1
2476-6763
Tarbiat Modares University
4895
Comparison between phase space-based local chaotic models for riverflow forecasting
Anis-hoseini1
Masoud
^{
b
}
Zakermoshfegh
Mohammad
^{
b
}Jundi-Shapur university of technology
1
9
2015
15
3
13
24
18
03
2014
12
08
2015
Generally, The dynamics which is observed in time series of a hydrologic system variable have been considered as complex and random behavior. During last decades, using various artificial intelligence approaches such as chaos theory to analyze and prediction of hydrologic systems have been increased. In chaos theory viewpoint, complexity and random-like behavior of a system can be resulted from a simple and hidden determinism. Therefore, systems such as dominant hydrologic system which controls flow in a river can have this kind of determinism. If such determinism is existed, can be observed through system phase space, which can be reconstructed using a time series by lags method. Based on such a pattern that formed in reconstructed phase space, various prediction models can be used to forecast system behavior in future. Hence, chaotic behavior of the Kashkan river daily discharge time series have been studied using False Nearest Neighbors and Lyapunov Exponent methods which evaluated fractal attractor and sensitivity to initial condition as two major characteristics of a chaotic system. Average Mutual Information method was used to determine optimal delay time in phase space reconstruction by delay method. In this paper, it has been suggested to use first global minimum of mutual information function as standard to select optimal delay time. According to the results which have been obtain by these methods, chaotic behavior in daily runoff time series of the Kashkan river have been observed. In False Nearest Neighbors method, the percent of false neighbors have been significantly decreased due to rising embedding dimension of phase space, which have been shown the existence of a fractal attractor in system phase space. In lyapunov exponent method, the sensitivity to initial condition has been evaluated through reconstructed phase space and positive lyapunov exponent has been obtained. Hence, chaos theory-based models can be used to forecast daily runoff in this system. Various local models were used to make prediction based on reconstructed phase space and the results have been compared. Local Average and Local Polynomial was among local models that employed in this study. In addition, as a new hybrid approach, Multi Layer Prespetron Artificial Neural Networks have been used to local modeling based on phase space. All prediction results show appropriate quality of local prediction models in base of attractor pattern in phase space of dominant system of the Kashkan river flow. The accuracy which have been resulted from local hybrid model with Artificial Neural Networks, have been not shown significant difference with other current local models such as Local Average and Local Polynomial prediction methods. However, the Local Polynomial model has been shown better forecasting accuracy in compare with other methods. Totally, Local chaotic methods are suggested to make daily prediction of runoff in the Kashkan river.
5595
A Numerical Investigation on the Appropriate Corner Radii of Beam Web Opening in Steel Moment Frames
Akrami
Vahid
^{
d
}
Erfani
Saeed
^{
e
}
^{
d
}Amirkabir University of Technology
^{
e
}Amirkabir University of Technology
1
9
2015
15
3
14
25
16
03
2014
12
08
2015
Web openings may be provided in structural floor beams for different purposes. The corner radii of web openings can have a significant effect on stress and strain concentrations around the opening. AISC's design guide for steel and composite beams with web openings states that web openings are not recommended for members subjected to significant high cycle-low stress or low cycle-high stress fatigue loading even if a rational corner radii is provided for web openings. This is because, at the time the specification was written, there were only limited references available to the committee which indicates the need for further studies in this field. In this paper, effect of opening corner radii on cyclic behavior of steel moment connections with Reduced Web Beam Section (RWBS) is investigated using finite element analysis. For this purpose, a T-shaped moment connection (without web opening) which has been tested under cyclic loading by another author is used as the reference model. To see effect of opening corner radii, the reference model is considered with square and rectangular web openings of different corner radii. Fracture initiation in models is simulated using Cyclic Void Growth Model (CVGM) which is based on micro-void growth and coalescence. According to this model, fracture under cyclic loading is predicted to occur when the void size exceeds the critical value. Based on the results, for both square and rectangular openings the maximum equivalent plastic strain and fracture index at the opening corners will decrease as the opening corner radii increase. For openings with small corner radii the fracture index at corners will be very high. This is in accordance with recommendation of ASCE 23-97 which indicates that these configurations should not be used in real practice. However, it should be noticed that in the case of rectangular opening the damage index at the corners may be greater than unity even if ASCE 23-97 limitations are met. This means that if it is intended to achieve high rotation capacity at RWBS connections, ASCE 23-97 requirement about minimum corner radii may be non-conservative. As another result, as the opening corner radii increase local buckling around the web opening occurs at higher rotations. In addition to the local effects, the choice of opening corner radii can also affect the global behavior of RWBS connections. In the case of rectangular perforation, as the opening corner radii increase the load carrying and rotation capacity of connection increase too. This is because in these models, the weakening area prevents welds from failure and fracture occurs in the opening corners. As a result, as the opening corner radii increase the fracture index at opening corners decreases and hence the connection can undergo higher rotation capacities. This is not true for square perforation where fracture occurs at connection welds and the connection rotation capacity makes no change as the opening corner radii increase. As a general recommendation it can be said that web openings with the largest corner radii (elongated circular holes) is the best case for perforated steel connections.
