In previous studies on suction box dewatering, three mechanisms were identified that determine the dry content of a web, viz. web compression, displacement of water by air and rewetting. In the present work, the relative importance of the three mechanisms was investigated through direct measurement of the web deformation, the dry content changes during and after the suction pulse, the air flow through the fibre network and the saturation of the web after the suction pulse. Suction pressure, suction time and rewetting time were varied. The experiments were done with chemical and mechanical pulp webs of various grammages. It was found that a large web deformation took place during the suction pulse, particularly at its beginning. Compression dewatering was found to be the most dominant dewatering mechanism. Displacement dewatering started after most of the web compression had occurred. Its contribution to the increase in dry content was most pronounced for higher suction pressures, longer suction times and for chemical pulp webs. A surprisingly large expansion of the web was observed immediately after the suction pulse. This expansion was the effect of rewetting. This rewetting strongly reduced the dry content of the web if the web had not been immediately separated from the forming fabric at the end of the suction pulse. Under the conditions studied, the decrease in dry content amounted to the order of 3 to 6 %. Rewetting was smaller for longer suction times and higher suction pressures. A considerable air flow through the web occurred under these conditions. This air flow apparently moved water from the forming fabric into the suction box, thus making less water available for rewetting. Rewetting for mechanical pulp webs was more pronounced and took place faster than for chemical pulps. The use of a membrane on top of the web during suction box dewatering proved to be advantageous for reducing the air flow through the web. However, under the conditions investigated, the dry content could not be improved. Although the web compression was increased when using a membrane, especially at a higher suction pressure, rewetting after the suction pulse had an even larger negative impact on the dry content, which, as a result, was lower. / QC 20100924

A method has been developed for flexible modelling of multi-component twin-wire blade formers. Features such as suction devices, loadable blades, curved blades, and partial contact between the blades and the forming fabrics are easily incorporated. New results include a series of calculations demonstrating the non-trivial interaction between the pressure pulses when the blades are positioned successively closer together, the effects of suction on the pressure pulse generated by a blade applied to the opposing wire, and how blades of modest curvature do not necessarily stay in contact with the fabric along their full width and the implications of this on the pressure gradients in the machine direction. The behaviour of the fibre mats as they experience the first of the blade pulses (after having been formed over a roll) is then considered in detail. Typically, the thickness of the mats decreases during the pulse, which reduces the rate of deposition of new fibres onto the webs. The amount of fibres in the sheets therefore changes marginally. Nevertheless, the resistance to drainage presented by the fibre network is seen to increase significantly due to the low permeability in highly compressed layers of the mat. As a result of the pressure gradients in the machine direction, the shear stresses in the plane of the fibre sheets can attain several hundred Pascal next to the forming fabrics. Further, a model for sheared consolidation of flocculated suspensions is presented that extends the concept of a concentration dependent yield stress, previously employed in studies of uniaxial consolidation, to comprise flocculated phase shear strength. Rate-dependent viscous stresses are also incorporated. The theory is applied to the problem of combined compression and shearing of a strongly flocculated suspension contained between two plates, one being fixed and acting as a perfectly permeable filter, the other movable and acting as a piston by which the load is applied. Qualitatively, the evolution of the volume fraction of solids exhibits the same behaviour as during uniaxial consolidation without shear. Applying shear is however predicted to increase the rate of the drainage process, due to a reduced load bearing capacity of the flocculated phase, and correspondingly higher pore pressures. / QC 20101022

