| 1. |
- Das, Sumit Kumar, et al.
(author)
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Assessment of various isogeometric contact surface refinement strategies
- 2024
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Nature. - 1678-5878 .- 1806-3691. ; 46:4
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Journal article (peer-reviewed)abstract
- Since its inception, isogeometric analysis (IGA) has shown significant advantages over Lagrange polynomials-based finite element analysis (FEA), especially for contact problems. IGA often uses C1-continuous non-uniform rational B-splines (NURBS) as basis functions, providing a smooth description of kinematic variables across the contact interface. This leads to increased accuracy and stability in the numerical solutions. However, from the existing literature on isogeometric contact analysis, it is not yet clear what interpolation order and continuity of NURBS one should employ to accurately capture the distribution of contact forces across the contact interface. The present work aims to fill this gap and provides a comparative assessment of different NURBS-based standard (conventional) refinement strategies for contact problems within the IGA framework. A recently proposed refinement strategy, known as the varying-order (VO) based NURBS discretization, has demonstrated its capability to refine geometry through the implementation of order elevation in a controlled manner. However, a detailed investigation that directly compares the VO based NURBS discretization with the standard NURBS discretization has not yet been carried out. Therefore, a thorough study of the VO based discretization strategy is also conducted, evaluating its effectiveness in comparison with the standard discretization strategy for contact problems. For this, a few examples on contact problems are solved using an in-house MATLAB® code. The solution to these examples shows that quadratic order standard NURBS discretization is sufficient to achieve the desired level of solution accuracy just by increasing the mesh size. It is further demonstrated that VO based discretization can achieve much higher accuracy than standard discretization, even with a coarse mesh, by generating additional degrees of freedom in the contact boundary layer. In addition, VO based discretization makes considerable savings in analysis time to achieve the same accuracy level as standard discretization.
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| 2. |
- Dashtimanesh, Abbas, et al.
(author)
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A three-dimensional SPH model for detailed study of free surface deformation, just behind a rectangular planing hull
- 2013
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Verlag. - 1678-5878 .- 1806-3691. ; 35:4, s. 369-380
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Journal article (peer-reviewed)abstract
- Transom wave behind planing hulls is a complicated physical phenomenon that has lead to computational challenge for many researchers. On the other hand, smoothed particle hydrodynamics (SPH) which is known as a meshless Lagrangian approach can simulate free surface flows with strongly nonlinear physics. Therefore, effort has been made in the current study to develop a 3D-SPH code for three-dimensional simulation of transom stern flow behind a rectangular planing hull. It is also aimed to give some new physical insights into this highly nonlinear problem. Different techniques such as sub particle scale turbulence model and moving least square density filter among others are also implemented. To validate the developed 3D-SPH code, the benchmark problem of dam breaking is investigated. Moreover, to verify the capability of the presented SPH model for transom flow simulation, previous experimental studies at low Froude numbers are considered. Comparisons display good agreement between the numerical results and experimental findings. Furthermore, a detailed discussion about rooster tail formation is presented.
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| 3. |
- Fatahian, H., et al.
(author)
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Performance enhancement of Savonius wind turbine using a nanofiber-based deflector
- 2022
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Science and Business Media Deutschland GmbH. - 1678-5878 .- 1806-3691. ; 44:3
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Journal article (peer-reviewed)abstract
- This research presented a unique deflector called a nanofiber-based deflector for Savonius wind turbine to achieve the best performance with a high self-starting capability. The objective of this novel deflector produced from nanofibers was to diminish the detrimental effect of the complicated wake zone made behind the standard solid deflector, which had not yet been analyzed. Different PVA and PLA nanofibers concentration ratios were evaluated experimentally before being included in the numerical simulation to find the most appropriate porosity value and average pore size. These nanofibers with concentration ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 (v/v) were fabricated by electrospinning method. Then, the performance of conventional Savonius turbine and deflector arrangements was thoroughly studied using Computational Fluid Dynamics. Variations of power, torque, and flow structure were compared between configurations of the deflector and the conventional Savonius rotor to prove how the nanofiber-based deflector improved the performance of the turbine. It was revealed that a suitable porosity value existed for attaining the maximum performance of the Savonius turbine. Furthermore, utilizing a PVA75/PLA25 deflector with φ = 0.89, greater average torque and power coefficients (Cm and CP) values were obtained. It is worth mentioning that using PVA75/PLA25 and PVA deflectors with greater porosity values completely eliminated the severe vortices behind the deflector. In rotation angles ranging from 100°–200° to 290°–360°, PVA75/PLA25 deflector substantially increased the CP. The average CP was raised by 7 and 9% using solid and PVA75/PLA25 deflectors, respectively. Accordingly, the solid and PVA75/PLA25 deflectors enhance not only the power coefficient but also the ability to self-start. At a rotation angle of 0°, the PVA75/PLA25 deflector outperformed the solid deflector by 87%, improving the static torque coefficient (Cms).
