COMPARISON OF THREE DIFFERENT WOODY PLANT SPECIES FOR THEIR ABILITY TO UTILIZE NUTRITIONAL ELEMENTS SUPPLIED IN THE FORM OF BIOSOLIDS AND MINERAL FERTILIZERS

Crop production systems of the future will need to focus on recycling rather than flow- through of mineral nutrients. Much of the nutrients that leave agricultural systems with crop products eventually end up in household waste and sewage. Returning nutrientrich products from wastewater treatment to agricultural soils must be done in an environmentally sound and culturally acceptable manner. More than 300,000 hectares of forest have been planted in the United Arab Emirates (UAE), consisting mainly of native species, such as Prosopis cineraria (Ghāf) and Vachellia tortilis (Samr). It has been proposed that sewage sludge, the dry residue from wastewater treatment, is returned to crop production via land application to these forests, as they are not directly used in food production for human consumption nor are they in close proximity to human settlements. However, little is known about how native desert trees would respond to such an additional fertilizer supply. In the present study, the ability of Ghāf and Samr trees to utilize nutrients provided either in the form of sewage sludge as biofertilizers or mineral fertilizer salts was compared. Wild jasmine shrubs (Clerodendrum inerme) were included as a third species in this experiment because they are an exotic and faster growing woody plant. The young jasmine shrubs were grown in the greenhouse in pots filled with sandy dune soil to which nutrients were added at three different levels. The nutrients were supplied either in the form of sewage sludge or mineral fertilizers. The soil prepared for fertilization with sewage sludge was mixed with 3.2, 6.4 and 12.8 g of dry sewage sludge per kg of dry soil, respectively. This was equivalent to 60, 120 and 240 mg N per kg dry soil. Plants were harvested nine months after the start of the experiment, and their dry weight and shoot nutrient uptake were evaluated. Compared to the desert tree species, wild jasmine shrubs had significantly higher dry weights at the end of the experiment. Nevertheless, none of the species showed a positive growth response to the increase in the supply of nutritional elements. Wild jasmine shrubs showed increased uptake of macronutrients with increasing fertilizer supply and were equally capable of utilizing nutrients from sewage sludge and mineral fertilizers. No increase in elemental uptake in response to increasing fertilizer supply was observed in the indigenous trees. The growth of Ghāf trees responded negatively to a high supply of sewage sludge but not to a high supply of mineral fertilizer. The results of our study suggest that the ability to absorb and utilize nutrients supplied in the form of sewage sludge may be limited in desert trees such as Ghāf and Samr. The potential to utilize sewage sludge could be increased by planting exotic species which have higher growth and element uptake potential compared to indigenous trees

Hollow vortices and wakes past Chaplygin cusps

By using analytic tools for 2D rotational inviscid flow, the stagnation points of Pocklington hollow vortices are replaced by Chaplygin cusps, that is, by regions of fluid at rest. By solidifying the bounding free streamlines, solid bodies are obtained along whose walls adverse pressure gradients are avoided. These results are relevant to the theory and practice of control of separated flow at high Reynolds number. Examples are presented pertinent to single bodies and cascade of bodies which trap hollow vortices or generate open hollow wake

Iterative Methods for Model Reduction by Domain Decomposition

We propose a method to reduce the computational effort to solve a partial differential equation on a given domain. The main idea is to split the domain of interest in two subdomains, and to use different approximation methods in each of the two subdomains. In particular, in one subdomain we discretize the governing equations by a canonical scheme, whereas in the other one we solve a reduced order model of the original problem. Different approaches to couple the low-order model to the usual discretization are presented. The effectiveness of these approaches is tested on numerical examples pertinent to non-linear model problems including the Laplace equation with non-linear boundary conditions and the compressible Euler equations

Accurate Sharp Interface Scheme for Multimaterials

We present a method to capture the evolution of a contact discontinuity separating two different material. A locally non-conservative scheme allows an accurate and stable simulation while the interface is kept sharp. Numerical illustrations include problems involving fluid and elastic problems

