Numerical simulation of turbidity current using V2-f turbulence model

The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model ( 2 n - f model) has been used to simulate the motion of turbid density currents laden with fine solid particles. During the last few years, the 2 n - f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. The 2 n - f model has also proved to be superior to other RANS (Reynolds-Averaged Navier-Stokes) methods in many fluid flows where complex flow features are present. This current becomes turbulent at low Reynolds number (order 1000). The k -e model, which was standardized for high Reynolds number and isotropic turbulence flow, cannot simulate the anisotropy and nonhomogenous behavior near the wall. In this study, the turbidity current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been validated by available experimental data sets. Moreover, results have been compared with the standard k -e turbulence model. The deposition of particles and the effects of their fall velocity on concentration distribution, Richardson number, and the deposition rate are also investigated. The results show that the coarse particles settle rapidly and make the deposition rate higher

Evolutionary algorithm for multi-objective exergoeconomic optimization of biomass waste gasification combined heat and power system

This paper conducts research on Thermodynamic modeling of the Fluidized bed Gasification and Exergoeconomic evaluation to determine the total cost of a combined heat and power system with pressurized fluidized bed gasifier. The paper presents use of multi-objective evolutionary optimization for the system's total cost minimization and Exergetic efficiency maximization, and has been compared to conventional iterative optimization method. It shows that by evaluating with conventional iterative optimization, Exergetic efficiency of total system can reach to 56.09% while using multi-objective evolutionary optimization it is 53.32%. However the product cost achieved by evolutionary optimization is about 6.3% less than the value of iterative optimization.6 page(s

A Large-Signal Nonlinear Equivalent Circuit Model for CMUTs Operating in Collapse and Non-Collapse Modes

Capacitive Micromachined Ultrasonic Transducers (CMUTs) Collapse mode operation offers higher electro-mechanical coupling and transmit pressure compared to non-collapse mode. This paper proposes an Equivalent Circuit Modeling (ECM) approach capable of accurately predicting the large-signal CMUT behavior in both collapse and non-collapse modes. A lumped-parameter nonlinear Equivalent Circuit Model representing the CMUT as a two-port network is implemented in LTSpice. Electro-mechanical and acoustic transduction is described by coupled nonlinear differential equations, i.e., a time-varying capacitance equation relating voltage and current at the electrical port and a force equation balancing elastic, electrostatic, and radiation forces. The nonlinear parameters are computed by Finite Element Modeling (FEM) and implemented in LTSpice using arbitrary behavioral sources and look-up tables

Embedded Sacrificial Layers for CMUT Fabrication

IEEE Sensors (2015 : Busan, SOUTH KOREA)Capacitive Micromachined Ultrasonic Transducers (CMUTs) are generally fabricated either by conventional sacrificial release process or by wafer bonding technique. In the former, sacrificial layers are patterned with deposited materials on the substrate. This current work reports a development on the aforementioned technique wherein sacrificial islands are embedded inside grooves opened by DRIE in the substrate itself. The depth of the grooves and the thickness of the sacrificial layer are identical in dimension. As the first membrane layer between the top electrode and vacuum gap reduces the device sensitivity, it needs to be kept as thin as possible. Conformality of the deposition technique, however, requires a deposition thickness at least equal to the sacrificial layer. Hence one cannot go below a certain first membrane layer thickness. The present method is expected to solve such problems in CMUT fabrication. The present technique keeps the substrate completely flat even after sacrificial patterning, hence aiding the consecutive process steps such as electrode deposition and patterning. The described method does not increase process complexity other than an additional RIE step. Using this technique CMUTs with 5.6 MHz center frequency have been manufactured and tested.IEEE Sensors Council, IEEE Societie