Unsymmetric extensions of Wilson’s incompatible four‐node quadrilateral and eight‐node hexahedral elements

2021 ◽  
Author(s):  
Ying‐Qing Huang ◽  
Yuan‐Fan Yang ◽  
Ji‐Zhen Wang ◽  
Xiao‐Chuan Liu ◽  
Hai‐Bo Chen
Keyword(s):  
Hexahedral Elements

Finite Element Analysis of the Distributed Vibration Absorbers for Structural Noise Control

2005 ◽  
Author(s):  
Ashwini Gautam ◽  
Chris Fuller ◽  
James Carneal
Keyword(s):  
Finite Element ◽  
Numerical Model ◽  
Base Plate ◽  
Element Model ◽  
Fe Model ◽  
Vibration Absorbers ◽  
Element Analysis ◽  
Poroelastic Media ◽  
Hexahedral Elements ◽  
Component Models

This work presents an extensive analysis of the properties of distributed vibration absorbers (DVAs) and their effectiveness in controlling the sound radiation from the base structure. The DVA acts as a distributed mass absorber consisting of a thin metal sheet covering a layer of acoustic foam (porous media) that behaves like a distributed spring-mass-damper system. To assess the effectiveness of these DVAs in controlling the vibration of the base structures (plate) a detailed finite elements model has been developed for the DVA and base plate structure. The foam was modeled as a poroelastic media using 8 node hexahedral elements. The structural (plate) domain was modeled using 16 degree of freedom plate elements. Each of the finite element models have been validated by comparing the numerical results with the available analytical and experimental results. These component models were combined to model the DVA. Preliminary experiments conducted on the DVAs have shown an excellent agreement between the results obtained from the numerical model of the DVA and from the experiments. The component models and the DVA model were then combined into a larger FE model comprised of a base plate with the DVA treatment on its surface. The results from the simulation of this numerical model have shown that there has been a significant reduction in the vibration levels of the base plate due to DVA treatment on it. It has been shown from this work that the inclusion of the DVAs on the base plate reduces their vibration response and therefore the radiated noise. Moreover, the detailed development of the finite element model for the foam has provided us with the capability to analyze the physics behind the behavior of the distributed vibration absorbers (DVAs) and to develop more optimized designs for the same.

Automatic 3-D Crack Propagation Calculations in Industrial Components: A Pure Hexahedral versus a Combined Hexahedral-Tetrahedral Approach

2007 ◽  
Vol 348-349 ◽  
pp. 45-48
Author(s):  
Guido Dhondt
Keyword(s):  
Crack Propagation ◽  
Computing Time ◽  
Propagation Direction ◽  
Hexahedral Elements ◽  
Crack Propagation Direction ◽  
Low Weight ◽  
Out Of Plane ◽  
Hexahedral Meshes ◽  
Crack Faces

In recent years, increased loading and low weight requirements have led to the need for automatic crack tracing software. At MTU a purely hexahedral code has been developed in the nineties for Mode-I applications. It has been used extensively for all kinds of components and has proven to be very flexible and reliable. Nevertheless, in transition regions between complex components curved cracks have been observed, necessitating the development of mixed-mode software. Due to the curvature of the crack faces, purely hexahedral meshes are not feasible, and therefore a mixture of hexahedral elements at the crack tip, combined with tetrahedral in the remaining structure has been selected. The intention of the present paper is to compare both methods and to point out the strength and weaknesses of each regarding accuracy, complexity, flexibility and computing time. Furthermore, difficulties arising from the out-of-plane growth of the crack such as the determination of the crack propagation direction are discussed.

