Structural Modal Analysis Research Articles

Numerical investigation of a large composite wind turbine with different spar profiles using finite-element method

We currently notice a substantial growth in the wind energy sector worldwide. This growth is expected to be even faster in the coming years. This means that a massive number of wind turbine blades will be produced in the forthcoming years. There is a large potential for materials savings in these blades. The analysis of designed blade is done in dynamic loading. Five types of spars cross-section are taken in this work. The blade and spar are of composite material. The Finite element modal analysis of designed blade is done in ABAQUS. The scope of the present work is to investigate the structural modal analysis of full-scale 48m fiberglass composite wind turbine blades for 5MW horizontal axis wind turbine and through this to assess the potential for materials savings and consequent reductions of the rotor weight. The entire wind turbine can benefit from such weight reductions through decreased dynamics loads and thus leave room for further optimization. A numerical work has been used to address the most adequate spar shape and to get an understanding of the complex structural behavior of wind turbine blades. Five different types of structural reinforcements helping to prevent undesired structural elastic mechanisms are presented. Comparisons of the eigenfrequencies observed in the full-scale tests are presented and conclusions are drawn based on the mechanisms found.

Advances in swift analysis of structures: Near-regular structures, and optimal analysis and design

In this paper a review of optimal analysis of structures is presented. Different methods of swift analyses are employed for various problem formulations. Depending on the problem at hand, a proper combination of graph products, sub-structuring methods, finite difference method and manipulating the stiffness matrix manipulation is selected to achieve the most efficient design. Design problems can be classified as three types. The first type includes the solution of near-regular structures using graph products and sub-structuring methods. These structures consist of two groups. In the first group, the main structure contains some additional members with respect to its corresponding regular structure while the structures in the second group contain some additional nodes with respect to the corresponding regular structures. The second type of problems includes the simultaneous optimal analysis and optimal design of structures. The presented method is applicable to an arbitrary structure and the optimal solution is obtained by manipulating the stiffness matrices and taking advantages of the iterations during design process. The third type of problems includes the efficient modal analysis of structures using a combined finite difference method and graph products. Boundary-value and initial-value differential equations are solved using finite difference method and graph products, and then the method is applied to the dynamic equations of modal analysis.

Floor Dynamic Assessment on Laboratory due to Ground Borne Vibrations Using ModalV Analysis from Passing Vehicles

High-tech development on laboratory with high resolution and sensitive device is increased nowadays. This equipment requires very sensitive location to accommodate in a special room, because it may cause improper functioning for a certain devise which required low level of vibration. Due to this problem, the aim of this study are to perform the structural response on two story laboratory subjected to ground vibration input due to traffics and to assess the level of vibration at the floor. The vibrations input are measured by using portable equipment called Laser Doppler Vibrometer. The field measurement is done at the laboratory Block E, Faculty of Mechanical and Manufacturing Engineering at Universiti Tun Hussein Onn Malaysia (UTHM). Finite element ANSYS software is fully utilized to model the building structure and perform analysis in order to determine structural modal and transient analysis for the building. Time history response from ANSYS post-processing is transferred into ModalV analysis in MATLAB software in order to evaluate the vibration criteria level of the floor according to specific overseas guideline. It was found that the vibration response on the middle slab of the first floor at level Vibration Criteria, VC-A or maximum particle velocity level at 50μm/s. Vibration Criteria (VC) curve analysis on floor slab indicated the highest vibration will occur at the middle of floor slab and the lowest vibration will occur at the edge of slab which near the column and below VC-E level for ground floor slab.

Modal analysis of structures under non-stationary excitation

The search for mathematical–numerical models to be applied in the design or optimization of civil structures may require adjustment and validation based on experimental data. However, in many cases, when performing dynamic assessment in field structures, it is common to face the situation where it is impossible to stop the running of certain equipment. In this case, all measurements performed on the building and the neighboring structures will be corrupted by noise generated during the operation of these machines. Clearly, many parameter estimation algorithms used to characterize the dynamic behavior of a structure, which are based on the assumption of prior knowledge of the input force in their formulations, may give poor results. In this context, a modal analysis procedure based on the adaptive filter RLS/QRD is described. In this analysis, the measured vibration signal is corrupted by a harmonic noise, in particular, in the presence of signals from the actual machine or other nearby machines. The specific characteristics of the modeling and the hypotheses associated with the harmonic signals are explained. The fact that the excitation force is considered not to be time-invariant in the model, but the frequency varies over time, allows the modal parameters to be identified even under non-stationary conditions. In order to investigate the influence of harmonic noise on the estimated values, a numerical model of the ASCE benchmark structure was used to simulate some practical situations.