3492
Simulation of Dam break flows using Weakly compressible moving-particle semi-implicit method
1
9
2015
15
3
25
37
03
09
2014
29
07
2015
Simulation of free surface flows using Weakly compressible moving-particle semi-implicit method Mesh-free particle (Lagrangian) methods, such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH), are the newest methods in computational fluid dynamics, which have been applied in flow problems with large deformations and inconsistency. The aim of ths research was to develop and improve the simulation of free surface flows, using the new method of weakly compressible MPS (WC-MPS). In the MPS method, pressure is determined by solving Poisson equation. This equation is solved implicitly, which needs too much computer time. In the present research, the WC-MPS method is used to calculate pressure. In this method, as in SPH method, the state equation is used. This equation is solved explicitly, which does not occupy too much computer time. To evaluate the proposed method, the famous applied flow problem of dam break is analyzed. The program is written in C language and validations are performed for this code. To compare the Lagrangian approach with Eulerian approach, dam break is modeled by using FLOW-3D software too. The results of modeling approaches and physical models showed that both approaches have acceptable accuracy in modeling the free surface flow, but the accuracy of Lagrangian approach, especially the WC-MPS, is more than Eulerian approach. The proposed methos had some pressure oscillations, which were analyzed thereafter. Simulation of free surface flows using Weakly compressible moving-particle semi-implicit method Mesh-free particle (Lagrangian) methods, such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH), are the newest methods in computational fluid dynamics, which have been applied in flow problems with large deformations and inconsistency. The aim of ths research was to develop and improve the simulation of free surface flows, using the new method of weakly compressible MPS (WC-MPS). In the MPS method, pressure is determined by solving Poisson equation. This equation is solved implicitly, which needs too much computer time. In the present research, the WC-MPS method is used to calculate pressure. In this method, as in SPH method, the state equation is used. This equation is solved explicitly, which does not occupy too much computer time. To evaluate the proposed method, the famous applied flow problem of dam break is analyzed. The program is written in C language and validations are performed for this code. To compare the Lagrangian approach with Eulerian approach, dam break is modeled by using FLOW-3D software too. The results of modeling approaches and physical models showed that both approaches have acceptable accuracy in modeling the free surface flow, but the accuracy of Lagrangian approach, especially the WC-MPS, is more than Eulerian approach. The proposed methos had some pressure oscillations, which were analyzed thereafter. Simulation of free surface flows using Weakly compressible moving-particle semi-implicit method
2581
Laboratory study on cyclic behaviour and pore water pressure generation of Boushehr calcareous sand
Jafarian
Yaser
1
9
2015
15
3
37
50
14
09
2013
12
08
2015
As a disastrous cyclic response of soils, liquefaction commonly takes place in the saturated soils overlaid in seismic regions. Earthquake excitation in loose deposits enforces the soil particles to displace towards a more compacted state. This tendency causes generation of excessive pore water pressure when drainage is prevented or its rate is less than the generation rate. Comprehensive laboratory investigations have been carried out so far in order to capture cyclic behavior of silicate soils. However, cyclic behaviour and liquefaction resistance of calcareous soils has not been fully recognized as well. Calcareous soils evolve from biological resources due to the physiochemical process of marine organisms. Such soils have excessive crushing capability; and thus, their mechanical behaviour is expected to be different than that of terrestrial soil deposits. The current study presents results of several undrained cyclic tests on isotropically and anisotropically consolidated samples of Boushehr calcareous sand. The tests were conducted via a triaxial machine in strain-controlled condition. Bulk samples of the sand were gathered from the coast of Boushehr city located in the southwest of Iran, north bank of Persian Gulf. The sand samples were reconstituted with dry deposition method of sample preparation under various initial relative densities and confining pressures. The consolidation phase of the tests was performed in drained condition for either isotropically or anisotropically consolidated samples. The cyclic loading phase of the tests was conducted by multi-stage procedure in order to recognize soil potential for excess pore water pressure generation. Various levels of controlled cyclic axial strains were applied on the sample in each stage of the cyclic loading phase and the samples were allowed to be drained at the end of each stage. The results are presented in terms of threshold shear strain and dissipated strain energy concept. Comparison is made between the tests results and those reported by the previous studies. The results revealed that liquefaction resistance of the studied sand increases with increasing initial relative density and effective confining pressure whereas the samples with high initial effective stress never liquefied even after one hundred cycles of loading. Relationships between excess pore water pressure and the normalized number of cycles as well as the normalized dissipated strain energy are studied and compared with the relationships presented by the previous researchers for silicate sands. According to the results, such relationships are strongly affected by type of cyclic loading i.e. strain or stress-controlled when excess pore water pressure is correlated to the normalized number of cycles. In fact, evaluation of excess pore pressure is more reasonable to be done with the normalized strain energy in order to minimize the influence of loading type. The threshold shear strain for the studied sand was found to be 0.015% which is comparable with this value for silicate sands.