Se ha llevado a cabo:A) Un estudio de las propiedades básicas del suelo no saturado (tipo limo) a escala microestructural, incluyendo esqueleto sólido, fase liquida y fase gaseosa. B) Elaboración de un modelo conceptual discontinuo de comportamiento. La geometría interna esta construida por partículas, agua retenida en forma de meniscos alrededor de los contactos y aire ocupando los restantes poros. La interfase liquido gas esta gobernada por la succión y la tensión superficial. Los meniscos tienen un efecto rigidizador del esqueleto.Se observa la posible redistribución de la humedad y del aire, quedando acoplados en definitiva los aspectos mecánicos y de flujo.C) En base a lo anterior, implementación de un modelo numérico discontinuo de ensayo de comportamiento basado en ordenador. Se ha adaptado y modificado el D.E.M. de P.A. Cundall (diferencias finitas explicitas en el tiempo), indicado en el caso que se trata, con no-linealidades geométricas. Se han desarrollado importantes algoritmos de control geométrico. D) Verificación parcial del modelo y aplicación a casos típicos en suelo no saturado, especialmente el colapso.En conjunto es una herramienta útil para su estudio y permite apreciar algunos interesantes mecanismos de actuación de la succión a escala microscópica.

During mechanical ventilation, patients are connected to the ventilator by an endotracheal tube. The tube needs to be cleaned from mucus by suction, which can cause negative effects such as lung collapse, hypoxemia and desaturation. These can be avoided by preoxygenation, change of ventilator settings, use of closed suction systems and recruitment manoeuvres. The aim of the study was to investigate the effects of endotracheal suction during different ventilator settings and by different suction methods. A method to reverse side effects was investigated. In anaesthetized pigs, the effect of suction during volume and pressure-controlled ventilation was investigated, and the effect of different suction systems and catheter sizes were compared. Suction efficacy was investigated in a bench study. The effect of recruitment manoeuvre added after suction, i.e. post-suction recruitment manoeuvre was evaluated. Endotracheal suction causes lung volume loss leading to impaired gas exchange, an effect that is more severe in pressure-controlled ventilation than in volume-controlled ventilation. When 14 French suction catheters were used more side effects were found compared to 12 French catheters, but no difference was found between open and closed suction system in pressure-controlled ventilation. Open suction system was more effective to remove mucus compared to closed system. Post-suction recruitment manoeuvre restored the side effects after the first recruitment when it was applied directly after suction. In conclusion, open endotracheal suction causes impairment in gas exchange and lung mechanics, and more so in pressure-controlled than in volume-controlled mode. These changes can be minimized if smaller suction catheters are used. A post-suction recruitment manoeuvre applied directly after suction restores lung function. It is obvious that the recruitment manoeuvre should be added directly after suction, because if the manoeuvre is delayed and the lung is collapsed and left collapsed, it will be more difficult to recruit the lung.

The sediment resuspension and turbidity created during dredging operations is both an economical and environmental issue. The movement of sediment plumes created from dredging operations has been predicted with numerical modeling, however, these far-field models need a “source term” or near-field model as input. Although data from field tests have been used to create near-field models that predict the amount of material suspended in the water column, these results are skewed due to limitations such as non-uniform sediment distributions, water currents, and water quality issues. Laboratory investigations have obtained data for turbidity during dredging operations, but these results do not take advantage of the most contemporary testing methods. The purpose of this dissertation is to provide an estimation of turbidity created during a cutter suction dredging operation. This estimation was facilited by the development of resuspension measurement and data acquisition techniques in a laboratory setting. Near-field turbidity measurements around the cutter head were measured in the Haynes Coastal Engineering Laboratory at Texas A&M University. The laboratory contains a dredge/tow tank that is ideal for conducting dredging research. A dredge carriage is located in the dredge/tow tank and is composed of a carriage, cradle, and ladder. Acoustic Doppler Velocimetry (ADV) and Optical Backscatter Sensor (OBS) measurements were taken at specific points around the cutter head. The variables of suction flow rate, cutter speed, and the thickness of cut were investigated to understand their specific effect on turbidity generation and turbulence production around the cutter head. A near-field advection diffusion model was created to predict resuspension of sediment from a cutter suction dredge. The model incorporates the laboratory data to determine the velocity field as well as the turbulent diffusion. The model is validated with laboratory testing as well as field data. Conclusions from this research demonstrate undercutting consistently produced larger point specific turbidity maximum than overcutting in the laboratory testing. An increase in suction flow rate was shown to increase production and decrease turbidity around the cutter head. In general, an increase in cutter speed led to an increase in turbidity. The thickness of cut produced less resuspension for a full cut versus a partial cut. Data for a “shallow cut” also produced less turbidity generation than partial cuts. The numerical model was compared to all laboratory testing cases as well as the Calumet Harbor and New Bedford cutter resuspension data and produced suitable MRA values for all tests. The numerical model produced higher point specific regions of turbidity for undercutting but produced larger mean values of turbidity for overcutting.

