Effect of Geometry Precision and Load Distribution on Branch Mechanical Response

The main objective of this work is to check the compatibility of Finite element method (FEM) to determine the modal parameters of the rotor system and to compare the results with analytical method. Current work is an attempt to implement different finite element (FE) models for the estimation of modal parameters. Two different order elements from Beam, Axisymmetric and Solid FE models are considered. The analysis is carried out on the rotor system and the accuracy of the results and the computation time of the FE models are estimated. The FE results are compared with the analytical method. It is observed that FE model can be used to simulate even at higher order frequencies, which is a limitation of analytical model. The analysis shows that the FE results closely match with analytical method and also the study summarizes that proper choosing of FE helps in developing rotor models in both a desirable accuracy and efficiency. Finally, a Campbell diagram is generated using the analytical method and FEM. The critical speeds are also calculated from the Campbell diagram. The closeness of the results between the two methods is checked.

Recently, the hard disk drive (HDD) industry has tried to use a compatible spindle system regardless of the number of disks because of the resulting cost reduction and standardization of components. The center of gravity (CG) location predominantly affects the disk and slider off-track vibration, which is why the rocking mode of a spindle system is affected by the CG. Any changes to the CG affect the operational vibration of the spindle system. In a compatible fluid dynamic bearing (FDB) spindle system, changing the number of disks may alter the CG. Nevertheless, research into the compatibility of FDB designs has not been undertaken. In this study, FDB design parameters were selected to reduce the slider off-track vibration with variations in the CG considering a compatible spindle system. First, a verified finite element (FE) model of a spindle system was constructed. The amplitude and frequency of the rocking mode were compared between a one-disk spindle system and a two-disk spindle system using the FE model, considering the relationship between the CG location, which is changed by the number of disks, and the location of the upper and lower journal bearings. HDD prototypes were then manufactured using the improved design. Based on the manufactured spindle system, the variations in the rocking mode characteristics and slider off-track vibration were measured and operational vibration tests were performed to verify the effect of the number of disks on the slider off-track vibration. An improved FDB spindle design was developed with a reduced rocking mode, and a compatible spindle system was proposed.

Thermally induced vibration (TIV) of composite laminate subjected to suddenly applied heating is studied using finite element (FE) method in this paper. Some Python programs written by the authors are used to process the data of the analysis flow, and complete the pre- and post-process of FE models used in the four analyses. An equivalent displacement method is proposed to calculate equivalent temperature load. Dynamic responses of six composite laminates with different sizes are analyzed with solid FE models and shell FE models. The results gotten by FE method are in close proximity to that gotten by classic theory and shear theory under certain conditions. It is proved that the TIV analysis method proposed in this paper is reliable and efficient. The TIV analysis with FE method based on equivalent displacement method can solve the dynamic response of a structure due to sudden changes of temperature or suddenly applied heating.

In this paper, a finite element model updating (FEMU) method is proposed based on the response surface model (RSM) and genetic algorithm (GA) to establish a high-precision finite element (FE) model of space station scientific experiment racks. First, the fine solid and mixed FE models are established, respectively, and a comparison of the modal test results is conducted. Then, an orthogonal experimental design is used to analyze the significance of the parameters, and the variables to be modified are determined. The design parameters are sampled via the Latin hyperbolic method and are substituted into the FE model to obtain the modal parameters of the scientific experiment rack. The mapping relationship between the design and modal parameters is fitted by constructing the Kriging function, and the RSM is established. The design parameters of the scientific experiment rack are optimized via GA, and the initial FE model is updated, which has the advantage of improving the computing efficiency. Finally, the updated FE model of the experiment rack is verified by frequency sweep and random vibration tests. The experimental results show that the proposed approach has high precision and computing efficiency, and compared with the test results, the modal frequency errors of the updated model are within 5%, and the vibration response errors under random excitation of the updated model are within 7%.