7717
Angle Shear Connectors Capacity
Khalilian
Marzieh
^{
n
}
^{
n
}Sharif University
1
9
2015
15
3
51
62
14
01
2014
12
08
2015
The steel-concrete composite beams are increasingly used in bridge and building construction in recent years. In this system, a shear connection between steel and concrete should be provided to effectively transfer the shear forces and to make the two materials act as a single unit. The mechanical shear connectors provide this means. They are the essential component of any composite beam system. Many studies have been performed on shear connectors and many different steel shapes have been suggested for connectors. The steel studs and channels are the most popular code accepted connectors. However, economic considerations continue to motivate the development of new products. Present knowledge of the capacity and behavior of the shear connectors are mainly limited to the data obtained from the push-out or beam tests with the latter being more expensive and accurate. Therefore, analytical procedures that can predict the nonlinear response and the capacity of the composite beams are necessary when the experimental resources are not available. In this study a three-dimensional FE model using the computer code ABAQUS is developed to simulate the push-out tests of angle shear connectors. The main objective of this study is to investigate the behavior and to find the ultimate strength of angle shear connectors in a solid slab. In order to obtain dependable results from the FE analysis, all components of the connection should be correctly modeled. There are four parts in this model: concrete slab, shear connector, steel beam and the rigid base. Because of symmetry, only a quarter of the push-out specimen is modeled.Nonlinear material and large displacement capability are employed. The load-slip behavior, capacity and maximum displacement at failure obtained from the finite element model were validated against available push-out test results. The results show the FEM can predict the capacity of the angle shear connectors with adequate precision. Using the FE model, a parametric study was conducted to evaluate the effect of variations in angle dimensions and concrete strength. The parametric study reveals that: • The capacity of angle connector increases with increasing concrete strength. • The Flange width has no measurable effect on angle connector capacity and its behavior. • The height of the angle has no considerable effect on load-displacement behavior of the connector. • The capacity of angle connector increases whereas the maximum slip decreases with increasing angle thickness. • The stress value is not constant along the angle length and it decreases from the center of the angle towards the edges. The shorter the length of the connector, the lower the stress change. Therefore, long angle shear connectors become ineffective. An equation is suggested to predict the angle effective length. Finally, an equation is proposed to predict the ultimate shear strength of the angle connectors.
3237
Evaluation of kinetic models in water salinity reduction by phytoremediation method with three halophyte plants
Ganjidoust
Hossei
^{
o
}
^{
o
}P.O.Box 14155-4838
1
9
2015
15
3
63
72
08
01
2014
12
08
2015
Water scarcity has led to the search for alternative water resources. One solution is the recycling of wastewater for irrigation. Wastewater treatment is often based on biological systems such as activated sludge or other engineered units in urban areas. In rural areas, low-cost, environmentally-friendly alternative treatments such as constructed wetlands (CW), are more common. CWs are man-made planted systems that utilize natural processes to improve water quality for human benefit. Salinity in treated wastewater is often increased, especially in arid and semi-arid areas. Phytoremediation can be used to remove much of this problem. Phytoremediation is the use of plants for remedying water and soil pollution. This approach is based on plants that are especially tolerant to salt environments. Around 1% of all plant species are halophytes that can complete their life cycle in relatively high saline environments, as much as 200 mM NaCl or more. In the current study, we addressed the problem of soilsalinization due to the use of treated wastewater that is often more saline than fresh water, especially in desert environments. We aimed at testing the potential to recruit halophyte plants for salt phytoremediation in constructed wetlands. Therefore this study was performed to evaluate the ability of reducing salinity of wastewater by three halophyte plant species such as Frankenia, Atriplex and Festuca. The experiments were performed with different concentrations of saltwater. Reducing the electrical conductivity, salt removal and its uptake rate, the concentration of sodium stored in plant tissues at different levels of salinity, were analyzed. Also by matching the data with Michaelis- Menten and Lineweaver- Burk kinetic models, some results were obtained from each plant. The electrical conductivity decreased with increasing salinity levels in all three species. The highest salt absorption amount in Frankenia was in 4500 µs/cm about 20 percent, in Festuca was in 2600 µs/cm about 17 percent and Atriplex was in 5000 µs/cm about 14 percent. Of course reducing of salt uptake in each plant had its own reason for example; Atriplex plants due to having less compatible with wetland situation, Festuca plants due to facing with salinity stress and Frankenia plants because of salt replenishment faced with yield loss and withered state. Based on these results Frankenia, Festuca and Atriplex plants during the treatment with saline water, had the first order of kinetic equation with a correlation coefficient of respectively 97.7, 95.9 and 97.01, gradually with increasing of salinity these plants had the kinetic equations of 2, 0 and 1 order that as this result, Atriplex plants showed more resistance in salt uptaking. In reduction range also Atriplexand Frankenia had a better performance. The highest conformity of data in Frankenia plant related to Lineweaver- Burk and Atriplex plant related to Michaelis- Menten.