Structural Strength and Modal Analysis of a Certain Type of Heavy Vehicle Frame

This article make a research based on a certain type of heavy vehicle, In the research, we have made some analyses on structure reliability of the heavy truck with the assistance of some simulation platforms, such as computer aided design, finite element analysis, etc.. Based on the establishment of a correct finite element analysis model, analysis method is mainly about some research of the frame, such as typical working conditions of static analysis and modal analysis. Through these work, we can have a better understanding about the static and dynamic characteristic of the frame, so that we can find out the advantages and disadvantages of the car.

Fuzzy variational principle for modal analysis of structures and its application

In this paper, the modal analysis to estimate eigenvalue and eigenvector of structures with fuzzy parameters is presented. By introducing fuzzy parameters into the Rayleigh quotient variation, the fuzzy variational principle is developed. The fuzzy finite element method is proposed as the application of the fuzzy variational principle. The proposed fuzzy finite element method can obtain fuzzy eigenvalues and fuzzy eigenvectors directly. However, when the conventional fuzzy finite element methods are used for fuzzy analysis, the fuzzy parameters have to be transformed into the interval parameters before the calculation and the fuzzy results are subsequently constructed by the interval results. The proposed method avoids these roundabout procedures in comparison with the conventional fuzzy finite element methods. Therefore, the proposed method can reduce the computational cost and increase computational efficiency. Numerical examples are presented to illustrate the validity and feasibility of the proposed method.

REINFORCED CONCRETE ELEMENTS SUBJECTED TO FIRE ATTACK

In these days of rapid urbanization the frequency of accidents due to fire are high. Structural sustenance thereafter is always doubtful. Non availability of technical literature on concrete behavior at elevated temperatures is the reason for this shortcoming. Even if such information is available, it is too inadequate to predict the longevity of the structure and its utility for occupation. In this backdrop the present study using FEM approach is taken up to evaluate the extent of damage due to fire attack making use of MSC Nastran. The accidents due to fire are more frequently caused by electric short circuiting in the control panel rooms in high raised buildings. The damage caused to column elements is often considered more critical as the columns are the principal load carrying members transferring loads from the superstructure to footings. In the present study heat propagation in a portion of a column member subjected to heat of 1000 0 C acting for duration of two hours is evaluated using MSC Nastran. The temperature variation across the thickness of concrete is studied considering the variation of thermal conductivity with temperature and porosity. The propagation of heat and the corresponding distress to concrete is determined from surface to the central core of the column along the shorter dimension. The output results obtained from the transient thermal analysis module of Nastran are fed as inputs to the structural analysis module to obtain the stresses and strains caused by fire. A large data of such information with varying parameters of temperature, duration of fire attack and concrete properties is proposed to be generated to be used later as set of training patterns to train a BOPN based neural net paradigm. The information from the neural net output would be used for working out the sizes of equivalent structural elements in the distressed structure. The revised structural configuration with the distressed RC element replaced by equivalent elements should facilitate the structural assessment.

Investigation of the Effect of Structural System on the Behaviour of the Behavior of the Buildings with Sheer-Wall Frame System

This research aims to study and to compare structural members load carrying capacity for frame structure and shear wall- frame structure. Comparisons are made for different column dimensions and different locations of shear walls. Commercial software package, ideCAD Static 7, is employed for dynamic modal analysis of structures.

Follower Effect of Internal Pressure on Modal Analysis of a Space Inflatable Structure

The stress distribution and modal behavior of a space inflatable torus was investigated by nonlinear finite element numerical method. This paper focused on the effect of follower pressure on the modal analysis of the torus, including the effect of configuration change and follower pressure stiffness, and focused on validating the follower pressure stiffness FEM model and its applicability to modal analysis. Research shows that the changed configuration slightly increases the natural frequencies. The follower pressure stiffness significantly reduces the natural frequencies and changes mode shapes order. The modal results are in good agreement with the corresponding shell theory solutions, indicating that the finite element model of the follower pressure stiffness for the inflatable structure modal analysis in this paper is accurate enough and reasonable.

온실기초의 구조물-지반 상호작용 해석을 위한 유한요소 모델링

In this study, structural behavior of plastic greenhouse foundation was investigated using rational finite element modeling for structures which have different material properties each other. Because the concrete foundation of plastic greenhouse and soil which surround and support the concrete foundation have very different material property, the boundary between two structures were modeled by a interface element. The interface element was able to represent sliding, separation, uplift and re-bonding of the boundary between concrete foundation and soil. The results of static and dynamic analysis showed that horizontal and vertical displacement of concrete foundation displayed a decreasing tendency with increasing depth of foundation. The second frequency from modal analysis of structure including foundation and soil was estimate to closely related with wind load.

