Measurement Campaign Research Articles

Rotaphone-D, A New Model of Six-Degree-of-Freedom Seismic Sensor: Description and Performance

Abstract A new model of the Rotaphone-D short-period seismic sensor with six degrees of freedom is introduced. The basis of the instrument is horizontal and vertical geophones in a special paired arrangement. The instrument is designed for simultaneous and collocated measurements of rotational and translational components of ground motion. The basic principle of measurement is briefly described. Careful calibration is necessary for this type of measurement, which has two parts: a preliminary calibration based on laboratory measurements of the characteristics of the individual geophones, and a subsequent in situ calibration, which takes into account the actual physical conditions during field measurements and is performed during the processing of the measured data. The effect of the calibration is demonstrated by specific laboratory tests. The laboratory tests have confirmed the correct functioning of the instrument. The frequency range of Rotaphone-D is from 2 to 80 Hz and is therefore optimal for monitoring local seismicity. The instrument was subsequently used in field measurements during two several-month measurement campaigns in California, United States. Examples of six-component records from two sites—The Geysers and Long Valley Caldera—are presented and briefly interpreted from a seismological perspective. Basic instrument parameters are given. The instrument is lightweight, portable, easy to install, and offers several interesting applications, which are briefly discussed. Six-component measurements (translational and rotational) have become a powerful tool, especially in volcanic seismology and in monitoring induced seismicity.

Influences of lidar scanning parameters on wind turbine wake retrievals in complex terrain

Abstract. Scanning lidars enable the collection of spatially distributed measurements of turbine wakes and the estimation of wake properties such as magnitude, extent, and trajectory. Lidar-based characterizations, however, may be subject to distortions due to the observational system. Distortions can arise from the resolution of the measurement points across the wake, the projection of the winds onto the beam, averaging along the beam probe volume, and intervening evolution of the flow over the scan duration. Using a large-eddy simulation and simulated measurements with a virtual lidar model, we assess how scanning lidar systems may influence the properties of the retrieved wake using a case study from the Perdigão campaign. We consider three lidars performing range-height indicator sweeps in complex terrain, based on the deployments of lidars from the Danish Technical University (DTU) and German Aerospace Center (DLR) at the Perdigão site. The unwaked flow, measured by the DTU lidar, is well-captured by the lidar, even without combining data into a multi-lidar retrieval. The two DLR lidars measure a waked transect from different downwind vantage points. In the region of the wake, the observation system reacts to the smaller spatial and temporal variations of the winds, allowing more significant observation distortions to arise. While the measurements largely capture the wake structure and trajectory over its 4–5 D extent, limited spatial resolution of measurement points and volume averaging lead to a quicker loss of the two lobes in the near wake, smearing of the vertical bounds of the wake (< 30 m), wake center displacements up to 10 m, and dampening of the maximum velocity deficit by up to a third. The virtual lidar tool, coupled with simulations, provides a means for assessing measurement capabilities in advance of measurement campaigns.

Galileo and BeiDou AltBOC Signals and Their Perspectives for Ionospheric TEC Studies.

For decades, GNSS code measurements were much noisier than phase ones, limiting their applicability to ionospheric total electron content (TEC) studies. Ultra-wideband AltBOC signals changed the situation. This study revisits the Galileo E5 and BeiDou B2 AltBOC signals and their potential applications in TEC estimation. We found that TEC noises are comparable for the single-frequency AltBOC phase-code combination and those of the dual-frequency legacy BPSK/QPSK phase combination, while single-frequency BPSK/QPSK TEC noises are much higher. A two-week high-rate measurement campaign at the ACRG receiver revealed a mean 100 sec TEC RMS (used as the noise proxy) of 0.26 TECU, 0.15 TECU, and 0.09 TECU for the BeiDou B2(a+b) AltBOC signal and satellite elevations 0-30°, 30-60°, and 60-90°, correspondingly, and 0.22 TECU, 0.14 TECU, and 0.09 TECU for the legacy B1/B3 dual-frequency phase combination. The Galileo E5(a+b) AltBOC signal corresponding values were 0.25 TECU, 0.14 TECU, and 0.09 TECU; for the legacy signals' phase combination, the values were 0.19 TECU, 0.13 TECU, and 0.08 TECU. The AltBOC (for both BeiDou and Galileo) SNR exceeds those of BPSK/QPSK by 7.5 dB-Hz in undisturbed conditions. Radio frequency interference (the 28 August 2022 and 9 May 2024 Solar Radio Burst events in our study) decreased the AltBOC SNR 5 dB-Hz more against QPSK SNR, but, due to the higher initial SNR, the threshold for the loss of the lock was never broken. Today, we have enough BeiDou and Galileo satellites that transmit AltBOC signals for a reliable single-frequency vTEC estimation. This study provides new insights and evidence for using Galileo and BeiDou AltBOC signals in high-precision ionospheric monitoring.

