Frequency dependent Krylov vectors for second-order damped systems

1999 ◽  
Vol 13 (11) ◽  
pp. 798-806
Author(s):  
Yoon-Gyeoung Sung ◽  
Joey K. Parker
Keyword(s):  
Second Order ◽  
Frequency Dependent ◽  
Damped Systems ◽  
Krylov Vectors

Frequency-Dependent Second-Order Hyperpolarizability of Carbon Clusters: A Semiempirical Investigation

1995 ◽  
Vol 117 (22) ◽  
pp. 6101-6108 ◽  
Author(s):  
Marianna Fanti ◽  
Giorgio Orlandi ◽  
Francesco Zerbetto
Keyword(s):  
Second Order ◽  
Carbon Clusters ◽  
Frequency Dependent

A System Identification Method for Excitation-Frequency Dependent Rotordynamic Coefficients

2012 ◽  
Author(s):  
Timothy W. Dimond ◽  
Amir A. Younan ◽  
Paul Allaire
Keyword(s):  
System Identification ◽  
Measurement Uncertainty ◽  
Excitation Frequency ◽  
Frequency Dependent ◽  
Rotordynamic Coefficients ◽  
Adjoint Systems ◽  
Dynamic Coefficients ◽  
Backward Whirl ◽  
Identification Technique ◽  
Damped Systems

Experimental identification of rotordynamic systems presents unique challenges. Gyroscopics, generally damped systems, and non-self-adjoint systems due to fluid structure interaction forces mean that symmetry cannot be used to reduce the number of parameters to be identified. Rotordynamic system experimental measurements are often noisy, which complicates comparisons with theory. When linearized, the resulting dynamic coefficients are also often a function of excitation frequency, as distinct from operating speed. In this paper, a frequency domain system identification technique is presented that addresses these issues for rigid-rotor test rigs. The method employs power spectral density functions and forward and backward whirl orbits to obtain the excitation frequency dependent effective stiffness and damping. The method is highly suited for use with experiments that employ active magnetic exciters that can perturb the rotor in the forward and backward whirl directions. Simulation examples are provided for excitation-frequency reduced tilting pad bearing dynamic coefficients. In the simulations, 20 and 50 percent Gaussian output noise was considered. Based on ensemble averages of the coefficient estimates, the 95 percent confidence intervals due to noise effects were within 1.2% of the identified value. The method is suitable for identification of linear dynamic coefficients for rotordynamic system components referenced to shaft motion. The method can be used to reduce the effect of noise on measurement uncertainty. The statistical framework can also be used to make decisions about experimental run times and acceptable levels of measurement uncertainty. The data obtained from such an experimental design can be used to verify component models and give rotordynamicists greater confidence in the design of turbomachinery.

Second‐Order Instrumentation Systems with Frequency‐Dependent Stiffness and Damping

1959 ◽  
Vol 31 (11) ◽  
pp. 1457-1462 ◽  
Author(s):  
Eric Rule ◽  
Fred J. Suellentrop ◽  
Thomas A. Perls
Keyword(s):  
Second Order ◽  
Frequency Dependent ◽  
Stiffness And Damping

Frequency-Dependent Second Harmonic Generation in Acentric Chromophoric Self-Assembled NLO Materials

1994 ◽  
Vol 351 ◽  
Author(s):  
Shlomo Yitzchaik ◽  
Paul M. Lundquist ◽  
Weiping Lin ◽  
David R. Kanis ◽  
Mark A. Ratner ◽  
...  
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Self Assembly ◽  
Second Harmonic ◽  
Second Order ◽  
Frequency Dependent ◽  
Aligned Arrays ◽  
Nlo Materials ◽  
Charge Transfer Excitation ◽  
Self Assembled

ABSTRACTAn attractive and challenging approach to the construction of robust, thin film materials with large second-order optical nonlinearities is the covalent self-assembly of aligned arrays of high-β molecular chromophores into multilayer superlattices. In this paper, we describe the dispersion of second harmonic generation (SHG) in a self-assembled (SA) monolayer containing a stilbazolium chromophore. The frequency-dependent measurements were performed on 25 Å thick monolayers on glass using a tunable (0.4–2 μm) light source based on optical parametric amplification (OPA). The SHG spectrum contains a clear two-photon resonance at hω = 1.3eV. The maximum in the second-order susceptibility coincides with a low energy chromophore-centered charge-transfer excitation at 480 nm. The experimental SHG dispersion values compare favorably with theoretical results computed using a sum-over-states (SOS) formalism. However, the measured values exhibit a somewhat broader band response than the theoretical curve, and the origin of this behavior is discussed.

