Sound absorption of porous structures:a design tool for road surfaces

The sound radiation caused by tyre/road noise can be reduced significantly by the use of porous road surfaces. A hybrid analytical/numerical modelling approach has been developed to predict the sound absorption coefficient of such road surfaces. Furthermore, the modelling approach has been used as a design tool to optimise the sound absorption of porous road surfaces in the design phase. Using this design tool, two porous surfaces have been developed and constructed at a special test area. These road surfaces have been measured extensively for both sound absorption and for noise radiation in combination with different tyres. This research is carried out within the project `Silent and Safe Road Traffic'. The goal of this project was to find methods and measures to reduce the noise from tyre/road interaction while ensuring (wet) grip. The developed hybrid analytical/numerical modelling approach is based on the combination of the solutions of two subsystems: an analytically described background sound field and a numerically solved scattered sound field describing the scattering of the sound waves on the (assumed rigid) porous structure. Furthermore, the sound absorption caused by viscothermal effects inside the air-filled pores is included analytically in the modelling approach. Also, the sound absorption coefficient for oblique incidence can be predicted using this modelling approach. This is an important property when considering tyre/road noise, since most traffic noise is received at oblique incidence. Therefore, the sound absorption for oblique incidence should be considered when predicting the noise reduction by porous road surfaces. The main advantage of the developed hybrid modelling approach compared to a full numerical model is the low computation time, because (1) no mesh refinement is needed for the mesh of the structure inside the air-filled pores, since the viscothermal effects inside the pores are included analytically, and (2) the air domain surrounding the structure can be relatively small, since the scattering problem is localised around the porous structure and the background sound field is included analytically. In addition, the developed modelling approach can be applied to predict the sound absorption for any three-dimensional porous structure. The work presented here focuses on structures of tube resonators and on granular structures. Both types of porous structures are used for the validation of the modelling approach. For normal incidence, the modelling approach is validated using the impedance tube technique. The correlation between the measured sound absorption coefficient and the predicted sound absorption coefficient was extremely good for both the tube resonators and structures of stacked glass marbles. To validate the modelling approach for oblique incidence, a large sound hard box filled with glass marbles was measured using a small cubic microphone array. This validation was more complex, since the measurement technique introduced various uncertainties. However, the model results and measurement results showed good correlation. Furthermore, the developed modelling approach was adjusted in such a way that structures made from sound absorbing materials can be modelled as well. To demonstrate this, a structure of coupled tube resonators has been designed and manufactured with the 3D printing technique, an upcoming technique suitable for manufacturing complex sound reducing panels. The measured sound absorption coefficient of this sample showed an influence of the material properties on the sound absorption coefficient, which could be predicted fairly well with the adjusted modelling approach

Prediction of Sound Absorption of Stacked Granular Materials for Normal and Oblique Incident Sound Waves

Tire-road noise is a problem in many (densely) populated areas. It can be significantly reduced by using porous asphalt concrete. A challenge is to develop porous asphalt concrete, such that the most dominant frequencies in tire-road noise will be absorbed by the road surface. It is especially important to also reduce and absorb oblique incident sound waves, since tires radiate noise normal to the tire surface, which means oblique incident waves on the road surface. Predicting the behavior of porous asphalt concrete using models is complex, especially when non-local effects and scattering effects are included. The objective of this paper is to show a modeling approach to predict sound absorption for oblique incident waves in three-dimensional porous materials. Using this method, one is able to predict the sound absorption of porous road surfaces in the design phase. This modeling approach includes a two-step approach in which first the viscothermal energy dissipation inside the pores between the rigid materials (stones) are estimated and then, secondly, the non-local effects such as scattering on the st ones within the porous road surface are computed using a finite element model. The combination of both sound fields gives the total sound field in and above the three-dimensional porous material, which is used to determine the sound absorption coefficient. The analytical viscothermal and scattering solution are discussed in this paper and the modeling approach is validated with experiments using a box with stacked marbles for several angles of incidence

Prediction of sound absorption of stacked granular materials for normal and oblique incident sound waves

Tire-road noise is a problem in many (densely) populated areas. It can be significantly reduced by using porous asphalt concrete. A challenge is to develop porous asphalt concrete, such that the most dominant frequencies in tire-road noise will be absorbed by the road surface. It is especially important to also reduce and absorb oblique incident sound waves, since tires radiate noise normal to the tire surface, which means oblique incident waves on the road surface. Predicting the behavior of porous asphalt concrete using models is complex, especially when non-local effects and scattering effects are included. The objective of this paper is to show a modeling approach to predict sound absorption for oblique incident waves in three-dimensional porous materials. Using this method, one is able to predict the sound absorption of porous road surfaces in the design phase. This modeling approach includes a two-step approach in which first the viscothermal energy dissipation inside the pores between the rigid materials (stones) are estimated and then, secondly, the non-local effects such as scattering on the st ones within the porous road surface are computed using a finite element model. The combination of both sound fields gives the total sound field in and above the three-dimensional porous material, which is used to determine the sound absorption coefficient. The analytical viscothermal and scattering solution are discussed in this paper and the modeling approach is validated with experiments using a box with stacked marbles for several angles of incidence