Characterization of maritime traffic noise in two areas of the Mediterranean

One of the objectives of the European JPI Oceans DeuteroNoise project is to investigate the soundscapes within different sea basins. Measurement campaigns, including the recording of raw noise data (wave files), have been carried out in the Venice Lagoon, in the North Adriatic and on Barcelona shore. In this work we will present the first results. The data acquired were processed to obtain the characteristic spectrum and noise levels; subsequently the velocity of the particles will be acquired and analysed. The analysis of the recorded data involves the design of a taxonomy of anthropogenic noise sources, e.g. large ships, small boats or any other existing noise source. The recorded data were labelled with these sources, describing their main audio characteristics (spectral distribution, temporal evolution, etc.) for their characterization and future blind identification. Throughout the measurement period, ship and route data were acquired using AIS (Automatic Identification System) and Vessel Monitoring System (VMS) in the measurement sites. The preliminary analysis and labelling, together with ship and route data, will allow the reproduction of acoustic environments of anthropogenic origin in laboratories and the creation of acoustic maps of the basins investigated using commercial software.

Has the German vehicle fleet become quieter? - Results of a measurement campaign using SPB and CPX measurements

In the past, the German Environment Agency has carried out several measurement campaigns to determine the noise behavior of the German vehicle fleet. The aim of the current project was to identify any trends in comparison to previous campaigns. Autonomous pass-by measurements were carried out at 30 locations throughout Germany in accordance with DIN EN ISO 11819-1 (SPB) with the aim of recording at least 1000 vehicles per location. As the road surface influences the pass-by noise, near-field measurements according to DIN EN ISO 11819-2 (CPX) were carried out to determine the homogeneity of the road surface at each measurement location. In parallel to the CPX measurements, texture measurements according to DIN EN ISO 13473 were carried out to quantify the relevant geometric parameters of the road surface. The presentation describes the methodology of these measurements and presents the final results including a comparison with data from the 2012 and 2002 measurement campaigns.

Study on subway resilient wheel's influence on noise inside the vehicle and in the bogie area through the in-situ measurements

Based on a new type of resilient wheel installed on a subway train, a measurement campaign is devised to evaluate the effectiveness of the resilient wheel in reducing noise. For reference, the same series of tests are carried out on another train of the same type but fitted with conventional wheels. The measurements involve the noise of various parts of the vehicle-track system which are used to investigate the sources of wheel-rail rolling noise, the noise inside the vehicle, and the noise close to the wheels. The series of tests are conducted on the normal-conditioned and corrugated track on which the two sets of trains pass through at difference speeds. It is found that the decrease of interior noise measured on the corrugated track is within the range of 0.2~10.5 dB(A), which is greater than on normal conditioned track after using the resilient wheels. This attributes to the frequency range available for vibration reduction by using the resilient wheel covers the dominant frequency range of the excitation from corrugation.

Source localization at low frequency using deconvolution of the waveguide impulse response

Matched-mode processing (MMP) methods have been widely investigated for source localization and geoacoustic inversion. For horizontal line arrays (HLA), it aims at retrieving the horizontal wavenumbers and thus at inferring source range and bearing. In this work, the matched-mode is performed by applying the deconvolution of the waveguide response in a narrowband context in order to improve the localization accuracy. Deconvolution usually refers to a sparse framework when the number of sources is smaller than the number of sensors of the HLA. The Orthogonal Matching Pursuit algorithm is then used in this work. First results from numerical simulations for Pekeris waveguide highlight better localization accuracy than MMP. The deconvolution shows as well stronger robustness to mismatch in the sound speed values of the seabed. Results from measurement campaign, involving large HLA, low to ultra-low frequency and water depth up to 1500 m are investigated as well.

Predicting the impact of wind turbine noise: general overview and results of the PIBE project

The PIBE project aims to improve wind turbine noise prediction methods and to explore new solutions for noise reduction. This five years project brought together French experts in aeroacoustics, sound propagation, experimental noise characterization and wind engineering, and was structured around three work packages. The first one aimed to study amplitude modulation phenomena and focused particularly the characterization of dynamic stall noise. Specific aerodynamic and acoustic measurements were carried out in a wind tunnel, showing the influence of several stall regimes on noise production. The second work package focused on quantifying the uncertainties of noise prediction methods. It developed an open-access online application (WindTUNE) that quantifies uncertainties on noise prediction of a wind farm, and a parametric and uncertainties calculation tool for the engineering application Code-TYMPAN. This axe also produced an open-access database of a 400 days campaign of meteorological and acoustical measurements around a wind farm. The last work package investigated new noise reduction devices using blades with modified leading and/or trailing edges. The efficiency of the solutions were characterized in a wind tunnel, both acoustically and aerodynamically. The paper presents the main results obtained at the end of the project.

