scholarly journals Using Finite Element Approach for Crashworthiness Assessment of a Polymeric Auxetic Structure Subjected to the Axial Loading

Polymers ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1312 ◽  
Author(s):  
Ali Farokhi Nejad ◽  
Roozbeh Alipour ◽  
Mozafar Shokri Rad ◽  
Mohd Yazid Yahya ◽  
Seyed Saeid Rahimian Koloor ◽  
...  
Keyword(s):  
Analytical Solution ◽  
Compressive Loading ◽  
Computational Cost ◽  
Axial Loading ◽  
Polyurethane Foams ◽  
Absorption Enhancement ◽  
Aspect Ratios ◽  
Auxetic Structures ◽  
Element Approach ◽  
Tube Versus

Polyurethane foams are one of the most common auxetic structures regarding energy absorption enhancement. This present study evaluates the result reliability of two different numerical approaches, the H-method and the P-method, to obtain the best convergence solution. A polymeric re-entrant cell is created with a beam element and the results of the two different methods are compared. Additionally, the numerical results compare well with the analytical solution. The results show that there is a good agreement between converged FE models and the analytical solution. Regarding the computational cost, the P-method is more efficient for simulating the re-entrant structure subjected to axial loading. During the second part of this study, the re-entrant cell is used for generating a polymeric auxetic cellular tube. The mesh convergence study is performed on the cellular structures using the H- and P- methods. The cellular tube is subjected to tensional and compressive loading, the module of elasticity and Poisson’s ration to calculate different aspect ratios. A nonlinear analysis is performed to compare the dynamic response of a cellular tube versus a solid tube. The crashworthiness indicators are addressed and the results are compared with equivalent solid tubes. The results show that the auxetic cellular tubes have better responses against compressive loading. The primary outcome of this research is to assess a reliable FE approach for re-entrant structures under axial loading.

Evaluation of axial performance of tapered piles from centrifuge tests

2000 ◽  
Vol 37 (6) ◽  
pp. 1295-1308 ◽  
Author(s):  
M Hesham El Naggar ◽  
Mohammed Sakr
Keyword(s):  
Analytical Solution ◽  
Reasonable Agreement ◽  
Compressive Loading ◽  
Axial Loading ◽  
Centrifuge Modeling ◽  
Cohesionless Soil ◽  
Scale Model ◽  
Rational Approach ◽  
Centrifuge Tests ◽  
Cylindrical Piles

The performance of tapered piles under axial compressive loading was investigated using centrifuge model tests. Model tapered and cylindrical piles were installed in cohesionless soil and subjected to axial loading. The objectives of this study were to understand the performance characteristics of tapered piles and develop a rational approach for their design. The results of axial compressive loading tests on 12 one-tenth scale model piles with different taper angles in a centrifuge setup are presented and discussed. Six piles were instrumented and six piles were not. The load distribution along the shaft of instrumented piles was measured and the results were compared with an analytical solution in terms of the taper coefficient Kt. The comparison showed a reasonable agreement between Kt values established from the experiments and those obtained from the analytical solution. A simple rational approach was proposed for the design of tapered piles. The proposed approach was used to calculate the bearing capacity of the tested piles, and reasonable agreement with the measured values was obtained. The results of this study suggest that the pile taper should be limited to the top 20-25 pile diameters of the pile length for optimum efficiency.Key words: tapered piles, pile capacity, axial performance, centrifuge modeling, shaft resistance.

Analytical solution and finite element approach to the dense re-entrant unit cells of auxetic structures

2019 ◽  
Vol 230 (6) ◽  
pp. 2171-2185 ◽  
Author(s):  
M. Shokri Rad ◽  
H. Hatami ◽  
Z. Ahmad ◽  
A. Karimdoost Yasuri
Keyword(s):  
Finite Element ◽  
Analytical Solution ◽  
Finite Element Approach ◽  
Unit Cells ◽  
Auxetic Structures ◽  
Element Approach

Numerical Investigation on the Effect of Different Physiological Cancerous Breast Parameters on the Output of Microwave Ablation

