Range Of Parameter Variations Research Articles

A novel approach to conventional power system stabilizer design using tabu search

A tabu search (TS) based power system stabilizer (PSS) is presented in this article. The proposed approach uses the TS algorithm to search for the optimal settings of conventional lead-lag power system stabilizer (CPSS) parameters. Incorporation of the TS algorithm in the PSS design significantly reduces the time consumed in the design process. One of the main advantages of the proposed approach is the fact that the TS algorithm leads to the optimal solution regardless of the initial guess. The performance of the proposed PSS under different disturbances and loading conditions is investigated for single machine infinite bus and multimachine power systems. The eigenvalue analysis and simulation results show the effectiveness of the proposed PSSs to damp out the local and the interarea modes of oscillations and work effectively over a wide range of loading conditions and system parameter variations.

Robust controller design for matrix second-order systems with structured uncertainty

Matrix second-order systems arise frequently in the formulation of dynamic systems in classical mechanics, robotics, aerodynamics and many others. Though formulation of the control design problem in matrix second-order form has many advantages, there is very little literature available on this topic-even for nominal case. In this paper, we design controller gains directly in matrix second-order formulation for robust stability in a specified range of parameter variations. The stabilizing controller gains for the entire parameter variations range are obtained from only two given extreme matrices without formulating or checking the stability of other vertex matrices of the family. The design algorithm is computationally efficient and simple.

FURTHER RESULTS FOR MODAL CHARACTERISTICS OF ROTATING TAPERED TIMOSHENKO BEAMS

The in-plane and out-of-plane modes of free vibration of a tapered Timoshenko beam mounted on the periphery of a rotating rigid hub are investigated. The finite element method is used to discretize the beam. This formulation permits unequal breadth and depth taper ratios as well as unequal element lengths. The effects of shear deformation, rotary inertia, hub radius, setting angle, and spinning rotation are considered. The generalized eigenvalue problem is defined using explicit expressions for the mass and stiffness matrices and numerical solutions are generated for a wide range of parameter variations. Explicit expressions of Southwell coefficients are presented for the first time for the case of rotating uniform and tapered Timoshenko beams. Comparisons are made wherever possible with exact solutions and other numerical results available in the literature. Extended results are obtained to serve as a benchmark solution for other numerical techniques and specialized applications.

Amylose chain behavior in an interacting context I. Influence of a nonchair ring on the maltose conformations

In the presence of steric constraints, flexible forms, i.e., skew (S), boat (B) or half-boat (H), were evoked from experimental data and conformational analyses by molecular mechanics calculations for glucopyranose rings of amylose fragments. This important case, occurring, for example, in amylose-amylase complexes, requires careful analysis of these flexible ring forms prior to any further conformational study. The influence of a nonchair (flexible) form on the maltose conformation is systematically evaluated, with an appropriate strategy using “semirelaxed” maps and comparing them with those obtained from already known chair-chair (4C1-4C1) maps. Therefore, new low-energy maltose conformations are described and classified from flexible-chair and chair-flexible maps. These conformations are well dispersed inside significantly larger contours in the (φ, ψ) projection. In a second stage, the consequence of these flexible ring forms is discussed in terms of amylose propagation apart from these new maltose conformations. Two propagation parameters are defined (τ, ω), related to the local curvature of the chain and the relative orientation of the two mean ring planes. Low-energy conformations of 4C1-4C1 maltose have almost the same curvature between the two rings, whereas their relative orientations have well-identified ω values. On the contrary, the presence of one flexible conformation considerably increases the variation range of both propagation parameters. Thus, new low-energy conformations allow local curvatures yielding from almost perpendicular to linear pairs of glucopyranose rings with relative orientation covering about three-fourths of the total domain. This description is essential to understand amylose conformations in catalytic site and subsites of the amylases. © 1996 John Wiley & Sons, Inc.

Solution of the non-LTE problem for molecular gas in planetary atmospheres: superiority of accelerated lambda iteration

A general formulation is given of the multi-level rotation–vibrational non-LTE problem for a mixture of radiating molecular gases in a planetary atmosphere, treating explicitly the coupling of molecular energy levels by collisionally induced energy transfer processes and by band overlap. Various limiting cases of non-LTE effects are discussed. Three techniques—lambda iteration, matrix and accelerated lambda iteration—which are used to solve these problem are discussed and compared. In the case of the CO 2 non-LTE problem in the Earth's atmosphere, it is demonstrated that accelerated lambda iteration is far superior to the other algorithms in minimizing computer time and storage and in converging much more rapidly; moreover the convergence rate is insensitive to the initial population estimates and to wide range of variation in the model input parameters. Accelerated lambda iteration therefore makes possible the calculation of much larger and more physically complete atmospheric and molecular models.