Sound insulation characterisation of innovative natural ventilated façade in the context of living lab installations

Building acoustic standards like EN 14351 and ISO 10140 regulate the measurement of sound insulation of transparent elements, with indications of the test sample dimensions, test conditions, and criterions of adaptations of the results to different on-site conditions. However, given the research on innovative transparent building envelope including internal ventilation as double skin facades, these methodologies present limitations related to the characterization of the high variability of operating conditions in real in-field conditions. To this aim the acoustic performance could be explored with more flexible methods inside the multi-domain context of Living Labs, which present an opportunity for multiple characterizations and testing costs reduction. This work investigates the possibility of using the sound-intensity probe method to evaluate the airborne sound insulation of a transparent building element with internal ventilation. For this purpose, a comparative measurement campaign has been performed on the same building element installed in two Living Labs. The results show good compatibility between the different measurements and scales supporting the application of this methodology for comparative studies in the perspective of innovative building components measurements, and the application in Living Labs.

Mapping human voice in urban spaces

Human voice plays a pivotal role as a sound source in urban environments. Despite the plethora of natural sound sources present in urban spaces, human voice often stands out as one of the sound source, exerting a significant influence on the perception and affection of these spaces. However, compared to other aspects of urban soundscapes, such as traffic noise (air, road, rail), human voice cartography and modelling remains relatively underexplored, with limited historical development and scholarly attention. This research gap led to the deployment of an experimental protocol in Nantes, France, to produce a comprehensive voice sound map and compare it to perceptual data. This protocol involved the collection of sound level measurements during two distinct measurement campaigns using the NoiseCapture smartphone application, coupled with surveys capturing perceptual information such as the circumplex circle of affect, perceived presence of sound sources, emergence of sound sources, and variability of the sound environment. Additionally, sound environment simulations were conducted using NoiseModelling. The present paper shows the method used to evaluate the audibility of human speech in urban spaces. During the presentation, comparisons with perceptual measurements will be presented.

Uncertainties in numerical predictions and experimental characterization of wind farm noise

Wind Turbine Noise (WTN) variability is often related to the influence of local micrometeorology as well as to space and time variations in the ground properties. Thus, the PIBE Project (2020-2024) aims to estimate these variabilities and their associated uncertainties. Its objective is to enable engineering companies or wind farm developers to estimate more accurately the risk of noise. In the WP2 of the PIBE project, 3 approaches are explored: (i) a NUMerical approach through the development of a metamodel, (ii) an EXPerimental approach through a major in-situ measurement campaign lasting more than 1 year, and (iii) a STATistical approach consisting in the evaluation of WTN variability. The NUM approach consists in sound emission calculation of each wind turbine using the Amiet's theory, and sound propagation calculation using a wide-angle Parabolic Equation (WAPE) modelling. The EXP part of the PIBE project has led to the development of a large database, accessible via a dedicated Shiny application. The last approach (STAT) has been carried out using both an open-access online tool called WindTUNE and an open-source tool based on Code_TYMPANTM, namely OCP. The 3 approaches (NUM + EXP + STAT) are presented and the corresponding results are discussed.

Data assimilation for noise mapping using CNOSSOS - A Danish Case Study

Noise maps play a significant role in developing noise mitigation policies. However, maps based on noise simulation models are likely to be uncertain due to underlying model uncertainties and parameterization. This research work explores the feasibility of data assimilation techniques to address this issue. A noise measurement campaign was carried out at two locations in the Central Jutland Region of Denmark. Consequently, 76 days (1 September-15 November 2019) (N = 1824 hours) of measured hourly A-weighted, energy equivalent, sound pressure level data (LAeq1h in dBA) was available for this case study. In addition, traffic counting data was available. The LAeq1h (dBA) levels were then simulated using the EU noise prediction standard, CNOSSOS. The comparison of daily averaged measured and simulated noise levels reveals the Root Mean Squared Error (RMSE) in the range of 1.4 - 2.8 dBA. Subsequently, data assimilation techniques, such as the Best Linear Unbiased Estimator (BLUE) and Bayesian Inverse Inference, are used to produce improved, hourly, so-called analysis maps with the minimum error covariance. The oral presentation and short article will present details of model inputs and simulations, data assimilation as well as the strengths and limitations of this research.

