Mojtaba Moatamedi

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...

On dimensionless loading parameters for close-in blasts

Close-range blasts pose a threat through severe damage to structures and injury or death. In this work, the spatial and temporal descriptions of a localised blast load are presented using 6 non-dimensional parameters. These are found to be solely functions of the charge stand-off distance to diameter ratio for a cylindrically-shaped charge. Numerical simulations of a localised blast are performed using AUTODYN, where the pressure variation on a rigid barrier for various charge stand-off/diameter combinations is obtained. The least-square regression is then utilised to obtain the relationship between stand-off/diameter ratio and dimensionless loading parameters. The relevant expressions and dimensionless charts are presented. The proposed equations are verified by comparing experimental data with numerical results obtained by finite element analysis (FEA) of blast loaded steel plates (using the user-defined subroutine VDLOAD implemented in the FEA package ABAQUS/Explicit). Excellent correlation of the measured permanent displacement with numerically predicted results is obtained.

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.

Experimental and Numerical Study of Pressure in a Shock Tube

This paper presents the behavior of pressure in an air–water shock tube. In this work, high-pressure air (at 100 bar) interacts with water (at 1 atm ∼ 1 bar) through an orifice in a 100 mm constant diameter tube. The experiments are repeated with three different orifice plate diameters of 4, 8, and 15 mm. The variation of pressure during the transient stage is recorded in these experiments and it is found that with increasing orifice diameter, the amplitude of the pressure increases linearly with time when all other conditions are unchanged. The same phenomenon is simulated using the ls-dyna® software using an arbitrary Lagrangian Eulerian (ALE) method to solve the problem numerically. Simulations are made with a range of orifice diameters. The experimental results confirm the validity of the simulations algorithm. The simulations also demonstrated that the pressure behaves linearly with orifice diameter only when orifice diameter is less than 15% of the tube diameter.

Finite element analysis of human femur bone

An effort is made to analyse the stresses experienced by the human femur. In order to achieve these results a CAD model was developed by using the 3-D scanning of generic human femur for an individual of 70 kg weight (approx. averaged adult weight). The marrow cavity has been approximated as a hollow cylinder. The FEM model was built using solid tetrahedral element (20-noded 186 structural solid, ANSYS®). The model was analysed for its sensitivity. The results were computed for the range of loads. In this analysis, the maximum stress and its location were noted. In addition, the critical value of load was estimated for ultimate failure (i.e. fracture). The evaluated results give an understanding of the natural safety factor. The presented results are of significant importance in replication of the natural design parameters in creating the synthetic bone substitutes.

Design of water shock tube for testing shell materials

This paper presents design considerations for a shock tube experimental rig used to investigate the dynamic failure mechanisms of shell geometries subjected to water shock impact loading. In such setup, it is desirable that the drive pressure used within the tube can provide a wide range of impulsive loads on the test structures and some flexibility can be achieved on the applied pulse durations. With this aim a review of various existing shock tube experimental setup is presented and choices are made based on scientific merits. Finally design parameters are drawn for right set of conditions required for the experiments.

Study of CRFP Shell Structures under Dynamic Loading in Shock Tube Setup

The paper gives the study of the response of carbon fiber reinforced polymers (CRFP) quasi-isotropic shell structures under the influence of dynamic loading. The quasi-isotropic CRFP shell specimens are fabricated using Multipreg E720 laminates. These laminates are laid in such a way that shell structure has equal strength and mechanical properties in the two-dimensional (2D) plane and hence can be regarded as quasi-isotropic. In this study, the dynamic loading is generated using shock waves in a shock tube experimental setup. The strain and pressure data is collected from the experiments. Additional tests are carried out using Material Test System (MTS) for both tensile and flexural response of CRFP. Results obtained from experiments are compared with numerical simulations using ANSYS Multiphysics 14.0 finite element method (FEM) package. The numerical simulation and experimental results are found to be in good agreement.

Multiphysics design optimization for aerospace applications: Case study on helicopter loading hanger

This paper presents the Multiphysics technique applied in the design optimization of a loading hanger for an aerial crane. In this study, design optimization is applied on the geometric modelling of a part being used in an aerial crane operation. A set of dimensional and loading requirements are provided. Various geometric models are built using SolidWorks® Computer Aided Design (CAD) Package. In addition, Finite Element Method (FEM) is applied to study these geometric models using ANSYS® Multiphysics package. Appropriate material is chosen based on the strength to weight ratio. Efforts are made to optimize the geometry to reduce the weight of the part. Based on the achieved results, conclusions are drawn.

Conceptual design of high speed supersonic aircraft: A brief review on SR-71 (Blackbird) aircraft

The paper presents the conceptual design of high-speed supersonic aircraft. The study focuses on SR-71 (Blackbird) aircraft. The input to the conceptual design is a mission profile. Mission profile is a flight profile of the aircraft defined by the customer. This paper gives the SR-71 aircraft mission profile specified by US air force. Mission profile helps in defining the attributes the aircraft such as wing profile, vertical tail configuration, propulsion system, etc. Wing profile and vertical tail configurations have direct impact on lift, drag, stability, performance and maneuverability of the aircraft. A propulsion system directly influences the performance of the aircraft. By combining the wing profile and the propulsion system, two important parameters, known as wing loading and thrust to weight ratio can be calculated. In this work, conceptual design procedure given by D. P. Raymer (AIAA Educational Series) is applied to calculate wing loading and thrust to weight ratio. The calculated values are compared against the actual values of the SR-71 aircraft. Results indicates that the values are in agreement with the trend of developments in aviation.