A study on mode of failures in spur gears under optimized conditions

The concept of design space formed with module and pinion number of teeth has been utilized in establishing an optimized design of a spur gear mesh and studying the dominating mode of failure under such condition. An attempt has been made in the present work for critically studying the behaviour of mode of failure for a large range of parameter variations for 20 commonly used gear materials for both 20° and 25° pressure angle, full depth spur gears. Minimum centre distance has been chosen as the optimization objective function and an in-depth study of bending, pitting and scoring mode of failures has been attempted.

Output prediction of cone crushers

The output prediction of cone crushers has been focused on both by the aggregate producing industry and the mining industry as the demands for higher quality and lower costs increase. In this paper a method for prediction of cone crusher performance is presented By using the method both product size distributions and total capacity can be predicted. By combining these results a Crusher Performance Map (CPM) is obtained. The CPM is a description of crusher performance over a wide range of variation in the operational parameters. Therefore the CPM can be used for optimization and choice of operational machine parameters for an individual crusher as a part of a crushing plant.

Predicting the relative sensitivity of forest production in Ireland to site quality and climate change

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 10:51-67 (1998) - doi:10.3354/cr010051 Predicting the relative sensitivity of forest production in Ireland to site quality and climate change Christine L. Goodale1,*, John D. Aber1, Edward P. Farrell2 1Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824, USA2Department of Environmental Resource Management, University College Dublin, Agriculture Building Belfield, Dublin 4, Ireland *E-mail: christy.goodale@unh.edu Most model-based predictions of climate change effects on forest ecosystems have used either potential or static descriptions of vegetation and site, removing the effects of direct management or land use. In this paper we use a previously developed and validated model of carbon and water balances in forest ecosystems (PnET-II) to assess the relative sensitivity of forest production in Ireland to predicted climate change and to ambient variability in site quality. After validating the model against measured productivity for 2 sets of stands, we ran the model using existing variation in site quality, represented as differences in foliar N concentration, and also for predicted changes in climate and atmospheric CO2. Resulting variations in productivity were compared with those due to potential errors in the specification of input parameters and to variation in current ambient climate across the region. The effects on net primary production (NPP) and wood production of either ambient variation in climate or predicted changes in temperature, precipitation and CO2 are quite small (0 to 30%) relative to the effects of ambient variability in site quality (up to 400%). The range of possible variation in other user-specified physiological parameters resulted in changes of less than 10% in model predictions. We conclude that site-specific conditions and management practices result in a range of forest productivity that is much greater than any likely to be induced by climate change or CO2 enrichment. We also suggest that it is essential to understand and map spatial variability in site quality, as well as to understand how the productive capacity of landscapes will change in response to management and pollution loading, if we are to predict the actual role that climate change will play in altering forest productivity and global biogeochemistry. Regional modeling · Validation · Foliar nitrogen · Sitka spruce Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 10, No. 1. Online publication date: April 09, 1998 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 1998 Inter-Research.

Control of a large space structure using MMAE/MMAC techniques

The application of moving-bank multiple model adaptive estimation and control (MMAE/MMAC) algorithms to an actual spade structure (Space Integrated Controls Experiment (SPICE)) being examined at Phillips Laboratory at Kirtland AFB, NM, is presented. The structure consists of a large platform and a smaller platform connected by three legs in a tripod fashion. Kalman filtering and LQG (linear system, quadratic cost, Gaussian noise) control techniques are utilized as the primary design tools for the components of the MMAE/MMAC. Implementing a bank of filters or controllers increases the robustness of the algorithms when uncertainties exist in the system model, whereas the moving bank is utilized to reduce the computational load. Several reduced-order models are developed from the truth model using modal analysis and modal cost analysis. The MMAE/MMAC design with a substantially reduced-order filter model provides an excellent method to estimate a wide range of parameter variations and to quell oscillations in the structure.