Impact of surrounding environment on impinging supersonic jets resonances and their hysteretical behavior

Supersonic jets impinging on flat surface produce intense acoustic tones. Recent measurement campaigns have indicated that the surrounding environment geometry or its acoustic treatment can drastically change the observed resonance frequencies and amplitudes at identical flow regimes. For example, at supersonic speeds, a hard walled external nozzle shape leads to the existence of two main types of resonances: antisymmetric resonances (with frequencies close to the free jet screech) and axisymmetric resonances. Frequencies associated to those different resonances are very distinct. We have observed that Applying a simple non-reflective material to the outer surfaces of the nozzle suppresses the axisymmetric resonances and that antisymmetric resonances seems to be contained in the frequency range of existence of trapped acoustics modes, known to be responsible for screech resonances. Additionally, when no acoustic treatment is applied on the nozzle wall, the experiments show that the switch between different resonance regimes (symmetric - antisymmetric), induced by changes in Mach number, has an hysteretical behavior. To the authors' knowledge, this has been rarely discussed in the literature and adds to the actual complexity of the aeroacoustic behavior of such jet flows, especially when modeling is considered.

Noise propagation variations over long distances over water

This paper investigates the short temporal variations of noise propagation over a water surface for long distances. Analysis is formed on the results of a measurement campaign for downwind noise propagation over water for elevated sound sources. Noise propagation over water for elevated noise sources is specifically relevant for offshore wind turbines, near shore wind turbines or wind turbines on land close to large water bodies. The measurement setup is a height-adjustable sound source placed at three different heights 81 m, 50 m and 30 m above ground and microphones positioned downwind at shore and ~100 m inland at three different distances over water from the sound source ~3 km, ~5 km and ~7 km. The meteorological conditions wind speed, wind direction, atmospheric stability, temperature, humidity, etc. were monitored continuously at both ends of the setup, utilizing both a tall met mast, a wind profiler and sonic anemometers at multiple heights. The results are used for improving auralisations of noise from offshore wind turbines and offshore wind farms. In addition to this a semi-analytical model for propagation over water is tested.

Sound insulation of access floors on CLT

The acoustic performance of access floors resting on concrete slabs has been long investigated. When such flooring solutions are used on lightweight construction systems, estimates of impact sound insulation improvements cannot be transferred without relevant loss of accuracy. To gain understanding on such behaviour, an experimental campaign has been carried out at the Building Envelope Lab of the Free University of Bozen-Bolzano on 16 access floors mounted on a 200 mm CLT slab. Three different panels (calcium silicate, encapsulated calcium silicate and encapsulated chipboard panels), two different pedestals (standard and resilient), and three flooring solutions (bare, carpet tiles, acoustic carpet tiles) were studied. Impact sound insulation measurements were carried out using both the tapping machine and the rubber ball as source. The results discuss in detail the outcomes of the measurement campaign as well as the relation between the two impact sources chosen.

Industrial plant noise mitigation starting from the plant first runs

The article summarizes a noise impact mitigation study that was carried out in the Liguria region in Northern Italy, between July 2020 and March 2022 on a large industrial plant that produces zinc oxide. The authors were summoned at the plant first run tests, so this study started without a participation in the industry planning and design phases. We followed the main machine installations and perfected the mitigation project accordingly: priorities were updated after each assessment and new modelization. This approach was carried out with different SPL measurement campaigns and the use of sound-intensimetry and a beam-forming SEVENBEL antenna. A SoundPLAN 3d model was updated step by step, defining a designing ad hoc noise control strategies and solutions, in order to respect the Italian administrative noise regulations. The mitigation works were directed by one of the authors and included different approaches: such as some large cylindrical silencers on the smoke stacks, sound barriers and insulating coatings, as well as fan velocity optimization.

Advancements in railway noise simulation: assessment of tools for virtual validation

In pursuit of more efficient and cost-effective measurement campaigns, the railway industry is embracing the prospect of virtual validation based on simulations. The primary obstacle lies in the need for noise simulation tools capable of accurately replicating complex sources, installation effects, noise propagation, ground reflection and, for some cases, the diffraction in the different train surfaces. This paper presents insights derived from European project Shift2Rail S2R-CFM-CCA-01-2019 Energy and Noise & Vibration WP6, concentrating on the validation and enhancement of two exterior noise simulation tools, tailored for railway applications. The paper covers four reference cases, simulating exterior noise at standstill with diverse noise sources and varying source locations and noise emission (i.e. electrical noise, cooling, etc.). A correlation with previously conducted measurements at typical receiver locations (7.5 meters from the track centerline) is carried out. The measurements were conducted in a "controlled" configuration, isolating as much as possible the analyzed noise source and gathering all the needed information about the ground and train geometry. The evaluation between measurements and simulations is done against a global and a 1/3rd octave band criteria with successful results. Finally, key features essential for achieving more accurate simulations are listed.

