Yasser M. Ahmed

The adverse effects of flow-diverter stent-like devices on the flow pattern of saccular intracranial aneurysm models: computational fluid dynamics study.

BackgroundStent deployment across the aneurysmal neck has been established as one of the endovascular methods to treat intracranial aneurysms with or without coils.ObjectiveThe purpose is to study the possible adverse effects of deployment of the new flow-diverter stent-like devices (FD) on the flow characteristics of saccular aneurysm models.MethodsNumerical simulations of the blood flow patterns in the artificial models of three aneurysms were studied. One model was designed without an FD stent, the second model with one FD stent, and the third model with two stents. Numerical simulation for incompressible laminar blood flow was conducted in the three artificial cerebral aneurysm models by means of computational fluid dynamics.ResultsThere was a noticeable increase in the values of the circumferential pressure distributed on the walls of the aneurysm after stent deployment; this led to an increase the tension of the aneurysm surface and was considered to be an adverse effect. This pressure increase was further aggravated by the deployment of another stent. However, there is a beneficial effect of using FD stents, translating into the reduction of the flow velocity inside the aneurysm and wall shear stress at the inflow zone. This reduction decreases further with the deployment of another stent.ConclusionAneurysms become tenser after the deployment of one flow-diverter stent and (more tense still) after after the deployment of another stent. This principle should be kept in mind when choosing which group of aneurysms is the best candidate for such a treatment strategy. This study recommends deploying several FD stents during endovascular procedures until complete arrest of the blood flow occurs during the procedure; otherwise, the aneurysm may become tenser and dangerous if a slow blood flow jet still exists inside it at the end of the procedure.

Hydrodynamic Resistance Reduction of Multi-Purpose Amphibious Vehicle due to Air Bubble Effect

Multipurpose Amphibious Vehicles (MAV) and other blunt shaped floating vehicles encounter the problem of a large bow wave forming and hydrodynamic resistance at high speeds. This wave formation is accompanied by higher resistance and at a critical speed results in bow submerging or swamping. Three new shapes of hull bow design for the multipurpose amphibious vehicle were conducted at several speeds to investigate the hydrodynamic phenomena using Computational Fluid Dynamics (CFD, RANS code), which is applied by Ansys-CFX14.0 and Maxsurf. The vehicle’s hydrodynamic bow shapes were able to break up induced waves and avoid swamping. Comparative results with the vehicle fitted with U-shape, V-shape and Flat-shape of hull bow, showed that the U-shape of the hull bow has reduced the total resistance to 20.3% and 13.6% compared with the V-shape and flat shape respectively. Though, the U-shape of hull bow is capable to increase the amphibious operating life and speed of vehicle. Also it has ability to reduce the vehicle’s required power, fossil fuel consumption and wetted hull surface. On the other hand, the use of air cushions to support marine vehicles, heavy floating structures and in other operation is well known. The main problem in Multi-purpose Amphibious Vehicles (MAV) is the amount of power needed in order to overcome the hydrodynamic resistance acting on the hull which is included the frictional and pressure resistances. Therefore, more power is needed to move the MAV forward. In this respect, more fuel will be required to operate the amphibious vehicles. This problem could be effectively reduced by the introduction of the air cushion concept. With the air being drawn from top of craft to the cavity below the hull will produce some cushioning effect and also help to reduce skin friction drag. In this paper, air cushion effect will be studied in rigid surface cavity instead of using flexible skirts. This would avoid the problem of high maintenance due to replacement of damaged skirts. Finally, the MAV will be supported using air cavity and bubbles generated by an air pump (compressor and air pressure vessel) to pushes the hull of multi-purpose amphibious vehicle up and reduce the frictional resistance due to draft and wetted surface reduction and layer of air between hull surface and water. This research would be done via CFD (ANSYS-CFX 14.0) and analyzed the hydrodynamic resistance

Experimental investigation of a wing-in-ground effect craft

The aerodynamic characteristics of the wing-in-ground effect (WIG) craft model that has a noble configuration of a compound wing was experimentally investigated and Universiti Teknologi Malaysia (UTM) wind tunnel with and without endplates. Lift and drag forces, pitching moment coefficients, and the centre of pressure were measured with respect to the ground clearance and the wing angle of attack. The ground effect and the existence of the endplates increase the wing lift-to-drag ratio at low ground clearance. The results of this research work show new proposed design of the WIG craft with compound wing and endplates, which can clearly increase the aerodynamic efficiency without compromising the longitudinal stability. The use of WIG craft is representing an ambitious technology that will help in reducing time, effort, and money of the conventional marine transportation in the future.

Propeller Effect on 3D Flow at the Stern Hull of a LNG Carrier Using Finite Volume Method

Numerical study and RANS simulations have been applied to investigate the incompressible free surface flow around the stern hull of Liquefied Natural Gas (LNG) ship affected by working propeller behind of her. Experimental works are carried out using LNG ship model in Marine Teknologi Center (MTC) of Univrsiti Teknologi Malaysia (UTM) to verify the computational fluid dynamic (CFD) results. Ansys-CFX 14.0 based on viscous flow finite volume code using the two-phase Eulerian–Eulerian fluid approach and shear stress transport (SST) turbulence model have been used in this study. A tetrahedral unstructured combined with prism grid were used with the viscous flow code for meshing the computational domain of water surface around it. CFD simulation has been verified using available experimental results. Finally, the flow structure, streamlines, velocity and pressure distribution around stern hull and propeller zone are discussed and analysed.

