DAWRS: A Differential - Algebraic System Solver by the Waveform Relaxation Method

We investigate the concurrent solution of low-index differential-algebraic equations (DAE’s) by the waveform relaxation (WR) method, an iterative method for system integration. We present our new simulation code, DAWRS (Differential - Algebraic - Waveform Relaxation Solver), to solve DAE’s on parallel machines using the WR methods, and describe new techniques to improve the convergence of such methods. As experimental results, we demonstrate the achievable concurrent performance to solve DAE’s for a class of applications in chemical engineering

Catalisadores metalocênicos suportados para a produção de poliolefinas: revisão das estratégias de imobilização

The inadequacy of strategies used for the heterogeneization of metallocene catalysts is pointed out as one of the main causes of the lack of industrial employability of such polymerization catalysts. The main problems are the necessity of large quantity of MAO (cocatalyst) and the inability to control molecular mass distribution of the polymers. Based on this background, the main strategies for the heterogeneization of metallocenes are here reviewed. The advantages and disadvantages of each strategy are presented and discussed on theoretical and practical perspective. Considering the results reported on the different researches, outcomes of heterogeneization strategies are pointed out

Employing process simulation for hazardous process deviation identification and analysis

To improve industrial safety, several hazard analyses of processes are available. The HAZOP is one of the most frequently employed and analyzes hazardous process deviations based on heuristic knowledge. Despite the wide application of the technique, new developments are especially important to enhance industrial safety. In this sense a systematic procedure is proposed for hazardous process deviation identification and analysis that employs process simulation and heuristic evaluation. Process simulation enables the analysis of process behaviors caused by device malfunctions and the performance of deviation analysis that considers the process non-linearities and dynamics. A comparison between the HAZOP and the proposed procedure is presented using a pump startup system case study, wherein the better system interpretation and results regarding abnormal process conditions are highlighted. A second case study applies the procedures to an offshore oil production process, showing the advantages of employing process simulation for studying deviation during a dynamic process's abnormal behavior

Tuning of Model Predictive Controllers Based on Hybrid Optimization

A tuning procedure for a model predictive controller (MPC) is presented for multi-input multi-output systems. The approach consists of two steps based on a hybrid method: the goal attainment method and a variable neighborhood search. In the first step, the weights of the MPC objective function are obtained, minimizing the square error between the closed-loop response of the internal controller model and a predefined desired reference trajectory. In the second step, the integer variables of the problem (prediction and control horizons) are obtained, minimizing the square error between the closed-loop response and an optimal trajectory, aiming a controller with low computational cost and good performance. The proposed method was tested in two benchmark processes using different MPC formulations, showing satisfactory results

Model Reformulation and Global Optimization of Oil Production Using Gas Lift

Gas lift technology is one of the most common methods used for wells with insufficient reservoir pressure. It makes use of gas reinjection to enhance individual well production. When several wells are used to produce a reservoir, a problem arises regarding the selection about how to produce each well so that overall production can be maximized. To accomplish it, one needs to determine the optimal production of each well and how much gas ought to be injected. In this article, we revise previous efforts and present a new MINLP model, which we solve globally using RYSIA, a recently developed global optimization algorithm (Faria and Bagajewicz, <i>AICHE J</i>. <b>58</b> (<i>8</i>) 2320–2335)

Utilização da técnica de birrefringência em reômetro multipasse para a diferenciação de grades de poliestireno cristal

O entendimento de como as propriedades reológicas afetam o comportamento dos polímeros nas operações de processamento, por meio de diferentes técnicas experimentais, é de fundamental importância para ser possível prever e avaliar a estrutura final destes materiais. Neste contexto, o objetivo deste trabalho é aplicar a técnica de birrefringência para diferenciar dois grades de poliestireno cristal. Foram realizados experimentos em um reômetro multipasse que permitiram a aquisição de imagens de birrefringência, que representam o campo de tensão do escoamento, e obteve-se a queda de pressão durante os experimentos. Ao se compararem os padrões de birrefringência dos dois poliestirenos foi possível distinguir os materiais e verificar que o escoamento da amostra de maior massa molar é mais complexo, com maior birrefringência e tensão mais elevada. Os resultados obtidos, além de contribuírem para a caracterização reológica, podem ser empregados no estudo comparativo de modelos constitutivos e desenvolvimento de códigos computacionais