Modeling of Welded Joints in a Pyramidal Truss Sandwich Panel Using Beam and Shell Finite Elements

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Ke Yuan ◽  
Weidong Zhu
Keyword(s):  
Welded Joints ◽  
Natural Frequencies ◽  
Welded Joint ◽  
Shell Element ◽  
Element Model ◽  
Modal Parameters ◽  
Main Step ◽  
Solid Element ◽  
Pyramidal Truss ◽  
Elastic Modes

Abstract Pyramidal truss sandwich panels (PTSPs) are widely used in engineering structures and their face sheets and core parts are generally bonded by the welding process. A large number of solid elements are usually required in the finite element (FE) model of a PTSP with welded joints to obtain its accurate modal parameters. Ignoring welded joints of the PTSP can save many degrees of freedom (DOFs), but significantly change its natural frequencies. This study aims to accurately determine modal parameters of a PTSP with welded joints with much fewer DOFs than those of its solid element model and to obtain its operational modal analysis results by avoiding missing its modes. Two novel methods that consider welded joints as equivalent stiffness are proposed to create beam-shell element models of the PTSP. The main step is to match stiffnesses of beam and shell elements of a welded joint with those of its solid elements. Compared with the solid element model of the PTSP, its proposed models provide almost the same levels of accuracy for natural frequencies and mode shapes for the first 20 elastic modes, while reducing DOFs by about 98% for the whole structure and 99% for each welded joint. The first 14 elastic modes of a PTSP specimen that were measured without missing any modes by synchronously capturing its two-faced vibrations through use of a three-dimensional scanning laser vibrometer (SLV) and a mirror experimentally validate its beam-shell element models created by the two proposed methods.

Quick Aeromechanical Assessment of Turbine Blades Based on Shell Element Based Models

2014 ◽  
Author(s):  
Suryarghya Chakrabarti ◽  
Letian Wang ◽  
K. M. K. Genghis Khan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Natural Frequencies ◽  
Turbine Blades ◽  
Computation Time ◽  
Shell Element ◽  
Element Model ◽  
Shell Elements ◽  
Barrier Coating ◽  
Order Of Magnitude

A fast finite element model based tool has been developed to calculate the natural frequencies of fundamental modes of cooled gas turbine bladed disk assemblies during conceptual design. The tool uses shell elements to model the airfoil, shank, and disk, and achieves order of magnitude reduction in computation time allowing exploration of a wide design space at the preliminary design stages. The analysis includes prestress effects due to centrifugal loading and approximate temperature loading on the parts. Sensitivity studies are performed to understand the relative impact of design features such as airfoil internal geometry, bond coat, and thermal barrier coating on the system natural frequencies. Critical features are selected which need to be modeled to get an accurate natural frequency estimate. The results obtained are shown to be within 5% of the frequencies obtained from a full-fidelity finite element model. A case study performed on seven blade designs illustrates the use of this tool for quick aeromechanical assessment of a large number of designs.

The Experimental Study and Numerical Estimation of Fracture Toughness of Heterogeneous Welded Joints

2013 ◽  
Vol 592-593 ◽  
pp. 173-176 ◽  
Author(s):  
Egor Moskvichev
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Welded Joints ◽  
Welded Joint ◽  
Element Model ◽  
Fracture Parameter ◽  
J Integral ◽  
Numerical Estimation ◽  
Mechanical Heterogeneity ◽  
Numerical Finite Element

In this paper the mechanical heterogeneity of welded joints was studied. The experimental results show that the mechanical properties and fracture toughness vary significantly in zones of welded joint. To estimate the fracture parameter J-integral a numerical finite-element model based on the random variation of yield strength was proposed.

Analysis of Free Vibration Characteristics and Mode Shapes of a Semi-Submersible Platform

2011 ◽  
Author(s):  
Jonas W. Ringsberg ◽  
Per Ernholm ◽  
Love Hogstro¨m
Keyword(s):  
Free Vibration ◽  
Natural Frequency ◽  
Fundamental Frequency ◽  
Natural Frequencies ◽  
Wave Spectrum ◽  
Shell Element ◽  
Element Model ◽  
Beam Element ◽  
Resonance Frequencies ◽  
Exciting Wave

