Finite Element Model Correlation for Offshore Structures

1992 ◽  
Vol 114 (3) ◽  
pp. 154-164 ◽  
Author(s):  
R. L. Tawekal ◽  
M. M. Bernitsas
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Offshore Structures ◽  
Offshore Structure ◽  
Numerical Predictions ◽  
Large Perturbation ◽  
Large Admissible Perturbations ◽  
Static Deflection Measurements ◽  
Model Correlation

Agreement between measured response of an offshore structure and numerical predictions using an initial finite element model (IFEM) is in general poor. An algorithm is developed, which produces an updated finite element model (UFEM) that is fully correlated with respect to modal and static deflection measurements. An incremental nonlinear methodology based on large admissible perturbations in cognate space is used to produce the UFEM by postprocessing results of the initial FEA. No other FEA or trial and error are required. Iterations within each increment are used only to correct for dependence of hydrodynamic excitation on correlation variables. The UFEM corresponds to a real structure and may differ from the IFEM in response and correlation variables by 100–300 percent depending on correlation measures and structural size. Several numerical applications for three offshore structures are used to assess the strength, limitations, and cost of the large perturbation methodology.

Comparing Measured Responses of an Offshore Structure with Operational Modal Analysis assisted Classical Model Approach

2020 ◽  
pp. 1-10
Author(s):  
Bruna Nabuco ◽  
Sandro D. Amador ◽  
Evangelos I. Katsanos ◽  
Ulf T. Tygesen ◽  
Erik Damgaard Christensen ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Modal Analysis ◽  
Element Model ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Wave Forces ◽  
Wave Load ◽  
Offshore Structure

Abstract Aiming to ensure the structural integrity of an offshore structure, wave-induced responses have been measured during normal operating conditions. Operational Modal Analysis is applied to the data obtained from continuously monitoring the structure. Sensors placed only on the topside of an offshore platform are sufficient to provide information to identify the modal properties of the structure, such as natural frequencies, damping ratios, and mode shapes. A finite element model is created and updated in line with the identified dynamic properties for applying a modal expansion technique in the interest of accessing information at any point of the structure. Wave radars are also placed at the platform from which the wave forces are calculated based on basic industrial standard models. In this way, the wave kinematics are estimated according to the linear wave theory associated with Wheeler stretching. Since this study is related to offshore structures composed by slender elements, the wave forces are estimated using Morison formulation. By assigning typical values to the drag and inertia coefficients, wave loads are estimated and applied to the updated finite element model. For the diffraction effect, the wave load has also been evaluated according to MacCamy and Fuchs theory. The responses obtained from this procedure are compared with measured responses. In addition to describing the process, this paper presents a case study to verify the theory using monitoring data from a tripod jacket. Results indicate realistic response estimation that contributes to the knowledge about the state of the structure.

Finite-Element Modelling of Ballistic Impact of Plain-Woven Aramid Fabric

2014 ◽  
Vol 553 ◽  
pp. 769-773 ◽  
Author(s):  
E.A. Flores-Johnson ◽  
J.G. Carrillo ◽  
R.A. Gamboa ◽  
Lu Ming Shen
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Finite Element Modelling ◽  
Permanent Deformation ◽  
Element Model ◽  
Ballistic Impact ◽  
Elastic Model ◽  
Numerical Predictions ◽  
Aramid Fabric ◽  
The Finite Element Model

In this work, a 3D finite-element model of the ballistic impact of a multi-layered plain-woven aramid fabric style 720 (Kevlar®129 fibre, 1420 denier, 20×20 yarns per inch) impacted by a 6.7-mm spherical projectile was built at the mesoscale in Abaqus/Explicit by modelling individual crimped yarns. Material properties and yarn geometry for the model were obtained from reported experimental observations. An orthotropic elastic model with a failure criterion based on the tensile strength of the yarns was used. Numerical predictions were compared with available experimental data. It was found that the finite-element model can reproduce the physical experimental observations, such as the straining of primary yarns and pyramidal-shaped deformation after perforation. The permanent deformation of fabric targets predicted by the numerical simulations was compared with available experimental results. It was found that the model fairly predicted the permanent deformation with a difference of about 21% when compared with experiments.

Prediction of Geometrically Induced Localization Effects Using a Subset of Nominal System Modes

2019 ◽  
Author(s):  
Thomas Maywald ◽  
Christoph R. Heinrich ◽  
Arnold Kühhorn ◽  
Sven Schrape ◽  
Thomas Backhaus
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Reduced Order Model ◽  
Vibration Measurement ◽  
Mode Shapes ◽  
Compressor Stage ◽  
Order Model ◽  
Reduced Order ◽  
Numerical Predictions

Abstract It is widely known that the vibration characteristics of blade integrated discs can dramatically change in the presence of manufacturing tolerances and wear. In this context, an increasing number of publications discuss the influence of the geometrical variability of blades on phenomena like frequency splitting and mode localization. This contribution is investigating the validity of a stiffness modified reduced order model for predicting the modal parameters of a geometrically mistuned compressor stage. In detail, the natural frequencies and mode shapes, as well as the corresponding mistuning patterns, are experimentally determined for an exemplary rotor. Furthermore, a blue light fringe projector is used to identify the geometrical differences between the actual rotor and the nominal blisk design. With the help of these digitization results, a realistic finite element model of the whole compressor stage is generated. Beyond that, a reduced order model is implemented based on the nominal design intention. Finally, the numerical predictions of the geometrically updated finite element model and the stiffness modified reduced order model are compared to the vibration measurement results. The investigation is completed by pointing out the benefits and limitations of the SNM-approach in the context of geometrically induced mistuning effects.

