Subjective response of people to simulated sonic booms in their homes

In order to determine the effect of the number of sonic boom occurrences on annoyance, a computer-based system was developed for studying the subjective response of people to the occurrence of simulated sonic booms in their homes. The system provided a degree of control over the noise exposure not found in community surveys and a degree of situational realism not available in the laboratory. A system was deployed for eight weeks in each of 33 homes. Each day from 4 to 63 sonic booms were played as the test subject went about his or her normal activities. At the end of the day, the test subjects rated their annoyance to the sonic booms heard during the day. The sonic booms consisted of different combinations of waveforms, levels, and occurrence rates. The experiment confirmed that the increase in annoyance resulting from multiple occurrences can be modeled by the addition of the term "10 * log(number of occurrences)" to the sonic boom level. Of several noise metrics considered, perceived level was the best annoyance predictor. Comparisons of the subjective responses to the different sonic boom waveforms found no differences that were not accounted for by the noise metrics.     

Scattering of sonic booms by anisotropic turbulence in the atmosphere

An earlier paper [J. Acoust. Soc. Am. 98, 3412-3417 (1995)] reported on the comparison of rise times and overpressures of sonic booms calculated with a scattering center model of turbulence to measurements of sonic boom propagation through a well-characterized turbulent layer under moderately turbulent conditions. This detailed simulation used spherically symmetric scatterers to calculate the percentage of occurrence histograms of received overpressures and rise times. In this paper the calculation is extended to include distorted ellipsoidal turbules as scatterers and more accurately incorporates the meteorological data into a determination of the number of scatterers per unit volume. The scattering center calculation overpredicts the shifts in rise times for weak turbulence, and still underpredicts the shift under more turbulent conditions. This indicates that a single-scatter center-based model cannot completely describe sonic boom propagation through atmospheric turbulence.     

Awakening effects of simulated sonic booms and aircraft noise on men and women

In the course of several studies, 22 male and female subjects, ranging in age from 5–75 years, have been stimulated while asleep by simulated sonic booms (ranging in intensity from 0·6 to 5·0 lb/ft² (239·5 N/m²), as if measured out of doors at ground level) and by indoor recordings of subsonic jet flyover noise (ranging in intensity from 101 to 119 PNdB, as if measured out of doors). The summarized results of these studies suggest that (i) children (5–8 years of age) are uniformly unaffected by noise during sleep; (ii) older subjects are more sensitive to noise than younger subjects; (iii) women are more sensitive to noise during sleep than are men; (iv) within an age group, individuals may vary widely with respect to their relative sensitivities to noise during sleep; and (v) the frequency of behavioral awakening is a function of the intensity of both the simulated sonic booms and the subsonic jet flyover noise.     

A computational analysis of sonic booms penetrating a realistic ocean surface

The last decade has seen a revival of sonic boom research, a direct result of the projected market for a new breed of supersonic passenger aircraft, its design, and its operation. One area of the research involves sonic boom penetration into the ocean, one concern being the possible disturbance of marine mammals from the noise generated by proposed high-speed civil transport (HSCT) flyovers. Although theory is available to predict underwater sound levels due to a sonic boom hitting a homogeneous ocean with a flat surface, theory for a realistic ocean, one with a wavy surface and bubbles near the surface, is missing and will be presented in this paper. First, reviews are given of a computational method to calculate the underwater pressure field and the effects of a simple wavy ocean surface on the impinging sonic boom. Second, effects are described for the implementation of three additional conditions: a sonic boom/ocean "wavelength" comparison, complex ocean surfaces, and bubbles near the ocean surface. Overall, results from the model suggest that the realistic ocean features affect the penetrating proposed HSCT sonic booms by modifying the underwater sound-pressure levels only about 1 decibel or less.     

Establishing an upper bound for window response to the sonic boom

Investigations conducted in various sonic boom test programs have proven that the acoustic coupling between windows and passageways in buildings must be considered in any attempt to arrive at an understanding of the response of windows to sonic boom excitation. The dynamic pressure inside a structure depends upon whether the windows are open or closed, and the response of the window depends upon the strength of acoustical coupling.     

Diffraction of sonic booms around buildings resulting in the building spiking effect

The diffraction of a sonic boom around a building of finite dimensions yields amplification of the front shock and a positive spike that follows the tail shock in the pressure waveform recorded at the incident side of the building's exterior surface. This physical phenomenon is consistently found both in the data obtained from a 2006 NASA flight test and field experiment, and in the finite-difference time-domain simulation that models this particular experiment, and the authors call it the "building spiking" effect. This paper presents an analysis of the numerical and the accompanying experimental results used to investigate the cause of this effect. The simulation assumes linear acoustics only, which sufficiently describes the physics of interest. Separating the low and high frequency components of boom recordings using optimal finite impulse response filters with complementary magnitude responses shows that the building spiking effect can be attributed to the frequency dependent nature of diffraction. A comparison of the building spiking effect of a conventional N-wave and a low-amplitude sonic boom shows that a longer shock rise time leads to less pronounced amplification of the exterior pressure loading on buildings, and thus reveals an advantage of shaping a boom to elongate its rise time.     

