Sharif Digital Repository

Re-circulating cooling water systems offer the means to remove heat from a wide variety of industrial processes that generate excess heat. Such systems consist of a cooling tower and a heat-exchanger network that conventionally has a parallel configuration. However, reuse of water between different cooling duties allows cooling water networks to be designed in a series arrangement. This results in performance improvement and increased cooling tower capacity. In addition, by the integration of ozone treatment into the cooling tower, the cycle of concentration can be increased. The ozone treatment also dramatically reduces the blow-down that, in turn, is environmentally constructive. In this... 

Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices, Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this paper instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user hand... 

A framework to calculate a quantitative measure of seismic resilience using the Endurance Time (ET) method is introduced. ET method is a response-history based analysis procedure where structures are subjected to gradually intensifying dynamic excitations and their performance is assessed based on their response at different excitation levels, reducing the required computational effort. First, a prototype hospital building is optimally designed through three distinct design philosophies: prescriptive design code, performance based design criteria, and value based seismic design method. In value based design method, the design sections of structural elements are assumed as optimization... 

In multi-tower heliostat fields, although heliostats are capable of aiming at different receivers during the day, due to different orientations, neighboring heliostats might affect shading and blocking efficiency of each other reciprocally. In the proposed method of this paper, considering the mentioned effects and based on a group decision-making approach, each heliostat chooses the best receiver thus ensuring the highest possible instantaneous efficiency of the field. As a case study, this method is applied for the optimal design of a multi-tower field. Then, the field performance is simulated in a case where heliostats make decisions individually without considering the interactions.... 

The duct inverse design in fluid flow problems usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, an iterative inverse design method for 2-D subsonic ducts is presented. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall's pressure distribution is reached. The flow field at each step is analysed using Euler equations and the advection upstream splitting... 

Engines that extract energy from low-grade heat sources, e.g., from other processes, have received considerable attention recently. The use of Fluidyne, which is a liquid piston Stirling engine, is quite popular. Herein, we explore the use of liquid-to-vapor phase change in a Fluidyne. This provides two considerable differentiators; (1) exploitation of very low temperature difference ΔT≈30 K, and (2) relatively low temperature ΔT≈330 K heat sources, for producing mechanical work, and thus electrical energy. The influence of three operating parameters, i.e., input heat flux, working fluid, and filling ratio, on the performance of the engine was characterized. Their optimum values, which yield... 

In this paper, dynamic modelling and control of WindPACT 1.5 MW wind turbine in Region 2 for extracting the maximum energy from wind is investigated (where the wind velocity is greater than ‘cut in’ and below ‘rated’ wind speeds). In this region, the generator torque must regulate the rotor speed in its optimal value while the blade pitch angle is considered constant in its optimal value. To achieve a more accurate model, wind turbine is modeled as an electromechanical system with two masses dynamics. A new method based on adaptive neuro fuzzy inference system (ANFIS) is considered for wind speed estimation; where rotor speed, output power and pitch angle are inputs of such system and... 

This paper deals with a fractional calculus based control strategy for chaos suppression in the 3D chaotic systems. It is assumed that the structure of the controlled chaotic system has only one control input. In the proposed strategy, the controller has three tuneable parameters and the control input is constructed as fractional-order integration of a linear combination of linearized model states. The tuning procedure is based on the stability theorems in the incommensurate fractional-order systems. To evaluate the performance of the proposed controller, the design method is applied to suppress chaotic oscillations in a 3D chaotic oscillator and in the Chen chaotic system. © 2008 Springer... 

In the conventional seismic design methods, heightwise distribution of equivalent seismic loads seems to be related implicitly on the elastic vibration modes. Therefore, the employment of such a load pattern does not guarantee the optimum use of materials in the nonlinear range of behavior. Here a method based on the concept of uniform distribution of deformation is implemented in optimization of the dynamic response of structures subjected to seismic excitation. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. It is shown that the seismic performance of such a structure is better than those... 

Dynamic compaction (DC) is a common soil improvement technique, used extensively worldwide. DC treatment design is usually based upon empirical relations and past experience. The common problem with all empirical relations is oversimplification of the mechanisms, and the use of parameters that are highly dependent on engineering judgement. In this paper, a developed finite-element code is used for modelling the impact behaviour of dry and moist sandy soil. The code is verified against the results of centrifuge tests. Then the validity of the popular Menard empirical relation for determination of improvement depth in DC design is investigated. The effect of initial relative density, tamper... 

Isolated, high-density DC-DC converters play a crucial role in the power supply unit of information technology industries. By virtue of high efficiency and high power density, LLC resonant converters-among the rest of DC-DC converters-are suitable candidates for this application. The magnetic structure of this converter, however, is a bulky, dissipative part, which has a considerable portion of power loss. Improvement in the size and efficiency of the LLC transformer will lead to an overall enhancement of power density and efficiency of the converter. Nevertheless, the optimization of planar transformers for the LLC converter has not been studied enough. This paper proposes a... 

