An experimental study was designed to examine and document the development and structures of turbulent 3D offset jets. The generic 3D wall jets at the same Reynolds numbers was used as the basis of comparison. The experiments were performed using a high resolution particle image velocimetry technique to perform velocity measurements at three Reynolds numbers based on the jet exit diameter and velocities of 5000, 10000 and 20000 and four jet offset height ratios of 0.5, 1.0, 2.0 and 4.0. The measurements were performed in the streamwise/wall-normal plane from 0 to 120 jet exit diameters and in the streamwise/lateral plane from 10 to 80 jet exit diameters. The velocity data were analyzed using (i) mean velocities and one-point statistics such as turbulence intensities, Reynolds stresses, triple velocity products and some terms in the transport equations for the turbulence kinetic energy, (ii) two-point velocity correlations to study how the turbulence quantities are correlated as well as the length scale and angle of inclination of the hairpin-like vortex structures, and (iii) proper orthogonal decomposition to examine the energy distribution and the role of the large scale structures in the turbulence intensities and Reynolds shear stresses. The decay of the maximum mean velocities and spread of the jet half widths became independent of Reynolds number much earlier in the generic wall jet than the offset jets. The flow development is delayed with increasing offset heights. The decay rate and wall-normal spread rate increased with the offset heights, whereas the lateral spread rate decreased with offset heights, which is consistent with previous studies. The two-point auto-correlations and the proper orthogonal decomposition results indicate the presence of more large scale structures in the outer and self-similar regions than in the inner and developing regions. The iso-contours of the streamwise autocorrelations in the inner regions were inclined at similar angles of β = 11.2 ± 0.6 degrees, which are in good agreement with reported values in boundary layer studies. The angles decrease with increasing distance from the wall.

An experimental study was undertaken to investigate the effect of roughness on the characteristics of separated and reattached turbulent shear flow downstream of a backward facing step. Particle image velocimetry technique was used to conducted refined velocity measurements over a reference smooth acrylic wall and rough walls produced from sandpaper 36 and 24 grits positioned downstream of a backward facing step, one after another. Each experiment was conducted at Reynolds number based on the step height and centerline mean velocity of 7050. The results showed that sandpaper 36 and 24 grits increased the reattachment length by 5% and 7%, respectively, compared with the value obtained over the smooth wall. The distributions of the mean velocities, Reynolds stresses, triple velocity correlations and turbulence production are used to examine roughness effects on the flow field downstream of the backward facing step. Two-point auto-correlation function and proper orthogonal decomposition (POD) are also used to investigate the impact of wall roughness on the large scale structures.

An experimental study was designed to examine and document the development and structures of turbulent 3D offset jets. The generic 3D wall jets at the same Reynolds numbers was used as the basis of comparison. The experiments were performed using a high resolution particle image velocimetry technique to perform velocity measurements at three Reynolds numbers based on the jet exit diameter and velocities of 5000, 10000 and 20000 and four jet offset height ratios of 0.5, 1.0, 2.0 and 4.0. The measurements were performed in the streamwise/wall-normal plane from 0 to 120 jet exit diameters and in the streamwise/lateral plane from 10 to 80 jet exit diameters. The velocity data were analyzed using (i) mean velocities and one-point statistics such as turbulence intensities, Reynolds stresses, triple velocity products and some terms in the transport equations for the turbulence kinetic energy, (ii) two-point velocity correlations to study how the turbulence quantities are correlated as well as the length scale and angle of inclination of the hairpin-like vortex structures, and (iii) proper orthogonal decomposition to examine the energy distribution and the role of the large scale structures in the turbulence intensities and Reynolds shear stresses. The decay of the maximum mean velocities and spread of the jet half widths became independent of Reynolds number much earlier in the generic wall jet than the offset jets. The flow development is delayed with increasing offset heights. The decay rate and wall-normal spread rate increased with the offset heights, whereas the lateral spread rate decreased with offset heights, which is consistent with previous studies. The two-point auto-correlations and the proper orthogonal decomposition results indicate the presence of more large scale structures in the outer and self-similar regions than in the inner and developing regions. The iso-contours of the streamwise autocorrelations in the inner regions were inclined at similar angles of β = 11.2 ± 0.6 degrees, which are in good agreement with reported values in boundary layer studies. The angles decrease with increasing distance from the wall.