Predicting wind-induced vibrations of high-rise buildings using unsteady CFD and modal analysis

This paper investigates the wind-induced vibration of the CAARC standard tall building model, via unsteady Computational Fluid Dynamics (CFD) and a structural modal analysis. In this numerical procedure, the natural unsteady wind in the atmospheric boundary layer is modeled with an artificial inflow turbulence generation method. Then, the turbulent flow is simulated by the second mode of a Zonal Detached-Eddy Simulation, and a conservative quadrature-projection scheme is adopted to transfer unsteady loads from fluid to structural nodes. The aerodynamic damping that represents the fluid–structure interaction mechanism is determined by empirical functions extracted from wind tunnel experiments. Eventually, the flow solutions and the structural responses in terms of mean and root mean square quantities are compared with experimental measurements, over a wide range of reduced velocities. The significance of turbulent inflow conditions and aeroelastic effects is highlighted. The current methodology provides predictions of good accuracy and can be considered as a preliminary design tool to evaluate the unsteady wind effects on tall buildings.

Stochastic Dynamic Analysis of Structures with Spatially Uncertain Material Parameters

This paper investigates the uncertainty quantification in structural dynamic problems with spatially random variation in material and damping parameters. Uncertain and locally varying material parameters are represented as stochastic field by means of the Karhunen–Loève (KL) expansion. The stiffness and damping properties of the structure are considered uncertain. Stochastic finite element of structural modal analysis is performed in which modal responses are represented using the generalized polynomial chaos (gPC) expansion. Knowing the KL expansions of the random parameters, the nonintrusive technique is employed on a set of random collocation points where the structure deterministic finite element model is executed to estimate the unknown coefficients of the polynomial chaos expansions. A numerical case study is presented for a cantilever beam with random Young's modulus involving spatial variation. The proportional damping constants are estimated from the experimental modal analysis. The expected value, standard deviation, and probability distribution of the random eigenfrequencies and the damping ratios are evaluated. The results show high accuracy compared to the Monte-Carlo (MC) simulations with 3000 realizations. It is also demonstrated that the eigenfrequencies and the damping ratios are equally affected from material uncertainties.

Structural Analysis of Solid Rocket Motor Grain with Aging and Damage Effects

The nonlinear viscoelastic behavior of composite solid propellants is studied by using a three-dimensional thermoviscoelastic constitutive model. In this model, the effects of the time-dependent Poisson ratio, aging, damage, and thermoviscoelasticity are considered. Viscoelastic constitutive equations are numerically discretized into an incremental form by using integration algorithms. An Abaqus-based user material subroutine is presented, and a structural analysis module for solid rocket motor grain is built. Based on the analysis module, the structural responses of solid rocket motor grain are analyzed when subjected to typical loadings during its service life. Obtained results indicate that, differing from the classic linear viscoelastic model, the present model gives satisfactory numerical results closely consistent to the actual performance variation of the propellant. The designed structural analysis module could be applied to the structural analysis for practical solid rocket motors.

Integrated aeroelastic and control analysis of wind turbine blades equipped with microtabs

This paper presents the results of an investigation into the performance of different controllers in active load control of wind turbine blades equipped with microtabs. A bang–bang (BB) controller, a linear quadratic regulator (LQR) a proportional integral derivative (PID) and a sliding mode controller (SMC) are synthesised for load alleviation. The performance of the synthesised controllers in load alleviation is evaluated by employing WTAC (Wind Turbine Aeroelastic and Control), a wind turbine simulator incorporating an unsteady aerodynamic module, a structural analysis module and a control module. The variable-speed pitch-controlled NREL-5 MW is adopted as the case study. Using frequency domain analysis it is shown that for the studied case all controllers have more or less the same performance at rejecting the first rotational frequency loads. It is also shown that all controllers are more effective at rejecting loads with lower frequencies. BB and PID controllers, although capable of rejecting low frequency loads, may cause amplification of loads with higher frequencies. Investigating the performance of four controllers at different wind speeds for the studied wind turbine, it is observed that the effectiveness of BB and PID controllers reduces with wind speed but on the other hand SMC and LQR perform better at higher wind speeds. Introducing a new parameter, life index, the performance of different controllers in terms of the actuation wear is investigated. It is shown that LQR cause less actuation wear compared to SMC, while having comparable performance in load alleviation.

