The Left Ventricular Assist Device (LVAD) is a rotary mechanical pump that is implanted in patients with congestive heart failure to help the left ventricle in pumping blood in the circulatory system. The rotary type pumps are controlled by varying the pump motor current to adjust the amount of blood flowing through the LVAD. One important challenge in using such a device is the desire to provide the patient with as close to a normal lifestyle as possible until a donor heart becomes available. The development of an appropriate feedback controller that is capable of automatically adjusting the pump current is therefore a crucial step in meeting this challenge. In addition to being able to adapt to changes in the patient's daily activities, the controller must be able to prevent the occurrence of excessive pumping of blood from the left ventricle (a phenomenon known as ventricular suction) that may cause collapse of the left ventricle and damage to the heart muscle and tissues. In this dissertation, we present a new suction detection system that can precisely classify pump flow patterns, based on a Lagrangian Support Vector Machine (LSVM) model that combines six suction indices extracted from the pump flow signal to make a decision about whether the pump is not in suction, approaching suction, or in suction. The proposed method has been tested using in vivo experimental data based on two different LVAD pumps. The results show that the system can produce superior performance in terms of classification accuracy, stability, learning speed, iv and good robustness compared to three other existing suction detection methods and the original SVM-based algorithm. The ability of the proposed algorithm to detect suction provides a reliable platform for the development of a feedback control system to control the current of the pump (input variable) while at the same time ensuring that suction is avoided. Based on the proposed suction detector, a new control system for the rotary LVAD was developed to automatically regulate the pump current of the device to avoid ventricular suction. The control system consists of an LSVM suction detector and a feedback controller. The LSVM suction detector is activated first so as to correctly classify the pump status as No Suction (NS) or Suction (S). When the detection is “No Suction”, the feedback controller is activated so as to automatically adjust the pump current in order that the blood flow requirements of the patient’s body at different physiological states are met according to the patient’s activity level. When the detection is “Suction”, the pump current is immediately decreased in order to drive the pump back to a normal No Suction operating condition. The performance of the control system was tested in simulations over a wide range of physiological conditions.

An experimental study was carried out on a single-ply low-slope roof using a series of different underlayment layers to test and understand distributional characteristics of negative air pressure throughout the roof assembly, when subjected to suction pressure corresponding to different wind speeds. Various underlayments were tested at the Research & Demonstration Facility at Virginia Polytechnic Institute and State University to develop design guidelines for the installation of recently developed omni-directional roof vent on low slope membrane roofing systems. The newly designed and patented low-pressure roof vent works on Bernoulli and Venturi air flow principals and helps prevent uplift and detachment of the roofing membrane during storm or high wind conditions by creating a negative pressure zone underneath the roof membrane. The objective of this research is to further develop the Pressure Equalizing Vent System by testing the wind vent in combination with different underlayments and to determine the appropriate tributary area of each vent under dynamic wind conditions. The determined area of influence of each wind vent therefore serves as a guideline for appropriate spacing of the vents on the roof. It will also suggest the wind speed at which the pressure is lowered and its ability to weather storm events. The pressure sensors permanently installed beneath the membrane will continuously monitor the pressures in and around the wind vent. An additional objective of the research project is to understand the distributional characteristics of negative pressure in various layers of roof assembly in combination with varying underlayment membranes under different suctionals pressure to further develop the Pressure Equalizing Vent System. The proposal seeks to develop a cost effective roof assembly method, which can withstand the effect of extreme wind through improved understanding of air movement through different layers of roof assembly. The study explores the effect of various underlayments on spatial and distributional character of pressure field on the single ply flat roof deck in combination with omni-directional roof vent system. / Master of Science

This thesis presents a series of direct numerical simulations (DNS) performed in order to understand the discrepancy in the literature regarding turbulent asymptotic suction boundary layers (TASBLs) at low Reynolds numbers. The hypothesis to be tested is that the main reason for higher turbulence intensities observed in experiments compared to DNS is that the latter exhibits intermittent patches of laminar flow, developing both temporally and spatially. This hypothesis is confirmed here by comparing simulations with and without tripping, where the former removed patches of laminar flow thereby establishing a fully developed turbulent state with higher turbulence intensities compared to its naturally developing counterpart. The DNS were performed at different suctions rates corresponding to Reynolds numbers above the critical value of 270. The statistics taken from the simulations at different streamwise positions also support the developing character of the flow with increasing intermittency further downstream. Thus, it can be concluded that the actual flow state at these marginal Reynolds numbers is indeed an intermittent one, with lower fluctuation values as the experimental data would indicate.

