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This paper presents the development of an experimental setup for acoustic noise characterization of electric motors. It describes the sound measurement microphones utilized in the setup and discusses the application of octave bands and A-weighting in noise measurement. Various methods for acoustic noise measurement and sound power calculation, including those based on sound pressure and sound intensity, are also covered. Given the relatively noisy test environment and restricted access around the test setup, discrete point sound intensity measurement is selected for sound power calculation. Initially, a stationary probe-holding fixture is designed and fabricated for sound intensity measurements. To enhance the fixture's flexibility and the accuracy of the measurements, a transportable fixture is subsequently designed and fabricated. The necessary hardware and software settings for acoustic noise characterization are then developed. Finally, the setup is used to conduct acoustic noise characterization of an IPM motor, validating the application of the transportable probe-holding fixture. [ABSTRACT FROM AUTHOR]

The primary cause of noise from vehicular traffic while travelling at speeds over 30 km/h is tyre/road interaction. To reduce this noise source, tyre/road sound emissions research has been carried out using different approaches. Most of this research has been centred around track tests, leading to the development of various track and road-based methods for evaluating tyre/road noise emissions. The CPX (Close-Proximity), along with the CPB (Controlled Pass-By), the CB (Coast-By) and the SPB (Statistical Pass-By), methods are the most common ones. Nevertheless, since Reg. (EC) 1222/2009 came into force, only the CB method, defined in Reg. (EC) 117/2007, can be used to obtain tyre/road noise emission type approval values in Europe. However, current track test methods have important limitations, such as the variability of the results depending on the test track or the test vehicle, the repeatability, the influence of environmental variables or, the main aspect, the limitation of the registered magnitude in these tests, which is the sound pressure level. The Alternative Drum test method (A-DR) was developed in 2015 in order to avoid these disadvantages. However, it involves a complex and time-consuming microphone array for each test. With the purpose of improving the A-DR test method, a new methodology based on drum tests, the ISO 11819-2 and the ISO 3744 standards, was developed. This paper describes the new Alternative CPX Drum test method (A-CPX-DR) and validates it by testing several tyres according to the CB, the A-DR and the A-CPX-DR test methods and comparing their results. This research has demonstrated that all three methods have equivalent sound spectra and obtain close equivalent sound pressure levels for type approval of tyres in the EU, while drum tests have shown greater accuracy. For both reasons, the new A-CPX-DR methodology could be used for tyre/road noise emission type approval in a more precise and cheaper way. [ABSTRACT FROM AUTHOR]

The primary cause of noise from vehicular traffic while travelling at speeds over 30 km/h is tyre/road interaction. To reduce this noise source, tyre/road sound emissions research has been carried out using different approaches. Most of this research has been centred around track tests, leading to the development of various track and road-based methods for evaluating tyre/road noise emissions. The CPX (Close-Proximity), along with the CPB (Controlled Pass-By), the CB (Coast-By) and the SPB (Statistical Pass-By), methods are the most common ones. Nevertheless, since Reg. (EC) 1222/2009 came into force, only the CB method, defined in Reg. (EC) 117/2007, can be used to obtain tyre/road noise emission type approval values in Europe. However, current track test methods have important limitations, such as the variability of the results depending on the test track or the test vehicle, the repeatability, the influence of environmental variables or, the main aspect, the limitation of the registered magnitude in these tests, which is the sound pressure level. The Alternative Drum test method (A-DR) was developed in 2015 in order to avoid these disadvantages. However, it involves a complex and time-consuming microphone array for each test. With the purpose of improving the A-DR test method, a new methodology based on drum tests, the ISO 11819-2 and the ISO 3744 standards, was developed. This paper describes the new Alternative CPX Drum test method (A-CPX-DR) and validates it by testing several tyres according to the CB, the A-DR and the A-CPX-DR test methods and comparing their results. This research has demonstrated that all three methods have equivalent sound spectra and obtain close equivalent sound pressure levels for type approval of tyres in the EU, while drum tests have shown greater accuracy. For both reasons, the new A-CPX-DR methodology could be used for tyre/road noise emission type approval in a more precise and cheaper way.

