The extreme motion and load of ships have been assessed using a linear frequency domain method or a linear energy spectral method and RAOs, which may be too approximate to be used for estimation of ship motion in severest seas. The new technology uses simulation in the time domain to deal with the non-linear responses to the random seas. However, the current simulation technique has been successful only up to the sea state of 7 (“high seas”), defined by the significant wave height of 9 meters. The above cannot provide the extreme wave loads and motions for seas higher than the sea state 7. The ultimate goal of this work would be to develop a new technique that can simulate responses to the seas of states 8 and 9. The objective of the present study is to simulate the vertical relative motion and wave topping of a moored ship in the time domain by varying the significant wave heights. The analysis was able to predict with a fair accuracy the relative motion characteristics of a freely floating body in the head and beam sea conditions. The resonance aspects and its significance in the overall response are also analyzed.

The main objective of the present work is the removal of inclusions from silicon scrap and metallurgical grade silicon. To reach this goal, two various routes are investigated. First, settling of SiC particles from molten silicon followed by directional solidification is reported in this thesis. Then, removal of SiC and Si3N4 inclusions in silicon scrap by filtration with foam filters and wettabilities of silicon on graphite materials are studied. To supply the increasing needs of the photovoltaic industry it is necessary to produce a low cost silicon feedstock. One of the many routes established from the industry is the Solsilc project. This project aims to produce solar-grade silicon by carbothermal reduction of silicon, based on the use of very pure raw materials. The high carbon content of about 700 mass ppm of the silicon in the form of SiC particles, needs to be removed before the Solsilc silicon could be used as a feedstock to PV industry. Settling of SiC particles in molten silicon was investigated. This part of the work was in cooperation with SINTEF Materials & Chemistry. Two experiments were conducted and the cast silicon ingots were analyzed by light microscopy and LECO carbon analyzer. The results showed that the number of inclusions in the middle of the ingots was less than in the bottom and top. The removal efficiency was above 96% in the middle part of an ingot and the total carbon content measured by LECO was < 25 mass ppm. The difference in density between the particles and the melt gives the SiC particles a relatively high settling velocity leading to a high removal efficiency. Pushing and engulfment of SiC particles by solidification front was also studied. Directional solidification of silicon that followed settling pushes the particles to the top of the ingot. The presence of SiC particles in the middle of the ingot is explained by engulfment. Top-cut silicon scrap represents a considerable loss of the PV silicon. Removal of inclusions from the silicon scrap would make it possible to recycle it to feedstock in the PV cell production. This was carried out by filtration with ceramic foam filters. Carbon and SiC foam filters with various pore sizes were employed in the filtration experiments. They were provided by Eger-Sørensen, a Norwegian company and Foseco AB in Sweden. The top-cut silicon scrap came from REC-Scan Wafer. Characterization of inclusions in silicon scrap before and after filtration experiments took place. Two techniques were developed and used in this work. First, extraction of inclusions by acid dissolution of the silicon was carried out. The SiC and Si3N4 particles collected afterwards were analyzed and counted by automated light microscopy. In the second technique, silicon samples were ground and polished with diamond paste. Microscopic analysis consisted of measuring the surface area of the inclusions found in the silicon samples. Results show that inclusions in top-cut solar cell silicon scrap are needle-like Si3N4 particles and round SiC inclusions. The removal efficiency for a 30 ppi SiC filter is more than 99%. The inclusions remaining after filtration are mainly SiC particles smaller than 10 µm. The experiments show that the filtration efficiency increases with decreasing filter pore size. Some filter cakes that mainly consist of large Si3N4 inclusions are found on the top surface of the filter. Deep bed filtration is the mechanism responsible for the removal of small particles. After taking into consideration various models for the foam filters the main conclusion is that interception seems to be the main removal mechanism of inclusions in silicon. Settling appears to play a minor role for our system. A new model named branch model explains better the experimental results. Due to the low wetting angle between molten metal and the filter material, capillary forces drive the melt through the filter. Therefore, the melt velocity through the filter is high. This justifies the usage of potential flow in the branch model.   It is shown that molten silicon may be contaminated in contact with the refractories. Since purity for solar cell silicon is crucial, contamination must be minimized. Graphite crucibles may be a source of relatively high levels of Al, Fe, and P. In the filtration process, wettability of the molten silicon with the filter material is very important. Thus, spreading and infiltration of molten silicon into the graphite substrates were also investigated in this thesis. Five different graphites were provided by Svenska Tanso AB. They are in use as refractories in the PV industry and vary from each other in porosity, density, and average pore size. The sessile drop technique is employed to study the wetting behavior of molten silicon on the graphite materials. The measured contact angles show that molten silicon does not initially wet carbon materials. However, due to the chemical reaction between Si and C, a SiC layer is formed in the interface between molten silicon and the graphite. Formation of this layer lowers the contact angles finally reaching equilibrium wetting angles of molten silicon with SiC materials. Spreading of molten silicon is affected not only by the reaction formed SiC layer, but also by the surface finish. The final contact angles, also called equilibrium contact angles, decrease with increasing surface roughness of the graphites. Infiltration of silicon into graphites is mainly related to the average pore size of graphite materials. Materials with large pores are penetrated deeper by the liquid silicon. Zero contact angles of the silicon with graphites are found in materials with both high surface roughness and large average pore size. These results indicate that graphites for use in the PV industry should have a small average pore size. The surface of the graphite in direct contact with silicon should be smooth (low roughness).

No description available.

No description available.

