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Articles 1  16 of 16
FullText Articles in Mechanical Engineering
Development Of The Compact Jet Engine Simulator From Concept To Useful Test Rig, Henry H. Haskin
Development Of The Compact Jet Engine Simulator From Concept To Useful Test Rig, Henry H. Haskin
Mechanical & Aerospace Engineering Theses & Dissertations
NASA had a goal to develop a set of modeling tools for designing next generation civil transport aircraft with reduced noise, emissions and increased fuel efficiency by 2016. To verify the models, a database of aerodynamic and acoustic data was needed for an unconventional flying wing design that was predicted to meet the goals. A Compact Jet Engine Simulator (CJES) was needed as the jet source for the 5.8% scale model. UltraCompact Combustor Technology from the Air Force Research Laboratory was used to reduce the conventional burner acoustic test rigs down to the required scale size. The Air Force ...
On A Time Domain Boundary Integral Equation Formulation For Acoustic Scattering By Rigid Bodies In Uniform Mean Flow, Fang Q. Hu, Michelle E. Pizzo, Douglas M. Nark
On A Time Domain Boundary Integral Equation Formulation For Acoustic Scattering By Rigid Bodies In Uniform Mean Flow, Fang Q. Hu, Michelle E. Pizzo, Douglas M. Nark
Mathematics & Statistics Faculty Publications
It has been wellknown that under the assumption of a uniform mean flow, the acoustic wave propagation equation can be formulated as a boundary integral equation. However, the constant mean flow assumption, while convenient for formulating the integral equation, does not satisfy the solid wall boundary condition wherever the body surface is not aligned with the assumed uniform flow. A customary boundary condition for rigid surfaces is that the normal acoustic velocity be zero. In this paper, a careful study of the acoustic energy conservation equation is presented that shows such a boundary condition would in fact lead to source ...
Development Of The Compact Jet Engine Simulator From Concept To Useful Test Rig, Henry H. Haskin
Development Of The Compact Jet Engine Simulator From Concept To Useful Test Rig, Henry H. Haskin
Mechanical & Aerospace Engineering Theses & Dissertations
Two Compact Jet Engine Simulator (CJES) units were designed for integrated wind tunnel acoustic experiments involving a Hybrid Wing Body (HWB) vehicle. To meet the 5.8% scale of the HWB model, Ultra Compact Combustor technology from the Air Force Research Laboratory was used. The CJES units were built and integrated with a control system in the NASA Langley Low Speed Aero acoustic Wind Tunnel. The combustor liners, plugâ€”vane and flow conditioner components were built inhouse at Langley Research Center. The operation of the CJES units was mapped and fixes found for combustor instability tones and rig flow noise ...
Perfectly Matched Layer Absorbing Boundary Conditions For The Discrete Velocity BoltzmannBgk Equation, Elena Craig
Perfectly Matched Layer Absorbing Boundary Conditions For The Discrete Velocity BoltzmannBgk Equation, Elena Craig
Mathematics & Statistics Theses & Dissertations
Perfectly Matched Layer (PML) absorbing boundary conditions were first proposed by Berenger in 1994 for the Maxwell's equations of electromagnetics. Since Hu first applied the method to Euler's equations in 1996, progress made in the application of PML to Computational Aeroacoustics (CAA) includes linearized Euler equations with nonuniform mean flow, nonlinear Euler equations, flows with an arbitrary mean flow direction, and nonlinear clavierStokes equations. Although BoltzmannBGK methods have appeared in the literature and have been shown capable of simulating aeroacoustics phenomena, very little has been done to develop absorbing boundary conditions for these methods. The purpose of this ...
ParallelSparse Symmetrical/Unsymmetrical Finite Element Domain Decomposition Solver With MultiPoint Constraints For Structural/Acoustic Analysis, Siroj Tungkahotara, Willie R. Watson, Duc T. Nguyen, Subramaniam D. Rajan
ParallelSparse Symmetrical/Unsymmetrical Finite Element Domain Decomposition Solver With MultiPoint Constraints For Structural/Acoustic Analysis, Siroj Tungkahotara, Willie R. Watson, Duc T. Nguyen, Subramaniam D. Rajan
Civil & Environmental Engineering Faculty Publications
Details of parallelsparse Domain Decomposition (DD) with multipoint constraints (MPC) formulation are explained. Major computational components of the DD formulation are identified. Critical roles of parallel (direct) sparse and iterative solvers with MPC are discussed within the framework of DD formulation. Both symmetrical and unsymmetrical system of simultaneous linear equations (SLE) can be handled by the developed DD formulation. For symmetrical SLE, option for imposing MPC equations is also provided.
