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Articles 1 - 11 of 11
Full-Text Articles in Mechanical Engineering
The Relationship Between Induced Fluid Structure And Boundary Slip In Nanoscale Polymer Films, Nikolai V. Priezjev
The Relationship Between Induced Fluid Structure And Boundary Slip In Nanoscale Polymer Films, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The molecular mechanism of slip at the interface between polymer melts and weakly attractive smooth surfaces is investigated using molecular dynamics simulations. In agreement with our previous studies on slip flow of shear-thinning fluids, it is shown that the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that at sufficiently high shear rates, the slip flow over atomically flat crystalline surfaces is anisotropic. It is demonstrated numerically that the friction coefficient at the liquid-solid interface (the ratio of viscosity and slip length) undergoes a transition from a …
Slip Boundary Conditions For The Moving Contact Line In Molecular Dynamics And Continuum Simulations, Nikolai V. Priezjev, Anoosheh Niavarani
Slip Boundary Conditions For The Moving Contact Line In Molecular Dynamics And Continuum Simulations, Nikolai V. Priezjev, Anoosheh Niavarani
Mechanical and Materials Engineering Faculty Publications
The problem of the moving contact line between two immiscible fluids on a smooth surface is revisited using molecular dynamics (MD) and continuum simulations. In MD simulations a finite slip is allowed by choosing incommensurate wall-fluid densities and weak wall-fluid interaction energies. The shear stresses and velocity fields are extracted carefully in the bulk fluid region as well as near the moving contact line. In agreement with previous studies, we found slowly decaying partial slip region away from the contact line. In steady-state shear flows we extract the friction coefficient along the liquid-solid interface, the local slip length, and the …
Modeling The Combined Effect Of Surface Roughness And Shear Rate On Slip Flow Of Simple Fluids, Nikolai V. Priezjev, Anoosheh Niavarani
Modeling The Combined Effect Of Surface Roughness And Shear Rate On Slip Flow Of Simple Fluids, Nikolai V. Priezjev, Anoosheh Niavarani
Mechanical and Materials Engineering Faculty Publications
Molecular dynamics (MD) and continuum simulations are carried out to investigate the influence of shear rate and surface roughness on slip flow of a Newtonian fluid. For weak wall-fluid interaction energy, the nonlinear shear-rate dependence of the intrinsic slip length in the flow over an atomically flat surface is computed by MD simulations. We describe laminar flow away from a curved boundary by means of the effective slip length defined with respect to the mean height of the surface roughness. Both the magnitude of the effective slip length and the slope of its rate-dependence are significantly reduced in the presence …
Impact Of Induced Defects On Rotor Life Assessment, Ashley Winfield Whitney-Rawls
Impact Of Induced Defects On Rotor Life Assessment, Ashley Winfield Whitney-Rawls
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There is an economic need to reduce the conservatisms of current lifing methods and extend component life. Extending component usage increases the probability of failure during operation. Therefore, the risk of continued service must be quantified before life extension concepts can successfully be implemented. The current FAA approved software for the certification of new rotor designs, only accounts for defects present prior to service. Defects due to the handling of components during inspection and material fatigue will induce defects during service and need to be included in any analysis of component life extension. Component life extension analysis of an Inconel …
Stochastic Mistuning Simulation Of Integrally Bladed Rotors Using Nominal And Non-Nominal Component Mode Synthesis Methods, Joseph A. Beck
Stochastic Mistuning Simulation Of Integrally Bladed Rotors Using Nominal And Non-Nominal Component Mode Synthesis Methods, Joseph A. Beck
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Mistuning prediction in integrally bladed rotors is often done with reduced order models that minimize computational expenses. A common model reduction technique used for mistuning applications is the component mode synthesis method. In this work, two modern component mode synthesis methods are used to generate mistuned response distributions that will be used to determine if the two methods are statistically indistinguishable. The first method, nominal mode approximation, assumes an airfoil geometric perturbation alters only the corresponding substructure modal stiffnesses while its mode shapes remain unaffected. The mistuned response is then predicted by a summation of the nominal modes. The second …
Experimental Studies Of Turbulent Boundary Layers Over A Rough Forward-Facing Step And Its Coarse Scale Resolution Approximations, Huiying Ren