7287
Optimizing of spatial allocation for manucipal solid waste collection utilizing GIS
salimi
ali
1
9
2015
15
3
73
85
11
05
2011
31
05
2015
Urbanization and population density in big cities, including gathering materials and urban waste and pollution is followed by increasing environmental pollution so that a much significant percentage of municipal budgets, especially in large cities and municipalities, is spent to collect waste materials. On the hand, the use of computer softwares, in accordance with the daily discriminate increases of environmental issues and management of urban waste are growing. One of the most important case that distinguishes GIS from other systems is the existence of distinct functions in spatial analysis. Including network analysis functions, one feature of network analysis can be finding the shortest path which is the most important applicant in transportation issues. One of the issues of allocation is the issue of allocation of areas where the facilities are used. There are three components in allocation issue: 1. Applicant’s services. (It is the capacity of waste collection depository.) 2.The sever (The machines with the capacity of specific waste collection and road network) 3. The objective function or the cost ( it is the time in this research.) What is at stake in this issue is to set a time to optimize the time to collect the waste. It primarily reduces the time for collection and reduces cost, manpower, distances and environmental pollution. First, the overall research method have been collected and described to optimize the paths, and then a specific methodology will be introduced. material and method Understanding the current situation, it is classified into two general and case studies. In the overall social structure, utilizing the communication network and access routes will be studied and the amount of waste produced, the method of operation and maintenance are studied in order to collect the waste and review the current situation regarding waste management system performance. Major impact on waste producers is dedicated to the study of the area population itself. In this context, it is necessary to determine the scope of the population, family size and population density. Other feature of the area is devoted to the user. User types in this area of study such as the existing users of residential, offices commercial, educational, health, culture and sport should be studied. Each user’s share along with specifications and plans within the designated user is produced at this stage. Like the previous stage, the users are determined according to the block scheme in each block. Communication network is the most important feature of each area of study to determine optimal routes. The information that is needed to be fully collected includes the followings: Names of all studied streets of area, length of the streets, width, bilateral and unilateral streets, and the street traffic if they are unilateral. As already explained, what is important in this research is to optimize the path of collected waste, resulting the time reduction in waste collecting. So to obtain the required time, it is necessary to have the average speed of each vehicle in every street and it should be marked with the relationship between the speed and the time along the way. Speed of vehicles on streets is usually determined by the type of vehicle, street width and traffic levels. It is necessary to obtain this speed through field studies. At nights the traffic is not involved, but the type and speed of vehicles, and the width of streets must be achieved. Eventually we have to determine two speeds for every street, one for days and one for nights and it should be recorded in the Arc GIS information. Now , by modeling the problem with the software, it is described. Initially utilizing GIS a network is formed including roads and reservoir network. The network should be marked whether the streets are bilateral and direction of unilateral streets. The area is divided into N optimal ranges according to the number and capacity of machines. For the allocation options in, Arc GIS service area should be used. Our service areas are reservoir sites. After introducing the service areas which are reservoir sites and have a certain capacity, The problem will be solved. The study area s divided into some optimal ranges according to the number of machines to collect the waste. Now in each divided area, we should choose the most optimal route to collect the waste. This route should be selected and begun from the first reservoir tank to the nearest machines station. Passing all tanks to the final tank, which is close to the transmitting station, Arc GIS chooses the optimal path.
11533
Nonlinear Analysis of Unreinforced Masonry Buildings Using Distinct Element Method
Mohebkhah
Amin
^{
}
Sarvecheraghi
Ahmad
^{
}Dean of Civil and Architectural Eng. Faculty
1
9
2015
15
3
85
92
02
07
2013
12
08
2015
The majority of building population in Iran and other developing countries consists of unreinforced masonry buildings and sometimes confined masonry (CM) buildings. In such buildings, masonry shear walls are the main earthquake resistant components. The Iranian seismic standard IS2800 provides some specifications for seismic design and construction of confined and reinforced masonry buildings which all are based on the observed behavior of them during the past destructive earthquakes. In other words, the specifications are merely qualitative. This shows the necessity of assessment of masonry buildings behavior both experimentally and numerically. Despite the extensive numerical studies available in the literature, it seems that the lateral load behavior of masonry buildings cannot be properly investigated by continuum mechanics based methods such as traditional finite element method. As an alternative to the available finite element methods, a distinct/discrete element method (DEM) can be used to investigate the nonlinear lateral load behavior of masonry buildings. Distinct element method has the capability to con-sider large displacements, shear sliding and complete joints openings between bricks as well as automatic detection of new contacts during the analysis process. In this paper a two-dimensional numerical model is developed using distinct element method using the specialized distinct element software UDEC (Itasca, 2004) for the nonlinear static analysis of unreinforced masonry buildings subjected to in-plane monotonic loading. The Univer-sal Distinct Element Code (UDEC) is a 2D program based on the DEM to simulate the behavior of jointed materials subjected to either static or dynamic loading. The developed DEM model is validated using the results of a two-story unreinforced masonry building designed and tested based on the Iranian seismic standard IS2800 regulations at the Building and Housing Research Center (BHRC). Due to low intensity of gravitational normall stresses in conventional masonry buildings, the bricks were built using an elastic material model. In order to develope a DEM micro-model based on interface elements with zero thickness, the size of the bricks was expanded by the mortar thickness in both directions and the elastic properties of the expanded brick were assumed to be the same as that of the real brick. Howevr, For the joints, simulating the characteristics of the mortar, a Mohr–Coulomb slip model was employed. It was found that the model can be used confidently to simulate nonlinear behavior of unreinforced masonry buildings for parametric studies. The Iranian seismic standard IS2800 specifications pertain mainly to the masonry shear walls percentage need in each direction. In other words, the perpendicular shear walls are not taken into account in masonry buildings’ lateral load capacity calculations. However, unreinforced masonry buildings resist lateral loads through box action behavior of all constituent components (i.e. walls, foundation and diaphragms). Therefore, a parametric study was conducted to investigate the contribution of perpendicular masonry shear walls on buildings’ lateral load capacity. Parametric study showed that perpendicular masonry shear walls contribute considerably to the shear capacity of the masonry building.
