Combining experimental techniques with non-linear numerical models to assess the sorption of pesticides on soils

2012 ◽  
Vol 129-130 ◽  
pp. 62-69 ◽  
Author(s):  
Zoi Magga ◽  
Dimitra N. Tzovolou ◽  
Maria A. Theodoropoulou ◽  
Christos D. Tsakiroglou
Keyword(s):  
Numerical Models ◽  
Experimental Techniques ◽  
Non Linear

scholarly journals Comparison of Two Numerical Algorithms for Computing the Effects of Mistuning of Fan Flutter

2016 ◽  
Author(s):  
L. Salles ◽  
M. Vahdati
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Numerical Algorithms ◽  
Mode Shapes ◽  
Minimal Amount ◽  
Aeroelastic System ◽  
Cpu Time ◽  
Influence Coefficients ◽  
Non Linear ◽  
The Time Domain

The aim of this paper is to study the effects of mistuning on fan flutter and to compare the prediction of two numerical models of different fidelity. The high fidelity model used here is a three-dimensional, whole assembly, time-accurate, viscous, finite-volume compressible flow solver. The Code used for this purpose is AU3D, written in Imperial College and validated for flutter computations over many years. To the best knowledge of authors, this is the first time such computations have been attempted. This is due to the fact that, such non-linear aeroelastic computations with mistuning require large amount of CPU time and cannot be performed routinely and consequently, faster (low fidelity) models are required for this task. Therefore, the second model used here is the aeroelastic fundamental mistuning model (FMM) and it based on an eigenvalue analysis of the linearized modal aeroelastic system with the aerodynamic matrix calculated from the aerodynamic influence coefficients. The influence coefficients required for this algorithm are obtained from the time domain non-linear Code by shaking one blade in the datum (tuned) frequency and mode. Once the influence coefficients have been obtained, the computations of aero damping require minimal amount of CPU time and many different mistuning patterns can be studied. The objectives of this work are to: 1. Compare the results between the two models and establish the capabilities/limitations of aeroelastic FMM, 2. Check if the introduction of mistuning would bring the experimental and computed flutter boundaries closer, 3. Establish a relationship between mistuning and damping. A rig wide-chord fan blade, typical of modern civil designs, was used as the benchmark geometry for this study. All the flutter analyses carried out in this paper are with frequency mistuning, but the possible consequences of mistuned mode shapes are briefly discussed at the end of this paper. Only the first family of modes (1F, first flap) is considered in this work. For the frequency mistuning analysis, the 1F frequency is varied around the annulus but the 1F mode shapes remain the same for all the blades. For the mode shape mistuning computations, an FE analysis of the whole assembly different mass blades is performed. The results of this work clearly show the importance of mistuning on flutter. It also demonstrates that when using rig test data for aeroelastic validation of CFD codes, the amount mistuning present must be known. Finally, it should be noted that the aim of this paper is the study of mistuning and not steady/unsteady validation of a CFD code and therefore minimal aerodynamic data are presented.

Seismic Assessment and Retrofitting of an Under-Designed RC Frame Through a Displacement-Based Approach

2017 ◽  
pp. 36-58
Author(s):  
Marco Valente ◽  
Gabriele Milani
Keyword(s):  
Seismic Response ◽  
Numerical Models ◽  
Seismic Assessment ◽  
Original Structure ◽  
Rc Frame ◽  
Existing Structures ◽  
Dynamic Analyses ◽  
Non Linear ◽  
Displacement Based ◽  
Southern European Countries

Many existing reinforced concrete buildings were designed in Southern European countries before the introduction of modern seismic codes and thus they are potentially vulnerable to earthquakes. Consequently, simplified methodologies for the seismic assessment and retrofitting of existing structures are required. In this study, a displacement based procedure using non-linear static analyses is applied to a four-storey RC frame in order to obtain an initial estimation of the overall inadequacy of the original structure as well as the extent of different retrofitting interventions. Accurate numerical models are developed to reproduce the seismic response of the RC frame in the original configuration. The effectiveness of three different retrofitting solutions countering structural deficiencies of the RC frame is examined through the displacement based approach. Non-linear dynamic analyses are performed to assess and compare the seismic response of the frame in the original and retrofitted configurations.

