Pulsation theory.
Pulsation in cepheid instability strip in H-R DIAGRAM, giving equations for spherically symmetric motion
BINARY STAR↗
SEARCH · Engineering Papers
Results for “strip theory”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Stability of flow over axisymmetric bodies with porous suction strips
Linear triple deck, closed form solutions for mean-flow quantities are developed for axisymmetric incompressible flow past a body with porous strips. The solutions account for upstream influence and are linear superpositions of the flow past the body without suction plus the perturbations due to the suction strips. Flow past the suctionless body is calculated using the Transition Analysis Program System, and a simple linear optimization scheme to determine number, spacing, and mass flow rate through the strips on an axisymmetric body is developed using the linear, triple-deck, closed-form solutions. The theory is demonstrated by predicting optimal strip distributions, and the effect of various adverse pressure-gradient situations on stability is studied.
Nayfeh, A. H.↗
Autonomous Eco-Driving with Traffic Light and Lead Vehicle Constraints: An Application of Best Constrained Interpolation
Eco-Driving is a critical technology for improving automotive transportation efficiency. It is achieved by modifying the driving trajectory over a particular route to minimize required propulsion energy. Eco-Driving can be approached as an optimal control problem subject to driving constraints such as traffic lights and positions of other vehicles. Best interpolation in a strip is a problem in approximation theory and optimal control. The solution to this problem is a cubic spline. In this research, we demonstrate the connection between Eco-Driving and best interpolation in the strip. By exploiting this connection, we are able to generate optimal Eco-Driving trajectories that could be driven with an autonomous system. Using the simulation tool FASTSim, we can evaluate the trajectories using conventional, hybrid electric, and fully electric vehicle models. Our results quantify the energy efficiency improvements that can be achieved with the proposed approach.
Mahmoud, Yara Hazem↗
Autonomous Eco-Driving with Traffic Light and Lead Vehicle Constraints: An Application of Best Constrained Interpolation
Eco-Driving is a critical technology for improving automotive transportation efficiency. It is achieved by modifying the driving trajectory over a particular route to minimize required propulsion energy. Eco-Driving can be approached as an optimal control problem subject to driving constraints such as traffic lights and positions of other vehicles. Best interpolation in a strip is a problem in approximation theory and optimal control. The solution to this problem is a cubic spline. In this research, we demonstrate the connection between Eco-Driving and best interpolation in the strip. By exploiting this connection, we are able to generate optimal Eco-Driving trajectories that could be driven with an autonomous system. Using the simulation tool FASTSim, we can evaluate the trajectories using conventional, hybrid electric, and fully electric vehicle models. Our results quantify the energy efficiency improvements that can be achieved with the proposed approach.
Mahmoud, Yara Hazem↗
Transverse impact by RCCs on S-glass and Kevlar® FRC strips
This study aims to isolate interactions between plies and tows and reveal fundamental physics involved in transverse impact on fiber-reinforced composite (FRC) structures. Composite strips were sectioned from large panels and characterized by optical photography, three-dimensional synchrotron X-ray computed tomography, and scanning electron microscopy (SEM). Each strip was impacted perpendicularly by a right circular cylinder (RCC) projectile at a velocity ranging from ~ 150 to 600 m/s. The global strip behavior, as well as localized deformation and failure of the strip near the projectile corner, were both captured by high-speed optical imaging. S-Glass FRC strips were observed to fail in tension ahead of the RCC projectiles’ flat surfaces while Kevlar® FRC strips fractured at the projectile corners. The concept of critical velocity region previously used for impact on yarns was introduced to define different failure modes of each composite strip type. The strip damage extent was found to increase with the impact velocity and reach the maximum at the upper limit of the critical velocity region. Above the critical velocity region, the damage extent decreased with impact velocity. Wave propagations and load histories in the composite strips during impact were quantified and compared with Smith’s theory. Finally, critical velocities of single fibers, yarns, and composite strips and ballistic limits of single-ply and multi-ply composite panels were compared to provide insight into the design of impact-resistant fabrics and composites.