2020 ◽  
Vol 3 (3) ◽  
Author(s):  
Jatin Kumar ◽  
Ramjee Repaka
Keyword(s):  
Tumor Size ◽  
Microwave Ablation ◽  
Tumor Therapy ◽  
Computational Cost ◽  
Tumor Location ◽  
Independent Study ◽  
Ablation Volume ◽  
Thermal Therapies ◽  
Key Factor ◽  
Element Approach

Abstract Microwave ablation (MWA) is a newly developed minimally invasive tumor therapy which possesses several advantages over the existing thermal therapies. Despite the several advantages, MWA also suffers same disadvantages similar to other thermal therapies like poor control over ablation volume. Sensitivity of different tissue parameters is the key factor to design a MWA protocol. In this work, sensitivity analysis has been conducted to quantify the effect of three cancerous breast parameters, viz., breast composition, tumor location, and tumor size, on the efficacy of MWA of breast cancer. Ablation volume has been taken as the indicator of the ablation efficacy during MWA procedure. A Taguchi's design of experimental approach has been utilized to optimize the number of simulations required for the analysis and then analysis of variance (ANOVA) has been performed to predict the most sensitive parameter along with their individual contribution. Finite element approach-based simulations have been performed in a multiphysics software. First, a grid-independent study has been established to optimize the number of mesh elements and to reduce the computational cost. Then, after finding the most optimum grid size, all the simulations have been performed in accordance with the protocol obtained from Taguchi's design of experiment approach and finally statistical analysis software has been used for analyzing Taguchi's design. It has been found that, the breast composition to be the most significant factor, with maximum contribution in ablation volume, among three considered factors followed by tumor location and tumor size, respectively.

Improving Steady CFD to Capture the Effects of Radial Mixing in Axial Compressors

2019 ◽  
Author(s):  
Lorenzo Cozzi ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Andrea Schneider ◽  
Pio Astrua
Keyword(s):  
Steady State ◽  
Gas Turbines ◽  
Turbulent Viscosity ◽  
Computational Cost ◽  
Axial Compressor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Axial Compressors ◽  
Rans Model ◽  
Aspect Ratios

Abstract The axial compressors of power-generation gas turbines have a high stage count, blades with low aspect ratios and relatively large clearances in the rear section. These features promote the development of strong secondary flows. An important outcome deriving from the convection of intense secondary flows is the enhanced span-wise transport of fluid properties mainly involving the rear stages, generally referred to as “radial mixing”. An incorrect prediction of this key phenomenon may result in inaccurate performance evaluation and could mislead the designers during the compressor design phase. As shown in a previous work, in the rear stages of an axial compressor the stream-wise vorticity associated with tip clearance flows is one of the main drivers of the overall span-wise transport phenomenon. Limiting it by circumferentially averaging the flow at row interfaces is the reason why a steady-state analysis strongly under-predicts radial mixing. To properly forecast the span-wise transport within the flow-path, an unsteady analysis should be adopted. However, due to the high blade count, this approach has a computational cost not yet suitable for industrial purposes. Currently, only the steady-state full-compressor simulation can fit in a lean industrial design chain and any model upgrade improving its radial mixing prediction would be highly beneficial for the daily design practice. To attain some progresses in RANS model, its inherent lack of convection of stream-wise vorticity must be addressed. This can be done by acting on another mixing driver, able to provide the same outcome, that is turbulent diffusion. In particular, by enhancing turbulent viscosity one can promote span-wise diffusion, thus improving the radial mixing prediction of the steady approach. In this paper, this strategy to update the RANS model and its application in simulations on a compressor of the Ansaldo Energia fleet is presented, together with the model tuning that has been performed using the results of unsteady simulations as the target.

Singular Perturbation Solution for a Two-Phase Stefan Problem in Outward Solidification

2019 ◽  
Author(s):  
Minghan Xu ◽  
Saad Akhtar ◽  
Mahmoud A. Alzoubi ◽  
Agus P. Sasmito
Keyword(s):  
Boundary Condition ◽  
Porous Media ◽  
Analytical Solution ◽  
Singular Perturbation ◽  
Stefan Problem ◽  
Moving Boundary ◽  
Computational Cost ◽  
Perturbation Solution ◽  
Two Phase ◽  
Moving Boundary Condition

