Krister Larsson

A (10,3)-b net by sulfate hydrogen-bonded biimidazolate complexes

The synthesis and crystal structure of Δ-[Cr(Hbiim)(H2biim)2]SO4·H2O (H2biim = biimidazole) are presented. A network is formed by sligthly distorted Δ-[Cr(Hbiim)(H2biim)2]2+ octahedra triple bridged by sulfate anions to give a (10,3)-b net. The final structure is given by three such interpenetrating nets, all with the same chirality on chromium. It is shown that the same net and interpenetration occur in [Fe(H2biim)3]CO3·MeOH.

Modeling of tangential contact forces

The main noise source from vehicles at speeds greater than 50 km/h is the tires. To reduce traffic noise it is therefore necessary to understand the noise generation mechanisms in the contact between tire and road. The paper presents an improvement of an earlier developed acoustic rolling model concerning a smooth tire rolling on a rough surface. This model consists of three steps. First, the radial contact forces between road and tire are calculated. These forces give the vibrations of the tire, which finally give the sound radiation from the tire. A method to include the tangential forces into the rolling model is the topic of this paper. To do this, the influence of the tread blocks on the force transmission from the road to the belt of the tire has to be known. A FEM‐model of one tread block is made in order to determine its dynamical properties. A simplified model of the block is established, by only taking into account the two lowest modes in the frequency range of interest (i.e., up to 3 kHz). This...

The influence of belt and tread band stiffness on the tire noise generation mechanisms

A brief introduction to a theoretical model is presented which describes a smooth tire rolling on a rough road surface. The model is limited to a two‐dimensional contact between tire and road. It includes the vibration properties of the tire, the nonlinear contact, and the sound radiation. It is also taking into account the influence of the acoustic properties of the road surface. The model is applied to determine the sound radiated due to the tire vibrations and the local deformations of the tread band. A parameter study is presented which shows the influence of the bending stiffness of the belt and the stiffness of the tread band on the noise generation and radiation mechanisms. The study also considers the influence of the surface roughness of the road. In this way it is possible to quantify which part of the roughness spectrum is leading to sound generation via tire vibration and which part of the roughness spectrum is involved in the local deformation of the tread band.

Social benefit analysis of reduced noise from electrical city buses in Gothenburg

The city of Gothenburg is the second largest city in Sweden and has an ambitious traffic strategy to increase the share of public transport substantially until 2035. At the same time the city is growing due to urbanization and the densification of the city leads to an anticipated growth in city bus traffic. However, noise from buses might lead to negative consequences for the citizens and electrical buses could be a way to reduce noise and emissions from the public transport system. In this study a comparison of noise levels and social costs of bus types with different powertrains are presented. Initially, noise emissions from three bus types were measured on a test track. The propulsion noise was extracted and coefficients for the Nord2000 Road prediction model were adapted. The Nord2000 model was used to calculate facade noise levels in the city center, as well as in a smaller focus area. The predicted noise levels were used to calculate health effects according to DALYs, as well as social costs according to ASEK. In addition, indoor maximum noise levels were calculated for typical facade cases based on the measurements. The results show that the largest benefits from electrical buses are obtained during acceleration, for example, at bus stops, and for maximum levels indoors. However, these situations are not taken appropriately into account in current social cost models.The city of Gothenburg is the second largest city in Sweden and has an ambitious traffic strategy to increase the share of public transport substantially until 2035. At the same time the city is growing due to urbanization and the densification of the city leads to an anticipated growth in city bus traffic. However, noise from buses might lead to negative consequences for the citizens and electrical buses could be a way to reduce noise and emissions from the public transport system. In this study a comparison of noise levels and social costs of bus types with different powertrains are presented. Initially, noise emissions from three bus types were measured on a test track. The propulsion noise was extracted and coefficients for the Nord2000 Road prediction model were adapted. The Nord2000 model was used to calculate facade noise levels in the city center, as well as in a smaller focus area. The predicted noise levels were used to calculate health effects according to DALYs, as well as social costs accordi...

On the uncertainty of measurement of dynamic stiffness of resilient materials

The apparent dynamic stiffness of resilient materials used for example under floating floors is measured according to the standard ISO 9052-1:1989 (EN 29052-1:1992). Basically, the material under test is loaded by a load plate corresponding to 200 kg/m2 and the resonance frequency of the first vertical mode of the mass-spring system formed by the load plate and the resilient material under test is determined. The resonance frequency then gives the dynamic stiffness. The standard allows for several excitation techniques such as swept sine, continuous noise, or impact excitation. Additionally, vibration excitation at the base as well as force excitation on the load plate is allowed. In this study, the uncertainty because of excitation of multiple vibration modes is investigated in detail. A model for the load plate on an elastic foundation representing the test setup is developed. The model is verified towards measurements and a parameter study is performed. The results show that additional modes may be exc...