Three-Dimensional Parametric Finite-Volume Homogenization of Periodic Materials with Multi-Scale Structural Applications

2018 ◽  
Vol 10 (04) ◽  
pp. 1850045 ◽  
Author(s):  
Qiang Chen ◽  
Guannan Wang ◽  
Xuefeng Chen
Keyword(s):  
Finite Volume ◽  
Three Dimensional ◽  
Functionally Graded ◽  
Attractive Alternative ◽  
Matrix Assembly ◽  
Functionally Graded Composite ◽  
Multi Scale ◽  
Hexahedral Elements ◽  
Stiffness Matrices ◽  
Structural Applications

In order to satisfy the increasing computational demands of micromechanics, the Finite-Volume Direct Averaging Micromechanics (FVDAM) theory is developed in three-dimensional (3D) domain to simulate the multiphase heterogeneous materials whose microstructures are distributed periodically in the space. Parametric mapping, which endorses arbitrarily shaped and oriented hexahedral elements in the microstructure discretization, is employed in the unit cell solution. Unlike the finite-element (FE) technique, the expressions for local stiffness matrices are derived explicitly, enabling efficient global stiffness matrix assembly using an easily implementable algorithm. To demonstrate the accuracy and efficiency of the proposed theory, the homogenized moduli and localized stress distributions produced by the FE analyses are given for comparisons, where excellent agreement is always obtained for the 3D microstructures with different geometrical and material properties. Finally, a multi-scale stress analysis of functionally graded composite cylinders is conducted. This extension further increases the FVDAM’s range of applicability and opens new opportunities for pursuing other areas, providing an attractive alternative to the FE-based approaches that may be compared.

Scale Resolving CFD Investigations of Aerothermal Field and Emissions of a Lean Burn Aeroengine Combustor

2021 ◽  
Author(s):  
S. Paccati ◽  
L. Mazzei ◽  
A. Andreini ◽  
S. Patil ◽  
S. Shrivastava ◽  
...  
Keyword(s):  
Pressure Fluctuations ◽  
Computational Cost ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Tetrahedral Mesh ◽  
Main Stream ◽  
Nox Emissions ◽  
Lean Burn ◽  
Emission Data ◽  
Hexahedral Elements

Abstract Due to the increasingly stringent international limitations in terms of NOx emissions, the development of new combustor concepts has become extremely important in order for aircraft engines to comply with these regulations. In this framework, lean-burn technology represents a promising solution and several studies and emission data from production engines have proven that it is more promising in reducing NOx emissions than rich-burn technology. Considering the drawbacks of this combustion strategy (flame stabilization, flashback or blowout or the occurrence of large pressure fluctuations causing thermo-acoustics phenomena) as well as the difficulties and the high costs related to experimental campaigns at relevant operating conditions, Computational Fluid Dynamics (CFD) plays a key role in deepening understanding of the complex phenomena that are involved in such reactive conditions. During last years, large research efforts have been devoted to develop new advanced numerical strategies for high-fidelity predictions in simulating reactive flows that feature strong unsteadiness and high levels of turbulence intensity with affordable computational resources. In this sense, hybrid RANS-LES models represent a good compromise between accurate prediction of flame behaviour and computational cost with respect to fully-LES approaches. Stress-Blended Eddy Simulation (SBES) is a new global hybrid RANS-LES methodology which ensures an improved shielding of RANS boundary layers and a more rapid RANS-LES “transition” compared to other hybrid RANS-LES formulations. In the present work, a full annular aeronautical lean-burn combustor operated at real conditions is investigated from a numerical point of view employing the new SBES approach using poly-hexcore mesh topology, which allows to adopt an isotropic grid for more accurate scale-resolving calculations by means of fully regular hexahedral elements in the main stream. The results are compared to experimental data and to previous reference numerical results obtained with Scale Adaptive Simulation formulation on a tetrahedral mesh grid in order to underline the improvements achieved with the new advanced numerical setup.

Aerothermal Optimization of Fully Cooled Turbine Blade Tips

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Valeria Andreoli ◽  
James Braun ◽  
Guillermo Paniagua ◽  
Cis De Maesschalck ◽  
Matthew Bloxham ◽  
...  
Keyword(s):  
Turbine Blade ◽  
Heat Load ◽  
Performance Enhancement ◽  
Navier Stokes ◽  
Multi Objective Optimization ◽  
Multi Objective ◽  
Hexahedral Elements ◽  
Sst Model ◽  
Blade Tip ◽  
Novel Strategy

