12,833 research outputs found
Design considerations of non-axisymmetric exhausts for large civil aero-engines
In order to reduce fuel consumption, the next generation of aero-engines are expected to operate with higher bypass ratios and lower fan pressure ratios. This will improve the propulsive efficiency of the power plant and reduce specific fuel consumption. Higher bypass ratios will be mostly accommodated with larger fan diameters. However, this will increase the size and mass of the powerplant, which could penalise the overall aircraft drag and erode some of the aero-engine cycle benefits. In addition, future configurations may require more close-coupled installations with the airframe due to structural and ground clearance requirements. This tendency may further exacerbate the adverse aerodynamic installation effects. A better integration of UHBR aero-engines with the airframe could be achieved with non-axisymmetric separate-jet exhausts. Non-axisymmetric configurations of the bypass nozzle can improve the performance of the aircraft by mitigating some of the penalising aerodynamic effects induced by the installation of the power plant. In this context, three-dimensional configurations of exhaust systems are parametrised and integrated with the propulsion system through a refined control of the geometry. The power plant is installed on the NASA Common Research Model and assessed with CFD. The design of non-axisymmetric exhausts is embedded in a relatively low-cost optimisation process. The method is based on response surface models and targets the optimisation of the aircraft net vehicle force for different design concepts of non-axisymmetric exhaust systems and several installation configuration. It is concluded that the optimisation of installed non-axisymmetric exhausts can benefit the overall aircraft net vehicle force between 0.5-0.9% of the engine nominal thrust, depending on the installation position.Rolls-Royce pl
Numerical study on the structural response of a masonry arch bridge subject to flood flow and debris impact
Extreme flood flows in rivers and the floating debris they carry have the potential to generate significant impact forces on bridges spanning the watercourse. Recent flood events have highlighted the vulnerability of masonry arch bridges in flood events. This paper explores the structural response of a typical masonry arch bridge subject to flood flow and impact from flood-borne debris using a validated numerical modelling approach. The meshless method smoothed particle hydrodynamics (SPH) is used to model the fluid behaviour giving the pressure distributions on a single-span arch bridge arising from both the fluid and debris impact. Taking the pressure-time histories derived from the SPH model, the response of the bridge structure is then simulated using a nonlinear finite element (FE) model via Abaqus/Explicit. The effects of submergence ratio of bridge components: abutment, arch barrel, spandrel wall, debris orientation and flow velocity are explored. Results indicate that the debris impact resulted in greatest increase in the stresses in the bridge with a fully submerged abutment and side-on (0-degree) debris orientation. The influence of the debris impact with end-on (90-degree) orientation on the structural response was relatively low despite its higher peak pressure values. Moreover, for the type of realistic flow scenarios considered, significant local tensile stresses can be generated in the spandrel wall and arch barrel leading to structural damage
Machine learning approach towards predicting turbulent fluid flow using convolutional neural networks
Using convolutional neural networks, we present a novel method for predicting turbulent fluid flow through an array of obstacles in this thesis. In recent years, machine learning has exploded in popularity due to its ability to create accurate data driven models and the abundance of available data. In an attempt to understand the characteristics of turbulent fluid flow, we utilise a novel convolutional autoencoder neural network to predict the first ten POD modes of turbulent fluid flow. We find
that the model is able to predict the first two POD modes well although and with less accuracy for the remaining eight POD modes. In addition, we find that the
ML-predicted POD modes are accurate enough to be used to reconstruct turbulent flow that adequately captures the large-scale details of the original simulation
Meso-scale FDM material layout design strategies under manufacturability constraints and fracture conditions
In the manufacturability-driven design (MDD) perspective, manufacturability of the product or system is the most important of the design requirements. In addition to being able to ensure that complex designs (e.g., topology optimization) are manufacturable with a given process or process family, MDD also helps mechanical designers to take advantage of unique process-material effects generated during manufacturing. One of the most recognizable examples of this comes from the scanning-type family of additive manufacturing (AM) processes; the most notable and familiar member of this family is the fused deposition modeling (FDM) or fused filament fabrication (FFF) process. This process works by selectively depositing uniform, approximately isotropic beads or elements of molten thermoplastic material (typically structural engineering plastics) in a series of pre-specified traces to build each layer of the part. There are many interesting 2-D and 3-D mechanical design problems that can be explored by designing the layout of these elements. The resulting structured, hierarchical material (which is both manufacturable and customized layer-by-layer within the limits of the process and material) can be defined as a manufacturing process-driven structured material (MPDSM). This dissertation explores several practical methods for designing these element layouts for 2-D and 3-D meso-scale