Importance of Enclosed Gas for Modal Analysis of Space Inflatable Structure

The stress distribution and modal characteristics of a space inflatable torus is investigated using the nonlinear finite element method. This paper focused on the effect of enclosed air on the modal analysis of the torus, including the effect of follower pressure load and the effect of the interaction between the enclosed air and the torus structure. Research shows that follower pressure stiffness significantly reduces the natural frequencies and changes mode shapes order. The fluid-structure interaction obviously reduces the natural frequencies, and the in-plane translation mode is observed. Follower pressure stiffness has no effect on the in-plane translation mode. Fluid-structure interaction decreases the natural frequencies of the modal considering the follower load effect, but it does not change mode shapes order. The effect of enclosed gas seriously reduces the natural frequencies, changes mode shapes order, and produces the in-plane translation mode.

Design of a Micro-Nano Positioning Platform Based on Stick-Slip Driving

Micro-nanopositioning platform is a core component for micro-nanooperation. The static and dynamic characteristics of platform will determine its precision level. This paper presented a new 2-D micro-nanoplatform based on stick-slip driving. By using static structural module and modal analysis module of ANSYS software, the stress and natural frequency of pedestal were analyzed. The driving frequency of piezoelectric ceramic was selected far away from the natural frequency to avoid resonance. Dynamic performance of pedestal was also analyzed with ANSYS transient module. Simulation results show that the presented platform has excellent static and dynamic performance.

Application of SVD-TLS Based Parameter Estimation Method in Aircraft Structural Modal Parameter Identification

Structural modal analysis is an important element in design and testing of an aircraft, but the determination of the model order is a difficulty, in order to solve this problem, this paper advanced a Singular Value Decomposition and Total Least Squares combined method to determine the model order, and then identify the aircraft structural modal parameters. Simulation in using of aircraft flight test telemetry vibration data prove that the model order determined by this method is reasonable, and can be used to aircraft structural modal parameters identification.

Influence of Pole and Slot Combinations on Magnetic Forces and Vibration in Low-Speed PM Wind Generators

In this paper, radial forces and torque ripple characteristics are investigated in permanent magnet (PM) machines having different pole and slot combinations. Using the PM machines with concentrated windings could be beneficial in direct-drive wind generators since it is possible to reduce the size and weight of the generator. The PM machines with concentrated windings having a large number of poles are compared to investigate the effect of pole and slot combinations on force and vibration characteristics in low-speed generators. Cogging torque waveforms and torque ripple are investigated using time-stepping finite-element analysis. Analysis of radial forces is presented, including investigation on radial force density distribution, total forces on teeth, and time-dependent force waveforms on a tooth. Structural analysis and experimental modal analysis are performed on the prototype generator. The main mode of vibration in the prototype machine is observed experimentally and the results are in good agreement with the simulations.

Structural Strength and Modal Analysis of Heavy Truck Driving Axle Housing

The automobile drive axle housing is an important safety component in vehicle. The 3D model of the drive axle housing is established in CATIA,Based on the actual use conditions for a heavy truck drive axle housing, this paper used finite element analysis software ANSYS to analyze the strength, stiffness and modal of the axle housing, which results show that the design of the axle housing is rational. These results of static analysis and modal analysis can provide some references for the development of new products and the structure optimization design in the future.

Design of wideband vibration-based electromagnetic generator by means of dual-resonator

This paper describes the design of a wideband electromagnetic energy harvester that utilizes a novel dual-resonator method to improve the operational frequency range of the vibration-based generator. The device consists of two separate resonator systems (coil and magnet), which each comply with their respective resonance frequencies. This is because both resonators are designed in such a way that both magnet and coil components will oscillate at an additive phase angle, and hence create greater relative motion between the two dominating resonance frequencies, which realizes the wideband generator. Each resonator system consists of a distinctive cantilever beam, one attached with four magnets and steel keepers, the other attached with a copper coil and stainless steel holder as the free end mass. Both cantilevers are clamped and fitted to a common base that is subjected to a vibration source. Basic analytical models are derived and a numerical model is implemented in MATLAB-Simulink. Electromagnetic, structural modal and static mechanical analysis for the design of the prototype are completed using ANSYS finite element tools. For a 0.8ms−2 acceleration, the open-loop voltage obtained from the experiment shows a good correlation with those from the simulation. Peak induced voltage is measured to be 259.5Vrms as compared to 240.9Vrms from the simulator at 21.3Hz, which implies an error range of 7.7%. The results also indicate that there is a maximum of 58.22% improvement in the induced voltage within the intermediate region which occurs at the intersection point between the output response plots of two single resonator generators.