Showing 13–24 of 670 results
Adaptive boundary control of a flexible marine installation system
In this paper, boundرایگان!
In this paper, boundary control of a marine installation system is developed to position the subsea payload to the desired set-point and suppress the cable’s vibration. Using Hamilton’s principle, the flexible cable coupled with vessel and payload dynamics is described as a distributed parameter system with one partial differential equation (PDE) and two ordinary differential equations (ODEs). Adaptive boundary control is proposed at the top and bottom boundaries of the cable, based on Lyapunov’s direct method. Considering the system parametric uncertainty, the boundary control schemes developed achieve uniform boundedness of the steady state error between the boundary payload and the desired position. The control performance of the closed-loop system is guaranteed by suitably choosing the design parameters. Simulations are provided to illustrate the applicability and effectiveness of the proposed control.
An Adaptive IHS Pan-Sharpening Method
The goal of pan-sharرایگان!
The goal of pan-sharpening is to fuse a low spatial resolution multispectral image with a higher resolution panchromatic image to obtain an image with high spectral and spatial resolution. The Intensity-Hue- Saturation (IHS) method is a popular pan-sharpening method used for its efficiency and high spatial resolution. However, the final image produced experiences spectral distortion. In this letter, we introduce two new modifications to improve the spectral quality of the image. First, we propose imageadaptive coefficients for IHS to obtain more accurate spectral resolution. Second, an edge-adaptive IHS method was proposed to enforce spectral fidelity away from the edges. Experimental results show that these two modifications improve spectral resolution compared to the original IHS and we propose an adaptive IHS that incorporates these two techniques. The adaptive IHS method produces images with higher spectral resolution while maintaining the high-quality spatial resolution of the original IHS .
Analytical solution for axisymmetric thermoelastodynamic problems in a transversely isotropic half-space under a surface loading
In the present studyرایگان!
In the present study, the theory of coupled thermoelastodynamic is applied to determine the displacement, temperature and stress (DTS) fields of a torsionless axisymmetric transversely isotropic half-space under a surface loading. The basic equations of coupled thermoelasticity consist of the equations of motion and the energy equation, which forms a set of completely coupled partial differential equations for the displacement and temperature fields. Potential method is employed for uncoupling the set of basic equations of coupled thermoelasticity. With the aid of a potential function existed in the literature, the system of equations are uncoupled, where a sixth order partial differential equation is received. Displacement components and temperature are written with respect to the potential function in cylindrical coordinate system. The Laplace and Hankel integral transforms are employed to suppress the time and radial variables, respectively. One may apply the inverse Hankel and Laplace transforms to determine the DTS fields and other quantities of interest in physical (space-time) domain. Eventually, the integrand functions of DTS components are obtained analytically.
APPLICATION OF SEISMIC BASE ISOLATION TECHNOLOGY IN IRAN
Application of baseرایگان!
Application of base isolation techniques in Iran goes back to hundreds of years ago and even to ancient times. Installing pieces of wood between the foundation and the walls of buildings is among the earthquake resistant construction techniques that have been applied in some areas of Iran in the past. However, contrary to other technologies which are generally adapted soon after their development, modern seismic base isolation technology took almost a quarter of a century to be adapted and utilized in Iran. This paper presents the historical as wells as the modern application of seismic base isolation technology in Iran.
APPLICATION OF SPECTRAL FINITE ELEMENT METHOD IN ANALYSIS OF TRANSIENT ELASTODYNAMIC PROBLEMS
Dealing with wave prرایگان!