scholarly journals An Algorithm for the Numerical Integration of Perturbed and Damped Second-Order ODE Systems

Mathematics ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 2028
Author(s):  
Fernando García-Alonso ◽  
José Antonio Reyes ◽  
Mónica Cortés-Molina
Keyword(s):  
Numerical Integration ◽  
Structural Dynamics ◽  
Truncation Error ◽  
First Integral ◽  
Second Order ◽  
New Method ◽  
Series Method ◽  
Initial Value ◽  
Satellite Problem ◽  
Damped Systems

A new method of numerical integration for a perturbed and damped systems of linear second-order differential equations is presented. This new method, under certain conditions, integrates, without truncation error, the IVPs (initial value problems) of the type: x″(t)+Ax′(t)+Cx(t)=εF(x(t),t), x(0)=x0, x′(0)=x0′, t∈[a,b]=I, which appear in structural dynamics, astrodynamics, and other fields of physics and engineering. In this article, a succession of real functions is constructed with values in the algebra of m×m matrices. Their properties are studied and we express the solution of the proposed IVP through a serial expansion of the same, whose coefficients are calculated by means of recurrences involving the perturbation function. This expression of the solution is used for the construction of the new numerical method. Three problems are solved by means of the new series method; we contrast the results obtained with the exact solution of the problem and with its first integral. In the first problem, a quasi-periodic orbit is integrated; in the second, a problem of structural dynamics associated with an earthquake is studied; in the third, an equatorial satellite problem when the perturbation comes from zonal harmonics J2 is solved. The good behavior of the series method is shown by comparing the results obtained against other integrators.

Static- and frequency-dependent NLO properties of dithienothiophene and thienothiophene bridges — A computational investigation

2020 ◽  
Vol 19 (05) ◽  
pp. 2050018
Author(s):  
Sagar B. Yadav ◽  
Nagaiyan Sekar
Keyword(s):  
Density Functional ◽  
Nonlinear Optical ◽  
Chemical Reactivity ◽  
Second Order ◽  
Basis Sets ◽  
Frequency Dependent ◽  
Nlo Properties ◽  
Reactivity Descriptors ◽  
Hartree Fock ◽  
Perturbation Potential

We have explored detailed linear and nonlinear optical properties of push-pull systems bearing thienothiophene and dithienothiophene spacers. By using density functional theory (DFT), frequency-dependent strategies were applied to examine the polarizability ([Formula: see text] and hyperpolarizability ([Formula: see text] and [Formula: see text]. The set of global and range-separated hybrid functionals with different Hartree–Fock (HF) exchange percentage at two basis sets cc-pVDZ and cc-pVTZ were used to evaluate the nonlinear optical (NLO) properties. The observed trends in the absorption maxima supported by perturbation potential analysis; as the absorption maxima increases, the respective amplitude potential decreases. For the investigated compounds, [Formula: see text]-conjugation along with the type of substituted acceptor plays a crucial role in the enhancement of NLO properties. The presence of acceptor group and length of conjugation increase between the D and A group; the first- and second-order intrinsic hyperpolarizability increases, leads to enhanced first- as well as second-order hyperpolarizability. Bond length alternation (BLA)/bond order alteration (BOA) exploration suggested that compounds attain cyanine limit. The trends in NLO properties for investigated compounds are supported by chemical reactivity descriptors, hardness and hyperhardness analysis. The polarizability is linearly correlated with the hyperpolarizability parameters ([Formula: see text] and [Formula: see text] and shows a good regression coefficient by figures of merit analysis.

Transfer Function Coefficients Calculation of the High Pass Frequency-Dependent Second-Order Components Using Special Phase Frequency Response Values

2021 ◽  
Vol 105 ◽  
pp. 161-166
Author(s):  
Hanna Ukhina ◽  
Ivan Afanasyev ◽  
Valerii Sytnikov ◽  
Oleg Streltsov ◽  
Pavel Stupen
Keyword(s):  
Transfer Function ◽  
Frequency Response ◽  
Digital Filter ◽  
Second Order ◽  
Robotic Systems ◽  
Frequency Dependent ◽  
Digital Frequency ◽  
Order Components ◽  
High Pass

In this work, adjustable second-order digital frequency-dependent components that are used in robotic systems are considered. The obtained approximations of the PFR dependence on the ripple level allow us to find the digital filter transfer function denominator coefficients' values that result contributes to a more rapid rearrangement of their responses in robotic systems.

Sign in / Sign up

Export Citation Format

Share Document