Largescale (up to 25 million unknowns involving complex numbers) structural and acoustic Finite Element (FE) analysis are used to evaluate the parallel computational performance of the proposed DD implementation using ...
Computation Of Shock Induced Noise In Imperfectly Expanded Supersonic Jets, Bulent Imamoglu
Computation Of Shock Induced Noise In Imperfectly Expanded Supersonic Jets, Bulent Imamoglu
Mechanical & Aerospace Engineering Theses & Dissertations
Screech noise exists only in imperfectly expanded jets. The exit pressure of imperfectly expanded jets does not match ambient pressure, so expansion or compression waves appear out of the nozzle and generate shock cell patterns. Screech is generated by the interaction of shock cells and instability waves. Many experiments and computations have been done to model screech noise, but it is not yet a very well known subject.
A numerical study is performed to understand screech generation mechanisms and to compare with latest experiments. A supersonic underexpanded jet of 25.4 mm diameter is modeled for cases of Mach numbers ...
Nonlinear Response And Fatigue Estimation Of Aerospace Curved Surface Panels To Acoustic And Thermal Loads, Adam Przekop
Nonlinear Response And Fatigue Estimation Of Aerospace Curved Surface Panels To Acoustic And Thermal Loads, Adam Przekop
Mechanical & Aerospace Engineering Theses & Dissertations
This work presents a finite element modal formulation for large amplitude free vibration of arbitrary laminated composite shallow shells. The system equations of motion are formulated first in the physical structuralnode degrees of freedom (DOF). Then, the system is transformed into general Duffingtype modal equations with modal amplitudes of coupled linear bendinginplane modes. The linear bendinginplane coupling is due to the shell curvature as well as unsymmetric lamination stacking. Multiple modes, inplane inertia, and the firstorder transverse shear deformation for composites are considered in the formulation. A triangular shallow shell finite element is developed from an extension of the triangular ...
Pulsed Optoacoustics In Solids, Zibiao Wei
Pulsed Optoacoustics In Solids, Zibiao Wei
Electrical & Computer Engineering Theses & Disssertations
Optoacoustic techniques are widely used to probe and characterize target materials including solids, liquids and gases. Included in such applications are diagnoses of thin films and semiconductor materials. The need to obtain greater spatial resolution requires the generation of shorter optoacoustic pulses. For such pulses, nonthermal effects may be quite important. On the other hand, even when an optoacoustic pulse is generated by an initially nonthermal technique, the thermal aspects become important in its evolution and propagation. The research undertaken in this Ph.D. dissertation included the generation and detection of optoacoustic signals through the thermal elastic mechanism. Several applications ...
Piezoceramic Actuator Placement For Acoustic Control Of Panels, Jeffrey S. Bevan
Piezoceramic Actuator Placement For Acoustic Control Of Panels, Jeffrey S. Bevan
Mechanical & Aerospace Engineering Theses & Dissertations
Optimum placement of multiple traditional piezoceramic actuators is determined for active structural acoustic control of flat panels. The structural acoustic response is determined using acoustic radiation filters and structural surface vibration characteristics. Linear Quadratic Regulator (LQR) control is utilized to determine the optimum state feedback gain for active structural acoustic control. The optimum actuator location is determined by minimizing the structural acoustic radiated noise using a modified genetic algorithm. Experimental tests are conducted and compared to analytical results.
Anisotropic piezoceramic actuators exhibit enhanced performance when compared to traditional isotropic piezoceramic actuators. As a result of the inherent isotropy, these advanced ...
Computational Modeling Of Airborne Noise Demonstrated Via Benchmarks, Supersonic Jet, And Railway Barrier, Moumen Idres
Computational Modeling Of Airborne Noise Demonstrated Via Benchmarks, Supersonic Jet, And Railway Barrier, Moumen Idres
Mechanical & Aerospace Engineering Theses & Dissertations
In the last several years, there has been a growing demand for mobility to cope with the increasing population. All kinds of transportation have responded to this demand by expanding their networks and introducing new ideas. Rail transportation introduced the idea of highspeed trains and air transportation introduced the idea of highspeed civil transport (HSCT). In this expanding world, the noise legislation is felt to inhibit these plans. Accurate computational methods for noise prediction are in great demand.
In the current research, two computational methods are developed to predict noise propagation in air. The first method is based on the ...
Continuous Adjoint Sensitivity Analysis For Aerodynamic And Acoustic Optimization, Kaveh Ghayour
Continuous Adjoint Sensitivity Analysis For Aerodynamic And Acoustic Optimization, Kaveh Ghayour
Mechanical & Aerospace Engineering Theses & Dissertations
A gradientbased shape optimization methodology based on continuous adjoint sensitivities has been developed for twodimensional steady Euler equations on unstructured meshes and the unsteady transonic small disturbance equation. The continuous adjoint sensitivities of the Helmholtz equation for acoustic applications have also been derived and discussed.
