Structural Geometric Nonlinearities Research Articles

Stability Analysis of Construction Factors for Partially Cable-Stayed Bridges with Multiple Towers and High Piers

Partially cable-stayed bridges have the characteristics of continuous rigid-frame bridges and cable-stayed bridges, making them a novel composite bridge system. This study focuses on the construction project of a multi-tower high-pier curved partially cable-stayed bridge to investigate the bridge’s stability during construction. The Midas/Civil software was used to establish a model for key construction stages of the bridge, considering structural linear elasticity and geometric nonlinearity. The study examines the impact of static wind loads, asymmetric construction of the main girder, closure sequence, and the load and detachment of the hanging basket on the bridge’s stability during construction. The results indicate that static wind loads have a significant impact on structural geometric nonlinearity, with a maximum reduction of 4.99%. Asymmetric construction at both ends of the main girder can cause structural instability and should be avoided. The geometric nonlinearity stability coefficient for the hanging basket load decreased by 10.83% during the maximum no-cable stage and by 7.84% during the cable stage, significantly affecting the stability during construction. A bridge closure sequence of side-span, secondary midspan, and midspan provides the most stable condition during the construction phase. The results of this study can inform the construction of similar partially cable-stayed bridges.

Effects of structural geometric nonlinearities on the transonic aeroelastic characteristics of wing

The structural geometric nonlinearity has a great influence on the transonic aeroelastic characteristics of aircraft wings, which is an important problem for the aerodynamic and structural design of wing. In this paper, a CFD/CSD coupling method based on the high precision in-house solver is first established, and the reliability of the CFD and the CFD/CSD coupling method is then verified. Subsequently, the effects of geometric nonlinearity on the transonic aeroelastic characteristics of wing under different dynamic pressures are studied. The results show that: (1) At low dynamic pressure conditions, for geometric linear wing structure, limit-cycle oscillation occurs at various angles of attack, and the limit-cycle oscillation amplitude decreases with the increases of angle of attack. At low angle of attack, the wing deformation characteristics are dominated by first bending and first torsion, and the first torsion weaken as the angle of attack increases. For the geometric nonlinear wing structure, the limit-cycle oscillation occurs only at an attack angle of 0° As the angle of attack increases, the structural displacement eventually exhibits static deformation characteristics. (2) Under high dynamic pressure conditions: the displacement of geometric linear wing structure presents a divergent trend. For geometric nonlinear wing structure, the limit-cycle oscillation amplitude decreases first and then increases with the increase of the angle of attack. At low angle of attack, the deformation characteristics of the wing are dominated by first bending and first torsion. With the increase of the angle of attack, the first torsion weakens, while the second bending strengthen. With the further increase of the angle of attack, the second bending weaken and become co-dominated by the first bending and first torsion. It can be seen from the above results that the aeroelastic characteristics of both the geometric linear structure and the geometric nonlinear structure wings are significantly different. These findings provide valuable insights for the meticulous design of aircraft wings.

Aeroelastic reduced-order modeling for efficient static aeroelastic analysis considering geometric nonlinearity

The computational fluid dynamic/computational structural dynamic (CFD/CSD) coupling method plays an important role in static aeroelastic problems accounting for structural geometric nonlinearity. However, a huge computational burden comes from the CFD simulation, which also dominates the computational cost of the CFD/CSD coupling method. Therefore, this paper presents a reduced-order framework for steady aerodynamics to replace the CFD simulation, which is then coupled with the CSD solver for efficient static aeroelastic analysis considering geometric nonlinearity. Results first show that the proposed approach is capable of accurately predicting the surface pressure distribution of a high-aspect-ratio wing in its rigid undeformed shape at different Mach numbers and angles of attack, with at most a 2.5% relative error compared to CFD simulation. In addition, the geometrically nonlinear structure, a seminal benchmark without a tip slender body, is simulated by a three-dimensional open-source finite element solver coupled with either the CFD solver or the proposed reduced-order models (ROMs). The results demonstrate that the proposed ROM/CSD coupling approach can reflect the deformation and surface pressure distribution at static aeroelastic equilibrium with high accuracy and efficiency, thereby reducing the total computational cost at least five times while maintaining reasonable accuracy.

