Torsional Coupling Effects Research Articles

Study on coupled mode flutter parameters of large wind turbine blades

As the size of wind turbine blades increases, the flexibility of the blades increases. In actual operation, airflow flow can cause aerodynamic elastic instability of the blade structure. Long blades may experience coupled mode flutter due to the bending torsion coupling effect, leading to blade failure. Based on Euler Bernoulli beam theory combined with Theodorsen non directional aerodynamic loads, a blade flutter characteristic equation is established through finite element method. Taking NREL 5 MW wind turbine blades as an example, analyze the influence of parameter changes in different regions of the blades on flutter characteristics. Research has found that paramter changes in the tip region of blade have the greatest impact on flutter characteristics. The vibration frequency shows an overall upward trend with the increase of waving stiffness and torsional stiffness. The flutter velocity of the three regions tends to stabilize as the bending stiffness decreases. The blade flutter speed increases with the increase of torsional stiffness. The radius of gyration is inversely proportional to the flutter frequency and flutter velocity. The impact of centroid offset on blade structure flutter frequency is minimal, but the centroid offset in the tip region has a greater impact on flutter velocity. Increasing the torsional frequency can prevent coupled mode flutter and provide a theoretical basis for blade flutter prevention design.

Refined Analysis of Spatial Three-Curved Steel Box Girder Bridge and Temperature Stress Prediction Based on WOA-BPNN

Bridges often improve the visual appeal of urban landscapes by incorporating curve elements to create iconic forms. However, it is noteworthy that curved bridges have unique mechanical properties under loads compared to straight bridges. This study analyzes a spatial three-curved steel box girder bridge based on an actual engineering case with a complex configuration. Initially, the finite element software Midas/Civil 2021 is utilized to establish a beam element model and a plate element model to examine the structural responses under dead loads in detail. Then, two different temperature gradient distribution models are employed for the temperature effect analysis. The backpropagation neural network (BPNN) optimized by the WOA algorithm is trained as a surrogate model for finite element models based on the results of temperature stress simulation. The results reveal that the bending–torsion coupling effect in the second span of the spatial three-curved steel box girder bridge is pronounced, with the maximum torque reaching 40% of the bending moment. The uneven distribution of cross-section stress is particularly significant at the vertices, where the shear lag coefficient exceeds 3. Under the action of temperature gradients, the bridge displays a warped stress state; the stress results obtained from the exponential model exhibit a 21% increase compared to BS-5400. Optimization of the weights by the WOA algorithm results in a significant improvement in prediction accuracy, and the convergence speed is improved by 30%. The coefficient of determination (R2) for predicting temperature stress can reach as high as 0.99.

Influence of Topological Defects on the Mechanical Response of Unit Cells of the Tetrachiral Mechanical Metamaterial

The primary benefit of metamaterials is that their physical and mechanical properties can be controlled by changing the structure geometry. Numerical analysis tools used in this work offer a few advantages over full-scale testing, consisting of an automated process, as well as lower material and time costs. The investigation is concerned with the behavior of unit cells of the tetrachiral mechanical metamaterial under uniaxial compression. The base material is studied within an elastic mathematical model. The influence of topological defects of the unit cell on the metamaterial properties is studied for the first time. Defects, and especially topological defects, play a decisive role in the mechanical behavior of materials and structures. The unit cell without defects reveals orthotropy of properties. Torsion of a cell with a chiral structure is induced by the rotation of all tetrachiral walls, and therefore it is sensitive to the introduction of defects. There are cases of increased torsion as well as of no compression–torsion coupling effect. In the latter case, the unit cell experiences only shear. The effective Young’s modulus is calculated to vary in the range from 23 to 57 MPa for unit cells of different topologies. With the successive introduction of defects in two walls, the studied characteristics increase, correlating with each other. A further increase in the number of defects affects the characteristics in different ways. The introduction of two more defects in the walls decreases torsion and increases Young’s modulus, after which both characteristics decrease. The introduction of topological defects in all walls of the unit cell leads to the orthotropic behavior of the cell with the opposite sign of torsion.

