31 research outputs found
Rainfall Microphysical Observations Using the High-Speed Optical Disdrometer
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Rainfall microphysical observations are conducted using the High-Speed Optical Disdrometer (HOD). The main objective of this study is to observe microphysical properties of raindrops such as drop shape, fall velocity/ acceleration, drop size distribution, oscillation, and collision using the HOD. The HOD is a new optical disdrometer that consists of a state of the art camera with high-speed video recording capability, an LED light, and a sensor unit. The High-speed camera points at the LED light and captures the backlit silhouettes of the particles. The sensor unit sends a digital signal to the camera when a drop passes through the sensor unit. The digital signal of the sensor unit triggers the camera and camera capture a pre-defined number of frames of the drop. The raindrop images are then digitally processed using an image processing software built in-house. The captured raindrop from the sequential images provides a wide range of raindrop microphysical information such as drop shape, oscillation, collision, and fall speed. The HOD was laboratory tested with high-precision spherical lenses of different sizes to ascertain the accuracy of the image-processing algorithm. In addition, water drops were generated in the laboratory using needles of different sizes attached at the bottom of a constant head tank. The drops were then freely fallen through the measurement volume of the HOD, which confirms the proficiency of the sensor system around the focal plane of the high-speed camera. The HOD was field tested at different geographic locations, and its measurement capabilities were evaluated by comparisons with measurements from a collocated commercial disdrometer and rain gauges. iv These evaluations confirmed the research readiness of this new optical disdrometer. Using the HOD, binary raindrop collisions were observed during the field experiments for the first time. However, no spontaneous breakup was observed. These observations of binary raindrop collisions provide a strong support for the postulated governing role of raindrop collisions in defining DSD shape evolution.Civil and Environmental Engineerin
NANO-CHARACTERIZATION OF TYPE-G CEMENT SLURRY INCORPORATING NANOCLAY CURED UNDER HIGH TEMPERATURE AND PRESSURE
No full textAbstract: Type-G cement slurry with various admixtures commonly used in oil/gas well cementing (OWC) incorporating 1, 2 and 3% nanoclay particles by weight of cement were produced. A water/cement ratio of 0.44 was used and the mixes were subjected to a temperature of 290° F and a pressure of 4666 psi for 48 hours. First, the effect of nanoclay on compressive strength evolution was investigated. Second elastic and viscoelastic characteristics of the cementitious mixes were characterized using nanoindentation. The nanoindentation tests enabled evaluating the maximum indentation depth, plastic depth, and the reduced elastic modulus. Furthermore, dwell time of 60 seconds was used to evaluate creep compliance of the cement mixes incorporating nanoclay. Fracture toughness was estimated from the nanoindentation data during the dwell loading period. Scanning electron microscope (SEM) and X-ray diffraction (XRD) microstructural analyses were conducted to explain the results observed using nanoindentation. Furthermore, finite element modeling was used to simulate the nanoindentation test and to extract the stress-strain Type-G cement material incorporating nanoclay and cured under high temperature and pressure. Moreover, The experimental observations showed that nanoclay improved compressive strength evolution with time compared with neat cement and eliminated strength retrogression problem. Furthermore, using 1 and 2% nanoclay resulted in insignificant change (-28 to +12%) of the reduced elastic modulus compared with neat cement. However, a high content of 3% nanoclay resulted in a significant increase of (+54%) in the reduced elastic modulus and a significant reduction in creep compliance compared with neat cement. Fracture analysis of nanoindentation data showed a significant improvement of fracture toughness due to the addition of nanoclay. XRD analysis and SEM investigations proved that the incorporation of nanoclay in the cement mix transforms the Calcium Hydroxide (CH) to calcium silicate hydrate (C-S-H) and reduced capillary porosity leading to higher elastic modulus and reduced creep compliance compared with neat cement. Finally, the extracted stress-strain curves using the finite element method shows that adding nanoclay resulted in stiffening OWC paste. The significance of nanoclay seems strongly dependent on the nanoclay content and the quality of its mixing with cement
Experimental Investigation of Hybrid Beams Utilizing Ultra-High Performance Concrete (UHPC) as Tension Reinforcement
No full textUltra-high performance concrete (UHPC) is a new generation concrete with extremely high tensile and compressive strength, high durability, and ductility. UHPC offers tremendous opportunities for use in new thin and slender structural concrete elements and repair of existing concrete structures and has an excellent potential to replace conventional steel reinforcement in normal concrete (NC) members. This paper investigated the potential application of a hybrid NC-UHPC beam using a thin UHPC layer on the tension face to cater to tensile stresses, eliminating the need for passive steel reinforcement. Four-point flexural load tests were performed on 24 composite beams with a thin UHPC layer overlaid with NC. The parameters considered include the thickness of the UHPC layer, depth, and span of the beam. A linear behavior categorizes the flexural behavior of the hybrid NC-UHPC beam up to the ultimate load, after which the hybrid