The structural acoustic properties of stiffened shells

Yu Luan
2008 Journal of the Acoustical Society of America  
Effects of sound on marine mammals have traditionally been defined either as injury or disruption of behavior. The earliest concern about behavioral disruption was that elevated noise could reduce the range of communication by masking faint signals. Few studies have documented this effect, but recent work emphasizes mechanisms animals use to compensate for elevated noise. Many studies have documented changes in behavior as a function of exposure, but it has proven difficult to relate these to
more » ... fects on the welfare of individual animals or on the status of populations. Promising approaches to interpreting effects include avoidance of habitat, energetics of foraging, and applying models of anti-predator behavior to human disturbance. During the 1990s acoustic criteria for injury were designated based upon temporary hearing loss. Accumulating evidence of atypical mass strandings of beaked whales coincident with naval sonar exercises suggest that injury or death may result from behavioral responses of some species at lower exposure levels in some settings. A tagged beaked whale showed similar but weaker responses to experimental playback of a mid-frequency sonar sound compared to calls of killer whales, suggesting that anti-predator response may harm animals after exposure to levels of sound very unlikely to cause injury directly. Introduced by Luigi Maffei, Second University of Naples, Italy 11:10 1aID2. New Trends in Aeroacoustics: From acoustic analogies to direct numerical simulations. Daniel Juvé ͑Ecole centrale de Lyon, Modern aeroacoustics started in the early 1950's when Lighthill developed his famous acoustic analogy in an attempt to understand, and reduce, the terrifying noise generated by jet aircrafts. For nearly 50 years the subject of aerodynamic sound was dominated by approaches based upon this analogy or variants of it. Recently, the availability of powerful computing facilities combined with the development of numerical algorithms specially designed to simulate sound propagation over large distances has paved the way for Љa second golden age of aeroacousticsЉ ͑to quote Lighthill himself͒. In this talk we will first give an overview of this evolution from acoustic analogies to computational aeroacoustics ͑CAA͒. Typical illustrations of the CAA approach will then be presented and applications for transportation systems will be discussed. 1a MON. AM 2969 2969 Invited Papers 1:00 1pAAa1. Spatial decay, behaviour and space planning models European and International standards on open office acoustics. Pierre Chigot ͑Saint Gobain Ecophon SA, box 30030, 60 291 Rantigny, France,͒ Recent standardisation work on open plan offices acoustics is characterized by a shift in the way room acoustics is handled. Spatial decay ͑expressed through rate of spatial decay per doubling of distance, DL2͒ is preferred to temporal decay ͑expressed through reverberation time, RT͒. The complexity of open plan office acoustic design results from the fundamental contradiction of communication and concentration. DL2 reflects better the challenges of sound control in such rooms, which is basically sound propagation control. Beyond, this contradiction, specific space analysis models and tools can help to visualize the acoustic interactions between workstations, teams and departments accommodated in the same room. These models are now ready to be included in standardization work. International technical standard for field measurements of DL2 integrates new descriptive models for open plan office acoustics, taking into account geometric proportions, presence of screens and furniture as well as group behaviour and speech characteristics, such as increased energy contents at low frequencies, voice levels, raised hearing sensitivity at high frequencies. Also, normative guidelines from Netherlands and France integrating this approach will be presented.
doi:10.1121/1.2932806 fatcat:zohbewf2k5h7fly2hoqzfdk42e