Numerical Investigation of Nonlinear Structural Responses in Ablation Problem

2019 ◽  
Author(s):  
Rui Fu ◽  
James Roger ◽  
Sean McDaniel ◽  
Jonathan Wenk ◽  
Alexandre Martin
Keyword(s):  
Numerical Investigation ◽  
Nonlinear Structural ◽  
Structural Responses

Identification of model-free structural nonlinear restoring forces using partial measurements of structural responses

2016 ◽  
Vol 20 (1) ◽  
pp. 69-80 ◽  
Author(s):  
Y Lei ◽  
SJ Luo ◽  
MY He
Keyword(s):  
Power Series ◽  
Structural Parameters ◽  
Structural System ◽  
Restoring Force ◽  
Model Free ◽  
Nonlinear Structural ◽  
Structural Nonlinearities ◽  
Restoring Forces ◽  
Structural Responses ◽  
Nonlinear Behaviors

Identification of nonlinear structural system is an important but challenging task for structural health monitoring. Due to the complexities of structural nonlinearities, it is hard to establish proper mathematical models for some structural nonlinear behaviors. Moreover, only partial structural responses can be measured in practice; it is essential to conduct identification of nonlinear structural systems using only partial measurements of structural responses. To cope with these issues, an algorithm is proposed in this article for the identification of some model-free structural nonlinear restoring forces using only partial measurements of structural responses. First, an equivalent linear structural system is introduced for the identification of the locations of structural nonlinearities. Then, a model-free structural nonlinear restoring force is approximated by a power series polynomial. The unknown coefficients of the power series polynomials together with other structural parameters are identified by the extended Kalman filter so that the characteristics of the behaviors of the model-free of nonlinear restoring forces can be identified. Some numerical examples including the identification of two nonlinear multi-story shear frames and a planar nonlinear truss with different structural nonlinear restoring forces are used to validate the proposed algorithm.

A Two-stage Parametric Identification of Strong Nonlinear Structural Systems with Incomplete Response Measurements

2016 ◽  
Vol 16 (04) ◽  
pp. 1640022 ◽  
Author(s):  
Lijun Liu ◽  
Ying Lei ◽  
Mingyu He
Keyword(s):  
Kalman Filter ◽  
Unscented Kalman Filter ◽  
Structural Parameters ◽  
Nonlinear Problems ◽  
Parametric Identification ◽  
Structural Systems ◽  
Two Stage ◽  
Incomplete Response ◽  
Nonlinear Structural ◽  
Structural Responses

Compared with the identification of linear structural parameters, it is more difficult to conduct parametric identification of strong nonlinear structural systems, especially when only incomplete structural responses are available. Although the extended Kalman filter (EKF) is useful for structural identification with partial measurements of structural responses and can be extended for the identification of nonlinear structures, EKF approximates nonlinear system through Taylor series expansion and is therefore not effective for the identification of strong nonlinear structural systems. Other approaches such as the unscented Kalman filter (UKF) have been proposed for the identification of strong nonlinear problems. Based on the fact that nonlinearities exist in local areas of structures, a straightforward two-stage identification approach is proposed in this paper for the identification of strong nonlinear structural parameters with incomplete response measurements. In the first stage, the locations of nonlinearities are identified based on the EKF for the identification of the equivalent linear structures. In the second stage, the UKF is utilized to identify the parameters of strong nonlinear structural systems. Therefore, the parametric identification of strong nonlinear structural parameters is simplified by the proposed approach. Several numerical examples with different nonlinear models and locations are used to validate the proposed approach.

Estimation of time to stationarity in geometrically nonlinear structural responses

2012 ◽  
Vol 331 (19) ◽  
pp. 4359-4372
Author(s):  
Aakarsh Chaudhary ◽  
S. Michael Spottswood ◽  
X.Q. Wang ◽  
Marc P. Mignolet
Keyword(s):  
Geometrically Nonlinear ◽  
Nonlinear Structural ◽  
Structural Responses ◽  
Estimation Of Time

A New Procedure for the Nonlinear Structural Response Analysis of Offshore Installations in Explosions

2014 ◽  
Author(s):  
Jeom Kee Paik ◽  
Jerzy Czujko ◽  
Sang Jin Kim ◽  
Jong Chan Lee ◽  
Bong Ju Kim ◽  
...  
Keyword(s):  
Structural Response ◽  
Response Analysis ◽  
Shell Elements ◽  
Nonlinear Structural ◽  
Offshore Installations ◽  
Industry Practice ◽  
Design Values ◽  
Structural Responses ◽  
Explosion Accidents ◽  
Nonlinear Structural Response

This paper is a sequel to the previous two papers by the authors presented at SNAME annual meetings in 2012 and 2013. The key tasks for measuring and managing risks associated with hydrocarbon explosions include defining explosion loads and computing structural responses. In industry practice, such response analysis often involves applying uniformly distributed explosion loads to structures according to their nominal design values. However, uniformly distributed loads based on nominal values of structural design may not always fully reflect the actual situations of real explosion accidents, mainly because the actual characteristics of both explosion loads and structural responses are extremely nonlinear. Therefore, it is highly desirable to identify the non-uniform distributions of explosion loads and directly apply them to structures for the response analysis. To accomplish this, technical challenges must be met in terms of refined computations for loads, structural responses and interfaces between load definitions and structural analyses. This study develops a new procedure to resolve such challenges. In this procedure, FLACS computational fluid dynamics (CFD) simulations are applied to the characterization of blast loads. ANSYS/LS-DYNA nonlinear finite element methods (using plate-shell elements) are applied for nonlinear structural response analysis, and a computer program named FLACS2DYNA is developed to automatize the direct export of the FLACS simulations to the ANSYS/LS-DYNA computations. The contribution of this study is demonstrated through an applied example using a hypothetical topside structure of a VLCC-class FPSO that is exposed to hydrocarbon explosions. This example shows that the developed procedure can enable fast, accurate and reliable nonlinear structural response analysis, and subsequently allow better assessment and management of explosion risks.

A New Procedure for the Nonlinear Structural Response Analysis of Offshore Installations in Fires

2013 ◽  
Author(s):  
Jeom Kee Paik ◽  
Jerzy Czujko ◽  
Jeong Hwan Kim ◽  
Sung In Park ◽  
Shafiqul Islam ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Thermal Response ◽  
Structural Response ◽  
Fire Risk ◽  
Response Analysis ◽  
Nonlinear Structural ◽  
Offshore Installations ◽  
Fire Loads ◽  
Structural Responses ◽  
Nonlinear Structural Response

The quantitative assessment and management of the risks associated with fire require integrated computations of fire loads and their consequences. The objective of this paper is to present a new procedure for the nonlinear structural response analysis of offshore installations during fires. The procedure comprises calculation of fire loads using computational fluid dynamics (CFD) simulation, thermal response analysis and nonlinear structural response analysis in fire which are key elements in the framework of the fire risk assessment and management. KFX code is used to perform the fire CFD simulation; whereas the analyses of both thermal and nonlinear structural responses are performed using the LS-DYNA code. Models for such analysis can be developed with shell elements to represent the structures with required accuracy. A computer program known as KFX2DYNA is applied to automatically import the results of the KFX simulations which are directly exported to LSDYNA for the analyses of both heat transfer and nonlinear structural responses, making fire risk analysis fast, accurate and reliable. An experimental scenario with a simply supported I-girder under fire is used to validate the procedure. The applicability of the procedure is demonstrated using the example of a fire in the hypothetical topside structure of a VLCC-class FPSO.

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