The need for experimental and analytical modeling in the field of deep water offshore anchoring technologies is high. Suction caisson and drag embedment anchors (DEA) are common anchors used for mooring structures in deep water. The installation process of drag embedment anchors has been highly empirical, employing a trial and error methodology. In the past decade analytical methods have been derived for modeling DEA installation trajectories. However, obtaining calibration data for these models has not been economical. The development of a small scale experimental apparatus, known as the Laponite Tank, was developed for this thesis. The Laponite Tank provides a quick and economical means of measuring DEA trajectories, visually. The experimental data can then be used for calibrating models. The installation process of suctions caissons has benefited from from a more rational approach. Nevertheless, these methods require refinement and removal methodology requires development. In this thesis, an algorithm for modeling suction caisson installation in clay has been presented. An analytical method and modeling algorithm for removal processes of suction caissons in clay was also developed. The installation and removal models were calibrated to field data. These analytical and experimental studies can provide a better understanding of installation of drag embedment anchors and the installation and removal of suction caissons.

This experiment is to investigate the effects of fluid with and without mass injection through a slit on the vortex shedding from a single cylinder. We research Reynolds Numbers on ranges from 800 to 4000. We used four kinds of ways which contain no mass injection, steady blowing, steady suction and oscillatory jet to study of the wake behind a circular cylinder under excitation in this experiment. No mass injection is measured for the sake of its reliability and comparability of experiment. Steady blowing and suction are applied to influence the wake flow. An oscillatory jet is used to influence the wake flow with varying frequencies and amplitudes. The experiment looks forward to use the results of this experiment so as to research into the effects on the wake flow, including the velocity values of fluctuation and turbulence intensity of the vortices structure, the dominant frequency in the flow pattern on a single cylinder. The main parameters in the study are the frequency, momentum and the location of the blowing and suction jet, which are a steady jet or unsteady oscillatory jet. Flow visualization has been carried out to investigate the interaction of steady or unsteady fluid perturbation and the vortex shedding of a cylinder.

Suction caissons with a smaller aspect (length to diameter) ratio are increasingly used for supporting offshore structures, such as wind turbines and oil and gas production facilities. The design of these stubbier foundations is usually governed by lateral loads from wind, waves, or currents. It is desired to have more physical understanding of the behavior of less slender suction caissons under cyclic lateral loading condition and to have robust design tools for analyzing these laterally loaded caissons. In this study, one-g model tests with 1:25 and 1:50 suction can foundation scale models with an aspect ratio of one are conducted in five different soil profiles: normally consolidated clay, overconsolidated clay, loose siliceous sand, cemented siliceous sand, and cemented calcareous sand. This test program involves monitoring settlements, lateral displacements (walking), tilt, lateral load and pore water pressures in the suction can during two-way cyclic lateral loading at one, three and five degrees of rotation. The model foundations are monitored during installation, axial load tests, and pullout tests. In one and two-degree (±0.5 and ±1 degree) rotation tests, the suction can does not have significant walking or settlement in all the five soil profiles after 1000 load cycles. However, more significant walking or settlement may occur at extreme conditions such as the 5-degree (±2.5 degrees) rotation tests. Gaps between the foundation wall and the soil may also form in these extreme conditions in overconsolidated clay, cemented siliceous sand, and cemented calcareous sand. Plastic limit analysis, finite element analysis, and finite difference analysis are used to evaluate the laterally loaded suction can in clay. The plastic limit analysis originally developed for more slender suction caissons appears to predict a lateral capacity close to the measured short-term static capacity of the caisson with an aspect ratio of one when undisturbed undrained shear strength of soil is used. However, this plastic limit model underestimates the long-term cyclic lateral load capacity of the caisson when the remolded undrained shear strength was used. The finite element model developed in this study can simulate the development and effect of a gap between the foundation and surrounding soil as observed in the experiments in overconsolidated clay. The lateral load-displacement response predicted by this finite element model matches well with the experimental data. Finally, finite difference analysis for a rigid caisson with lateral and rotational springs was developed by fitting the lateral load-displacement response of the suction can in clay. The calibrated p-y curves for rigid caisson are significantly stiffer and have higher ultimate resistance than the p-y curves recommended by API which is consistent with other studies. This finite difference model provides an efficient approach to analyze a laterally loaded caisson with a small aspect ratio in clay. / text

