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Work environment
Published in Michelle Rita Grech, Tim John Horberry, Thomas Koester, HUMAN FACTORS in the MARITIME DOMAIN, 2019
Michelle Rita Grech, Tim John Horberry, Thomas Koester
To give a definition, noise is often loosely described as “unwanted sound.” Sound is really an auditory sensation that is due to pressure fluctuations of acoustic waves (oscillations about the ambient pressure of the atmosphere, consisting of longitudinal vibration of air molecules). For humans, it is a variation of pressure in the ear, which can be detected by receptor cells in the ear. The two most important characteristics for us are frequency and intensity (which correspond in lay terms to pitch and loudness). People vary in their interpretation of sound. Some people may label sound as noise, which might not be considered as noise by different people or in different situations.
Ultrasonics
Published in Dale Ensminger, Leonard J. Bond, Ultrasonics, 2011
Dale Ensminger, Leonard J. Bond
Ultrasonic waves are also termed both acoustic and elastic waves. Acoustic waves are compression waves that propagate in gases and many liquids. This gives a shared theoretical base for many medical imaging, SONAR, and industrial applications involving fluids. The term elastic waves is, in many cases, considered to be applied just to waves in solids and with propagation properties that depend upon the elastic properties of the medium as they move in response to vibrations. Such waves can occur in many forms including compression, shear, surface, and interface vibrations. These waves again have a shared theoretical base, which goes well outside ultrasonics and is encountered in fields of study as diverse as NDT/NDE, seismology, and electronics. In interactions with structure, scattering, and the underlying theory, depends upon the ratio between feature size and wavelength of the radiation. Distinct scattering regimes are identified: for small features, where dimensions are a small fraction of a wavelength, “Rayleigh scattering” applies; for larger features, where dimensions are several wavelengths, “long wavelength scattering and ray theory” apply; and in the interim regime, “mid-frequency scattering” features are of the order of a wavelength and numerical methods have been used to solve many otherwise analytically intractable problems. Recent years have seen a cross fertilization in both forward and inverse scattering theories in several fields of study and across many wavelength scales, and the diversity of these interactions is illustrated in Figure 1.3 (after [4]). Fundamentals of ultrasonic wave phenomena are discussed in Chapter 2.
A
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[general] Alsosound waves are periodic compression and expansion patterns propagating through a medium. Acoustic waves are longitudinal waves, in contrast to electromagnetic waves (i.e., transverse). The amplitude of acoustic waves is derived from the molecular motion or the local pressure. Acoustic waves require a medium, unlike electromagnetic waves (see Figure A.29).
Crack propagation studies in strain hardened concrete using acoustic emission and digital image correlation investigations
Published in European Journal of Environmental and Civil Engineering, 2022
A. Thirumalaiselvi, B. S. Sindu, Saptarshi Sasmal
According to ASTM E 1316 (ASTM E, 2006), AE is described as elastic waves emitted from the material due to the sudden release of localised stress energy. The working principle of AE technique depends on the release of energy from multiple locations inside the material which then propagate as elastic waves (Chaipanich et al., 2010). Emitted acoustic waves due to internal structural changes such as damage initiation, evolution etc., are recorded by suitable transducers which transform them to an electric waveform. The schematic representation is shown in Figure 2(a). Different AE parameters are defined as typically shown in Figure 2(b). Amplitude (dB) is the maximum voltage of the AE waveform, threshold (dB) is the minimum amplitude set by the user based upon the environmental noise, rise time is the time elapsed from first threshold crossing to peak amplitude, counts are the number of times an AE waveform passes over the threshold amplitude defined by the user, duration is the time between initial and final threshold crossings, AE energy is the area (above the defined threshold value) under the amplitude versus time plot (Tragazikis et al., 2016).
Three-Dimensional Lattice Boltzmann Model for Acoustic Waves Emitted by a Source
Published in International Journal of Computational Fluid Dynamics, 2021
Jaouad Benhamou, Salaheddine Channouf, Mohammed Jami, Ahmed Mezrhab, Daniel Henry, Valéry Botton
The waves propagate in water, which is considered as homogeneous throughout the confined cavity, with constant thermophysical properties. Physically, the travel of an acoustic wave through a fluid (water) creates small perturbations in pressure, density, and velocity. These perturbations (Kinsler et al. 2000) are expressed by: where the quantities , and are small fluctuations, and the parameters , , and () are the pressure, density, and velocity of the undisturbed fluid (fluid at rest). In these expressions, and refer to the dependence on space and time.
Nonlinear Ultrasonic Second Harmonic Assessment of Concrete Defects Based on Embedded Piezoelectric Sensors
Published in Research in Nondestructive Evaluation, 2020
Jun Chen, Chenglong Yang, Qingdong Wang, Ning Xu, Taotao Zhang
The principle of piezoelectricity is the reciprocal conversion of energy between electrical charges and mechanical vibrations. The vibrations propagate across the solid media and form the acoustic wave. Piezoelectric sensors, therefore, function as both the generation device of acoustic vibration when subjected to the electrical voltage and the generation device of electric charges when subjected to the acoustic stress.