Browsing by Author "Rafiqul Islam, Mohammad"

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Magneto-hydrodynamic Flow through a Rotating Rectangular Straight and Curve Duct with Magnetic Field
(©University of Dhaka, 2024-11-19) Rafiqul Islam, Mohammad
This research involves a numerical exploration of the characteristics of fully developed, steady, viscous, incompressible flow within a curved duct with square and rectangular cross-sections. The study considers both isothermal and non-isothermal conditions, while also accounting for the influence of magnetic fields, Hall currents, and Ion-slip currents. In this investigation, the dimensions of the cross-section are defined as having a height of 2h and a width of 2d. The analysis covers curved ducts with both square and rectangular cross sections for both isothermal and non-isothermal flow scenarios. In both cases, the aspect ratio is taken as l = 1 or 2 or 3, whereas the curvature of the duct ranges from 0.01 to 5. Also, the behaviour of the flow characteristic is investigated for non-isothermal flow through the straight duct in the presence of Hall and Ion-slip currents. A pressure gradient force, known as Dean Forces, is applied in the direction of the curved duct's centreline. This flow is further influenced by a combination of forces, including gravitational force, Lorentz force, centrifugal force, and Coriolis force. The gravitational force exerts its effect on the fluid. Additionally, the Lorentz force results from the interaction of electric and magnetic forces, while centrifugal and Coriolis forces stem from the duct's rotation and curvature. To model this complex system, governing equations are derived from the Navier–Stokes and Energy equations using cylindrical coordinates. These equations are then converted into their non-dimensional forms through the customary non-dimensional analysis. The spectral approach is used as the main instrument to perform the calculations. Additionally, as auxiliary tools, the Newton-Raphson, Collocation, Chebyshev polynomial, and arc-length procedures are employed. The arc-length method has been used to avoid the difficulties near the point of inflection and calculate the results at this point. The flow depends on the Taylor number υ δ δ d Tr 0 2 2 2 Ω = (Rotation parameter), Magnetic parameter ρυ B σ d M e 2 0 2 = , Grashof Number 2 3 υ β T g d Gr ∆ = ammeter Hall parameter ) (m , and Ion-slip parameter ) (α . The study examines the impact of Tr, Grand Dnon flow characteristics to compare and validate the findings with prior research. The primary objective of this investigation is to elucidate how M, m, and α influence flow characteristics within both rotational square and rectangular curved ducts, as well as in straight square ducts. Both co-rotating and counter rotating flow patterns are investigated here. Finally, a general discussion and conclusions on the solutions to the problems considered in the research study for different values of the magnetic, Hall, and Ion-slip parameters on the flow properties in some particular cases of Dean Number and different duct curvature are described.
Numerical modelling of slab-column joint of RC flat plates
(Department of Civil Engineering, 2014-02) Rafiqul Islam, Mohammad; Hossain, Dr. Tahsin Reza
In the design of reinforced concrete flat plates, the region around the column always pose a critical analysis problem where punching shear failure occurs due to brittle nature of this failure mode. Column tends to punch through the slab because of the shear stresses that act around the perimeter of the column and develop a failure surface in the form of a truncated cone or pyramid shape. This punching shear failure is one of the topics of intensive research work in the recent years. The slabcolumn connection behaviour is also critical as it transfers combined gravity and lateral loads. The performance of slab-column connection has often been less than satisfactory under seismic action. This has prompted the design community to establish rather restrictive rules for flat plate system in earthquake prone region. Before carrying out numerical model of slab-column connection, some existing literatures on the relevant field based on experimental investigation, analytical methods, numerical models and various codes of practice are thoroughly reviewed. A numerical model of slab-column joint of RC flat plate have been generated by using ‘ABAQUS’ software based on nonlinear finite element method. For nonlinear finite element analysis, material nonlinearity is modeled by considering the nonlinear effects due to cracking and crushing of concrete and yielding of steel reinforcement. A complete model requires the elastic properties, inelastic stressstrain relations and failure criteria of concrete. Regarding the concrete material behaviour, a nonlinear user-defined material approach based on the concrete damage plasticity model is used. On the other hand, reinforcing steel behaves as an elasticperfectly plastic material. A sensitivity analysis has been performed for mesh density to obtain a reliable solution. The numerical results of present finite element model have been verified with the experimental results and other numerical results. A satisfactory result has come in between the present numerical results and the experimental results or other numerical results which indicates the suitability and accuracy of present finite element model. All loads are applied in terms of displacement control criteria. A systematic parametric study of material and geometric parameters like concrete compressive strength, the amount of longitudinal reinforcement, yield stress of steel, effect of compression reinforcement, slab thickness, column dimensions and boundary conditions is carried out to identify the effects of different parameters on punching shear strength of flat plates. ACI 318-08/BNBC 2006 code provision is found to be more conservative in case of punching shear design of flat plates. It underestimates the influence of maximum material and geometric parameters to predict the actual punching capacity. Hence, a modification to the ACI 318- 08/BNBC 2006 code equation has been discussed and verified against the results of present finite element results. Four different slab-column joint of RC flat plates have been modeled numerically under different design specifications and analyzed to study the effects of different load combinations and loading sequence. The design and performance of these slabs have been discussed considering ACI 318-08/BNBC 2006 code provisions. It has been found that strength of slab-column connection improves if seismic design is performed. The performance of flat plate high-rise building structure with shear-wall has been checked under combined gravity and lateral loads considering different seismic zone. The percentage of moment transfer through different strip of slab is also analyzed under gravity and lateral loads.
Strength comparison of masonry wall made of clay burnt brick with frog mark and machine made brick without frog mark
(Department of Civil Engineering, 2017-07-03) Rafiqul Islam, Mohammad; Raquib Ahsan, Dr.
ABSTRACT Compressive strength, shear strength and Modulus of elasticity of masonry are significant parameters when considering structural masonry design. For simulation of structural behavior of masonry buildings, performance of embedded joint is important from the point of view of seismic design. Masonry structures of Bangladesh are mostly designed for vertical loads. The structural elements such as walls which were designed for vertical loads only, have to carry lateral load as well during an earthquake. Important masonry parameters are compressive strength, flexural strength, shear strength, modulus of elasticity etc. An attempt has been made in this study to correlate compressive strength, shear strength and wall stiffness, for clay burnt bricks with frog mark and machine made bricks without frog mark. In this experimental study, eight prisms and eight (10") URM wall specimens with a size of 5 × 3 were constructed with two different types of bricks, i.e clay burnt brick with frog mark and machine made brick without frog mark. Two types of mortar thicknesses 1/2" and 3/4" were used in the test specimens. The prism specimens were tested under axial compression normal to the bed joints and the wall specimens were tested under horizontal incremental cyclic loading along with constant axial compressive load. Lateral loading was applied using a loading control pattern. The specimens were tested under cyclic loading conditions displacing them laterally, along the axis of the walls and their load-deformation behavior was measured by dial gauges. It is observed that, increasing mortar thickness prism ultimate strength increases 18.0% for clay burnt brick and with increasing mortar thickness prism ultimate strength increases 1.3% for machine made brick. On the other hand, with the increasing mortar thickness ultimate shear strength decreases 9.6% for clay burnt brick with frog mark and with increasing mortar thickness ultimate shear strength decreases 8.0% for machine made bricks without frog mark. In clay burnt brick shear strength is 12.5% more than machine made brick. Increasing mortar thickness ductility decreases 22.0% for clay burnt brick and 20.0% for machine made bricks.