Compromise optimization of a composite plate with a given probability of realization

A method is proposed for solution of the problem of the compromise optimization of three properties of a composite plate (thermal conductivity, stability, and the probability P* of design realization), which depend on three initial stochastic data with constant average values, and two variable initial data. The geometry of the domain of plate properties, the curve of optimal Pareto solutions, and the scatter ellipses is determined at four points for a given range of variable parameters. A method of constructing the curves of optimal Pareto solutions for the following assigned probabilities of design realization is proposed and numerically implemented: P*=0.40, 0.80, and 0.95. The generalized efficiency function ΦΣ (ΦΣ → max, 0 ≤ ΦΣ ≤ 1) of the first two properties decreases from 0.74 to 0.23 as the numerical value of P* increases from 0.40 to 0.95. A family of isolines ΦΣ = const is plotted for all three properties investigated, and max ΦΣ determined as 0.63.

Control of an Inverted Pendulum Using Direct Model Reference Adaptive Control

This paper presents the design of a robust direct model reference adaptive control (DMRAC) algorithm with focus on the satisfaction of an almost strictly positive real (ASPR) condition over the maximal range of parameter variations of the plant, and its application to an inverted pendulum. To alleviate the ASPR condition, the pendulum is augmented with a feedforward compensator optimized for robustness. A DMRAC algorithm ensuring asymptotic model following is then integrated with the feedforward compensator design. These new experimental results validate the algorithm's use and applicability to the control of an inverted pendulum with a variety of parameter uncertainties. On presente la conception d'un algorithme robuste de reglage adaptif a 'reference au modele directe (DMRAC) qui dois satisfaire la condition de realization positive presque partout (PPP) et son application a un pendule renverse. Pour alleger la condition PPP, le pendule est ameliore' par l'ajout d'un compensateur "feed-forward" qui est optimise' pour la robustess. Puis, un algorithme DMRAC qui assure que la modele soit suivi asymptotiquement est integre' dans la realisation du compensateur. Les nouvaux resultats experimentaux verifient l'usage et l'application de l'algorithme pour regler le pendule renverse' avec des incretitudes sur les valeurs des parametres.

Sliding mode control for a combined active‐passive power‐conditioning equipment

AbstractWhen compared with ideal conditions, the implementation of active shunt filtering exhibits shortcomings caused by the generation of switching ripple, the limited frequency of filtering and the non‐ideal behaviour of both network and load. It is hence necessary to deal with high harmonics by means of passive filtering elements. The power conditioning equipment put forward in this paper consists of an active filter combined with a passive LC filter. The sliding mode control proposed is particularly rugged and capable of achieving the desired line current with a distorting load and over a wide variation range of network parameters. Numerical simulations and experimental results are reported.

Computer controlled measurement and analytical modelling of flow stresses during hot deformation of the cooper alloy CuZn42Mn2

The increasing utilisation of FE-programs for the description and optimization of hot forming processes (forging, extrusion etc.) has created considerable demand for precise materials data of formability at high temperatures. The quality of the FE-simulations is highly dependent on the quality and reliability of boundary conditions data. Especially, data on flow stresses versus strain, strain-rate and temperature are required. One of the applicable experimental methods is the upset test of cylindrical samples. In this work, a new high precision instrument called “deformation dilatometer” with a wide range of experimental parameter variations was used. The instrument is monitored and controlled by a versatile computer software, which can create different temperature-time conditions under vacuum or inert gas atmosphere. Deformation is accomplished under computer controlled, constant strain-rate. The reproduceability of the resulting flow stress curves is high, even at small flow stresses. Experimental results of a copper alloy (CuZn42Mn2) at different deformation temperatures and strain-rates were fitted to an analytical model describing the strain-rate-temperature dependence of the flow stress. Finally, the analytical model will be used for the implementation of flow stress values in the newest version of the special purpose FE-program PressForm for the optimization of extrusion manufacturing.

An electrical network model of intracranial arteriovenous malformations: analysis of variations in hemodynamic and biophysical parameters.

