Koorosh Naghshineh

Material tailoring of structures to achieve a minimum radiation condition

A strategy is developed for designing structures that radiate sound inefficiently in light fluids. The problem is broken into two steps. First, given a frequency and overall geometry of the structure, a surface velocity distribution is found that produces a minimum radiation condition. This particular velocity distribution is referred to as the ‘‘weak radiator’’ velocity profile. Second, a distribution of Young’s modulus and density distribution is found for the structure such that it exhibits the weak radiator velocity profile as one of its mode shapes. In the first step, a finite element adaptation of the integral wave equation is combined with the Lagrange multiplier theorem to obtain a surface velocity distribution that minimizes the radiated sound power. In the second step, extensive use of structural finite element modeling as well as linear programming techniques is made. The result is a weak radiator structure. When compared to a structure with uniform material properties, the weak radiator struct...

Active control of sound power using acoustic basis functions as surface velocity filters

An improved method of active structural acoustics control is presented that is based on the minimization of the total power radiated from any structure expressed in terms of a truncated series sum. Each term of this sum is related to the coupling between the orthogonal eigenvectors of the radiation impedance matrix (referred to as ‘‘basis functions’’ in this paper) and the structural surface velocity vector. The basis functions act as surface velocity filters. These acoustic basis functions are found to be weak functions of frequency but their corresponding weighting coefficients increase monotonically with frequency. The minimization of the radiated power is shown to result in a structural surface velocity vector that couples poorly to those acoustic basis functions that account for high‐efficiency sound radiation. This strategy is demonstrated numerically for a clamped–clamped baffled beam in air. Point force primary and control actuators (shakers) are used to explore the control mechanisms. As expected...

Creating accessible science museums with user-activated environmental audio beacons (ping!).

In 2003, Touch Graphics Company carried out research on a new invention that promises to improve accessibility to science museums for visitors who are visually impaired. The system, nicknamed Ping!, allows users to navigate an exhibit area, listen to audio descriptions, and interact with exhibits using a cell phone–based interface. The system relies on computer telephony, and it incorporates a network of wireless environmental audio beacons that can be triggered by users wishing to travel to destinations they choose. User testing indicates that the system is effective, both as a way-finding tool and as a means of providing accessible information on museum content. Follow-up development projects will determine if this approach can be successfully implemented in other settings and for other user populations.

Narrow band active control of sound radiated from a baffled beam using local volume displacement minimization

Abstract Further development of a control technique for reduction of sound radiated from vibrating structures is presented. This control technique is based on minimization of local volume displacement, velocity, or acceleration of a vibrating structure. Multiple, single-input/single-output cancellation devices are used. Each device controller employs a motion sensor and an acoustic actuator (loudspeaker). The motion sensor signal is related to the local volume displacement of the structure which is then reduced by a loudspeaker driven with an equal but opposing volume displacement. Previous work showed the successful implementation of this technique for uniformly vibrating radiators. This paper presents the development of this technique for reduction of sound radiated from a vibrating beam. A PVDF sensor was used for measurement of local volume displacement of the beam. This sensor was used in conjunction with an internal pressure sensor mounted in the loudspeaker enclosure. Sound reductions of up to 20 dB were achieved within a narrow range of vibration frequencies (centered around the first beam mode). Finally, design of a single integrated sensor is suggested for implementation of many PVDF sensors on a beam.

A design method for achieving weak radiator structures using active vibration control

A general strategy is devised for achieving minimum radiation of sound from structures subjected to a harmonic excitation force. A quadratic expression is written for the total sound power radiated from a structure in terms of the primary excitation and actuator (control) forces. Using the Lagrange multiplier theorem and the penalty approach, a single control force vector is found which results in minimum radiated sound power (weak radiator). A general formation is represented for the single frequency excitation case. This formulation is then extended to the case of a structure subjected to a broadband excitation force. The numerical implementation of these formulations is discussed for a baffled beam. Application of this formulation is demonstrated for shaker actuators as well as PZT surface actuators. Results for a single frequency weak radiator show that when the response of the structure with control is compared to that of the structure without control, four important observations can be made. First, ...

