Duc-Anh An-Vo

Nonlinear Optimisation Using Production Functions to Estimate Economic Benefit of Conjunctive Water Use for Multicrop Production

Uncertainty and shortages of surface water supplies, as a result of global climate change, necessitate development of groundwater in many canal commands. Groundwater can be expensive to pump, but provides a reliable supply if managed sustainably. Groundwater can be used optimally in conjunction with surface water supplies. The use of such conjunctive systems can significantly decrease the risk associated with a stochastic availability of surface water supply. However, increasing pumping cost due to groundwater drawdown and energy prices are key concerns. We propose an innovative nonlinear programing model for the optimisation of profitability and productivity in an irrigation command area, with conjunctive water use options. The model, rather than using exogenous yields and gross margins, uses crop water production and profit functions to endogenously determine yields and water uses, and associated gross margins, respectively, for various conjunctive water use options. The model allows the estimation of the potential economic benefits of conjunctive water use and derives an optimal use of regional level land and water resources by maximising the net benefits and water productivity under various physical and economic constraints, including escalating energy prices. The proposed model is applied to the Coleambally Irrigation Area (CIA) in southeastern Australia to explore potential of conjunctive water use and evaluate economic implication of increasing energy prices. The results show that optimal conjunctive water use can offer significant economic benefit especially at low levels of surface water allocation and pumping cost. The results show that conjunctive water use potentially generates additional AUD 57.3 million if groundwater price is the same as surface water price. The benefit decreases significantly with increasing pumping cost.

Responses of Nitrogen Utilization and Apparent Nitrogen Loss to Different Control Measures in the Wheat and Maize Rotation System

Nitrogen (N) is an essential macronutrient for plant growth and excessive application rates can decrease crop yield and increase N loss into the environment. Field experiments were carried out to understand the effects of N fertilizers on N utilization, crop yield and net income in wheat and maize rotation system of the North China Plain (NCP). Compared to farmers’ N rate (FN), the yield of wheat and maize in reduction N rate by 21–24% based on FN (RN) was improved by 451 kg ha-1, N uptakes improved by 17 kg ha-1 and net income increased by 1671 CNY ha-1, while apparent N loss was reduced by 156 kg ha-1. The controlled-release fertilizer with a 20% reduction of RN (CRF80%), a 20% reduction of RN together with dicyandiamide (RN80%+DCD) and a 20% reduction of RN added with nano-carbon (RN80%+NC) all resulted in an improvement in crop yield and decreased the apparent N losses compared to RN. Contrasted with RN80%+NC, the total crop yield in RN80%+DCD improved by 1185 kg ha-1, N uptake enhanced by 9 kg ha-1 and net income increased by 3929 CNY ha-1, while apparent N loss was similar. Therefore, a 37–39% overall decrease in N rate compared to farmers plus the nitrification inhibitor, DCD, was effective N control measure that increased crop yields, enhanced N efficiencies, and improved economic benefits, while mitigating apparent N loss. There is considerable scope for improved N use effieincy in the intensive wheat -maize rotation of the NCP.

Modeling strain localisation in a segmented bar by a C2-continuous two-node integrated-RBF element formulation

We propose a local C2-continuous 2-node integrated-RBF nelement (IRBFE) method for the numerical modeling of strain nlocalisation due to material discontinuity in a segmented elastic bar. The proposed local 2-node IRBFE method can be nbased on structured or unstructured point collocation procedures where both accuracy and efficiency are achieved. We introduce an effective way to exactly handle the material discontinuity by means of integration constants. Numerical results obtained for a bimaterial bar are compared with those from the analytic, and finite element methods, demonstrating the advantage of the present approach. It will be shown that the solution is C2-continuous except at the bimaterial interface where the actual physical discontinuity is captured.

IRBFN-based multiscale solution of a model 1D elliptic equation

Many engineering problems have a wide range of length scales in their solutions. Direct numerical simulations for these problems typically require extremely-large amounts of CPU time and computer memory, which may be too expensive or impossible on the present supercomputers. In this paper, we present a high-order method, based on the multiscale basis function framework and integrated radial-basis-function networks, for solving multiscale elliptic problems in one dimension.

Simulation of Newtonian-fluid flows with C2-continuous two-node integrated-RBF elements

In this paper, the C2-continuous control-volume method based on 2-node integrated radial basis function elements (IRBFEs) [CMES, vol.72, no.4, pp.299-334, 2011] are further developed for the simulation of incompressible viscous nflows in two dimensions. Emphasis is placed on (i) the 2-node IRBFE discretisation of the stream function-vorticity formulation on Cartesian grids; and (ii) the development of a high order upwind scheme based on 2-node IRBFEs for the case of simulating convection-dominant flows. High levels of accuracy and efficiency of the present method are demonstrated by solving the lid-driven cavity problem.