Vertical Root Mean Square Research Articles

Vibration Analysis and Control of a Vibration Screed System for Asphalt Pavers

To reduce shaking of a vibration screed system (VSS) and improve the paving performance of an asphalt paver (AP), the root-mean-square (RMS) acceleration responses at points on the front and rear screed floors are analyzed via an experimental method. A 3D nonlinear dynamic model of the VSS is also built to evaluate the influence of the dynamic parameters of the VSS on the compression efficiency, paving quality, and working stability of the AP based on the objective functions of the vertical, pitching, and rolling RMS values at the centre of gravity of the screed. The angular deviations, $alpha$ and $gamma$, of the tamper are then controlled to improve the paving performance. The research results show that the excitation frequency, $f_{t}$, and both angular deviations, $alpha$ and $gamma$, of the tamper strongly affect the paving performance. The compression efficiency is quickly enhanced, while both paving quality and working stability are significantly reduced with increasing the excitation frequency $f_{t}$ and reducing the angular deviations. $alpha$ and $gamma$. and vice versa. Additionally, the screed shaking and paving performance of the AP are remarkably improved by control of the angular deviations, $alpha$ and $gamma$, under different working conditions.

The Contribution of Multispectral Satellite Image to Shallow Water Bathymetry Mapping on the Coast of Misano Adriatico, Italy

The results of absolute satellite-derived bathymetry (SDB) are presented in the current study. A comparative analysis was conducted on empirical methods in order to explore the potential of SDB in shallow water on the coast of Misano, Italy. Operations were carried out by relying on limited in situ water depth data to extract and calibrate bathymetry from a QuickBird satellite image acquired on a highly dynamic coastal environment. The image was processed using the log-band ratio and optimal band ratio analysis (OBRA) methods. Preprocessing steps included the conversion of the raw satellite image into top of atmosphere reflectance, spatial filtering, land and water classification, the determination of the optimal OBRA spectral band pairs, and the estimation of relative SDB. Furthermore, calibration and vertical referencing were performed via in situ bathymetry acquired in November 2007. The relative bathymetry obtained from different band ratios were vertically referenced to the local datum using in situ water depth in order to obtain absolute SDB. The coefficient of determination (R2) and vertical root mean square error (RMSE) were computed for each method. A strong correlation with in situ field bathymetry was observed for both methods, with R2 = 0.8682 and RMSE = 0.518 m for the log-band ratio method and R2 = 0.8927–0.9108 and RMSE = 0.35 m for the OBRA method. This indicated a high degree of confidence of the SDB results obtained for the study area, with a high performance of the OBRA method for SDB mapping in turbid water.

Simulation case study of displacement monitoring using network derived positioning

Network-based real-time kinematic (NRTK) GNSS (Global Navigation Satellite System) is among the most commonly used surveying technique in many countries for various applications that requires a single GNSS receiver. The main principle of this system is to generate reliable error models that can mitigate dispersive (e.g. ionospheric delay) and non-dispersive (e.g. tropospheric delay and orbit bias) errors, which are the main sources of the degradation of positioning accuracy. In this study, the performance of NRTK positioning for deformation and landslide monitoring is investigated using a simulation apparatus. For this purpose, 20 simulated two-dimensional and vertical displacements are conducted within a two-month period in 2019. The 24-h NRTK data with 1-s sampling intervals are obtained using a CHC N72 GNSS reference receiver for each displacement. The 24-h NRTK data are mutually subdivided into 12-, 6-, 3- and 1-h non-overlapping sessions to investigate the effect of observation time on monitoring displacement performance. Two filtering methods – namely, averaging the raw observations and averaging the observations derived from Kalman filtering – are chosen for each session. The displacements obtained from the filtered NRTK observations are compared to the simulated (true) displacements. Another experiment is carried out to monitor the displacement in real time using first-order low-pass and moving-average filters. The NRTK data are collected during the displacement for a real-time experiment. The results of the experiments indicate that 1-sigma horizontal and vertical Root Mean Square errors (RMSEs) of displacements between the filtered NRTK data and true displacements are determined to be 1.5 and 5.4 mm, respectively, using 24-h data. The results also suggest that no significant difference is observed between the filtering methods for most of the points. The RMSE of the two-dimensional displacement direction between the azimuth angle derived from the filtered NRTK data and the azimuth angle of true direction is found to be 15° for 3 mm displacement using 24-h data. For detecting the displacements visually in real time, the minimum magnitude of displacements needs to be 7 mm and 10 mm for the horizontal and vertical components, respectively, to distinguish the displacements from the noise.