Hand Arm Vibration Syndrome (HAVS) is a collective term for the symptoms arising from the prolonged use of vibrating hand tools. An investigation into the literature on available screening tools for HAVS was conducted. A screening tool is used for the quick identification of certain symptoms without a full medical check up, and is for use by mine medical personnel for the determination of workers with HAVS symptoms and those without. Twenty-two non-exposed volunteers were tested with the screening tools and forty-two rock drill operators. Only the rock drill operators had a medical examination and standardised tests for HAVS diagnoses, to determine their HAVS diagnosis and severity. This diagnosis was used as the standard for the evaluation, of existing screening tools and for developed screening tool, sensitivity for the detection of HAVS symptoms. The screening tools chosen were a traditional tuning fork, a similar tuning fork but mounted into a box with a set excitation unit and a two-point discriminator set a 3mm, 6mm, and 10mm apart. The results showed that a screening questionnaire that specifically focuses on the symptoms of HAVS has better sensitivity and specificity to identify cases. A two-point discriminator with variable distance points, where patients have to distinguish between one pin prick and two, was able to identify HAVS cases when the distance was set at 3mm. However, the sensitivity of the two-point discriminator was lower than the sensitivity of the questionnaire. / Dissertation (MSc)--University of Pretoria, 2007. / Industrial and Systems Engineering / Unrestricted

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Master thesis is about designing two point mechanical crank press with nominal force 8 000 kN and with variability width of workbench. First part of thesis is focused on present production of two point mechanical presses. In next part is designing of press with two torque motors. This solution provides wide width range of workbench.

Indoor positioning systems (IPS) has seen an increase in demand because of the needto locate users in environments where Global Navigation Satellite Systems (GNSS) lacksaccuracy. The current way of implementing an IPS is often tedious and time consuming.However, with the improvements of position estimation and object detection on phones,a lightweight and low-cost solution could become the standard for the implementationphase of an IPS. Apple recently included a Light Detection And Ranging (LiDAR) sensorin their phones, greatly improving the phones depth measurements and depth understanding.This allows for a more accurate virtual representation of an environment. This thesisstudies the accuracy of ARKit’s reconstructed world and how different environments impactthe accuracy. The thesis also investigates the use of reference points as a tool to map thereconstructed environment to a geo-referenced map, such as Google Maps and Open StreetMap. The results show that ARKit can create virtual representations with centimetre levelaccuracy for small to medium sized environments. For larger or vertical environments,such as corridors or staircases, ARKit’s SLAM algorithm no longer recognizes previouslyvisited areas, causing both duplicated virtual environments and large drift errors. With theuse of multiple reference points, we showed that ARKit can and should be considered asa viable tool for scanning and mapping small scale environments to geo-referenced floorplans.

