Now showing 1 - 10 of 19
  • Publication
    CFD Modelling of Helicopter Downwash and Assessment of its impact on Pedestrian Comfort
    This study used computational fluid dynamics (CFD) study to investigate the impact of helicopter downwash on pedestrian comfort. The initial stage of the study involves the development of a helicopter downwash model that was compared to experimental values which showed some degree of coherence with areas situated downstream of the helicopter rotor. The initial stage was used to find suitable modelling parameters and an adequate resolution of computational mesh to produce a reliable helicopter downwash model. The final stage of the study is to integrate a helicopter in a built environment and assess the impact of downwash on pedestrian comfort. The concluding stage of the study showed that helicopter downwash effects can impose discomforting conditions in the immediate vicinity of the helicopter along with some minute propagating effects further downstream. Although its magnitude is smaller compared to effects of prevailing wind a local mitigation must be separately planned to deal with the effects of helicopter downwash.
  • Publication
    A Numerical Study of the Effect of Wind Barriers on Traffic and the Bridge Deck
    (Civil Engineering Research Association of Ireland, 2020-08-28) ; ;
    Wind actions can have a great impact on both bridges and traffic on bridges. However, structures designed to shelter the traffic from wind can influence the aerodynamic performance of the bridge deck, especially for long-span bridges. This study compares the effect of non-perforated walls and perforated walls used as wind barriers for traffic by conducting Computational Fluid Dynamics (CFD) simulations on three-dimensional geometries of a four-lane bridge deck. Steady-state simulations employ the Reynolds-Averaged Navier Stokes (RANS) method with the k-epsilon turbulence model and all simulations use parallel computing. An open-sourced software OpenFOAM is used.
  • Publication
    A numerical study on the sheltering effects of the central wind barriers on the Rose Fitzgerald Kennedy Bridge
    This study aims to examine the sheltering effects of central wind barriers installed near the pylons of the Rose Fitzgerald Kennedy Bridge. A full-scale Computational Fluid Dynamics (CFD) model is developed, which includes high-precision geometries of the bridge and the terrain. Simulations using this model are performed at realistic wind conditions as boundary conditions are mapped from mesoscale Weather Research and Forecasting (WRF) simulations. Wind velocities at multiple locations on the bridge predicted by the CFD simulations are compared with field measurement data where a good agreement is reached. The validated model is then applied with bridge geometries with and without the central wind barriers at high wind conditions. Comparisons between these two groups of simulations show that the wind barriers can effectively reduce wind velocities on traffic lanes near the pylon, which validates the current design of the barriers on the bridge.
  • Publication
    A Lagrangian Cell-Centred Finite Volume Method for Metal Forming Simulation
    The current article presents a Lagrangian cell-centred finite volume solution methodology for simulation of metal forming processes. Details are given of the mathematical model in updated Lagrangian form, where a hyperelastoplastic J2 constitutive relation has been employed. The cell-centred finite volume discretisation is described, where a modified discretised is proposed to alleviate erroneous hydrostatic pressure oscillations; an outline of the memory efficient segregated solution procedure is given. The accuracy and order of accuracy of the method is examined on a number of 2-D and 3-D elastoplastic benchmark test cases, where good agreement with available analytical and finite element solutions is achieved.
    Scopus© Citations 20  828
  • Publication
    Quantifying the impact of bridge geometry and surrounding terrain: wind effects on bridges
    The safety and serviceability of long-span bridges can be significantly impacted by wind effects and therefore it is crucial to accurately estimate them during bridge design. This study develops full-scale 3-Dimensional CFD (computational fluid dynamics) simulation models to replicate wind conditions at the Rose Fitzgerald Kennedy Bridge in Ireland. The neglection of bridge geometries and the use of small scales in previous studies are significant limitations, and both the bridge geometry and surrounding terrain are included here at full-scale. Input values for wind conditions are mapped from weather simulations that apply the Weather Research and Forecasting (WRF) model. Wind velocities at four different points calculated by CFD simulations are compared with corresponding data collected from SHM field measurements. The calculated time-averaged wind velocities at four different locations on the bridge are shown to have relative differences of less than 10% to the measured wind velocities by anemometers 90% of the time. The maximum relative difference among all comparisons was only 15%, shown to be partially due to the inclusion of the full bridge and terrain geometry.