High-Resolution and Accurate Topography Reconstruction of Mount Etna from Pleiades Satellite Data

The areas characterized by dynamic and rapid morphological changes need accurate topography information with frequent updates, especially if these are populated and involve infrastructures. This is particularly true in active volcanic areas such as Mount (Mt.) Etna, located in the northeastern portion of Sicily, Italy. The Mt. Etna volcano is periodically characterized by explosive and effusive eruptions and represents a potential hazard for several thousands of local people and hundreds of tourists present on the volcano itself. In this work, a high-resolution, high vertical accuracy digital surface model (DSM) of Mt. Etna was derived from Pleiades satellite data using the National Aeronautics and Space Administration (NASA) Ames Stereo Pipeline (ASP) tool set. We believe that this is the first time that the ASP using Pleiades imagery has been applied to Mt. Etna with sub-meter vertical root mean square error (RMSE) results. The model covers an area of about 400 km2 with a spatial resolution of 2 m and centers on the summit portion of the volcano. The model was validated by using a set of reference ground control points (GCP) obtaining a vertical RMSE of 0.78 m. The described procedure provides an avenue to obtain DSMs at high spatial resolution and elevation accuracy in a relatively short amount of processing time, making the procedure itself suitable to reproduce topographies often indispensable during the emergency management case of volcanic eruptions.

Validating UAS-Based Photogrammetry with Traditional Topographic Methods for Surveying Dune Ecosystems in the Spanish Mediterranean Coast

In the past few years, unmanned aerial systems (UAS) have achieved great popularity for civil uses. One of the present main uses of these devices is low-cost aerial photogrammetry, being especially useful in coastal environments. In this work, a high-resolution 3D model of a beach section in Guardamar del Segura (Spain) has been produced by employing a low maximum takeoff mass (MTOM) UAS, in combination with the use of structure-from-motion (SfM) techniques. An unprecedented extensive global navigation satellite system (GNSS) survey was simultaneously carried out to statistically validate the model by employing 1238 control points for that purpose. The results show good accuracy, obtaining a vertical root mean square error (RMSE) mean value of 0.121 m and a high point density, close to 30 pt/m2, with similar or even higher quality than most coastal surveys performed with classical techniques. UAS technology permits the acquisition of topographic data with low time-consuming surveys at a high temporal frequency. Coastal managers can implement this methodology into their workflow to study the evolution of complex, highly anthropized dune-beach systems such as the one presented in this study, obtaining more accurate surveys at lower costs.

Bundle adjustment of satellite images based on an equivalent geometric sensor model with digital elevation model

