• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 887
  • 403
  • 286
  • 153
  • 145
  • 61
  • 45
  • 35
  • 30
  • 30
  • 26
  • 17
  • 14
  • 13
  • 10
  • Tagged with
  • 2622
  • 848
  • 256
  • 238
  • 233
  • 171
  • 170
  • 164
  • 146
  • 144
  • 132
  • 128
  • 126
  • 124
  • 118
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

An investigation of velocity profiles in non-isothermal laminar flow of a liquid

Bell, Charles James 08 1900 (has links)
No description available.

Inspection times and general ability

McCrory, C. January 2002 (has links)
No description available.

Evaluation of ADCP wave measurements

Boyd, Jeremy David. 12 1900 (has links)
ornia. Data were first corrected for dropouts. Next the data quality was verified through a consistency check on the redundant velocity measurements of opposing beams, an evaluation of high frequency spectral noise levels, and a comparison of velocity and pressure measurements using linear wave theory. Finally wave height and direction spectra estimated from the ADCP data were compared to data from a directional wave buoy. The analysis revealed that the ADCP data can suffer from low signal to noise ratios in benign conditions and deeper water. Whereas the wave height estimates are sensitive to these errors, the wave direction estimates are surprisingly robust.

Incorporating target mensuration system for target motion estimation along a road using asynchronous filter

Yap, Kwee Chye. 12 1900 (has links)
In support of TNT experiments, the NPS UAV laboratory has developed a Vision-Based Target Tracking (VBTT) system for a Small Unmanned Aerial Vehicle (SUAV). This system provides an autonomous target tracking capability, while simultaneously estimating the target's velocity and position.The accuracy of the existing system can be improved by providing external corrections to the target position estimation from the georectification system (GIS). This thesis addresses the implementation of an asynchronous correction scheme into the target position estimation filter. The current autonomous position estimation algorithm provides 20-30 meters accuracy. The external correction system (Perspective View Nascent Technologies (PVNT)) is expected to provide target position accuracy of 1-2 m. However, a delay of up to 10 seconds is expected. Therefore, in order to improve the accuracy of current estimation of target motion, a new asynchronous correction technique that incorporates the more accurate PVNT data is proposed. To further improve the target motion estimation, it was also proposed to incoprate a known road model into the filter and compare its performance with the original filter.

Induction motor speed sensing and control

Zhu, Chaoying January 1993 (has links)
No description available.

The velocity of second sound near the Lambda point

Johnson, David Lawrence January 1969 (has links)
Direct measurements have been made of the velocity of second sound in liquid helium over the temperature range T[subscript ʎ]-T from 1.3 x 10⁻² K to 5 x 10⁻⁶K. Using previously determined relationships for the specific heat, superfluld density, and thermal conductivity near the lambda point, consistency has been demonstrated between the measurements, velocities predicted by superfluld hydrodynamics, and certain scaling law predictions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Supercritical speed response of circular saws

Yang, Longxiang January 1990 (has links)
This study investigates the dynamics of circular saws at supercritical speeds. A classical governing equation of a circular saw subjected to transverse and membrane forces is derived in both body-fixed and space-fixed coordinate systems. The transverse loads are generalized as spring, damping and out of plane cutting forces, and the membrane loads include rotational, thermal and in-plane cutting forces. Galerkin's Method is used to study the natural and forced response of a saw blade, and the effects of spring and damping on the stability at supercritical speed are discussed. An idling experiment is conducted to comprehend the fundamental behavior of circular saws at supercritical speed. The natural frequency, the steady state response, the flexibility and the runout variation of the circular saws are measured. The nonlinear vibration of the thin blade is observed. The effects of a spring-damper system and heating on the stability of a circular saw are investigated. A cutting test is conducted to find out the dominant parameters of supercritical speed cutting. At first, the prehminary experiments of the standard blade are conducted. Then, tip side cutting marks are discussed, and finally, the phenomenon of unstable cuttings are presented. The general solution of a rotating string subject to an elastic constraint is developed. Based on this, the discrepancy between theoretical and experimental stability results is analysed for a guided rotating disk. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Modelling machine induced noise and vibration in a ship structure