42 ENGINEERING↗
Reactivity of Sulfur Vacancy-Rich MoS 2 to Water Dissociation
Exposed Mo atoms on the surface of MoS 2 can catalyze certain useful chemical reactions, including the dissociation of water to produce hydrogen. However, a comprehensive understanding of water reactivity on defective MoS 2 surfaces remains elusive. Here, we use in situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to investigate water dissociation reactions on MoS 2 surfaces before and after Ar + ion beam bombardment. To make the surfaces reactive, we treated them with Ar + ion beam sputtering first, which created exposed Mo sites. Using ultraviolet photoelectron spectroscopy (UPS) and density of states calculations conducted using density functional theory (DFT), we verified that stripping the surface of sulfur atoms creates metallic surface states that can catalyze water dissociation. At elevated H 2 O pressures, XPS measurements combined with DFT calculations suggested the presence of four distinct surface species from dissociated water. Specifically, we found that oxides and hydroxides are prominent at the surface, while chemisorbed and physisorbed H 2 O molecules are also present. In conclusion, this study provides new insights that reveal the prospects of surface-engineered MoS 2 as a catalyst for water dissociation.
08 HYDROGEN↗
Application of critical COD and plastic instability concepts to fracture of shells
The paper deals with the initiation, growth, and possible arrest of fracture in shell structures containing initial defects which may be approximated by an isolated part-through crack. The main study is restricted to the structures in which the net section of the shell wall around the defect zone is fully yielded. The problem is solved by using an 8th order shallow shell theory with a conventional plastic strip model to account for the plastic deformations. Using the critical COD or the plastic instability as fracture criterion, the results are applied to the fracture propagation and arrest in shells. The calculated results are then compared with those obtained from the experiments on zircaloy, aluminum, and steel pipes.
Erdogan, F.↗
Preferential enhancements of the solar flare-accelerated nuclei carbon to zinc from about 20-300 MeV/nucleon
IMP 8 satellite measurements with a charged-particle telescope are examined which show that three large solar flares in late 1977 displayed preferential enhancements of abundances from C through Fe at energies of about 20 to 400 MeV/nucleon. It is found that the differential energy spectra of C, O, Mg, Si, and Fe, as well as protons and helium, are best fitted by power laws in energy per nucleon or rigidity with an index of 2.3 + or - 0.2, that the spectra of most of the even-Z nuclei have essentially the same slope, and that all the enhancements were independent of energy in the range from 20 to 300 MeV/nucleon. A plot of enhancement factor vs. Z is presented which clearly demonstrates the preferential enhancement of abundances with increasing Z in one of the solar flares, where the nuclei reached such high energies that they must have escaped the corona fully stripped of electrons. Implications for theories of solar-flare acceleration of the nuclei are considered.
Dietrich, W. F.↗
A UGO/EUTD Solution for the Scattering and Diffraction from Cubic Polynomial Strips
A uniform geometrical optics (UGO) and an extended uniform geometrical theory of diffraction (EUTD) solution is developed for the scattering and diffraction from perfectly conducting cubic polynomial strips. The new solution overcomes the difficulties of the classic GO/UTD solution near caustics and composite shadow boundaries. The approach for constructing the UGO/EUTD solution is based on a spatial domain physical optics (PO) radiation integral representation for the scattered field which is then reduced using a uniform asymptotic procedure. New uniform reflection, zero-curvature diffraction, and edge diffraction coefficients are derived and involve the ordinary and incomplete Airy integrals as canonical functions. Higher order effects such as double edge diffraction, edge-excited creeping waves, and whispering gallery modes are not examined in this work. The UGO/EUTD solution is very efficient and provides useful physical insight into the various scattering and diffraction processes. It is also universal in nature and can be used to effectively describe the scattered fields from flat, strictly concave or convex, and concave-convex boundaries containing edges. Its accuracy is confirmed via comparison with some reference moment method (MM) results.