The extreme motion and load of ships have been assessed using a linear frequency domain method or a linear energy spectral method and RAOs, which may be too approximate to be used for estimation of ship motion in severest seas. The new technology uses simulation in the time domain to deal with the non-linear responses to the random seas. However, the current simulation technique has been successful only up to the sea state of 7 (“high seas”), defined by the significant wave height of 9 meters. The above cannot provide the extreme wave loads and motions for seas higher than the sea state 7. The ultimate goal of this work would be to develop a new technique that can simulate responses to the seas of states 8 and 9. The objective of the present study is to simulate the vertical relative motion and wave topping of a moored ship in the time domain by varying the significant wave heights. The analysis was able to predict with a fair accuracy the relative motion characteristics of a freely floating body in the head and beam sea conditions. The resonance aspects and its significance in the overall response are also analyzed.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Surface active agents have been successfully employed in numerous industrial, agricultural and biomedical applications for decades. Trisiloxane surfactants in particular have proved to be exceptionally effective as wetting enhancers; hence the name ‘superspreaders’. Since the early ‘90s these extraordinary surfactants have become an irreplaceable component in various products and processes. However, the true nature of their specific wetting behaviour has not been fully revealed and their underlying wetting mechanisms are still poorly understood despite substantial scientific interest during the last decades. In this thesis is an attempt to shed light on specific wetting and spreading behaviour of trisiloxane solutions. Commercial superspreader products were tested in various environments in order to get further insight into their performance in specific practical applications. Experimental investigation of wetting of superspreader solutions on surfaces of different hydrophobicity and comparison to that of a conventional surfactant revealed superiority of trisiloxanes. Exceptional interfacial activity was explained in terms of the specific chemical structure and ‘T’-shape of the molecule. However, sensitivity of the trisiloxane head to low pH and long-time ageing in aqueous environment was revealed. Performance of binary mixtures of commercial superspreaders and conventional surfactant was also assessed. Behaviour of trisiloxanes in the capillary action was studied. Finally, a comprehensive mathematical model for trisiloxane wetting, which incorporates diffusion as the governing factor of the wetting process, was developed.

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No description available.

The wettability of materials is important in many natural and industrial processes. In this thesis, the wettability of chemically heterogeneous surfaces was investigated with respect to the size, shape and orientation of individual defects. Heterogeneous surfaces were structured by photolithography, using self-assembled monolayers (SAMs) of diverse functionality and, thus, wettability. In order to maximise any possible departure from theory, the wettability of the high-and low-energy regions of these heterogenous surfaces was chosen to differ substantially. The purity of the defects was optimized by studying the SAM formation and the patterning processes, whilst the influence of roughness was minimized. The focus of this work is therefore on chemical heterogeneity. The Wilhelmy plate method was employed to ascertain the wetting behaviour of individual high- and low-energy defects. Simultaneous measurement of the capillary force and the plate position allowed full characterization of the wettability at the defect boundaries. In addition, integration of the Wilhelmy trace enabled the work associated with advancing or receding a liquid over these defects to be quantified. / The defect boundary orientation was of critical importance to the wetting behaviour. Wetting boundaries perpendicular to the liquid front did not result in any deviation from theoretical predictions. Wetting boundaries that were arranged parallel to the liquid front, however, caused contact line pinning which, in turn, caused contact angle hysteresis. Therefore these boundaries are directly responsible for the departure from wetting theory for heterogeneous surfaces (i.e. the Cassie Equation). These observations are consistent with earlier studies of wetting hysteresis by Johnson and Dettre (1964) and Neumann and Good (1972). Extending their work, this thesis examined the extent of wetting hysteresis at individual rectangular defects with respect to the defect dimensions. The nature of wetting hysteresis was studied quantitatively and, as a result, a simple model for hysteresis was proposed. This model predicts that, for a high-energy defect, the work associated with an advancing liquid will always be less than the theoretical value due to capillary rise within the effect. However, the work associated with a receding liquid will be equal to the theoretical prediction (the opposite is true for low-energy defects). The proposed model was validated for two different liquids (water and ethylene glycol) rectangular and circular defects of macroscopic dimensions. For these surfaces, the empirical data and the proposed model showed excellent agreement for both high- and low-energy defects. This agreement is strong evidence that high- and low-energy defects induce distinctly different wetting behaviour on heterogeneous surfaces. / The proposed model for hysteresis was qualitatively applied to heterogeneous surfaces containing micro- and nanoscopic defects. For micropatterns of high- and low-energy defects, of identical composition, the wettability was entirely different. High-energy defects induced a deviation from theory for only the advancing contact angles, whilst low-energy defects only influenced the receding angles. These observations were qualitatively consistent with the outcomes predicted by the proposed model for hysteresis. For nanoscopic defects, however, the advancing contact angles were consistent with Cassie's law within reasonable error. The derivation of Cassie's equation assumes that there is no capillary rise within the chemical defects. The capillary rise within a nanoscopic defect must be extremely small, according to extrapolation of measurements performed on macro and microscopic defects. Therefore, consistency between the wettability of nanoscopic defects and Cassie equation predictions might be expected. The hysteresis mechanism outlined within this thesis can be quantitatively applied to macroscopic defects, whereas its application to micro and nanoscopic defects is qualitative. / Finally, several applications of this fundamental research, which are directly related to real systems, have been outlined. These include mineral flotation, oil recovery, liquid movement, directed crystallization, Secondary Ion Mass Spectrometry for flotation analysis and patterning of inorganic surfaces. / Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2004.