Numerical Parametric Study of Piezocone Penetration Test in Clays

This paper presents a numerical model for the simulation of the piezocone penetration test that is used to carry out a parametric study of the piezocone penetration test in cohesive soils. The piezocone penetration is numerically simulated using an axisymmetric elasto-plastic large deformation finite-element analysis code. The numerical simulation is accomplished in two stages. First, the piezocone is expanded radially from an initial small radius (0.1ro) to the piezocone radius, ro, at the specified depth. Second, the continuous penetration of the piezocone is simulated by applying incremental vertical displacements of the nodes representing the piezocone boundary. The constraint approach is used to model the soil-piezocone interface friction. The Mohr-Coulomb frictional criterion is used to define the sliding potential of the nodes. The main objective of this paper is to present the numerical model and to investigate the effect of the lateral and vertical stresses and the overconsolidation ratio on the cone tip resistance and the developed excess pore pressure around the piezocone. The variation of the horizontal and vertical hydraulic conductivity coefficients on the developed spatial excess pore pressure and its dissipation are also investigated. The results of the numerical study are also compared with the miniature piezocone penetration tests in cohesive soil specimens conducted at the Louisiana State University Calibration Chamber. Results of this study are in good agreement with the measured values.     

Conductance-capacitance and voltage behavior of 1% Os-doped YMnO3/p-Si contacts under varying frequencies

The admittance characterizations of the ferroelectric Perovskite Materials 1% Osmium (Os)-doped YMnO₃ and p-Si contacts were conducted by capacitance–voltage (C–V) and conductance–voltage (G–V) curves at various frequencies. In measurements performed in this study, it was seen that the device behaves like a metal/oxide layer/semiconductor (MOS) or a metal/insulator layer/semiconductor (MIS) capacitor, just because of the ferroelectric thin film at the metal/Si substrate interface. Therefore, an accumulation region (saturation region) formed in the forward bias C–V and G–V curves at each frequency. The accumulation region series resistance value R_sc was determined from the C–V and G–V curves. The R_sc value ranged from 652 Ω at 20 kHz to 56 Ω at 1000 kHz. Furthermore, the series resistance R_s versus V curves with frequency as a parameter were plotted from the C–V and G–V data. A peak appeared around 0.0 V in the R_s vs V curve at each frequency. The peak position of the R_s shifted towards positive voltages from approximately ? 0.2 V at 20 kHz to about 0.10 V at 1000 kHz. The peak position in the corrected conductance vs voltage curves shifted towards positive voltages from approximately 0.0 V at 20 kHz to about 0.20 V at 1000 kHz. It was seen that the series resistance effect caused the highest error in the capacitance occurs in accumulation and in some part of the depletion region at C–V and G–V results depending on frequency. So to conclude, it is not possible to disregard the series resistance everytime. Therefore, the series resistance must be measured and must be considered at the measured admittance.

     

Hydropower Optimization for the Lower Seyhan Basin System in Turkey using dynamic programming

Abstract

Dynamic programming with successive approximation has been used in the past for optimizing multi-reservoir water resources systems. In this study, a State Incremental Dynamic Programming (SIDP) model is developed for energy optimization of multi-reservoir systems. A random file access method is used to generate initial and intermediate data and cope with the curse of dimensionality of dynamic programming. The conventional dynamic programming method is used for each single reservoir to find the initial trajectory of the reservoirs. Then, the computer program developed in the study is applied to the multipurpose-multi-reservoir system in lower Seyhan basin, which comprises six reservoirs, some serial and some parallel. Extended historical flows are used to first maximize firm energy in the critical period, and then total energy over the entire period of flow records. The program is run with 50-year long segments (20 flow scenarios) of the synthetic flow data generated by using the hec-4 generalized computer program to account for the stochastic nature of streamflows. A 20% approximate increase in total energy is obtained by using the developed model for the lower seyhan basin system as compared to that calculated previously by conventional methods.     

Hysteresis and Compensation Behaviors of Mixed Spin-1 and Spin-2 Hexagonal Ising Nanowire System

By utilizing the framework of the effective field theory with correlation, hysteresis and compensation behaviors of mixed spin-1 and spin-2 hexagonal Ising nanowire system is investigated in detail. The effects of Hamiltonian parameters on hysteresis behaviors are discussed, in detail. The compensation behavior of the system is also studied and according to values of Hamiltonian parameters, the Q-, S-, R-, and N-type compensation behaviors is obtained in the system. Finally, the obtaining results are compared with some experimental and theoretical results and found in a qualitatively good agreement.