beam shows a non-brittle failure, and softening ensues associated with cracking, increased deflection, and loss of load resisting capacity. The unfinished top surface of the UHPC layer and the overlying NC developed a full composite action without any slip. It was found that a two-day self-curing of the UHPC layer was found to be essential for the development of a strong bond between the layers. The random dispersion and orientation of steel fibers in the UHPC can lead to a decreased tensile response for larger hybrid NC-UHPC beams. The experimental results validate the potential of hybrid NC-UHPC beams as an attractive, structurally feasible, and alternative sound form of construction in terms of their high flexural strength and corrosion-free service life. The proposed unreinforced hybrid system could be used in the construction of precast beams and slabs for residential as well as industrial buildings. Further research, including full-scale load testing of the hybrid beam, is needed prior to practical applications
Dynamic Response of Reinforced Concrete Bridge Piers Subjected to Combined Axial and Blast Loading
No full textA Comparative Study of Rainfall Observations during GPM IPHEx Field Campaign
No full textMeasurement capabilities of a new optical disdrometer called High-speed Optical Disdrometer (HOD) were evaluated through a comparative study with the 2- Dimensional Video Disdrometer (2DVD), and the Pluvio200 weighing bucket rain gauge. All instruments were collocated at the Maggie Valley site of the Integrated Precipitation Hydrology Experiment (IPHEx) field campaign. This field campaign was a joint effort between NASA’s Global Precipitation Measurement (GPM) ground validation program, Duke University, and NOAA’s Hydrometeorology Test bed- South East. Collocated measurements were conducted for a heavy rain event (conditional mean rain rate of 18.7 mm h-1 based upon 2DVD) on May 13, 2014. This comparative study seeks the degree of agreement among precipitation measuring instruments for the rain total, raindrop size distribution, and fall velocity.This study was funded by the National Science Foundation grant # AGS-1144846 to the third autho
Application of Nanotechnology in Oil Well Cementing
No full textAbstract
Nanotechnology provides a wide variety of methods to resolve industrial issues, which could not be addressed previously using customary methods. It helps enable researchers to alter properties of bulk materials at the nanometer scale. Various nanomaterials have been successfully applied in many areas of petroleum engineering, particularly in drilling fluids, lost circulation, enhanced oil recovery (EOR), and cementing. This study examines the mechanical and microstructural properties of oil well cement with nanozeolite.
During this research, API Class G cement was used with various concentrations of nanozeolite. Compressive strength development of Class G cement, with and without nanozeolite, was studied using an ultrasonic cement analyzer (UCA) for 24 hours under high-pressure and high-temperature (HP/HT) conditions. The porosity and permeability of set Class G cement admixed with nanozeolite was also analyzed in an automated permeameter/porosimeter after 24 hours of curing. Microstructural examination of cement samples was performed using scanning electron microscopy (SEM).
Three important parameters during well cementing operations included time to achieve 50- and 500-psi compressive strength and time to achieve 2,000-psi compressive strength. These parameters were significantly altered by adding a small percentage of nanozeolite to the neat Class G cement. The addition of nanozeolite resulted in a decrease in transition time and accelerated achievement of 2,000-psi strength. Furthermore, the porosity and permeability of the set Class G cement specimens with nanozeolite decreased substantially, thus indicating a dense microstructure of the matrix. This was confirmed by microstructural investigations using SEM. Nanozeolite is nonhazardous, nontoxic and is compatible with API Class G cement.
Nanozeolite can be an effective oil well cement additive because it enhances early strength, and the final compressive strength helps improve cement durability. The accelerated compressive strength development can help decrease wait-on-cement (WOC) time, thus lowering operation costs. Additionally, denser microstructure can help restrain the invasion of corrosive formation fluids.</jats:p
Nano-Characterization of Type-G Cement Slurry Incorporating Nanoclay Cured Under High Temperature and Pressure
No full textOn the Applicability of Ground-Based Microwave Radiometers for Urban Boundary Layer Research
No full textSignificant knowledge gaps exist in our understanding of urban boundary layer processes, particularly the hygrothermal state. The earth system community has successfully used microwave radiometers for several decades. However, the applicability in complex urban environments has never been adequately tested. Here, observations from a microwave radiometer are compared to radiosonde readings in a densely urbanized site in Houston, Texas. The site was influenced by both an urban heat island and the sea breeze phenomenon. The analysis showed significant disagreement between the virtual potential temperature predicted by the microwave radiometer and the radiosonde for all periods within the boundary layer. However, the values were reasonably comparable above the boundary layer. The microwave radiometer incorrectly predicted an inversion layer instead of a mixed layer during convective periods. The microwave radiometer measurements deviated from the radiosonde measurements throughout the lower troposphere for the relative humidity
Microstructural and Strength Investigation of Geopolymer Concrete with Natural Pozzolan and Micro Silica
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