The current investigation presents a global natural frequency and mode shape analysis of a semi-submersible platform. The purpose is to evaluate the separation in frequency between the semi-submersible’s global natural frequencies and the exciting wave spectrum. Two types of finite element models are compared: a beam element model and a shell element model. The main differences in the models are the level of resolution in details and model complexity. It is shown that both beam and shell element models can be used for the analysis. However, the beam element model is recommended for a first approximate assessment of the fundamental natural frequency and the interval/spectrum of global resonance frequencies compared to the wave spectrum. The shell element model is recommended when a more thorough analysis is required. In addition, the natural frequencies of the semi-submersible are calculated for free vibration in air. The fundamental frequency was 1.9 Hz for the beam element model and 1.5 Hz for the shell element model. When weights corresponding to a submerged structure in operation mode are considered, including the effects of added mass, the fundamental frequency for the first mode using the beam element model was decreased to 0.7 Hz, and to 0.6 Hz when using the shell element model. When compared to the DNV world wave spectrum’s highest frequency of 0.29 Hz it is concluded that the natural frequencies of the semi-submersible are at a sufficient distance from the exciting wave spectrum.

An Aeromechanical Screening Tool for Turbine Blades

2017 ◽  
Author(s):  
Suryarghya Chakrabarti ◽  
Andrew Grafitti ◽  
Brian Potter
Keyword(s):  
Structural Design ◽  
Screening Tool ◽  
Natural Frequencies ◽  
Turbine Blades ◽  
Shell Element ◽  
Element Model ◽  
Design Tool ◽  
Frequency Error ◽  
Concept Design ◽  
Gas Turbine Blades

A design tool has been developed to calculate the natural frequencies of shrouded or unshrouded gas turbine blades in seconds to allow designers to perform aeromechanical frequency avoidance checks in the early concept design phase. The tool derives its inputs from a pitch-line aerodynamic calculation and a 1D structural design tool and uses a NACA-based airfoil section generator to create the airfoil sections. It then generates a shell-element based finite element model for the blade and disk sector, performs a pre-stressed modal analysis, and ranks the blades according to their frequency margins with specified aerodynamic drivers. Validation studies comparing this simplified model to high-fidelity solid element FEA models show the frequency error to be below 5% for most cases. The speed of this tool allows for frequency assessment of thousands of designs in a few hours allowing the designer to perform large spacefilling DoEs and select a flow path which minimizes the chances of fundamental mode crossings in later design stages..

Factors Influencing Natural Frequencies in a Prestressed Concrete Panel for Damage Detection

2014 ◽  
Vol 69 (3) ◽  
Author(s):  
L. D. Goh ◽  
A. A. Rahman ◽  
N. Bakhary ◽  
B. H. Ahmad
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Damage Detection ◽  
Prestressed Concrete ◽  
Natural Frequencies ◽  
Element Model ◽  
Modal Parameters ◽  
Actual Structure ◽  
Modal Test ◽  
The Finite Element Model

Modal parameters such as natural frequencies, mode shapes, and damping ratios are widely used as damage indicators in the field of vibration-based damage detection. These modal parameters can be easily obtained by conducting the modal test on the actual structure or from the finite element model. However, many publications are focusing only on the relationship between the modal parameters and the changes in structural properties for damage detection. There are a limited number of publications discussing on the factors that may affect the modal parameters for damage detection. Hence, this paper provides a study on the level of influence of several factors on the natural frequencies of a prestressed concrete panel. The factors that are considered in this study are the size of element used in the numerical model, the dimension of the structural element, and the prestressing force applied in the prestressed concrete panel. The natural frequencies computed from the finite element model are also verified with the actual measured natural frequencies that are determined through the modal test conducted in the laboratory. 

scholarly journals Experimental Studies on Finite Element Model Updating for a Heated Beam-Like Structure

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Kaipeng Sun ◽  
Yonghui Zhao ◽  
Haiyan Hu
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Finite Element Model ◽  
Natural Frequencies ◽  
Model Updating ◽  
Element Model ◽  
Modal Parameters ◽  
Finite Element Model Updating ◽  
Time Varying ◽  
The Finite Element Model

An experimental study was made for the identification procedure of time-varying modal parameters and the finite element model updating technique of a beam-like thermal structure in both steady and unsteady high temperature environments. An improved time-varying autoregressive method was proposed first to extract the instantaneous natural frequencies of the structure in the unsteady high temperature environment. Based on the identified modal parameters, then, a finite element model for the structure was updated by using Kriging meta-model and optimization-based finite-element model updating method. The temperature-dependent parameters to be updated were expressed as low-order polynomials of temperature increase, and the finite element model updating problem was solved by updating several coefficients of the polynomials. The experimental results demonstrated the effectiveness of the time-varying modal parameter identification method and showed that the instantaneous natural frequencies of the updated model well tracked the trends of the measured values with high accuracy.