The shear stress in an unsaturated soil increases rapidly with limited shear strain to a peak value and then drops gradually with a further increase in the shear strain until a residual value is reached. In other words, there is a significant strain-softening behavior under large shear deformation. A variety of geotechnical structures (e.g., slopes, foundations, retaining walls and piles) associated with unsaturated soils typically undergo a large progressive deformation prior to reaching failure conditions due to the influence of environmental factors (e.g., rainfall infiltration and wetting-drying cycles). As a result, the shear strength of soils in sliding zones typically reduces from a peak to a residual value with the progressive development of large shear deformation, while the shear strength of soils in other zones are still at the peak level. In other words, in many scenarios the strain-softening behavior of unsaturated soils can significantly influence the mechanical behavior of geo-structures. Therefore, a thorough understanding of the shear strength behavior of unsaturated soils during strain-softening is required to reliably interpret the mechanical behavior of geo-structures that undergo large shear deformation. Significant advances have been made during the last thirty years to understand and model the strain-softening behavior of unsaturated soils. Most of these studies however focus on the strain-softening behavior within a relatively small shear deformation due to the limitations of the experimental apparatuses. Only limited experimental studies under large shear deformation were reported based on the modified suction-controlled ring shear apparatus. Therefore, more investigations are still required to provide a comprehensive understanding of the shear strength behavior of unsaturated soils during strain-softening under large shear deformation. Studies presented in this thesis are directed towards investigating the shear strength behavior of unsaturated soils during strain-softening and its application in geotechnical engineering practice. The following studies have been conducted: (i) A state-of-the-art review of the strain-softening behavior of unsaturated soils published in the literature during the past three decades is summarized. The physical mechanisms and modelling methods of the strain-softening behavior and the peak, critical and residual shear strength of unsaturated soils are investigated. (ii) A disturbed state concept model is proposed to predict the variation of shear stress in unsaturated soils during strain-softening process under drained condition. Five sets of experimental data gathered from the literature on unsaturated soils varying from coarse- to fine-grained soils are used to verify the proposed model. The proposed model can provide reasonable predictions for the strain-softening stress-strain relationships of various types of unsaturated soils. The model is simple in concept and all the required parameters can be obtained from conventional saturated and unsaturated shearing tests and pressure plate tests. (iii) Two sets of suction-controlled multistage ring shear tests are conducted on unsaturated SP-SM soil and Indian Head till (IHT), respectively. The variation of the shear stress, void ratio, and water content of specimens during shearing (the shear displacement reaches 100 mm) under multi levels of net normal stress and matric suction are described and discussed. The influence of matric suction and net normal stress on the residual shear strength envelops of unsaturated soils are critically discussed. (iv) A model for predicting the residual shear strength for a wide range of unsaturated soils comprising coarse- to fine-grained soils is developed in terms of two stress state variables (i.e., the net normal stress and matric suction) by using the soil water characteristic curve as a tool. The model is formulated and validated based on experimental data in a series of suction-controlled ring shear tests using the axis-translation technique, including the two sets of tests (SP-SM and IHT) conducted in this research and another three sets of tests (SM, SC-SM and CH) gathered from the literature. The fitting parameters are related to the plasticity index (Iₚ); thus, only four basic parameters (i.e., cᵣ', φᵣ', Sᵣ and Iₚ) are included in this approach. (v) A series of slope stability analyses of a landslide in unsaturated condition are conducted using Geoslope software based on the peak and residual shear strength parameters. The analyses results highlight the role of residual shear strength in the slope stability of unsaturated soils. In summary, the mechanical behavior of unsaturated soils under large shear deformation is comprehensively investigated in this thesis. The experimental results of the suction-controlled ring shear tests reported in this research contribute towards understanding the fundamental shear strength behavior of unsaturated soils during strain-softening under large shear deformation. The models proposed in this research provide simple tools to predict the shear strength of unsaturated soils under different levels of shear deformation.