The propensity of intracranial arteriovenous malformations (AVMs) to hemorrhage is correlated significantly with their hemodynamic features. Biomathematical models offer a theoretical approach to analyse complex AVM hemodynamics, which otherwise are difficult to quantify, particularly within or in close proximity to the nidus. Our purpose was to investigate a newly developed biomathematical AVM model based on electrical network analysis in which morphological, biophysical, and hemodynamic characteristics of intracranial AVMs were replicated accurately. Several factors implemented into the model were altered systematically to study the effects of a possible wide range of normal variations in AVM hemodynamic and biophysical parameters on the behavior of this model and its fidelity to physiological reality. The model represented a complex, noncompartmentalized AVM with four arterial feeders, two draining veins, and a nidus consisting of 28 interconnected plexiform and fistulous components. Various clinically-determined experimentally-observed, or hypothetically-assumed values for the nidus vessel radii (plexiform: 0.01 cm-0.1 cm; fistulous: 0.1 cm-0.2 cm), mean systemic arterial pressure (71 mm Hg-125 mm Hg), mean arterial feeder pressures (21 mm Hg-80 mm Hg), mean draining vein pressures (5 mm Hg-23 mm Hg), wall thickness of nidus vessels (20 microns-70 microns), and elastic modulus of nidus vessels (1 x 10(4) dyn/cm2 to 1 x 10(5) dyn/cm2) were used as normal or realistic ranges of parameters implemented in the model. Using an electrical analogy of Ohm's law, flow was determined based on Poiseuille's law given the aforementioned pressures and resistance of each nidus vessel. Circuit analysis of the AVM vasculature based on the conservation of flow and voltage revealed the flow rate through each vessel in the AVM network. An expression for the risk of AVM nidus rupture was derived based on the functional distribution of the critical radii of component vessels. The two characteristics which were used to judge the fidelity of the theoretical performance of the AVM model against the physiological one of human AVMs were total volumetric flow through the AVM (< or = 900 ml/min), and its risk of rupture (< 100%). Applying these criteria, a series of 216 (out of 260) AVM models using different combinations of these hemodynamic and biophysical parameters resulted in a physiologically-realistic conduct of the model (yielding a total flow through the AVM model varying from 449.9 ml/min to 888.6 ml/min, and a maximum risk of rupture varying from 26.4 to 99.9%). The described novel biomathematical model characterizes the transnidal and intranidal hemodynamics of an intracranial AVM more accurately than previously possible. A wide range of hemodynamic and biophysical parameters can be implemented in this AVM model to result in simulation of human AVMs with differing characteristics (e.g. low-flow and high-flow AVMs). This experimental model should serve as a useful research tool for further theoretical investigations of a variety of intracranial AVMs and their hemodynamic sequelae.

Sensitivity analysis for chemical process optimization

A sensitivity analysis methodology based on continuation techniques is applied to chemical engineering processes. The method is based on the trace of the optimal solution path of a process model under multiple model parameter variations of finite magnitude. The first-order stationarity conditions form a system of parameterized nonlinear equations. The solution of the equation set for different values of the parameters is obtained using continuation methods (PITCON). The behavior of the optimal solution path is studied around singular points. Simple tests are used to detect singularities due to violation of the strict complementarity, linear independence constraint qualification or second-order optimality conditions. The example cases involve single and multiple unit models with equation sets of moderate to large size. The method can handle active constraint set changes and can determine the range of model parameter variations in a given direction for which the model is feasible. It can be used to determine the most sensitive unit in a plant for a given disturbance and calculate multiple solutions to the stationarity conditions for the same parameter values.

Flexible response: DNA supercoiling, transcription and bacterial adaptation to environmental stress