mechanical problems, focusing ultimately on design-for-fracture. Three different fracture conditions are explored: (1) cases where a crack must be prevented or stopped, (2) cases where the crack must be encouraged or accelerated, and (3) cases where cracks must grow in a simple pre-determined pattern. Several new design tools, including a mapping method for the FDM manufacturability constraints, three major literature reviews, the collection, organization, and analysis of several large (qualitative and quantitative) multi-scale datasets on the fracture behavior of FDM-processed materials, some new experimental equipment, and the refinement of a fast and simple g-code generator based on commercially-available software, were developed and refined to support the design of MPDSMs under fracture conditions. The refined design method and rules were experimentally validated using a series of case studies (involving both design and physical testing of the designs) at the end of the dissertation. Finally, a simple design guide for practicing engineers who are not experts in advanced solid mechanics nor process-tailored materials was developed from the results of this project.U of I OnlyAuthor's request
Evolutionary Multi-Objective Aerodynamic Design Optimization Using CFD Simulation Incorporating Deep Neural Network
An evolutionary multi-objective aerodynamic design optimization method using
the computational fluid dynamics (CFD) simulations incorporating deep neural
network (DNN) to reduce the required computational time is proposed. In this
approach, the DNN infers the flow field from the grid data of a design and the
CFD simulation starts from the inferred flow field to obtain the steady-state
flow field with a smaller number of time integration steps. To show the
effectiveness of the proposed method, a multi-objective aerodynamic airfoil
design optimization is demonstrated. The results indicate that the
computational time for design optimization is suppressed to 57.9% under 96
cores processor conditions
Effects of wind turbine rotor positioning on tornado induced loads
This study investigates the loads induced by a large-scale tornado simulation on a horizontal axis wind turbine (HAWT) to assess the influence of three-dimensional flows with respect to the HAWT position. The loads were analyzed under two rotor operational conditions, idling and parked, at five radial distances. Subsequently, experimental validation of the numerical code HIW-TUR was conducted by evaluating the induced moments for various yaw and pitch angles. The experimental results demonstrated that the bending moment was the most important in terms of magnitude and variation with respect to the HAWT position. Furthermore, The HIW-TUR code accurately identified the magnitude and HAWT configuration that leads to the maximum mean moments induced by the tornado. It was proved that by varying the yaw angle of the rotor plane and blade orientation to parallel to the tornado tangential component, the overall loads could be reduced to the minimum values
Review of Methodologies to Assess Bridge Safety During and After Floods
This report summarizes a review of technologies used to monitor bridge scour with an emphasis on techniques appropriate for testing during and immediately after design flood conditions. The goal of this study is to identify potential technologies and strategies for Illinois Department of Transportation that may be used to enhance the reliability of bridge safety monitoring during floods from local to state levels. The research team conducted a literature review of technologies that have been explored by state departments of transportation (DOTs) and national agencies as well as state-of-the-art technologies that have not been extensively employed by DOTs. This review included informational interviews with representatives from DOTs and relevant industry organizations. Recommendations include considering (1) acquisition of tethered kneeboard or surf ski-mounted single-beam sonars for rapid deployment by local agencies, (2) acquisition of remote-controlled vessels mounted with single-beam and side-scan sonars for statewide deployment, (3) development of large-scale particle image velocimetry systems using remote-controlled drones for stream velocity and direction measurement during floods, (4) physical modeling to develop Illinois-specific hydrodynamic loading coefficients for Illinois bridges during flood conditions, and (5) development of holistic risk-based bridge assessment tools that incorporate structural, geotechnical, hydraulic, and scour measurements to provide rapid feedback for bridge closure decisions.IDOT-R27-SP50Ope
Investigation of microparticle behavior in Newtonian, viscoelastic, and shear-thickening flows in straight microchannels
Sorting and separation of small substances such as cells, microorganisms, and micro- and nano-particles from a heterogeneous mixture is a common sample preparation step in many areas of biology, biotechnology, and medicine. Portability and inexpensive design of microfluidic-based sorting systems have benefited many of these biomedical applications. Accordingly, we have investigated microparticle hydrodynamics in fluids with various rheological behaviors (i.e., Newtonian, shear-thinning viscoelastic and shear-thickening non-Newtonian) flowing in straight microchannels. Numerical models were developed to simulate particles trajectories in Newtonian water and shear-thinning polyethylene oxide (PEO) solutions. The validated models were then used to perform numerical parametric studies and non-dimensional analysis on the Newtonian inertia-magnetic and shear-thinning elasto-inertal focusing regimes. Finally, the straight microfluidic device that was tested for Newtonian water and shear-thinning viscoelastic PEO solution, were adopted to experimentally study microparticle behavior in SiO2/Water shear-thickening nanofluid
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