ISO 2041:2009 pdf free download – Mechanical vibration, shock and condition monitoring一Vocabulary.
1.43
complex response
response of a system expressed as a complex quantity witn amplitude ana phase angle from a specified excitation
NOTE See the notes under complex excitation (1.42).
1.44
modal analysis
vibration analysis method that characterizes a complex structural system by its modes of vibration, i.e. its natural frequencies, modal damping and mode shapes, and based on the principle of superposition
1.45
modal matrix
linear transformation matrix which consists of the eigen vectors or modal vectors of a system
NOTE It renders the system both inertially and elastically uncoupled, i.e. the modal mass and modal stiffness matrices are transformed into diagonal matrices.
1.46
modal stiffness
stiffness element associated with a specified mode of vibration
1.47
modal density
number of modes per unit bandwidth
NOTE Modal density is a measure widely used in structural dynamics as a diagnostic tool in assessing vibration power flow in complex, structural systems. It can play a crucial role in determining changes In vibration power flow that may be a precursor to fatigue failure in some part of the structure, or a metric used in structural condition monitoring evaluations. In addition to these applications, It is a parameter required by the Statistical Energy Analysis method for evaluating the high- frequency response of complex structures and in selecting appropriate vibration-control methods and devices.
1.48
mechanical impedance
complex ratio of force to velocity at a specified point and degree-of-freedom in a mechanical system
NOTE 1 The force and velocity may be taken at the same or different points and degrees-of-freedom in the system undergoing simple harmonic motion.
NOTE 2 In the case of torsional mechanical impedance, the terms ‘forc& and velocity should be rep’aced by torque and angular velocity, respectively.
NOTE 3 In general, the term impedance applies to linear systems only.
NOTE 4 The concept is extended to non-linear systems where the term ‘incremental impedance is used to describe a similar quantity.
1.49
direct mechanical Impedance
driving point mechanical impedance
complex ratio of the force to velocity taken at the same point or degree-of-freedom in a mechanical system during simple harmonic motion
NOTE See the notes under mechanical Impedance (1.48).
1.50
transfer (mechanical) impedance
complex ratio of the force applied at point 1, in a specified degree-of-freedom in a mechanical system, to the velocity at another pointj in a specified direction or degree-of-freedom in the same system, during simple harmonic motion
NOTE See the notes under mechanical impedance (1.48)
1.59
dynamic mass
complex ratio of force to acceleration
1.60
accelerance
frequency-dependent ratio of the spectrum, or spectral density, of the acceleration to the spectrum, or spectral density, of the force
1.61
spectrum
description of a quantity as a function of frequency or wavelength
1.62
level (of a quantity)
logarithm of the ratio of the quantity to a reference of the same kind
NOTE 1 The base of the logarithm. the reference quantity and the kind of level shall be specified
NOTE 2 Examples of kinds of levels in common use are electric-power level, sound-pressure level, and voltage- squared level.
NOTE 3 The definition is expressed symbolically as.