Mohammed K. Ibrahim

Comparison of properties of steel slag and crushed limestone aggregate concretes

Abstract Steel slag is produced as a by-product during the oxidation of steel pellets in an electric arc furnace. This by-product that mainly consists of calcium carbonate is broken down to smaller sizes to be used as aggregates in asphalt and concrete. They are particularly useful in areas where good-quality aggregate is scarce. This research study was conducted to evaluate the mechanical properties and durability characteristics of steel slag aggregate concrete in comparison with the crushed limestone stone aggregate concrete. The durability performance of both steel slag and crushed limestone aggregate concretes was evaluated by assessing water permeability, pulse velocity, dimensional stability and reinforcement corrosion. The results indicated that the durability characteristics of steel slag cement concretes were better than those of crushed limestone aggregate concrete. Similarly, some of the physical properties of steel slag aggregate concrete were better than those of crushed limestone aggregate concrete, though the unit weight of the former was more than that of the latter.

Effectiveness of concrete surface treatmentmaterials in reducing chloride-induced reinforcement corrosion

Abstract The effectiveness of concrete surface treatment materials, such as silane, siloxane, acrylic coating, etc., in reducing chloride-induced reinforcement corrosion was investigated. Two sets of reinforced concrete specimens were cast. In the first set, reinforcement corrosion was accelerated by impressing an anodic potential of 2 V and the time to cracking was monitored. The second set of concrete specimens were immersed in the chloride solution and reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. Among the surface treatment materials investigated, silane, silane/siloxane with top coat and acrylic coating were effective in reducing the rate of reinforcement corrosion. Furthermore, the data developed in this investigation indicated that the performance of coatings can be quickly evaluated using impressed current technique.

Mixing Enhancement of Compressible Jets by Using Unsteady Microjets as Actuators

Lateralsteady/unsteadyinjectionofanarrayofmicrojets,whichareplacedalongthecircumferenceofthenozzle exit of a primary jet at equal intervals of azimuthal angle, was studied experimentally to clarify the characteristics of mixing and noise of compressible primary jets. Two modesof the microjets wereinvestigated: axisymmetric and antisymmetric injections. Fully expanded and underexpanded primary jets issued from a convergent nozzle are considered in thepresent study. Theunsteady microjets wereinjectedata Strouhal number Srof0.16, based on the nozzle exit diameter and the velocity at the nozzle exit, for two cases of total mass injection: 4 and 6% of primary jet mass e ow rate. Results of the mean e owe eld showed that the antisymmetric injection has a higher spreading ratethan the steady and unsteady axisymmetric injections in terms of centerlinevelocity decay. Thoseresults were cone rmed from linear stability analysis, which showed that antisymmetric modes for natural disturbances are more unstable in the downstream region than the corresponding axisymmetric modes. Moreover, reduction in the radiated noise was observed in steady axisymmetric injection. Thus, these results suggest that unsteady microjets have the potential for future use as a device for shear e ow control.

Durability of proprietary cementitious materials for use in wastewater transport systems

Abstract Several methods and materials, such as high performance coatings, fiber glass reinforced linings, special mortars, brick or ceramic linings, etc., are used to protect concrete from sulfuric acid attack in a sewage environment. Two proprietary high alumina cementitious lining materials, CC and SC, are recent additions to the list of protective materials used in the Arabian Gulf. This paper documents the findings of a laboratory study under accelerated conditions as well as a two-year field study of CC and SC in a wastewater lift station in Jubail, Saudi Arabia. In the laboratory investigations, 50 mm cube mortar specimens prepared using: (1) SC, (2) CC, (3) Type I+8% silica fume cement, (4) Type I+20% fly ash cement and (5) Type I cement were exposed to 2% sulfuric acid for 150 days. The laboratory specimens were tested for weight reduction, compressive strength, sulfate content, and alkalinity. In the field, the walls and ceiling of a wastewater manhole were coated using the proprietary lining materials, SC and CC, and were exposed to a normal sewage service environment. Performance of the liner materials was monitored for sulfate content and alkalinity after 6, 12 and 24 months of exposure. The analysis and evaluation test data generated from the accelerated laboratory study and the field study, which lasted for 24 months, showed that SC performed better than other materials tested in this investigation.

Computational Fluid Dynamics Validation Study of Wake-Capturing Capability for Flat-Plate Wake

This paper studies a computational fluid dynamics validation study of wake-capturing capability for unsteady flow characteristics. The computational fluid dynamics code used in this study is based on the Cartesian grid system with octree mesh refinement and uses a weighted essentially nonoscillatory numerical scheme to achieve higher-order accuracy to preserve unsteady flow characteristics. Flow properties in the flat-plate wake flowfield, such as mean velocity, root mean square of perturbation velocity, and frequencywise power spectrum of flow velocity, were chosen to validate the computational fluid dynamics code. The comparison between computational fluid dynamics results and experimental data showed good agreement for mean velocity and low-frequency fluctuations.

