Variable Formulation Search for the Cutwidth Minimization Problem

Many optimization problems are formulated as min–max problems where the objective function consist of minimizing a maximum value. In this case, it is usual that many solutions of the problem has associated the same value of the objective function. When this happens it is difficult to determine which solution is more promising to continue the search. In this paper we propose a new variant of the Variable Neighbourhood Search methodology to tackle this kind of problems. The new variant, named Variable Formulation Search, makes use of alternative formulations of the problem to determine which solution is more promising when they have the same value of the objective function in the original formulation. We do that in shaking, local search and neighbourhood change steps of the basic Variable Neighbourhood Search. We apply the new methodology to the Cutwidth Minimization Problem. Computational results show that our proposal outperforms previous algorithms in the state of the art in terms of quality and computing time.     

Calorific energy required during in-service welding of pipelines for petroleum transport

The thermal behaviour during in-service repair welding of oil transportation pipes was studied using finite element analysis in the present paper. Regression equations that relate peak temperature of the inner surface of the pipe and cooling time between 800 and 500°C in the heat-affected zone to the welding heat input, preheat temperature and convective heat transfer coefficient were obtained. The former parameters govern, respectively, the possibility of burn-through and cold cracking, and the latter parameters define the thermal behaviour during welding. The existence of conditions that simultaneously satisfy the equations obtained, for different combinations of related variables, was proved. Graphical representations of relevant practical importance, developed from the solution of obtained equations, are presented.     

On the Relationship Between J-Integral and Crack Tip Opening Displacement in Elastic-Plastic Fracture Mechanics

The relationship between J-integral (J) and crack tip opening displacement (δ), considered fundamental for elastic-plastic fracture mechanics, can be established based on prior knowledge of the constraint factor m, which depends on the work hardening exponent and the material’s yield strain. Both J and δ were simultaneously determined at fracture initiation and at different points along the resistance curves for a number of structural steels. The corresponding m values were calculated and then compared with the predictions made by different models. The results indicate that the experimentally determined m values are in fair agreement with the predictions made by ASTM over the whole range of flow parameters considered in this study. The Hutchinson-Rice-Rosengren singularity-based predictions result in overestimating m for steels considered to be of low strength and high strain hardening exponent. Predictions made by other models are predominantly higher in comparison with their experimental counterparts.     

A population dynamics approach for the water distribution problem

The water distribution system (WDS) is composed of several elements, where flow control is one of the most important components needed in order to provide a satisfactory level of service. In order to achieve an adequate level of water in the distribution tanks, we need to dynamically control the flow. Here, we propose a population dynamics approach in order to control tanks, by allocating in them the maximum uniform volume. The feedback interconnected systems reach a stable equilibrium point for both approaches presented (i.e. replicator and supply dynamics), and more specific an asymptotically stable equilibrium point for the replicator dynamics case. The stability analysis uses some passivity concepts and classic Lyapunov theory for a closed-loop system that combines the population dynamics (controller), and the WDS (process). We show via simulations the operation under different scenarios.     

Changes occurring during the parboiling of upland rice and in the maceration water at different temperatures and soaking times

The objective of this work was to investigate the influence of temperature and soaking time on the quality of grains from two upland rice cultivars. Response surface methodology and a central compound rotational design were used. The data obtained for the cultivars BRS Primavera and BRS Sertaneja varied, respectively, between 27.7–55.0% and 26.0–51.7% for the Husk‐Splitting Index; between 0.8–5.0% and 0.0–4.0% for the incidence of ‘banana’ grains; between 0.0–2.0% and 0.0–1.2% for non‐gelatinised grains; and between 0.2–0.7% and 0.2–0.8% for soluble solids in the maceration water. Because BRS Primavera grains had a narrower shape, they absorbed the water faster and consequently presented a greater amount of physical defects, although the losses to the water were smaller than BRS Sertaneja.     

Prediction of concrete initial setting time in field conditions through multivariate regression analysis

Construction of large concrete structures usually requires pouring multiple batches of concrete mixes along 1 day, which creates setting irregularities that increase the potential of crack development within pours. For the case of bridge decks, it is recommended that the initial concrete material should stay plastic over the entire casting operation of a poured bridge segment. Uniform setting of multiple batches is possible if setting times could be predicted and controlled in field conditions. In this study, more than 70 different Class K concrete mixes were manufactured and cast in field conditions, which provided material characteristics along with environmental data that were used to predict concrete initial setting times through multivariate regression analysis. Two prediction models were achieved, corresponding to the addition of set retarding and set accelerating admixtures, respectively. Validating field tests demonstrated that good predictions of concrete initial setting times can be accomplished with 2% error, when accurate field weather forecasts are available. This work also demonstrates the use of the prediction relations, with the objective of achieving uniform thermo-mechanical properties of a pouring sequence in the field.