Modeling and model updating of a full-scale experimental base-isolated building

Large-scale seismic structural tests are crucial to validating both structural design methodologies and the effectiveness of seismic isolation devices. However, considering the significant costs of such tests, it is essential to leverage data from completed tests by taking advantage of numerical models of the tested structures, updated using data collected from the experiments, to complete additional studies that may be difficult, unsafe or impossible to test physically. However, updating complex numerical models poses its own challenges. The first contribution of this paper is to develop a multi-stage model updating method suitable for high-order models of base-isolated structures, which is motivated and evaluated through modeling and model updating of a full-scale four-story base-isolated reinforced-concrete frame building that was tested in 2013 at the NIED E-Defense laboratory in Japan. In most studies involving model updating, all to-be-updated parameters are typically updated simultaneously; however, given the observation that the superstructure in this study predominantly moves as a rigid body in low-frequency modes and the isolation layer plays a minor role in all other modes, this study proposes updating parameters in stages: first, the linear superstructure parameters are updated so that its natural frequencies and mode shapes match those identified via a subspace system identification of the experimental building responses to low-level random excitations; then, the isolation-layer device linear parameters are updated so that the natural frequencies, damping ratios and mode shapes of the three isolation modes match. These two stages break a large-scale linear model updating problem into two smaller problems, thereby reducing the search space for the to-be-updated parameters, which generally reduces computational costs regardless of what optimization algorithm is adopted. Due to the limited instrumentation, the identified modes constitute only a subset of all modes; to match each identified mode with a FEM mode, the second contribution is a procedure proposed to compare each identified mode with a candidate set of FEM modes and to select the best match. Further, nonlinear isolation-layer device models are proposed, updated and validated with experimental data. Finally, combining the isolation-layer devices’ nonlinear models with the updated superstructure linear FEM, the final result is a data-calibrated nonlinear numerical model that will be used for further studies of controllable damping and validation of new design methodologies, and is being made available for use by the research community, alleviating the dearth of experimentally-calibrated numerical models of full-scale base-isolated buildings with lateral–torsional coupling effects.

Contribution of tension–torsion coupling effect on elastic properties of chiral and anti-chiral structures

Tension-induced rotation and rotation-induced tension are two types of tension–torsion coupling (TTC). The rotation deformation along with TTC effect is a major factor that can induce the planar porous structure to exhibit the auxetic behavior, but why do some structures have numerous rotations but do not exhibit the auxetic behavior? In this study, we propose an analytical framework to address this issue by quantitatively analyzing the independent effects of direct bending of ligaments and rotation of rigid rings on the mechanical properties of the chiral and antichiral honeycombs. The chirality and the angle between force and ligament mainly affect rotation of rigid rings and direct bending of ligaments, respectively. The analytical expressions of TTC coefficients, Poisson’s ratio and Young’s modulus of antichiral-4, antichiral-3 and chiral-3 honeycombs are derived. The effects of the eccentric distance, the rotation stiffness, the tension and bending stiffness of ligaments on the TTC coefficients, Poisson’s ratio and Young’s modulus are revealed via analytical expressions and numerical results. This work provides a guideline for tailoring Young’s modulus and Poisson’s ratio by tuning the TTC effect to alter the relative strength of direct and rotation-induced deformations in the porous structures from a theoretical point of view.

Numerical investigation of bending–torsion coupling effect on aeroacoustic noise of a flexible unmanned aerial vehicle propeller

The recent explosion in interest into the use of UAVs for a wide range of commercial applications has also raised awareness of the issue of noise coming from UAVs. This paper introduces a method for predicting the aeroacoustic noise of a flexible UAV propeller while considering bending–torsion coupling. Numerical simulations of a flexible UAV propeller are conducted under hovering conditions to investigate the coupling effect on noise prediction using a fluid–structure interaction and acoustic model based on Formulation 1A of Farassat. The bending–torsion coupling leads to additional bending-induced torsional deformation along with considerable increases in noise and the overall sound pressure level. The results indicate that the noise evaluated without the coupling was underestimated compared to that evaluated with the coupling. Finally, the bending–torsion coupling is shown to be essential for precisely predicting the noise of a rotating flexible UAV propeller to respond to strengthening noise regulations.

