Areas Of Steep Gradients Research Articles

Simulation of Unconfined Aquifer Flow Based on Parallel Adaptive Mesh Refinement

AbstractThe density of a numerical mesh is a key component for the quality of the numerical solution. Common methods in groundwater simulations rely on meshes generated prior to simulation, which lead to unnecessary or insufficient degrees of freedom (dofs). In this study we use Adaptive Mesh Refinement (AMR) to substitute the subjective mesh generation process with a more rigorous approach where new dofs are iteratively added to the solution of an initial coarse mesh based on a solution error estimation. The simulation is solved on a succession of meshes through which the mesh density is increased in areas of steep gradients in the solution variable. Here, we apply the approach to unconfined aquifer flow which is a non‐linear problem commonly encountered in groundwater modeling. By taking advantage of the iterative nature of AMR we arrive at an efficient solver approach. We treat the position of the unconfined boundary as an additional unknown which is estimated iteratively. The first iterations are executed rapidly as the mesh is rather coarse, while the free boundary adapts to the computed water table position as close as the mesh density allows. In this study we demonstrate the viability of the proposed unconfined aquifer simulation method to a series of 2D hypothetical examples under several conditions and stresses as well as a 3D test case. In all cases the AMR was able to automatically resolve the solution in areas with steep hydraulic head gradient, using appropriately higher density to achieve high localized refinement and accuracy.

Increasing the Spatial Resolution of Visual Field Tests Without Increasing Test Duration: An Evaluation of ARREST.

PurposeThe Australian Reduced Range Extended Spatial Test (ARREST) approach was designed to improve visual field spatial resolution while maintaining a similar test duration to clinically used testing algorithms. ARREST does not completely threshold visual field locations with sensitivity < 17 dB, and uses the presentations saved to test new locations in areas of steep gradient within the visual field. Previous assessments of ARREST's performance have used computer simulation. In this study, we cross-sectionally assessed the performance of ARREST in people with visual field loss.MethodsWe tested 23 people with glaucoma (mean age: 71 ± 8 years) with established visual field loss. Three visual field procedures were performed using the Open Perimetry Interface: cZEST and ARREST on the Octopus 900 perimeter (Haag-Streit AG, Switzerland), and a reference standard (best available estimate [BAE]) on the Compass perimeter (CenterVue SpA, Italy). ARREST was compared against the cZEST and the BAE.ResultsOn average, ARREST added seven new locations (range = 0–15) to a visual field test. There was no significant difference in the number of stimulus presentations between procedures (mean = 259 ± 25 [ARREST] vs. 261 ± 25 [cZEST], P = 0.78). In classifying threshold values < 17 dB, ARREST performed similarly when compared against BAE.ConclusionsThis study provides empirical evidence to support conclusions from previous computer simulations that ARREST can be used to increase spatial sampling in regions of interest without increasing test time.Translational RelevanceARREST is a new approach that augments current visual field testing procedures to provide better spatial description of visual field defects without increasing test duration.

The Impact of the Two-Way Coupling between Wind Wave and Atmospheric Models on the Lower Atmosphere over the North Sea

The effects of coupling between the atmospheric model of the Consortium for Small-Scale Modelling-Climate Limited-area Modelling (CCLM) and the wind wave model (WAM) on the lower atmosphere within the North Sea area are studied. Due to the two-way coupling between the models, the influences of wind waves and the atmosphere on each other can be determined. This two-way coupling between these models is enabled through the introduction of wave-induced drag into CCLM and updated winds into WAM. As a result of wave-induced drag, different atmospheric parameters are either directly or indirectly influenced by the wave conditions. The largest differences between the coupled and reference model simulation are found during storm events as well as in areas of steep gradients in the mean sea level pressure, wind speed or temperature. In the two-way coupled simulation, the position and strength of these gradients vary, compared to the reference simulation, leading to differences that spread throughout the entire planetary boundary layer and outside the coupled model area, thereby influencing the atmosphere over land and ocean, although not coupled to the wave model. Ultimately, the results of both model simulations are assessed against in situ and satellite measurements, with a better general performance of the two-way coupled simulation with respect to the observations.

Controlled cost of adaptive mesh refinement in practical 3D finite element analysis

In this paper, attention is restricted to mesh adaptivity. Traditionally, the most common mesh adaptive strategies for linear problems are used to reach a prescribed accuracy. This goal is best met with an h-adaptive scheme in combination with an error estimator. In an industrial context, the aim of the mechanical simulations in engineering design is not only to obtain greatest quality but more often a compromise between the desired quality and the computation cost (CPU time, storage, software, competence, human cost, computer used). In this paper we propose the use of alternative mesh refinement with an h-adaptive procedure for 3D elastic problems. The alternative mesh refinement criteria allow to obtain the maximum of accuracy for a prescribed cost. These adaptive strategies are based on a technique of error in constitutive relation (the process could be used with other error estimators) and an efficient adaptive technique which automatically takes into account the steep gradient areas. This work proposes a 3D method of adaptivity with the latest version of the INRIA automatic mesh generator GAMHIC3D.

