an economically justifiable production of these fine contours may be expected in the near future.
Within simulation influences of piston shape variations on viscous friction, leakage and the load bearing capacity of the gap between piston and cylinder is investigated systematically. The result shows an enormous, so far unused optimization potential for these three criteria. Basis of this theoretical investigation is the numerical solution of Reynolds equation and the equations of motion for the piston, considering the force balance between fluid forces inside the gap and external forces.
A second part of the thesis deals with experiment. In order to verify simulation results and to investigate the mixed friction area, a special test device has been developed. The so called Tribopump measures friction forces between piston and cylinder at the rotat-ing cylinder block of an axial piston machine under real operating conditions. The experimental investigation includes also influences of surface qualities and structures.
The vortex type fluid oscillatory flowmeter based on measurement of vortex hydrodynamic vibration generated by specific flow passage, and the frequency of fluid oscillations is in direct proportion to flow rate. There are two kinds of vortex type oscillatory flowmeter: vortex flowmeter and vortex precession flowmeter. Since it has the advantage of no moving components, impulse signal output, strong medium adaptability, high measurement accuracy, wide measurement range, low-pressure drop, no zero drift and easy to maintenance, it is wide accepted that the vortex type fluid oscillatory flowmeter is ideal flowmeter in the measurement of gas, liquid, steam and mix/corrosive fluid. However, it has unsolved disadvantages up to present time, such as poor noise immunity in low flux, low interference immunity and adhesion of the sensor surface that affects the meter sensitivity.
In order to overcome those defects, we chose the fluid oscillation characteristics of vortex type fluid oscillatory flowmeter as research subject on the basis of the former achievement. The technique of fluid mechanics simulation and the technique of modern fluid mechanics experiment were applied to research on the fluid oscillation characteristics of vortex flowmeter and vortex precession flowmeter. In this work, a new dual triangulate bluff body vortex flowmeter was developed, the flux lower limit value of which lower by 50% that of the old single bluff body vortex flowmeter. The linear correlation of the correlation between the velocity pressures of fluid disturbs wave and that of vortex precession in vortex precession flowmeter was brought to light, and a spectrum phase discrimination method based on FFT to remove the effect of fluid pulsating interference on vortex precession flowmeter was advanced.
In summary, the dissertation at first successfully developed a new high performance dual bluff body vortex flowmeter by using CFD technique and the modern fluid mechanics experiment technique. And then, it researched on fluid oscillation characteristics and anti-interference method of vortex precession flowmeter. At last, the new anti-interference method of vortex precession flowmeter was advanced.
The hydraulic with inverter is a new kind of energy saving transmission technique. High power & high inertia pump-control-motor speed governing system with inverter is the basic transmission system of hydraulic systems with inverter, and it has extensive potential application in many kinds of equipments such as tunnel boring machine, hydraulic heave machine and injection machine. But it has main key problems such as long response time, low speed stiffness, imperfect control performance and efficiency because it includes inverter and electromotor.
The main research contents are as follows. The performance simulating in time domain and open loop step experiment of pump-control-motor speed governing system with inverter is made. The energy consumption analysis and experiment of the two systems, which are pump-control-motor speed governing system with inverter and hydraulic speed governing system with inlet throttle, are given. Software direct compensating motor speed loss of open loop pump-control-motor speed governing system with inverter is studied deeply in theory and experiment. Compounded compensation control on pump-control-motor speed governing system with inverter is made. The applications of fuzzy control, single neuron control and genetic algorithm in pump-control-motor speed governing system with inverter are studied, and some useful conclusions are obtained.
In the past decades, with the development of industrial technology, many progresses have been made in displacement sensors. But how to measure the dimensions of nonmetallic bodies or transparent bodies by non-contact method still remains as a problem. Recently, an electrical servo air micrometer has been developed for this purpose. It is a combination of an air micrometer and an electrical servo actuator. It controls the electrical servo actuator by setting the backpressure of the air micrometer constant. The displacement of measured object then can be obtained from the displacement of the actuator. Though the performance of the electrical servo air micrometer is fairly well, its structure is too complicated and its cost is also excessively expensive.
In this thesis, a new displacement sensor was researched. The sensor can be seen as a combination of an air micrometer and an air servo actuator. The air servo actuator consists of a nozzle, a piston, a cylinder (cover) and a variable restriction. The piston floats from the cylinder wall with aerostatic bearing, so that there is almost no friction to the piston. An optical linear scale embedded detects the piston’s displacement. It detects displacement similar to an air micrometer. The nozzle of the sensor can follow the measured object automatically. The displacement of measured object can be obtained from the displacement of the actuator. Compared with the electrical servo air micrometer, the new displacement sensor is much simpler in structure and will be much cheaper in cost.
This thesis developed around the proposal, design, analysis and test of the air servo displacement sensor. After modeling the sensor, appropriate parameters of the sensor were found out. And the aerostatic bearing and the flow force acting on the nozzle were also researched. According to analyzing results, a prototype of the sensor were designed and manufactured out.
The characteristics of the sensor were tested experimentally. According to experiment results, the simple and cheap air servo system in the sensor could act functionally. And the sensor showed good static characteristics: its resolution and repeatability are 0.5µm; its nonlinear error is below 2µm. In other word, the sensor had an accuracy of 0.02% F.S. with a measuring range beyond 10mm. The dynamic characteristics of the sensor were also investigated and compared with simulation results.
In short, the development of the air servo displacement sensor has been completed at first stage. This sensor can keep the advantages of a conventional air micrometer and get much wider measuring range. And we want to improve its performance in the future. It is expected that the sensor can be used in some industrial fields where other displacement sensors are not adaptable.
Edited by Z. Li, Y. Zhu and B. Li
Publisher: International Academic Publishers
ISBN: 7-5062-5862-5
Edited by K. T. Koskinen and M. Vilenius
Publisher: Tampere University of Technology
ISBN: 952-15-0973-2