Optimal setpoint chasing in dynamic positioning of deep‐water drilling and intervention vessels

Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal‐plane about desired position and heading co‐ordinates defined by the operator. A three degrees‐of‐freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi‐submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust‐induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work‐over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co‐ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi‐submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd.     

Oscillatory Metastability in Optical Network Synchronizer Circuits

Synchronization of signal packets is required in networks in order to route the packets. Due to changes in the interarrival times of the packets the inputs to the routing circuits may exhibit oscillatory metastability. Oscillatory metastability can be eliminated in optical circuits by the addition of logic signal stretch. This can be done because the propagation time of optics can be precisely controlled. An algorithm for inserting logic signal stretch to eliminate oscillatory metastability is presented herein.     

Potassium catalysis in the pyrolysis behaviour of short rotation willow coppice

Short rotation willow coppice (SRC) and a synthetic biomass, a mixture of the basic biomass components (cellulose, hemicellulose and lignin), have been investigated for the influence of potassium on their pyrolysis behaviours. The willow sample was pre-treated to remove salts and metals by hydrochloric acid, and this demineralised sample was impregnated with potassium. The same type of pre-treatment was applied to components of the synthetic biomass. Characterisation was performed using thermogravimetric analysis with measurement of products by means of Fourier transform infrared spectroscopy (TGA-FTIR) and pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS). A comparison of product distributions and kinetics are reported. While the general features of decomposition of SRC are described well by an additive behaviour of the individual components, there are some differences in the magnitude of the influence of potassium, and on the products produced. For both SRC and the synthetic biomass, TGA traces indicate catalytic promotion of both of the two-stages of biomass decomposition, and potassium can lower the average apparent first-order activation energy for pyrolysis by up to 50 kJ/mol. For both SRC and synthetic biomass the yields and distribution of pyrolysis products have been influenced by the presence of the catalyst. Potassium catalysed pyrolysis increases the char yields markedly and this is more pronounced for synthetic biomass than SRC. Gas evolution profiles during pyrolysis show the same general features for both SRC and synthetic biomass. Relative methane yields increase during the char formation stage of pyrolysis of the potassium doped samples. The evolution profiles of acetic acid and formaldehyde change, and these products are seen in lower relative amounts for both the demineralised samples. A greater variation in pyrolysis products is observed from the treated SRC samples compared to the different synthetic biomass samples. Furthermore, substituted phenols from lignin pyrolysis are more dominant in the pyrolysis profiles of the synthetic biomass than of the SRC, implying that the extracted lignins used in the synthetic biomass yield a greater fraction of monomeric type species than the lignocellulosic cell wall material of SRC. For both types of samples, PY-GS-MS analyses show that potassium has a significant influence on cellulose decomposition markers, not just on the formation of levoglucosan, but also other species from the non-catalysed mechanism, such as 3,4-dihydroxy-3-cyclobutene-1,2-dione.     

Non-parametric estimate of the system function of a time-varying system

The task of identifying an unknown dynamic system is made easier with prior knowledge on its behaviour. Using a frequency domain approach, the non-parametric maximum likelihood estimator of the system function, associated with the time-dependent impulse response of a time-varying system, is constructed. This is accomplished by the use of a simple linear least squares fitting algorithm, applied to the spectral response of the system to a multisine excitation. The noise variance on the system function is estimated simultaneously, and modelling errors can be detected, as illustrated on a simulation example.     

Social desirability and the randomized response technique.

The randomized response technique (RRT) is designed to increase respondents' willingness to answer truthfully questions of a sensitive or socially undesirable nature. This study tested the hypothesis that the difference between the proportion of "yes" responses obtained under self-administered direct questioning and the proportion of "yes" responses obtained under an RRT procedure would be related to the social desirability of a "yes" response to the question. The hypothesis was confirmed by data from 404 undergraduates; the RRT may provide more valid responses to items of a socially desirable and undesirable nature. The RRT deserves more attention because it can circumvent biases due to untruthful responding, demand characteristics, and evaluation apprehension as well as assure the confidentiality of the data. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neue Triterpens?uren der Weintraubenschale

Zusammenfassung Die Cuticula von Traubenschalen enthält neben Oleanolsäure noch 3-Oxo-olean-12-en28-säure, 3-Hydroxi-olean-12-en-28-aldehyd, 3,29-Dihydroxi-olean-12-en-28-säure sowie zwei bisher unbekannte Triterpensäuren. Ihre Strukturen werden durch spektroskopische Daten als 16-Hydroxi-3-oxo-olean-12-en-28-säure und 16-Hydroxi-3-oxo-oleana-1,12-dien-28-säure belegt.

