Esteve Codina

Adjustment of O-D trip matrices from observed volumes: An algorithmic approach based on conjugate directions

Abstract This paper presents a new algorithmic alternative to the O–D matrix adjustment problem from observed link volumes when it is formulated as a mathematical programming problem with a bilevel structure. The algorithmic approach presented is based on a method for nondifferentiable optimization due to Wolfe that can be interpreted as a conjugate directions method with better convergence properties as shown with a set of computational tests. Closely related to the algorithm presented, the problem of approximating gradients of the upper level function is discussed and a new and consistent approach is presented and analyzed with a detailed description of the algorithmic aspects involved.

An empirical methodology for prediction of shape and flow rate of a free-falling non-submerged liquid and casting iron stream:

The work presented in this article demonstrates the use of an empirical and simplified approach based on an optical technique and a home-made ad hoc code that give knowledge of the shape and falling velocity of a free-falling non-submerged liquid stream to predict its typology and flow rate. The visualization photographic technique is a non-intrusive robust technique which can be applied to high-temperature liquids in harsh environments, such as an iron stream in a foundry. This technique allows predicting the liquid stream boundaries and contours without any type of treatment on the fluid. As a result of employing this empirical methodology, three flow typologies for a water stream are proposed and demonstrated experimentally. Comparisons with experimental data reveal satisfactory estimations of mean flow quantities. Finally, the approach used based on experimental visualization is carried out in an iron stream of a foundry, not being disruptive to in-situ foundry operations and showing its potential to improve performance of the cast parts’ properties during the casting phase and revealing to be a useful tool for process optimization.

Influence of the interteeth clearances on the flow ripple in a gerotor pump for engine lubrication

A gerotor pump, which is widely used in the automotive industry for engine oil lubrication, produces an instantaneous flow fluctuation and the estimation of this is fundamental in order to evaluate the pump quality for silent and smooth operation. The intricate aspects of the pumping process of a gerotor pump make computational fluid dynamics the appropriate tool for modelling and simulation to provide insights into its flow characteristics. Because the instantaneous flow is rather dependent on the teeth contact, a new boundary condition of a virtual wall was developed, which allows simulation of the teeth contact in the interteeth radial clearances. This new boundary condition is utilized in a three-dimensional model of the gerotor pump with mesh deformation and remeshing at every time step by means of a home-made ad-hoc code programmed by the present authors and named viscous wall cell. The code has been integrated into the computational fluid dynamics solver. The interteeth clearances are studied under the following different operating conditions (working pressures and rotational velocities): first, no contact points (no teeth contact is studied in order to prove that, even if the interteeth radial clearance is sufficiently small, the leakage cannot be negligible); second, all contact points (the ideal approach is considered with zero interteeth radial clearances used to model zero manufacturing tolerances); third, one contact point at different locations (the existence of manufacturing tolerances and the teeth contact approach make the pump’s operation and its pumping mechanism more realistic in the simulation). The numerical instantaneous flow is compared with the analytical instantaneous flow, with the instantaneous flow modelled by using the bond graph technique, and with the experimental determination of the flow ripple for a specific unit. The results obtained show the importance of simulating the teeth contact and prove to be an excellent estimation of the instantaneous flow behaviour to obtain the dynamic properties of a gerotor pump under more realistic conditions than its design.

New algorithmic alternatives for the O-D matrix adjustment problem on traffic networks

Abstract In the last years the O–D matrix adjustment problem using link counts on a traffic network modelled by means of a static user equilibrium approach has been formulated advantageously by means of bilevel programs. The algorithms developed to solve the problem present heuristic components in a lesser or greater degree. In this paper two new algorithmic alternatives are presented for this problem. The first alternative is an hybrid scheme proximal point-steepest descent that is based on a development of Codina for the approximation of the steepest descent direction of the upper level function and the second alternative is developed by Garcia and Marin and consists of solving a sequence of simplified bilevel programs. In order to highlight the characteristics of the two methods a set of test problems have been solved in conjunction with other well known methods, such as the method of Spiess, the method of Chan, the method of Yang as well as with an adaptation of the Wolfe’s conjugate directions method for non-differentiable optimization, in order to provide a better perspective of their advantages and tradeoffs.

A combined methodology for transportation planning assessment. Application to a case study

Abstract Traffic assignment models based on the user-equilibrium approach are one of the most widely used tools in transportation planning analysis. Resulting flows offer a static average view of the expected use of the road infrastructure under the modeling hypothesis. This information has usually been enough for the planning decisions. The planned infrastructure is probably sufficient for average demand, but time-varying traffic flows, i.e., at peak periods, combined with the influence of road geometry, can produce undesired congestion that can not be forecasted or analysed with the static tools. There is a clear case for a change in the analysis methodology such as combination of a traffic assignment tool, with a microscopic traffic simulator. This paper illustrates, by means of a case study, the combination of a well-known traffic assignment tool, the EMME/2 model, with a microscopic traffic simulator, Advanced Interactive Microscopic Simulator For Urban And Non-Urban Networks (AIMSUN2) with emphasis on the description of the specific interfaces that make consistent the combination of both tools in the Generic Environment for Traffic Analysis and Modeling (GETRAM) environment. Models for complex transportation systems should be the combination of mathematical models and computer models, to overcome, for example, the difficulties of the integration of modeling tools. GETRAM environment has an open and flexible computer architecture suitable for such purposes.

