Model-based control of a Rijke tube combustion instability

A Rijke tube is used to demonstrate model-based control of a combustion instability, where controller design is based on measurement of the unstable system. The Rijke tube used was of length 0.75m and had a grid-stabilised laminar flame in its lower half. A microphone was used as a sensor and a loudspeaker as an actuator for active control. The open loop transfer function (OLTF) required for controller design was that from the actuator to the sensor. This was measured experimentally by sending a signal with two components to the actuator. The first was a control component from an empirically designed controller, which was used to stabilise the system, thus eliminating the non-linear limit cycle. The second was a high bandwidth signal for identification of the OLTF. This approach to measuring the OLTF is generic and can be applied to large-scale combustors. The measured OLTF showed that only the fundamental mode of the tube was unstable; this was consistent with the OLTF predicted by a mathematical model of the tube, involving 1-D linear acoustic waves and a time delay heat release model. Based on the measured OLTF, a controller to stabilise the instability was designed using Nyquist techniques. This was implemented and was seen to result in an 80dB reduction in the microphone pressure spectrum. A robustness study was performed by adding an additional length to the top of the Rijke tobe. The controller was found to achieve control up to an increase in tube length of 19%. This compared favourably with the empirical controller, which lost control for an increase in tube length of less than 3%.

The Los Alamos General Circulation Model hydrologic cycle

As the global population has increased, so have human influences on the global environment. ... How can we better understand and predict these natural and potential anthropogenic variations? One way is to develop a model that can accurately describe all the components of the hydrologic cycle, rather than just the end result variables such as precipitation and soil moisture. If we can predict and simulate variations in evaporation and moisture convergence, as well as precipitation, then we will have greater confidence in our ability to at least model precipitation variations. Therefore, we describe here just how well we can model relevant aspects of the global hydrologic cycle. In particular, we determine how well we can model the annual and seasonal mean global precipitation, evaporation, and atmospheric water vapor transport.

Geographic patterns in the lag of temperature response to insolation for El Niño vs. La Niña conditions [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): The most important control on the annual cycle of temperature is insolation, with secondary influences from terms related to moisture, yet direct statistical analysis of the moisture-driven modulations (such as El Niño) of the response of temperature to insolation are not available. We have examined one aspect of the relationship between insolation and the instrumental record of maximum daily temperature - the lag between the two - at 252 stations in the western United States.

Studies on the seasonal cycle of sea surface temperatures, salinities and phytoplankton in Puttalam Lagoon, Dutch Bay and Portugal Bay along the west coast of Ceylon.

The monthly average temperatures at Puttalam Lagoon, Dutch Bay, Portugal Bay towards Kovilmunai and Portugal Bay towards Pallugaturai showed a distinct annual cycle. The peak was in April and values gradually fell till September. There was a further gradual fall in temperature from October to January. The highest temperatures in all four stations were in April. The highest salinities in all the stations were from May to October i.e., during the south-west monsoon. The salinities at Dutch Bay and Portugal Bay were high in March and April corresponding to the highest temperatures reached during these months. Two maxima have been observed in phytoplankton production. A primary maximum in May-June and a secondary maximum in October. The primary and secondary maxima are due to the influx of nutrient laden waters from the rivers Kal Aru and Pomparippu Aru. The phytoplankton producing blooms were Rhizosolenia alata. Rhizosolenia imbricata, Chaetoceros lascinosus, Chaetoceros pervianus, Ch,aetoceros diversus, Coscinodiscus gigas, Thallasionema nitzschioides, Thalassiosira subtilis, Thallassiothrix frauenfeldii, Asterionella japonica, Sceletonema costatum, Bacteriastrum varians and Biddulphia sinensis. Sudden outbursts of a single species were common. These diatoms were species of Chaetoceros and Rhizosolenia, and Thallassiothrix frauenfeldii. Wide fluctuations have been observed in the distribution of phytoplankton but no definite conclusions can be drawn as the period of observation was only one year.