The purpose of this study is to evaluate the effect of the number of diffusers placed in the same room, as well as the effect of diffusers with a flat area (8.4, 13.2, and 18 m2) on the calculated sound absorption coefficient in a reverberation room, when an iterative procedure based on the evaluation of the sound power level is applied (this is done by using the sound power equation and substituting with different values of equivalent absorption area on both sides of the transformed equation to reach the correct value for absorption area, which achieves equality on both sides of the equation in order to achieve the goal). The sound absorption coefficient at random incident of three materials having different degrees of absorption—has been measured in a reverberation room according to ISO 345: a highly absorbent material (sponge) a medium absorbent material (rubber) and a low absorbent material (wood).There is a noticeable convergence between the calculated and measured sound absorption coefficient from the usual ISO 354 procedure and from the sound power level equation from ISO 3741,when diffusers are present. The difference in sound power level is close to 1.0 dB depending on the position of the source with the diffuser area. Thanks to the diffusers effect, the difference between the measured and the calculated sound absorption coefficient can be considerably reduced. [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional fluid-structural and vibro-acoustics coupled model of a gear pump is presented. Gear pumps represent the majority of the positive displacement machines used for flow generation in fluid power systems. Typically, the dynamics of gear pumps are dependent on the characteristics of the fluid dynamics inside the pump, which translates into vibrations to the housing. These vibrations then propagate to the surrounding medium and emit sound. The purpose of this study is to propose a three-dimensional fully integrated computational model to simulate the complete gear pump behaviour from the fluid dynamics to the structural vibrations, up to the vibroacoustic response. In this hybrid configuration, a transient CFD (Computational Fluid Dynamics) model is first developed to simulate the 3D flow field with a deforming and re-meshing approach to take into account the variation of the volume between the gears. Second, the internal pressure field calculated at each time step is then used as a loading into a structural FEM (Finite Element Method) model of the gear pump to compute the actual stresses and deformations of the housing. Third, the results of the structural response are used as excitation in a vibroacoustic sub-model to simulate the radiated noise using a high-order FEM technique. The comparison between the numerical and experimental flow curves validates the CFD model. The sound power calculations from the vibroacoustic model show good comparison with the sound intensity measurements around the pump casing, confirming the validity of the proposed coupled model. The described CFD-FEM approach proves to be a powerful gear pump design tool: it provides a reliable estimate of gear pump working parameters such as fluid power and vibroacoustic characteristics, starting from the CAD (Computer-Aided Design) geometry of the components. Furthermore, being one of the first multi-domain simulation models of a gear pump, this work can be useful to researchers as a starting point to correlate the noise emitted with the internal flow in full 3D conditions. [ABSTRACT FROM AUTHOR]

This paper presents the development of an experimental setup for acoustic noise characterization of electric motors. It describes the sound measurement microphones utilized in the setup and discusses the application of octave bands and A-weighting in noise measurement. Various methods for acoustic noise measurement and sound power calculation, including those based on sound pressure and sound intensity, are also covered. Given the relatively noisy test environment and restricted access around the test setup, discrete point sound intensity measurement is selected for sound power calculation. Initially, a stationary probe-holding fixture is designed and fabricated for sound intensity measurements. To enhance the fixture’s flexibility and the accuracy of the measurements, a transportable fixture is subsequently designed and fabricated. The necessary hardware and software settings for acoustic noise characterization are then developed. Finally, the setup is used to conduct acoustic noise characterization of an IPM motor, validating the application of the transportable probe-holding fixture.

