Density Field Data Research Articles

Data assimilation to determine the electrohydrodynamic force of plasma actuator

The electrohydrodynamic (EHD) force is the main flow control mechanism of plasma actuators (PAs), and a thorough understanding of the EHD force field is important for the practical application of PAs. However, because it is difficult to directly measure the EHD force field, a methodology for determining the unobservable EHD force field is required. In this study, we developed a new methodology using a data assimilation (DA) method which utilizes both experimental data and numerical simulation. The methodology was based on computational fluid dynamics and ensemble four-dimensional variational method and enabled us to determine the unobservable EHD force field from experimentally observable flow field data. Through numerical experiments, we demonstrated that the methodology can inversely estimate the EHD force field using time-series velocity and density field data with sufficient precision. Moreover, the results show that either the velocity or density field data are sufficient to estimate the EHD force field. The proposed DA methodology provides key factors for determining the flow field, such as the maximum value, extent, and vertical position of the maximum value of the EHD force field. Our methodology that estimates EHD force fields from the experimentally observed flow field data is also useful for understanding other EHD flows, which are the phenomena involving plasma and flow.

Relating Ndesign to Field Compaction: A Case Study in Minnesota

High field density helps in increasing the durability of asphalt pavements. In a current research effort, the University of Minnesota and the Minnesota Department of Transportation (MnDOT) have been working on designing asphalt mixtures with higher field densities. One critical issue is the determination of the Ndesign values for these mixtures. The physical meaning of Ndesign is discussed first. Instead of the traditional approach, in which Ndesign represents a measure of rutting resistance, Ndesign is interpreted as an indication of the compactability of mixtures. The field density data from some recent Minnesota pavement projects are analyzed. A clear negative correlation between Ndesign and field density level is identified, which confirms the significant effect of Ndesign on the compactability and consequently on the field density of mixtures. To achieve consistency between the laboratory and field compaction, it is proposed that Ndesign should be determined to reflect the real field compaction effort. A parameter called the equivalent number of gyrations to field compaction effort (Nequ) is proposed to quantify the field compaction effort, and the Nequ values for some recent Minnesota pavement projects are calculated. The results indicate that the field compaction effort for the current Minnesota projects evaluated corresponds to about 30 gyrations of gyratory compaction. The computed Nequ is then used as the Ndesign for a Superpave 5 mixture placed in a paving project, for which field density data and laboratory performance test results are obtained. The data analysis shows that both the field density and pavement performance of the Superpave 5 mixture are significantly improved compared with the traditional mixtures. The results indicate that Nequ provides a reasonable estimation of field compaction effort, and that Nequ can be used as the Ndesign for achieving higher field densities.

Depth of influence of rolling dynamic compaction

The depth of influence of rolling dynamic compaction (RDC) was investigated in a field trial using a four-sided impact roller. Earth pressure cells (EPCs) were placed at varying depths at a site consisting of homogeneous soil conditions. EPCs measured pressures imparted by RDC at 3·85 m depth; however, the largest magnitudes of pressure were confined to the top 2 m beneath the ground surface. These results were complemented by field density data, penetrometer and geophysical testing. A number of published case studies using the 8 t four-sided impact roller, for either improving ground in situ or compacting soil in thick layers, are summarised in this paper. Finally, equations are presented that predict first, the effective depth of improvement, appropriate for determining the depth to which the ground can be significantly improved in situ, and, second, the depth of major improvement for RDC, appropriate for thick-layer compaction.

Assessment of soil compaction properties based on surface wave techniques

Soil compaction plays an important role in every construction activities to reduce risks of any damage. Traditionally, methods of assessing compaction include field tests and invasive penetration tests for compacted areas have great limitations, which caused time-consuming in evaluating large areas. Thus, this study proposed the possibility of using non-invasive surface wave method like Multi-channel Analysis of Surface Wave (MASW) as a useful tool for assessing soil compaction. The aim of this study was to determine the shear wave velocity profiles and field density of compacted soils under varying compaction efforts by using MASW method. Pre and post compaction of MASW survey were conducted at Pauh Campus, UniMAP after applying rolling compaction with variation of passes (2, 6 and 10). Each seismic data was recorded by GEODE seismograph. Sand replacement test was conducted for each survey line to obtain the field density data. All seismic data were processed using SeisImager/SW software. The results show the shear wave velocity profiles increase with the number of passes from 0 to 6 passes, but decrease after 10 passes. This method could attract the interest of geotechnical community, as it can be an alternative tool to the standard test for assessing of soil compaction in the field operation.