Wang, Wei-Hui January 2000 (has links)
Most high speed vessels are fitted with powerful high speed engines which are installed in confined spacesa nd, as a consequencec, ausea n extremely high level of noise and vibration. Often structure-borne sound power is transmitted to a sound carrying structure from a source via a number of contact points. In turn, the noise and vibration are propagated in the structure and could possibly cause an undesired noise radiation. In this study, a model for predicting power flow based on the mobility theory has been addressed. The unique parts of the study include the establishment of the relationship of mobility functions with respect to four-pole parameters and the dynamic stiffness coefficients of a coupled machine/mount/foundation system. Also expressions to represent the sound input power, the output power and the transmitted power in relation to mobility functions are clarified. From a detailed analysis of relevant literature, it is shown that no validated models for predicting the propagation of structure-bome noise within the intermediate frequency range of 125 Hz to lkHz exist. As a consequence, a new numerical stress wave model has been developed to bridge this knowledge gap. This innovative approach extends the earlier works of Cremer, Heckl and Ungar in the field of stress wave propagation. Finally, a novel holistic model has been developed to line up the transmission, propagation and radiation predictions of a machine induced noise and vibration in ship's structure to take in account the fluid-structure interaction effect. A number of experiment measurements have been performed to validate the established models. From the comparisons, the prediction models are shown to be credible with an accuracy higher than 95 per cent. The established models are of a generic nature and can be applicable to diverse engineering fields regarding to the predictions of structure-borne noise and vibration transmission, propagation and radiation. Applications of these models to characterize the vibration reduction countermeasures,a s in the case of resilient mounts and squeeze-film damping plates, from a machine are also discussed.

High-speed railway embankments : a comparison of different regulation

Alamaa, Angelica January 2016 (has links)
Swedish transport administration initiated this Master Thesis project and the aim was to compare regulations for the design of high-speed railways from three European countries: France, Germany and Spain. The reason why this is of interest for the Swedish transport administration is the design of the first Swedish high-speed railway, called Ostlänken. Therefore, a literature study of the regulations and other literature regarding high-speed railway has been carried out. A basic description of railway components, slab track and ballasted tracks is presented. Ballasted embankments usually consist of a trackbed layer (ballast onto subballast), and the ultimate thickness of this layer is discussed, as there are a number of methods available to calculate the appropriate thickness, with a number of different design parameters. These design methods results in different trackbed thickness and choosing the “wrong” method might lead to an overestimation or underestimation of the trackbed layer. Constructing a ballastless railway line means that the ballast is replaced by another material, usually a slab made of reinforced concrete or asphalt, and the rail is cast onto this slab. Countries design their slab using different methods. Germany has constructed high-speed railway lines with a slab track solution, generally slabs with low flexible stiffness. France has until recently constructed their high-speed line ballasted but is now developing a new slab track technique, called NBT (New Ballastless Track) and Spain uses various methods. It is difficult to compare the regulations, however, there are some factors that at least begin to explain the differences between the countries: the frost hazard, the inherent ground quality, purpose with the railway (mixed traffic, solely passenger traffic, etc.), design parameters (life, axle load, etc.). Furthermore, the settlement requirements, soil classification and bearing capacity are factors that varies from country to country, but the origin for this variation is harder to detect.

Active suspensions for flexible-bodied rail vehicles

Foo, Tuan-Hoe (Edwin) January 2000 (has links)
This work investigated the design of classical and optimal control strategies to actively control the flexible modes of a high speed railway vehicle body. It explored the novel idea of adding a third actuator at the centre of the vehicle body to suppress the flexible body modes (i.e. first symmetrical and first asymmetrical) in addition to the actuators located across the front and rear secondary suspensions. The aim is to minimise the level of vibration and improve the ride quality (comfort). Both the two and three actuators are considered in the classical and optimal control strategies investigated.

Page generated in 0.0615 seconds