Constantinides, Evagoras D.↗
Combined density functional theory/kinetic Monte Carlo investigation of surface morphology during cycling of Li-Cu electrodes
In this work, we employed a combined density functional theory and kinetic Monte Carlo approach in order to investigate the nanoscale behavior of lithium stripping and plating on lithium-copper nanoalloys. Density functional theory calculations were used to develop an atom-by-atom understanding of the nucleation behavior of lithium on copper surfaces with different surface morphologies. We found that nanometric pits resulted in significantly more favorable lithium deposition when compared to pristine or lightly-defective Cu surfaces, which is in agreement with previous experimental studies. We then used density functional theory and constrained ab initio molecular dynamics to develop interaction and reaction parameters for a larger-scale kinetic Monte Carlo model in order to provide insight into the stripping and plating behavior of nanostructured Li-Cu nanoalloy anodes. Substantial losses in capacity and strong indications of morphological change were observed for a wide range of Cu:Li ratios over 100 cycles. We observed a complex relationship between the nanoparticle composition and the properties of the formed solid-electrolyte interphase.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Subsonic and Supersonic Flutter Analysis of a Highly Tapered Swept-Wing Planform, Including Effects of Density Variation and Finite Wing Thickness, and Comparison with Experiments
The flutter characteristics of several wings with an aspect-ratio of 4.0, a taper ratio of 0.2, and a quarter-chord sweepback of 45 deg. have been investigated analytically for Mach numbers up to 2.0. The calculations were based on the modified-strip-analysis method, the subsonic-kernel-function method, piston theory, and quasi-steady second-order theory. Results of t h e analysis and comparisons with experiment indicated that: (1) Flutter speeds were accurately predicted by the modified strip analysis, although accuracy at t h e highest Mach numbers required the use of nonlinear aerodynamic theory (which accounts for effects of wing thickness) for the calculation of the aerodynamic parameters. (2) An abrupt increase of flutter-speed coefficient with increasing Mach number, observed experimentally in the transonic range, was also indicated by the modified strip analysis. (3) In the low supersonic range for some densities, a discontinuous variation of flutter frequency with Mach number was indicated by the modified strip analysis. An abrupt change of frequency appeared experimentally in the transonic range. (4) Differences in flutter-speed-coefficient levels obtained from tests at low supersonic Mach numbers in two wind tunnels were also predicted by the modified strip analysis and were shown to be caused primarily by differences in mass ratio. (5) Flutter speeds calculated by the subsonic-kernel-function method were in good agreement with experiment and with the results of the modified strip analysis. (6) Flutter speed obtained from piston theory and from quasi-steady second-order theory were higher than experimental values by at least 38 percent.
Yates, Carson, Jr.↗
Improved finite strip Mindlin plate bending element using assumed shear strain distributions
A linear finite strip plate element based on Mindlin/Reissner plate theory is developed. The analysis is suitable for both thin and thick plates. In the formulation new transverse shear strains are introduced and assumed constant in each two-code linear strip. The element stiffness matrix is explicitly formulated for efficient computation and computer implementation. Numerical results showing the efficiency and predictive capability of the element for the analysis of plates are presented for different support and loading conditions and a wide range of thicknesses. No sign of shear locking phenomenon was observed with the newly developed element.
Chulya, Abhisak↗
A Geometrical Approach to Bell's Theorem
Bell's theorem can be proved through simple geometrical reasoning, without the need for the Psi function, probability distributions, or calculus. The proof is based on N. David Mermin's explication of the Einstein-Podolsky-Rosen-Bohm experiment, which involves Stern-Gerlach detectors which flash red or green lights when detecting spin-up or spin-down. The statistics of local hidden variable theories for this experiment can be arranged in colored strips from which simple inequalities can be deduced. These inequalities lead to a demonstration of Bell's theorem. Moreover, all local hidden variable theories can be graphed in such a way as to enclose their statistics in a pyramid, with the quantum-mechanical result lying a finite distance beneath the base of the pyramid.
