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An appraisal on the soil wetting water retention characteristic curve determined from mini disk infiltrometer and sensor measurements

Naik Aparimita Priyadarshini, Pekkat Sreeja

Acta Geophysica

2023

Vol. 71, no. 2

961--982

Direct determination of wetting water retention characteristics curve (WWRCC) is time-consuming, needs destructive sampling and invasive sensor placement, and, at times, is difficult to measure due to rapid wetting. The objective of this study was to critically analyze the use of a handy mini disk infiltrometer’s (MDI’s) measurements for indirect determination of WWRCC parameters (α, n) and saturated hydraulic conductivity (Ks). The α, n, and Ks were estimated by considering cumulative infiltration (CI), volumetric water content (VWC), and soil water potential (SWP) measurements, divided into 17 subcases and 924 inverse simulations. The inverse simulation was improved by considering measured final VWC as an additional input if α, n, and Ks were estimated from MDI measurements. The simulated CI, VWC, and SWP compared well with the measured results with low root mean square error (RMSE) (10–5 m3 for CI,≤ 10–2 m3 /m3 for VWC, and 10–1 m for SWP). The mean values determined from all the statistically comparable cases for two soil textures, loam and silt loam, were, respectively, α (m−1) equal to 1.43 and 0.41, and n equal to 1.5 and 1.61. The WWRCC developed using the mean α and n values was close to the measured curves and significantly different from the texture-based pedo transfer function (PTF) estimation. Furthermore, the Ks values estimated from the inverse analysis of MDI measurements were comparable with reference falling head permeameter measurements for both the soils. The observations from this study demonstrated that MDI is a reliable, non-invasive, and non-destructive method for quick indirect estimation of α, n, and Ks.

From orthogonal to tangential control of underactuated mechanical systems in partly specified motion - a case study illustration

Blajer W., Seifried R.

International Journal of Applied Mechanics and Engineering

2012

Vol. 17, no. 3

689-706

Underactuated mechanical systems have fewer control inputs than degrees of freedom. Their performance goal may be realization of specified in time outputs, treated as servo-constraints on the system, whose number is equal to the number of inputs. The solution to the inverse simulation problem (servo-constraint problem), that is the determination of an input control strategy that forces an underactuated system to complete the partly specified motion, is a challenging task. This is because mechanical systems may be "underactuated" in several ways and, as opposed to the passive constraint reactions which are orthogonal to the constraint manifold, the control forces may be arbitrary oriented with respect to the servo-constraint manifold. The diversity of servo-constraint problems is discussed using a simple spring-mass system mounted on a carriage, and is related to multiple issues: formulations in generalized coordinates and output-involved coordinates, orthogonal or tangential realization of servo-constraints, the arising ODE/DAE forms of the governing equations, and existence of the uncontrolled internal dynamics. Some computational issues are finally reported, with relevant simulation results for the sample case example.