Now showing 1 - 10 of 17
  • 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
    Meso-scale thermal and solidification modelling for metallic additive manufacturing processes
    The emergence of additive manufacturing (AM) in recent decades signifies a paradigm shift in how we think about manufacturing. Throughout history, breakthroughs in manufacturing were focused on mass production, with a “one size fits all” mentality. Whilst for large batch size applications this has invariably decreased unit manufacturing costs, increased throughput and decreased prices for customers, it also imposes significant limitations for small batch production. Conventional manufacturing requires many highly specialised steps and equipment, requiring significant resources to establish and setting the barrier to entry unfeasibly high for fledgeling SMEs to enter the manufacturing space. Coupled with this, it inevitably forces manufacturers to be unresponsive to their customers’ needs, as changes to a product or manufacturing process are costly, and require significant machine downtime. Additive manufacturing on the other hand offers virtually limitless freedom to the manufacturer to make changes to a product, even for a one-off bespoke application, without significant machine downtime or costly modification to the manufacturing process. Perhaps even more importantly, since parts are generated additively many of the restrictions that traditional machining imposes on part design no longer apply, allowing for near-net- shape, highly optimised structures to be realised. However, these advantages do not come without a cost. Widespread adoption of AM is still hampered by less than ideal mechanical performance.
  • 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
    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
    Development of mapped stress-field boundary conditions based on a Hill-type muscle model
    (Wiley Blackwell (John Wiley & Sons), 2014-04-07) ; ; ;
    Forces generated in the muscles and tendons actuate the movement of the skeleton. Accurate estimation and application of these musculotendon forces in a continuum model is not a trivial matter. Frequently, musculotendon attachments are approximated as point forces; however, accurate estimation of local mechanics requires a more realistic application of musculotendon forces. This paper describes the development of mapped Hill-type muscle models as boundary conditions for a finite volume model of the hip joint, where the calculated muscle fibres map continuously between attachment sites. The applied muscle forces are calculated using active Hill-type models, where input electromyography signals are determined from gait analysis. Realistic muscle attachment sites are determined directly from tomography images. The mapped muscle boundary conditions, implemented in a finite volume structural OpenFOAM (ESI-OpenCFD, Bracknell, UK) solver, are employed to simulate the mid-stance phase of gait using a patient-specific natural hip joint, and a comparison is performed with the standard point load muscle approach. It is concluded that physiological joint loading is not accurately represented by simplistic muscle point loading conditions; however, when contact pressures are of sole interest, simplifying assumptions with regard to muscular forces may be valid.
      551Scopus© Citations 4
  • Publication
    A Block-Coupled Finite Volume Methodology for Linear Elasticity and Unstructured Meshes
    The current article presents a new implicit cell-centred Finite Volume solution methodology for linear elasticity and unstructured meshes. Details are given of the implicit discretisation, including use of a Finite Area method for face tangential gradients and implicit non-orthogonal correction. A number of 2-D and 3-D linear-elastic benchmark test cases are examined using hexahedral, tetrahedral and general polyhedral meshes; solution accuracy and efficiency are compared with that of a segregated procedure and a commercial Finite Element software, where the new method is shown to be faster in all cases.
      698Scopus© Citations 54
  • 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
    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.
      716Scopus© Citations 16