For some sound sources, the function of the square of sound pressure amplitudes on the sphere in the far field is an integrable function or can be integrated with geometrical simplifications, so an exact or approximated analytical expression for the sound power can be calculated. However, often the sound pressure on the sphere in the far field can only be defined in discrete points, for which a numerical integration is required for the calculation of the sound power. In this paper, two new algorithms, Anchored Radially Projected Integration on Spherical Triangles (ARPIST) and Spherical Quadrature Radial Basis Function (SQRBF), for surface numerical integration are used to calculate the sound power from the sound pressures on the sphere surface in the far field, and their solutions are compared with the analytical and the finite element method solution. If function values are available at any location on a sphere, ARPIST has a greater accuracy and stability than SQRBF while being faster and easier to implement. If function values are available only at user-prescribed locations, SQRBF can directly calculate weights while ARPIST needs data interpolation to obtain function values at predefined node locations, which reduces the accuracy and increases the calculation time. [ABSTRACT FROM AUTHOR]

For some sound sources, the function of the square of sound pressure amplitudes on the sphere in the far field is an integrable function or can be integrated with geometrical simplifications, so an exact or approximated analytical expression for the sound power can be calculated. However, often the sound pressure on the sphere in the far field can only be defined in discrete points, for which a numerical integration is required for the calculation of the sound power. In this paper, two new algorithms, Anchored Radially Projected Integration on Spherical Triangles (ARPIST) and Spherical Quadrature Radial Basis Function (SQRBF), for surface numerical integration are used to calculate the sound power from the sound pressures on the sphere surface in the far field, and their solutions are compared with the analytical and the finite element method solution. If function values are available at any location on a sphere, ARPIST has a greater accuracy and stability than SQRBF while being faster and easier to implement. If function values are available only at user-prescribed locations, SQRBF can directly calculate weights while ARPIST needs data interpolation to obtain function values at predefined node locations, which reduces the accuracy and increases the calculation time.

Sound power estimation is a widely investigated research topic. Some of its state-of-the-art measurement solutions include taking velocity values on the source boundary, discrete pressure assessment on a virtual outer surface or evaluations with a sound intensity probe. The increased availability of microphone arrays proposes a new tool to obtain these results. The inverse boundary element method, the equivalent source method, the Helmholtz equation least-squares, and an approach based on the radiation resistance matrix provide vectorized formulations for estimating sound power. In this study, the results for different regularization techniques on the sound power deviation from a discrete line source are presented based on a backward reconstruction scheme from simulated sound pressure field points on four microphone arrays. Additionally, in this study, time improvement between single-frequency calculations and multi-frequency execution on multiple graphics processing units is presented. The outcome shows good accuracy and reduced computation time in graphics card implementations. [ABSTRACT FROM AUTHOR]

Wheel polygon amplitude can greatly affect wheel-rail vibration and sound radiation. Based on multi-body dynamics theory, a vehicle-track rigid-flexible coupling dynamics model was established. According to the actual running wear condition of the wheel, the wheel-rail vibration response was calculated and analyzed (the order of wheel polygons is 20, and the polygon amplitude is 0.01/0.02/0.03/0.04 mm, respectively). Together with the finite element/boundary model of the wheel, the calculated wheel-rail force was used as an external incentive to analyze the effects of polygon amplitude on the time-frequency domain of wheel noise. The research results show that: when the polygon order is 20, with the increase of polygon amplitude, the wheel-rail vertical force and the acceleration of wheel, rail and track slab increase gradually. It's also found that the rail acceleration is obviously more sensitive to the amplitude than the track slab acceleration, while the vertical displacement of the rail and track slab is less sensitive to the polygon amplitude. At the same amplitude, the closer to the wheel rolling line, the more obvious the sound pressure decreases with the increase of height. At different amplitudes, the sound pressure at different positions will increase with the rise of the polygon amplitude. The root mean square value of sound power increases gradually with the addition of amplitude: When the amplitude changes from 0.01 mm to 0.04 mm, the calculated sound power increases by 4.1 dB. [ABSTRACT FROM AUTHOR]

Consider that the sound dipole source in the flow field is composed of multiple micro-spherical oscillating sources. An aerodynamic sound source identification method is established by the relationship among the oscillating source, the radiated sound pressure, and the pressure gradient of flow in the near-wall flow field, and the formula for calculating the sound power of the sound dipole source in unsteady flow is derived. It shows that the power of sound dipole sources is proportional to the square of the oscillating force or pressure gradient. The combination of the formula and CFD method is further applied to the flow around the cylinder, which clearly presents the sound power and location characteristics of sound dipole sources. Further, the relationship between the sound source and the flow separation, or flow vortex shedding, is analyzed. The corresponding correlation analysis is also carried out, which indicates that the sound dipole source exists in a finite area of the attached wall. The front end of the area is at the separation point along the circumferential direction of the wall, and the end is at the location where the separation vortex completely falls off and a trailing vortex begins to form. In addition, the thickness of the area exists along the radial direction and gradually increases backward. [ABSTRACT FROM AUTHOR]

