= Ole Døssing
{c}
\b[Ole Døssing] is the credited author of Brüel & Kjær's <Structural Testing Part I: Mechanical Mobility Measurements by Ole Døssing>, whose title page identifies the author and an April1988revision. The handbook develops experimental ways to relate applied <force> to structural motion, with emphasis on measured <frequency responses> rather than vibration amplitude alone.<Structural Testing Part I: Mechanical Mobility Measurements by Ole Døssing>[Title page, Preface and printed pp14–16]{ref}
The distinction is important when diagnosing a vibrating structure. A large response may reflect a large applied <force>, a strong structural response at that frequency, or both. The handbook describes measuring the exciting <force> and the motion simultaneously, using a force transducer, an <accelerometer> and a dual-channel analyzer. The complex ratio retains both magnitude and <phase>. It distinguishes <mechanical accelerance>, acceleration divided by <force>, from <mechanical driving-point mobility>, velocity divided by <force> at the same point.<Structural Testing Part I: Mechanical Mobility Measurements by Ole Døssing>[Printed pp14–21, frequency-response definitions and measurement estimators]{ref}
An original known-mass check makes the apparatus interpretable. For a freely translating mass $m=0.50\,\mathrm{kg}$ in a regime where suspension forces are negligible, <Newton's second law> predicts
$$
\frac{a}{F}=\frac1m=2.0\,\mathrm{kg^{-1}}.
$$
A10newton sinusoidal <force> amplitude should therefore produce20metres per second squared of <acceleration> amplitude in the same phase. With the convention $e^{i\omega t}$, velocity amplitude is $a/(i\omega)$, so at $\omega=100\,\mathrm{rad\,s^{-1}}$ the <mechanical driving-point mobility> is $-0.020i\,\mathrm{m\,N^{-1}\,s^{-1}}$. Confusing the two response ratios loses both a factor of frequency and the phase shift.
Døssing's handbook describes this known-mass <measurement calibration> as a check of the complete response-to-force measurement chain. The mass must move in the intended direction and its effective moving mass must be understood. It checks a ratio of transducer responses, rather than separately determining each transducer's absolute sensitivity.<Structural Testing Part I: Mechanical Mobility Measurements by Ole Døssing>[Printed p43, Calibration]{ref}
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