Numerical Research on The Stability of Launching Devices During Firing

An important problem in studying the sloped rocket launch is to determine the oscillations and their effects on the initial conditions of the rocket path. Tiffs phenomenon influences the stability of the launching device and the firing precision. It is assumed that the launching device and the moving rocket form a complex oscillating system that join togefller into a sum of rigid bodies botmd by elastic elements （the vehicle chassis, the tilting platform and the rockets in the containers）. The calculations of the launching device oscillations during the launch by numerical methods are presented.     

Removal of transient disturbances from oscillating measurements using nearest neighbors imputation

Transient disturbances in process measurements compromise the accuracy of some methods for plant-wide oscillation analysis. This paper presents a method to remove such transients while maintaining the dynamic features of the original measurement. The method is based on a nearest neighbors imputation technique. It replaces the removed transient with an estimate which is based on the time series of the whole measurement. The method is demonstrated on experimental and industrial case studies. The results demonstrate the efficacy of the method and recommended parameters. Furthermore, inconsistency indices are proposed which facilitate the automation of the method.     

Fixed-order loop shaping robust controller design for parametric models to damp inter-area oscillations

The inter-area oscillations are common in power systems and can occur due to the changes in the load or generating power especially in long transmission lines. This paper presents the design of a robust fixed-order loop shaping controller to damp out the inter-area oscillations and to enhance the stability of the power system. The proposed loop shaping method is based on the shaping of the open-loop transfer function in the Nyquist diagram through minimizing the quadratic error between the actual and the desired open loop transfer functions in the frequency domain. The proposed method is robust with respect to multi-model uncertainty. Despite other robust controller design methods, the proposed approach deals with the entire system i.e. there is no need to reduce the system and still leads to a lower order controller. In addition, most of the robust methods are heavily dependent on selecting some weight filters which is not required in the proposed approach. This method is applied to the two-area four-machine system and 68 bus system and the effectiveness and robustness of the proposed method in damping inter-area oscillations are validated using case studies.     

BUOYANCY EFFECTS ON THE FORCED CONVECTION ALONG VERTICALLY MOVING SURFACES

The buoyancy effects on the laminar boundary layer heat transfer from vertically moving flat plate and cylinder are studied by a coordinate perturbation method for the cases of prescribed surface temperature and prescribed wall heat flux. Universal expressions are given to show the temperature distributions and the increase of heat transfer rate with the increase of the buoyancy force parameter.     

Single and coupled electrochemical bursters during the electrodissolution/passivation of iron

The ability to produce bursting electrochemical oscillations via the slow external variation of the applied potential is investigated during the electrodissolution/passivation of iron in sulfuric acid. The results are compared with those concerning spontaneous electrochemical bursting in the presence of chloride ions. Moreover, an assembly of two electrochemical Fe/H₂SO₄bursters is studied experimentally. The effect of phase space topology on synchrony is explored by studying the coupled response for different types of electrochemical bursters.     

Non-steady activity during methane combustion over Pd/Al2O3 and the influences of Pt and CeO2 additives

Methane combustion over Pd/Al₂O₃ catalysts with and without added Pt and CeO₂ in both oxygen-rich and methane-rich mixtures at temperatures in the range 250–520°C has been investigated using a temperature-programmed reaction procedure with on-line gas analysis (FTIR). During the temperature loop under oxygen-rich conditions, there was an appreciable hysteresis in the activity of unmodified Pd/Al₂O₃, which was greatly enhanced over Pd–Pt/Al₂O₃. Over both catalysts the hysteresis was reversed under slightly methane-rich atmospheres, and as temperature was reduced, a sudden collapse or fluctuations in activity were shown respectively over Pd–Pt/Al₂O₃ and Pd/Al₂O₃. Such non-steady behaviour was almost eliminated over Pd/Al₂O₃–CeO₂. Under a very narrow range of conditions and over a Pd/Al₂O₃ packed bed, oscillation of methane combustion was observed.     

A method for closed-loop identification of Nyquist curve in three quadrants

This paper proposes a generalization of Ziegler–Nichols' (ZN) experiment that allows the closed-loop identification of Nyquist curve of a linear plant in three quadrants. As in the standard ZN method, no extra equipment is needed. Moreover, sustained undamped oscillations in the plant are not required, since the identification may be accomplished with damped oscillations only. The plant may even be unstable, assuming the used controller is able to stabilize the plant.     

Effect of heating orientation on oscillatory thermocapillary flow in liquid bridges

Oscillatory thermocapillary flow in liquid bridges of high Prandtl number fluids is investigated experimentally as well as numerically. Heat loss from the free surface is shown to have significant influence on the onset of oscillations. In the present work the surrounding air flow pattern is changed by heating the liquid bridge from the top or from the bottom. The results show that the local free surface heat transfer rate, especially near the hot wall, has strong effects on the oscillations.     

STUDY OF SOME UNIQUE FEATURES OF RATIO-DEPENDENT MODELS FOR PREDATOR-PREY-SUBSTRATE INTERACTIONS IN CONTINUOUS CULTURES

This article studies the dynamics of ratio-dependent models for continuous bioreactors involving interactions between predator, prey, and a limiting substrate. Ratio-dependent models, for which the growth rate of predator is a function of the ratio of prey to predator abundance, have recently received growing attention and were shown to exhibit more interesting behavior than the classical (strictly) prey-dependent models. It is shown that in addition to predicting areas of predator washout and areas of total washout, the studied examples of ratio-dependent models predict areas for which the species coexist either at steady state or in oscillatory mode for any initial population values. The studied models also predict a unique feature for which the interacting species can coexist or wash out depending on their initial values. The objective of this article is to study in some detail this interesting behavior that makes ratio-dependent models better candidates in predicting predator-prey interactions in real biological life.     

Control of Wind-Induced Self-Excited Oscillations by Transfer of Internal Energy to Higher Modes of Vibration. II: Application to Taut Cables

In Part I of this paper, a theoretical basis is presented using a two-degrees-of-freedom model. In this second part of the study, the passive control and the two types of semiactive controls introduced in Part I are examined numerically for a taut cable experiencing wind-induced galloping motion. The passive and the semiactive control schemes for taut cables show a good similarity with the results obtained for the two-degrees-of-freedom model. The potential of using these control schemes in practical applications to flexible structures is demonstrated.