Independent constraints on local non-Gaussianity from the peculiar velocity and density fields

Primordial, non-Gaussian perturbations can generate scale-dependent bias in the galaxy distribution. This in turn will modify correlations between galaxy positions and peculiar velocities at late times, since peculiar velocities reflect the underlying matter distribution, whereas galaxies are a biased tracer of the same. We study this effect, and show that non-Gaussianity can be constrained by comparing the observed peculiar velocity field to a model velocity field reconstructed from the galaxy density field assuming linear bias. The amplitude of the spatial correlations in the residual map obtained after subtracting one velocity field from the other is directly proportional to the strength of the primordial non-Gaussianity. We construct the corresponding likelihood function use it to constrain the amplitude of the linear flow $\beta$ and the amplitude of local non-Gaussianity $f^{\rm NL}_{\rm local}$. Applying our method to two observational data sets, the Type-Ia supernovae (A1SN) and Spiral Field \textit{I}-band (SFI++) catalogues, we obtain constraints on the linear flow parameter consistent with the values derived previously assuming Gaussianity. The marginalised 1-D distribution of $|f^{\rm NL}_{\rm local}|$ does not show strong evidence for non-zero $f^{\rm NL}_{\rm local}$, and we set 95% upper limits $|f^{\rm NL}_{\rm local}|<51.4$ from A1SN and $|f^{\rm NL}_{\rm local}|<92.6$ from SFI++. These limits on $f^{\rm NL}_{\rm local}$ are as tight as any set by previous large-scale structure measurements. Our method can be applied to any survey with radial velocities and density field data, and provides an independent check of recent CMB constraints on $f^{\rm NL}_{\rm local}$, extending these to smaller spatial scales.

Numerical simulation of the hydrodynamics of a port and effect of a wave-driven seawater pump

A three-dimensional numerical model was adapted to study the circulation, stratification and mixing patterns inside the port of El Sauzal. Salinity, temperature and density field data were measured, showing that density variations were mainly due to the temperature field with a very small contribution from salinity. The model simulated surface currents and the temperature field. The simulation was compared against field data showing that the model reproduces satisfactorily the circulation, stratification and mixing patterns. Surface circulation and vertical mixing were mainly forced by the tide, although winds greater than 6 m s–1 became the main forcing of vertical mixing and surface circulation. The surface currents traveled outside the port during ebb tide and vice versa during flood tide; however, with winds greater than 6 m s–1, the surface velocity followed the wind direction. When a discharge of 0.2 m3 s–1 was introduced into the system, the simulation showed an increase of 0.5 cm s–1 in the surface current velocity, during ebb tide. The vertical temperature structure increased as much as the discharge temperature (17.2ºC). This result verifies that a controlled discharge could improve circulation and mixing, reducing the residence time and improving the levels of oxygen in the water.

Modelling the motion of an internal solitary wave over a bottom ridge in a stratified fluid

A series of laboratory experiments has been carried out to investigate the passage of an internal solitary wave of depression over a bottom ridge, in a two-layer fluid system for which the upper and lower layer is linearly-stratified and homogeneous respectively. Density, velocity and vorticity fields induced by the wave propagation over the ridge have been measured simultaneously at three locations, namely upstream, downstream and over the ridge crest, for a wide range of model parameters. Results are presented to show that wave breaking may occur for a sufficiently large wave amplitude and a strong ridge blockage factor, with accompanying mixing and overturning. Density field data are presented (i) to illustrate the overturning and mixing processes that accompany the wave breaking and (ii) to quantify the degree of mixing in terms of the wave and ridge parameters. For weak encounters, good agreement is obtained between the laboratory experimental results (velocity and vorticity fields induced by the wave propagation) and the predictions of a recently-developed fully nonlinear theory. Discrepancies between theory and experiment are discussed for cases in which breaking and mixing occur.

Hydrography and estimation of density currents in the southern part of the Bay of Campeche, Mexico

This paper reports the temperature, salinity and sigma-t distributions at the surface, 10 and 30 m depth, derived from data obtained in the autumn of 1987 in the southern part of the Bay of Campeche, as well as the density distribution along two cross sections which intersect near the most important river system in the region. Based on density field data, density driven currents and the vertical stratification were estimated, the latter by means of the potential energy anomaly. A strong haline gradient, that dominates the sigma-t distribution and is associated with the discharge of the rivers in the region, was observed. The calculated potential energy anomaly had a maximum value of 70 J m–3 near the mouth of the Grijalva-Usumacinta system and the San Pedro and San Pablo rivers. The surface current induced by the density gradient was estimated at 11.2 cm s–1 northeastward. On the other hand, the distribution of isohalines and isopycnals at the surface and 10 m depth showed certain symmetry with respect to a normal axis to the coast. This axis was displaced towards the west of the mouth of the Grijalva-Usumacinta system, suggesting the existence of a littoral current in the east-west direction.