Model order reduction by convex displacement interpolation

We present a nonlinear interpolation technique for parametric fields that exploits optimal transportation of coherent structures of the solution to achieve accurate performance. The approach generalizes the nonlinear interpolation procedure introduced in [Iollo, Taddei, J. Comput. Phys., 2022] to multi-dimensional parameter domains and to datasets of several snapshots. Given a library of high-fidelity simulations, we rely on a scalar testing function and on a point set registration method to identify coherent structures of the solution field in the form of sorted point clouds. Given a new parameter value, we exploit a regression method to predict the new point cloud; then, we resort to a boundary-aware registration technique to define bijective mappings that deform the new point cloud into the point clouds of the neighboring elements of the dataset, while preserving the boundary of the domain; finally, we define the estimate as a weighted combination of modes obtained by composing the neighboring snapshots with the previously-built mappings. We present several numerical examples for compressible and incompressible, viscous and inviscid flows to demonstrate the accuracy of the method. Furthermore, we employ the nonlinear interpolation procedure to augment the dataset of simulations for linear-subspace projection-based model reduction: our data augmentation procedure is designed to reduce offline costs -- which are dominated by snapshot generation -- of model reduction techniques for nonlinear advection-dominated problems

Integration of multi-fidelity methods in parametrized non-intrusive reduced order models for industrial applications

Exploring the behavior of complex industrial problems might become burdensome, especially in high-dimensional design spaces. Reduced Order Models (ROMs) aim to minimize the computational effort needed to study different design choices by exploiting already available data. In this work, we propose a methodology where the full-order solution is replaced with a Proper Orthogonal Decomposition based ROM, enhanced by a multi-fidelity surrogate model. Multi-fidelity approaches allow to exploit heterogeneous information sources, and consequently reduce the cost of creating the training data needed to build the ROM. To explore the multi-fidelity ROM capabilities, we present and discuss results and challenges for an automotive aerodynamic application, based on a geometric morphing of the DrivAer test case with multi-fidelity fluid-dynamics simulations

Design Optimization Based on Multi-fidelity Metamodels

This paper illustrates how multi-fidelity metamodels can be efficiently applied to save time and costs in parametric design optimization, which normally requires simulating numerically a large number of designs. Datasets of high fidelity (HF) and middle-low fidelity (LF) simulations, obtained for instance from computational models solved by grid discretizations of different accuracy, can be used together to feed the surrogate model, improving the accuracy of the response function prediction and reducing the overall computational cost at the same time. The methodologies proposed in this paper include adaptive Design of Experiments algorithms to define the optimal dataset of design simulations, and efficient multi-fidelity surrogate methods for scalar fields (Cokriging) and vector fields (Reduced Order Models). All the methods are tested and applied to CFD test cases

ADER scheme for incompressible Navier-Stokes equations on Overset grids with a compact transmission condition

A space-time Finite Volume method is devised to simulate incompressible viscous flows in an evolving domain. Inspired by the ADER method, the Navier-Stokes equations are discretized onto a space-time overset grid which is able to take into account both the shape of a possibly moving object and the evolution of the domain. A compact transmission condition is employed in order to mutually exchange information from one mesh to the other. The resulting method is second order accurate in space and time for both velocity and pressure. The accuracy and efficiency of the method are tested through reference simulations.Une méthode des volumes finis spatio-temporels est conçue pour simuler des écoulements visqueux incompressibles dans un domaine évolutif. Inspirée de la méthode ADER, les équations de Navier-Stokes sont discrétisées sur un maillage spatio-temporel overset qui est capable de prendre en compte à la fois la forme d’un objet éventuellement en mouvement et l’évolution du domaine. Une condition de transmission compacte est employée afin d’échanger mutuellement des informations d’un maillage à l’autre. La méthode résultante est d’une précision de second ordre dans l’espace et dans le temps pour la vitesse et la pression. La précision et l’efficacité de la méthode sont testées sur des cas test pris de la littérature

Free-form deformation, mesh morphing and reduced-order methods: enablers for efficient aerodynamic shape optimisation

The work provides an integrated pipeline for the model order reduction of turbulent flows around parametrised geometries in aerodynamics. In particular, Free-Form Deformation is applied for geometry parametrisation, whereas two different reduced-order models based on Proper Orthogonal Decomposition (POD) are employed in order to speed-up the full-order simulations: the first method exploits POD with interpolation, while the second one is based on domain decomposition. For the sampling of the parameter space, we adopt a Greedy strategy coupled with Constrained Centroidal Voronoi Tessellations, in order to guarantee a good compromise between space exploration and exploitation. The proposed framework is tested on an industrially relevant application, i.e. the front-bumper morphing of the DrivAer car model, using the finite-volume method for the full-order resolution of the Reynolds-Averaged Navier-Stokes equations