This study presents the development of refined three dimensional (3D) finite element (FE) models with the ability to reliably simulate the mechanical behavior of full-scale bolted T-stub connections. FE models incorporated material nonlinearity, geometric nonlinear behavior, several contact interactions between faying surfaces, and prescribed displacements for generating initial bolt pretension. These FE models were used to compare experimental test results, which verify that advanced FE modeling methods make a notable contribution to reproducing the overall behavior of connections and components accurately, including the moment-rotation curves. In addition, the FE models provide some useful information which is difficult to obtain during physical testing, i.e., the distribution of stress and strain, friction forces between shear faying surfaces, and bolt reaction forces. The validated FE models are also used for additional parametric studies so as to comprehensively understand their response mechanisms. Moreover, the observation of FE analysis results supports the statement that connection models presented herein were designed to reach the yielding of connection components when the structural beam produces its full plastic moment at the plastic hinge.

Skull stiffness of children is of great significance to protect brain tissues during traffic accidents. In this paper, the effects of skull stiffness on traumatic brain injury (TBI) are investigated by using a validated 6-year-old child head finite element (FE) model according to Chinese standard GB/T 24550-2009 Results showed that the HIC value, intracranial pressure, Von Mises stress and shear strain of brain tissue increased with the decrease of skull stiffness during the impact of FE model with engine hood. Therefore, the injury risk of the child head decreases with the increase of skull stiffness. And the skull with higher stiffness can provide a better protection for brain tissues during traffic accidents.

Beam-like structures are the most common components in real engineering, while single side damage is often encountered. In this study, a numerical analysis of single side damage in a free-free beam is analysed with three different finite element models; namely solid, shell and beam models for demonstrating their performance in simulating real structures. Similar to experiment, damage is introduced into one side of the beam, and natural frequencies are extracted from the simulations and compared with experimental and analytical results. Mode shapes are also analysed with modal assurance criterion. The results from simulations reveal a good performance of the three models in extracting natural frequencies, and solid model performs better than shell while shell model performs better than beam model under intact state. For damaged states, the natural frequencies captured from solid model show more sensitivity to damage severity than shell model and shell model performs similar to the beam model in distinguishing damage. The main contribution of this paper is to perform a comparison between three finite element models and experimental data as well as analytical solutions. The finite element results show a relatively well performance.

There has been a growing demand for nonlinear model updating procedures in the structural dynamics community as advanced vehicles have started to incorporate nonlinearity into their designs. Finite element (FE) model updating is difficult for a nonlinear structure for several reasons: there may be many unknown parameters in the FE model so that multiple solutions may exist, and it is very expensive to compute the structure’s nonlinear normal modes from a full FE model that are an excellent metric to use for nonlinear updating. A recent work showed that some of these challenges can be overcome by updating a nonlinear reduced order model (ROM) rather than the full FE model. The updated ROM can be used to compute response statistics, stresses and ultimately life of the structure. However, one drawback of this approach is that one does not gain physical insight into which parameters in the FE model were in error, and so it is difficult to transfer the lessons learned to future FE models. This work explores the feasibility of updating a FE model to correlate with a ROM with a set of known parameters. The target ROM parameters consist of the linear stiffness and the nonlinear stiffness coefficients which have been identified previously by updating the ROM to correlate with experimental measurements. In this process an optimization routine is setup in which the free parameters are those of the FE model, such as boundary stiffness springs, imperfections, pre-stress, etc. The optimization procedure is wrapped around a ROM creation algorithm that iteratively tunes the FE parameters, creates a ROM, and evaluates the ROM parameters with respect to the target ROM in order to minimize the objective function. This work will demonstrate the procedure on a numerical example of a curved beam in order to verify its effectiveness on the nonlinear model updating.