Evaluation of Fatigue Strength of Similar and Dissimilar Welded Joints of Modified 9Cr–1Mo Steel

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Shigeru Takaya
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Strain Distribution ◽  
Evaluation Method ◽  
Welded Joint ◽  
Element Model ◽  
Fast Breeder Reactor ◽  
Good Agreement

This paper presents an evaluation method for the fatigue strength of similar and dissimilar welded joints of modified 9Cr–1Mo steel, which is a candidate structural material for demonstration of fast-breeder reactor being developed in Japan. The discontinuity of the mechanical properties across a welded joint causes a nonhomogeneous strain distribution, and this effect should be considered in the evaluation of the fatigue strength of welded joints. In this study, a “two-element model,” which comprises base metal and welded metal, was employed. First, the strain ranges of each element are calculated, and second, the fatigue lives of each element are evaluated. Finally, the shorter fatigue life is selected as the fatigue life of the welded joint. The failure position can be also estimated by this model. The evaluation results were compared with experimental data obtained at elevated temperature, and the results were in good agreement.

Simulation of Damage Scenarios in an FRP Composite Suspension Footbridge

2005 ◽  
Vol 293-294 ◽  
pp. 599-606 ◽  
Author(s):  
R.A. Votsis ◽  
M.M. Abdel Wahab ◽  
M.K. Chryssanthopoulos
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Natural Frequencies ◽  
Element Model ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Limit States ◽  
Damage Scenarios ◽  
Frp Composite ◽  
Initial Strains

Simulations of damage scenarios were carried out using a finite element model of a newly constructed FRP composite footbridge, the Wilcott footbridge. This footbridge represents a new generation of suspension footbridges that have lightweight decks made of pultruded glass fibre reinforced polymer (GFRP) composite elements. It offers several advantages over conventional steel or concrete footbridges, e.g. speed of installation, high resistance to corrosion and saving in weight and foundations. On the other hand, its lightness and slenderness make it more sensitive to dynamic effects, both at serviceability and ultimate limit states. A finite element model using 3-D beam elements was constructed and damage scenarios were simulated and introduced in the model. The natural frequencies, mode shapes as well as time responses due to pedestrian loading were predicted. Different size of delamination in the composite deck was simulated at various locations along the bridge. The sensitivity of natural frequencies and mode shapes due to delamination were assessed by comparing the results of the damaged deck to those of the reference intact deck. The effect of changes in the cables’ initial strains on the modal parameters was also examined, and the sensitivity of modal parameters to cable degradation was assessed.

Finite Element Analysis of Drive Axle Housing Based on the Solid Element and the Shell Element

2011 ◽  
Vol 383-390 ◽  
pp. 5681-5685 ◽  
Author(s):  
Jing Shun Fu ◽  
Jun Feng Wang ◽  
Jin Wang
Keyword(s):  
Finite Element ◽  
Shell Element ◽  
Element Model ◽  
Bend Strength ◽  
Element Analysis ◽  
Stress Situation ◽  
Solid Element ◽  
Drive Axle ◽  
Strength And Stiffness ◽  
Drive Axle Housing

The finite element model of drive axle housing was built by using the solid element and the shell element respectively. Vertical bend strength and stiffness under 2.5 times of fully load of the drive axle housing were calculated by finite element method. By comparing the results of the vertical bend strength and stiffness of both models, we could know that both of the two models can be used to analyze the whole stress situation of drive axle housing. Because there were fewer elements of drive axle housing model based on shell element, the amount of final calculation was less. It is more feasible to analyze the whole stress situation of drive axle housing by establishing drive axle housing based on shell element.

Evaluation of Fatigue Strength of Similar and Dissimilar Welded Joints of Modified 9Cr-1Mo Steel

2014 ◽  
Author(s):  
Shigeru Takaya
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Strain Distribution ◽  
Welded Joint ◽  
Element Model ◽  
Fast Breeder Reactor ◽  
Weld Joints ◽  
Homogeneous Strain

This paper presents evaluation methods of fatigue strength of similar and dissimilar welded joints of modified 9Cr-1Mo steel which is a candidate structural material for a demonstration fast breeder reactor being developed in Japan. The discontinuity of mechanical properties across welded joint causes a non-homogeneous strain distribution, and this effect should be taken into account for evaluation of fatigue strength of weld joints. In this study, ‘2-element model’, which is consisted of base metal and weld metal, was employed. Firstly, strain ranges of each element are calculated, and secondly fatigue lives of each element are evaluated. Finally, shorter fatigue life is chosen as fatigue life of the weld joint. Failure position can be also estimated by this model. Evaluation results were compared with experimental data at elevated temperature, and it was shown that they agree well.

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