High-precision georeferencing of satellite stereo images becomes a key issue in multi-source data integration, geometric processing, and analysis for many remote sensing applications. Using existing geographic data, including readily available public data, as geometric reference for georeferencing satellite imagery is an effective and feasible way to improve the positional accuracy and reduce the costs and workforce restrictions on ground control points (GCPs) acquisition. This study proposes a novel bundle adjustment approach of push broom satellite imagery based on an equivalent geometric sensor model (EGSM). As an extension of the collinearity equations, EGSM is equivalent to the rigorous geometric sensor model, whose interior and exterior orientation parameters have clear geometric interpretations. The initial values of EGSM’s parameters can be completely recovered from the RPCs and optimized within the block adjustment without using any metadata of the satellite imagery. Furthermore, a publicly accessible digital elevation model (DEM) is used as constraints in the bundle adjustment to improve the direct georeferencing accuracies without GCPs. A set of pseudo observation equations is incorporated into the EGSM associated with appropriate weights based on the estimated variance of height differences between the tie points and the DEM surface. The performance of the proposed approach was evaluated by using 143 stereo scenes of Chinese Ziyuan-3 (ZY-3) images and the global DEM data SRTM GL3, ASTER GDEM, and AW3D30. The experimental results revealed that the proposed approach could improve not only vertical accuracies but also horizontal accuracies of satellite stereo images. The geopositional accuracy after adjustment is dependent on the quality and accuracy of the reference DEM itself. With AW3D30 as exclusive controls, the horizontal and vertical root mean square errors (RMSEs) of the experimental images are reduced from 17.3 m and 2.6 m to 2.5 m and 1.5 m, respectively. The horizontal accuracy corresponds to about 1.2 pixels in the image space, and the vertical accuracy is about 0.6 pixels with the base-height ratio of ZY-3 stereo images being 0.81. The generazation ability of the approach was further proved by the experiments of WorldView-3 stereo images.

Monitoring of avulsion channel evolution and river morphology changes using UAV photogrammetry: Case study of the gravel bed Ondava River in Outer Western Carpathians

This paper presents results from monitoring the chute cutoff in the meander bend of the Ondava River in Eastern Slovakia. An avulsion channel was formed in the central part of the meander neck during 2010 flood events, and here we describe the mechanism of evolution and post‐cutoff avulsion channel adjustment using drones, unmanned aerial vehicle (UAV) photogrammetry and field survey. Monitoring by UAV images began on 15 June 2012 with 78 processed images, followed by 259 images during April 2014 and 375 from 18 July 2014. The majority of UAV digital elevation model (DEM) errors in the study area were associated with vegetation cover, with the average vertical root mean square error (RMSE) of the UAV‐DEM on bare ground at 0.209 m compared with 0.673 m in vegetated areas. The chute cutoff was formed by floodplain headcutting during meander neck overflow and headcut migration was directed by floodplain sediment structure and land use. Although low river discharge after the 2010 floods stabilised the avulsion channel by vegetation succession, recurrent two‐yearly interval flooding increased the avulsion channel bank erosion from 36.9 m3/month (June 2012–April 2014) to 425.6 m3/month (April 2014–July 2014).

DEM generation using Ziyuan-3 mapping satellite imagery without ground control points

ABSTRACTThis article proposes a digital elevation model (DEM) generation approach using the Shuttle Radar Topography Mission (SRTM) DEM as the elevation constraint without ground control points. First, during the process of image block adjustment, we took advantage of the relatively high vertical accuracy of the SRTM-DEM in flat terrain regions and applied effective constraints on the object-space elevation-corrected value of tie points using the SRTM-DEM, achieving improved vertical accuracy for large-scale block adjustments. Subsequently, for the DEM matching process, multiple two-linear array stereo image pairs were obtained from along-track and across-track images with different look angles over the same region after the block adjustment. Then, the matching result of each stereo image pair underwent weighted fusion, before being used to generate the final DEM product. This approach can effectively enhance the matching quality and grid density of the final DEM product. The DEM generation experiment, using Ziyuan-3 images covering 186,000 km2 of Hubei Province, China, showed that the matching quality of the 10 m grid DEM was excellent. The vertical root mean square errors were 1.5 m in the flat regions and 2.96 m in the mountainous regions, thus achieving China’s 1:25,000 scale specification requirement for DEM products.