The rail–wheel interaction can induce train and track vibrations and consequently lead to noise impact, passengers’ discomfort, high maintenance cost, etc. Due to the complexity of the rail–wheel interaction and the high cost of field tests, as well as the difficulties in data collection, numerical analyses have been widely resorted to for predicting the train and track vibrations, for which numerous numerical models have been developed. According to track modeling approaches, numerical models can be generally divided into two categories, i.e. beam models and continuum finite element (FE) models. In this paper, these two models are systematically compared and discussed. First, a typical beam model of Wu and Thompson [T. X. Wu and D. Thompson, On the parametric excitation of the wheel/track system, J. Sound Vib. 278(4) (2004) 725–747.] is introduced, based on which a modified model is then established. Secondly, a plane continuum FE model with high mesh quality is established, in which the transition mesh generation, contact treatment and element size determination are presented. Numerical tests are conducted to validate the proposed plane FE model. Finally, both the beam and the plane continuum FE models are examined through typical rail–wheel interaction examples, in which the linear response of the track as well as the rail–wheel vibrations under both a single rolling wheel and two rolling wheels are analyzed. The results show that most of the vibration trends obtained from the two models agree well with each other. Nevertheless, it is noteworthy that the continuum FE model has superiorities, especially for analyzing vibrations at higher frequencies. The present study can be of considerable help for designers and engineers in the railway industry to achieve the trade-off between the simulation demands and the computational cost.

A finite element based method for estimating natural frequencies of locally damaged homogeneous beams

This paper presents a finite element (FE) model for simulation of trawl board and pipeline pullover interaction. The considered trawl gear system is referred to as a single otter trawl. This system consists of a single trawl net, two trawl boards and a fishing vessel which are connected by steel ropes. The trawl net was modelled by a new simplified trawl net model ensuring high computational efficiency. This trawl net model can simulate the correct tension level in the steel ropes connecting the trawl net and the trawl boards during the pipeline interaction phase, which is crucial to obtain a realistic trawl board interaction behaviour. The trawl boards were modelled as 6-DOF rigid bodies which were assigned a tailormade hydrodynamic load model based on a 3-parameter interpolation scheme both for the added mass and the forward-speed induced loads. Compared to previous work, the applied interpolation scheme was extended and improved in terms of parameter choice and number of parameters. The forward-speed induced loads consist of drag and lift loads. These loads were estimated by flume tank testing considering numerous trawl board configurations in terms of angle of attack, board-seabed inclination angle and gap between the trawl board and the seabed. Detailed measurements of the trawl board applied in the flume tank test were done to obtain an accurate description of the contact geometry, the centre of gravity and the rotational mass properties. The proposed FE model was validated against model test results of trawl board pull-over considering variation of pipeline height, pipeline diameter and trawling velocity. The FE model was found to give very good agreement with the model test in terms of build-up of pipeline interaction forces, peak force level and duration. The FE model is therefore regarded as applicable for use in design analysis of pipeline and trawl board pull-over interaction.

Collapse of transmission towers due to downbursts is often initiated by local failure of key structural members, while the local failure of key structural members is related to local material and geometrical nonlinearities. This paper presents a multi-scale finite element (FE) model for the failure analysis of transmission towers under downburst-induced wind loading. The potential local failure areas of the tower are modeled by shell or solid elements, and the remaining parts by beam elements. In this way, the failure of the tower can be accurately simulated on the one hand and the computational effort can be reduced on the other hand. This paper first introduces how to determine the downburst-induced wind loading on transmission towers. Both the conventional beam and multi-scale FE models of the transmission tower are then developed and used in the failure analysis. A comparison of the failure results obtained by the two FE models show that the multi-scale FE model can effectively simulate the stress concentration of angle members around the bolt connections and the cross-section plastic collapse of key structural members, leading to a different failure pattern for the tower from the conventional FE method. It is suggested that the multi-scale FE model should be used for better accuracy in the failure analysis of transmission towers under downburst loading.