A computational model has been developed to study the effects of left ventricular assist devices (LVADs) on the cardiovascular system during a ventricular collapse. The model consists of a toroidal pulsatile blood pump and a closed loop circulatory system. Together, they predict the pump's motor current traces that reflect ventricular suck-down and provide insights into torque magnitudes that the pump experiences. In addition, the model investigates likeliness of a suction event and predicts reasonable outcomes for a few test cases. Ventricular collapse was modeled with the help of a mock circulatory loop consisting of a artificial left ventricle and centrifugal continuous flow pump. This study also investigates different suction detection schemes and proposes the most suitable suction detection algorithm for the TORVAD pump, toroidal left ventricular assist device. Model predictions were further compared against the data sampled during in vivo animal trials with the TORVAD system. The two sets of results are in good accordance. / text

Deep foundations, such as piles and suction caissons, are used throughout an offshore oil and gas production facility in deepwater. Ideally, the values of geotechnical properties for foundation design are determined by results from geotechnical investigation programs performed at the site of the foundation. However, the locations for facilities are not known exactly when soil borings are drilled and the footprint of a facility in deepwater can be very large with numerous foundation elements spread out over miles. Therefore, it is not generally feasible to perform a site-specific investigation for every foundation element. The objective of this research is to assess, analyze and model spatial variability in geotechnical properties for offshore foundations. A total of 97 geotechnical investigations from 14 offshore project sites covering the past twenty years of deepwater development in the Gulf of Mexico are compiled into a database. The geologic setting is primarily a normally to slightly overconsolidated marine clay, and the property of interest for the design of deep foundations is the undrained shear strength. The magnitude and characteristics of variability in design undrained shear strengths are analyzed quantitatively and graphically. Geostatistical models that describe spatial variability in the design shear strength properties to the distance away from the available information are developed and calibrated with available information from the database. Finally, a methodology is presented for incorporating the models into a reliability-based design framework to account for spatial variability in foundation capacity. Design examples are presented to demonstrate the use of the reliability methodology. Based on the design undrained shear strength profiles for the past 20 years in this Gulf of Mexico deepwater area, the design undrained shear strength varies spatially but does not depend on the time or method for site investigations. There are nonlinear spatial relationships in the point shear strength laterally and vertically due to stratigraphy such that depth-averaged shear strengths are correlated over further distances than point shear strengths. The depositional forces are an important factor causing spatial variations in the undrained shear strength, with greater variation and less spatial correlation in the more recent hemipelagic deposits (about upper 60 feet) than the deeper turbidite deposits and along the shelf versus off the shelf. The increased conservatism required in deep foundation design due to spatial variability when site specific strength data are not available is generally small with less than a five percent increase required in design capacity in this geologic setting. / text