SRTM‐assisted block adjustment for stereo pushbroom imagery

AbstractThis paper proposes a stereo‐image block‐adjustment algorithm without ground control points (GCPs) by adopting a Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) as a height assistant. Using dense, evenly distributed tie points on images used in the block adjustment, the initial height values of tie points are derived directly from the SRTM DEM. In the subsequent block‐adjustment iterative computation, the height correction value for tie points is rigorously restricted by the SRTM DEM elevation. A total of 509 ZY‐3 satellite stereo‐images across 190 000 km2 of China's Hubei Province were used for this block‐adjustment experiment. The results show that the vertical root mean square errors (RMSEs) are improved from 7·2 to 2·3 m without GCPs, while the RMSEs in flat and mountainous terrain are improved to 1·5 and 2·8 m, respectively, fulfilling the vertical accuracy requirement of China's 1:25 000 scale mapping.

Human runners exhibit a least variable gait speed

ABSTRACTThis study characterises the relationship between gait variability and speed in runners using data from trunk accelerations in each axis.Twelve participants of varying fitness ran on the treadmill with three sessions of six randomly ordered self-selected speeds. A VO2max test was conducted on the fourth session. Running gait was tracked with inertial sensors. The occurrence of a mid-range speed was analysed for the anterior–posterior, vertical and lateral directional coefficient of variation (CV) of root mean square (RMS) acceleration data.One participant with noisy gait signals was omitted. The results show all remaining participants consistently showed significant quadratic U-shaped relationships between vertical RMS CV acceleration and speed. Neither anterior–posterior nor lateral RMS CV acceleration were clearly related to speed. These least variable gait speeds were similar to estimates of optimal speed derived from minimum cost of transport with speed.In conclusion, there exists a mid-range speed for each runner with the least variable gait in the vertical direction, and this occurred significantly more often than would be expected by chance (P < 0.05). However, there are no prominent patterns for the anterior–posterior and lateral directions. This finding supports anecdotal evidence from runners and coaches concerning gait consistency.

Lidar-based mapping of flood control levees in South Louisiana

ABSTRACTFlood protection in south Louisiana is largely dependent on earthen levees, and in the aftermath of Hurricane Katrina the state’s levee system has received intense scrutiny. Accurate elevation data along the levees are critical to local levee district managers responsible for monitoring and maintaining the extensive system of non-federal levees in coastal Louisiana. In 2012, high resolution airborne lidar data were acquired over levees in Lafourche Parish, Louisiana, and a mobile terrestrial lidar survey was conducted for selected levee segments using a terrestrial lidar scanner mounted on a truck. The mobile terrestrial lidar data were collected to test the feasibility of using this relatively new technology to map flood control levees and to compare the accuracy of the terrestrial and airborne lidar. Metrics assessing levee geometry derived from the two lidar surveys are also presented as an efficient, comprehensive method to quantify levee height and stability. The vertical root mean square error values of the terrestrial lidar and airborne lidar digital-derived digital terrain models were 0.038 m and 0.055 m, respectively. The comparison of levee metrics derived from the airborne and terrestrial lidar-based digital terrain models showed that both types of lidar yielded similar results, indicating that either or both surveying techniques could be used to monitor geomorphic change over time. Because airborne lidar is costly, many parts of the USA and other countries have never been mapped with airborne lidar, and repeat surveys are often not available for change detection studies. Terrestrial lidar provides a practical option for conducting repeat surveys of levees and other terrain features that cover a relatively small area, such as eroding cliffs or stream banks, and dunes.

Ionospheric error contribution to GNSS single-frequency navigation at the 2014 solar maximum

For single-frequency users of the global satellite navigation system (GNSS), one of the main error contributors is the ionospheric delay, which impacts the received signals. As is well-known, GPS and Galileo transmit global models to correct the ionospheric delay, while the international GNSS service (IGS) computes precise post-process global ionospheric maps (GIM) that are considered reference ionospheres. Moreover, accurate ionospheric maps have been recently introduced, which allow for the fast convergence of the real-time precise point position (PPP) globally. Therefore, testing of the ionospheric models is a key issue for code-based single-frequency users, which constitute the main user segment. Therefore, the testing proposed in this paper is straightforward and uses the PPP modeling applied to single- and dual-frequency code observations worldwide for 2014. The usage of PPP modeling allows us to quantify—for dual-frequency users—the degradation of the navigation solutions caused by noise and multipath with respect to the different ionospheric modeling solutions, and allows us, in turn, to obtain an independent assessment of the ionospheric models. Compared to the dual-frequency solutions, the GPS and Galileo ionospheric models present worse global performance, with horizontal root mean square (RMS) differences of 1.04 and 0.49 m and vertical RMS differences of 0.83 and 0.40 m, respectively. While very precise global ionospheric models can improve the dual-frequency solution globally, resulting in a horizontal RMS difference of 0.60 m and a vertical RMS difference of 0.74 m, they exhibit a strong dependence on the geographical location and ionospheric activity.

