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排序方式: 共有561条查询结果,搜索用时 15 毫秒
21.
ABSTRACT A multistage system comprising an upflow anaerobic sludge blanket (UASB) followed by anoxic unit and then oxic activated sludge (AS) with biofilm is studied in El-Berka WWTP, Egypt. Different organic loading wastewaters of chemical oxygen demand (COD) less than 500 mg/L till 3000 mg/L are tested during the study. The hydraulic retention time (HRT) varies for each loading from 7.5 to 10 to 15 h. The UASB reactor accomplishes the removal efficiency of 50%–70% of influent COD. The overall system performs the removal efficiency of 95% of influent COD and NH4-N. Also, the results are verified by a modified mathematical model. 相似文献
22.
A mechanistic model has been developed for determining the stratified boundary for condensing flows in horizontal and slightly inclined tubes. Two formulations, a complete and a simplified version are considered for the equilibrium liquid level. Good agreement is found between the two formulations and generalized results were derived from the simplified version of the model. From these results, the effect of condensation is shown to be equivalent to adding a small upward inclination in adiabatic gas-liquid flow. The predicted transition line is compared with flow-regime data of different fluid properties, tube diameters, and inclinations. The predictions agreed reasonably well with the data. 相似文献
23.
This paper investigates the effect of the EDL at the solid–liquid interface on the liquid flow and heat transfer through a micro-channel formed by two parallel plates. The complete Poisson–Boltzmann equation (without the frequently used linear approximation) was solved analytically in order to determine the EDL field near the solid–liquid interface. The momentum equation was solved analytically taking into consideration the electrical body force resulting from the EDL field and the energy equation was solved analytically taking viscous dissipation into consideration. Effects of the channel size and the strength of the zeta-potential on the electrostatic potential, the streaming potential, the velocity profile, the temperature profile, the volume flow rate, the apparent viscosity, the friction factor, and Nusselt number are presented and discussed. Results of the present analysis, which are based on the complete Poisson–Boltzmann equation, are compared with a simplified analysis that used a linear approximation of the Poisson–Boltzmann equation. 相似文献
24.
Robust decentralized PID-based power system stabilizer design using an ILMI approach 总被引:1,自引:0,他引:1
Thanks to its essential functionality and structure simplicity, proportional-integral-derivative (PID) controllers are commonly used by industrial utilities. A robust PID-based power system stabilizer (PSS) is proposed to properly function over a wide range of operating conditions. Uncertainties in plant parameters, due to variation in generation and load patterns, are expressed in the form of a polytopic model. The PID control problem is firstly reduced to a generalized static output feedback (SOF) synthesis. The derivative action is designed and implemented as a high-pass filter based on a low-pass block to reduce its sensitivity to sensor noise. The proposed design algorithm adopts a quadratic Lyapunov approach to guarantee α-decay rate for the entire polytope. A constrained structure of Lyapunov function and SOF gain matrix is considered to enforce a decentralized scheme. Setting of controller parameters is carried out via an iterative linear matrix inequality (ILMI). Simulation results, based on a benchmark model of a two-area four-machine test system, are presented to compare the proposed design to a well-tuned conventional PSS and to the standard IEEE-PSS4B stabilizer. 相似文献
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Time-cost trade-off analysis represents a challenging task because the activity duration and cost have uncertainty associated with them, which should be considered when performing schedule optimization. This study proposes a hybrid technique that combines genetic algorithms (GAs) with dynamic programming to solve construction projects time-cost trade-off problems under uncertainty. The technique is formulated to apply to project schedules with repetitive nonserial subprojects that are common in the construction industry such as multiunit housing projects and retail network development projects. A generalized mathematical model is derived to account for factors affecting cost and duration relationships at both the activity and project levels. First, a genetic algorithm is utilized to find optimum and near optimum solutions from the complicated hyperplane formed by the coding system. Then, a dynamic programming procedure is utilized to search the vicinity of each of the near optima found by the GA, and converges on the global optima. The entire optimization process is conducted using a custom developed computer code. The validation and implementation of the proposed techniques is done over three axes. Mathematical correctness is validated through function optimization of test functions with known optima. Applicability to scheduling problems is validated through optimization of a 14 activity miniproject found in the literature for results comparison. Finally implementation to a case study is done over a gas station development program to produce optimum schedules and corresponding trade-off curves. Results show that genetic algorithms can be integrated with dynamic programming techniques to provide an effective means of solving for optimal project schedules in an enhanced realistic approach. 相似文献
28.
Soliman A. Mahmoud Ahmed S. Elwakil Ahmed M. Soliman 《International Journal of Electronics》2013,100(12):1441-1451
Novel grounded and floating CMOS active nonlinear resistors with odd symmetrical characteristics are designed. The nonlinear resistors are then incorporated into two chaotic oscillator circuits based on a CMOS current feedback op amp (CFOA). The slopes of both the negative and positive segments of the nonlinear characteristics are voltage controlled, allowing for a wide range of dynamic behaviour to be observed and easily tuned in a period doubling route to chaos. Nonlinear current–voltage characteristics are derived in a piecewise-linear form and shown possibly to be modelled using a cubic polynomial approximation. PSPICE simulations using a standard 2.0 μm technology file and numerical simulations of the derived chaotic mathematical models are included. 相似文献
29.
This paper develops a Bayesian analysis in the context of record statistics values from the two-parameter Weibull distribution. The ML and the Bayes estimates based on record values are derived for the two unknown parameters and some survival time parameters e.g. reliability and hazard functions. The Bayes estimates are obtained based on a conjugate prior for the scale parameter and a discrete prior for the shape parameter of this model. This is done with respect to both symmetric loss function (squared error loss), and asymmetric loss function (linear-exponential (LINEX)) loss function. The maximum likelihood and the different Bayes estimates are compared via a Monte Carlo simulation study. A practical example consisting of real record values using the data from an accelerated test on insulating fluid reported by Nelson was used for illustration and comparison. Finally, Bayesian predictive density function, which is necessary to obtain bounds for predictive interval of future record is derived and discussed using a numerical example. The results may be of interest in a situation where only record values are stored. 相似文献
30.
A new CMOS voltage‐controlled fully‐differential transconductor is presented. The basic structure of the proposed transconductor is based on a four‐MOS transistor cell operating in the triode or saturation region. It achieves a high linearity range of ± 1 V at a 1.5 V supply voltage. The proposed transconductor is used to realize a new fully‐differential Gm‐C low‐pass filter with a minimum number of transconductors and grounded capacitors. PSpice simulation results for the transconductor circuit and its filter application indicating the linearity range and verifying the analytical results using 0.35 μm technology are also given. 相似文献