Water Distribution System Analysis: Newton-Raphson Method Revisited

Looped water distribution systems are conventionally analyzed using iterative methods such as Cross, Linear, Newton-Raphson, and Gradient algorithm methods. Depending on the unknown (hydraulic head or discharge), the methods are characterized as h or Q methods. This paper focuses on the h-Newton-Raphson method, which uses the Darcy-Weisbach head loss equation. The paper presents a procedure for improving the h-Newton-Raphson iterative procedure by directly calculating the discharge of each branch by using the Swamee and Jain equation. The proposed procedure leads to a simplified algorithm and more accurate determination of the Jacobian matrix, which accelerates the convergence of the algorithm.     

Acknowledgement of Reviewers 2021

Water Resources Management -     

Oscillations, SE(2)-snakes and motion control: a study of the Roller Racer

This paper is concerned with the problem of motion generation via cyclic variations in selected degrees of freedom (usually referred to as shape variables) in mechanical systems subject to non-holonomic constraints (here the classical system of a disc rolling without sliding on a flat surface). In earlier work, we identified an interesting class of such problems arising in the setting of Lie groups, and investigated these under a hypothesis on constraints, that naturally led to a purely kinematic approach. In the present work, the hypothesis on constraints does not hold, and as a consequence, it is necessary to take into account certain dynamical phenomena. Specifically we concern ourselves with the group SE (2) of rigid motions in the plane and a concrete mechanical realization dubbed the 2-node, 1-module SE (2)snake. In a restricted version, it is also known as the Roller Racer (a patented ride/ toy). Based on the work of Bloch, Krishnaprasad, Marsden and Murray, one recognizes in the example of this paper a balance law called the momentum equation, which is a direct consequence of the interaction of the SE (2)-symmetry of the problem with the constraints. The systematic use of this type of balance law results in certain structures in the example of this paper. We exploit these structures to demonstrate that the single shape freedom in this problem can be cyclically varied to produce a rich variety of motions of the SE (2)-snake. In their study of the snakeboard, a patented modification of the skateboard that also admits the group SE (2) as a symmetry group, Lewis, Ostrowski, Burdick and Murray exploited the same type of balance law as that discussed here to generate motions. A key difference, however, is that, in the present paper, we have only one control variable and thus controllability considerations become somewhat more delicate. In the present paper, we give a self-contained treatment of the geometry, mechanics and motion control of the Roller Racer.     

Towards a Drought Watch System based on Spatial SPI

Regional Drought can be assessed through various meaningfulprocedures mainly related to the expected consequences. However, a general knowledge of the occurrence of drought, thearea which is affected, its severity and its duration are ofgreat importance for a series of decisions, which may beappropriate for a variety of activities. From the existingsimple and popular indices used for the estimation of drought,the Standardised Precipitation Index, known as SPI, seems to winuniversal applicability. A method based on the estimation of SPIover a geographical area and its use for characterising drought,is presented in this paper. Applications of the method arepresented using a digital terrain model and a simple computercalculating routine. It is shown that the proposed procedurecan be easily applied and can support a Drought Watch System foran area of mesoscale dimensions.     

Polychaete-Like Undulatory Robotic Locomotion in Unstructured Substrates

A biological paradigm of versatile locomotion and effective motion control is provided by the polychaete annelid worms, whose motion adapts to a large variety of unstructured environmental conditions (sand, mud, sediment, water, etc.), and could thus be of interest to replicate by robotic analogs. Their locomotion is characterized by the combination of a unique form of tail-to-head body undulations (opposite to snakes and eels), with the rowing-like action of numerous lateral appendages distributed along their long segmented body. Focusing on the former aspect of polychaete locomotion, computational models of crawling and swimming by such tail-to-head body undulations have been developed in this paper. These are based on the Lagrangian dynamics of the system and on resistive models of its interaction with the environment, and are used for simulation studies demonstrating the generation of undulatory gaits. Several biomimetic robotic prototypes have been developed, whose undulatory actuation achieves propulsion on sand and other granular unstructured environments. Extensive experimental studies demonstrate the feasibility of robot propulsion by tail-to-head body undulations in such environments, as well as the agreement of its qualitative and quantitative characteristics to the predictions of the corresponding computational models.