Experimental Investigation on 3D Flow around a Single T-Shaped Spur Dike in a Bend

The flow field around a T-shaped spur dike located in a 90° bend is investigated experimentally. The three-dimensional Acoustic Doppler Velocimeter (ADV) was used for measuring the flow field. The comparison of the three dimensional components of velocity was made in different sections of the bend and the differences of the flow pattern along the bend was analyzed. The observations showed the significant effect of the spur dike on the secondary flow patterns. Some horizontal vortices with a counter-clock-wise direction were also observed in the up and down stream of the spur dike near the outer bank of the bend. In addition, the vortices and reverse flows in the up and down stream of the spur dike, the changes of the secondary flow and vorticity are also addressed in this study

Description of the G-A Infiltration Model Using Chu and Chow Viewpoints

The soil infiltration process is one of the hydrological cycle processes, attracting the attention of the hydrologists more than any other process. This process provides conversion of the raw rainfall into the excess rainfall; and ultimately the excess rainfall is used for describing the rainfall-runoff models. In most of the infiltration models, the rainfall is introduced to the model as steady and is converted into the excess rainfall. In this paper, through using Green-Ampt model and the double-ring tests results performed in seven pits in one of the indicator catchment south of the country, the model parameters have been estimated, and the excess rainfall resulting from the unsteady raw rainfall has been calculated using deterministic model and using two entirely different viewpoints. After making sure of the conditions and limitations of both viewpoints, the necessary grounds have been provided for distinguishing between time scale implemented in the model and time scale used for observation of the unsteady rainfall as well as their influence on such indexes as the runoff depth, the runoff peak and the cumulative infiltration. The bright point of this paper is consideration of the difference between the concepts of \u201cModel Time Scale\u201d and \u201cObservation Time Scale\u201d. Taking into notice of the change trend of infiltration, run-off and their change ratios against the changes of these two time scales, the researcher must suitably select between the \u201cModel Time Scale\u201d and \u201cObservation Time Scale\u201dof the rainfall and considers the optimum value of these time intervals in calculation of the excess rainfall and their influence on the run-off rainfall models

Numerical simulation of flow pattern at a divergent pier in a bend with different relative curvature radii using ansys fluent

In this work, the three-dimensional flow around piers in river meanders under rigid bed conditions was modeled. The software ANSYS FLUENT was used to perform the simulation. The study was carried out in a 180° curve accompanied by cylindrical piers with a diameter of 5 cm and a slope angle of 21° under rigid bed conditions. The results of the comparisons showed that this model can help simulate the flow pattern around inclined bridge piers in bended channels with acceptable accuracy. To analyze the flow pattern, the work was followed by studying the effect of the parameters that affect the physics of the problem: the relative radius of curvature of the curve, the location of the piers within the 180° curve, and the arrangement of the piers relative to the flow direction. The results showed that increasing the relative radius of curvature as well as the range of the bend reduced the tangential velocity values; the minimum tangential velocity value occurred at a relative radius of curvature of 5. With the pier group installed in the direction of flow, the maximum secondary flow power occurred at the 60° position at about 18.8%, while with the pier group installed across the flow, the maximum secondary flow power occurred at the 120° position at 14.2%. A comparison of the vorticity at the perpendicular and downstream positions showed that the vorticity values at the 60° and 120° positions were greater than the corresponding values at the 90° position in both cases

RSS-Based Sensor Localization in the Presence of Unknown Channel Parameters

This correspondence studies the received signal strength-based localization problem when the transmit power or path-loss exponent is unknown. The corresponding maximum-likelihood estimator (MLE) poses a difficult nonconvex optimization problem. To avoid the difficulty in solving the MLE, we use suitable approximations and formulate the localization problem as a general trust region subproblem, which can be solved exactly under mild conditions. Simulation results show a promising performance for the proposed methods, which also have reasonable complexities compared to existing approaches

Bearing-only target localization with uncertainties in observer position

In this paper, the bearing-only target localization problem when the observer positions are subject to error is investigated. In this problem, the angle of arrival of the transmitted signal between target and observer are used to estimate the target position. It is assumed that not only the bearing measurements are corrupted by noise but also the exact position of observer is not available to the estimator. The accuracy of estimated location of target depends on the reliability of information from the observer position. Therefore, the previously published algorithms considering only the bearing measurement noise do not meet the expected performance when the observer positions are subject to error. The maximum likelihood, the least squares and total least square algorithms and a new method of localization based on weighted total least squares approach are developed for this problem. The corresponding Cram´er-Rao lower bound (CRLB) is derived for this problem. Computer simulations are performed to evaluate the performance of the proposed algorithms. Simulation results show that the new method can attain the CRLB for sufficiently high SNR

Evaluation of Different Methods for Considering Bar-Concrete Interaction in Nonlinear Dynamic Analysis of RC Frames by Using Layer Section Theory