Dealing with wave propagation phenomena using classical finite element method (FEM) results in some inefficiencies and inaccuracies in the solution. Spectral finite element method (SFEM) as a method based on FEM, presents some new features that makes it much more suitable and useful for solving wave propagation problems. The excellent characteristic of SFEM is that the mass matrix is diagonal because of the choice of the Lagrange interpolation function supported on Legendre-Gauss-Lobatto (LGL) points in conjunction with LGL integration rule. Therefore numerical calculations can be significantly efficient in comparison with the classical FEM. On the other hand choice of high order elements using specific shape functions gives us the possibility to increase the accuracy of the solution while decreasing the total number of elements used for the domain of the problem thus decreasing the analysis time. In this paper, a SFEM-based code is represented and verified, and then some wave propagation problems in elastic solid domains are solved using this code showing the capabilities of SFEM in solving elastodynamic problems.Some problems are solved using different spectral elements, and analysis time, accuracy of the solution and costs of analysis in different solutions is compared to analytical and/or numerical solutions available in the literature.
Assessment of Equivalent Static Earthquake Analysis Procedure for Structures with Mass Irregularity in Height
Sudden changes in st...رایگان!
Sudden changes in structural dimensions and mass irregularities are inevitable in urban buildings. Most building codes have different analysis and design previsions for such buildings. In this article, such provisions based on the Iranian seismic code of practice (Standard No. 2800), which is to a great extent similar to UBC-97 model code, are verified in order to assess the provisions for different types of structures. Thus, four two-dimensional residential type steel structures with 4, 8, 12 and 16 stories and with different forms of mass irregularities in height are designed using the standard equivalent static procedure per the Iranian Seismic Code of practice. The designed structures, then, were subjected to different nonlinear static (pushover) and dynamic analyses. Two levels of irregularities, i.e. 150 and 300 percents, located at the heights equal to 50% and 75% of the overall height of the structures, have been considered. The results show that the static procedure adapted in the code results in much higher internal forces, story shears and overturning moments in various parts of the structures compared to the dynamic results. Also, this study shows that lateral inter-story drifts obtained using the equivalent static procedure and dynamic analyses are quite comparable for short buildings. For taller buildings, in contrast, dynamic analyses showed less inter-story drifts. It is also observed that mass irregularities in height could be responsible for more contribution of higher modes in seismic response of such structures
Autoclaved aerated concrete behavior under explosive action
Autoclaved aerated cرایگان!
Autoclaved aerated concrete AAC is widely used in construction, mainly in masonry as infill walls. Exterior AAC walls may Ž . be subjected to different actions including accidental lateral dynamic loading and local fragments’ impact. The present paper studies some of the dynamic characteristics of AAC walls under localized high-intensity impact, such as the number of cracks and their dependence on the boundaries location, the initiation of spalling and the contribution of face treatment and face reinforcement on enhancing the materials response. Some comparisons are made with earlier results on hardened cement paste specimens.
Bee Colony Optimization of Tuned Mass Dampers for Earthquake Vibrations of High-rise Buildings Including Soil Structure Interaction
This paper investigaرایگان!
This paper investigates the optimization of Tuned Mass Dampers (TMDs) for high-rise buildings. The model is assumed as a 40 story building with 160m height considering the translation and rotation of foundation. The Soil Structure Interaction (SSI) is considered for the better prediction of building’s response. To illustrate the results, Bam earthquake data is applied to the model. The three soil types, i.e. soft, medium and dense soil are utilized, and the results are compared with the fixed based model. The model is based on time domain analysis, and Newmark method is used to obtain the displacement, velocity and acceleration of different elements. The Artificial Bee Colony (ABC), a heuristic method based on the behavior of bees forage for food, is employed to obtain the best parameters for TMD device. The design variables are assumed as mass, damping and spring stiffness quantity. The objective is to decrease both the maximum displacement and acceleration of the building. The results show that the presented model can be effectively applied to evaluate the response of high-rise buildings including SSI effects. It is indicated that the results obtained by this model is more accurate than the results of fixed based model. The effects of TMD on the oscillations of structures including different soil characteristics are also investigated. It is shown that the TMD is more effective for soft soil foundations. It is also shown that how the bee colony optimization technique can be employed to design the optimum TMD for the minimum displacement and acceleration. This study leads the researchers to the better understanding of earthquake oscillations of the high-rise buildings, and helps the designers to achieve the optimized TMD for the structures.
