Comparing the time-eigenvalues of the natural mode equation by weight balancing and α-k methods

2021 ◽  
Vol 162 ◽  
pp. 108486
Author(s):  
Yasushi Nauchi ◽  
Alexis Jinaphanh ◽  
Andrea Zoia
Keyword(s):  
Natural Mode

Experimental Investigation of Vortex-Induced Vibrations on Yawed and Inclined Flexible Cylinders

2021 ◽  
pp. 1-16
Author(s):  
Daniel P. Vieira ◽  
Guilherme R. Franzini ◽  
Fredi Cenci ◽  
Andre Fujarra
Keyword(s):  
A Priori ◽  
Flexible Structures ◽  
Resonance Region ◽  
Offshore Structures ◽  
Natural Mode ◽  
Flexible Cylinder ◽  
Decomposition Scheme ◽  
Independence Principle ◽  
Modal Amplitude ◽  
Time Histories

Abstract An experimental setup was built to investigate the Vortex-Induced Vibration (VIV) phenomenon on yawed and inclined flexible cylinders, in which five yaw angles θ = 0°, 10°, 20°, 30° and 45° and five azimuth angles ß = 0°, 45°, 90°, 135°, and 180° were combined. The experiments were carried out in a towing tank facility at Reynolds numbers from 1800 to 18000, comprising vibrations up to the eighth natural mode. Time histories of displacements were recorded using a submerged optical system that tracks 17 reflective targets. A modal decomposition scheme based on Galerkin's method was applied, aiming multimodal behavior investigations. Such an approach allowed the analysis of the modal amplitude throughout time, revealing interesting results for such a class of VIV tests. The flexible cylinder total response is generally a combination of two or more modes. Only for azimuths 0°, 90°, and 180°, a unimodal response was observed for the two first lock-in regimes. The frequency response showed that, when the response was multimodal, non-dominant modes can follow the vibration frequency of the dominant one. Assuming a priori the Independence Principle (IP) valid to define the reduced velocities (Vr), it was observed that the resonance region was restricted to 3 <= Vr <= 8 for the tested cases, indicating that the IP can be at least partially applied for flexible structures. As the literature scarcely explores the simultaneous yawed and inclined configurations, the present work may contribute to further code validation and improvements regarding the design of slender offshore structures.

Approximate Formulas for Cylindrical Shell Free Vibration Based on Vlasov’s and Enhanced Vlasov’s Semi-Momentless Theory

2018 ◽  
Author(s):  
Igor Orynyak ◽  
Yaroslav Dubyk
Keyword(s):  
Cylindrical Shell ◽  
Boundary Conditions ◽  
Circular Cylindrical Shell ◽  
Equations Of Motion ◽  
Middle Surface ◽  
Axial Direction ◽  
Mode Shapes ◽  
Natural Mode ◽  
Transverse Deflection ◽  
Approximate Formulas

Simple approximate formulas for the natural frequencies of circular cylindrical shells are presented for modes in which transverse deflection dominates. Based on the Donnell-Mushtari thin shell theory the equations of motion of the circular cylindrical shell are introduced, using Vlasov assumptions and Fourier series for the circumferential direction, an exact solution in the axial direction is obtained. To improve the results assumptions of Vlasov’s semimomentless theory are enhanced, i.e. we have used only the hypothesis of middle surface inextensibility to obtain a solution in axial direction. Nonlinear characteristic equations and natural mode shapes, are derived for all type of boundary conditions. Good agreement with experimental data and FEM is shown and advantage over the existing formulas for a variety of boundary conditions is presented.

scholarly journals AN EFFICIENT METHOD FOR HAND GESTURE RECOGNITION USING ROBUST FEATURES VECTOR

2021 ◽  
Vol 6 (22) ◽  
pp. 25-35
Author(s):  
A F M Saifuddin Saif ◽  
Zainal Rasyid Mahayuddin
Keyword(s):  
Gesture Recognition ◽  
Efficient Method ◽  
Industrial Revolution ◽  
Hessian Matrix ◽  
Vital Role ◽  
Hand Gesture Recognition ◽  
Hand Gesture ◽  
Natural Mode ◽  
Interest Points ◽  
Human Machine Interaction

Integration of technology for the Fourth Industrial Revolution (IR 4.0) has increased the need for efficient methods for developing dynamic human computer interfaces and virtual environments. In this context, hand gesture recognition can play a vital role to serve as a natural mode of interactive human machine interaction. Unfixed brightness, complex backgrounds, color constraints, dependency on hand shape, rotation, and scale variance are the challenging issues which have an impact on robust performance for the existing methods as per outlined in previous researches. This research presents an efficient method for hand gesture recognition by constructing a robust features vector. The proposed method is performed in two phases, where in the first phase the features vector is constructed by selecting interest points at distinctive locations using a blob detector based on Hessian matrix approximation. After detecting the area of the hand from the features vector, edge detection is applied in the isolated hand followed by edge orientation computation. After this, templates are generated using one and two dimensional mapping to compare candidate and prototype images using adaptive threshold. The proposed research performed extensive experimentation, where a recognition accuracy rate of 98.33% was achieved by it, which is higher as compared to previous research results. Experimental results reveal the effectiveness of the proposed methodology in real time.