Evidence of wave front folding of sonic booms by a laboratory-scale deterministic experiment of shock waves in a heterogeneous medium

The influence of the planetary boundary layer on the sonic boom received at the ground level is known since the 1960s to be of major importance. Sonic boom propagation in a turbulent medium is characterized by an increase of the mean rise time and a huge variability. An experiment is conducted at a 1:100,000 scale in water to investigate ultrasonic shock wave interaction with a single heterogeneity. The experiment shows a very good scaling with sonic boom, concerning the size of the heterogeneities, the wave amplitude, and the rise time of the incident wave. The wave front folding associated with local focusing, and its link to the increase of the rise time, are evidenced by the experiment. The observed amplification of the peak pressure (by a factor up to 2), and increase of the rise time (by up to about one magnitude order), are in qualitative agreement with sonic boom observations. A nonlinear parabolic model is compared favorably to the experiment on axis, though the paraxial approximation turns out less precise off axis. Simulations are finally used to discriminate between nonlinear and linear propagations, showing nonlinearities affect mostly the higher harmonics that are in the audible range for sonic booms.     

An experimental and analytical study of a new flap valve for generating simulated sonic booms

The design, operation, and performance of a sonic boom simulator, featuring a radically new dual-flap valve and electromechanical control system, are described. This new flap valve with its large maximum throat area (160 cm²) was designed to regulate the air flow from a low pressure reservoir (up to 0·2 atm overpressure) into the apex of a large pyramidal horn (25 m long, 3 m × 3 m base), where the incoming low speed air flow (up to 150 m/s) produces a travelling simulated sonic boom or N-wave with relatively little superposed high frequency noise. As a consequence, the full scale simulated sonic boom is virtually free of superposed jet noise, a major advance over past work with such horn-type simulators. Additionally, an advanced gasdynamic analysis of the reservoir coupled with an advanced acoustic analysis of the wave motion in the horn is presented to predict the characteristics of the simulated sonic boom—wave form, amplitude, duration, and rise time. Predicted and measured overpressure signatures are shown to be in excellent agreement.     

Predicting the vibroacoustic response of satellite equipment panels

Modern satellites are constructed of large, lightweight equipment panels that are strongly excited by acoustic pressures during launch. During design, performing vibroacoustic analyses to evaluate and ensure the integrity of the complex electronics mounted on the panels is critical. In this study the attached equipment is explicitly addressed and how its properties affect the panel responses is characterized. FEA and BEA methods are used to derive realistic parameters to input to a SEA hybrid model of a panel with multiple attachments. Specifically, conductance/modal density and radiation efficiency for nonhomogeneous panel structures with and without mass loading are computed. The validity of using the spatially averaged conductance of panels with irregular features for deriving the structure modal density is demonstrated. Maidanik's proposed method of modifying the traditional SEA input power is implemented, illustrating the importance of accounting for system internal couplings when calculating the external input power. The predictions using the SEA hybrid model agree with the measured data trends, and are found to be most sensitive to the assumed dynamic mass ratio (attachments/structure) and the attachment internal loss factor. Additional experimental and analytical investigations are recommended to better characterize dynamic masses, modal densities and loss factors.     

The thermal effects on the negative refraction of sonic crystals

The thermal effects on the refractive direction of a sonic crystal consisted of steel rods in air background is investigated. By means of varying the temperature, the refractive direction and the range of the incident angle with the negative refraction are changed accordingly due to the variations of the air density and sound speed. The focus behaviors, intensity and distance, of the sonic crystal plane lens with varying temperature are studied. Moreover, at certain frequencies and incident angles, the refractive angles can be changed from negative to positive by varying the temperature of a sonic crystal with air background. The tunable sonic crystal can be used to design various novel ultrasonic devices.     

Electromagnetic transient response of a conducting cylinder driven by a solenoid

Using an idealized two-dimensional model we consider the transient response when particular currents or voltages are applied to an infinite solenoid encircling a homogeneous cylinder. The results may be used to determine the degree and type of changes in the bulk electrical characteristics of a cylindrical test object as compared to a standard.     

向列液晶表面弹性能K13项的物理效应及检验方法

通过解析推导和数值计算的方法，得到了平衡态指向矢满足的微分方程和边界条件.研究了表面弹性能K13项对磁场作用下的弱锚定向列液晶盒Fréedericksz转变性质的影响.结果表明，表面弹性能K13项的存在对液晶系统的自由能有很大的影响，从而改变转变的性质，诱导液晶盒在阈值点发生一级Fréedericksz转变.给出了发生一级转变的物理条件，它除了与液晶的结构和材料有关外，还依赖于液晶表面弹性能K13项，同时给出了由此判断K13项是否存在的检验方法. 关键词： 表面弹性能K13项 弱锚定 Fréedericksz转变     

Transfer matrix modeling of the vibroacoustic response of multi-materials structures under mechanical excitation

In several automotive and aircraft applications there is a need for simple tools to assess quickly and accurately the performance of sound packages. Statistical energy analysis (SEA) and the transfer matrix method (TMM) are examples of such methods. The used methodology (for modeling sound packages) is well validated for acoustic excitations (airborne). However, a simple and reliable methodology is still lacking for mechanical excitations (structure-borne). This work concentrates on the latter. It presents and compares three different simple approaches to model the vibration and acoustic response of a mechanically excited structure with an added noise control treatment. Various examples are presented to confirm their relevance and accuracy in comparison to more exact and costly methods, such as the finite element method. In particular, it is shown that the TMM with a size correction (FTMM) is accurate enough to eliminate the classical assumption of low coupling classically assumed in SEA modeling of sound packages and/or compute efficiently the structure-borne insertion loss of sound packages used in SEA and FEM models.