9231
Assessment the Effective Parameters on Punching Shear in Slab-Column Connections and Strengthed with FRP
1
9
2015
15
3
93
104
24
11
2013
12
08
2015
Many flat slab -column frame structures have been built in many parts of the world, since the beginning of the century. The absence of beams makes the form work simple, increase the clear story height, and decreases total building height. However brittle punching failure is a problem that unnecessarily limits the widespread use of flat plates in active earthquake zones. Many slab -column connections in flat plate structures were damaged and failed in punching shear after the 1985 Mexico City earthquake, the 1989 Loma Prieta earthquake, and the 1994 Northridge earthquake. These shows that slab–column connections are prone to punching shear failure when lateral forces, due to earthquake loading, cause substantial unbalanced moments to be transferred from the slab to the column. Slabs with low or medium reinforcement ratios tend to fail in flexure rather than in punching shear. For slabs with reinforcement ratios of 1% and more, the mode of failure tends to be the punching shear type of failure. Fiber-Reinforced Polymers (FRPs) have gained increasing popularity in retrofit of reinforced concrete members in the last two decades. Using FRP materials to enhance slabs in flexure is very desirable from the application point of view due to the ease of handling and installing. FRP material, unlike steel, are not subject to either corrosion or rust in the long term. There is limited amount of research available on srengthening of slab connections. These studies include investigations where the slabs were strengthened using FRP laminates around a central stub column or bonded over the entire width of the slab. with regard to flexural strengthening, externally bonded FRP strips have been used for the strengthening of one way slabs as well as two way slabs. The determination of the structural behavior of FRP–strengthened concrete slabs requires extensive experimental and/or advanced numerical methods. as far as theoretical methods are concerned, Reitman and Yankelevsky have developed a nonlinear finite element grid analysis based on the yield line theory. Other researchers have employed finite element packages to investigate the structural behavior of strengthened slabs with FRP that a full bond between the concrete and the adjacent strengthening FRP materials was assumed. Recently, Binici and Bayrak reported the test results of a strengthening method using carbon fiber reinforced polymers (CFRPs) as shear reinforcement. Previous studies concentrated on enhancing shear capacity of slab-column connections for new construction. Stirrups, bent up bars and shear studs were used as shear reinforcement in previous studies. This study investigates the application of different methods of strengtheing of flat slabs. At first, slabs were model in ABAQUS in order to study the parameters that influences punching shear capacity. Analytical result indicate that increasing concrete compressive strength improves punching shear capacity. Based on this result, steel reinforcement ratios determines the mode of failure. Then, FEM models of slab were strengthend, and type of strengthening, type of FRP materials, number of strip and layer were investigated. The results show that using FRP strip increases punching shear capacity and reduces energy absorption.
3051
Control point grid improvement in isogeometric analysis of axisymmetric structures using error estimation methods based on stress recovery
mirzakhani
aboozar
^{
}
Hassani
Behrooz
^{
}
khanlari
karen
^{
}
ga
a
^{
}Faculty member
^{
}Faculty member
^{
}Faculty member
1
9
2015
15
3
105
118
05
04
2014
12
08
2015
This research is devoted to the adaptive solution and control point net improvement of axisymmetric problems in isogeometric analysis using the error estimation based methods for stress recovery. For this purpose, after the calculation of the energy norm, the estimated value of error in the vicinity of each control point is assigned to the neighboring members of a hypothetical truss-like structure as an artificial thermal gradient. By analysis of this network of rods under the temperature variations a new arrangement of control points is obtained. Repeating this process of thermal isogeometric analysis will eventually lead to a better distribution of errors in the domain of the problem and results in an optimal net of control points for the calculation of the integrals. To demonstrate the performance and efficiency of the proposed method, two axisymmetric elasticity problems with available analytical solutions are considered. The obtained results indicate that this innovative approach is effective in reducing errors of axisymmetric problems and can be employed for improving the accuracy in the context of the isogeometric analysis method. Innovated method of this research focuses on adaptive analysis and Network improving of axisymmetric problems in isogeometric analysis using error estimation methods based on stress recovery. For this purpose after calculation the energy norm, estimated value of error in the vicinity of control points is assigned to each rod as the thermal gradient. Thus after analyzing the hypothetical rods network under the temperature changes a new arrangement of control points and knot vectors can be obtained. The use of multi-cycle of this process in isogeometric analysis will lead to a better distribution of errors in the domain and thus achieve optimal network to calculate the integrals. To measure the efficiency of this method and demonstrate the increased carefully in axisymmetric problems, which has the analytical solution, two elasticity problem is evaluated. The results show that innovative network improving method has good efficiency to reduce the error rate and can be used to increase the accuracy of isogeometric analysis results. Innovated method of this research focuses on adaptive analysis and Network improving of axisymmetric problems in isogeometric analysis using error estimation methods based on stress recovery. For this purpose after calculation the energy norm, estimated value of error in the vicinity of control points is assigned to each rod as the thermal gradient. Thus after analyzing the hypothetical rods network under the temperature changes a new arrangement of control points and knot vectors can be obtained. The use of multi-cycle of this process in isogeometric analysis will lead to a better distribution of errors in the domain and thus achieve optimal network to calculate the integrals. To measure the efficiency of this method and demonstrate the increased carefully in axisymmetric problems, which has the analytical solution, two elasticity problem is evaluated. The results show that innovative network improving method has good efficiency to reduce the error rate and can be used to increase the accuracy of isogeometric analysis results.