Technological operations of drilling holes are performed on drilling machines. Experimental studies conducted for these types of machines and carried out at machine operators’ workplaces have shown that even at idle, sound pressure levels exceed sanitary standards by 5 - 9 dB in the mid-frequency part of the spectrum. Since during processing the cutting tool goes deeper into the part and the length of the spindle overhang increases, which is significantly greater than the length of the cutting tool. The presented results of theoretical studies make it possible to determine the levels of the spectral components of acoustic characteristics by calculation at the design stage of the corresponding drilling technological processes.

The numerically efficient solution describing the sound radiation from a circular source located in a flat, rigid baffle is obtained. For this purpose, a half-space was divided into two subregions coupled through continuity equations. The Helmholtz equation was solved in both subregions. The proposed method can be used for circular baffled sources in the case when fluid–structure interactions are included, as well as for an input from a waveguide or cavity. The validity and numerical efficiency of the presented solution were tested assuming that a clamped circular plate is a source. The numerical simulations show that the results given by the proposed method agree with those given by the known integral solution. The exceptions are the field points at which the integral formulas fail and provide incorrect values of the sound pressure. Hence, the presented formulas can be the only method to perform accurate calculations at troublesome field points. The numerical efficiencies of the obtained formulas and integral ones were compared by estimating the value of the appropriate time ratios. The numerical analysis shows that the proposed method can be used to significantly improve calculations of the sound power and the sound pressure. • Improvement in calculations of the sound pressure and the sound power. • Formulas to efficiently calculate the sound field from a baffled circular source. • Proposed formulas versus the known integral solution. [ABSTRACT FROM AUTHOR]

This study investigates Active Structural Acoustic Control (ASAC) applied to sandwich plates featuring Functionally Grade (FG) porous Graphene-Platelet-Reinforced Piezoelectric (GPLRP) materials. These plates incorporate a core layer with internal pores and GPLs dispersed in a metal matrix, along with piezoelectric sensors and actuators. Using a spatial state-space formulation based on linear 3D piezoelasticity theory, a semi-analytical solution is derived for the vibroacoustic response of these sandwich plates. The mechanical properties of the porous core are modeled using a closed-cell metal foam. The effects of various parameters, including porosity distributions, porosity coefficient, weight fractions of nanofiller, and geometric parameters on the radiation efficiency and radiated sound power have been investigated. Then, the validation of the proposed model is examined by comparing the natural frequencies calculated in the present study to those from the literature. This comparison allows us to assess the accuracy and reliability of our model against established findings. Radiated sound power reduction from mechanically excited structures is achieved by employing a dual-stage Proportional Integral–Proportional Derivative with Filter (PI-PDF) controller, optimized using Grey Wolf Optimization (GWO). Finally, several numerical simulations are conducted to validate the effectiveness and accuracy of the proposed active control strategy. [ABSTRACT FROM AUTHOR]