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| 4. |
- Fentaye, Amare Desalegn, et al.
(author)
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Gas path fault diagnostics using a hybrid intelligent methodfor industrial gas turbine engines
- 2018
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer. - 1678-5878 .- 1806-3691. ; 40
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Journal article (peer-reviewed)abstract
- There are many challenges against an accurate gas turbine fault diagnostics, such as the nonlinearity of the engine health,the measurement uncertainty, and the occurrence of simultaneous faults. The conventional methods have limitations ineffectively handling these challenges. In this paper, a hybrid intelligent technique is devised by integrating an autoassociativeneural network (AANN), nested machine learning (ML) classifiers, and a multilayer perceptron (MLP). The AANNmodule is used as a data preprocessor to reduce measurement noise and extract the important features for visualisation andfault diagnostics. The features are extracted from the bottleneck layer output values based on the concept of the nonlinearprincipal component analysis (NLPCA). The nested classifier modules are then used in such a manner that fault and no-faultconditions, component and sensor faults, and different component faults are distinguished hierarchically. As part of the classification,evaluation of the fault classification performance of five widely used ML techniques aiming to identify alternativeapproaches is undertaken. In the end, the MLP approximator is utilised to estimate the magnitude of the isolated componentfaults in terms of flow capacity and isentropic efficiency indices. The developed system was implemented to diagnose up tothree simultaneous faults in a two-shaft industrial gas turbine engine. Its robustness towards the measurement uncertaintywas also evaluated based on Gaussian noise corrupted data. The test results show the derivable benefits of integrating twoor more methods in engine diagnostics on the basis of offsetting the weakness of the one with the strength of another.
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| 5. |
- Ferreira, Guilherme Rezende Bessa, et al.
(author)
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Exploring a locus of maximum metal transfer stability of the short-circuiting GMAW process based on the reignition voltage peaks
- 2021
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Science and Business Media Deutschland GmbH. - 1678-5878 .- 1806-3691. ; 43:11
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Journal article (peer-reviewed)abstract
- The welding process stability is a critical factor regarding the quality of the manufactured products in the Industry. There are two approaches to assess the metal transfer stability based on droplet transfer period: scanning arc voltage or scanning wire feed speed. Studies based on each of the approaches can be found in current literature, but there are no reported studies evaluating the role of the arc reignition voltage peak (RiVP) on stability. Thus, this paper aimed to propose a novel method to assess the short-circuiting gas metal arc welding metal transfer stability based on arc reignition voltage peak distribution, via wire feed speed scanning route, and compare the effectiveness of the proposed method to the existing ones. First, the authors depicted the fundamentals of the ideal metal transfer (the most stable). A novel stability index based on the RiVP distribution was introduced. The results showed that the methodology was capable of defining a locus of maximum metal transfer stability through the arc RiVP regularity. It also demonstrated that, in a regular short-circuiting transfer mode, the RiVP obeys an expected distribution. Besides, the most regular arc reignition-related quantity was directly related to the most regular period-related characteristic. After validating the methodology, the proposed method was demonstrated to be, potentially, a novel manner to assess and seek the maximum stability of the short-circuiting gas metal arc welding process.
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| 6. |
- Garcia, Raphael Rustici, et al.
(author)
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Relevant factors for the energy consumption of industrial robots
- 2018
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : SPRINGER HEIDELBERG. - 1678-5878 .- 1806-3691. ; 40:9
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Journal article (peer-reviewed)abstract
- This work investigates the energy consumption of industrial robots in the context of automotive industry. The purpose is to identify the most influencing parameters and variables and to propose best practices with focus on energy efficiency. The analysis approach is composed of three experiments performed in a simulation environment that test different values of programming parameters and variables, such as joint speed, acceleration, robot payload. The first experiment focuses on energy consumption of robots at standstill. The second one considers the robot moving along different paths. Finally, the third one analyses how the joint friction is affected by load, speed and temperature and how it influences the energy consumption. Results show that at standstill, it is important to reduce dwell time, select an energy efficient position and reduce the programmed value of the timer responsible for turning off the servomotors. While moving, it is important to select maximum continuous termination for intermediate points and avoid low speeds. Regarding friction variation, results show that at high motor speed, low temperatures increase energy consumption. In order to evaluate the contribution of the best practices in a real environment, they are applied to a welding robotic cell of an automotive industry.
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| 7. |
- Ghadimi, P., et al.
