The purpose of this study was to develop a composite manufacturing process that would be able to deliver Class A surface finished products in the context of mould manufacturing methods. The problem required solving was to overcome the time needed to prepare Class A surfaces, by developing a composite manufacturing process that will deliver Class A surface finished products straight from the mould. The process was aimed at the entire development process, from mould and plug design up to the finished product. A literature study and a factory mould survey were conducted with a view to obtain the necessary insights into surface finishing and composite manufacturing. These surveys were followed by seven constructional tests which determined the most appropriate solutions for the proposed manufacturing processes. Test 1 was used to determine a quality finish standard for composites from the sanding grits used to finished composite surfaces versus surface roughness values used in other industries. The standard determined that a P800 finish has a roughness between 0.200 and 0.150 um and constitutes a Class A3 finish. P1000 to P1200 have a roughness between 0.150 um to 0.100 um and constitutes a Class A2 finish. Finally a P2000 and higher have a roughness of 0.100 um and lower and constitutes Class A1 surface finish. After the standard was set, the tests for finishing of the moulds, plugs and parts commenced. Test 2 was conducted on the CNC manufacturing of plugs out of Nuceron651 tooling board. Tool path parameters were varied in a matrix. The samples with the best surface finish value were cut with a step-over of 0.5 and feed of 800 mm/min. These parameters were found to be the most influential. Test 2 and 4 revealed that the plug surface finishing should commence with conventional 2K paint finishing, with a possibility of acrylic split surface. This process produced projected mould surfaces between 0.150 um and 0.200 um, which can be categorised as Class A-3. Test 5 and 6 determined methods for improving the mould surface quality and durability. It was established that the tooling gelcoat should be applied whilst being heated and backed with at least two layers of glass veil and a steady increase of GSM of structural glass fibres to prevent print-through. Test 3 determined that the mould corners could be strengthened with rovings pressed into the corner. It was also established that the moulds surfaces will require finishing after demoulding. The final moulds were manufactured from a fibreglass composite structure with tooling gelcoat surface. A number of guidelines and a set process were developed in order to produce moulds with a surface finish of average 0.9 um, equivalent to Class A1. Release agents were tested in Test 7, and the Loctite Frekote 770-NC release system was deemed appropriate for use with In Mould Coating (IMC) of 2K Paint. These elements were all synthesised into plug, mould and part manufacturing processes. The proposed processes were validated by the manufacturing of a JS instrument panel, which delivered a Class A2, 0.175 um, finish with IMC of 2K paint. With only a minor sanding of P3000 grit and polishing, the part was made into a Class A1 surface, measured at 0.63 um. The study proved that it is possible to produce Class A finished part with IMC. This method can provide a solution aimed at the elimination of P600 and lower finishing of composite parts manufactured with IMC. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This thesis investigates the flow field and pressure distributions around cylinders at trans-critical Reynolds numbers using the k-ε Realizable turbulence model. A steady state 2-D and 3-D Fluent® model is successfully developed to evaluate the effects of changing various modelling parameters on the static pressure distribution around an infinite and finite cylinder. These parameters include surface roughness, cylinder rotation and air viscosity at the cylinder surface. The subsequent results obtained are compared to each other and to data trends from literature as well as measured experimental results and are found to be in good agreement. In addition a method for calibrating all developed methods based on their shear stress curves over a flat plate model is also successfully developed. The main objective is to find an appropriate single parameter which can be used for the rigorous adjustment of the pressure distribution around a cooling tower, which will allow for improved sensitivity analysis and modelling of cooling tower performance under wind conditions with and without meridional ribs located on the outer shell surface. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die vloeiveld en druk verdelings rondom silinders by trans-kritiese Reynolds getalle deur gebruik te maak van die k-ε Realizable turbulensie model. ‘n Bestendige toestand 2-D en 3-D Fluent® model is suksesvol ontwikkel om die uitwerking van die verandering van verskeie model parameters op die statiese druk verdeling rondom ‘n oneindige en eindige silinder te evalueer. Die laasgenoemde parameters sluit in oppervlak grofheid, silinder rotasie en lug viskositeit by die silinder wand. Die daaropeenvolgende resultate wat verkry word, word met data tendense uit die literatuur asook gemete data vanuit eksperimente vergelyk en goeie ooreenkoms i.t.v die data tendense is gevind. Verder is ‘n metode vir die suksesvolle kalibrasie van die ontwikkelde numeriese tegnieke ontwikkel. Die laasgenoemde kalibrasie metode is gebaseer op die vergelyking van skuifspanning kurwes vir vloei oor ‘n plat plaat model. Die hoofdoel van die navorsing is om ‘n geskikte enkele parameter te vind wat gebruik kan word vir die effektiewe aanpassing van die druk verdeling rondom ‘n koeltoring wat sal lei tot verbeterde sensitiwiteits analise en modellering van koeltoring verrigting onder wind toestande met en sonder meridionale ribbes geleë op die buitenste dop oppervlak.

