Showing 8 results for Rve
M. Ghodsi and K. Bazargan,
Volume 20, Issue 1 (7-2001)
Abstract
In this paper
, a fast method for automatic generation and scientific design of Persian letters is proposed. Scientific typeface design is an approach in which fonts are described by mathematical curves with well-defined parameters, where these parameters can be automatically tuned. METAFONT is a language suitable for the type of design used in this work. This language is particularly useful in designing Persian fonts because it can be used to simulate the pen movements of a calligrapher through automatic conversion of the scanned bitmap image of a font into a METAFONT program, which can in turn, produce the font at a high quality. A complete software has been implemented based on these algorithms that works interactively with the user to facilitate the font design.
M. Jafarboland, H. R. Momeni and N. Sadati,
Volume 21, Issue 2 (1-2003)
Abstract
Various methods are presented to control the attitude of satellite due to lack of information of yaw axis attitude so far.
In this paper, a new method is used which is more general and is applicable to all types of satellites, with at least one controller.
This method is not limited to YAW axis and can control the two other axes as well. One feature of this approach is the ability to be modified for large angle maneuvers for special applications.
A new observer is also proposed for the controller, which causes the angles attitude to be kept in desirable values, with minimum control effort and more accuracy. Simulation results show that compare with methods using the complete all axis information, this approach is satisfactory.
Keywords: Attitude control, PID controlley, BIBO stability, pseudo observer
S. Monajem,
Volume 24, Issue 1 (7-2005)
Abstract
When rails are laid in a railway track, small gaps are left between the ends of adjoining rails to allow for the expansion of the rails when the temperature rises. Rail joints are provided to form a continuous rail path which are normally laid in standard lengths bolted together by fishplates. When two rail joints are exactly opposing each other, they are called square
(side by side) joints. Manufacturers produce rails with different standard lengths. The inner line of rails in a curve is shorter than the outer line therefore, it would be complicated to have square joints by using only rails of standard length for both inner and outer rails in the curve. If some short rails were used in the inner line, it would be possible for all joints of rails to lie opposite each other in a precise manner. It is clear that equal rail lengths can easily create square joints along the straight portion of the track. In curves with larger radii, there is a substantial difference between inner and outer arcs of the cruve. Manufacturers producing different standard lengths also produce some short rails in two or three different lengths. This paper presents a simple method of finding the location of joints in the railway curve. Previous methods (used in European and American railways) use some short rails (3 or 4 short rails) with different lengths for the inner arc. In this method, short rails of one single length are used.
M. Jafarboland, N. Sadati, and H. R. Momeni,
Volume 25, Issue 1 (7-2006)
Abstract
Control of a class of uncertain nonlinear systems, which estimates unavailable state variables, is considered. A new approach for robust tracking control problem of satellite for large rotational maneuvers is presented in this paper. The features of this approach include a strong algorithm to estimate attitude, based on discrete extended Kalman filter combined with a continuous extended Kalman filter and attitude nonlinear model, and a robust controller based on sliding-mode with perturbation estimation. Estimation accuracy in this method is five times higher than other recent approaches based on Kalman filter. We have used sliding-mode controller in this paper. Not only the controller and the corresponding observer but also their composition must be robust. To make this controller robust against the uncertainty of parameters, the robust Kalman filter is used. Based on interval algebra, an upper bound and a lower bound are estimated for state variables of the system and considering these bounds in indicating the sliding conditions, stability of the controller in combination with the observer will be satisfied simultaneously. The simulation results show the capability of this method in spite of different uncertainty levels (up to %50).
E. Ebrahimnia-Bajestan, H. Niazmand,
Volume 36, Issue 1 (9-2017)
Abstract
In this paper, numerical simulation of flow and heat transfer of Al2O3/water nanofluid has been carried out through three different geometries involving a straight pipe, a 90o curved pipe and a 180o curved pipe under constant heat flux condition. Employing singe-phase model for the nanofluid, the Navier-Stokes and energy equations for an incompressible and laminar flow have been solved in a body fitted coordinate system using a homemade code based on control-volume approach, while all thermophysical properties of the nanofluid are dependent on considered temperature. The effects of different nanoparticle concentration and centrifugal forces on the temperature and pressure field have been examined in detail. The accordance of numerical results with experimental data expresses the accuracy of the employed numerical method for simulating flow and heat transfer in the curved pipes, as well as the accuracy of the single-phase model of the nanofluid. The Presented results indicated that both the nanoparticle and curvature effects improve the heat transfer characteristics dramatically, but at the expense of considerable increase in pressure drop. Furthermore, the results showed that in order to obtain the optimum operating conditions of nanofluids, different parameters such as heat transfer enhancement and pressure drop must be considered simultaneously. Finally, a method has been proposed to indicate the proper nanofluid and flow geometry for special practical applications.
M. Ettefagh, H. Mirab , R. Fathi,
Volume 36, Issue 2 (3-2018)
Abstract
One of the new methods for powering low-power electronic devices employed in the sea, is using of mechanical energies of sea waves. In this method, piezoelectric material is employed to convert the mechanical energy of sea waves into electrical energy. The advantage of this method is based on not implementing the battery charging system. Although, many studies have been done about energy harvesting from sea waves, energy harvesting with considering random JONWSAP wave theory is not fully studied up to now. The random JONSWAP wave model is a more realistic approximation of sea waves in comparison of Airy wave model. Therefore, in this paper a vertical beam with the piezoelectric patches, which is fixed to the seabed, is considered as energy harvester system. The energy harvesting system is simulated by MATLAB software, and then the vibration response of the beam and consequently the generated power is obtained considering the JONWSAP wave theory. In addition, the reliability of the system and the effect of piezoelectric patches uncertainties on the generated power are studied by statistical method. Furthermore, the failure possibility of harvester based on violation criteria is investigated.
F. Taheri-Behrooz, H. Khayyam Rayeni,
Volume 37, Issue 2 (3-2019)
Abstract
In this paper A progressive damage model based on multi-scale modeling has been developed to predict the initiation and propagation of damage in plain weave fabrics. For this purpose, microscopic damage in yarns and resin is calculated by an RVE (Representative Volume Element) FE simulation. By applying suitable boundary conditions of RVE, macro-scale average stresses were derived to extract the components of the equivalent stiffness matrix. Finally, by developing UMAT and USDFLD subroutines in the ABAQUS commercial software, the strength of the woven composite rings is predicted numerically. In order to confirm the numerical predictions, composite rings using the woven glass tapes of 5 cm width and epoxy resin are fabricated according to ASTM D2290 and tested. A good correlation between experimental and numerical results could confirm the accuracy of the finite element simulation.
A. Panjebashi Naghsh, K. K. Esmaeili. Torkanpouri ,
Volume 40, Issue 2 (1-2022)
Abstract
One of the new methods for powering low power electronic devices is the use of mechanical energies due to vibrations. In this method, the piezoelectric material is employed for converting the mechanical energy of vibration into the electrical energy. The advantage of this method is needlessness of using the battery charging system. In this paper, the functionally graded (FG) cantilever with the piezoelectric layer is considered as energy harvester system. The mathematical model of the system is constructed and the governing equation for electromechanical coupling is presented. Then the effects of the system parameters on the generated power is studied. Finally, by considering uncertainties in energy harvester parameters, the effect of uncertainties on the produced energy is investigated by Monte-Carlo simulation method for the first time. The results show that although the amount of generated power in the first natural frequency is higher than the other frequencies, but around the first natural frequency, the effect of uncertainties is increased and thus, the reliability of the energy harvester will be decreased.
