An Impact Excitation System for Repeatable, High-Bandwidth Modal Testing of Miniature Structures

If a laser Doppler vibrometer is used in a continuously-scanning mode to measure the response of a vibrating structure, its output spectrum contains side-bands from which the response mode shape, as defined along the scan line, may be obtained. With impact excitation, the response is the summation of a set of exponentially-decaying sinusoids which, in the frequency domain, has peaks at the natural frequencies and at `sideband' pseudo-natural frequencies, spaced at multiples of the scan frequency. Techniques are described for deriving natural mode shapes from these, using standard modal analysis procedures. Some limitations as to the types of mode which can be analysed are described. The process is simple and speedy, even when compared with a normal point-by-point impact test survey. Information may also be derived, using a circular scan, on the direction of vibration, and angular vibration, at individual points.

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Modal testing using impact excitation and a scanning LDV

10.1117/12.307718 ◽

1998 ◽

Author(s):

Anthony B. Stanbridge ◽

A. Z. Khan ◽

David J. Ewins

Keyword(s):

Modal Testing ◽

Impact Excitation

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Nonlinear Modal Testing Performed by Pulsed-Air Jet Excitation System

Nonlinear Dynamics, Volume 1 - Conference Proceedings of the Society for Experimental Mechanics Series ◽

10.1007/978-3-319-29739-2_15 ◽

2016 ◽

pp. 155-170

Author(s):

M. Piraccini ◽

D. Di Maio ◽

R. Di Sante

Keyword(s):

Modal Testing ◽

Excitation System ◽

Air Jet

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Recent Radiative and Collisional Atomic Data of Astrophysical Interest

International Astronomical Union Colloquium ◽

10.1017/s0252921100107596 ◽

1988 ◽

Vol 102 ◽

pp. 129-132

Author(s):

K.L. Baluja ◽

K. Butler ◽

J. Le Bourlot ◽

C.J. Zeippen

Keyword(s):

Mass Production ◽

Bound States ◽

Physical Models ◽

Impact Excitation ◽

Electron Impact Excitation ◽

Atomic Data ◽

Isoelectronic Sequence ◽

Astrophysical Interest ◽

Radiative Transitions ◽

Forbidden Transitions

SummaryUsing sophisticated computer programs and elaborate physical models, accurate radiative and collisional atomic data of astrophysical interest have been or are being calculated. The cases treated include radiative transitions between bound states in the 2p4and 2s2p5configurations of many ions in the oxygen isoelectronic sequence, the photoionisation of the ground state of neutral iron, the electron impact excitation of the fine-structure forbidden transitions within the 3p3ground configuration of CℓIII, Ar IV and K V, and the mass-production of radiative data for ions in the oxygen and fluorine isoelectronic sequences, as part of the international Opacity Project.

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A New AID for Interpolating and Assessing Collision Strengths and Rate Coefficients

International Astronomical Union Colloquium ◽

10.1017/s0252921100107535 ◽

1988 ◽

Vol 102 ◽

pp. 107-110

Author(s):

A. Burgess ◽

H.E. Mason ◽

J.A. Tully

Keyword(s):

Significant Loss ◽

Impact Excitation ◽

Rate Coefficients ◽

Electron Impact Excitation ◽

Graphical Display ◽

Practical Procedure ◽

Positive Ions ◽

Allowed Transition ◽

Computational Errors ◽

Existing Data

AbstractA new way of critically assessing and compacting data for electron impact excitation of positive ions is proposed. This method allows one (i) to detect possible printing and computational errors in the published tables, (ii) to interpolate and extrapolate the existing data as a function of energy or temperature, and (iii) to simplify considerably the storage and transfer of data without significant loss of information. Theoretical or experimental collision strengths Ω(E) are scaled and then plotted as functions of the colliding electron energy, the entire range of which is conveniently mapped onto the interval (0,1). For a given transition the scaled Ω can be accurately represented - usually to within a fraction of a percent - by a 5 point least squares spline. Further details are given in (2). Similar techniques enable thermally averaged collision strengths upsilon (T) to be obtained at arbitrary temperatures in the interval 0 < T < ∞. Application of the method is possible by means of an interactive program with graphical display (2). To illustrate this practical procedure we use the program to treat Ω for the optically allowed transition 2s → 2p in ArXVI.

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