New Proportionate Affine Projection Algorithm

A new proportionate-type affine projection algorithm with intermittent update of the weight coefficients is proposed. It takes into account the “history” of the proportionate factors and uses a fast recursive filtering procedure. Also, the effect of using dichotomous coordinate descent iterations is investigated. Simulation results indicate that the proposed algorithm has improved performance and much lower computational complexity than other proportionate affine projection algorithms. Therefore it represents a practical solution for acoustic echo cancellation systems.

Gyro Rock Crusher and Asphalt Plant Sound Power Levels

Sound power levels including the distribution into octaves from a large 149 kW (200 horsepower) gyro rock crusher and separate asphalt plant are presented. These NIST-traceable data are needed for estimating sound pressure levels at large distances (such as occurs on adjoining property to a quarry) where atmospheric attenuation may be significant for the higher frequencies. Included are examples of the computed A-weighted sound pressure levels at a distance from the source, including atmospheric attenuation. Substantial low-frequency sound power levels are noted which are greatly reduced in the far-field A-weighted sound pressure level calculations.

Modeling High-Frequency Tire Tread Vibration as a Group of Traveling Bending Waves

Tire noise is one of the major causes of road traffic noise. The high-frequency component dominates tire radiation noise, which is caused by tire tread bending vibration excited by rough road surface textures. As a result of such complicated phenomena, including very complicated tread vibration modes in the high-frequency range, heavy damping, and non-periodic patterns of the road surface texture, the modal analysis approach may appear to have a low potential for analyzing this problem. Based on the above considerations, we attempted to model the tread vibration phenomenon as a group of traveling bending waves excited at an array of pavement chippings. By setting the tread shoulders as reflecting lines, the interference effect of diagonally propagating direct and reflected waves is clarified. The vibration propagation speed and decay rate were estimated through shaker tests. The shape of the probability distribution function of the chippings intervals affects the traveling wave patterns. These observations will help engineers to develop less noisy tires.

An Approach for Structural-Acoustic Optimization of Ribbed Panels Using Component Mode Synthesis

Component mode synthesis (CMS) is an approach used to couple dynamics of complex structures using modes of individual components. A CMS approach is developed to determine the response of a ribbed panel based on the individual rib and plate modes. The CMS method allows for rapid evaluation of noise-control designs as component modes need to be solved only once. Since efficient evaluation is required for global design optimization procedures, the CMS approach can be well suited in optimization problems. A simple structural-acoustic optimization problem was created to demonstrate the utility of the formulation by finding the optimal rib location and material to reduce sound radiation for a point-driven plate. Several parameters of the optimization algorithm are varied to test convergence speed and accuracy.

Approaches to Urban Noise Management in India

Noise pollution in urban areas is recognized as a major environmental concern in India. The lack of infrastructure and fast paced life in major metropolitan cities of India has made the urban environment extremely crowded, busy as well as noisy and as a result the millions of people living in the major metropolitan areas are suffering from the impacts of noise pollution. Noise levels are escalating at such a rate that it has become a major threat to the quality of human lives. Direct links between noise and health have been established by research conducted over the past few decades. There are several causes for urban degradation such as population migration, environmental considerations not adequately being incorporated into master plans, uncoordinated and haphazard development, weak implementation of plans and laws and inadequate institutional competences and resource crunch. This paper discusses the causal factors, impacts and the different approaches adopted by the Central Government as well as some major State Pollution Control Boards to curb the urban noise problem and the need for looking into non-conventional solutions such as Ecocity programme to bring in visible environmental improvement.

What Kind of Friction Model Is Needed to Predict Brake Squeal?