scholarly journals Finite Element Model Correlation of an Investment Casting Process

2014 ◽  
Vol 797 ◽  
pp. 105-110 ◽  
Author(s):  
Eva Anglada ◽  
Antton Meléndez ◽  
Laura Maestro ◽  
Ignacio Domínguez
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Investment Casting ◽  
Material Properties ◽  
Casting Process ◽  
Element Model ◽  
Experimental Measurements ◽  
Manual Adjustment ◽  
Investment Casting Process ◽  
Model Correlation

The achievement of reliable simulations, in the case of complex processes as is the investment casting, is not a trivial task. Their accuracy is significantly related with the knowledge of the material properties and boundary conditions involved, but the estimation of these values usually is highly complex. One helpful option to try to avoid these difficulties is the use of inverse modelling techniques, where experimental temperature measurements are used as base to correlate the simulation models. The research presented hereafter corresponds to the correlation of a finite element model of the investment casting process of two nickel base superalloys, Hastelloy X and Inconel 718. The simulation model has been developed in a commercial software focused specifically on metal casting simulation. The experimental measurements used as base for the adjustment, have been performed at industrial facilities. The methodology employed combines the use of an automatic tool for model correlation with the manual adjustment guided by the researchers. Results obtained present a good agreement between simulation and experimental measurements, according to the industrial necessities. The model obtained is valid for the two studied cases with the only difference of the alloy material properties. The values obtained for the adjusted parameters in both cases are reasonable compared with bibliographic values. These two circumstances suggest that the obtained correlation is appropriate and no overfitting problems exist on it.

Numerical Simulation of Rotational Behavior of Bolted Glulam Beam-to-Column Connections with Slotted-In Steel Plates

2016 ◽  
Vol 858 ◽  
pp. 22-28 ◽  
Author(s):  
Ming Qian Wang ◽  
Xiao Bin Song ◽  
Xiang Lin Gu
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Damage Evolution ◽  
Numerical Study ◽  
Material Model ◽  
Element Model ◽  
Rotational Behavior ◽  
Failure Behavior ◽  
Glulam Beam ◽  
Numerical Predictions

This paper presents the results of a numerical study on rotational behavior of bolted glulam beam-to-column connections. Since wood often exhibited complex failure behavior under different loading states, a three dimensional anisotropic damage analysis model of wood was initially developed based on continuum damage mechanics theory for progressive failure analysis of wood. The damage model basically consisted of two ingredients: the failure criterion proposed by Sandhaas was chosen to capture the damage onset; three independent damage variables were adopted to control the ductile and brittle damage evolution process of wood. This material model was implemented in a commercial available finite element method based code using a user-material subroutine. Finite element model of bolted connection coupled with the proposed material model was established to further investigate the failure modes and moment resistance of such connections. It was found that the damage evolution progress was very similar to the crack development from experimental tests. By comparing the experimental results and numerical predictions, a fair agreement of the initial stiffness and moment resistance was found with modeling error less than 3%, which implied that the finite element model was suitable to simulate the rotational behavior of such connections. This research could provide the reference for the design of bolted glulam connections in heavy timber structures.

scholarly journals Stress Concentration Factor of A Two-Planar Double KT Tubular Joint due to In-Plane Bending Loading in Steel Offshore Structures

2018 ◽  
Vol 177 ◽  
pp. 01006
Author(s):  
Prastianto Rudi Walujo ◽  
Hadiwidodo Yoyok Setyo ◽  
Fuadi Ibnu Fasyin
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Element Model ◽  
Offshore Structures ◽  
Geometrical Parameters ◽  
Offshore Structure ◽  
Wide Range ◽  
Tubular Joint

The purpose of this study is to investigate the proper Stress Concentration Factor (SCF) of a 60° two-planar DKT tubular joint of a tripod wellhead offshore structure. So far, calculation of SCF for a multi-plane tubular joint was based on the formulation for the simple/uniplanar tubular joints that yield in over/under prediction of the SCF of the joint. This situation in turn decreasing the accuracy of fatigue life prediction of the structures. The SCF is one of the most important parameters in the tubular joint fatigue analysis. The tubular joint is modelled as finite element models with bending loads acting on the braces that cover a wide range of dimensionless geometrical parameters (β, τ, γ). The effect of such parameters on the SCF distribution along the weld toe of braces and chord on the joint are investigated. Validation of the finite element model has shown good agreement to the global structural analysis results. The results of parametric studies show that the peak SCF mostly occurs at around crown 2 point of the outer central brace. The increase of the β leads to decrease the SCF. While the increase of the τ and γ leads to increase the SCF. The effect of parameter β and γ on the SCF are greater than the effect of parameter τ.

scholarly journals Model Reduction and Sensor Placement Methods for Finite Element Model Correlation

AIAA Journal ◽  
2016 ◽  
Vol 54 (12) ◽  
pp. 3941-3955 ◽  
Author(s):  
J. F. Mercer ◽  
G. S. Aglietti ◽  
A. M. Kiley
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Model Reduction ◽  
Sensor Placement ◽  
Element Model ◽  
Model Correlation
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