Adaptive control of combustion instabilities for unknown sign of the high frequency gain

A type of adaptive, closed-loop controllers known as self-tuning regulators present a robust method of eliminating thermoacoustic oscillations in modern gas turbines. These controllers are able to adapt to changes in operating conditions, and require very little pre-characterisation of the system. One piece of information that is required, however, is the sign of the system's high frequency gain (or its 'instantaneous gain'). This poses a problem: combustion systems are infinite-dimensional, and so this information is never known a priori. A possible solution is to use a Nussbaum gain, which guarantees closed-loop stability without knowledge of the sign of the high frequency gain. Despite the theory for such a controller having been developed in the 1980s, it has never, to the authors' knowledge, been demonstrated experimentally. In this paper, a Nussbaum gain is used to stabilise thermoacoustic instability in a Rijke tube. The sign of the high frequency gain of the system is not required, and the controller is robust to large changes in operating conditions - demonstrated by varying the length of the Rijke tube with time. Copyright © 2008 by Simon J. Illingworth & Aimee S. Morgans.

Control charts: an application in shrimp canning

Control chart is a statistical tool which can be employed with advantage to learn the situation in the process (whether it is under control or not). There are different kinds of control charts but one which is most commonly used is the control chart for variables, known as X-R chart. This chart can be used for measurable characteristics in food industry like appearance, colour, sizes and dimensions for chemical properties such as moisture, fat and many other analytical counts and measurements. Since construction and maintenance of such charts involve a recognizable amount of time and effort, they should not be used indiscriminately but only where it can be definitely shown that their use improves the overall operation. Since one control chart can be used for only one quality attribute, those for which the charts are used should be selected with care (Kramer and Twigg, 1962). In this article, the procedure of setting up a variable control chart is described with observations taken on filling operation of cans in a shrimp canning factory.

Chemical control of psychrophilic bacterial spoilage of fish 1. Isolation and identification of psychrophilic bacteria from marine fish

Making use of the streak plate technique and low temperature incubation, 28 cultures belonging to six genera namely, Achromobacter, Flavobacterium, Pseudomonas, Micrococcus, Vibrio and Alcaligenes were isolated from different varieties of marine fish. The growth studies indicated that all of them were able to grow between -5 and +5°C within a week's time and none of them showed growth at 37°C. The optimum temperature of growth for all these cultures was in the range 25-28°C. Among these only one, i.e., a Vibrio sp., was found to be an obligate psychrophile.

Origin of rabbit (Oryctolagus cuniculus) in China: evidence from mitochondrial DNA control region sequence analysis

A fragment of mitochondrial DNA (mtDNA) control region (similar to700 bp) was sequenced in 104 individuals from 20 breeds (three Chinese domestic breeds, five recently derived breeds and 12 introduced breeds) of domestic rabbits, Oryctolagus cuniculus . Nineteen sites were polymorphic, with 18 transitions and one insertion/deletion, and eight haplotypes (A1, A2, A3, A4, A5, A6, A7 and A8) were identified. Haplotype A1 was the most common and occurred in 89 individuals. In the 25 Chinese rabbits, only haplotype A1 was observed, while four haplotypes (A1, A3, A5 and A6) were found in 26 recently derived individuals. Haplotype A2 was shared by seven individuals among three introduced strains. The other six haplotypes accounted for 0. 96-1. 92% of the animals. Combined with the published sequences of European rabbits, a reduced median-joining network was constructed. The Chinese rabbit mtDNAs were scattered into two clusters of European rabbits. These results suggest that the (so-called) Chinese rabbits were introduced from Europe. Genetic diversity in Chinese rabbits was very low.

Studies on the probable sources of fungal infection and the control measures in a fish seed farm

The causes of mortality of fry of cultivable fishes in a fish seed farm were investigated. The mortality was due to fungal infection and the pathogen was Saprolegnia sp. The sources of infection were unhygienic breeding hapas, spawnery hapas in the cemented ponds, hatching jars and excess feeding. Application of one kg slaked lime followed by 75g of CuSo sub(4)(l-0.5 p.p.m.) and 150g of KMno sub(4)(2-1 p.p.m.) per each nursery (158m³ water) controlled the pathogen.