Predictive models of friction-induced vibration have proved elusive despite decades of research. There are many mechanisms that can cause brake squeal; friction coupled systems can be highly sensitive to small perturbations; and the dynamic properties of friction at the contact zone seem to be poorly understood. This paper describes experimental and theoretical work aimed at identifying the key ingredients of a predictive model. A large-scale experiment was carried out to identify squeal initiations using a pin-on-disc test rig: approximately 30,000 squeal initiations were recorded, covering a very wide range of frequencies. The theoretical model allows for completely general linear systems coupled at a single sliding point by friction: squeal is predicted using a linearised stability analysis. Results will be presented that show that almost all observed squeal events can be predicted within this model framework, but that some subsets require innovative friction modelling: predictions are highly dependent on the particular choice of friction model and its associated parameters.

Preamplifier With Ultra Low Frequency Cutoff for Infrasonic Condenser Microphone

Measuring infrasonic sound sets high requirements on the instruments used. Typically the measurement chain consists of a microphone and a preamplifier. As the input resistance of the preamplifier forms a high pass filter with the capacitance of the microphone in the picofarad range, measuring ultra low frequencies becomes a challenge. The electric preamplifier presented in this paper together with a prepolarized condenser microphone form a measurement system. The developed preamplifier connects the microphone signal directly to the input of an operational amplifier with ultra high input impedance. The bias current for the preamplifier further complicates the signal amplification. A configuration of two diode-connected FETs provide the input bias current. The resulting input impedance of nearly 1 TΩ yields a total lower limiting −3 dB cutoff frequency of 8 mHz and a dynamic range of 95 dB. Being able to measure down to ultra low frequencies in the infrasonic frequency range will aid actors in the debate on wind turbine noise. Sonic booms from supersonic flights include frequencies down to 10 mHz and the preamplifier proposed in this paper will aid scientists trying to modify the N-shaped shock wave at high level which prohibits flights in land zones.

Acoustic Performance of Louvred Facades for Brisbane Domestic Airport: An Integrated Approach

Maximising cross ventilation is a low energy method of naturally ventilating and providing heating and cooling to deep plan spaces. Significant reduction in the emission of greenhouse gases can be achieved through minimising the use of mechanical systems in regions with climatic conditions that support the use of natural ventilation. Arup has provided input into the design of a louvered facade for the control of external noise for Brisbane Domestic Airport. A full scale prototype facade was constructed and noise transmission loss measurements were undertaken. The results indicate that significant noise reduction can be achieved to enable compliance with the internal noise limits for airport terminals, whilst using natural ventilation. The findings from this research will directly benefit building designers and innovators in the pursuit of achieving sustainable building design.

Design of a Variable Thickness Plate to Focus Bending Waves

This paper describes the design of a thin plate whose thickness is tailored in order to focus bending waves to a desired location on the plate. Focusing is achieved by smoothly varying the thickness of the plate to create a type of lens, which focuses structure-borne energy. Damping treatment can then be positioned at the focal point to efficiently dissipate energy with a minimum amount of treatment. Numerical simulations of both bounded and unbounded plates show that the design is effective over a broad frequency range, focusing traveling waves to the same region of the plate regardless of frequency. This paper also quantifies the additional energy dissipated by local damping treatment installed on a variable thickness plate relative to a uniform plate.

Application of the Beam-Forming Technique for Damage Detection in Composite Plate

The utilization of guided waves generated and sensed by an array of phased sensors allows steering the wave-front in a specific direction (beamforming technique). In this work a linear array of sensors is used to generate an ultrasonic wavefront steered in a specific direction. Numerical simulations are carried out with the LS-DYNA, an explicit Finite Element (FE) code, on a CFRP plate. The damage to be identified is a delamination produced by an impact (BVID). The array of sensors consists of a number of disk-shaped piezo patches. From the echo reflected and returning back to the array, it’s possible to evaluate the time of flight of the signal (TOF) from which the distance of the damage from the sensors array can be determined, and the angular position of the crack by evaluating the time shift of the signal received by each sensor in the array. The experimental tests are carried out in a 0.5m × 0.5m ×2.2 mm CFRP plate with the same sensor array and delamination used in the simulation. A number of receivers located along the panel edges have been also used to detect the damage direction in pitch-catch mode.