Showing 6 results for Free Surface
Saeed Farzin, Yousef Hassanzadeh, Mohammad Taghi Alami, Rouhollah Fatehi,
Volume 14, Issue 4 (7-2014)
Abstract
A consistent implicit Incompressible Smoothed Particle Hydrodynamics (ISPH) method based on projection approach is proposed for solving violent free surface flow problems. In this way, two consistent discretization schemes are employed for first and second spatial derivatives. In this study, it is shown that in explicit ISPH solvers, the field variables and the positions of particles in the process of numerical differentiation are estimated at two different time steps. So, the incompressibility is not completely satisfied. In the present approach, an iteration loop is implemented, in each time-step. Thus, at the end of each time-step both velocity and the positions used in divergence estimation are at the new time-level. The proposed ISPH method is validated in free surface flow problems involving 2-D dam break benchmarks in which both wet and dry beds are considered. Among the advantages of the present implicit method is being more accurate and stable than the explicit one, despite use of lower number of particles and greater time-step sizes. Also, it provides significant improvement in free surface simulations and pressure distribution results.
Volume 15, Issue 3 (9-2015)
Abstract
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
Behnam Cheraghi, Babak Mirzavand Boroujeni, Maziar Shafaee,
Volume 16, Issue 4 (6-2016)
Abstract
Free hydroelastic coupled vibration analysis of frictionless liquids with a free surface in spherical tanks with a flexible bottom has been performed. The side wall has been considered to treate as a rigid body. The flexible bottom treats as a membrane at a certain distance bellow the center point, and the free surface is considered as a cross cutting at the top of the center point. The spherical coordinate system is adopted to derive the governing coupled equations, and finally a vibration analysis is carried out, using the traditional Galerkin's method, leading to closed-form solutions. Effects of various system parameters, i.e., membrane tension, liquid density, geometric parameters of the system such as the container radius, free surface distance discriminate parameter, and bottom distance discriminate parameter on the vibration behavior are investigated. The novelty of the present work is to obtain direct formulas for hydroelastic coupled vibration analysis of the mentioned system, which can be easily used in engineering design applications. Coupling between two mode numbers can be clearly seen in results, in other words, there is a coupling between vibration modes as interaction in spherical geometry.
Amir Nasseroleslami, Mahmood Salari,
Volume 16, Issue 6 (8-2016)
Abstract
ََAbstract Recognition of the dynamical behavior and vibrations of marine structures, submerged in vicinity of the water free surface, is one of the most important issues in design of the marine structures. It is obvious that physical properties of the ambient fluid have some influences on vibrational frequencies of the structures. For the structures that have exposed under the influences of asymmetric environmental conditions, prediction of their dynamical behaviors is more complicated. In this paper the effects of immersion depth on first natural frequency of a bounded circular plate that was placed parallel in vicinity of the water surface, are studied numerically and experimentally. Based on the author’s knowledge, the techniques used for exciting the plate and measurements of natural frequencies are innovations of this research. Numerical solutions are done by using of the ABAQUS software. Comparisons of the numerical and experimental results show a good consistency. The investigations showed by increasing of the immersion depth, so the ratio of the depth to plate diameter reached to a certain value, the natural frequencies were also decreased. After that it remained constant while the immersion depths of plate were increased.
, , Amir Ehsan Jaberi,
Volume 22, Issue 10 (10-2022)
Abstract
Magnetic abrasive finishing process (MAF) is one of the latest advanced machining processes. After eight decades have passed since the registration of the magnetic abrasive polishing process, the applicability of this method has been proven in finishing all kinds of surfaces, including flat, cylindrical and free surfaces. In this research, the influence of MAF process movement parameters on the concave surface of cold-worked steel has been investigated experimentally using the response surface method. These parameters include rotational speed, linear speed, gap between abrasive brush and workpiece, magnetic flux density and curvature angle. For this purpose, a spherical head magnet is used and the powder used is prepared by mechanical alloying method. Cold-worked steel is used in the manufacture of roll forming molds, which is used in air engines to shape compressor and turbine blades, and also to investigate the feasibility of the MAF process on the workpiece surface with high hardness and yield stress, such as Cold work steel is selected. According to the results, the optimal value of the magnetic flux density is 0.55 tesla, and with the increase of the distance between the abrasive brush and the workpiece, the surface roughness changes initially increase and decrease after passing the optimal value.
Volume 23, Issue 6 (11-2023)
Abstract
Vortex drops are compact hydraulic structures used in surface water and sewer collection systems to convey runoff from higher to lower elevations by creating a rotational flow inside vertical shafts. These structures are composed of three main parts: the intake, drop shaft, and dissipation chamber. Tangential intake is a steep tapering channel that generally has a junction with a rectangular approach channel with the horizontal bottom at the beginning and a narrow slot at the connection with the drop shaft. Many factors need to consider in the design of vortex drop shafts with proper hydraulic performance. The review of previous studies and the guideline designs for this structure indicates that most design relations were obtained either based on simplified assumptions or by conducting limited tests on laboratory scale models, which can cause desirable operation in practice. These conditions have forced engineers to set up laboratory models or numerical simulations of the initial design to evaluate the proper performance of the structure in big projects. With this introduction, one of the problems in the surface water collection network of Tehran is conveying high volumes of runoff from the surface of streets at the highway intersections to a lower level in the underground tunnels or pipes. Therefore the authorities pay more attention to necessary considerations in the design and use of these types of structures for the safe transfer of runoff downstream. In this paper, using numerical modeling, the hydrodynamics of flow in a real vortex drop shaft with tangential intake has been studied. In the design stage, a vortex drop structure in Tehran's urban drainage has been selected and evaluated by the Flow-3D numerical model. Based on the latest available design methods, Several tangential intakes with different geometry were assessed separately. Finally, the performance of the final drop shaft was simulated and analyzed using the numerical model. The final design simulation results showed that the flow in the tangential intake would enter the vertical shaft without forming a hydraulic jump. The flow in the vertical shaft is spirally attached to the wall with a central air core. A key design parameter is the ratio of the air core area to the drop shaft cross-sectional area that was greater than 0.49. The efficiency of energy losses at the tangential intake is about (9-15%), in the vertical shaft is about (23-40%), and in the energy dissipating chamber is (70-71%) depending on the flow rate. The energy loss efficiency in the whole structure was about (80-84%). The depth size needed to create a water cushion in the energy dissipation chamber was considered for three depths of 0.4D, 0.5D, and 0.6D. After numerical modeling, the appropriate depth for the water cushion was determined to be 0.6D. The results of the simulations indicated that the use of existing design methods only sometimes leads to optimal hydraulic performance in the structure. Therefore, reviewing the existing design methods, simulating the flow in the designed drop shaft, or setting up a laboratory model before finalizing the design is necessary.