Combining contemporary and traditional project management tools to resolve a project scheduling problem
In this paper we exaرایگان!
In this paper we examine a construction project involving the building of large concrete slabs for three buildings in an office park complex. There are finish-to-start (FS) as well as start-to-start (SS) and finishto- finish (FF) precedence relationships among the project activities. We prepare an initial project schedule using Microsoft Project and manually validate the results using the precedence diagramming method (PDM) procedure. When the client informs us that the schedule must be shortened we find that Microsoft Project does not have the capability for resolving our particular time/cost tradeoff issues. So we revert to the traditional approach for resolving time/cost tradeoffs in projects and develop an original linear programming formulation for the time/cost tradeoff problem when a project is modeled as a precedence diagram. By combining contemporary (Microsoft Project) and traditional (a linear programming time/cost tradeoff model) project management tools we are able to successfully resolve the scheduling issues associated with the slab construction project. Further, we demonstrate the anomalous effects of start-to-start (SS) and finish-to- finish (FF) relationships via our construction project example in which the solution to the time/cost tradeoff problem requires that certain activities be lengthened in order to shorten the project duration.
Comparison between Seismic Behavior of Suspended Zipper Braced Frames and Various EBF Systems
Zipper frames are in...رایگان!
Zipper frames are intended to improve on the behavior of conventional inverted-V-braced frames, which show poor performance taking place from the early buckling of braces in the lower story. A zipper frame affords better performance by forcing simultaneous buckling of all braces. In this article, seismic behaviors of zipper braced frames and three types of eccentrically braced frames are evaluated using finite element simulation. Two dimensional finite element models have been created for three-story onebay frames for various bay lengths and different arrangement of braces. Seismic response of frames subjected to near-fault ground motions (LA21) has been studied through dynamic analysis, considering no nlinearity of geometry and materials. For this purpose, SAP2000 has been used. Results have been ompared and structural response of steel frames and some other parameters such as ductility of frames, maximum base shear and optimized link length have been investigated. Against other researches, in this article, the ratio of maximum shear over the weight of structure and its relation to behavior of structure has also been studied. It was found that optimized link length in EBF systems which caused to maximum du ctility of frame is about 30 percent of the bay length. Moreover, the results showed that zipper frames provide desirable post buckling behavior and exhibit more ductility.
Compliance of Rigid Arbitrary Shape Foundations Using 1 DOF BEM
In this study the reرایگان!
In this study the relationship between the dynamic force and displacement (impedance or compliance) is evaluated for rigid foundations with arbitrary shape resting on a half-space medium, consisting of homogeneous, isotropic, linear elastic materials with constant Boundary Element Method, (1 DOF). Green’s function is computed for half-space and presented in explicit form. By using BEM formulation the stress beneath foundations and compliance of them are obtained. The vertical compliance of a rigid circular disc which is calculated by this method is compared by semi-closed form solution and verifies the accuracy and efficiency of this method. the vertical and rocking compliance functions for rigid rectangular and some arbitrary shape foundations are obtained. And also, the variation of stress distribution pattern beneath square and circular foundations with frequency is studied and these results are compared with the results of the other methods.
Critical appraisal of piping phenomena in earth dams
This paper presentsرایگان!
This paper presents a comprehensive review of published literature on soil piping phenomena. The first tools to design earth dams to resist piping were developed during 1910–1935. Filter criteria for dispersive soils was refined in the 1970’s. Piping phenomena are generally defined as: (1) heave, (2) internal erosion, (3) backwardserosion, although other modes are possible. Recent work on piping highlights the limitations of the occurrence of piping and the role that design and construction may play in a large percentage of piping failures. Standardized laboratory procedures are available to assess piping potential in cohesive materials, but no such methods exist for noncohesive soils. However, methods are available for evaluation of self-filtration potential. Recent advances in computer technology have facilitated the evaluation of seepage and deformation in embankments but computational methods for evaluation of piping potential are currently limited.