Design and navigation control of an advanced level CANSAT

This paper presents design and navigation control of an advanced level comeback CanSat which is going to be launched to an altitude of about 400 m using an amateur rocket from ground level. The CanSat uses advanced and ultra-light microcontroller, pressure and temperature sensors, 3-axis accelerometer, 3-axis gyro, camera, GPS, IR distance measuring sensor, and RF communication module to communicate with the ground station PC. Three actuators are considered in this work for flight and ground segments control. They are the motor driven propeller, elevator and rudder. For the flight segment, parachute and attitude control are used to control the CanSat descent rate, attitude and heading. For the ground segment control; both the propeller and the rear landing gear of the CanSat is used for heading toward a predefined location on the ground. The rear landing gear is connected to the rudder rotational axis. An indigenous navigation control and electronic circuit design with the test results also are presented in this paper.

Experimental Investigation of Screech-Tone Characteristics of Jet Interaction with a Flat Plate

The screech-tone characteristics of an underexpanded jet in the vicinity of a flat plate in which the jet is emitted from a circular sonic nozzle and interacts with a flat plate placed parallel to the jet axis have been investigated experimentally. The flow is visualized using the schlieren technique, and the unsteady pressure on the flat plate as well as the sound pressure level in the far field are measured for different jet-plate separation distances. It is found that screech tone vanishes when the flat plate comes close to the jet axis. However, there is an azimuthal directivity in its propagation, which depends on jet-plate separation distance. In addition, the highly oscillating baseline jet flow is suppressed by the jet-plate interaction, and screech tone completely disappears when the jet-plate separation distance becomes less than 0.61 of the jet diameter.

The Effects of Vane-Type Tabs on Flow and Acoustic Fields of Supersonic Jet

Vortex generators of vane-type tabs were placed at diametrically opposite locations along the circuntfcrcnce of a circular supersonic .jct nozzle exit. A nozzle with a design Mach nutnbcr of’ I .33 was used for the present investigation. The effects of lhe vane-type tab 011 both tlow field and acouslic tield were studied espcriment;~ll~. ‘l’wv modes of vane-type tabs, i.e. stationary and free-to-rotate. were studied tier different values of the noL/,ic pressure ratio. defined as the ratio of the jet total pressure IO the ambient pressure. Pitor probe surveys show that the vane-type tabs generate streamwise vortices, or tip vortices, which spread the jet more in terms of the decay of centerline velocity than the baseline jet. Acoustic measuretncnts show that overall sound pressure level. OASPL. was significantly reduced up to t 0 dB and screech tones were also baseline jet with a thrust penalty of about I .5-I% per vane. suppressed compared with the Parameters related with the vane-type tabs are protrusion height into the flow, vane angle. and the number of vanes, and ;I parametric study has been systematically performed.

Towards understanding the physics of supersonic jet screech

Jet flows have been a subject of intensive theoretical, numerical, and experimental investigations during last several decades. Many fluid dynamicists and specialists in computer simulations have endeavored to learn more about very complicated structures in jet flows. This interest have been in the first turn feeding by the desire to understand basic mechanisms of strong noise generated by high-speed jets, in particular very intense tones known as jet screech.

Spreading Enhancement of Axisymmetric Supersonic Jet by the Use of Micro Jets

Lateral steady/unsteady injection of an array of micro-jets, which are placed along the circumference of the nozzle exit of a primary jet at equal azimuthal angle intervals, were studied experimentally to clarify the characteristics of mixing and noise of compressible primary jets. Specifically two modes of the micro-jets: axisymmetric and antisymmetric, or flapping, injections were investigated. Fully-expanded and under-expanded primary jets issued from a convergent, or sonic, nozzle are considered in the present study. The unsteady micro-jets were injected at a Strouhal number, St, of 0.16, based on the nozzle exit diameter and the velocity at the nozzle exit, which is close to one of sub-harmonics of the most amplified Strouhal number, for two cases of total unsteady mass injection: 4% and 6%. Results of the mean flow field showed that the antisymmetric injection has a higher spreading rate than the steady and unsteady axisymmetric injections in terms of centerline velocity decay. Even with 50% reduction in the unsteady mass injection, the antisymmetric mode was excited, which persisted even downstream of the potential core region. Those results were confirmed from a linear stability analysis of a fully-expanded jet, which showed that antisymmetric modes for natural disturbances are more unstable in the downstream region than the corresponding axisymmetric modes. Moreover, reduction in the radiated noise was observed in the case of steady axisymmetric injection. Thus, these results suggest that unsteady micro-jets have the potential for future use as a device for shear flow control.