11414
Experimental investigation of dynamic behavior of sandstone under high strain rates
Nadi
Alireza
^{
}
Goshtasbi
Kamran
^{
}
Naghdabadi
Reza
^{
}
Arghavani
Jamal
^{
}
Ashrafi
Mohammad Javad
^{
}
^{
}Tarbiat Modares university
^{
}Tarbiat Modares university
^{
}Sharif university of technology
^{
}Sharif university of technology
^{
}Sharif university of technology
1
9
2015
15
3
119
128
12
03
2014
12
08
2015
Rock dynamics as a branch of rock mechanics deal with dynamic behavior of rocks under high loading rates. Considering that many problems in rock engineering including earthquackes, explosions and projectile penetrations deal with high loading rates, rock dynamics has been of high significance to explore. In order to design and stability analysis of many of defense and military structures constructed on and in rocks, designating of dynamic behavior of rocks under different loading rates is essential. However, detailed understanding of rock dynamics has been of high challenge due to the additional ‘4th’ dimension of time. The split Hopkinson pressure bar test (SHPB) is the most applicable and famous technique in determination of dynamic behavior of materials under high loadin rates. In this thechnique, a pressure wave with a high domain is dispatched to the specimen and the reflected and transmitted waves of specimen will be captured by means of strain gauges glued on the bars of Hopkinson apparatus. A dynamic stress-strain curve will be obtained for the specimen applying some known equations upon physical conditions of SHPB test. A great majority of studies have been shown that dynamic strength of rocks increases with an increase in loading rate. Also, it has been shown that inertial and heterogeneity effects are the most impressive factors on dynamic strength increase of rocks under high loading rates. It is of note that Inertial effect boils down to a sudden increase in inner pressure of rock. Although, heterogeneity causes a more proper dynamic stress equilibrium as well as an increase in strain rate of specimen before the failure relative to those of homogenous one. The more the loading rate is, the more the strength of rock increases. In the present study, efforts have been applied to explore the effect of loading rate on dynamic behavior of rocks using split Hopkinson pressure bar as the most known and common apparatus in studying dynamic behavior of materials under high loading rates. The specimens have been cored of the same block of sandstone with a diameter of 21.5 mm and aspect ratio of 2. First of all, some quasi- static tests including uniaxial and Brezilian have been done to obtain uniaxial compressive strength, Young’s modulus, poison’s ratio and tension strength. In the meantime, Ultra-sonic test has been applyied to group the specimens of same p-wave velocity before doing Hopkinson test. The dynamic stress-strain curves for the specimen under different loading rates have been gained after capturing incident, reflected and transmitted waves by the strain gauges. Results show that there is an intense dependence of dynamic strength of sandstone to the loading rate so that with imposing the strain rate of 150 s^(-1) on the specimen, the dynamic strength of sandstone has been increased to 260 MPa from 160 MPa in quasi-static conditions. That’s why DIF, as the ratio of quasi-static strength to the dynamic one, has been obtained 1.6 at the 150 s^(-1) strain rate.
6425
An experimental study on the hydroelastic behavior of continuous and multi component very large floating structures with hinge connection against waves
^{
}
^{
}
^{
}
^{
}professor Shahid Bahonar University of Kerman
^{
}M.Sc
^{
}Assistant Professor of Mechanical Engineering, Faculty of Mechanical Eng
1
9
2015
15
3
129
140
02
06
2014
12
08
2015
.Hydroelastic behavior plays a significant role in designing and constructing very large floating structures. There are different ways to reduce structure displacement and its stress due to wave. These structures are usually made separately out of the sea, and then components are connected to each other with rigid connection in installation location. Connecting components with joint connections to each other is one way to reduce the hydroelastic response. In this paper, the hydroelastic behavior of continuous structures is compared experimentally with structures composed of two and three sections. In order to simulate the hydroelastic behaviors of floating structure, the applied floating structure was 300 meters in height, 60 meters in width and its bending rigidity was equal to 4.77×1011 N.m2. Experimental model of aluminum was fabricated with length, width and height of 2, 0.55 and 0.04 meters respectively. polyethylene was used beneath aluminum plate in order to provide floating. The first model had no connection in its length; it was continuous. In the second model which consisted of two sections with 1 meter in length, there was a joint connection as a cross line in the middle of it. The third model consisted of three sections is made up by attaching three aluminum plates 67 centimeters in length which were connected together by hinges. In a wave generated tank of Graduate University of Advanced Technology laboratory with 16 meters in length and 1 meter in width and height, strain and vertical displacement measured at different points of experimental model. 5 regular waves’ periods of 0.67, 0.80, 0.91, 1.01 and 1.10 seconds were created. water depth was 70 centimeter. Comparison of the results shows that in all three models, the displacement in long waves is more than other waves. Also, in the models with hinge connection compared to the continuous model, the stress has been significantly reduced and its value has almost halved. At the first wave whose period is 0.67 second, the maximum stress is almost equal in the models with connections; so the models with three components reflected better performance regarding displacement and bending in comparison with other models. Due to the second wave (with periods of 0.8) displacement in the model with three components was less than the others, but the stress of this model was more than the model with two components. In such a case, in structure designing regarding the ratio of wave length to structure length, the more significant factor (displacement or stress) for the project must be preferred. In the last three waves (waves with longer length) the continuous model had less displacement. On the other hand, in this model which had no connections, the stress was more than the other cases. Therefore, a parameter which may offer both advantages can't be recommended. Since bending moment difference in the continuous model is twice more than the models with joint connections, if the structure displacement be within permissible limit of the project, using joint connection would be economical in designing.