In this paper, the bond-slip effect has been applied to the numerical equations in the process of nonlinear dynamic analysis of reinforced concrete frames. The formulation is similar to that of the layer section theory, but the perfect bond assumption has been removed. The precision of the proposed method in considering the real nonlinear behavior of reinforced concrete frames has been compared to the precision of two other suggested methods for considering bond-slip effect in layer model. Among the capabilities of this method for seismic analysis are its ability of modeling the embedded lengths of bars within joints and nonlinear modeling of bond-slip. The precision of the analytical results were compared with the experimental ones achieved from a one bay two storey frame under seismic loading on the shaking table. According to the numerical results, the presence or absence of bond effect in numerical modeling and analysis will bring about considerable different results, including results for deformation and forces. All the studied methods for inserting the bond-slip effect into the layer model can relatively improve the accuracy of analytical results compared to experimental ones. The proposed method of this study has proved to enjoy the highest accuracy with regard to time-history seismic analysis of reinforced concrete frames. Among the capabilities of the proposed method, we may refer to its ability to model beam-column and joint element\u2019s nonlinear behavior separately

RSS-based sensor localization with unknown transmit power

Received signal strength (RSS)-based single source localization when there is not a prior knowledge about the transmit power of the source is investigated. Because of nonconvex behavior of maximum likelihood (ML) estimator, convoluted computations are required to achieve its global minimum. Therefore, we propose a novel semidefinite programming (SDP) approach by approximating ML problem to a convex optimization problem which can be solved very efficiently. Computer simulations show that our proposed SDP has a remarkable performance very close to ML estimator. Linearizing RSS model, we also derive the partly novel least squares (LS) and weighted total least squares (WTLS) algorithms for this problem. Simulations illustrate that WTLS improves the performance of LS considerably

Does Use of Twitter by Political Leaders Matter in a Health Crisis? The Perspective of COVID-19

While extant literature has reached a consensus on the effectiveness of Twitter in crisis communication, this paper contextualizes the use of Twitter specifically by political leaders during the COVID-19 crisis. We first identify political leaders on Twitter using machine learning techniques and then examine the significant properties of their networks. The findings demonstrate that the network of political leaders on Twitter is relatively dense and well-connected. However, a few nodes are highly prominent and have a large number of connections. Our study detects twenty-three communities of political leaders and observes the evidence of political polarization in the network. We also find two large communities representing the Republican and Democratic parties at the national-level. The remaining communities are reasonably well-balanced in size and center at the state-level. In further analysis, we plan to investigate the patterns of COVID-19 crisis communications through this network and explore the association with COVID-19 outcomes using panel data

Experimental Study of the Effect of Base-level fall at the Beginning of the Bend on Reduction of Scour around a Rectangular Bridge Pier Located in the 180 Degree Sharp Bend

Base-level fall in river beds occurs due to varying natural or unnatural causes. Base-level fall causes the change in the behavior of flow at the location of drop in base-level. In such situations, most of scour occur at the foot of the slope, and slope wall retreats in the upstream direction. This phenomenon widens the wall of the river bank, thus leading to its destruction. The amount of bed topography variations and scour around a rectangular bridge pier with an oblong nose located in the 90 degree angle of a 180 degree sharp bend was studied in this work by generating base-level fall at the beginning of the 180 degree sharp bend, and it was compared with a case without a base-level fall. The results indicated that in the case of base-level fall at the upstream side of the bridge pier, increase in flow depth, as well as reduction in velocity at the area around the pier, is observed, and the maximum depth of scour hole and the volume of scour hole around the pier respectively reduce by 73 and 97% in comparison with those in the case where no base-level fall occurs

Effect of Scour Hole on Lateral Buckling of Offshore Snaked Lay Pipeline

Submarine pipeline is one of the most popular research filed that many researchers focus on solving the issue of buckling of pipeline. The snaked laying is an effective method to control the lateral buckling. The scour below offshore pipeline may affect the efficiency and performance of the snake lay pipeline. The objective of this study was to investigate the effect of scour hole on the buckling of seawater pipelines. A three-dimensional numerical model developed to investigate the effect of scour below offshore pipeline subjected to wave and current by using Abaqus software and Aqua Module. The results indicated that vertical deformation of straight pipeline increased by increasing scour hole depth. This value changed 4.85 cm to 32.87 for holes 11 to 200 cm respectively, but these parameters of the snake lay pipelines were not affected by the presence of scour hole. Moreover, the effective axial force of snacked lay pipelines reduced 5 times in comparison to straight pipeline by applying wave and current. The results indicated that the value of stress of snaked-lay pipeline was independent on scour hole depth. Therefore, this pipeline was effective method to limit and control buckling even in the presence of scour below i