Prediction of pipeline scour depth in clear-water and live-bed conditions using group method of data handling

In the present study, the Group method of data handling (GMDH) network was utilized to predict the scour depth below pipelines. GMDH network was developed using back propagation. Input parameters that were considered as effective parameters on the scour depth included those of sediment size, geometry of pipeline, and approaching flow characteristics. Training and testing performances of the GMDH networks have been carried out using nondimensional data sets that were collected from the literature. These data sets are related to the two main situations of pipelines scour experiments namely clear-water and live-bed conditions. The testing results of performances were compared with the support vector machines (SVM) and existing empirical equations. The GMDH network indicated that using of back propagation produced lower error of scour depth prediction than those obtained using the SVM and empirical equations. Also, the effects of many input parameters on the scour depth have been investigated.     

Laboratory Investigation of Stilling Basin Slope Effect on Bed Scour at Downstream of Stepped Spillway: Physical Modeling of Javeh RCC Dam

Stepped spillway and stilling basin are one of the most important energy dissipation structures. Eventhough, most of energy dissipated by these structures, but in skimming flow, the upstream flow motion is nonaerated and the residual energy capable to destroyed structures during floods. In this study, effect of stilling basin slope on bed scour, downstream of Javeh dam was investigating. Experiments performed in hydraulic structures laboratory of the University of Kerman with six different discharges (5, 7, 13, 17, 25 and 30 l/s.m) and five various stilling basin slope (0.02, 0.01, 0, ?0.01 and???0.02). The parameters such as maximum scour depth (d_s), flow velocity (in three point), water depth on upstream and downstream of stepped spillway and stilling basin, the distance of the maximum scour depth to sill (L_s) and the gheometery of scour hole measured. Result shown that when stilling basin slopes was 0.02, the average of maximum relative scour depth, 47% Increased and in ?0.02, 52.2% Decreased. In addition, the distance of maximum scour depth until stilling basin increased by increasing and decreased by decreasing the stilling basin slope.

     

Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

The thermal properties of epoxy‐based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the “synergistic” filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size‐dissimilar fillers, has a well‐defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of f_g = 15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches f_Cu ≈ 40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, f_g = 40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. A thermal conductivity of 13.5 ± 1.6 Wm^?1K^?1 is achieved in composites with binary fillers of f_g = 40 wt% and f_Cu = 35 wt%. It has also been demonstrated that the thermal percolation can occur prior to electrical percolation even in composites with electrically conductive fillers. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.     

Modeling of cohesive crack growth in partially saturated porous media; a study on the permeability of cohesive fracture

Modeling the water flow in cohesive fracture is a fundamental issue in the crack growth simulation of cracked concrete gravity dams and hydraulic fracture problems. In this paper, a mathematical model is presented for the analysis of fracture propagation in the semi-saturated porous media. The solid behavior incorporates a discrete cohesive fracture model, coupled with the flow in porous media through the fracture network. The double-nodded zero-thickness cohesive interface element is employed for the mixed mode fracture behavior in tension and contact behavior in compression. The modified crack permeability is applied in fracture propagation based on the data obtained from experimental results to implement the roughness of fracture walls.     

Services and supporting architecture of the ESA OBP system

The ESA on-board processing (OBP) satellite system using on-board regeneration and baseband circuit switching has been designed to provide ISDN connectivity and services to users on a Pan-European basis. It is thus seen at its periphery as a 2 Mb/s primary rate access, hence allowing for the interconnection of equipment and terminals compatible with this standard interface. Among the various possible network architectures that the system could support, the business-oriented closed networks look most promising. It has therefore been retained as a prime design driver for OBP system developments. Optionally, connectivity can be offered in an optimized manner to pure data networks, e.g. for LAN-to-LAN interconnection at rates up to 1 Mb/s. In the paper, communication services and networking capabilities offered by the system are briefly reviewed. The internal characteristics of the satellite system allowing for such capabilities are then reviewed and the corresponding performance outlined. The system is shown to be compatible with critical CCITT performance criteria.     

Hybrid Computational Simulation and Study of Terahertz Pulsed Photoconductive Antennas

A photoconductive antenna (PCA) has been numerically investigated in the terahertz (THz) frequency band based on a hybrid simulation method. This hybrid method utilizes an optoelectronic solver, Silvaco TCAD, and a full-wave electromagnetic solver, CST. The optoelectronic solver is used to find the accurate THz photocurrent by considering realistic material parameters. Performance of photoconductive antennas and temporal behavior of the excited photocurrent for various active region geometries such as bare-gap electrode, interdigitated electrodes, and tip-to-tip rectangular electrodes are investigated. Moreover, investigations have been done on the center of the laser illumination on the substrate, substrate carrier lifetime, and diffusion photocurrent associated with the carriers temperature, to achieve efficient and accurate photocurrent. Finally, using the full-wave electromagnetic solver and the calculated photocurrent obtained from the optoelectronic solver, electromagnetic radiation of the antenna and its associated detected THz signal are calculated and compared with a measurement reference for verification.     

Modeling of cohesive crack growth using an adaptive mesh refinement via the modified-SPR technique

In this paper, an adaptive finite element procedure is presented in modeling of mixed-mode cohesive crack propagation via the modified superconvergent path recovery technique. The adaptive mesh refinement is performed based on the Zienkiewicz–Zhu error estimator. The weighted-SPR recovery technique is employed to improve the accuracy of error estimation. The Espinosa–Zavattieri bilinear cohesive zone model is applied to implement the traction-separation law. It is worth mentioning that no previous information is necessary for the path of crack growth and no region of the domain is necessary to be filled by the cohesive elements. The maximum principal stress criterion is employed for predicting the direction of extension of the cohesive crack in order to implement the cohesive elements. Several numerical examples are analyzed numerically to demonstrate the capability and efficiency of proposed computational algorithm.     

Improvement of Near-Dry Machining and Its Effect on Tool Wear in Turning of AISI 4142

In this study, improvement of near-dry machining (NDM) and its effect on tool wear in turning of AISI 4142 by carbide tool (DNMG 150608-PM) is investigated. First, the preparation of experimental setup was carried out, and then, some experiments to study the process were performed. Surface roughness was used as the criterion of finding the optimal conditions of fluid flow rate and frequency, and position and angle of nozzle. After optimization of the process, some experiments were performed to study tool life. Machining force, roughness, and tool wear were chosen as the criteria to determine the tool life. Obtained results show that the tool life in NDM is longer than that in dry machining.     

Application of a weakly compressible smoothed particle hydrodynamics multi-phase model to non-cohesive embankment breaching due to flow overtopping

The subject of present study is the application of mesh free Lagrangian two-dimensional non-cohesive sediment transport model applied to a two-phase flow over an initially trapezoidal-shaped sediment embankment. The governing equations of the present model are the Navier-Stocks equations solved using Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. To simulate the movement of sediment particles, the model considers a powerful two-part technique; when the sediment phase has rigid behavior, only the force term due to shear stress in the Navier-Stokes equations is used for simulation of sediment particles’ movement. Otherwise, all the Navier-Stokes force terms are used for transport simulation of sediment particles. In the present model, the interactions between different phases are calculated automatically, even with considerable difference between the density and viscosity of phases. Validation of the model is performed using simulation of available laboratory experiments, and the comparison between computational results and experimental data shows that the model generally predicts well the flow propagation over movable beds, the induced sediment transport and bed changes, and temporal evolution of embankment breaching.