Issues in optimal parameter estimation for the nonlinear Muskingum flood routing model

This study answers two questions raised in the parameter estimation optimization for the nonlinear Muskingum flood routing model. The first question is whether a new global optimum was still found after the existing global optimum had already been found. In order to fairly verify this question, a standard routing procedure for the nonlinear Muskingum model, which has not been clearly described previously, is proposed. Because the routing procedure was coded in a spreadsheet, any researcher can easily test it after downloading it. The second question is the reason why various approaches, such as Lagrange multiplier, Broyden–Fletcher–Goldfarb–Shanno (BFGS), genetic algorithm, harmony search and particle swarm optimization, have tackled only Wilson's data set as the parameter estimation optimization for the nonlinear Muskingum model, because Wilson's data have a unique structure which is differentiated from other data sets. This study also provides various data sets to compare.     

Generalised models of design interation using signal flow graphs

Changing customer preferences, demand for quality, and new technologies have led to very short product life cycles. This requires firms to have short product development lead times while keeping product costs low and quality high in order to stay competitive. In this context, we focus on improved understanding of time-consuming design iterations. We are creating tools for modeling product development projects in order to predict the performance of product development organisations. In this paper, signal flow graphs are presented as a flexible tool for design process modeling, and illustrated using an industrial example. Analysis of the model allows computation of the probability distribution of lead time and identification of the key drivers of lead time.     

Channel routing using neural networking

Abstract

The channel routing problem in an integrated circuit layout design involves making interconnections among terminals located on opposite sides of a rectangular channel. This problem has been proven to be NP‐complete and most currently available algorithms are heuristic. This paper proposes a neural network to handle the channel routing problem. Neural networking has been successfully applied to many combinatorial optimization problems. However, applying this technique to the channel routing problem has not ever been reported. This network allows users to preroute any critical nets and then invoke the network to complete the rest. User intervention also can speedup the operation of the router significantly. Typical examples from published literature are taken for experiments. The theoretic lower bounds are achieved in all examples.     

Analysis of flow behaviour of iron and steel using power law models

The tensile flow behaviour of mechanically milled iron and a low-alloy steel are analysed using power law models that describe the evolution of stress–strain during a tensile test. A new analytical power law equation is presented that is shown to be superior to the Hollomon and Ludwigson equation to describe the room temperature flow properties of the low-alloy steel over a wide strain rate range. It not only provides a better fit to the homogenous flow curve of the low-alloy steel but also predicts the maximum strength without the prior knowledge of the uniform strain. The new equation also fitted the flow curves of mechanically milled iron with grain sizes in nano to micrometer range.     

The urban unsteady and non pressure rain pipe flow routing by the dynamical wave method

The dynamical-wave method routing model of the unsteady and non-pressure rain pipe flow was be established by conservation of mass, momentum and energy in the city unsteady and non-pressure rain pipe flow, and it was resoled by applying the four concealing style differences and the pursue method. Results by experiment checking computations and comparative analysis state that this routing model can reflect flood peak propagate in pipeline attenuate and backwater etc. influence, has the higher calculation precision, possess vast sphere of application, and can adapts to performing the city rain pipe flow routing in t the distinct situation of the different incline degrees and enter runoff . This routing model supplies the scientific foundation to the Town rainfall piping design or checking, administration, and so on.     

Simultaneous removal of nickel and cobalt from aqueous stream by cross flow micellar enhanced ultrafiltration

Nickel and cobalt were simultaneously removed from aqueous feed using cross flow micellar enhanced ultrafiltration. Twenty kiloDalton polysulfone membrane was used and the rejection more than 99% was obtained. The effect of operating variables like inlet flow rate, inlet pressure, feed metal ions concentration, surfactant to metal ion (S/M) ratio and pH on the rejection of metal ions was investigated. Gel layer formation and concentration polarization was insignificant under the present experimental condition. Presence of salt in the aqueous feed results in drop in rejection from 99% to 88%. The distribution coefficient of solutes in the micellar phase and aqueous phase was estimated from ultrafiltration data. The loading of micelles was also estimated for both the nickel and cobalt ions which confirmed the reproducibility of the micellar enhanced ultrafiltration (MEUF) experiments.     