The biology and control of Caligus sp., an ectoparasite of the adult milkfish Chanos chanos Forskal

One unidentified species of copepod belonging to the genus Caliqus of the family Caigidae was found to infest the adult milkfish broodstock. To control the parasites infesting the adult milkfish, tests were made using the chemical (2,2,2-trichloro-1-hydroxyl)-phosphonic acid-dimethylethol (Neguvon) at a concentration of 0 . 25 ppm. It is noted that a concentration of 0 . 25 ppm of Neguvon maintained for 12-24 hours in the sabalo-containing tanks in a closed water system but with aeration is effective in controlling the parasites. Fish mortality during the experiment was due to inadequate aeration in the tanks.

Adaptive control of stiffness to stabilize hand position with large loads.

The goal of this work was to investigate stability in relation to the magnitude and direction of forces applied by the hand. The endpoint stiffness and joint stiffness of the arm were measured during a postural task in which subjects exerted up to 30% maximum voluntary force in each of four directions while controlling the position of the hand. All four coefficients of the joint stiffness matrix were found to vary linearly with both elbow and shoulder torque. This contrasts with the results of a previous study, which employed a force control task and concluded that the joint stiffness coefficients varied linearly with either shoulder or elbow torque but not both. Joint stiffness was transformed into endpoint stiffness to compare the effect on stability as endpoint force increased. When the joint stiffness coefficients were modeled as varying with the net torque at only one joint, as in the previous study, we found that hand position became unstable if endpoint force exceeded about 22 N in a specific direction. This did not occur when the joint stiffness coefficients were modeled as varying with the net torque at both joints, as in the present study. Rather, hand position became increasingly more stable as endpoint force increased for all directions of applied force. Our analysis suggests that co-contraction of biarticular muscles was primarily responsible for the increased stability. This clearly demonstrates how the central nervous system can selectively adapt the impedance of the arm in a specific direction to stabilize hand position when the force applied by the hand has a destabilizing effect in that direction.

The computer simulation of primate (Macaca mulatta) spatial visual delayed response and cerebral prefrontal control function

Cerebral prefrontal function is one of the important aspects in neurobiology. Based on the experimental results of neuroanatomy, neurophysiology, behavioral sciences, and the principles of cybernetics and information theory after constructed a simple model simulating prefrontal control function, this paper simulated the behavior of Macaca mulatta completing delayed tasks both before and after its cerebral prefrontal cortex being damaged. The results indicated that there is an obvious difference in the capacity of completing delayed response tasks for the normal monkeys and those of prefrontal cortex cut away. The results are agreement with experiments. The authors suggest that the factors of affecting complete delayed response tasks might be in information keeping and extracting of memory including information storing, keeping and extracting procedures rather than in information storing process.

D77, one benzoic acid derivative, functions as a novel anti-HIV-1 inhibitor targeting the interaction between integrase and cellular LEDGF/p75

Integration of viral-DNA into host chromosome mediated by the viral protein HIV-1 integrase (IN) is an essential step in the HIV-1 life cycle. In this process, Lens epithelium-derived growth factor (LEDGF/p75) is discovered to function as a cellular co-fa

Changes of urinary steroid conjugates and gonadotropin excretion in the menstrual cycle and pregnancy in the Yunnan snub-nosed monkey (Rhinopithecus bieti)

The Yunnan snub-nosed monkey (Rhinopithecus bieti) is one of the most endangered species in the world, and it is endemic to China. According to our knowledge, there was no information on reproduction for this species. The present study was designed to und

Hybrid model predictive control applied to switching control of burner load for a compact marine boi

This paper discusses the application of hybrid model predictive control to control switching between different burner modes in a novel compact marine boiler design. A further purpose of the present work is to point out problems with finite horizon model predictive control applied to systems for which the optimal solution is a limit cycle. Regarding the marine boiler control the aim is to find an optimal control strategy which minimizes a trade-off between deviations in boiler pressure and water level from their respective setpoints while limiting burner switches.The approach taken is based on the Mixed Logic Dynamical framework. The whole boiler systems is modelled in this framework and a model predictive controller is designed. However to facilitate on-line implementation only a small part of the search tree in the mixed integer optimization is evaluated to find out whether a switch should occur or not. The strategy is verified on a simulation model of the compact marine boiler for control of low/high burner load switches. It is shown that even though performance is adequate for some disturbance levels it becomes deteriorated when the optimal solution is a limit cycle. Copyright © 2007 International Federation of Automatic Control All Rights Reserved.