The highlights of the developments for the steady twodimensional Euler equations are the generalization of the airfoil surface boundary condition of the adjoint system to allow a proper closure of the Lagrangian functional associated with a general cost functional and the results for an inverse problem with density as the prescribed target. Furthermore, it has ...
The Solution Of Hypersingular Integral Equations With Applications In Acoustics And Fracture Mechanics, Richard S. St. John
The Solution Of Hypersingular Integral Equations With Applications In Acoustics And Fracture Mechanics, Richard S. St. John
Mathematics & Statistics Theses & Dissertations
The numerical solution of two classes of hypersingular integral equations is addressed. Both classes are integral equations of the first kind, and are hypersingular due to a kernel containing a Hadamard singularity. The convergence of a Galerkin method and a collocation method is discussed and computationally efficient algorithms are developed for each class of hypersingular integral equation.
Interest in these classes of hypersingular integral equations is due to their occurrence in many physical applications. In particular, investigations into the scattering of acoustic waves by moving objects and the study of dynamic Griffith crack problems has necessitated a computationally efficient technique ...
HighOrder FiniteDifference Schemes And Their Application To Computational Acoustics, Joe Leo Manthey
HighOrder FiniteDifference Schemes And Their Application To Computational Acoustics, Joe Leo Manthey
Mathematics & Statistics Theses & Dissertations
The primary focus of this study is upon the numerical stability of highorder finitedifference schemes and their application to duct acoustics. Since acoustic waves are known to be nondissipative and nondispersive, highorder schemes are favored for their low dissipation and low dispersion relative to the loworder schemes. The primary obstacle to the the development of explicit highorder finitedifference schemes is the construction of boundary closures which simultaneously maintain the formal order of accuracy and the numerical stability of the overall scheme. In this thesis a hybrid sevenpoint, fourthorder stencil for computing spatial derivatives is presented and the time stability is ...
The Modeling Of StructuralAcoustic Interaction Using Coupled Fe/Be Method And Control Of Interior Acoustic Pressure Using Piezoelectric Actuators, Yucheng Shi
Mechanical & Aerospace Engineering Theses & Dissertations
A coupled finite element (FE) and boundary element (BE) approach is presented to model full coupled structural/acoustic/piezoelectric systems. The dual reciprocity boundary element method is used so that the natural frequencies and mode shapes of the coupled system can be obtained, and to extend this approach to time dependent problems. The boundary element method is applied to interior acoustic domains, and the results are very accurate when compared with limited exact solutions. Structuralacoustic problems are then analyzed with the coupled finite element/boundary element method, where the finite element method models the structural domain and the boundary element ...
Analysis Of Random StructureAcoustic Interaction Problems Using Coupled Boundary Element And Finite Element Methods, Carl S. Pates Iii
Analysis Of Random StructureAcoustic Interaction Problems Using Coupled Boundary Element And Finite Element Methods, Carl S. Pates Iii
Mechanical & Aerospace Engineering Theses & Dissertations
A coupled boundary element(BEM)finite element(FEM) approach is presented to accurately model structureacoustic interaction systems. The boundary element method is first applied to interior, two and threedimensional acoustic domains with complex geometry configurations. Boundary element results are very accurate when compared with limited exact solutions.
Structureinteraction problems are then analyzed with the coupled FEMBEM method, where the finite element method models the structure and the boundary element method models the interior acoustic domain. The coupled analysis is compared with exact and experimental results for a simplistic model. Composite panels are analyzed and compared with isotropic results. The coupled ...
Finite Element Model Of A Timoshenko Beam With Structural Damping, Louis Ablen Roussos
Finite Element Model Of A Timoshenko Beam With Structural Damping, Louis Ablen Roussos
Mechanical & Aerospace Engineering Theses & Dissertations
A numerical integration technique, a modified version of the Newmark method, is applied to transient motion problems of systems with mass, stiffness, and small nonlinear damping. The nonlinearity is cast as a pseudoforce to avoid repeated recalculation and decomposition of the effective stiffness matrix; thus, the solution technique is dubbed the "pseudoforce Newmark method." Comparisons with exact and perturbation solutions in singledegreeoffreedom problems and with a Gearmethod numerical solution in a cantilevered Timoshenko beam finite element problem show the solution technique to be efficient, accurate, and, thus, feasible provided the nonlinear damping is small. As a preliminary step into the ...