Concrete in its unaltered form allows the mass transfer of fluids into and out of its microstructure. These fluids can contain detrimental solutes which change the chemistry of the cement paste and/or the corrosion properties of the reinforcement bars, most noticeably hydrogen carbonates (HCO3-), oxygen (O2) and chloride ions (Cl-). Water and its solutions containing salts, mostly sodium chloride (NaCl), can also cause physical damage due to phase changes (freezing and thawing).  External application of hydrophobic agents onto the cement paste surface is a well-known method to alter the mass transfer at this interface. Bulk application of hydrophobic agents in ready mixed concrete is also a possible route but alters the entire cement paste. This thesis presents relevant aspects concerning the use of bulk hydrophobic agents in concrete within a spectrum water to cement ratio   (w/c) = 0.40-0.50. The main focus was on triacylglycerides (TAG) and alkyl alkoxysilanes (“silanes”) with application rates 1-3% based on cement weight.  Alterations to the compressive strengths have been observed and documented over a three-year period. The relative drop in mechanical strength is inversely proportional to w/c. The higher the addition rate, the lower the compressive strength. Chemical differences within the hydrophobic groupings (TAG or “silanes”) resulted in different outcomes. This was most noticeable in the water absorption, compressive strengths and chloride diffusion.  Freeze thaw testing did show noticeable differences, the use of “silanes” was detrimental in these tests even in deionsed water. The exact mechanism is unknown, but thin section analysis shows a lack of air entrainer (even when added on the fresh concrete mix) and extensive cracking in the entire cement paste. The scaling in concrete with TAGs was smaller but needs further improving.  The main properties intended with these agents were the ability to alter the mass transfer of water or solutions into the cement paste. Capillary suction and diffusion were examined. Increasing the w/c reduces the effectiveness of the hydrophobic agents to resist water uptake. This was seen in capillary suction and uni-directional chloride diffusion testing. Processed TAGs were more effective in reducing chloride diffusion than the unprocessed chemical whereas, in some cases, the “silanes” actually increased the amount of chloride ions transferred into the cement paste. Only a slight positive effect can be seen at the lower inclusion rate (1%). Increasing the w/c reduces the resistance to chloride ion diffusion with the same dosage rate.  A field test station close to vehicular traffic was also established in 2018 and 2019, but the specimens have not been tested at this point in time. It is hoped that these and other future studies will lead to a complete PhD project. / Betong i sin oförändrade form tillåter masstransport av vätskor i och ur dess mikrostruktur. Dessa vätskor kan innehålla skadliga lösta ämnen som förändrar cementpastans kemi och/eller korrosionsegenskaperna hos armeringsjärnen, framför allt vätekarbonater (HCO3-), syre (O2) och kloridjoner (Cl-). Vatten och dess lösningar som innehåller salter, mestadels natriumklorider (NaCl), kan till och med orsaka fysisk skada på grund av fasförändringar (frysning och upptining). Extern applicering av hydrofoba medel på cementpastans yta är en välkänd metod för att ändra masstransport genom denna gränsyta. Bulkapplicering av hydrofoba medel i färdigblandad betong är också en möjlig väg, och resulterar i förändringar i hela cementpastan. Denna licentiatavhandling presenterar relevanta aspekter rörande användningen av bulk-hydrofoba medel i betong inom intervall av vattencementtal = 0,40-0,50 (vct). Huvudfokus låg på triacylglyceroler (TAG) och alkyl-alkoxisilaner (”silaner”) med inblandning 1-3 % baserat på cementvikt. Förändringar av tryckhållfasthet har observerats och dokumenterats under en treårsperiod. Den relativa reduktionen i mekanisk hållfasthet är omvänt proportionell mot vct. Ju högre tillsatsmängd i cementpastan desto lägre tryckhållfasthet. Kemiska skillnader inom de hydrofoba grupperna (TAG eller "silaner") resulterade i olika resultat. Detta var mest märkbart i vattenabsorption, tryckhållfasthet och kloriddiffusion. Frysprovning visade märkbara skillnader, användningen av "silaner" var skadlig i dessa tester även i avjoniserat vatten. Den exakta mekanismen är okänd, men tunnslipsanalys visar på brist på luftporbildare (även om den tillsätts i stora mängder i den färska betongblandningen) och omfattande sprickbildning i hela cementpastan. Avskalningen i betong med TAG var mindre men behöver ytterligare förbättras. De huvudsakliga egenskaperna avsedda med dessa medel var förmågan att förändra masstransport av vatten eller lösningar till cementpastan. Kapillärsugning och diffusion undersöktes. Att öka vct minskar effektiviteten hos de hydrofoba medlen för att motstå vattenupptagning. Detta sågs vid kapillärsugning och enkelriktad kloriddiffusionsprovning. Raffinerade TAG:er var effektivare att minska kloriddiffusion än den oraffinerade, medan "silanerna" i visa fall faktiskt ökade mängden kloridjoner som överfördes inne i cementpastan. Något positiva effekt kan ses vid den lägre inkluderingstillsatsen (1 %). Att öka vct minskar motståndet mot kloridjondiffusion. En fältteststation intill fordonstrafik etablerades också 2018 och 2019 men provkropparna har inte testats vid denna tidpunkt. Förhoppningen är att dessa och andra framtida studier ska leda till ett komplett doktorandprojekt. / <p>QC 230330</p>