Dynamic traffic assignment: Considerations on some deterministic modelling approaches

Research on how to model the dynamic behaviour of traffic flows efficiently and the development of algorithms to handle such models numerically has become a key activity in recent years as a consequence of the emerging applications of advanced technologies to transport. This paper offers a critical review of some of the most relevant formulations of the dynamic assignment problem and algorithms arising from both discrete and continuous models, emphasizing the underlying modelling hypothesis. Comments are made on the crucial underlying discussion on the basic implicit or explicit hypothesis and extensions to Wardrops principle and the corresponding equilibrium concept. Properties and shortcomings are described and commented on and in some cases illustrated with simple examples. The paper ends with a description of a recent continuous modelling proposal that seems to overcome one of the reported major shortcomings: the FIFO discipline observance of traffic flows. A set of concluding remarks and a comprehensive bibliography close the paper.

Computational fluid dynamics and particle image velocimetry assisted design tools for a new generation of trochoidal gear pumps

Trochoidal gear pumps produce significant flow pulsations that result in pressure pulsations, which interact with the system where they are connected, shortening the life of both the pump and circuit components. The complicated aspects of the operation of a gerotor pump make computational fluid dynamics the proper tool for modelling and simulating its flow characteristics. A three-dimensional model with deforming mesh computational fluid dynamics is presented, including the effects of the manufacturing tolerance and the leakage inside the pump. A new boundary condition is created for the simulation of the solid contact in the interteeth radial clearance. The experimental study of the pump is carried out by means of time-resolved particle image velocimetry, and results are qualitatively evaluated, thanks to the numerical simulation results. Time-resolved particle image velocimetry is developed in order to adapt it to the gerotor pump, and it is proved to be a feasible alternative to obtain the instantaneous flow of the pump in a direct mode, which would allow the determination of geometries that minimize the non-desired flow pulsations. Thus, a new methodology involving computational fluid dynamics and time-resolved particle image velocimetry is presented, which allows the obtaining of the instantaneous flow of the pump in a direct mode without altering its behaviour significantly.

Pressure effects on the performance of external gear pumps under cavitation

The numerical analysis of an external gear pump with cavitation effects has been validated with experimental data obtained by applying Time-Resolved Particle Image Velocimetry. The effect of inlet and outlet pressure on volumetric efficiency has been studied numerically. First, the Particle Image Velocimetry method was used to analyze the two-dimensional velocity field in the middle plane of the suction chamber of the gear pump. The main improvement, with respect to previous similar analysis is the use of alginate micro particles as tracers. It is seen that the two-dimensional model is able to characterize the flow field of the real pump in the region of the inlet chamber in which cavitation is expected. In a previous study, it was seen that a cavitation cloud acted as a virtual contact point at low pressure, being responsible for an increase on the volumetric efficiency. The first set of simulations represents the pump working with high outlet pressure. Now, the cavitation cloud is not present and cavitation no longer helps to improve the efficiency of the pump. The second set of simulations represents the pump with an inlet loss factor, which implies a mean inlet pressure below atmospheric conditions. This allows cavitation clouds to propagate upstream. Despite the larger cavitation clouds, volumetric efficiency only drops at high operating velocities, when some clouds become trapped between gears and casing and are transported to the pressure side.

Methodology based on best practice rules to design a new-born trochoidal gear pump

The trochoidal gear pump, also known as gerotor, owing to its remarkable advantages compared to other hydraulic pumps is chosen for many engineering applications. As each application is unique, the designer ought to be knowledgeable of the required specifications as a first task but need not be an expert in the hydraulic pump design. The review of the existing research reveals significant gaps to develop a new-born project and the work presented in this paper, drawn on existing research work and the authors’ own experience and know-how, aims to overcome them. The objective of the paper is then to provide a summary of the best practice rules to design a trochoidal gear pump from scratch achieving a thorough understanding. In the conceptual stage, making decisions come according to a predetermined set of four parameters known by the designer that will lead to the complete development of the trochoidal gear set. Afterwards, in the design process, the most important characteristics of the pump such as the porting, the pump construction, and the limitations are presented based on the significant explanations, with regard to each feature, selection, effects, and good practices. As a result, the methodology presented compiles the process of engineering in designing a new trochoidal gear pump as a catalogue of guidelines aiming to overcome a vague design due to a lack of knowledge. This collection of best practice rules intends to guide the designer to take good decisions early in the design process that limit design change later in the final stage—the prototype.

Method for Fluid Flow Simulation of a Gerotor Pump using OpenFOAM

A new approach based on the open source tool OpenFOAM is presented for the numerical simulation of a mini gerotor pump working at low pressure. The work is principally focused on the estimation of leakage flow in the clearance disk between pump case and gears. Two main contributions are presented for the performance of the numerical simulation. On one hand, a contact point viscosity model is used for the simulation of solid–solid contact between gears in order to avoid the teeth tip leakage. On the other hand, a new boundary condition has been implemented for the gear mesh points motion in order to keep the mesh quality while moving gears with relative velocity. Arbitrary coupled mesh interface (ACMI) has been used both in the interface between clearance disk in inlet/outlet ports and between clearance disk and interteeth fluid domain. Although the main goal of the work is the development of the numerical method rather than the study of the physical analysis of the pump, results have been compared with experimental measurement and a good agreement in volumetric efficiency and pressure fluctuations has been found. Finally, the leakage flow in the clearance disk has been analyzed.