Development and Validation of a Non-Linear Viscoelastic Viscoplastic Stress Model for a PFCB/PVDF Fuel Cell Membrane

2012 ◽  
Author(s):  
Jessica A. Wright ◽  
Michael W. Ellis ◽  
David A. Dillard ◽  
Scott W. Case ◽  
Robert B. Moore ◽  
...  
Keyword(s):  
Polyvinylidene Fluoride ◽  
Numerical Models ◽  
Proton Exchange ◽  
Mechanical Degradation ◽  
Stress Model ◽  
Uniaxial Creep ◽  
Non Linear ◽  
Viscoelastic Modulus ◽  
Linear Viscoelastic ◽  
Development And Validation

Proton exchange membranes (PEMs) in operating fuel cells are subjected to varying thermal and hygral loads while under mechanical constraint imposed within the compressed stack. Swelling during hygrothermal cycles can result in residual in-plane tensile stresses in the membrane and lead to mechanical degradation or failure through thinning or pinhole development. Numerical models can predict the stresses resulting from applied loads based on material characteristics, thus helping to guide the development of more durable membrane materials. In this work, a non-linear viscoelastic stress model based on the Schapery constitutive formulation is used with a Zapas-Crissman viscoplastic term to describe the response of a novel membrane material comprised of a blend of perfluorocyclobutane (PFCB) ionomer and polyvinylidene fluoride (PVDF). Uniaxial creep and recovery tests are used to establish the time dependent linear viscoelastic modulus as well as the fitting parameters for the non-linear viscoelastic viscoplastic model. The stress model is implemented in a commercial finite element code, Abaqus®, to predict the response of a membrane subjected to mechanical loads. The stress model is validated by comparing predicted and experimental responses for membranes subjected to stress relaxation and multiple step creep loads in uniaxial tension.

scholarly journals In-Plane Behaviour of Masonry Walls: Numerical Analysis and Design Formulations

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5780
Author(s):  
Thomas Celano ◽  
Luca Umberto Argiento ◽  
Francesca Ceroni ◽  
Claudia Casapulla
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Numerical Models ◽  
Experimental Tests ◽  
Element Model ◽  
Masonry Walls ◽  
Analysis And Design ◽  
Non Linear ◽  
Failure Loads ◽  
Modelling Approaches

This paper presents the results of several numerical analyses aimed at investigating the in-plane resistance of masonry walls by means of two modelling approaches: a finite element model (FEM) and a discrete macro-element model (DMEM). Non-linear analyses are developed, in both cases, by changing the mechanical properties of masonry (compressive and tensile strengths, fracture energy in compression and tension, shear strength) and the value of the vertical compression stress applied on the walls. The reliability of both numerical models is firstly checked by means of comparisons with experimental tests available in the literature. The analyses show that the numerical results provided by the two modelling approaches are in good agreement, in terms of both failure loads and modes, while some differences are observed in their load-displacement curves, especially in the non-linear field. Finally, the numerical in-plane resistances are compared with the theoretical formulations provided by the Italian building code for both flexural and shear failure modes and an amendment for the shape factor ‘b’ introduced in the code formulation for squat walls is proposed.