Abstract Mathematical modeling of phase change process in porous media can help ensure the efficient design and operation of thermal energy storage and pipe freezing. Numerical methods generally require high computational power to be applicable in practice. Therefore, it is of great interest to develop accurate and reliable analytical frameworks. This study proposes a singular perturbation solution for a two-phase Stefan problem that describes outward solidification in a finite annular space. The problem solves cylindrical heat conduction equations for both solid and liquid phases, with consideration of a moving boundary condition. Perturbation method takes the advantages of small Stefan number as the perturbation parameter, which intrinsically occurs in porous media. Furthermore, a boundary-fixing technique is used to remove nonlinearity in the moving boundary condition. Two different time scales are separately expanded and evaluated to facilitate the construction of a composite asymptotic solution. The analytical solution is verified against a general numerical model using enthalpy method and local volume-averaged thermal properties. The results indicate that the temperature profile of both phases can be well modeled by singular perturbation theory. The analytical solution is found to have similar conclusions to the numerical analysis with much lesser computational cost.

Approximate analytical solutions for a class of nonlinear stochastic differential equations

2018 ◽  
Vol 30 (5) ◽  
pp. 928-944 ◽  
Author(s):  
A. T. MEIMARIS ◽  
I. A. KOUGIOUMTZOGLOU ◽  
A. A. PANTELOUS
Keyword(s):  
Analytical Solution ◽  
Differential Equations ◽  
Stochastic Differential Equations ◽  
Approximate Analytical Solution ◽  
Transition Probability ◽  
Computational Cost ◽  
Closed Form Expression ◽  
Response Process ◽  
Approximate Analytical Solutions ◽  
Constant Diffusion

An approximate analytical solution is derived for a certain class of stochastic differential equations with constant diffusion, but nonlinear drift coefficients. Specifically, a closed form expression is derived for the response process transition probability density function (PDF) based on the concept of the Wiener path integral and on a Cauchy–Schwarz inequality treatment. This is done in conjunction with formulating and solving an error minimisation problem by relying on the associated Fokker–Planck equation operator. The developed technique, which requires minimal computational cost for the determination of the response process PDF, exhibits satisfactory accuracy and is capable of capturing the salient features of the PDF as demonstrated by comparisons with pertinent Monte Carlo simulation data. In addition to the mathematical merit of the approximate analytical solution, the derived PDF can be used also as a benchmark for assessing the accuracy of alternative, more computationally demanding, numerical solution techniques. Several examples are provided for assessing the reliability of the proposed approximation.

Load transfer of fibre-reinforced polymer (FRP) composite tapered piles in dense sand

2004 ◽  
Vol 41 (1) ◽  
pp. 70-88 ◽  
Author(s):  
Mohammed Sakr ◽  
M Hesham El Naggar ◽  
Moncef Nehdi
Keyword(s):  
Analytical Solution ◽  
Load Transfer ◽  
Compressive Loading ◽  
Centrifuge Modeling ◽  
Rational Approach ◽  
Dense Sand ◽  
Reinforced Polymer ◽  
Cylindrical Piles ◽  
Confining Pressures ◽  
Fibre Reinforced Polymer

This paper describes an experimental study conducted using a large, laboratory-scale testing facility to test pile segments at different stress levels. The objectives of the study were twofold: to examine the load-transfer mechanism of tapered piles in compression, and to evaluate the effect of pile material on pile performance characteristics. The results of axial compressive loading tests on 26 pile load tests were presented using fibre-reinforced polymer (FRP) concrete composite tapered piles and steel piles. Two installation techniques were used, including conventional head driving and toe driving using a new technique. Piles were tested at different confining pressures to represent a pile segment at depths of 4.0 and 8.0 m. The load distribution along the pile shafts was measured and the results were compared with those from an analytical solution in terms of the taper coefficient Kt. The comparison showed reasonable agreement between Kt values established from the experiments and those obtained from the analytical solution. The measured toe resistance of tapered and cylindrical piles was compared with those from the analytical solution. A simple rational approach was proposed for the design of tapered piles.Key words: tapered piles, FRP, pile capacity, axial performance, centrifuge modeling, shaft resistance, toe resistance.