The acoustic description of an industrial machine is crucial as it can provide information about its health status and assess the effectiveness of design modifications. Experimental acoustical measurements exist, but they may be impractical in noisy environments and limited by spatial requirements. Vibration-based approaches have been explored to overcome these limitations. However, the experimental procedure requires a large number of sensors. The aim of this work is to introduce a novel method which, starting from the vibration-based procedure, allows to reduce the number of sensors required to accurately estimate the sound power. An analysis of the number and the position of the accelerometers has been conducted to find the positions that better fit the resulting vibration-based sound power. An experimental campaign on a system consisting of a worm gear gearbox driven by an electrical motor has been used as a case study to verify the accuracy of the procedure. Acoustical based measurements were conducted and used as reference. Thus, starting from the data of twenty-seven accelerometers, the improved procedure was performed. The results will be plotted considering two and four accelerometers as input data and four operational conditions. The resulting vibration-based sound power levels demonstrate a good agreement in both octave bands and overall values. Furthermore, the trend of the radiation factor was investigated, aiming to determine the influence of parameters such as resistant torque and rotational velocity. • Experimental vibration-based procedure to evaluate the sound power of a complex geometry. • Definition of a procedure to reduce the number of required accelerometers for the vibration-based procedure. • Application of the optimization procedure in a variety of real-case scenarios. • Radiation efficiency assessment on a gearbox, employing both vibration-based and acoustical-based sound power levels. • Study on the influence of the velocity and the resistant torque on the resulting radiation efficiency. [ABSTRACT FROM AUTHOR]

The influence of acoustic radiation is considered in the prediction of noise attenuation effect of sound barrier, which provides a theoretical reference for further improving the insertion loss of sound barrier. Based on the theory of thin plate vibration, the vibration mode and natural frequencies of sound barrier under arbitrary boundary conditions are established by using two-dimensional beam function method, and the forced vibration response of the sound barrier is calculated based on the modal superposition method. MATLAB software (MathWorks Company, Natick, Massachusetts, USA) is used to calculate the natural frequencies and the radiated sound power level of the sound barrier, which indicated that the sound radiation caused by external excitation would significantly increase the sound pressure level at the received point, which should be considered as one of the influencing factors in the prediction of noise attenuation effect. The influence of diverse structural parameters on the radiated acoustic power is compared, providing an excellent reference for the design of sound barrier with low noise.

In many engineering challenges, the whole interaction between the structural domain and the acoustic domain must be taken into account, particularly for the acoustic analysis of thin structures submerged in water. The fast multipole boundary element approach is used in this work to simulate the external acoustic domain and the finite element method is used to describe the structural components. To improve coupling analysis accuracy, discontinuous higher-order boundary components are created for the acoustic domain. The isogeometric boundary element method (IGABEM) discretizes unknown physical fields by using CAD spline functions as basis functions. IGABEM is inherently compatible with CAD and can perform numerical analysis on CAD models without having to go through the time-consuming meshing process required by traditional FEM/BEM and volume parameterization in isogeometric finite element methods. IGABEM’s power in tackling infinite domain issues and combining CAD and numerical analysis is fully used when it is applied to structural form optimization of three-dimensional external acoustic problems. The structural-acoustic design and optimization procedures benefit from the use of structural-acoustic design sensitivity analysis because it may provide information on how design factors affect radiated acoustic performance. This paper provides adjoint operator-based equations for sound power sensitivity on structural surfaces and direct differentiation-based equations for sound power sensitivity on arbitrary closed surfaces surrounding the radiator. Numerical illustrations are provided to show the precision and viability of the suggested approach.

Consider that the sound dipole source in the flow field is composed of multiple micro-spherical oscillating sources. An aerodynamic sound source identification method is established by the relationship among the oscillating source, the radiated sound pressure, and the pressure gradient of flow in the near-wall flow field, and the formula for calculating the sound power of the sound dipole source in unsteady flow is derived. It shows that the power of sound dipole sources is proportional to the square of the oscillating force or pressure gradient. The combination of the formula and CFD method is further applied to the flow around the cylinder, which clearly presents the sound power and location characteristics of sound dipole sources. Further, the relationship between the sound source and the flow separation, or flow vortex shedding, is analyzed. The corresponding correlation analysis is also carried out, which indicates that the sound dipole source exists in a finite area of the attached wall. The front end of the area is at the separation point along the circumferential direction of the wall, and the end is at the location where the separation vortex completely falls off and a trailing vortex begins to form. In addition, the thickness of the area exists along the radial direction and gradually increases backward.