3600
Experimental Study of projectiles Penetration into Steel Fiber Reinforced High Strength Concrete Targets
1
9
2015
15
3
141
148
09
05
2014
12
08
2015
It is necessary to investigate the concrete performance against impact loads due to increasing use of concrete in structure for available materials in many regions in one hand, and war or terroristic events on the other hand. Normal concrete has weakness against projectiles. For example spalling, scabbing and multiple impacts reduce concrete potential to tolerate imposing loads. Hence, improving normal concrete characteristics for better performance against these loads is essential. So, increasing compressive strength is the first alternative. However, numerous investigations reported that increasing compressive strength resulted in brittleness of the concrete. While, improving the performance of concrete against impact loads is contradictory to brittleness. One of the recommended alternatives for enhancing compressive strength of concrete and prevailing of its brittleness is reinforcing high-strength concrete by still fiber. In this study the performance of normal and high strength concrete with and without steel fiber was evaluated against the impact of ogive nose projectile with 7.62 mm caliber diameter, 12.5 gr weight and 830 m/s impact velocity. Concrete targets included 18 semi-infinite thickness cylindrical samples. Results showed that the pressure strength reduced in the SFRHSC samples as compared with NC samples. This is due to air locking in the samples which may be arise from the one: no suitable vibration for decreasing concrete slump, and the second: discontinuity in the concrete aggregates resulting from the steel fibers with improper aspect ratio. Results of the penetration tests showed that increasing compressive strength duo to reduction in water to cementitious materials ratio and partial replacing the cement with silica fume decreased penetration depth, crater diameter and volume as 10, 15 and 23%, respectively. While, adding of 0.5% steel fiber reduced penetration depth, crater diameter and volume as 7, 10 and 58%, respectively. Furthermore, in all no fiber steel samples expanded cracks and then sample collapse were observed. However, there were small cracks in fiber steel samples and damaged region was significantly reduced. In other words, about double increasing in compressive strength of concrete (from 452 to 860 kg/cm2) and 0.5% adding still fibers had a little effect on decreasing penetration depth and crack diameter. However, the effect of still fiber on depressing crack volume resulting from impact projectile was 252% more than increasing compressive strength (Figure 1). Furthermore, reinforced sample by still fiber were more :union: after impact projectile compared with the samples without still fiber which were disturbed completely (Figure 2). Finally, it may be concluded that for improving concrete performnace against impact loads including explosion and projectile impact, it is better to increase the compressive strength of concrete by using stronger aggregate such as cilice and quartz rather than decreasing water:cementitious ratio, increasing cement quantity and using silica-fume. Figure 1. Spalling crater volume in different concrete samples Figure 2. Crack extension in SFRC (left) and NC (right) samples
10143
Evaluation of Nanoclay Effects on the Permanent Deformation of Hot Mix Asphalt
Ameri
Mahmoud
Vamegh
Mostafa
Rohoolamini
Hamed
bemana
keyvan
1
9
2015
15
3
149
158
30
11
2013
12
08
2015
Permanent deformation or rutting in wheel paths is one of the most important failure modes in asphalt pavements that affect the pavement life . Permanent deformation in asphalt mixtures can be defined as the unrecoverable cumulative deformation that occurs mainly at high temperatures in the wheel paths as a result of repeated traffic loading . The deformation results in depressions on the pavement surface along the wheel tracks relative to other points on the surface . Permanent deformation in wheel paths is one of the fundamental defects that occur due to lack of bearing capacity in flexible pavement layers . This type of defect usually occurs in the roads in the tropical areas . Rutting occurs due to cumulative non - reversible Permanent deformations in the pavement layers under repeated traffic loading . In order to increase pavement life and consequently decrease maintenance related traffic delays , great demands are placed on permanent deformation resistance of asphalt mixtures . Hot Mix Asphalt is composed of aggregates and asphalt binder . Properties of these materials have important effects on the pavement structure performance. Although , asphalt binder is a little part of mixture ( in comparison with aggregates ) , but has major effects on the performance , durability and stability of the asphalt concrete mixture . Any change in asphalt properties will result significant changes in the asphalt concrete mixture performance . Since asphalt cement ( AC ) never fully satisfying lacks the physical and mechanical properties , researchers are constantly trying to improve the asphalt cement properties . Asphalt cement modification will result improved quality and increased life of the pavement . Nano - particles is one of the additives that are used to modify the properties of asphalt cement . Nano - clays are unique materials as additives to make significant improvements in the material properties of polymer Nano -composites. Nano-clay polymer materials typically strengthen the mechanical properties, modulus and stability of these cases. In this research, it is assumed that subgrade, sub-base and base layers of flexible pavement have sufficient resistance to rutting. Nanoclay is used to modification of bitumen properties for Hot Mix Asphalt mixtures better bearing capacity and resistance to rutting. So, limestone aggregate with 4 degration number, AC 60-70 and two types of montmorillonite Nanoclay: Cloisite 15A and Cloisite 30B are used in this study. Marshall and Dynamic creep tests in two stress levels ( 300 and 450 KPa ) at 50 ° C , as well as rutting test on the HMA samples with 0 , 2 , 4 and 6 percent of each Nanoclay were performed . Test results show that adding Nanoclay will result the better performance of HMA samples .