Three-Dimensional Large Deformation Analyses of Plate Anchor Keying in Clay

2008 ◽  
Author(s):  
Dong Wang ◽  
Yuxia Hu ◽  
Mark F. Randolph
Keyword(s):  
Large Deformation ◽  
Three Dimensional ◽  
Eccentricity Ratio ◽  
Factors Affecting ◽  
Centrifuge Testing ◽  
Aspect Ratios ◽  
Element Approach ◽  
New Type ◽  
Plate Anchors ◽  
Pulling Force

Plate anchors are a relatively new type of offshore anchorage in deep water. Plate anchors are usually installed vertically, followed by rotation under eccentric pulling force. In normally consolidated clay, the embedment loss during keying may reduce the anchor capacity significantly. The keying behaviour of rectangular anchors is investigated here using a three-dimensional large deformation finite element approach. This approach adopts mesh regeneration to avoid severe distortion of soil elements, as well as mapping the stresses and material parameters from the old to the new mesh. To study the factors affecting the embedment loss, the loading eccentricity ratio was varied from 0.17 to 1.5 for aspect ratios of the anchors of 1 and 2. The strength profile and rigidity of soil and loading orientation were also varied. The numerical results agree well with centrifuge testing data. It is found the embedment loss depends strongly on the eccentricity ratio and orientation of pulling force, while the effects of soil rigidity and anchor aspect ratio are minimal.

Impact Response of Thin-Walled Tubes: A Prospective Review

2012 ◽  
Vol 165 ◽  
pp. 130-134 ◽  
Author(s):  
Fauziah Mat ◽  
K. Azwan Ismail ◽  
S. Yaacob ◽  
O. Inayatullah
Keyword(s):  
Compressive Loading ◽  
Axial Loading ◽  
Geometrical Parameters ◽  
Axial Deformation ◽  
Thin Walled Structures ◽  
Structural Applications ◽  
Thin Walled ◽  
Energy Absorbers ◽  
Energy Absorbing ◽  
The Impact

Thin-walled structures have been widely used in various structural applications asimpact energy absorbing devices. During an impact situation, thin-walled tubesdemonstrate excellent capability in absorbing greater energy through plastic deformation. In this paper, a review of thin-walled tubes as collapsible energy absorbers is presented.As a mean of improving the impact energy absorption of thin-walled tubes, the influence of geometrical parameters such as length, diameter and wall thickness on the response of thin-walled tubes under compression axial loading are briefly discussed. Several design improvements proposed by previous researchers are also presented. The scope of this review is mainly focus on axial deformation under quasi-static and dynamic compressive loading. Other deformations, such as lateral indentation, inversion and splitting are considered beyond the scope of this paper. This review is intended to assist the future development of thin-walled tubes as efficient energy absorbing elements.

Numerical and physical modeling of bar deformation under axial loading in the channel. Part 1

2020 ◽  
Author(s):  
N.T. Ovchinnikov ◽  
F.D. Sorokin
Keyword(s):  
Numerical Model ◽  
Analytical Solution ◽  
Physical Modeling ◽  
Axial Loading ◽  
Loss Of Stability ◽  
Load History ◽  
Nonlinear Bending ◽  
Initial Shape ◽  
Bending Waves ◽  
One Step

In two parts of the work, numerical and physical modeling of the deformation of the bar in the channel under axial compression is carried out. The regularities of nonlinear bending of the bar in the plane are revealed. Bar shapes are determined by the load history and can differ at the same force value. The solution is to find the shape with the lowest potential energy. The first part of the work describes the numerical model of the bar and the results of its application. The shapes of the bar bending under gradual loading are obtained, the studies coinciding with V.I. Feodosev’s analytical solution. Further research shows that the solution to the problem has a more complex ramified structure with various additional shapes. Deformation of the bar under gradual loading occurs in the form of a sequential variant appearance of bending waves in the bar under forces determined by the degree of non-uniformity of the lengths of potentially unstable sections and forming a range of shape instability. In variant transitions from one initial shape with a loss of stability, it is possible to obtain various subsequent shapes that differ in the sequence of deformation of the sections with one number of half-waves, or the number of generated half-waves. When a straight bar is loaded in one step, an increase in the force leads to a sequential increase in the number of bending half-waves in the corresponding ranges of the existence of shapes. The results obtained can be applied to the analysis of the operation of such bar objects as drill, casing, tubing strings in the well and cased pipelines, pipelines in the well and tunnel.

Sign in / Sign up

Export Citation Format

Share Document