Numerical Methods for Interlink Stiffness Formulations and Parameters Sensitivity of Out-of-Plane Bending in Mooring Chains

2019 ◽  
Author(s):  
Ceasar Edward ◽  
Arun Kr. Dev
Keyword(s):  
Fatigue Life ◽  
Numerical Methods ◽  
Material Properties ◽  
Plastic Material ◽  
Numerical Models ◽  
Critical Role ◽  
Research Work ◽  
Non Linear ◽  
Out Of Plane ◽  
Vertical Displacements

Abstract Mooring components used for offshore floaters are conventionally designed only to resist axial loads with minimum resistance to bending loads. However, the unprecedented failure of four mooring lines of the Girassol Buoy followed by new modifications of similar buoys exposed the gaps in the existing methodology for failure assessment. The root cause of this failure was attributed to the critical role of out-of-plane (OPB) bending induced fatigue which reduced the fatigue life by 95%. The methodology to incorporate OPB fatigue for failure assessments involves a complex process due to numerous parameters required in the formulations and variability of mooring configurations. One of the most critical steps required to simplify methodology is the formulation of the interlink stiffness, contact stiffness and global stiffness of the chain segment. Currently, the interlink stiffness is derived from full-scale laboratory testing which is expensive and has limitations in generating data for a range of configurations. This paper focuses on producing the interlink stiffness using numerical simulations based on non-linear FE analysis to capture the complex interlink contacts mechanism at the mating surface, elastic-plastic material properties considering non-linear isotropic and non-linear kinematic behaviors during OPB response modes, and compare the numerical models based on available experimental data. The numerical model developed for this research are designed to replicate real case OPB scenarios which induces both rotation and vertical displacements at the mooring connection points. This is different from models studied so far that induces only vertical displacements to study OPB responses which produces conservative results. Further to this, an exhaustive analysis of the key OPB inducing parameters like chain diameter, types, pre-tension, instantaneous tensions, proof loading, residual stress, material properties, boundary condition etc. are required for understanding the underlying failure mechanism. This research also investigates the key OPB parameters and analyze their inter-dependencies, proportionalities and relative sensitivities to understand their overall contribution to OPB failures. This paper presents the first part of this research work which focuses on some of these key aspects to generate the simplified methodology using numerical methods. The findings of this research can be used to generate a database of interlink stiffness for application to a range of mooring configurations and develop mathematical formulations for carrying out a direct assessment of OPB fatigue in combination with tension-tension fatigue failures and proposes potential mechanisms for improving the fatigue life.

scholarly journals EXPERIMENTAL TECHNIQUES AND NUMERICAL MODELS TO DETECT POLLUTANT EMISSION IN THE TRANSPORT SECTOR

2019 ◽  
Author(s):  
GUIDO MARSEGLIA ◽  
CARLO MARIA MEDAGLIA ◽  
FRANCISCO ALONSO ORTEGA ◽  
JUAN A. MESA ◽  
DAVID CANCA
Keyword(s):  
Numerical Models ◽  
Experimental Techniques ◽  
Pollutant Emission ◽  
Transport Sector

Structural Non-Linear Models and Simulation Techniques

2016 ◽  
pp. 540-584
Author(s):  
Jorge M. Delgado ◽  
Antonio Abel R. Henriques ◽  
Raimundo M. Delgado
Keyword(s):  
Computational Models ◽  
Linear Models ◽  
Civil Engineering ◽  
Numerical Models ◽  
Probabilistic Approach ◽  
Latin Hypercube Sampling ◽  
Computational Time ◽  
Rc Structures ◽  
Simulation Techniques ◽  
Non Linear

Advances in computer technology allow nowadays the use of powerful computational models to describe the non-linear structural behavior of reinforced concrete (RC) structures. However their utilization for structural analysis and design is not so easy to be combined with the partial safety factors criteria presented in civil engineering international codes. Trying to minimize this type of difficulties, it is proposed a method for safety verification of RC structures based on a probabilistic approach. This method consists in the application of non-linear structural numerical models and simulation methods. In order to reduce computational time consuming the Latin Hypercube sampling method was adopted, providing a constrained sampling scheme instead of general random sampling like Monte Carlo method. The proposed methodology permits to calculate the probability of failure of RC structures, to evaluate the accuracy of any design criteria and, in particular, the accuracy of simplified structural design rules, like those proposed in civil engineering codes.

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