Experimental study on the characteristics of longitudinal oscillating grid turbulence

Oscillating grid turbulence is an efficient way of studying complex turbulence and mass transport, while the turbulence generated by the existing vertical oscillating grid systems is quite different from the natural turbulence. A large scale grid turbulence experiment system is established, the grids conduct longitudinal oscillating rather than the traditional vertical oscillating, and the Particle Image Velocimetry is used to measure the flow fields. Tests of the instantaneous flow velocities show that the turbulence generated by this system has strong randomness and statistical regularity. All the longitudinal and vertical root mean square velocities vary rapidly near the grids, and tend to be stable at the middle of the grids. The longitudinal root mean square velocities are larger than the vertical values, and the ratio is about 1.5-2.0, which is close to the natural open channel flow. The fluctuation of the Reynolds stress near the grids is relatively large and decreases with the increasing distance from the grid, the Reynolds stress is about zero at the middle of the grids. The integral time and length scales near the grids are the smallest and increase linearly with the increasing distance from the grids, reaching the maximum at the middle of the grids. The flow velocity spectra obeys the Kolmogorov-5/3 theory. The statistical characteristics of the turbulence generated by this system are consistent with the traditional vertical oscillating grid turbulence, but the longitudinal and vertical turbulent intensities are more close to the natural open channel flow, laying the foundation for the studies of sediment and pollutant transports.

Correlative Analysis of Hydraulic Bushing of Suspension Control Arm and Full Vehicle Ride Comfort

To analyze and compare the vehicle performance effects of hydraulic bushings with those of the traditional rubber bushings of double wishbone front suspensions, we test the static and dynamic properties of the hydraulic bushings of control arms. The mechanical model is built in ADAMS and is then used as the basis for establishing the full vehicle model. The random road surface spectra of different levels are built using the harmony superposition method. The ride comfort of the full vehicle with a control arm installed with hydraulic and rubber bushings is simulated on random and bump roads. The frequency spectrum characteristic and root mean square (RMS) of the vertical and longitudinal acceleration of the foot floor and seat rail are calculated via power spectrum estimation, and the handling stability of the full vehicle is then simulated. The effects of the change in hydraulic bushing stiffness on ride comfort are finally analyzed. The following results are obtained. (1) The effects of such change on vehicle handling are relatively small regardless of the type of bushing used. (2) The vehicle shows acceptable ride comfort on level A and level B roads but shows poor ride comfort on bump road when a hydraulic bushing is used. (3) Large hydraulic bushing stiffness increases the vertical acceleration RMS on level A, level B, and bump roads. However, the variety of RMS is extremely small on level D roads, the responses of the vertical and longitudinal acceleration curves are slow, and the time oscillation of the curves is relatively long on bump road.

Accelerometry-based gait analysis predicts falls among patients with a recent fracture who are ambulatory: a 1-year prospective study.

