Showing 13 results for Stability
E. Esmailzadeh, H. R. Bahrampuri and N. Niksefat,
Volume 20, Issue 1 (7-2001)
Abstract
Articulated liquid cargo vehicles transporting inflammable fuels and dangerous chemical products require special consideration when traveling on urban roads or cruising at highway speeds. The road safety and handling of these kinds of vehicles may be adversely affected when negotiating sharp turns or travelling on slippery roads, which may result in either lateral instabilities or complete rollover of these tanker vehicles. Moreover, directional instabilities in these kinds of vehicle may also introduce an excessive yaw swing or may initiate the jack-
knifing of the articulated tanker trucks. In order to overcome the instabilities of these tanker vehicles, installation of lateral baffles in the form of separating walls in the tanker were considered. The static roll and yaw plane models of these vehicles including lateral translation of the liquid inside the tank were developed. Using the static roll model, the rollover threshold of the vehicle is analyzed and the effect of these separating walls on the stability of the vehicle is studied. The yaw plane model is then used to predict the transient response and stability of the tanker vehicle under various road maneuvers. The governing differential equations were solved numerically to obtain the simulation results and optimum values of the parameters.
Keywords: Tanker, Vehicle, Stability, vehicle dynamic, rollover, lateral baffles
M.e. Hamedani Golshan, H. Ghoudjehbaklou and H. Seifi,
Volume 20, Issue 2 (4-2001)
Abstract
Finding the collapse susceptible portion of a power system is one of the purposes of voltage stability analysis. This part which is a voltage control area is called the voltage weak area. Determining the weak area and adjecent voltage control areas has special importance in the improvement of voltage stability. Designing an on-line corrective control requires the voltage weak area to be determined by a sufficiently rapid and precise method. In this paper, a new algorithm based on assigning a vector to
each power system bus is presented. These vectors indicate buses conditions from the viewpoint of voltage stability. In this new method, using the clustering methods such as kohonen neural network, fuzzy C-Means algorithm and fuzzy kohonen algorithm, voltage control areas are determined The proposed method has advantages such as determining PV and PQ buses which belong to the weak area simultanously, under all operating conditions and without a need to system model. Also by comparing the results of applying clustering methods, it has been observed that, due to simplicity of implementation and precision of the results, the two dimensional kohonen neural network is a more suitable tool for clustering power system to voltage control areas than the fuzzy C-Means and fuzzy kohonen methods.
Keywords: Voltage stability, Voltage weak area, Voltage control area, Corrective control, Pattern recognition, Kohonen neural network, Fuzzy C-Means algorithm, Fuzzy Kohonen algorithm.
Gh. Yousefi, H.seifi and M. S. Ghazi-Zadeh,
Volume 21, Issue 1 (7-2002)
Abstract
In a de-regulated open access environment, reactive power is one of the ancillary services which must be provided by an Independent System Operator (ISO). In this paper, a new algorithm is proposed in which reactive power resources are initially so tuned that optimum security in terms of voltage profile and voltage stability are achieved while at the same time, the system losses are minimized. The resulting optimization case is solved as an Extended Multi-objective Optimal Power Flow (EMOPF) problem using Lexico Graphic Method (LGM). Thereafter, using the concept of Fair Resource Allocation (FRA), the reactive powers generated are distributed among existing transactions so that the costs incurred are properly and fairly recovered. The algorithm is successfully tested on a typical power system.
Keywords: Reactive Power, Reactive Power Management, Reactive Power Pricing, Voltage Profile, Voltage Stability, Deregulated Environment, Open Access
H. Nahvi and M. Sobhani,
Volume 22, Issue 2 (1-2004)
Abstract
In this paper, dynamic and stability analysis of a flexible cam-follower system is investigated. Equation of motion is derived considering flexibility of the follower and camshaft. Viscous and Coulomb frictions are considered in the rocker arm pivot. The normalized equation of motion of the system is a 2nd- order differential equation with periodic coefficients.
Floquet theory is employed to study parametric stability of the system. Stability diagrams are presented and the effects of varying cam profiles and motion events on the stability of the system are compared. Results show that viscous and Coulomb frictions stabilize the motion of the system
M. Eidiani, M. H. Modir Shanechi and E. Vaahedi,
Volume 23, Issue 2 (1-2005)
Abstract
Methods for calculating Available Transfer Capability (ATC) of the transmission systems may be grouped under Static and Dynamic methods. This paper presents a fast dynamic method for ATC calculations, which considers both Transient Stability Limits and Voltage Stability Limits as terminating criteria. A variation of Energy Function Method is used to determine the transient stability limit and the determinant of the Jacobian matrix of the system is used as an index to determine the voltage stability limit. A novel method is used to approximately calculate this determinant. Combining these two methods, an algorithm that calculates ATC, based on both voltage and angle dynamic stability is presented. The advantage of this algorithm, besides considering both voltage and angle dynamic stability, is its high speed. This speed of calculation makes the algorithm a perfect
candidate to be used in screening contingencies and to determine those cases that need to be further analyzed. To demonstrate the validity, efficiency, and the speed of the new method, it is employed in the calculation of ATC for numerical examples with 2, 3, 7 (CIGREE), 10, 30 (IEEE) and 145 (Iowa State) buses.
M. Kahrom, K. Alavie and M. M. Jafariean,
Volume 24, Issue 1 (7-2005)
Abstract
Neutral stability limits for wake flow behind a flat plate is studied using spectral method. First, Orr-Sommerfeld equation was changed to matrix form, covering the whole domain of solution. Next, each term of matrix was expanded using Chebyshev expansion series, a series very much equivalent to the Fourier cosine series. A group of functions and conditions are applied to start and end points in the mathematical domain of the solution so as to avoid error accomulation at these points. The scheme ends with two matrices which result from the Orr-Sommerfeld equation. These matrices are solved, in conjunction,
with boundary conditions ending up with a curve of neutral points of stability for an assumed velocity profile. Results are compared with other existing numerical methods and experiments, and the accuracy of the method is confirmed.