Tyre-road noise measurements: influence of tyre tread and road characteristics

Traffic noise is a well known problem. For speeds above approximately 40 km/h the noise is mostly tyre-road noise. The noise level depends on the tyre, the road and the interaction between the tyre and the road. There are various well-known methods to measure tyre-road noise and in this paper the measurement results of CPX, impedance tube and road roughness measurements are combined to investigate the relation between the radiated noise and the tyre tread design and road characteristics. All measurements have taken place on a special test area at Airport Twente, where 8 different type of asphalt surfaces were constructed. Two these tracks are based on new models for sound absorption and grip. Six of the tracks are porous asphalt concrete. To investigate the relation between tyre tread design and the sound radiation, three simple parameters are defined based on properties that are commonly considered when researching the influence of tyre tread. However, the parameters defined in this paper are simplified, such that they can be applied when no detailed knowledge of the tyre properties is available. The relation between road characteristics and sound radiation is investigated using the properties of the road, such as stone size, porosity and sound absorption, and some texture parameters as defined by the International Organisation of Standardization (ISO). The correlation between the tyre and road parameters and the sound radiation is investigated, both for the root mean square values and the octave bands of 500 Hz, 1000 Hz and 2000 Hz. The results show that both the tyre parameters as the road characteristics, such as porosity of the road and the sound absorption by the road, are important for a decrease in sound radiation. The influence of the porosity of the road and the sound absorption by the road on the radiated sound is more significant for the frequencies in the octave band of 2000 Hz than the influence of the investigated tyre treads on the radiated sound. However, in the octave band of 1000 Hz, the influence of the tyre tread parameters on the sound radiation is larger. Furthermore, a relation is found between the radiated sound and the maximum stone sizes in the asphalt concrete. The measurements show a clear correlation between the sound absorption of the tested tracks and the radiated sound: for an increasing sound absorption coefficient the sound radiation decreases. Moreover, the total sound radiation decreases more when the sound absorption of higher frequencies is increased

Experimental validation of a modelling approach to predict sound absorption for porous asphalt roads

Tyre-road noise is a serious problem. One of the parameters to reduce the noise radiation is the sound absorption coefficient of the road, which is (partly) determined by properties such as the porosity of the road, the size and shape of the stones. In this study, a novel `hybrid' (analytical/numerical) model is used to predict the three-dimensional sound field in and above porous structures -- modelled as rigid granular structures -- and to predict the absorption coefficient for oblique incident sound waves. In this modelling approach, the air inside the pores of the structure is considered, including viscothermal effects in the pores and scattering of the sound waves due to the, assumed, rigid granular structure, representing the pavement. In this paper, the validation of the hybrid (analytical/numerical) modelling approach with impedance tube measurements for normal incident sound waves is described for two three-dimensional configurations. It is concluded that this novel hybrid modelling approach has been validated with good results for normal incident plane waves

Predicting Sound Absorption of Stacked Spheres: Combining an Analytical and Numerical Approach

Tire-road noise is a serious problem, but can be significantly reduced by the use of porous asphalt concrete. Here, the sound absorption of the porous asphalt concrete is important and can be predicted by ground impedance models. Yet, modeling porous asphalt concrete is complex, especially when nonlocal effects and scattering effects are considered. The objective of this research is to predict the sound absorption coefficient for a three-dimensional porous structure. The proposed solution is obtained using a novel modeling approach, in which the total solution of the sound field is found by combining the solutions of two subsystems: a background sound field and a scattered sound field. The background sound field contains the (analytical) solution of the sound field including the viscothermal energy dissipation inside the pores of the porous asphalt concrete. In the second subsystem, the (numerical) solution for the scattering on the rigid stone skeleton of the pavement is found. For both subsystems, we use a model containing two layers: an air layer and a viscous air layer with a certain granular structure. The main advantage of this modeling approach is the (relatively) low computation time. In this paper, the proposed modeling approach and the validation of this approach are described. The modeling approach is validated for normal incident plane waves absorbed and scattered by various structures of stacked marbles, using the impedance tube technique. This approach can be applied to predict the absorption coefficient of porous structures, like asphalt concrete roads. Moreover, it can be used as design tool to optimize the sound absorption of new road surfaces

Tyre tread pattern noise optimization by a coupled source-human perception model

The current tyre design process uses many experimental evaluations and it may take therefore more than 2 years to develop a tyre. The use of simulation tools improves and speeds up this process. Research has shown that the human perception of tyre tread pattern noise is mainly determined by the noise characteristics: level, tonalness and modulation (also called drumming). In this paper a new source model and human perception model is described. The source modelling approach predicts the correct trends of the three tyre tread pattern noise characteristics. From the noise characteristics dedicated Sound Quality Metrics are defined: for level the Standard Deviation (STD), for tonalness the Order Prominence (OP) and for modulation the Multi- Order Modulation (MOM). Using these Sound Quality Metrics the human perception model is obtained by regression analysis, predicting the human perception of tyre tread pattern noise correctly (R2=0.94). The coupled source - human perception model enables a very fast optimization of a complete tyre tread pattern design to human comfort

Reproducibility Project: Psychology

Reproducibility is a defining feature of science, but the extent to which it characterizes current research is unknown. We conducted replications of 100 experimental and correlational studies published in three psychology journals using high-powered designs and original materials when available