T he impressive ability of bacteria to adapt to environmental change is a cause of both wonder and concern. These 'simple' organisms can cope with a wide range of variation in external physical and chemical parameters, such as temperature, pH, barometric pressure, osmolarity, oxygen availability, nutrient supply and the presence of toxic substances. Much of this adaptation involves resetting the transcriptional machinery of the cell, a topic of current intensive study. This research is influenced in some c a s e s by the realization that bacteria of industrial importance produce useful products when undergoing adaptation to stressful growth conditions, and in other cases by the observation that harmful bacteria frequently express virulenceenhancing factors in response to environmental cues. Many mechanisms determine the response of the transcriptional machinery to environmental signals. None of these mechanisms is entirely straightforward, even when an apparently simple one-to-one relationship seems to have been established between a given gene and a regulator. For example, the role of the RpoS {5 factor in promoting the transcription of a subset of eubacterial g e n e s in the stationary phase of growth has become complicated by issues concerning the precise mechanism through which RpoS expression is itself controlled 1. O n e of the most complicated issues in the field of transcriptional responses to environmental signals concerns the role of DNA topology and, in particular, DNA supercoiling. Supercoiling has the potential to influence strand separation in DNA, and hence DNA transactions such as transcription. It has been recognized since the mid-1980s that the degree of supercoiling of bacterial DNA varies with the growth conditions 2-4. If supercoiling varies in response to environmental influences, logic suggests that this could provide a (partial) mechanism through which transcription could be influenced by the environment. This is a nice hypothesis which deserves to be tested rigorously. Historically, the proU operon of Escherichia coli and Salmonella typhimurium has played an important role as a research tool in this field. This operon encodes a transport system for the osmoprotectant glycine-betaine, and its transcription is induced by about a hundredfold when the bacterial cell experiences an increase in osmotic pressure s. These increases in osmolarity also correlate with a reduction in the linking number of bacterial DNA 4. In other words, the DNA experiences an increase in negative supercoiling. Moreover, th i s change in linking number is accompanied by an increase in the free energy of the DNA, resulting in an enhanced ability to drive processes (such as cruciform extrusion), which depend on DNA strand separation 6. It s e e m s reasonable to propose that these same changes in supercoiling could drive processes (such as the formation of an open complex at the promoter) that would facilitate the transcription of operons such as proU. These discoveries, and the hypotheses that quickly developed from them, raise two separate yet

The Monte Carlo Multiply Scattered Components (MCMSC) approach for natural gamma-ray log interpretation

A new approach called the Monte Carlo Multiply Scattered Component (MCMSC) approach has been developed for natural gamma-ray logging tool interpretation. It consists of first determining individual scatter component library gamma-ray spectra for each of the three sources of natural gamma radiation (/sup 40/K, U, and Th) for a reference sample by Monte Carlo simulation. Then these scatter component library spectra, normalized to unit area, are used to obtain coefficients by the library least-squares (LLS) method with the natural radioisotope library spectra for a range of sample parameters such as borehole fluid density and composition as well as formation density and composition. Finally, empirical relationships are developed between the individual scatter component library coefficients and the sample parameters. It is found that the normalized scatter component libraries are insensitive to the formation lithology, and the range of allowable parameter variations covers most of the sedimentary formations. This approach allows one to construct the appropriate natural radioisotope libraries for /sup 40/K, uranium, and thorium for a sample with known characteristics in a very efficient and accurate manner. This, in turn, allows the calculation (again by the LLS method) of amounts of the three sources of natural gamma rays for any sample spectrum.

Design of Robust Feedforward Compensators for Direct Model Reference Adaptive Systems

Design of a robust direct model reference adaptive control algorithm focusing on the satisfaction of an almost strictly positive real condition (ASPR) for both single-input single-output and multi-input multi-output plants is presented. Systematic design procedures utilizing optimization methods and frequency domain design conditions for a feedforward compensator are developed so that the ASPR condition is satisfied over the maximal range of plant parameter variations.

μ synthesis of flexible rotor-magnetic bearing systems

The /spl mu/ synthesis design method was evaluated for a flexible rotor magnetic bearing system with a five-axis-control system using both simulations and experiments. After modeling the full-order system using the finite element method, the autors obtained a reduced-order model in the modal domain by truncating the flexible modes. After choosing appropriate weighting functions with respect to frequency, they designed the /spl mu/-synthesis control system using the /spl mu/-toolbox in MATLAB. They then carried out simulations of the control system for a flexible rotor magnetic bearing system with a five-axis-control system and obtained good performance. Next, they conducted experiments to verify the robustness of the controllers on a test rig during initial levitation. The /spl mu/ controllers provided robust stability and performance over a wide range of parameter variations in the test rig.

Flexibility test for heat exchanger networks with uncertain flowrates

According to Cerdá et al ( Computers ehem. Engng 14, 197, 1990), a heat exchanger network is structurally flexible for a given variation range of parameters if it guarantees operability (feasibility) and maximum energy recover in the whole set of operation points. In this paper we present a flexibility test (in the previous sense) at the level of heat matches when only heat capacity flowrate variations are allowed. This test is a mixed integer linear program which considers the whole set of operation points at once, and may be incorporated into any synthesis procedure of flexible heat exchanger networks [like the one proposed by Floudas and Grossmann ( Computers chem. Engng 11, 319, 1987)] that combines synthesis techniques and flexibility analysis.