Reasoning with multilevel flow models

Complex heterogeneous systems, such as power plants or petro-chemical process plants, nowadays contain complex automation for start-up and shut-down control and support systems for the operators. Often, however, the operator support and automation suffers from a lack of flexibility, and only functions for a number of well defined operating modes and pre-defined paths for the transition between these modes. This paper proposes an alternative and more flexible method for developing and describing intentional mode transitions, and for developing diagnostic systems, using Multilevel Flow Modeling (MFM). MFM models a system by expressing it in terms of its goals and in terms of elementary functions that describe the mass, energy and information flows in the system. This paper describes the use of MFM models as a basis for reasoning about the actions that are necessary to achieve the goals of a system or to obtain an intentional change in the system's mode. For this, data measured from the system must be used to update the state of the MFM model so that the state of the model reflects the state of the system. The outcome of the reasoning can be used as support for an operator or for automated control of complex systems. This paper defines the relevant states for goals and flow functions and presents a set of rules for determining these states on the basis of measurements from a process. The relations between goals and functions, and among functions themselves, are discussed. A mechanism is introduced to produce a change in the desired mode of a process, and expressed in rules to implement this change. The approach is explained at the hand of a simple example system. An MFM model of this example system is presented, and used to illustrate how measured variables can be used to calculate the states of the elements in the MFM model. At the hand of the same model the rules for inferring the states of goals and functions, and for determining the required actions will be illustrated.     

Steady flow past an elliptic cylinder inclined to the stream

The properties of steady two-dimensional flow past an elliptic cylinder inclined to the oncoming stream are investigated for small to moderate values of the Reynolds number for which good accuracy can be assured. The solutions are based on a numerical method of solution of the Navier-Stokes equations for incompressible fluids which ensures that all the correct conditions of the problem are satisfied. In particular, the solution is carried out in such a way that the vorticity decays rapidly enough at large distances from the cylinder for the lift and drag on the cylinder to be finite. Results are presented for the variation of lift, drag and streamline patterns with inclination and Reynolds number. Two elliptic cylinders (based on their minor-to-major axes ratio) are considered. For an elliptic cylinder with minor-to-major axes ratio 1:5, results are obtained for Reynolds numbers up to 40 and inclination varying from zero to 90°. Streamline plots for these results show a development of the solution from asymmetric flow at zero inclination (with no separation), through asymmetric flows with increasing inclination (with either no separation, separation with a single recirculating region, or separation with two recirculatory regions) to the symmetric flow at 90° incidence (with two counter rotating vortices). Of interest are asymmetric steady-state results which contain two recirculatory regions trailing the cylinder, one attached and one unattached to the cylinder. Results are also obtained for a second elliptic cylinder with minor-to-major axes ratio 1:10 at Reynolds numbers 15 and 30, inclination 45°. These results are found to be in good agreement with corresponding unsteady results taken to long times (which are tending to a steady state).     

Investigation of flow of a dust-laden stream in a laval nozzle

An experimental investigation has been made of the influence of the presence of solid particles in an air stream flowing in a Laval nozzle on the degree of expansion in the nozzle and on the noncalculability, i.e., the degree to which the discharge from the nozzle cannot be calculated, for particle mass fractions varying in the range 0.2–0.5. Shadow photographs are presented of the compression shocks at the outlet section of the nozzle in a dust-laden stream composed of air and solid particles.     

Comparison of three separated flow models

 An improved stochastic separated flow (ISSF) model developed by the present authors is compared with two other widely used trajectory models, the deterministic separated flow (DSF) model and the stochastic separated flow (SSF) model, in numerical simulations of gas–particle flows behind a backward-facing step. The DSF and ISSF models are found to need only 250 computational particles to obtain a statistically stationary solution of mean and fluctuating velocities of the particles, while the SSF model requires as many as 10,000 computational particles. Apart from comparing the sensitivity of required computational particles for different models, prediction capability of different models on mean velocities, fluctuating velocities and re-circulation region are also compared in this paper. Predicted results of streamwise mean velocity of particle phase agree well with experimental data for all the three models. For the mean fluctuating velocity of the particle phase, predictions using the ISSF model agree well with experiment data, while the DSF and the SSF models have a significant difference. Only the SSF and the ISSF models are capable of predicting re-circulation regions of the particle phase. As a comparison, the ISSF model has a distinct advantage over the other two models both in terms of accuracy and efficiency. Received 20 October 2001 / Accepted 5 February 2002     