Optimum placement and design of multiple tuned mass dampers for vibration control of asymmetric buildings

This study proposed a design procedure to determine the optimal location, moving direction, and system parameters of multiple tuned mass dampers systematically for vibration control of asymmetric buildings under dynamic loadings such as earthquake or wind excitations. A piece of computer software was developed as a postprocessor of any commercial structural analysis programs, such as ETABS, SAP2000, and so on. First, the modal parameters of target building structure were extracted from its finite element model. The optimum location and moving direction of the multiple tuned mass dampers system are determined based on the controlled mode shapes and both modal participating mass ratio and modal direction factor. Then, the optimal parameters of the multiple tuned mass dampers system were calculated by minimizing the mean square modal displacement response ratio of the controlled mode for the target building with and without multiple tuned mass dampers system. To evaluate control effectiveness, the responses of the building with and without multiple tuned mass dampers system were compared in both frequency and time domains. The analysis results from a 5-story building with different torsion-coupling degrees and a 46-story real building show that the proposed multiple tuned mass dampers system is quite effective in mitigating excessive floor vibration, base shear, and elapsed time of vibration due to earthquake excitations to enhance both structural safety and resident comfort. It is also concluded that the torsion-coupling effect should be considered in determining the optimum planar location of multiple tuned mass dampers system which is equivalent to mass increase of the multiple tuned mass dampers system and thus improves the control efficacy for asymmetric buildings.

Effects of Soil-Structure Interaction on Torsionally Coupled Base Isolated Machine Foundation under Earthquake Load

In this paper, the influence of soil-structure interaction (SSI) on a torsionally coupled turbo-generator (TG) machine foundation is studied under earthquake ground motions. The beneficial effects of base isolators in the TG foundation under earthquake ground motions are also studied duly, considering the effects of SSI. A typical TG foundation is analyzed using a three-dimensional finite element (FE) model. Two superstructure eccentricity ratios are considered to represent the torsional coupling. Soft soil properties are considered to study the effects of SSI. This research concludes that the effects of torsional coupling alter the natural frequencies, if ignored, could lead to unsafe design. The deck accelerations and displacements are increased with an increase in superstructure eccentricity. On the other hand, the deck accelerations and displacements are greatly reduced with the help of base isolators, thus confirming the beneficial use of base isolators in machine foundations to protect the sensitive equipment from the strong earthquake ground motions. However, the effects of SSI reduce the natural frequencies of the TG foundation resting on soft soil conditions and activate the higher mode participation, resulting in amplifying the response.

Theoretical analysis on the stiffness of compression–torsion coupling metamaterials

The compression–torsion coupling metamaterials constructed by cells based on chiral mechanism of inclined rods with weak transverse constraints, display superior compression–torsion properties among the metamaterials reported previously. Aiming at metamaterials of this type, a general representative cell is extracted to reveal the relationship between the load and the deformation with considering the compression–torsion coupling effect. The stiffness matrix of the chiral 3D cell is derived based on Euler beam theory and applying dummy-load method, which is expressed as functions of the geometry parameters of cell structures and the mechanical properties of base material. The analytical predictions show good agreement with the numerical simulations. Results show that there exist optimal inclined angles of the rods corresponding to the maximal shear stiffness and the maximal compression–torsion coupling stiffness, respectively, which are both determined by the ratio of circular loop diameter to inclined rod length. This work provides guidelines for the design and analysis of compression–torsion coupling metamaterials, and opens a new avenue for theoretically analyzing the deformation coupling problem.

Soil–structure interaction effect on seismic response of controlled asymmetric buildings

Lateral torsional coupling of asymmetric buildings governs their seismic response. Other than building eccentricity, the extent of this impact depends on the interaction of the building foundation with the surrounding soil – soil–structure interaction (SSI). This study investigates the seismic response of a representative asymmetric building, equipped with semi-active dampers, by accounting for the effect of SSI. Two semi-active damping schemes – friction-type and two-step viscous – are considered and their relative efficiencies are measured when compared with passive dampers. All analyses, including building eccentricity, SSI and dampers, are performed under ten earthquakes with different characteristics and peak intensities. Results obtained imply that SSI can have a significant impact on the lateral torsional coupling of the building if not realistically considered, and thus can greatly influence the seismic response of an asymmetric building. Comparative assessment between semi-active and passive dampers, with respective optimal damping parameters and placement, reveals the superiority of friction-type dampers over the others in reducing the response of the asymmetric building during seismic shaking. Nevertheless, all dampers are found to be efficient in regulating the seismic response of the asymmetric building–SSI system by lowering the adverse effect of lateral torsional coupling on the seismic response of the building.