Abstract Noise prediction from streamlined bodies such as wind turbine blades can be predicted accurately using CFD computations that use spatio-temporal turbulence models at the expense of high computational power. In this work, empirical methods proposed from BPM, Grosveld and Lowson are used to compute numerically to analyse the influence of rotor solidity factor on broadband trailing edge noise from a 2 MW horizontal axis wind turbine with a blade length of 37 m. Inputs to acoustic solver are the velocity vector field and boundary layer data which are obtained using blade element momentum and X-Foil. The outputs from acoustic solver are directivity and far field sound pressure on a receiver located at distance of 120 m from tower base. The results have shown that for a wind speed of 10 m/s measured at 10 m above ground, sound power level was found to increase between mid-bands to high frequencies for all three methods. Rotor solidity effect was illustrated at constant rotational speed of 17 RPM and receiver height of 0.5 m located in downwind position. A minimum difference of 1.5dBA was found at f ~ 100 Hz for Lowson method and maximum of ~ 2.8dBA at 1 kHz between two and three blade rotor. For BPM and Grosveld methods however, the sound levels were ~ 5dBA lower for two blade rotor than three blade rotor between f ~ 100 Hz and f ~ 1 kHz. The study also demonstrated that as number of blades increase by integral multiples, the effect on noise radiation from trailing edge of blades increase by 2-5dBA due to amplitude modulation.

• The small axial fans were 3D printed and tested according to ISO 5136 and ISO 5801. • Psychoacoustic metrics were compared under design and free discharge conditions. • Loudness, roughness and tonality showed the greatest impact on noise annoyance. • Individual modifications are not sufficient to reduce broadband noise. • A holistic, noise reduction strategy in the design of small axial fans is needed. This paper presents a comprehensive experimental investigation of a basic axial fan and its various modifications. The fan blades were designed according to recommendations from the literature. The prototypes were 3D printed and tested under different operating conditions in accordance with the ISO 5136 and ISO 5801 standards. The aim of the study was to investigate the effects of the axial fan design on the characteristic curve and on the acoustic and psychoacoustic properties of the emitted sound. The characteristic curves were influenced by geometrical features that can lead to obstruction of the flow. The A-weighted sound power level spectra showed that low-frequency (subharmonic) noise humps can be effectively reduced by modifications near the fan hub, while tonal noise in the mid-frequency range can be mitigated by blade root enlargement, small wing tips and low-amplitude edge serrations. The tonal noise was greatly affected by the addition of tip flanges and rotating shrouds, but these modifications reduced the high frequency noise. The psychoacoustic evaluation showed a higher sensitivity to the characteristics of the emitted noise compared to conventional A-weighted one-third octave spectra. While all modifications led to changes in psychoacoustic metrics, loudness, roughness and tonality showed the greatest variability and influence on psychoacoustic annoyance, while sharpness and fluctuation strength were less affected by the different modifications. The results presented emphasize the complex interplay between geometry, aerodynamics, acoustics and psychoacoustics in small axial fans and highlight the need for holistic approaches to fan design in order to solve noise-related problems. The 3D printed machines had similar energy and acoustic characteristics as traditionally manufactured fans, so the use of additive manufacturing techniques proved to be a cost-effective and practical step in the fan design process that could be easily implemented. [ABSTRACT FROM AUTHOR]

Damage to the running surfaces of wheels on railways poses a threat to road safety. They can lead to accidents and disasters. Wheels with a flat spot are the biggest threat. The paper reviews problems that arise when wheels with a flat spot come into contact with a rail, and the methods of their detection and diagnosis. However, the known methods for their determination are still very complex and not precise enough. The research presented is based on previous theoretical studies, during which a simplified mathematical model of the normal force arising from the contact of a wheel with a flat spot with a rail, assuming that as a result of this, a change in sound power is caused was developed and theoretical calculations were performed. It theoretically determined wheel damage during rolling caused by wheel-induced changes in associated sound power, i.e., preliminary values of diagnostic parameters and applied methods. Although initial theoretical research already exists, there was a lack of physical experiments to support the validity of the results of the theoretical model. This work presents the original plan and methodology of the physical experiment performed. A physical experiment performed with the ATLAS LG system and sound pressure measuring equipment showed the suitability and applicability of the theoretical model for the determination of wheel damage. [ABSTRACT FROM AUTHOR]

