Optimization of the Ultimate Bearing Capacity of Reinforced Soft Soils through the Concept of the Critical Length of Stone Columns

The objective of this paper is to develop an analytical equation based on the concept of the critical-length of columns in order to optimize the ultimate bearing-capacity of soft soils, supporting a strip footing and reinforced by a group of floating stone columns. Optimization procedure was performed on three-dimensional numerical models simulated on the Flac3D computer code, for various soft-soils with different undrained-cohesions (Cu=15–35kPa), reinforced by columns of varying lengths (L) and area replacement ratio (As=10-40%), considering different footing widths B. Obtained results indicate that the optimal bearing-capacity ratio (Ultimate bearing-capacity of reinforced soil/unreinforced soil) is reached for the column critical-length ratio (Lc/B) and increase with increase of the later ratio, depending on As and Cu. Analysis of results also showed that the optimal values of the bearing-capacity ratio in the reinforced soils remain bounded between the lower and higher values (1.28-2.32), respectively for minimal and maximal values of the critical-length ratio (1.1) and (4.4). Based on these results, a useful analytical equation is proposed by the authors, for the expression of the critical-length; thus ensuring an optimal pre-dimensioning of the stone columns. The proposed equation was compared with the data available in the literature and showed good agreement. Doi: 10.28991/cej-2021-03091737 Full Text: PDF

Prediction of Synchronization Time for Tractor Power-Shift Transmission Using Multi-Body Dynamic Simulation

HighlightsPrediction of synchronization time was performed for a power-shift transmission.We derived an analytical equation for synchronization time and developed a multi-body dynamics model.Model results were compared with results of a power-shift test on a synchronizer.Reduced computation and design time was achieved for automatic transmission design.Abstract. Synchronization time determines the capacity of a shift actuator for an automatic transmission system. Existing approaches for measuring this time only consider one rotational inertia and therefore cannot be applied to the power-shift transmission (PST) of a tractor with wet multi-plate clutches on both sides of the synchronizer. This study aims to predict the PST synchronization time by considering time-varying axial forces as first-order functions and the equivalent rotational inertias of the hub and the gear. First, we derive an analytical equation for the synchronization time. We then develop a multi-body dynamics (MBD) model that includes the drag torque of the wet multi-plate clutches. The MBD model is composed of a synchronizer, a linkage, and an output shaft of a shift actuator as a rigid-body system. A power-shift test was performed on the synchronizer at two shift stages requiring the maximum shift force of the system. The torque of the shift actuator (the input of the shift system) and the angular displacement of the output shaft of the shift actuator (the output of the shift system) were measured. The results of the simulation model were then compared with those of the shift test. Compared with the test results, the simulation results were validated within 7.63% accuracy, based on the maximum value for the torque of the shift actuator. The proposed equation was validated within a maximum error range of 8.25%. The proposed equation did not consider drag torque of the wet multi-plate clutches because that torque is much smaller than the cone torque of the synchronizer in the target shift system. The proposed equation can reduce computation time and will enable more precise sizing of the synchronizer and shift actuator in the early design stages of automatic transmissions. Keywords: Multi-body dynamics, Power-shift transmission, Synchronization time, Synchronizer, Tractor transmission.

THERMAL AND CALORIC EQUATIONS OF STATE FOR NITROGEN: APPLICATION TO CRYOGENIC INJECTION CONDITIONS

The real-gas analytical equation of state (EoS) for nitrogen is developed. The applicability domain of the EoS is verified in a wide range of density (from 0 to the value at the triple point, 0.867 g/cm3) and temperature (from 100 to 5000 K). The obtained EoS is introduced into the gasdynamic code for calculating multidimensional turbulent reactive flows.

Nuclear Material Measurement Based on Fast Neutron Multiplicity Counter

Fast neutron multiplicity counting (FNMC) analysis method, as a new non-destructive analysis method for nuclear materials, plays an increasingly important role in the measurement of nuclear material properties. Based on the derivation of the FNMC analytical equation of Pu material, the method of solving the sample parameters was given. By analyzing the mechanism of interaction of neutrons and matter, the model used by Geant4 (version 10.4) software was determined, and a set of three-layer, fast neutron multiplicity counters with six liquid scintillation detectors per layer was constructed. Using the fast neutron multiplicity counter to analyze the measured parameters, the detection efficiency variation was less than 0.4% within the 150g sample mass range, and the PuO2 fluctuation was less than the metal Pu. By studying the detection efficiency and the multiplicity counting rate as a function of sample mass, within the 150g sample mass range, both basically meet the model assumptions of the FNMC analytical equation. The metal Pu and PuO2 samples were set separately, and the FNMC analysis equation was solved. When the sample mass was within 150g, the sample mass solution deviation was less than 10%. The results show that the built-in fast neutron multiplicity counter can better measure Pu sample properties.

Experimental and numerical study on stiffness and damage of glass/epoxy biaxial weft-knitted reinforced composites

This paper deals with investigating the tensile characteristics of biaxial weft-knitted reinforced composites in terms of stiffness, strength and failure mechanism. The biaxial weft-knitted fabric was produced on an electronic flat knitting machine by E-glass yarns and then was impregnated with epoxy resin. Using an accurate geometrical model, the composite unit cell was designed in Abaqus software’s environment. Tensile tests were simulated in different directions on the created unit cell and the stiffness was calculated. By applying the proper failure theories, the composite strength was predicted and then critical regions of the unit cell were determined. In the next step, a micromechanical approach was also applied to estimate the same tensile features. Failure theories were also applied to predict the strength and most susceptible areas for failure phenomenon in the composite unit cell. The tensile properties of the produced composites were measured and compared with outputs of the finite element and micromechanical approaches. The results showed that the meso-scale finite element analysis approach can well predict the composite strength. In contrast, the meso-scale analytical equation model was not able to predict it acceptably because this model ignores the strain concentration. Both meso-scale finite element analysis and meso-scale analytical equation approaches predicted the similar locations for the composite failure in wale and course directions.

Parameter estimation of soil hydraulic characteristics by inverse modeling of the analytical equation for unsaturated subsurface water flow

In drip-irrigated systems, the understanding of the soil wetting pattern is essential in defining the area effectively irrigated, the spacing between the emitters and their installation depth, and the irrigation rate. Thus, this study aims to estimate soil hydraulic characteristics through inverse modeling of an analytical equation used in wetting bulb simulation based on soil moisture measurements obtained in the field. The parameters of the Gardner model, which describes the unsaturated soil hydraulic conductivity, and the van Genuchten model that describes the soil moisture retention curve, were estimated by inverse modeling techniques. The following options were considered: (A) estimating parameter β while considering the other parameters, Ko, θr, θs, α, n, and m, as known and obtained experimentally; (B) estimating parameters Ko and β while considering the experimental retention curve as known; (C) estimating parameters Ko, β, α, n, and m while considering the values of the θr and θs volumetric moisture as known; (D) estimating all the parameters of Gardner and van Genuchten models (Ko, θr, θs, α, n, and m). The results indicate that option D showed better concordance between the estimated and observed moisture values. Thus, the inverse modeling of the analytical equation is an important tool for irrigation design and management.