Hydrodynamic Design of New Type of Artificial Reefs

The purpose of this research work is to study the hydrodynamic characteristics of a new type of artificial reef structure, in order to provide a structure with low flow resistance, which will be a more suitable shelter for fishes and marine organisms. The idea of the new artificial reef is based on the streamlined bicycle helmet design concept. The hydrodynamic characteristics of the helmet and hollow cube artificial reefs (ARs) of the same volume have been studied at different water depths and wave frequencies of Malaysia seas using Computational Fluid Dynamics (CFD) method. The finite volume RANSE (Reynolds-Averaged Navier-Stokes Eqs.) code Ansys CFX was used for calculating the reefs drag force (FD) and flow characteristics, while the potential flow code Ansys Aqwa was used for calculating the reefs inertia force (FI). The Shear Stress Transport (SST) turbulence model was used in the RANSE code. The results of the two ARs were then compared for studying the hydrodynamic improvement due to the use of streamlined helmet artificial reef on the flow pattern around it. The streamlined body of the helmet artificial reef enhances the flow pattern at the aft region of the reef and provides flow zones with moderate flow speed at this area, which can help fishes and marine organisms from finding good shelter. The special shape of the different openings in the body of the helmet artificial reef improves the condition of the flow velocity distribution inside the unit than that of the hollow cube unit, which can increase the amount of the nutrient to the living fishes and organisms inside the reef.

Three-year experience of laparoscopic greater curvature plication in the treatment of morbid obesity

Background Laparoscopic greater curvature plication (LGCP) is a new restrictive bariatric procedure. The aim of the present study is to report the outcome of LGCP in 40 morbidly obese patients over a period of 3 years of follow-up. Patients and methods All procedures were completed laparoscopically. The mean operative time was 123.5 min (85-200 min) and the mean duration of hospital stay was 1.1 days (1-3 days). No intraoperative complications were reported. The mean excess weight loss was 34.93 ± 19.85% at the end of the study. Conclusion LGCP is feasible and safe when applied to morbidly obese patients, but it has an unsustainable effect on weight loss.

Comparison of numerical simulation with experimental result for small scale one seater wing in ground effect (WIG) craft

In this paper, three dimensional data and behavior of incompressible and steady air flow around a small scale Wing in Ground Effect Craft (WIG) were investigated and studied numerically then compar...

Numerical studies of vortex induced vibration of a circular cylinder at high reynolds number

Study of vibrations due to vortex shedding(VIV) in the wake of a cylinder that is exposed to a current is very important, especially for marine risers which are used to extract oil and gas from sea bed. The phenomenon of vortex induced vibration(VIV) has been one of the major concerns for hydrodynamic researchers due to its potential ability to cause severe fatigue damage, the hydrodynamics of VIV is a very complex subject to be dealt with. Though there are numbers of research papers about VIV simulation of a circular cylinder, most of them were related to 2D flow and lower Reynolds number. 3D numerical simulation of vortex induced vibration at high Reynolds number can be very challenging. To study 3D flow effect on VIV of a circular cylinder can be very challenging. Suitable mesh, appropriate turbulence model, strong computational resources are tricky issues to be dealt with before considering 3D simulation. In this paper CFX 3D solver is used to study VIV at higher reynolds number. CFX 3D solver is able to covert a 2D domain into a 3D computational domain by adding some thickness perpendecularly to the 2D plan. The shear stress transport detached eddy turbulence model has been used for simulating the turbulent flow around the cylinder for a Reynolds number Re=104, results from CFD are compared with existing experimental results. Hopefully discussion of this paper can be helpful for any future project that would deal with VIV simulation.

Use of CFD to Study the Resistance of Sprint Master Canoe

The resistance and the hydrodynamic characteristics of the Sprint Master canoe that is used in Universiti Teknologi Malaysia (UTM) have been studied at different speeds using Computational Fluid Dynamics (CFD) method. The resistance of the canoe at different speeds has been measured in UTM marine technology center (MTC). The finite volume code Ansys CFX has been used for carrying out the numerical simulations for the hull form of the canoe at the same experimental speeds. The Volume of Fluid method (VOF) has been used with Ansys CFX for capturing the free surface flow around the canoe hull at the same experimental speeds. The Shear Stress Transport (SST) turbulence model has been used in the RANSE code. The grid generator ICEM CFD has been used for building the grids for the RANSE code solver. The numerical results compare very well with the experimental results at the different speeds.

Numerical Study on Hydrodynamic Resistance of New Hull Design for Multipurpose Amphibious Vehicle

Multipurpose Amphibious V ehicles ( MAV ) and other blunt-shaped floating vehicles encounter the problem of a large bow wave forming at high speeds. This wave formation is accompanied by higher resistance and at a critical speed results in bow submergence or swamping. Three new shapes of hull bow design for the multipurpose amphibious vehicle were conducted at several speeds to investigate the hydrodynamic phenomena using Computational Fluid Dynamics (CFD, RANS code) which is applied by Ansys-CFX14.0 and Maxsurf. The vehicle’s hydrodynamic bow shapes were able to break up induced waves and avoid swamping. Comparative results with the vehicle fitted with U-shape, V-shape and Flat-shape of hull bow, showed that the U-shape of the hull bow has reduced the total resistance to 20.3% and 13.6% compared with the V-shape and flat shape respectively. Though, the U-shape of hull bow is capable to increase the amphibious operating life and speed of vehicle. Also it has ability to reduce the vehicle’s required power, fossil fuel consumption and wetted hull surface.