Enhanced broadband generator of dual buckled beams with simultaneous translational and torsional coupling

Introducing coupling effects to the nonlinear generator with multiple degrees of freedom is possible to further improve its bandwidth and power to some extent. However, due to the lack of synchronization mechanism, the dynamics of multiple degrees of freedom are inclined to interfere with each other. It hinders the desired high-energy motions and the performance is thus limited. In order to address this issue, a novel translationally and torsionally coupled generator of two degrees of freedom is proposed by putting two buckled beams on common elastic supports. In contrast with the magnetically-coupled approach in convention, a synchronization mechanism has been elaborated between the two buckled beams corresponding to two degrees of freedom with the help of both translational and torsional coupling. Stable high-energy motions can be obtained without interference over a wide frequency range and the two beams reach a stable synchronized status. Investigations show that the bandwidths of the two buckled beam are increased by 20% and 50% separately. Moreover, the total power performance is enhanced to 500% in comparison with the original case of no coupling. Conducted application evaluations imply that the translational and torsional coupling effects improve the power level, which can afford a higher load situation of the temperature and humidity sensor with 40% longer working time for monitoring environment of metro system.

Analysis of pendulums coupled by torsional springs for energy harvesting

Harvesting energy from ambient sources has been a recent topic of interest. A typical linear harvester is effective only near resonance, limiting its frequency bandwidth. In order to increase the efficiency and bandwidth of harvesters, various strategies have been proposed. Using multiple harvesters in a single device can harvest enough power over wider frequency band. In the present work, the effect of torsional coupling of the harvesters for low frequency vibration energy harvesting is investigated. Two pendulums with electromagnetic induction as the energy conversion mechanism is proposed. The performance of the device is studied theoretically and numerically. Cubic polynomials are used to model the pendulum nonlinearity. Fundamental harmonic oscillation are assumed to obtain the analytical solution. The effect of torsional coupling and pendulum length on the power harvested are reported.

Modal Analysis of Laminated “CAS” and “CUS” Box-Beams

Abstract In the paper, the authors discuss the numerical and experimental modal analysis of the cantilever thin-walled beams made of a carbon-epoxy laminate. Two types of beams were considered: circumferentially asymmetric stiffness (i.e., CAS) and circumferentially uniform stiffness (i.e., CUS) beams. The layer-up configurations of the laminate were chosen to get a vibration mode coupling effect in both analysed cases. The aim of the paper was to perform the numerical and experimental modal analysis of the composite structures, when a flapwise bending with torsion coupling effect or flapwise-chordwise bending coupling effect took place. Firstly, numerical studies by the finite element method was performed. The numerical simulations were carried out by the Lanczos method in the Abaqus software package. The natural frequencies and the corresponding free vibration modes were determined. Next, the experimental modal analyses of the CAS and CUS beams were performed. The test stand was consisted of a special grip, two beams with an adhered holder, the LMS Scadas III system with a modal hammer and an acceleration sensor. Finally, the results of both methods were compared.

Static analysis of thin-walled laminated composite closed-section beams with variable stiffness

Static behavior of thin-walled laminated composite closed cross-section beams having variable stiffness is investigated in this study. The analytical model used accounts for flexural–torsional coupling and warping effects as well as the variable stiffness along the contour of the cross-section of the beam. The variable stiffness is acquired by constructing the laminates with curvilinear fibres having certain specific paths. The orientation of fibres varies by depending on the fibre path along the contour of the cross-section in each layer. Equilibrium equations are derived by use of minimum potential energy principle. Although the formulation given can be applied to any shape of the closed cross-section with straight or curved edges, preliminary numerical results are presented only for box-beams. A displacement based finite element method is developed to solve the analytical model and to predict displacements and rotations under the effect of different types of loading conditions. Numerical results are obtained for different fibre paths and lay-up configurations and compared with the available solutions in the literature also with the results of a finite element analysis software using shell element.

Retrofit Design Methodology for Substandard R.C. Buildings with Torsional Sensitivity

ABSTRACTRecent earthquakes have revealed the susceptibility of non-ductile reinforced concrete (R.C.) buildings with deficiencies related to stiffness and/or mass irregularities in plan and elevation. This paper proposes a design methodology for the seismic upgrading of rotationally sensitive substandard R.C. buildings. The methodology aims to first eliminate the effect of torsional coupling on modal periods and shapes and then modify the lateral response shape of the building in each direction so as to achieve an optimum distribution of interstory drift along the building height. A case study is used to illustrate practical application of the proposed methodology.

