Sharif Digital Repository

Stepped spillways have been widely used in Roller Compacted Concrete (RCC) dams in the recent decades. Considering complexity of hydraulics of stepped chutes, their initial design involves pre-selection of some empirical formulae for calculation of flow characteristics and design parameters. In this paper, accuracy of several empirical formulae, proposed for calculating locations of aeration inception (LI), uniform flow (Lu) and rate of energy dissipation (ΔH/Hmax), were compared in relation to results of physical model tests of four stepped spillways and the preferred formulae, providing least amounts of relative errors, were identified. Such a feedback will be helpful for improvement of... 

In this paper, a combination of the Lagrangian meshfree method of SPH and Polyhedral DEM is presented to simulate the interaction between the free surface of water and solid objects possessing sharp edges and flat surfaces, such as armour units of breakwaters. Both SPH and DEM schemes are validated successfully against experimental data. The numerical scheme is utilized to inspect the stability of concrete cubic armours in rubble-mound breakwaters through systematic analyses with various geometrical parameters and environmental conditions. The numerical results regarding the required dimensions of the cubic blocks for providing stability of the armour units under the wave attack are compared... 

This paper addresses numerically-derived tsunami wave loads on bridge superstructures using smoothed particle hydrodynamics (SPH), which is a type of mesh-free methods. Although there exist some relationships for the case of impinged loads on bridges exerted by regular (sinusoidal) waves, for the case of solitary waves such as tsunamis, no relation has yet been proposed in the literature. This shortcoming is partly due to the lack of understanding the mechanism of wave action on the bridge superstructures. In this study, three water depths, three wave amplitudes and four submergence depths of the deck are considered for the process of numerical investigation of tsunami-induced loads on... 

Hydrodynamics of highly nonlinear cnoidal waves and their subsequent strong plunging breakers are among the least understood and most significant issues in coastal engineering. In this work, a weakly compressible smoothed particle hydrodynamics (SPH) formulation is used for the study of the generation and propagation of cnoidal waves and investigation of the characteristics of the induced strong plunging breakers. Numerical results show the capability of the SPH scheme for properly simulating the cnoidal waves. For the case of strong plunging breakers, dynamic and kinematic features of the flow are computed and compared with certain implementations of other numerical techniques. SPH is shown... 

Low-crested breakwaters have become more attractive because they do not hinder the beautiful coastal landscape and are more environmentally friendly comparing to traditional breakwaters. The available formulae for design of these types of structures mainly focus on wave transmission, reflection and dissipation aspects. However, stability of the armour blocks are not directly taken into account in the design process. In this study the Lagrangian meshfree method of SPH along with a discrete element method i.e. Polyhedral DEM are used to simulate the interaction between the sea water waves with different characteristics and low-crested breakwaters constructed using cubic armour blocks. SPH is... 

In this study, the energy concept along with the first- and third-order shear deformation theories (FSDT and TSDT) are used to predict the large deflection and through the thickness stress of FGM plates. These responses are studied and discussed as a function of plate thickness and the order "n" of a power law function which is considered for the through the thickness variation of the properties of the FGM plate. The results show that the energy method powered by the FSDT and FSDT is capable of predicting the effects of plate thickness on the deformation and the through the thickness stress. Here, also the effects of power "n" on the plate response is clearly depicted. Notably, the... 

Material selection for mechanical designs is an important task. Different approaches have been proposed to fulfill this job, so far. However, most of them work well with only quantitatively measurable properties of materials. Also, due to a wide range of materials available, the selection space finds a fuzzy characteristic. Therefore, here a simplified fuzzy logic approach is introduced to provide a powerful tool for easy dealing with the qualitative properties of materials and the corresponding fuzzy space. With this approach the volume of mathematics involved with the conventional methods reduces, considerably. The results show an excellent match with the Manshadi's method. © 2008 Elsevier... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the...