Adaptive mesh refinement for the control of cost and quality in finite element analysis

Adaptive strategies are a necessary tool to make finite element analysis applicable to engineering practice. In this paper, attention is restricted to mesh adaptivity. Traditionally, the most common mesh adaptive strategies for linear problems are used to reach a prescribed accuracy. This goal is best met with an h-adaptive scheme in combination with an error estimator. In an industrial context, the aim of the mechanical simulations in engineering design is not only to obtain greatest quality but more often a compromise between the desired quality and the computation cost (CPU time, storage, software, competence, human cost, computer used). In this paper, we propose the use of alternative mesh refinement criteria with an h-adaptive procedure for 3D elastic problems. The alternative mesh refinement criteria (MR) are based on: prescribed number of elements with maximum accuracy, prescribed CPU time with maximum accuracy and prescribed memory size with maximum accuracy. These adaptive strategies are based on a technique of error in constitutive relation (the process could be used with other error estimators) and an efficient adaptive technique which automatically takes into account the steep gradient areas. This work proposes a 3D method of adaptivity with the latest version of the INRIA automatic mesh generator GAMHIC3D.

New approach for automation of finite element analysis

In this paper we propose a new approach for an optimization of finite element analysis in elasticity. From a mechanical problem and a criterion of optimization, the procedure provides an approximate solution satisfying the prescribed criterion. An error measure based on the constitutive relation and an efficient adaptive technique which automatically takes into account steep gradient areas are used. With such a procedure, even a nonspecialist can carry out accurate finite element analysis. In particular, the user does not identify a priori the regions that must be refined. Several criteria of optimization have been developed and some examples show the efficiency of the method.

Performance of grass and rainforest riparian buffers in the wet tropics, Far North Queensland. 2. Water quality

Riparian lands have the potential to buffer streams from hillslope sediment and nutrient transport. Most research on buffers has been conducted under laboratory or manipulated field experimental conditions. Few quantitative data exist on buffer performance under natural field conditions. This study reports measured soil loss and evaluates the effectiveness of riparian buffers on planar and convergent slopes under field hydrological conditions in Far North Queensland. The conditions are extreme for testing the effectiveness of riparian buffers as the land is steep, intensely cropped and receives high intensity rainfall. Hillslopes cropped with bananas were monitored using paired flumes. Runoff, bedload, and suspended loads were measured leaving the crop (upper sites) and leaving the riparian buffers (lower sites). Highly variable hillslope soil losses of &lt;1 to &gt;70 t/ha per wet season were recorded. High rates of hillslope soil loss were from areas of steep gradient with little ground cover experiencing high rainfall intensity. On planar slopes, even with high soil loss, grass buffer strips were able to trap &gt;80% of the incoming bedload. Total N (TN), total P (TP) and suspended sediment (SS) loads were reduced between 25 and 65% by the planar slope grass buffer and within the first 15 m of the moderately convergent grass buffer. Loads leaving the moderately convergent buffer were often higher than those delivered from the crop, due to seepage after prolonged or high frequency rainfall. Under these conditions the buffer's main function is to prevent erosion rather than trap sediment and nutrients. Results from a highly convergent 5-ha hillslope, suggest that for buffers to be more effective in such topography, they should also be placed at the end of the crop rows, where contributing areas are smaller. Flow was able to concentrate within the crop and on at least one occasion was able to scour a 30-cm-wide channel through the entire width of the buffer releasing previously trapped material and making the buffer ineffective. A remnant rainforest buffer, receiving runoff from a planar slope, acted as a temporary store of sediment and nutrients that were reworked during subsequent events. This study demonstrates both a need for managed buffer strips on sloping tropical cropped land and identifies limitations on their potential effectiveness.

Alternative mesh optimality criteria for h-adaptive finite element method

Adaptive strategies are a necessary tool to make finite element analysis applicable to engineering practice. In this paper, attention is restricted to mesh adaptivity. Traditionally, the most common mesh adaptive strategies for linear problems are used to attain a prescribed accuracy. This goal is best met with an h-adaptive scheme in combination with an error estimator. In this paper we propose the use of alternative mesh optimality criteria with an h-adaptive procedure for 2D elastic problems. The alternative mesh optimality criteria allow us to attain maximum of accuracy with a prescribed number of elements or a prescribed memory size or a prescribed cpu time. These adaptive strategies are based on a technique of error in constitutive relation and adapted techniques of construction of admissible fields (the process could be used with other error estimators) and an efficient adaptive technique which automatically takes account the steep gradient areas. Some examples show the efficiency of the method.