Objective: To analysis of the therapeutic effect of different sound power focused ultrasound on pancreatic cancer in different periods. The patients with pancreatic cancer were divided into low-power group and high-power group. The treatment power of low-power group is 100～249 W, and the treatment power of high-power group is 250~350 W. The therapeutic effect was eval- uated using pain relief effect, tumor necrosis volume and volume ablation rate, VEGF and HGF levels, complications and survival time. The total effective rate of low power is 97.5 %, the total effective rate of high power group is 92.5 %, there is no significant difference between the two groups (P>0.05). Pancreatic cancer tumors of all patients showed varying degrees of necrosis, and the volume of the necrotic area gradually reduced within 1 to 3 months, which showed that the enhancement scan had no enhancement, and there was a ring-shaped enhancement zone around the tumor; The tumor volume ablation rate in the stage III-IV patients in the high-power group was significantly higher than the low-power group (P<0.05). Compared with before treatment, the levels of VEGF and HGF in patients in low-power group and high-power group III to IV stage were significantly decreased. Compared with the low-power group, the levels of VEGF and HGF in the high-power group in each period decreased more significantly (P<0.05). The incidence of complications in the high-power group and the low-dose group were 12.5 % and 15.0 %, respectively, and there was no statistical difference (P>0.05) after comparison. After treatment, the median survival time of patients in the low-power group was 6.37± 1.13 months, and the median sur- vival time of patients in the high-power group was 6.72± 1.34 months. There was no significant difference (P>0.05). Differ- ent sound power focused ultrasound ablation has better efficacy in treating pancreatic cancer in different periods, reducing patients' pain, prolonging the median survival time, and having better safety. [ABSTRACT FROM AUTHOR]

Since the determination of room acoustic parameters are requesting the sound power of the sound source. Few trials to publish the way of calibration and uncertainty estimation in details for the reference sound source were performed. So, it is very interesting to find a way to calibrate the reference sound source that can be used in different acoustic measurements. Also, there is a need to find the value uncertainty of due to the calibration of reference sound source. Sound power level of any sound source can be determined by means of sound pressure level measurements performed in accordance to relevant ISO standards. The calibration of reference sound source according to ISO 6926 may be implemented in a hemianechoic or reverberation room. The method and way of sound power calculations which may depend on number of microphones, their positions and place of measurements stated. Measurements of sound pressure level, reverberation time and background noise level were performed using traceable instruments by direct method in ISO3741. Then the calculation of sound power level in 1/3 octave band frequency was carried out for the reference sound source side by side with uncertainty contributions resulting from measurements. The values of uncertainty σR0 σomc respectively are in order of magnitude of 0.4 and 0.07 dB. The total uncertainty lies within the range of 0.7-1.0dB in the 1/3 octave band frequency from 125Hz to 10000Hz. [ABSTRACT FROM AUTHOR]

Noise prediction from streamlined bodies such as wind turbine blades can be predicted accurately using CFD computations that use spatio-temporal turbulence models at the expense of high computational power. In this work, empirical methods proposed from BPM, Grosveld and Lowson are used to compute numerically to analyse the influence of rotor solidity factor on broadband trailing edge noise from a 2 MW horizontal axis wind turbine with a blade length of 37 m. Inputs to acoustic solver are the velocity vector field and boundary layer data which are obtained using blade element momentum and X-Foil. The outputs from acoustic solver are directivity and far field sound pressure on a receiver located at distance of 120 m from tower base. The results have shown that for a wind speed of 10 m/s measured at 10 m above ground, sound power level was found to increase between mid-bands to high frequencies for all three methods. Rotor solidity effect was illustrated at constant rotational speed of 17 RPM and receiver height of 0.5 m located in downwind position. A minimum difference of 1.5dBA was found at f ~ 100 Hz for Lowson method and maximum of ~ 2.8dBA at 1 kHz between two and three blade rotor. For BPM and Grosveld methods however, the sound levels were ~ 5dBA lower for two blade rotor than three blade rotor between f ~ 100 Hz and f ~ 1 kHz. The study also demonstrated that as number of blades increase by integral multiples, the effect on noise radiation from trailing edge of blades increase by 2-5dBA due to amplitude modulation. [ABSTRACT FROM AUTHOR]