A three-beam lateral shearing interferometer has been developed. The three-beam shearing interferograms consist of two sets of fringes, one of which acts as a carrier whose intensity is modulated by the second set. The depth of modulation is directly proportional to the phase difference between the middle beam and the outer beams. Phase errors on the order of π/2 cause every other fringe to go from complete dark to complete bright. Therefore, phase errors much smaller than π/2 can be detected. The three-beam interferometer is implemented in three ways: (1) thin film thickness measurement, (2) surface roughness measurement, and (3) surface figure measurement. The three-beam interferometer implemented to measure thin film thickness and surface roughness is accurate to 25 Å. Surfaces with different microstructure are characterized. We have found that each of those surfaces may have one or more of the following: (1) random roughness, (2) slow waviness, and/or (3) periodic structure. The three-beam interferometer is also implemented for testing optical surfaces. The three-beam interferometer is more capable in detecting small zonal errors than the two-beam interferometer. Three-beam interferograms of different surfaces are produced and analyzed. The three-beam interferometer has many advantages: (1) it is a stable, common path interferometer, (2) white light can be instead of coherent light to get rid of the effects of speckle and dust particles, and (3) it is a very low cost interferometer.

An immersed boundary spectral method is used to simulate laminar boundary layer flow over a periodic array of cylindrical surface roughness elements. Direct comparisons are made with experiments by using a roughness-based Reynolds number Re[subscript k] of 216 and a diameter to spanwise spacing ratio d/[lamda] of 1/3. Near-field differences between three similar studies are presented and addressed. The shear layer developed over the roughness element produces the downstream velocity deficit region while splitting of the vortex sheet shed the trailing edge forms its lateral modes. Additional geometrical configurations are simulated for comparisons with experimental results and future analysis by linear stability theory. Total disturbance energy E[subscript rms] is fairly consistent with experimental results while spanwise energy components vary significantly. Physical relaxation of the disturbance wake is found to remain a prominent issue for this simulation technique. / text

Unsteady two-dimensional laminar flow of an incompressible viscous fluid over a periodically grooved wall is investigated by numerical simulation using two independent finite-difference methods. One is the vorticity-stream function method, and the other involves the vorticity-velocity induction law formulation. The fluid motion is initiated impulsively from rest and is assumed to be spatially periodic in the streamwise direction. The flow field, which includes the time development of the shear layer and the recirculating flow in the zone of separation, is examined in detail during the transient phase to the steady-state condition. The analytical and numerical formulations, which include the implementation of the boundary conditions, are derived in detail. The generation of vorticity at the solid surfaces is modelled differently in the two approaches. This vorticity production plays an important role in determining the surface-pressure distribution and the drag coefficient. Characteristics of the transient solution for a moderate Reynolds number in the laminar range are presented. Included with the graphical results are the temporal development of the constant stream function contours, including the dividing contour between the zone of separation and the main flow, and the constant vorticity contours. These latter contours show the interactions of separated vortices. The flow is found to approach a steady-state condition comprising an undisturbed uniform flow, a nonuniform irrotational flow, a shear layer adjacent to the grooved wall, and a recirculating vortex flow in the groove. Results also include the time development of the surface shear stress, surface pressure, drag coefficient and several typical velocity profiles, which characterize the flow in the recirculating region. Comparisons of the results obtained by the two numerical methods are made during the major development of the flow. The results showing the general features of the flow development including the time development of the shear layer, free shear layer and recirculating vortex flow are in good agreement. However, a significant deviation does exist at early times for the distribution of surface pressure, which accordingly has noticeable effect on the drag coefficient. Nevertheless, the gap between the distributions of surface pressure and drag coefficients dies out gradually as time progresses. The form of the stream function and vorticity contours at the steady state agrees well with those obtained from a recent numerical investigation of the steady flow in grooved channels.