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New triterpenic acids from the peel of grapes

Summary The grape-cuticle contains beside oleanolic acid, 3-oxo-olean-12-en-28-oic acid, 3-hydroxy-olean-12-en-28-aldehyde, 3,29-dihydroxy-olean-12-en-28-oic acid, and two yet hitherto unknown triterpenic acids. Their structures have been elucidated by spectroscopic methods to be l6-hydroxy-3-oxo-olean-12-en-28-oic acid and 16-hydroxy-3-oxo-oleana-1,12-dien-28-oic acid.

     

Characteristics of an immobilized lipase for the commercial synthesis of esters

The lipase-catalyzed synthesis of ester bonds has been well-documented lately and is of much current commercial interest. Immobilization of a fungal lipase on a unique macroporous support allows not only the ability to operate in non-aqueous media but to catalyze ester synthesis in quantitative yields, employing attractive commercial conditions. Catalyst dose and process configurations will be illustrated. The capability of the catalyst to operate efficiently in reverse under a variety of unnatural, hostile, solvent-containing environments will be discussed. The range of substrates for this immobilized lipase, Lipzome, has been investigated. The enzyme will catalyze ester synthesis with saturated, unsaturated and a variety of branched carboxylic acids. The alcohol specificity for this enzyme also is equally broad. A wide variety of straight-chain, branched and polar alcohols can be substrates. In addition, some examples of alcohol specificity for kinetic isomer resolution will be cited. Presented at the symposium “The Biology, Biotechnology and Technology of Lipases” at the 78th annual meeting of the American Oil Chemists’ Society held May 17–21, 1987, in New Orleans, Louisiana.     

Considering Prework on Industrial Projects

Prefabrication, preassembly, modularization, and off-site fabrication, collectively termed as prework have become more viable with recent advances in design and information technologies. These construction methods offer a substantial opportunity to improve project performance when circumstances merit. Successful implementation of these methods on a particular project requires systematic analysis and early decision making based on specific factors of the project. This paper identifies those factors influencing decisions on the use of prework, and current industry practices for evaluating the applicability of prework on industrial projects. It then presents a decision framework to assist industry practitioners with evaluating the applicability of prework on their project, and describes a computerized tool to aid project teams in the decision-making process. The developed framework and tool are useful and effective in the decision-making process, and easy to use, as validated by practitioners in the industry.     

Injury risk among children of low-income U.S.-born and immigrant mothers.

The number of immigrants in the United States is at an all time high, yet psychologists have largely ignored the domain of immigrant health. This article considers 1 aspect of immigrant health, risk for pediatric injury. A sample of over 5,000 5-year-old children from impoverished families was studied; approximately 13% had immigrant mothers. Children of immigrants had a significantly lower rate of injury in the prior year. This was particularly true of non-White children of immigrants. Three possible mediators for this finding--assistance with parenting, parenting style, and health care accessibility--were considered, but none explained the difference. The need for further research on the topic and implications of results for injury prevention are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Flexible Framework for Fault Tolerance in the Grid

This paper presents a failure detection service (FDS) and a flexible failure handling framework (Grid-WFS) as a fault tolerance mechanism on the Grid. The FDS enables the detection of both task crashes and user-defined exceptions. A major challenge in providing such a generic failure detection service on the Grid is to detect those failures without requiring any modification to both the Grid protocol and the local policy of each Grid node. This paper describes how to overcome the challenge by using a notification mechanism which is based on the interpretation of notification messages being delivered from the underlying Grid resources. The Grid-WFS built on top of FDS allows users to achieve failure recovery in a variety of ways depending on the requirements and constraints of their applications. Central to the framework is flexibility in handling failures. This paper describes how to achieve the flexibility by the use of workflow structure as a high-level recovery policy specification, which enables support for multiple failure recovery techniques, the separation of failure handling strategies from the application code, and user-defined exception handlings. Finally, this paper presents an experimental evaluation of the Grid-WFS using a simulation, demonstrating the value of supporting multiple failure recovery techniques in Grid applications to achieve high performance in the presence of failures.