Influence of decelerating flow on incipient motion of a gravel-bed stream

An experimental study on incipient motion of gravel-bed streams under steady-decelerating flow is presented. Experiments were carried out in a flume with two median grain sizes, d ₅₀ = 16.7 mm for a fixed-bed case and d ₅₀ = 8 mm for a mobile bed case. In addition, an effort is made to determine a simplified method for the estimation of bed shear stress in decelerating flow over fixed and mobile beds for use in field situations. From the observation of eleven fixed-bed and nine mobile-bed velocity profiles, it is revealed that the parabolic law method (PLM) and the Reynolds stress method are comparable for estimation of shear velocity in general. Also, the results show that the shear stress distribution adopts a convex form over fixed and mobile beds. Due to this form the critical Shields parameter value for decelerating flow is less than the reported values in literature. This paper supports Buffington & Montgomery (1997) statement that less emphasis should be given on choosing a universal shields parameter, and more emphasis should be given on choosing defendable values based on flow structure.     

Fleet management models and algorithms for an oil-tanker routing and scheduling problem

This paper explores models and algorithms for routing and scheduling ships in a maritime transportation system. The principal thrust of this research effort is focused on the Kuwait Petroleum Corporation (KPC) Problem. This problem is of great economic significance to the State of Kuwait, whose economy has been traditionally dominated to a large extent by the oil sector, and any enhancement in the existing ad-hoc scheduling procedure has the potential for significant savings. A mixed-integer programming model for the KPC problem is constructed in this paper. The resulting mathematical formulation is rather complex to solve due to the integrality conditions and the overwhelming size of the problem for a typical demand contract scenario. Consequently, an alternate aggregate model that retains the principal features of the KPC problem is formulated. The latter model is computationally far more tractable than the initial model, and a specialized rolling horizon heuristic is developed no solve it. The proposed heuristic procedure enables us to derive solutions for practical sized problems that could not be handled by directly solving even the aggregate model. The initial formulation is solved using CPLEX-4.0-MIP capabilities for a number of relatively small-sized test cases, whereas for larger problem instances, the aggregate formulation is solved using CPLEX-4.0-MIP in concert with the developed rolling horizon heuristic, and related results are reported. An ad-hoc routing procedure that is intended to simulate the current KPC scheduling practice is also described and implemented. The results demonstrate that the proposed approach substantially improves upon the results obtained using the current scheduling practice at KPC.     

Simultaneous fleet assignment and cargo routing using benders decomposition

In this paper, we incorporate the cargo routing problem into fleet assignment to model the fleet assignment more accurately. An integrated model and a Benders decomposition-based approach are developed to simultaneously obtain the optimal assignment of fleet to legs and the routing of forecasted cargo demand over the network. Computational experiments show that this integrated approach converges very fast for all different test scenarios.     

Forging of polygonal discs using the dual stream functions

Calculation and estimation of the final workpiece dimensions and required load forming via analytical solutions are likely to take long time and even sometimes exact solutions may not be found. However, by using numerical methods, estimations with high accuracy and high speed would be made possible by reducing calculation and processing time, also lowering the labouring and therefore the product cost.

In this study, the dual stream and so upper bound method have been used to investigate the metal flow and load requirements in open die forging of polygonal blocks. Due to extremely high speed of analysis, it enables to facilitate the automation of the process. The kinematically admissible velocity field was constructed for incompressible material. The forging load of a polygonal aluminium block, longitudinal flow and sideway spread and hence new dimensions were estimated within time of less than a second for one step deformation. Experiments were conducted using lead AA5454 and showed good correlation with the theoretical analysis of dual stream functions (DSF).     