The aim of this prospective study was to assess whether accelerometry-based gait analysis is associated with the incidence of falls among individuals who are ambulatory and recently had a fracture, and to compare the ability to discriminate body function and structure and activity measures. A total of 100 patients who fulfilled our inclusion criteria were enrolled. At hospital discharge, the following outcomes were assessed: timed-up-and-go test, five-times-sit-to-stand test, one-leg standing test, 5-m gait test, and gait analysis using a wireless three-axis accelerometer. Root mean square (RMS) and autocorrelation (AC) values were analyzed on the basis of the acceleration waveform. Follow-up assessment of falls and subsequent fractures was performed 12 months after the fracture. Eighty-five percent of the participants completed the follow-up at 12 months. During the 12 months of follow-up, 61 falls were reported by 34 patients (31 women, three men), for a fall rate of 40.0% (34/85). The fall group had significantly poorer body function and structure and activity measures compared with the no-fall group. In accelerometry-based gait analysis, RMS and AC in the vertical axis and RMS in the anteroposterior axis were significantly lower in the fall group compared with the no-fall group. Multivariate logistic regression analysis showed that only AC in the vertical axis was a significant predictor of falls. This finding suggests that trunk acceleration AC in the vertical axis showed good discriminative ability for predicting the incidence of falls among patients who are ambulatory and recently had a fracture.

ACCURACY ENHANCEMENT OF SRTM AND ASTER DEMS USING WEIGHT ESTIMATION REGRESSION MODEL

This paper assesses the accuracy of the SRTM v4.1 and ASTER GDEM v2 by comparing of sufficient number of ground control points (GCPs) with corresponding pixel values of DEMs heights for two locations in Egypt : Delta region(A) &West desert and Qena region (B). A new approach was developed for accuracy enhancement based on (Weight Estimation Regression models) ,with Topographic Position Index(TPI), Aspect, SRTM or ASTER DEM as independent variables and GCP as dependent values . Data were analyzed for each location separately and in combination ,using GIS and statistical software (SPSS). The results of this study showed that vertical Root Mean Square Errors (RMSE)for SRTM dataset range from 15.631 m in (A) to 7.868 m in (B). for ASTER dataset, RMSE ranges from 13.160 m in (A) to 12.357 m in (B) .For combined regions(A+B) :RMSE were 12.688 m and 12.7997 m for SRTM and ASTER datasets respectively . Concerning the accuracy enhancement of SRTM and ASTER DEMs , a significant improvement of Std. Error of Estimate (SEE) were detected in the two locations. For (A) SEE reduce from 13.584 to 9.502 for SRTM dataset and reduce from 12.538 to 9.101 for ASTER dataset. For (B) SEE reduced from 7.879 to 1.725 for SRTM dataset and from 11.006 to 5.769 for ASTER dataset . Also for combined region SEE reduced from 11.685 to 5.930 for SRTM dataset , and from 11.7624to 8.520 for ASTER dataset . The study also proved that TPI index for ASTER dataset give the best fit to the data for Weight Estimation procedure for better horizontal resolution (30m) . The results of assessments and the improvement approaches of SRTM and ASTER DEMs showed their level of suitability for many hydraulic , watershed, and environment applications.

IGeoTrans – a novel iOS application for GPS positioning in geosciences

The iGeoTrans is an iOS application designed for navigation purposes for iPhone, iPad and iPod Touch. This application uses Global Positioning System (GPS), Assisted GPS system, GLONASS, Wi-Fi and Cellular Network for positioning. The iGeoTrans has included datum transformations and map projections that enable users to convert the collected data between different coordinate systems for almost all areas in the world. In addition, other features are also included such as distance, area measurements, and GPS results could be exported to the AutoCad dxf format for GIS softwares. The average horizontal and vertical root mean square errors (RMSEs) for the static test are around 4.11 and 3.51 m, respectively. The horizontal RMSE for the dynamic outdoor test is around 2.72 m. The iGeoTrans application can be used to support surveying, mapping and geosciences fieldworks for any area in the world.