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High spatial resolution PIV experiments are performed in the x-y plane at two different spanwise positions to compare the turbulent boundary layers over smooth and rough forward-facing-steps as well as the rough step's two coarse scale-resolution approximations. The Reynolds number based on the step's mean height, Reh, is 3450 and the ratio of the boundary layer thickness to the step's height is δ/h = 8. The roughness topography on the top surface of the rough step is replicated from a realistic turbine blade and is intrinsically three-dimensional and highly irregular. The surface topographies of the coarse scale-resolution …
Characterization Of Internal Wake Generator At Low Reynolds Number With A Linear Cascade Of Low Pressure Turbine Blades, Chase A. Nessler
Characterization Of Internal Wake Generator At Low Reynolds Number With A Linear Cascade Of Low Pressure Turbine Blades, Chase A. Nessler
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Unsteady flow and its effects on the boundary layer of a low pressure turbine blade is complex in nature. The flow encountered in a low pressure turbine contains unstructured free-stream turbulence, as well as structured periodic perturbations caused by upstream vane row wake shedding. Researchers have shown that these conditions strongly influence turbine blade performance and boundary layer separation, especially at low Reynolds numbers. In order to simulate these realistic engine conditions and to study the effects of periodic unsteadiness, a moving bar wake generator has been designed and characterized for use in the Air Force Research Labs low speed …
Effect Of Free-Edges On Melt Pool Geometry And Solidification Microstructure In Beam-Based Fabrication Methods, Joy Elizabeth Davis
Effect Of Free-Edges On Melt Pool Geometry And Solidification Microstructure In Beam-Based Fabrication Methods, Joy Elizabeth Davis
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Laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. Based on the Rosenthal solution for a moving point-heat source, recent work has developed simulation-based process maps for the thermal conditions controlling microstructure (grain size and morphology) in beam-based deposition of semi-infinite geometries, where a steady-state melt pool exists away from free-edges. In the current study, the Rosenthal solution is modified to include the effects of free-edges. This is accomplished by …
Risk Quantification And Reliability Based Design Optimization In Reusable Launch Vehicles, Jason Maxwell King
Risk Quantification And Reliability Based Design Optimization In Reusable Launch Vehicles, Jason Maxwell King
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Due to the inherent natural variability of parameters with reusable launch vehicles, design considerations without use of a reliability or safety index may be unreliable and vulnerable to vehicle failures. Generally in preliminary air vehicle design little information is known regarding design variable uncertainties, consequently requiring a technique that can quantify epistemic uncertainties. Evidence Theory is employed to accomplish this task resulting in a reliability bound of belief and plausibility. Due to the discontinuous nature of the belief and plausibility function it is necessary to implement a continuous function known as plausibility decision to be used to calculate sensitivities that …
Aircraft Gearbox Dynamics Subject To Electromechanical Actuator Regenerative Energy Flow, Matthew S. Rutledge
Aircraft Gearbox Dynamics Subject To Electromechanical Actuator Regenerative Energy Flow, Matthew S. Rutledge
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To increase reliability and efficiency, standard aircraft components are being replaced with more electric subsystems aimed to reduce weight, conserve space, and improve energy management. One application of this process replaces standard hydraulic actuators used in flap or aileron movements with electromechanical actuators powered by an external generator. During different types of return movements, the electromechanical actuator will produce regenerative power that flows back through the generator and pulses into the engine-gearbox subsystem. The regenerative power, defined by characteristic amplitude, frequency, and other pulse attributes, coupled with the driving force produced by the engine may dramatically impact the performance and …
Computational Study Of Direct Fuel Injection In The Rotax 914 Engine, Brad Pollock
Computational Study Of Direct Fuel Injection In The Rotax 914 Engine, Brad Pollock
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Direct injection spark ignition (DISI) is a fuel delivery method in which the fuel is introduced directly into the combustion chamber of an internal combustion engine. Although direct fuel injection was first pioneered in the early 1920's, it has only recently become a reliable option due to advances made in control systems and injection technology. Direct injection enables increased fuel efficiency and higher power output than a conventional Port Fuel Injection (PFI) system. By delivering pressurized fuel directly into the cylinder, the degree of fuel atomization and the fuel vaporization rate are increased. Hence, the air/fuel mixture can be more …