The rotary Left Ventricular Assist Device (LVAD) is a mechanical pump surgically implanted in patients with end-stage congestive heart failure to help maintain the flow of blood from the sick heart. The rotary type pumps are controlled by varying the impeller speed to control the amount of blood flowing through the LVAD. One important challenge in using these devices is to prevent the occurrence of excessive pumping of blood from the left ventricle (known as suction) that may cause it to collapse due to the high pump speed. The development of a proper feedback controller for the pump speed is therefore crucial to meet this challenge. In this thesis, some theoretical and practical issues related to the development of such a controller are discussed. First, a basic nonlinear, time-varying cardiovascular-LVAD circuit model that will be used to develop the controller is reviewed. Using this model, a suction index is tested to detect suction. Finally we propose a feedback controller that uses the pump flow signal to regulate the pump speed based on the suction index and an associated threshold. The objective of this controller is to continuously update the pump speed to adapt to the physiological changes of the patient while at the same time avoiding suction. Simulation results are presented under different conditions of the patient activities. Robustness of the controller to measurement noise is also discussed.

No description available.

No description available.

No description available.

This thesis presents a novel technique named "Core Suction" for fabricating optical fiber preforms for manufacturing highly doped fibers (HDFs) for optical amplification (Raman effect based or Erbium fiber based). The technique involves drawing the molten non-conventional core glass material into the silica cladding tube to form the preform. The developed technique is simple, inexpensive and shows great potential for fabricating preforms of highly nonlinear non-conventional multi-component glasses as the core material. Preforms were made with various core glasses such as Schott SF6, Lead-Tellurium-Germanate, Lead-Tellurium-Germanate- Neodymium -Erbium and MM2 in silica cladding tubes and then pulled into fibers. The fabricated fibers were measured for refractive index profile, loss spectrum and spontaneous Raman spectra. Elemental analysis of the fiber samples was also performed using an electron microprobe. Erbium doped fiber amplifiers (EDFAs) were setup using 30 cm, 5cm and 1 cm lengths of fabricated erbium doped fibers and their gain spectra measured. The distributed gain spectrum for an EDFA was also measured using an optical frequency domain reflectometery (OFDR) technique. Commercial dispersion compensated fiber (DCF) with very high GeO2 doping was used to setup a Raman amplifier and the gain spectrum measured. One of the needs of Raman amplification in optical fibers is to predict an accurate Raman gain, based on the fiber's refractive index profile. A method of predicting Raman gain in GeO2 doped fibers is presented and the predicted Raman gain values are compared with the measured ones in the same fibers. Raman gain issues like the dependence of the Raman gain on the GeO2 concentration, polarization dependence were taken into account for the gain calculations. An experimental setup for Raman gain measurements was made and measurement issues addressed. Polarization dependence of the Raman gain in one kilometer of polarization maintaining fiber was also measured. / Ph. D.