In this paper, we present a design method of dual-band waveguide rectangular cavity filters, with a series in-line topology. The coupling matrix is based on asynchronously tuned designs, where two sets of resonances exist for the two bands. Thus the filter is inherently different than the typical dual-band designs in the literature, as existing designs utilize resonators at the same frequency. The design at Ku band validates the underlying idea and concept, and the theory of the detuned coupling matrix. This rectangular waveguide implementation can provide noticeable miniaturization in applications with high-power requirements  

In this paper, the influence of the excitation angle on the Endurance Time (TCT) analysis of skewed slab-on-girdcr bridges is studied. The excitation of the structure due to the critical angle produces maximum seismic responses that are sometimes significantly higher than the average. The modeled bridges are of slab-on-girder type that are typically used as highway bridges. The bridge models have skew angles of 0, 15, 30, 45, and CO degrees. The ET excitations exerted on structures cover a broad range of hazard levels. The results provide some insight with regard to choosing multiple excitation angles so as to balance computational costs and retain acceptable accuracy for practical design... 

Due to flexibility of thin plates, high-amplitude vibrations are observed when they are subjected to severe dynamic loads. Because of the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, Adaptable Vibration Suppressors (AVSs) as a semi-active control approach were utilized to suppress the vibrations in a free circular plate under the concentrative harmonic excitation. Using mode summation method, the mathematical model of the hybrid system including the plate and an arbitrary number of vibration suppressors was analyzed. By developing a complex multiple-loop algorithm, optimum values for the parameters of... 

Due to flexibility of thin plates, high-amplitude vibrations are observed when they are subjected to severe dynamic loads. Because of the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, Adaptable Vibration Suppressors (AVSs) as a semi-active control approach were utilized to suppress the vibrations in a free circular plate under the concentrative harmonic excitation. Using mode summation method, the mathematical model of the hybrid system including the plate and an arbitrary number of vibration suppressors was analyzed. By developing a complex multiple-loop algorithm, optimum values for the parameters of... 

In this paper, the influence of the excitation angle on the Endurance Time (TCT) analysis of skewed slab-on-girdcr bridges is studied. The excitation of the structure due to the critical angle produces maximum seismic responses that are sometimes significantly higher than the average. The modeled bridges are of slab-on-girder type that are typically used as highway bridges. The bridge models have skew angles of 0, 15, 30, 45, and CO degrees. The ET excitations exerted on structures cover a broad range of hazard levels. The results provide some insight with regard to choosing multiple excitation angles so as to balance computational costs and retain acceptable accuracy for practical design... 

Marine structures are typically sensitive to the direction of wind and waves, especially in extreme metocean conditions. The extreme metocean conditions and their associated predicted directions are not easily reachable from traditional design methodologies. In this research, the most probable combinations of different extreme metocean conditions along with their associated direction are predicted for the HyWind Scotland wind farm, Scotland. To achieve this, the Hierarchical Bayesian Modeling approach is applied to define the Joint Probability Distribution Function (JPDF) of four combinations of metocean parameters, including wave direction, wind direction and wind-wave misalignment. The... 

This work presents results on the development of robust H∞ control strategy for Networked Control Systems (NCSs) by involving uncertainties in both communication and controlled plant subsystems. The network-induced delays in both communication links (to and from the controller) are assumed to behave as Markov chains. An analytical approach is presented to calculate the transition probabilities of the Markovian network-induced delays. By employing the augmentation method, the resultant system is converted into a delay-free uncertain singular Markovian jump system with bounded transition probabilities. New conditions are established to assure that the uncertain NCS satisfies an H∞ performance... 

A fast and simple procedure for designing relatively wide band fractional delay (FD) all-pass filters is proposed and filters designed based on it are compared to those designed using Thiran’s method, which is one of the simplest, fastest and widely used approaches in designing FD all-pass filters. It is shown that filters designed using the introduced method have wider fractional group delay (fgpd) bandwidths compared to those obtained via Thiran’s technique, as well as some other desired properties. The designed filters are also demonstrated to be stable for several pairs of filter orders and fgpd values. r2007 Elsevier B.V. All rights reserved  

Appropriate sensors are a crucial necessity for the success of recognition systems. Nature has always coevolved sensors and recognition systems and this can also be done in artificially intelligent systems. To get a very fast isolated word speech recognition system for a small embedded speech recognizer, an evolutionary approach has been used to create together the required sensors and appropriate recognition structures. The input sensors are designed and evolved through inspiration by the human auditory system and the classification is done by artificial neural networks. The resulting system is compared with a widely used speech recognition system, and the results are quite satisfactory. ©...