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Papers by Mehran Rahmanian

Research paper thumbnail of Vortex-induced vibration of two cylinders with different diameters in close proximity

Research paper thumbnail of Vortex-induced vibration of two cylinders with different diameters in close proximity

Research paper thumbnail of Vortex-Induced Vibration of Two Side-by-Side Circular Cylinders of Different Diameters in Close Proximity in Steady Flow

Volume 4: Offshore Geotechnics; Ronald W. Yeung Honoring Symposium on Offshore and Ship Hydrodynamics, 2012

Research paper thumbnail of Lock-in study of two side-by-side cylinders of different diameters in close proximity in steady flow

Journal of Fluids and Structures, 2014

Research paper thumbnail of Vortex-Induced Vibration of Two Mechanically Coupled Cylinders of Different Diameters in Steady Flow

Volume 7: CFD and VIV; Offshore Geotechnics, 2011

Research paper thumbnail of Vortex induced vibration and vortex shedding characteristics of two side-by-side circular cylinders of different diameters in close proximity in steady flow

Journal of Fluids and Structures, 2014

This paper presents results of a numerical study of vortex-induced vibrations of two sideby-side ... more This paper presents results of a numerical study of vortex-induced vibrations of two sideby-side circular cylinders of different diameters in steady incompressible flow. The twodimensional Reynolds-averaged Navier-Stokes equations with a SST k-ω turbulence model are solved using the Petrov-Galerkin finite element method and the Arbitrary-Lagrangian-Eulerian scheme. The diameter ratio of the two cylinders is fixed at 0.1 and the mass ratio of both cylinders is 5.0. Both cylinders are constrained to oscillate in the transverse direction only. The Reynolds number based on the large cylinder diameter and free stream velocity is fixed at 5000. The effects of the reduced velocities of the cylinders on the vibration amplitude and vortex shedding regimes are investigated. It is found that for the range of parameters considered, collision between the two cylinders is dependent on the difference of the reduced velocities of the cylinders. Presence of the small cylinder in the proximity of the large one appears to have significant effects on the vortex shedding regime and vibration amplitude of the large cylinder.

Research paper thumbnail of Two degree of freedom vortex induced vibration tests of a riser model using spring bars

Tests have been performed on a riser model with low mass ratio subjected to uniform flows in a to... more Tests have been performed on a riser model with low mass ratio subjected to uniform flows in a towing tank at subcritical Reynolds numbers. Qualisys video motion capture system was used to measure VIV and Spring bars are used instead of commonly used parallel linkage mechanism for this kind of test. The circular cylinder of 100 mm in diameter and 1.5 m in length was towed vertically at constant speeds through the towing tank to simulate uniform current condition. Some key VIV parameters such as amplitude over diameter, lift and drag coefficients are presented against a non dimensional parameter known as reduced velocity to understand the effects of VIV on two degree of freedom system.The relative magnitude of the super-upper response branch vibration amplitudes are emphasised in this particular study. Results of this paper can be used as validation materials for CFD analysis that is very important to design riser system for oil and gas industry, also mentioned experiment procedure can be treated as a guide for future endeavour to perform similar kind of tests.

Research paper thumbnail of Vortex-induced vibration of two cylinders with different diameters in close proximity

Research paper thumbnail of Vortex-induced vibration of two cylinders with different diameters in close proximity

Research paper thumbnail of Vortex-Induced Vibration of Two Side-by-Side Circular Cylinders of Different Diameters in Close Proximity in Steady Flow

Volume 4: Offshore Geotechnics; Ronald W. Yeung Honoring Symposium on Offshore and Ship Hydrodynamics, 2012

Research paper thumbnail of Lock-in study of two side-by-side cylinders of different diameters in close proximity in steady flow

Journal of Fluids and Structures, 2014

Research paper thumbnail of Vortex-Induced Vibration of Two Mechanically Coupled Cylinders of Different Diameters in Steady Flow

Volume 7: CFD and VIV; Offshore Geotechnics, 2011

Research paper thumbnail of Vortex induced vibration and vortex shedding characteristics of two side-by-side circular cylinders of different diameters in close proximity in steady flow

Journal of Fluids and Structures, 2014

This paper presents results of a numerical study of vortex-induced vibrations of two sideby-side ... more This paper presents results of a numerical study of vortex-induced vibrations of two sideby-side circular cylinders of different diameters in steady incompressible flow. The twodimensional Reynolds-averaged Navier-Stokes equations with a SST k-ω turbulence model are solved using the Petrov-Galerkin finite element method and the Arbitrary-Lagrangian-Eulerian scheme. The diameter ratio of the two cylinders is fixed at 0.1 and the mass ratio of both cylinders is 5.0. Both cylinders are constrained to oscillate in the transverse direction only. The Reynolds number based on the large cylinder diameter and free stream velocity is fixed at 5000. The effects of the reduced velocities of the cylinders on the vibration amplitude and vortex shedding regimes are investigated. It is found that for the range of parameters considered, collision between the two cylinders is dependent on the difference of the reduced velocities of the cylinders. Presence of the small cylinder in the proximity of the large one appears to have significant effects on the vortex shedding regime and vibration amplitude of the large cylinder.

Research paper thumbnail of Two degree of freedom vortex induced vibration tests of a riser model using spring bars

Tests have been performed on a riser model with low mass ratio subjected to uniform flows in a to... more Tests have been performed on a riser model with low mass ratio subjected to uniform flows in a towing tank at subcritical Reynolds numbers. Qualisys video motion capture system was used to measure VIV and Spring bars are used instead of commonly used parallel linkage mechanism for this kind of test. The circular cylinder of 100 mm in diameter and 1.5 m in length was towed vertically at constant speeds through the towing tank to simulate uniform current condition. Some key VIV parameters such as amplitude over diameter, lift and drag coefficients are presented against a non dimensional parameter known as reduced velocity to understand the effects of VIV on two degree of freedom system.The relative magnitude of the super-upper response branch vibration amplitudes are emphasised in this particular study. Results of this paper can be used as validation materials for CFD analysis that is very important to design riser system for oil and gas industry, also mentioned experiment procedure can be treated as a guide for future endeavour to perform similar kind of tests.

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