Optimal turbine blade tip designs have the potential to enhance aerodynamic performance while reducing the thermal loads on one of the most vulnerable parts of the gas turbine. This paper describes a novel strategy to perform a multi-objective optimization of the tip geometry of a cooled turbine blade. The parameterization strategy generates arbitrary rim shapes around the coolant holes on the blade tip. The tip geometry performance is assessed using steady Reynolds-averaged Navier–Stokes simulations with the k–ω shear stress transport (SST) model for the turbulence closure. The fluid domain is discretized with hexahedral elements, and the entire optimization is performed using identical mesh characteristics in all simulations. This is done to ensure an adequate comparison among all investigated designs. Isothermal walls were imposed at engine-representative levels to compute the convective heat flux for each case. The optimization objectives were a reduction in heat load and an increase in turbine row efficiency. The multi-objective optimization is performed using a differential evolution strategy. Improvements were achieved in both the aerodynamic efficiency and heat load reduction, relative to a conventional squealer tip arrangement. Furthermore, this work demonstrates that the inclusion of over-tip coolant flows impacts the over-tip flow field, and that the rim–coolant interaction can be used to create a synergistic performance enhancement.

Method of Volume Coordinates — from Tetrahedral to Hexahedral Elements

2007 ◽  
pp. 381-381
Author(s):  
Hongguang Li ◽  
Song Cen ◽  
Yuqiu Long ◽  
Zhangzhi Cen
Keyword(s):  
Hexahedral Elements

Finite element remeshing in metal forming using hexahedral elements

2003 ◽  
Vol 141 (3) ◽  
pp. 395-403 ◽  
Author(s):  
M.L. Alves ◽  
J.L.M. Fernandes ◽  
J.M.C. Rodrigues ◽  
P.A.F. Martins
Keyword(s):  
Finite Element ◽  
Metal Forming ◽  
Hexahedral Elements

scholarly journals EQsimu: a 3-D finite element dynamic earthquake simulator for multicycle dynamics of geometrically complex faults governed by rate- and state-dependent friction

2019 ◽  
Vol 220 (1) ◽  
pp. 598-609 ◽  
Author(s):  
Dunyu Liu ◽  
Benchun Duan ◽  
Bin Luo
Keyword(s):  
Finite Element ◽  
Message Passing Interface ◽  
Fault System ◽  
Second Phase ◽  
Finite Element Code ◽  
Earthquake Cycle ◽  
Hexahedral Elements ◽  
Earthquake Simulator ◽  
State Dependent ◽  
Geometrically Complex

SUMMARY We develop a finite element dynamic earthquake simulator, EQsimu, to model multicycle dynamics of 3-D geometrically complex faults. The fault is governed by rate- and state-dependent friction (RSF). EQsimu integrates an existing finite element code EQdyna for the coseismic dynamic rupture phase and a newly developed finite element code EQquasi for the quasi-static phases of an earthquake cycle, including nucleation, post-seismic and interseismic processes. Both finite element codes are parallelized through Message Passing Interface to improve computational efficiency and capability. EQdyna and EQquasi are coupled through on-fault physical quantities of shear and normal stresses, slip-rates and state variables in RSF. The two-code scheme shows advantages in reconciling the computational challenges from different phases of an earthquake cycle, which include (1) handling time-steps ranging from hundredths of a second to a fraction of a year based on a variable time-stepping scheme, (2) using element size small enough to resolve the cohesive zone at rupture fronts of dynamic ruptures and (3) solving the system of equations built up by millions of hexahedral elements. EQsimu is used to model multicycle dynamics of a 3-D strike-slip fault with a bend. Complex earthquake event patterns spontaneously emerge in the simulation, and the fault demonstrates two phases in its evolution. In the first phase, there are three types of dynamic ruptures: ruptures breaking the whole fault from left to right, ruptures being halted by the bend, and ruptures breaking the whole fault from right to left. As the fault bend experiences more ruptures, the zone of stress heterogeneity near the bend widens and the earthquake sequence enters the second phase showing only repeated ruptures that break the whole fault from left to right. The two-phase behaviours of this bent fault system suggest that a 10° bend may conditionally stop dynamic ruptures at the early stage of a fault system evolution and will eventually not be able to stop ruptures as the fault system evolves. The nucleation patches are close to the velocity strengthening region. Their sizes on the two fault segments are different due to different levels of the normal stress.

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