The Lyric Mode

2021 ◽  
pp. 545-562
Author(s):  
Francesca Southerden
Keyword(s):  
Natural Mode ◽  
Lyric Poet ◽  
Love Lyric

Dante is before all other things a lyric poet and this chapter explores his commitment to lyric from his earliest compositions to the Commedia. For Dante, lyric is the natural mode for expressing desire and is particularly marked by pleasure. Indeed ‘modo’ is the word he uses in both Vita Nova and Commedia to represent the indissoluble bond between love and speech that animates the desiring subject and leads to the production of poetry. This chapter traces the significance of this word in the Occitan and early Italian love lyric, especially in its associations with measure (misura) and desire’s tendency to transgress it. It considers how the lyric mode is employed to convey the intensity of the love experience and the porous nature of the desiring body, especially in Dante’s relationship to Beatrice and as expressed in flexible and expansive forms of textuality that resist closure.

Quantifying the Impact of Medicalisation on the Distribution of Births over the Course of the Day

2020 ◽  
Vol 1 (1-2) ◽  
pp. 68-85
Author(s):  
Stuart Gietel-Basten
Keyword(s):  
Early Morning ◽  
Seasonal Effect ◽  
Natural Mode ◽  
Natural Setting ◽  
Female Autonomy ◽  
Human Births ◽  
The Times ◽  
The Impact ◽  
The Relationship ◽  
Negative Health Outcomes

Abstract Very few historical studies have been able to demonstrate the times of day when humans give birth in a ‘natural’ setting—i.e. outside of any hospital context or potential intervention. Two villages in the southwestern Russian Empire present rare examples of nineteenth-century baptism registers where time of birth were recorded. The evidence supports the thesis that ‘natural’ human births disproportionately occur between midnight and early morning. Evidence from the registers also show a seasonal effect, likely driven by the relationship between luminosity and melatonin production. The study, then, contributes to the ongoing debate regarding the medicalisation of childbearing, the deterioration of female autonomy in the sphere of childbearing, as well as other negative health outcomes. Historical evidence can demonstrate how far the circumstances of contemporary society differ from the ‘natural’ mode in something as fundamental as the time of the day when we give birth.

scholarly journals The Periods of RR Lyrae

1993 ◽  
Vol 139 ◽  
pp. 409-409
Author(s):  
Arthur N. Cox
Keyword(s):  
Asymptotic Giant Branch ◽  
Natural Mode ◽  
Composition Gradient ◽  
Near Surface ◽  
Rr Lyrae ◽  
Extensive Evaluation ◽  
Branch Model ◽  
Convective Core ◽  
Pure Helium ◽  
Nonradial Mode

AbstractRR Lyrae (0.566 day period) exhibits the Blasko effect that suggests another natural mode with almost the same period as the accepted fundamental radial mode. This mode might be nonradial, but no one has done an extensive evaluation of this idea. An investigation requires a model that includes the deep composition structure where g-modes of low angular (observable) degree have weight and amplitude. An RR Lyrae model including the outer half of the mass and more than 99% of the radius, based on an asymptotic giant branch model from Hollowell (private communication), see below, was used for this study. It includes composition gradient ramps between the primordial surface hydrogen and helium and the almost pure helium shell and the one between this helium shell and the convective core that is burning helium.Nonradial mode periods almost resonant with the radial fundamental mode period seem to occur for all low ℓ values. In addition to significant pulsation amplitudes in the composition gradient regions where the Brunt Väisälä frequency is large, these low degree and low radial order modes have near-surface amplitudes very similar to the low order radial modes. These modes are evanescent in the convective core. Classical K and γ effects give enough driving in the very low mass surface layers, so that important deep radiative damping for these modes does not completely stabilize nonradial g-mode pulsations. The g4, ℓ=1 mode gives a. double-mode RR Lyrae with Blasko effect.A nonradial mode may not always be visible, depending on how rotation presents the nonspherical pulsations to the observer. Thus the Blasko effect might come and go, as observed for maybe 20% of all RR Lyrae variables. For many, the Blasko effect may not be observable, even when a nonradial mode is there.

An Excitation Spectrum Criteria for the Vibration-Induced Fatigue of Small Bore Pipes

2002 ◽  
Author(s):  
Pierre Moussou
Keyword(s):  
Natural Frequency ◽  
Excitation Spectrum ◽  
Endurance Limit ◽  
Maximum Velocity ◽  
Young Modulus ◽  
Mode Shapes ◽  
Natural Mode ◽  
Velocity Spectrum ◽  
Bending Stress ◽  
Euler Beam

The purpose of the study is to determine an easy-to-use criterion to evaluate the risk of vibration induced fatigue of small bore pipes. The failure mechanism considered is the resonant amplification of a stationary broadband excitation of the main pipe by natural modes of the small bore pipe, leading to bending stresses above the fatigue limit of the steel. Based on the Euler beam theory, a simple model is built up for the natural mode shapes of the small bore pipe close to its root. It is shown that the velocity spectrum at the root of the small bore pipe is equal to the RMS value of the bending stress multiplied by a function of the natural frequency, the damping coefficient, the speed of elastic waves in the steel, the Young modulus and a non-dimensional factor weakly depending on the geometry of the small bore pipe. A maximum velocity spectrum can then be deduced, assuming that a small bore pipe vibrates mainly on its natural mode shapes. The maximum excitation spectrum is defined for each frequency ƒ as the one which would generate a maximum bending stress equal to the endurance limit of the steel, would the small bore pipe have a natural frequency equal to ƒ. Using envelope values of the dimensional factor, the stress intensification factor, the peak factor and the endurance limit of the steel, one obtains the following maximum velocity spectrum for the stainless steel: v<6mm/s/sqrt(ƒ) and the following maximum velocity spectrum for the ferritic steel: v<2.7mm/s/sqrt(ƒ) The velocity spectrum criterion appears less penalizing than the 12 mm/s criterion and more conservative than the strict enforcement of the ANSI-OM3 standard. Comparisons with former studies show that the velocity spectrum criterion leads to the correct fatigue diagnosis.

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