A Feasibility Test on the DGPS by Correction Projection Using MSAS Correction

Differential Global Positioning System-Correction Projection (DGPS-CP) algorithm, which has been suggested as a method of correcting pre-calculated position error by projecting range-domain correction to positional domain, is a method to improve the accuracy performance of a low price GPS receiver to 1 to 3 m, which is equivalent to that of DGPS, just by using a software program without changing the hardware. However, when DGPS-CP algorithm is actually realized, the error is not completely eliminated in a case where a reference station does not provide correction of some satellites among the visible satellites used in user positioning. In this study, the problem of decreased performance due to the difference in visible satellites between a user and a reference station was solved by applying the Multifunctional Transport Satellites (MTSAT) based Augmentation System (MASA) correction to DGPS-CP, instead of local DGPS correction, by using the Satellite Based Augmentation System (SBAS) operated in Japan. The experimental results showed that the accuracy was improved by 25 cm in the horizontal root mean square (RMS) and by 20 cm in the vertical RMS in comparison to that of the conventional DGPS-CP.

Lagrangian Formulation and Numerical Solutions to Dump Truck Vibrations Under HISLO Conditions

Heavy mining machinery has exposed the human body to extreme vibrations that may limit the performance of operators and further impact the overall system performance. Large capacity shovels and dump trucks have been deployed in surface mines to achieve economic, bulk production operations. The high-impact shovel loading operation (HISLO) causes severe truck vibrations that expose operators to whole-body vibrations (WBV) levels that may exceed ISO standards. The effects of these shockwaves on the human body are severe resulting in long-term lower-back disorders and other health problems. There is a need for fundamental and applied research to determine HISLO vibration levels, their comparisons to ISO 2631 limits, and the safety of operators under these conditions. A fundamental research has been carried to model these HISLO shockwave generation and propagation through the truck body and attenuated via the suspension mechanism and within the rollover protective structures (ROPS) cabin. The Lagrangian mechanics technique has been used to formulate the equations of motions governing the HISLO problem. The Fehberg fourth–fifth order Runge–Kutta (RKF45) numerical method in maple environment (maple classic Version 10.00, 2006, Maplesoft, a division of Waterloo Maple Inc., Waterloo, ON, Canada) is used to solve the equations of motions symbolically. The Lagrangian formulation and the RKF45 solutions provide efficient solutions to complex functions with stability, convergence, and minimum errors. The results of this analysis show that the vertical root mean square (rms) accelerations are equal to 3.56, 1.12, and 0.87 m/s2 for the operator's seat, lower-back, and cervical regions, respectively. These vibration levels also fall within the extremely uncomfortable zone compared to the ISO 2631-1 comfort zone (less than 0.315 m/s2), which pose severe health threats to truck operators over long-term exposure to these vibrations.

Acceleration statistics of solid particles in turbulent channel flow

Direct numerical simulations (DNS) are used here to study inertial particle acceleration statistics in the near-wall region of a turbulent channel flow. The study is motivated by observations in homogeneous isotropic turbulence (HIT) suggesting that when particle inertia increases, particle acceleration variance decreases due to both particle preferential accumulation and the filtering effect of inertia. In accordance with these studies, the present DNS shows that for increasing inertia, solid particle acceleration probability density functions (PDFs), scaled by the acceleration root-mean-square (RMS), depart from that of the fluid. The tails of these PDFs become narrower. However, in turbulent channel flow, as the Stokes number increases up to 5, the streamwise acceleration RMS in the near-wall region increases, while further increase of the Stokes number is characterized by the streamwise acceleration RMS decrease. In parallel, contrary to calculations in homogeneous isotropic turbulence, the conditional acceleration statistics of the fluid seen by the solid particle show that while the vertical and transverse acceleration RMS components remain close to the unconditional fluid acceleration, the longitudinal RMS component is remarkably higher in the near wall region. This feature is more pronounced as the Stokes number is increased. Additionally, the conditional acceleration PDFs overlap almost perfectly with the unconditional fluid PDFs, normalized by the acceleration RMS. The enhanced longitudinal acceleration variance of the fluid seen by the particles may be due to the spanwise alternation of high-and-low speed streaks. Depending on inertia, particles may respond to those fluid solicitations (experiencing an increase of the longitudinal acceleration RMS) or ignore the wall turbulent structures (presenting in that case a more homogeneous concentration).