基于梁格法的小半径钢筋混凝土弯箱梁桥空间受力特性分析

弯箱梁桥造型优美，能很好地适应和改善道路线型，近年来被广泛地应用于城市桥梁中。但弯箱梁受力复杂，需采用空间分析方法进行分析。本文采用MIDAS/Civil建立全桥梁格模型，分析了小半径弯箱梁结构的空间受力特性，研究了其在荷载作用下的位移以及支座反力特性。通过分析空间模型的计算结果，小半径弯箱梁结构存在明显的弯扭耦合效应，并可引起弯箱梁截面的扭转以及支座反力的不均匀等现象，通过设置支座预偏心可有效消减支座反力不均匀现象。 Curved box girder bridge is beautiful, can adapt to and improve the road linearity. In recent years, it has been widely used in urban bridges. But the force of curved box girder bridge is complex, it needs to use the spatial analysis method for analysis. In this paper, the full-bridge grid model was established by MIDAS/Civil based on grillage method, and the spatial force characteristics of the small radius curved box girder were analyzed, and the displacement and bearing reaction characteristics under the load were studied. By analyzing the calculation results of the space model, it can be seen that there are obvious bending and torsional coupling effects of the small radius curved box girder structure, which can cause the torsion of the cross section of the bending box and the nonuniformity of the bearing reaction. However, there is an effective reduction of the nonuniformity of the bearing reaction by bearing eccentricity.

Biophysical characterization of cofilin-induced extension–torsion coupling in actin filaments

Cofilin makes the actin filament flexible and thermally unstable by disassembling the filament and inducing bending and torsional compliance. Actin monomers bound to cofilin are able to chemically and mechanically interact in response to external forces. In this study, we performed two molecular dynamics tensile tests for actin and cofilactin filaments under identical conditions. Surprisingly, cofilactin filaments were found to be twisted, generating shear stress caused by torsion. Additionally, analysis by plane stress assumption indicated that the extension–torsion coupling effect increases the amount of principal stress by 10%. Using elasticity and solid mechanics theories, our study elucidates the role of cofilin in the disassembly of actin filaments under tensile forces.

Seismic response of torsionally coupled building with passive and semi-active stiffness dampers

The seismic response of single-storey, one-way asymmetric building with passive and semi-active variable stiffness dampers is investigated. The governing equations of motion are derived based on the mathematical model of asymmetric building. The seismic response of the system is obtained by numerically solving the equations of motion using state-space method under different system parameters. The switching and resetting control laws are considered for the semi-active devices. The important parameters considered are eccentricity ratio of superstructure, uncoupled lateral time period and ratio of uncoupled torsional to lateral frequency. The effects of these parameters are investigated on peak lateral, torsional and edge displacements and accelerations as well as on damper control forces. The comparative performance is investigated for asymmetric building installed with passive stiffness and semi-active stiffness dampers. It is shown that the semi-active stiffness dampers reduce the earthquake-induced displacements and accelerations significantly as compared to passive stiffness dampers. Also, the effects of torsional coupling on effectiveness of passive dampers in reducing displacements and accelerations are found to be more significant to the variation of eccentricity as compared to semi-active stiffness dampers.

Torsional flexural steady state response of monosymmetric thin-walled beams under harmonic loads

Starting with Hamilton's variational principle, the governing field equations for the steady state response of thin-walled beams under harmonic forces are derived. The formulation captures shear deformation effects due to bending and warping, translational and rotary inertia effects and as well as torsional flexural coupling effects due to the cross section mono-symmetry. The equations of motion consist of four coupled differential equations in the unknown displacement field variables. A general closed form solution is then developed for the coupled system of equations. The solution is subsequently used to develop a family of shape functions which exactly satisfy the homogeneous form of the governing field equations. A super-convergent finite element is then formulated based on the exact shape functions. Key features of the element developed include its ability to (a) isolate the steady state response component of the response to make the solution amenable to fatigue design, (b) capture coupling effects arising as a result of section mono-symmetry, (c) eliminate spatial discretization arising in commonly used finite elements, (d) avoiding shear locking phenomena, and (e) eliminate the need for time discretization. The results based on the present solution are found to be in excellent agreement with those based on finite element solutions at a small fraction of the computational and modelling cost involved.

Tangent Stiffness Matrix of Spatial Beam Element Considering Bend and Torsion Coupling Effect

Based on the spatial beam-column differential equations, the slope deflection equations considering second-order and bend-torsion coupling effect are established. The additional moment caused by torsion and bend deflection are taken into account. Then the finite element pattern of spatial beam-column considering the couple effect of torsion and bend is given. The tangent stiffness matrix and relevant program for nonlinear analysis are further obtained. By the nonlinear calculation and stability analysis of single component which has high accuracy or precise solution, the precision of the FEM model given in this paper is verified by comparing the results with that given in references.