S. Hatami, M. Azhari, and M.m. Saadatpour,
Volume 26, Issue 1 (7-2007)
Abstract
Based on classical plate theory, standard and spectral finite element methods are extended for vibration and dynamic stability of axially moving thin plates subjected to in-plane forces. The formulation of the standard method earned through Hamilton’s principle is independent of element type. But for solving numerical examples, an isoparametric quadrilateral element is developed using Lagrange interpolation functions. The spectral method is, in fact, the solution of motion equation for an axially moving plate. Although this method has some limitations concerning boundary condition of plate and in-plane forces, it leads to an exact solution of free vibration and stability of plates travelling on parallel rollers. The method can be used as a benchmark of accuracy of other numerical methods.
K. Abedi, M.r. Sheidaii,
Volume 26, Issue 1 (7-2007)
Abstract
Considering the vulnerability of double-layer grid space structures to progressive collapse phenomenon, it is necessary to pay special attention to this phenomenon in the design process. Alternate path method is one of the most appropriate and accepted methods for progressive collapse resistant design of structures. Alternate Path Method permits local failure to occur but provides alternate paths around the damaged area so that the structure is able to absorb the applied loads without overall collapse. Following the sudden initial local failure event, severe dynamic effects may arise which should be taken into account in determining the realistic collapse behavior of the structure. In this paper, a new methodology based on alternate path method is presented to apply dynamic effects of initial local failure. The method is called nonlinear dynamic alternate path method. Due to its capability to take account of dynamic nature of the failure, this method can be used to evaluate realistic collapse behavior of the structure and to investigate the vulnerability of the structure to progressive collapse phenomenon.
R. Ghasemi Asl, and B. Ghadiri,
Volume 26, Issue 1 (7-2007)
Abstract
In this paper, the equation of motion of an elastic 2 DoF wing model has been derived using Lagrange's method. The aerodynamic loads on the wing were calculated via the Strip-Theory and the effect of compressibility was included. Wing deflections due to bending and twist motions were determined using the Assume-Mode method. The aeroelastic equations were solved numerically using the V-g method. The results obtained for different types of wings were in good agreement with experimental data.
A. Eslami, H. Modaraei, and H. Ahmadi,
Volume 26, Issue 2 (1-2008)
Abstract
S. Deljavan, M. G. Kakroudi, J. Zaroodi, F. Rezaei,
Volume 35, Issue 1 (6-2016)
Abstract
Perovskite structures including oxygen vacancies are the most important group of the oxygen preamble membranes. These membranes have potentially attractive applications in the membrane reactors for partial oxidation of methane. Doping Perovskite phase in order to increase the oxygen vacancies and oxygen permeation, besides Perovskite structure stability, has been the main approach of the recent researches. In this research, tantalum was chosen as the appropriate dopant for Ba(Co0.8Fe0.2)O3−δ Perovskite phase, according to the tolerance factor calculations. The X ray patterns of synthesized Ba (Co0.7Fe0.2Ta0.1)O3−δ indicate that the Perovskite structure was formed. Powder density, thermal expansion coefficient measurements and bond strength studies using FT-IR analysis revealed that the chosen dopant not only increases the oxygen vacancies volume but also reduces the thermal expansion coefficient without significant changes of bond strength. Results showed that the novel Ba (Co0.7Fe0.2Ta0.1) O3−δ is a good choice for the membrane fabrication of methane partial reduction reactors.
E. Velayi, R. Norouzbeigi,
Volume 36, Issue 4 (3-2018)
Abstract
A superhydrophobic ZnO surface was prepared on the stainless steel mesh by a one-step chemical bath deposition method without chemical post-treatment. The effect of adding polyethylene glycol 6000 (PEG 6000) as an organic additive and the type of the alkaline agent were investigated on the morphological and wettability properties of ZnO surfaces. The prepared surfaces were characterized by X-ray Diffraction (XRD), stylus profilometer, Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) and Raman Spectrometer. The microstructure studies showed that the addition of PEG led to formation of densely branched and uniform ZnO rods with a length of 1.5 µm and a diameter of about 95 nm on the substrate. The surface wettability studies confirmed that the sample prepared in the presence of hexamethylenetetramine (HMTA) and 0.05 mM PEG with branched tree-like micro/nanostructure exhibited excellent superhydrophobic properties with the water contact angle (WCA) of 158.2°±1.5° and contact angle hysteresis (CAH) of 3.5°. In addition, the superhydrophobic showed good chemical stability in the pH range of 4 to 8.
A. Baradaran, M. Tavoosi,
Volume 37, Issue 3 (12-2018)
Abstract
In the present study, the structural, optical and thermal behaviors of GeO2-PbO-CaO-SrO glasses were investigated to achieve the highest optical properties and thermal stability. Accordingly, different 50GeO2-(50-x)PbO-xCaO and 50GeO2-(50-x)PbO-xSrO (x=0, 10, 20) germanate glasses were prepared by the conventional melt and quench technique between two steel sheets. The produced samples were characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FTIR) and UV-Vis spectroscopy. Based on the obtained results, the addition of CaO to glass composition reduced the glass phase forming ability as well as optical and thermal behaviors of the prepared glasses. In contrast, the presence of SrO had no destructive effect on the optical properties of the prepared glasses; the highest values of glass transition (580 oC) and crystallization temperature (831 oC) were achieved in the sample containing 20 mole% of SrO.