    Scopus© Citations 1  2
  • Publication
    An open-source finite volume toolbox for solid mechanics and fluid-solid interaction simulations
    Over the past 30 years, the cell-centred finite volume method has developed to become a viable alternative to the finite element method in the field of computational solid mechanics. The current article presents an open-source toolbox for solid mechanics and fluid-solid interaction simulations based on the finite volume library OpenFOAM. The object-oriented toolbox design is outlined, where emphasis has been given to code use, comprehension, maintenance and extension. The toolbox capabilities are demonstrated on a number of representative test problems, where comparisons are given with finite element solutions.
  • Publication
    Development of the Finite Volume Method for Hip Joint Stress Analysis
    (University College Dublin. School of Mechanical & Materials Engineering., 2012-10)
    Total Hip Arthroplasty is a surgical procedure that reforms the hip joint, replacing the pathological joint with an artificial prosthesis. Due to post-operative joint instability, complications such as dislocation are still a significant problem. Understanding the mechanics of the hip joint is key in the development of preventative methods to treat post-operative hip dislocation. The principal aim of this thesis is to develop a numerical model of the hip joint capable of realistically capturing musculoskeletal loading and joint mechanics. A finite volume structural solver, implemented in open-source software OpenFOAM, has been developed, which is capable of accurately predicting large displacements, large rotations and small strains. A contact procedure, based on an iterative penalty method, has been established and verified against the available Hertzian analytical solution. In order to accurately represent the musculotendon loading, Hill-type muscle models have been developed, and a novel mapped muscle attachment approach capable of accurately capturing the muscle fibre force directions has been implemented. A procedure for extracting the hip joint geometry from computed tomography and magnetic resonance imaging scans has been developed. A technique has been established to accurately extract the muscle-bone attachment sites from the tomographic images. Volumetric meshes of the bones have been constructed using hexahedral, tetrahedral, polyhedral and voxel based meshes and a comprehensive 3-D mesh analysis study has been conducted. Gait analysis has been performed on the same subject from which the tomography images were obtained, and custom analysis utilities have been developed to allow processing and visualisation of the data. Furthermore, a method has been established to process the obtained electromyography signals into a form suitable for input into the developed Hill-type muscle models. The hip joint has been simulated for three separate phases of the gait cycle. The relative positioning of the femur and pelvis bones has been determined from gait analysis, and the applied total hip joint forces have been established from literature. Each of the investigated models has been simulated with and without muscular loading, and the effect of muscle attachment approach has been investigated. The predicted average contact pressures and contact areas ranged from 5.93 to 10.1 MPa and 3.83 × 10-4 to 4.62 × 10-4 m2 respectively. Maximum von Mises stresses in the cortical bone ranged from 30 to 50 MPa and occurred in the acetabular roof, the body of the ilium superior to the acetabulum, near the iliosacral joint, the neck of the femur and the body of the femur. It has been found that the inclusion of musculotendon forces significantly
  • Publication
    Investigation of helicopter downwash effect on pedestrian comfort using CFD
    This study employed computational fluid dynamics (CFD) to investigate the impact of helicopter downwash on pedestrian comfort in a representative low-rise streetscape. A time-averaged approach was adopted, where propulsion from the helicopter blades was included using the so-called rotor disc method, as implemented in the open-source software OpenFoam. The modelling approach was validated by comparing downstream air velocities with experimental measurements. The effect of helicopter downwash on pedestrian comfort in a low-rise built environment, representative of an Irish city streetscape, was then analysed. It was found that pedestrian comfort significantly decreased in the immediate vicinity of the helicopter, while minor propagating effects were felt further downstream. The effects of building height, street width and prevailing winds were then examined. In general, it was found that taller buildings tended to improve street-level pedestrian comfort, while narrow streets surrounded by tall buildings tended to funnel the downwash towards the street level, decreasing pedestrian comfort. The main conclusion is that although the effect of helicopter downwash is smaller in magnitude compared with that of prevailing winds, a local mitigation must be established to deal with it.
    Scopus© Citations 2  151