Rubincam, David Parry↗
Interactive buckling of thin-walled structural components under static and dynamic loads
Recent advances in the study of interactive buckling of thin walled structural components achieved with the aid of finite strip technique used in conjunction with the theory of mode interaction are summarized. The interaction of the primary local mode with Euler buckling (in columns) and flexural torsional buckling (in columns and beams) is of primary interest. The interaction of two companion local modes with the overall mode is also considered briefly for the columns with doubly symmetric cross sections. The effect of dynamic loads in the form of suddenly applied and compression is also investigated.
Sridharan, S.↗
Coupled transient response of tiles bonded elastically to a finite flexible plate
Presented are several methods to study a system of tiles bonded elastically to a finite flexible plate responding to an impulse. First, a one-dimensional (1-D) approximation to the system is constructed using Timoshenko beam theory and transfer matrices. This simulates a strip one tile wide. Modal analysis determines the transient response to an impulse of short duration. Also presented are parametric studies of the effect of bond stiffness and the effect of stiffening from inplane stresses produced by large out-of-plane deflections. A two-dimensional (2-D) model is constructed from the eigenfunctions of the 1-D model in a Galerkin method using pairwise products of the 1-D modes as trial functions. Comparison of the two models establishes a factor applied to peak impulse pressure for results to agree.
El-Raheb, M.↗
Adaptive control of Space Station during nominal operations with CMGs
An adaptive control approach is investigated for the Space Station. The main components of the adaptive controller are the parameter identification scheme, the control gain calculation, and the control law. The control law is the Space Station baseline control law. The control gain calculation is based on linear quadratic regulator theory with eigenvalue placement in a vertical strip. The parameter identification scheme is a real-time recursive extended Kalman filter which estimates the inertias and also provides an estimate of the unmodeled disturbances due to the aerodynamic torques and to the nonlinear effects. An analysis of the inertia estimation problem suggests that it is possible to compute accurate estimates of the Space Station inertias during nominal CMG (control moment gyro) operations. The closed-loop adaptive control law is shown to be capable of stabilizing the Space Station after large inertia changes. Results are presented for the pitch axis.
Bishop, R. H.↗
Adaptive control of Space Station with control moment gyros
An adaptive approach to Space Station attitude control is investigated. The main components of the controller are the parameter identification scheme, the control gain calculation, and the control law. The control law is a full-state feedback space station baseline control law. The control gain calculation is based on linear-quadratic regulator theory with eigenvalues placement in a vertical strip. The parameter identification scheme is a recursive extended Kalman filter that estimates the inertias and also provides an estimate of the unmodeled disturbances due to the aerodynamic torques and to the nonlinear effects. An analysis of the inertia estimation problem suggests that it is possible to estimate Space Station inertias accurately during nominal control moment gyro operations. The closed-loop adaptive control law is shown to be capable of stabilizing the Space Station after large inertia changes. Results are presented for the pitch axis.
Bishop, Robert H.↗
Prediction of transonic flutter for a supercritical wing by modified strip analysis and comparison with experiment
Use of a supercritical airfoil can adversely affect wing flutter speeds in the transonic range. As adequate theories for three dimensional unsteady transonic flow are not yet available, the modified strip analysis was used to predict the transonic flutter boundary for the supercritical wing. The steady state spanwise distributions of section lift curve slope and aerodynamic center, required as input for the flutter calculations, were obtained from pressure distributions. The calculated flutter boundary is in agreement with experiment in the subsonic range. In the transonic range, a transonic bucket is calculated which closely resembles the experimental one with regard to both shape and depth, but it occurs at about 0.04 Mach number lower than the experimental one.
Yates, E. C., Jr.↗