Dynamic localization of unwanted events with machine learning-based method

In environmental acoustics measurements it is necessary to separate the contribution of the investigated source from the residual noise, by means of ambient noise measurements. Source separation is a complex task, especially for wind turbine noise, where long-term measurement campaigns are required. Although data analysis procedures that provide for this task are already in use, all of them require a preliminary step for anomalous events removal, i.e. events which are not characteristic of standard residual noise. This step can be complex and very time-expensive depending on the duration of the measurements and the measurement site. Depending on the specific site and source under evaluation, the variety of sounds that can be considered as unwanted for compliance with environmental acoustic regulations is heterogeneous, ranging from road vehicles, trains and planes to human and animal sounds and more. Nowadays, it is possible to extrapolate from an audio source the features that describe its semantics using machine learning. The approach presented in this paper aims to localize in time a specific event within a measurement containing several acoustic events, in order to label it and then proceed to remove the spurious events from the measurement.

Blade Surface Pressure Measurements in the Field and Their Usage for Aerodynamic Model Validation

ABSTRACTThis study presents results from a long‐term measurement campaign on a research wind turbine in the field. Pressure measurements are conducted at 25% blade radius over several months. Together with inflow measurements provided by a LiDAR system, they form an extensive dataset, which is used in the validation of numerical aerodynamic models. The model validation is conducted based on both ten‐minute average data as well as time‐resolved unsteady data. Initially, it is investigated how representative ten‐minute average pressure measurements are of the underlying unsteady aerodynamics. Binned ten‐minute average pressure distributions are then analysed together with their numerical counterpart, consisting of a combination of rotor and airfoil level aerodynamic/aeroelastic simulation results using average environmental and operating conditions as input. Finally, time‐resolved measurements and simulation results are compared, validating the aeroelastic tools' capability to reproduce unsteady aerodynamics.Overall, reasonable agreement is found between numerical simulations and field experiment data showcasing two aspects: Numerical tools based on blade element momentum theory and panel methods with viscous‐inviscid interaction remain relevant for simulating modern multi‐megawatt wind turbines, and long‐term pressure measurements provide invaluable means for validating such tools.

Performance of anhydrous ethanol and gasoline blends on a SI engine: Decoupling evaporation enthalpy and knock resistance

Blending bioethanol with gasoline is recognized as a rapid solution for mitigating nonrenewable carbon dioxide emissions. This approach proves particularly meaningful in markets where the production of this biofuel aligns with sustainable practices. Understanding the alterations in the combustion process holds significance within these markets, contributing to informed decision-making and fostering environmentally conscious practices. In this context, it is widely known that highly ethanol blended fuels can provide benefits regarding suppression of knocking combustion in spark ignited engines if the quality of the base-fuel is not deteriorated to maintain octane ratings. However, the results of engine knocking investigations can be affected by two effects simultaneously. Firstly, ethanol has a beneficial effect on knock suppression due to its high enthalpy of evaporation compared to gasoline, which results in inner mixture cooling especially with direct injection. Secondly, ethanol can have beneficial effects on knock suppression by its decreased self-ignition tendency. This paper provides the set-up and results of an adapted engine testing procedure to diminish the effects of evaporation enthalpy during the knocking investigations of different highly ethanol blended fuels. The presented testing procedure at a single-cylinder research engine includes three technical steps: (1) the engine is equipped with a port fuel injection in stoichiometric operation for all tested fuels; (2) the engine is operated with constant speed of 1500 rpm and constant spark timing of 33° firing top dead center; (3) the engine is operated with fuel individual settings for the intake manifold gas pressure and intake manifold gas temperature. These parameters are adjusted to test all fuels with similar in-cylinder conditions at spark timing. The differing heating values of the fuels obviously result in differing engine loads. However, the presented testing procedure is aimed to achieve comparable in-cylinder conditions at spark timing without the effect of evaporation enthalpy. The novelty of the study lies in its adapted engine testing procedure that mitigates the cross-effects of fuel properties and operational conditions to isolate the true influences on knock occurrence. The paper provides a comprehensive description of the theoretical backgrounds, experimental set-up and post-processing procedures and also shows the results of the first measurement campaign.