Simultaneous two-point three-component four-sensor hot-wire velocity measurements taken in three flows of aeroacoustic interest are here analyzed. The analyses provide information on the turbulence structure of the flows as it would be encountered by hypothetical noise producing blades passing through the flows. Two-point measurements taken in the first flow, a lifting wake from a rectangular NACA 0012 half wing, are used to calculate space-time correlation functions and 'pointwise' wave number frequency spectra. Two upwash spectra, calculated for locations in the region of the wake that is roughly homogenous in the spanwise direction, are direct estimates of the full wave number frequency spectra at their locations. As such, they are used to perform aeroacoustic calculations, and the results are compared to results achieved using the von Kármán isotropic spectrum. Amiet's approximation, where the wave number frequency spectra can be represented by the correlation length scales is found to hold reasonably well for the measured spectra. The two-point measurements in the second flow, a vortex/blade-tip interaction, are analyzed to provide information useful to researchers of blade-wake interaction noise produced by helicopter rotors. Space-time correlation functions and wave number frequency spectra are calculated for five cuts through the region of interaction. The correlation functions provide information concerning the turbulence length scales found in the interaction region. The spectra are compared to the von Kármán isotropic spectrum and found to be greatly different. However, the spectra do bear some resemblance to spectra calculated in the spanwise homogenous region of the lifting wake. The two-point measurements taken in the third flow, the wake from a fan cascade, are analyzed to provide information of use to modelers of broadband noise produced through rotor wake/stator interactions. In particular, space-time correlation functions are calculated for a grid of two-point measurements, which allows the estimation of the turbulence structure as seen by a passing stator blade. Space-time correlation functions and wave number frequency spectra are calculated for various stator configurations. The implications of engine operating speed and stator configuration for broadband noise production are discussed. <i> [Vita removed March 2, 2012. GMc]</i> / Master of Science

Magistro darbe pateikiami nauji rezultatai, gauti tiriant diskretųjį Šturmo ir Liuvilio uždavinį su viena klasikine (arba Noimano) ir antra nelokalia dvitaške kraštine sąlyga. Analitinėje dalyje pateikiama teorija, reikalinga nagrinėjamo uždavinio tyrimui ir trumpai pristatomi rezultatai, gauti tiriant panašų uždavinį. Projektinėje dalyje ištirta diferencialinio uždavinio ir baigtinių skirtumų schemų kompleksinės spektro dalies priklausomybė nuo nelokaliųjų kraštinių sąlygų parametrų $\gamma$ ir $\xi$. Dauguma tyrimo rezultatų pateikiama kompleksinės ir realiosios charakteristinių funkcijų grafikais. / In this Master thesis presented new results which are got investigated the Sturm--Liouville problem with one classical (or Neumann) and another two-point nonlocal boundary condition. In the analytical part are presented the theory, which is necessary to study the problem and presented the results of investigation a similar task. In the design part are investigated the spectrum in complex plane depends on the nonlocal boundary conditions parameters $\gamma$ and $\xi$ in differential problem and in the finite difference schemes. Simulation results are presented as graphs of complex-real characteristic functions.

An experimental study was designed to investigate the effect of different parameters on the development and structure of turbulent 3D offset jets. The present investigation considered the effects of offset height ratio, expansion ratio, surface roughness and rib placement on the flow dynamics of a turbulent 3D offset jet. The velocity measurements were performed using an acoustic Doppler velocimetry (ADV) and particle image velocimetry (PIV). Measurements were conducted within the symmetry and lateral planes. For the PIV technique, the measurements in the symmetry and lateral planes were conducted over a streamwise range of 0 ≤ x/bo ≤ 80 and 12 ≤ x/bo ≤ 60, respectively (where bo is the nozzle height). Likewise, velocity measurements using the ADV technique were conducted over a range of 4 ≤ x/bo ≤ 45 in both the symmetry and lateral planes. The velocity measurements were analyzed using both one-point and multi-point statistics. The one-point statistics included profiles of the mean velocities, Reynolds stresses and some of the budget terms in the turbulent kinetic energy transport equation. The quadrant analysis technique was used to investigate the dominant events that contribute towards the Reynolds shear stress. The two-point correlation analysis was used to investigate how the turbulence quantities are correlated. Information obtained from the two-point correlation analysis was also used to investigate the inclination of vortical structures within the inner and outer shear layers of the 3D offset jet. The direction of the positive mean shear gradient played an active role in the inclination of these vortical structures within the inner and outer shear layers. The reattachment process resulted in the breakdown of these structures within the developing region. Similarly, various length scales were estimated from these structures. The proper orthogonal decomposition was used to examine the distribution of the turbulent kinetic energy within the offset jet flow. Also, the dynamic role of the large scale structures towards the turbulent intensities, turbulent kinetic energy and Reynolds shear stress was investigated. / October 2016