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Trailing edge surface of aerofoil is an important source of broadband aerodynamic noise production. In this paper, three aerofoil self-noise mechanisms from turbulent boundary layer near trailing edge surface are studied. Numerical computations were performed for a three bladed 2 MW horizontal axis upwind turbine of blade length 37 m and source height of 80 m, for wind speeds of 8-15 m/s. A weighted 1/3rd octave band sound power levels (SPL) are evaluated for receiver located at distance of total turbine height and at 2 m above ground. The results obtained for sound power level using baseline models showed maximum values occurring between 300 Hz and 1 kHz region of spectrum. The trends for BPM model showed a reduction of ~2 dBA near 1 kHz region of spectrum at 10 m/s, but Grosveld’s and Lowson model were identical and agreed over the entire spectrum. The effect of rotational speed on sound power levels using three baseline models are illustrated at a wind speed of 8 m/s for 2 MW turbine. Results showed that for a change of ±10% rotor speed from the rated value, there is an increase of 2 to 6 dBA over the entire sound spectrum due to differences in blade tip speed.

Abstract Tyre/road sound emissions have been proved to be the main source of noise caused by road traffic when traveling at medium and high speeds (Sandberg and Ejsmont, 2002). Tyre/road noise has been widely studied among the last decades. However, an important part of this research has been focused, mainly, on track tests. Different track or road methods have been developed for measurement of tyre/road sound emissions. The most important ones are the Coast-By, the Close-Proximity, the Statistical Pass-By or the Controlled Pass-By methods. Among all of them, the Coast-By method has been raised in Europe as standard method concerning the approval of tyres with regard to tyre/road sound emissions as preconized in UNECE Regulation 117 (2007)[2]. However, all the above mentioned methods have several disadvantages such as the influence of environmental factors, the different results that can be obtained depending on the test track or the vehicle upon which the tests are carried out, the lack of repeatability or, the most important aspect, which is the limitation of the measured magnitude, the sound pressure level. A new methodology (Clar-Garcia et al., 2016) based on drum tests and the ISO 3744 (1994), which was developed in order to avoid these limitations, has been proved to be comparable to the Coast-By (CB) method. This paper describes how different tyres have been tested according to both the CB and the new Alternative Drum test method (A-DR) while their results have been compared. In order to be able to carry out this comparison, as the measured magnitudes and test conditions differ widely from one test to another, the standardised ISO 9613 sound propagation method (ISO 9613-2, 1996) has been applied to obtain the sound pressure value at 7.5 m from the sound power level of a tyre measured under laboratory-controlled conditions when rolling against a drum. Results have shown that both methods are not only comparable but also have remarkably similar sound spectra and, for that reason, the new methodology based on drum tests can be used in order to obtain tyre/road noise emission approved values. [ABSTRACT FROM AUTHOR]

Trailing edge surface of aerofoil is an important source of broadband aerodynamic noise production. In this paper, three aerofoil self-noise mechanisms from turbulent boundary layer near trailing edge surface are studied. Numerical computations were performed for a three bladed 2 MW horizontal axis upwind turbine of blade length 37 m and source height of 80 m, for wind speeds of 8-15 m/s. A weighted 1/3rd octave band sound power levels (SPL) are evaluated for receiver located at distance of total turbine height and at 2 m above ground. The results obtained for sound power level using baseline models showed maximum values occurring between 300 Hz and 1 kHz region of spectrum. The trends for BPM model showed a reduction of ~2 dBA near 1 kHz region of spectrum at 10 m/s, but Grosveld's and Lowson model were identical and agreed over the entire spectrum. The effect of rotational speed on sound power levels using three baseline models are illustrated at a wind speed of 8 m/s for 2 MW turbine. Results showed that for a change of ±10% rotor speed from the rated value, there is an increase of 2 to 6 dBA over the entire sound spectrum due to differences in blade tip speed. [ABSTRACT FROM AUTHOR]