Numerical investigation on mechanical properties of cellular lattice structures fabricated by fused deposition modeling

In this paper, we discuss the dynamics of beams with multiple delaminations. The objective of the study is to use the dynamic response of the delaminated beams in health monitoring of composite structures. As a first step, we present experimental results on the vibrations of a cantilever beam with multiple delaminations. These experiments are conducted by exciting the beam with piezoelectric actuators. The response is detected by using a high-speed video camera to study the existence of delamination opening modes in a beam with multiple delaminations. Then, an analysis of natural frequencies and mode shapes, for a delaminated beam, is presented by using analytical techniques. The measured dynamic responses of the beam with multiple delaminations are also presented. The experimentally detected nonlinear response is discussed. Introduction Delaminations or interlayer cracks and impact damages are typical defects observed in composite structures. The presence of these defects changes the dynamic characteristics of the structure . Some of the specific changes in the observed dynamic characteristics include changes in natural frequencies, changes in the mode shapes and changes in damping ratios. These changes can be used to identify the existence, location and magnitude of a delamination or an impact damage, before they can grow to their critical sizes. Studies, to date, are concerned with the dynamics of beams and plates with a single delamination. In this paper, we specifically discuss the structural dynamics of a beam with multiple delaminations. This information can be used to develop health-monitoring techniques for composite beams with multiple delaminations. In an earlier paper, Luo and Hanagud studied the effects of defects, like saw-cuts, impact damage and delamination, on the structural dynamic characteristics of composite beams. They have shown that perturbations in natural frequencies and modes of a beam, due to defects, can be used for health monitoring of structures. In particular, it has been shown that an integral equation that considers perturbations in curvature modes and natural frequencies can be very effectively used to detect local defects. To distinguish delaminations from other types of monitored (identified) defects Luo and Hanagud have discussed nonlinear effects like superharmonic response in the dynamic response of a harmonically excited delaminated beam. They considered only a single delamination. In this paper we study beams with multiple delaminations. More specifically, we discuss dynamic response and the changes in natural frequencies, mode shapes due to multiple delaminations in a composite beam. One of the earliest models for vibration analysis of composite beams with delaminations was proposed by Ramkumar et al. This model simply used four Timoshenko beams connected at the delamination edges to model a composite beam with one throughwidth delamination. The predicted frequencies, based on this model, were consistently lower than the results of experimental measurements. Wang et al. improved the analytical solution by including coupling between flexural and axial vibrations of the delaminated sublaminates. Using an isotropic beam with splits and the classical beam model, they found that the calculated natural frequencies were closer to experimental results. With similar considerations, Nagesh Gummadi and Hanagud formulated a finite element solution for arbitrary composite beams. In the finite element models, they considered a classical composite beam model as well as the beam model with high order shear deformations. Mujumdar and Suryanarayan have proposed a model which imposed a constraint between the delaminated sublaminates to force them to have the same flexural displacement. This model was unable to * Ph.D. Student, School of Aerospace Engineering † Professor, School of Aerospace Engineering, AIAA Member Copyright © 1999 The American Institute of Aeronautics and Astronautics Inc. All rights reserved

Based on the elaborate 3D solid finite element (FE) model established by ABAQUS software, a pseudo-static analysis was conducted on a special-shaped concrete-filled steel tubular column composite frame structure. The FE model considers the confinement effect of both the steel tubes and the tensile bars exerting on the core concrete. The results of the numerical analysis concerning failure modes, load-displacement hysteretic curves, load-displacement skeleton curves and stiffness degradation-displacement curves demonstrate a strong correlation with the existing quasi-static test data. Furthermore, an in-depth analysis was conducted on the impact of the axial compression ratio of column on the plastic energy dissipation distribution mechanism. With an axial compression ratio of the column ranging from 0.1 to 0.55, the composite frame structure primarily relies on the energy dissipation of beams, while the columns serve as supplementary support, thereby exemplifying the principle of “strong column-weak beam.” As the axial compression ratio rises to the range of 0.6–0.8, the composite frame structure transitions a “strong beam-weak column” structural system. Combined with the longitudinal compressive strain of the steel tube at the bottom of the column, a quantitative evaluation method for seismic damage is proposed, grounded in indexes of “stiffness damage” and “energy damage.” Then, the threshold values of energy damage and stiffness damage are determined across four distinct levels: “elastic stage in small earthquake,” “elasto-plastic stage in medium earthquake,” “plastic stage in heavy earthquake” and “failure stage.” The proposed method effectively evaluate the damage severity of special-shaped CFT column composite frame structure subjected to seismic events.