Information about the distribution of surface soil moisture can greatly benefit the management of agriculture and natural resource. However, direct measurement of soil moisture over larger areas can be impractical and expensive, which has led scientists to develop satellite based remote sensing techniques for soil moisture assessments. Retrieving soil moisture from radar satellite imagery often associated with the collection and use of ancillary field data on surface roughness. However, field data that is meant to characterize surface roughness is often unreliable, is expensive to collect and is nearly impossible to acquire for large scale applications. These issues represent barriers to the adoption and of radar data for mapping soil moisture over large areas.The research presented in the dissertation is aimed at the development of an operational soil moisture assessment system based solely on radar satellite data and a radar model, eliminating the field data requirements altogether. The research is directed towards a so-called equation-based solution of the problem as an alternative to the approach that requires the use of extensive field-data sets on surface roughness. This approach is based on the concept that if the number of equations are equal to the number of unknowns, then explicit solutions of all unknowns are possible. My research derived the necessary equations to solve for soil moisture and surface roughness. The derivation of the equations and how to use them to estimate soil moisture without using ancillary field data was demonstrated by my research. Validation results showed that the equation-based method that was developed is capable of providing more precise estimates of surface soil moisture than that of ancillary field-data supported method.

Roughness is a relatively untouched field considering its significance to natural scientists. In this thesis mathematical techniques for measuring the roughness of signals are constructed and investigated. Both one dimensional and two dimensional signals are tackled. Applications include geological profiles and biological surfaces. Mathematical techniques include Fourier and Wavelet Transforms. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

Flows over hydraulically smooth walls are predominant in turbulence studies whereas real surfaces in engineering applications are often rough. This is important because turbulent flows close to the two types of surface can exhibit large differences. Unfortunately, neither experimental studies nor theoretical studies based on conventional computational fluid dynamics (CFD) can give sufficiently accurate, detailed information about unsteady turbulent flow behaviour close to solid surfaces, even for smooth wall cases. In this thesis, therefore, use is made of a state of the art computational method “Direct Numerical Simulation (DNS)” to investigate the unsteady flows. An “in-house” DNS computer code is developed for the study reported in this thesis. Spatial discretization in the code is achieved using a second order, finite difference method. The semi-implicit (Runge-Kutta & Crank-Nicholson) time advancement is incorporated into the fractional-step method. A Fast Fourier Transform solver is used for solving the Poisson equation. An efficient immersed Boundary Method (IBM) is used for treating the roughness. The code is parallelized using a Message Passing Interface (MPI) and it is adopted for use on a distributed-memory computer cluster at University of Aberdeen as well as for use at the UK’s national high-performance computing service, HECToR. As one of the first DNS of accelerating/decelerating flows over smooth and rough walls, the study has produced detailed new information on turbulence behaviours which can be used for turbulence model development and validations. The detailed data have enabled better understanding of the flow physics to be developed. The results revealed strong non-equilibrium and anisotropic behaviours of turbulence dynamics in such flows. The preliminary results on the rough wall flow show the response of turbulence in the core and wall regions, and the relationship between the axial and the other components are significantly different from those in smooth wall flows.

In this paper, the performance of a new measurement system CITE (CNC Integrity Tracing Equipment) is investigated. CITE measurement system is the name given to the data acquisition hardware and software developed by University West for recording the movements of CNC machine tools. It can be used for monitoring of the milling process and recording the milling errors. The aim of this study is investigate the capability of the CITE system in prediction of the surface roughness. In an example cutting test, the CITE measurement system was used for recording selected sections in straight milling process and curved milling process. After that, surface roughness, predicted by the CITE measurement system, was compared with the CMM (Coordinate measurement machine). The investigation shows that the CITE measurement system is comparable to the CMM for evaluation of roughness in curved sections. In straight sections, the evaluation of roughness by CMM machine is close to the simulation values that predicts surface roughness considering tool run-out.

Approved for Public Release; Distribution is Unlimited / Littoral waters when compared to the open ocean create an environment of greater reverberation with acoustic energy scattering from the sea surface, bottom, topographic features, and regions that lack homogeneity within the volume. If the ocean surface is rough on the scale of an acoustic wavelength, considerable scattering can occur that can significantly influence coherent propagation. Because the rough surface is also evolving dynamically, such scattering can introduce Doppler shifting and spreading of the acoustic pulse spectrum. This thesis builds upon prior efforts in ocean acoustic modeling and is focused on examining surface scattering and its affect upon coherent propagation. The dynamics/physics associated with surface scattering are explored in detail and mathematical relationships are developed and employed in revisions to the Monterey Miami Parabolic Equation (MMPE) model. The thesis provides background information associated with the MMPE and highlights earlier work related to surface scattering. It presents a formal analysis of an exact surface scattering approach in the context of a continuous wave (CW) benchmark exercise and the Doppler shifts associated with a dynamic rough surface. It expands on prior rough sea surface work to include modeling based on an empirical fetch-limited ocean wave spectrum and compares modeling results with measured data. Interest in broadband pulse propagation in shallow water is increasing with the need for improved active sonar systems and with the growth of applications such as underwater acoustic communications. / Naval Undersea Warfare Center Division Newport