Reduction of sound radiated from vibrating structures via active control of local volume velocity

Abstract A new active noise-control technique has been developed for control of low-frequency sound generated by vibrating surfaces. The technique is based on minimizing the volume velocity. Noise reduction is achieved by distributing an array of control devices over the surface of the radiating structure (e.g. an aircraft fuselage interior). Each device consists of a motion-sensing mechanism, an analog control circuit, and a loudspeaker. The loudspeaker is driven such that it reduces the volume velocity of the radiating structure within its close proximity. This paper presents the theory behind this approach, as well as an experimental verification of this concept using a 10 in. uniformly vibrating circular plate and a single noise-control device. Broadband (50–500 Hz) sound reductions in the range of 10–20 dB were achieved over a wide spatial area. Since, in the final implementation of this concept, multiple devices will be employed on a nonuniformly vibrating structure, simulations of the performance of one, two, four, and six devices on a vibrating rectangular plate are presented.

Detection of Quiet Vehicles by Blind Pedestrians

AbstractThis paper examines participants who are blind, with and without normal hearing, regarding detection of forward approaching and backing vehicles operating in electric mode (identified in this paper as quiet vehicles) under low speed conditions. Testing under low ambient sound conditions involved evaluation of internal combustion engine vehicles, hybrid vehicles operating in electric mode (EM), and the same hybrid vehicles operating in EM but with five different artificially generated sounds. Three of the five artificial sounds improved detection relative to the internal combustion engine condition for both forward and backward detection tasks. Regression analysis indicated that significant predictors of forward detection performance include average wind speed, amplitude modulation of the signal, hearing loss in the 500xa0Hz range, vehicle velocity, minimum ambient sound level, and overall vehicle sound level in units of A-weighted decibels. The corresponding analysis for backward detection indicated...

A comparison of open-loop feedforward and closed-loop methods for active noise control using volume velocity minimization

Abstract This paper focuses on the application of the concept of volume velocity minimization to lower the sound generated by a vibrating surface. The motion of a vibrating surface is measured using an accelerometer, and a speaker is driven so that the net volume velocity of the two is lowered. This concept is tested on a two-speaker system. One speaker acts as the noise source, and the other as the control speaker (noise suppressor). Using this system, the effectiveness of three control strategies are evaluated—open-loop feedforward, closed-loop proportional, and closed-loop optimal control. The feedforward system gives noise reductions of 5–25xa0dB over the range from 100 to 800xa0Hz. The closed-loop systems give reductions of 5–30xa0dB over the range from 175 to 800xa0Hz. The feedforward system is found to have the best performance below the suppressor’s first resonance, while the closed-loop systems have best performance near the first resonance. Speaker coupling is found to have little effect on system performance.

Impact of adding artificially generated alert sound to hybrid electric vehicles on their detectability by pedestrians who are blind

A repeated-measures design with block randomization was used for the study, in which 14 adults with visual impairments attempted to detect three different vehicles: a hybrid electric vehicle (HEV) with an artificially generated sound (Vehicle Sound for Pedestrians [VSP]), an HEV without the VSP, and a comparable internal combustion engine (ICE) vehicle. The VSP vehicle (mean +/- standard deviation [SD] = 38.3 +/- 14.8 m) was detected at a significantly farther distance than the HEV (mean +/- SD = 27.5 +/- 11.5 m), t = 4.823, p < 0.001, but no significant difference existed between the VSP and ICE vehicles (mean +/- SD = 34.5 +/- 14.3 m), t = 1.787, p = 0.10. Despite the overall sound level difference between the two test sites (parking lot = 48.7 dBA, roadway = 55.1 dBA), no significant difference in detection distance between the test sites was observed, F(1, 13) = 0.025, p = 0.88. No significant interaction was found between the vehicle type and test site, F(1.31, 16.98) = 0.272, p = 0.67. The findings of the study may help us understand how adding an artificially generated sound to an HEV could affect some of the orientation and mobility tasks performed by blind pedestrians.

An Active Control Strategy for Achieving Weak Radiator Structures

A general control strategy is presented for active suppression of total radiated sound power from harmonically excited structures based on the measurement of their response. Using the measured response of the structure together with knowledge of its structural mobility, an equivalent primary excitation force is found at discrete points along the structure. Using this equivalent primary force and performing a quadratic optimization of the power radiated from the structure, a set of control forces is found at selected points on the structure that results in minimum radiated sound power. A numerical example of this strategy is presented for a simply supported beam in a rigid baffle excited by a harmonic plane wave incident at an oblique angle