Prediction of flow curves and forming limit curves of Mg alloy thin sheets using ANN-based models

Multivariable empirical models based on artificial neural networks were developed in order to predict the flow curves and forming limit curves of AZ31 magnesium alloy thin sheets, in warm forming conditions, vs. process parameters and fibre orientation. Experimental tensile and hemispherical punch tests were carried out in order to obtain the experimental data set, in terms of flow curves and forming limit curves, to be used to train the artificial neural networks. A preliminary study, based on the leave one-out-cross validation methodology, has proven the very good predictive capability of the ANN-based models in modelling both flow curves (flow stress level, curve shape and strain at the onset of necking) and forming limit curves (curve shape, major strain values and minor strain limit) under different process conditions and fibre orientations. Then, the generalisation capability of the neural models in capturing the effect of process parameters and fibre orientation on flow curves and formability has been proven by the excellent agreement, in terms of the high correlation coefficients, low relative errors and average absolute relative errors, between predicted and experimental results not investigated in the training set.     

Real-time routing in flexible flow shops: a self-adaptive swarm-based control model

This paper presents a self-adaptive, swarm-based control model for real-time part routing in a flexible flow-shop environment. The proposed control model is a multi-agent system that exhibits adaptive behaviour, which has been inspired from the natural system of the wasp colony. The production problem, which has been previously studied in the literature by several researchers, involves assigning trucks to paint booths in real-time in a flexible flow-shop environment with the objective of throughput maximization and minimization of number of paint flushes accrued by the production system, assuming no a priori knowledge of the colour sequence or colour distribution of trucks is available. The proposed control model is benchmarked with the results of previous studies reported in the literature in solving the same production problem. The proposed control model uses self-adapting threshold parameters to facilitate the production flow in real time. A simulation-based software environment is designed and developed to investigate its performance. The simulation results show that the proposed control model is more robust to environmental changes, and it outperforms the previously reported studies on the basis of throughput, number of setups, and cycle time performance measures.     

Ill- and well-posed models of granular flow

Summary A unified method of generating models for the flow of granular materials is used to confirm and extend the results of Schaeffer and co-workers [15], [17]–[19], namely that many existing models exhibit linear ill-posedness with regard to initial conditions. A model proposed in Harris [6], [7] is analyzed by the same method and it is established that, firstly, the model exhibits well-posedness under certain well-defined conditions, secondly, that when these conditions fail to hold, the model exhibits ill-posedness and thirdly, the mathematical ill-posedness corresponds to a real physical instability.     

One-dimensional models for blood flow in arteries

In this paper a family of one-dimensional nonlinear systems which model the blood pulse propagation in compliant arteries is presented and investigated. They are obtained by averaging the Navier-Stokes equation on each section of an arterial vessel and using simplified models for the vessel compliance. Different differential operators arise depending on the simplifications made on the structural model. Starting from the most basic assumption of pure elastic instantaneous equilibrium, which provides a well-known algebraic relation between intramural pressure and vessel section area, we analyse in turn the effects of terms accounting for inertia, longitudinal pre-stress and viscoelasticity. The problem of how to account for branching and possible discontinuous wall properties is addressed, the latter aspect being relevant in the presence of prosthesis and stents. To this purpose a domain decomposition approach is adopted and the conditions which ensure the stability of the coupling are provided. The numerical method here used in order to carry out several test cases for the assessment of the proposed models is based on a finite element Taylor-Galerkin scheme combined with operator splitting techniques.     

Numerical study on the spontaneous condensation flow in an air cryogenic turbo-expander using equilibrium and non-equilibrium models

The difficulty of data measurement in cryogenic environments and the complicated mechanism of nucleation process have restricted the design of wet type turbo-expander for cryogenic liquid plants. In this paper, equilibrium and non-equilibrium models are used to model the spontaneous condensation flow in a cryogenic turbo-expander along the main stream passage including nozzle, impeller and diffuser. The comparison shows a distinct difference of the predicted wetness fraction distribution along the streamline between the equilibrium model and the non-equilibrium model. In non-equilibrium model, the distributions of supercooling and nucleation rate along the length of turbo-expander are given for the analysis of flow characteristics. The comparison of outlet wetness fraction with the experimental data is also provided for verification and discussion. Both the effects of the rotation on nucleation and the effects of the nucleation on flow along suction side of the impeller are investigated.