Revision of the Swedish sound classification scheme for premises

The Swedish building code puts requirements on noise protection in new buildings. For residential buildings, minimum requirements are given directly in the building code, and demands for better acoustic quality are given in a sound classing scheme according to the Swedish Standard SS 25267, which has been revised in 2015. For premises, such as offices, schools, or hotels, the building code does not contain specific quantified minimum requirements on the acoustic properties, but refer instead to the sound classing standard SS 25268 for tabulated values. Sound class C corresponds to the minimum requirements for new buildings, and demands for better acoustic quality are given according to class B or class A. The sound classing standard for premises, SS 25268, is currently under revision, and during the last years, the needs for changes and updates have been collected in cooperation with stakeholders and experts. The paper presents the motivations for the revision and the status of the work. Ideas for major r...

Case-study evaluation of a combined noise barrier and solar panel in an urban area

The LIFE + project NOISUN, concluded in February 2016, had as main objective to demonstrate an innovative noise barrier that produces solar energy for distribution to local district heating systems. Specially adapted solar collectors were installed at a major transport thoroughfare for both road (the E20 motorway) and railway traffic in the Swedish municipality of Lerum, and the effect of the intervention was evaluated in several ways. In the beginning of the project, calculations of expected noise mitigation were performed. Before and after the noise barrier was erected two actions were performed: Questionnaires were sent out to concerned households, and sound level measurements were performed in combination with recordings of noise events. The insertion loss of the noise barrier showed to be very close to the estimations. The noise reduction was most pronounced for loud train pass-bys but not as much for road traffic noise from the E20 motorway (also, contributions from other streets made the room for r...

Application of LMS Algorithm to Measure Low-Frequency Transient Forces from Human Walking

Measurement and modeling of low frequency ground reaction forces (GRFs) from human walking have been the subjects of research in different fields from biomechanics to civil engineering and structural dynamics. Many of the existing models are developed based on experiments which alter natural walking by for example presence of force transducers, limitations in the speed and path of walking and replacing the real floor with a transducerfacilitated measurement rig. These alterations result in contact forces which do not represent real GRFs. In this study, a time-domain inverse measurement method based on LMS algorithm is used to measure low-frequency (<100 Hz) forces induced by human footsteps. The LMS-based force identification method is first validated for low-frequency excitations with less complexity in number of excitation positions and frequency content compared with the footsteps. The method is then applied to measure ground reaction forces created by human walking.

Identification of Low-Frequency Forces Induced by Footsteps on Lightweight Floors

Despite many advantages of wooden buildings, low-frequency noise disturbance, mainly from human footsteps on timber floors, is a major hindrance for widespread application of wood in multi-storey buildings. In many cases the impact noise evaluations of the wooden floors according to ISO 140-7 and ISO 717-2 standards do not correspond to subjective experiences. This study aims to investigate the characteristics of footstep forces to support further studies related to discrepancies between standard evaluations and low-frequency noise disturbances in lightweight buildings. Transient footstep forces in vertical direction made by different walkers and different footwear on two floor structures were measured and compared. The vertical footstep forces were then compared with the impact forces made by a standard tapping machine. Analysis revealed that footstep forces contain large amplitudes at low frequencies (20 < f < 50) which are not included in the standard evaluation procedure. Therefore, by extending the frequency range of the standard measurements down to 20 Hz and designing an accurate adaptation term for evaluations, a better correlation between standard impact noise evaluations and acoustic performance of the lightweight buildings might be achieved.

Time-Domain Modelling: Combining ESM and a Finite-Difference Method for Thermoacoustic Devices

Thermoacoustic devices are today mainly simulated using frequency-domain methods. Contrary to frequency-domain methods, time-domain methods may include non-linear effects and time-varying boundary conditions. However, time-domain modelling of thermoacoustic devices is computationally expensive, due to large differences in geometric length scales and time scales. The primary aim of this paper has been to model thermoacoustic devices with computational efficiency by using two different methods. The acoustic field outside the stack, based on the assumption of plane waves, is modelled using the efficient Equivalent Source Method (ESM), whereas the complex acoustic field in the stack is modelled using a finite-difference model. In a previous paper of the authors, ESM and a finite-difference model have been combined to model acoustic wave propagation, though thermal effects and heat flow to the stack plate were excluded. In this paper, however, these effects are included. The performance of the model is studied and compared to linear thermoacoustic theory. The proposed model may provide a useful tool for studying time-varying acoustic fields and temperature distributions in thermoacoustic devices.