Hassan Abbas Khawaja

Quantitative Analysis of Accuracy of Voidage Computations in CFD-DEM Simulations

CFD-DEM (Computational Fluid Dynamics — Discrete Element Modelling) is a two-phase flow numerical modelling technique, where the Eulerian method is used for the fluid and the Lagrangian method for the particles. The two phases are coupled by a fluid-particle interaction force (i.e. drag force) which is computed using a correlation. In a two-phase flow, one critical parameter is the voidage (or void fraction), which is defined as the ratio of the volume occupied by the fluid to the total volume. In a CFD-DEM simulation the local voidage is computed by calculating the volume of particles in a given fluid cell. For spherical particles, this computation is difficult when a particle is on the boundary of fluid cells. In this case, it is usual to compute the volume of a particle in a fluid cell approximately. One such approximation divides the volume of a particle into each cell in the same ratio as an equivalent cube of width equal to the particle diameter. Whilst this approach is computationally straight forw...

CFD-DEM Simulation of Propagation of Sound Waves in Fluid Particles Fluidised Medium

In this work, speed of sound in 2 phase mixture has been explored using CFD-DEM (Computational Fluid Dynamcis - Discrete Element Modelling). In this method volume averaged Navier Stokes, continuity and energy equations are solved for fluid. Particles are simulated as individual entities; their behaviour is captured by Newtons laws of motion and classical contact mechanics. Particle-fluid interaction is captured using drag laws given in literature. The speed of sound in a medium depends on physical properties. It has been found experimentally that speed of sound drops significantly in 2 phase mixture of fluidised particles because of its increased density relative to gas while maintaining its compressibility. Due to the high rate of heat transfer within 2 phase medium as given in Roy et al. (1990), it has been assumed that the fluidised gas-particle medium is isothermal. The similar phenomenon has been tried to be captured using CFD-DEM numerical simulation. The disturbance is introduced and fundamental frequency in the medium is noted to measure the speed of sound for e.g. organ pipe. It has been found that speed of sound is in agreement with the relationship given in Roy et al. (1990). Their assumption that the system is isothermal also appears to be valid.

CFD-DEM Simulation of Minimum Fluidisation Velocity in Two Phase Medium

In this work, CFD-DEM (computational fluid dynamics - discrete element method) has been used to model the 2 phase flow composed of solid particle and gas in the fluidised bed. This technique uses the Eulerian and the Langrangian methods to solve fluid and particles respectively. Each particle is treated as a discrete entity whose motion is governed by Newtons laws of motion. The particle-particle and particle-wall interaction is modelled using the classical contact mechanics. The particles motion is coupled with the volume averaged equations of the fluid dynamics using drag law.In fluidised bed, particles start experiencing drag once the fluid is passing through. The solid particles response to it once drag experienced is just equal to the weight of the particles. At this moment pressure drop across the bed is just equal to the weight of particles divide by the cross-section area. This is the first regime of fluidization, also referred as ‘the regime of minimum fluidization’.In this study, phenomenon of ...

Validation of Normal and Frictional Contact Models of Spherical Bodies by Fem Analysis

Contact forces between two spheres are computed, including the contact pressure (normal) and the frictional stress (tangential) using a finite element method (FEM). A CAD model of a part of a sphere was developed. A mesh was created using ANSYS® Solid 186, 20-Noded hexahedral element and analyzed for its sensitivity. ANSYS® Contact 174 and Target 170, 8-Noded surface elements were used. Contact pressure and frictional stress contours were calculated by varying the displacements. Normal and Tangential contact forces were computed by integrating contact pressure and frictional stress over the contact surface. The values obtained for the normal force were compared with the non-linear spring model as given by Hertz [1]. Similarly values of the tangential force were compared with the model of Mindlin and Deresiewicz (MD) [2]. The FEM results were found to be in agreement with the models.

Review of marine icing and anti-/de-icing systems

ABSTRACT The aim of this work is to review the phenomenon of icing in marine operations. The focus is on two main sources of icing, namely atmospheric and sea spray. The literature reveals that sea spray icing is the main contributor to marine icing. This work discusses the available ice accretion prediction models on ships and offshore structures. It also reviews the anti-/de-icing technologies that can be implemented on ships operating in cold climate regions. The significance of ice detection is acknowledged, and a brief review of various ice detection technologies is provided.

Determination of Thermal Properties of Fresh Water and Sea Water Ice using Multiphysics Analysis

The work reported in this paper is funded by the Norges forskningsrad, project no. 195153/160 in collaboration with Faroe Petroleum.

Multiphysics Simulation of Infrared Signature of an Ice Cube

Poster presented at The International Conference of Multiphysics, 10.12.15 - 11.12.15, London

Application of a 2-D approximation technique for solving stress analyses problem in FEM

With the advent of computational techniques and methods like finite element method, complex engineering problems are no longer difficult to solve. These methods have helped engineers and designers to simulate and solve engineering problems in much more details than possible with experimental techniques. However, applying these techniques is not a simple task and require lots of acumen, understanding, and experience in obtaining a solution that is as close to an exact solution as possible with minimum computer resources. In this work using the finite element (FE) method, stress analyzes of the low-pressure turbine of a small turbofan engine is carried out by employing two different techniques. Initially, a complete solid model of the turbine is prepared which is then finite element modelled with the eight-node brick element. Stresses are calculated using this model. Subsequently, the same turbine is modelled with four-node shell element for calculation of stresses. Material properties, applied loads (inertial, aerodynamic, and thermal), and constraints were same for both the cases. Authors have developed a “2-D approximation technique” to approximate a 3-D problem into a 2-D problem to study the saving invaluable computational time and resources. In this statistics technique, the 3-D domain of variable thickness is divided into many small areas of constant thickness. It is ensured that the value of the thickness for each sub-area is the correct representative thickness of that sub area, and it is within three sigma limit. The results revealed that technique developed is accurate, less time consuming and computational effort saving; the stresses obtained by 2-D technique are within five percent of 3-D results. The solution is obtained in CPU time which is six times less than the 3-D model. Similarly, the number of nodes and elements are more than ten times less than that of the 3-D model. ANSYS ® was used in this work.

Selection of High Performance Alloy for Gas Turbine Blade Using Multiphysics Analysis

With the extensive increase in the utilization of energy resources in the modern era, the need of energy extraction from various resources has pronounced in recent years. Thus comprehensive efforts have been made around the globe in the technological development of turbo machines where means of energy extraction is energized fluids. This development led the aviation industry to power boost due to better performing engines. Meanwhile, the structural conformability requirements relative to the functional requirements have also increased with the advent of newer, better performing materials. Thus there is a need to study the material behavior and its usage with the idea of selecting the best possible material for its application.In this work a gas turbine blade of a small turbofan engine, where geometry and aerodynamic data was available, was analyzed for its structural behavior in the proposed mission envelope, where the engine turbine is subjected to high thermal, inertial and aerodynamic loads. Multiphysi...

Optimization of Particle Search Algorithm for CFD-DEM Simulations

Discrete element method has numerous applications in particle physics. However, simulating particles as discrete entities can become costly for large systems. In time-driven DEM simulation most computation time is taken by contact search stage. We propose an efficient collision detection method which is based on sorting particles by their coordinates. Using multiple sorting criteria allows minimizing number of potential neighbours and defines fitness of this approach for simulation of massive systems in 3D. This method is compared to a common approach that consists of placing particles onto a grid of cells. Advantage of the new approach is independence of simulation parameters upon particle radius and domain size.