10367
The effect of bottom outlet geometry changes on hydraulic characteristics of flow
Ghazali
Fatemeh
Salehi Neyshabouri
Seyed Ali Akbar
Kavianpour
Mohammad Reza
1
9
2015
15
3
171
182
22
08
2012
12
08
2015
Outlet conduits are one of the important parts of dams. Due to the high flow rate and pressure drop, problems such as cavitation can affect these structures. Considering these problems, detailed design is necessary. Laboratory studies are usually carried out which are expensive, thus, numerical models for determining complex flow characteristics have attracted the attention of the designers. In this study, the numerical simulation of Jegin dam outlet conduit in south of Iran with the scale of 1:10 is provided and the results are verified by experimental information taken from physical model built and tested at Water Research Institute. Gate opening in this research is always 70% and the water head is the constant value of 38.6m. The research is focused on the intake gate and not the service one, so the service gate is always fully opened. FLUENT computer code is considered for the numerical model studies. In the numerical simulation the Finite volume mixture two phase flow scheme is used together with k–e turbulence model. The flow discharge and air supply from the air vent downstream of the gate is then computed by 3D numerical model for different channel geometries. Reasonable agreement between the numerical model and experimental results shows reliable performance of the numerical model. This study showed the ability of the numerical model to simulate the complex air water flow in high speed gated tunnels. This study also includes the effect of the height to width ratio of the conduit on flow discharge and aeration downstream of the gate. To do this, different numerical models are simulated among which the difference is the height to width ratio of the conduit. Height and width of the conduit are measured at the gate section and changes are applied in two cases of constant height (depth) and variable width, and constant width and variable height. Results show more aeration and more flow discharge while heightening and widening of the outlet. Flow discharge has also been determined as function of the height to width ratio of the conduit at gate section of the channels. One of the important results is that in comparison with the width changes, height changes of the channel affect hydraulic characteristics of flow more and the diagram rates vary more sharply. Researches show that 1.5 to 2 ranges for height to width ratio is the best range hydraulically and other ranges have effect on reducing aeration and Air demand ratio β (β in this research agrees more with the relation Kalinske and Robertson presented), so the pressure in a conduit may fall considerably below atmospheric pressure which results in cavitation and vibration. To avoid these problems, suggests not to heightening the conduit more than a specific value.
1721
Turbulent flow structure around submerged T-shape spur dike
1
9
2015
15
3
171
178
13
07
2013
12
08
2015
Spur dikes are the training structures that may be used for river bank erosion protections. These structures may increase the navigation depth. The spur dike creates stable pool for aquatic habitat. Most of the previous researches focused on scour hole dimensions and the flowfield around the emerged spur dikes. As the spur dikes may be submerged during the floods, in this paper, the flowfield around a submerged T-shape spur dike was investigated using Vecterino apparatus. The experiment was conducted in a channel with 8m length, 60cm width and 80 cm depth at TarbiatModares University (Tehran- Iran). The parameters that were investigated in this paper includes, mean velocities, turbulence parameters and streamlines. The results of this study indicate that the high velocity region of the flow elongates to the far distance of downstream in the upper layers. There is a recirculating flow downstream of spur dike. Due to the effect of the spur dike overflow, the downstream recirculating flow, rotates in the opposite direction as compare to the emerged spur dike. The recirculating flow elongates to the far distance of downstream as compare to the submerged trapezoidal spur dike. Turbulence parameters analyzed in this research include normal Reynolds stress, bed shear stresses, the probability of each process and triple correlations. Maximum normal Reynolds stresses were observed at the upstream tip of the spur dike. In addition, the maximum shear stress was observed at the same region. The high stress region around the spur dikes showed a shear layer region around the spur dikes. Analysis of the probability of the turbulent bursting events in streamwise direction shows that ejection and sweep events are the most probable events in the upstream section of the spur dikes. In the streamwise direction, the interaction events are the most probable process near the upstream tip of the spur dike, while ejection and sweep events in the widthwise direction are the most probable events near the upstream tip of the spur dike. In the downstream recirculation zone of the spur dike, the probability of the events approximately are the same in the streamwise direction and interaction events are the most probable events in widthwise directions. Triple correlations presented useful information about the turbulent bursting process. The triple correlation analysis in widthwise direction showed that the ejection is the strongest event in shear layer region. Triple correlation analysis in the streamwise direction, showed that ejection was the strongest event in the upstream of the spur dike and in the region between near channel wall and spur dike wing. This causes sediment transport in streamwise direction as suspended load. The interaction events are the strongest events in the downstream recirculation zone, hence the sediments were deposited in this region.