(author)
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Study of various numerical aspects of 3D-SPH for simulation of the dam break problem
- 2012
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Nature. - 1678-5878 .- 1806-3691. ; 34:4, s. 486-491
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Journal article (peer-reviewed)abstract
- Recently, the Smoothed Particle Hydrodynamics (SPH) method has been utilized as an effective tool for capturing details of the fluid flows. The Lagrangian nature of the SPH method facilitates the modeling of the free surface flows. In the present article, different numerical features of 3D-SPH are probed to find a set of options that can be used to achieve an accurate numerical simulation of the dam break problem. Several numerical techniques such as time stepping algorithm, filter density and viscosity treatment are considered as compiling options. Twelve sets of mentioned schemes are also chosen and the elevation of free surface flow is captured. The obtained results are compared against the experimental data existing in the literature. Finally, it is concluded that the Symplectic algorithm in conjunction with density filter and SPS turbulence model can be used to achieve the desired accurate numerical results.
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| 8. |
- Ghadimi, P., et al.
(author)
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Study of water entry of circular cylinder by using analytical and numerical solutions
- 2012
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Nature. - 1678-5878 .- 1806-3691. ; 34:3, s. 225-232
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Journal article (peer-reviewed)abstract
- Water impact phenomenon in the case of a circular cylinder is an important issue in offshore industry where cross members may be in the splash zone of the incident wave. An analytical method as well as a numerical solution are employed to study the water entry problem of a circular section. The procedure for derivation of the analytical formulas is demonstrated step by step. The volume of fluid (VOF) simulation of the water entry problem is also performed to offer comparison of the results of the linearized analytical solution with a fully nonlinear and viscous fluid flow solution. To achieve this, the FLOW- 3D code is utilized. Some consideration has also been given to the points of intersection of the free surface and the body, where the singularities exist in the free surface deformation and velocities, as predicted by the linear theory. These singularities appear to be avoided in the real fluid by the formation of jets which quickly break up into sprays under the action of surface tension. Slamming force, free surface profile, impact force, pressure distribution and evolution of intersection points are also presented and comparisons of the obtained results against the results of previous studies illustrate favorable agreements.
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| 9. |
- Jouybari, Nima Fallah, et al.
(author)
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An investigation of forces on a representative surface in a pulp flow through rotating and non-rotating grooves
- 2023
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer. - 1678-5878 .- 1806-3691. ; 45:5
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Journal article (peer-reviewed)abstract
- Softwood pulp flow in rotating and non-rotating grooves is numerically simulated in the present study to investigate the fluid flow and the forces acting on a representative surface mounted in the groove. The viscosity of softwood pulp with various consistencies is available from the measurements reported in the literature providing the opportunity to examine the effects of fiber consistency on the velocity and pressure distribution within the groove. The simulations are carried out in OpenFOAM for different values of gap thickness, angular velocity and radial positions from which the pressure coefficient and shear forces values are obtained. It is found that the shear forces within the gap increase linearly with the angular velocity for all fiber consistencies investigated and in both grooves. Also, this behavior can be successfully predicted by modeling the gap flow as a Couette flow in a two-dimensional channel. Meanwhile, a more detailed analysis of the flow kinetic energy close to the stagnation point using Bernoulli’s principle is carried out to provide a better understanding of the pressure coefficient variation with angular velocity in the non-rotating groove. A comparison of pressure coefficients obtained numerically with those calculated by considering the compression effects revealed that the comparison effects are dominating in the pulp flow within the groove.
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| 10. |
- Khodabandeh, Erfan, et al.
(author)
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Numerical investigation of thermal performance augmentation of nanofluid flow in microchannel heat sinks by using of novel nozzle structure : sinusoidal cavities and rectangular ribs
- 2019
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : SPRINGER HEIDELBERG. - 1678-5878 .- 1806-3691. ; 41:10
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Journal article (peer-reviewed)abstract
- In this paper, we present a numerical simulation of a laminar, steady and Newtonian flow of f-graphene nanoplatelet/water nanofluid in a new microchannel design with factors for increasing heat transfer such as presence of ribs, curves to enable satisfactory fluid mixing and changing fluid course at the inlet and exit sections. The results of this study show that Nusselt number is dependent on nanoparticles concentration, inlet geometry and Reynolds number. As the nanofluid concentration increases from 0 to 0.1% and Reynolds number from 50 to 1000, the Nusselt number enhances nearly up to 3% for increase in fluid concentration and averagely from 15.45 to 54.1 and from 14.5 to 55.9 for geometry with and without rectangular rib, respectively. The presence of ribs in the middle section of microchannel and curves close to hot walls causes a complete mixing of the fluid in different zones. When the nanoparticles concentration is increased, the pressure drop and velocity gradient will become higher. An increased concentration of nanoparticles in contribution with higher Reynolds numbers only increases the fraction factor slightly. (The fraction factor increases nearly 37% and 35% for Re = 50 and 1000, respectively.) The highest uniform temperature distribution can be found in the first zones of fluid in the microchannel and by further movement of fluid toward exit section, because of decreasing difference between surface and fluid temperature, the growth of temperature boundary layer increases and results in non-uniformity in temperature distribution in microchannel and cooling fluid. With decrease in the concentration from 0 to 0.1%, the average outlet temperature and FOM decrease nearby 0.62% and 6.15, respectively.
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