Multi-objective Design Optimization of Structural Geometric Nonlinearities for Response Attenuation of VLBI Antennae Subject to Aerodynamic Turbulence

Multi-objective Design Optimization of Structural Geometric Nonlinearities for Response Attenuation of VLBI Antennae Subject to Aerodynamic Turbulence

Three-dimensional nonlinear aerostatic stability analysis of long-span suspension bridges under skew wind

Based on the aerostatic force model under skew wind, considering the nonlinear and three-dimensional effects of aerostatic forces and also structural geometric nonlinearity, a method of three-dimensional nonlinear aerostatic stability analysis under skew wind is presented, and the corresponding computational procedure (SNAA-SW) is developed. By taking a suspension bridge- the Runyang suspension bridge over the Yangtze River as example, 3D nonlinear aerostatic stability analysis of the bridge under skew wind is conducted, and the skew wind effect on the aerostatic stability of long-span suspension bridges is ascertained. The results show that the skew wind effect does not change the aerostatic instability mode of suspension bridges, which shows a spatial bending-torsion coupled instability mode as the same as normal wind case. The skew wind has positive and negative effects on the aerostatic stability of suspension bridge under different wind attack angles, and the evolutions of critical wind speed of aerostatic instability with wind yaw angle are completely different from the cosine rule as proposed by the skew wind decomposition method, for most cases, the lowest critical wind speed of aerostatic instability occurs under skew wind. With the increase of wind yaw angle, the skew wind effect on the critical wind speed of aerostatic instability becomes more prominent, and the influence is between −10.7% and 8.1%. Therefore, the skew wind effect needs to be accurately considered in the aerostatic stability analysis of long-span suspension bridges in particular at large wind yaw angles.

Energy harvesting from the gust response of membrane wing using piezoelectrics

Micro-air vehicles face challenges in aerodynamic and endurance. This paper presents a novel gust response-based membrane wing energy harvester to solve these issues. An aero-electro-mechanical model based on CFD/CSD coupling method is established to investigate the dynamic response and the energy harvesting performance of this energy harvester under harmonic gust loads. The geometric nonlinearity of structure and aerodynamic nonlinearity are considered in this paper. The harmonic gust loads were obtained from a Navier–Stokes CFD solver based on unstructured meshes. The large deformation electro-mechanical finite element model was built based on the updated Lagrangian formulation and the principle of virtual work. The mean power density is defined to evaluate the energy harvesting performance. The effects of the external load resistance, the PVDF patch location, the gust amplitude and frequency, and Reynold number are studied, respectively. The results show that the optimal resistance of this energy harvester is 1.6kΩ, and the flexibility of the membrane wing improves the aerodynamic and energy harvesting performance greatly through increases the amplitude of odd super harmonics. The PVDF location has a relatively small impact on the energy harvesting performance except near end surfaces. The PVDF patch located at 0.1c–0.9c all can get better energy harvesting performance. When the equivalent angle of attack of gust amplitude exceeds 4 deg, the energy harvesting performance decreases slightly due to the formation and convection of leading-edge vortex. A sustained output power density of 5.31mW/cm3 is harvested at Re=25,000. The present work provides an effective theoretical basis for further studying energy harvesting of Micro air vehicles.

Lateral Parametric Vibration of Footbridge under Pedestrian Excitation considering the Time-Delay Effect

Pedestrian excitation may consequently cause large-scale lateral vibration of the long-span softness of footbridges. Considering the influence of structural geometric nonlinearity, a nonlinear lateral parametric vibration model is established based on the relationship between force and speed. Taking the London Millennium Footbridge as an example, the Galerkin method is applied to formulate parametric vibration equations. In addition, the multi-scale method is used to analyze the parametric vibration of footbridge system theoretically and numerically. The paper aims to find out the reasons for the large-scale vibration of the Millennium Footbridge by calculating the critical number of pedestrians, amplitude-frequency, and phase-frequency characteristics of the Millennium Footbridge during parametric vibration. On the other hand, the paper also studies the influence parameters of the vibration amplitude as well as simulates the dynamic response of the bridge during the whole process of pedestrians on the footbridge. Finally, the paper investigates influences of the time-delay effect on the system parameter vibration. Research shows that: the model established in the paper is reliable; the closer the walking frequency is to two times of the natural frequency, the fewer number of pedestrians are required to excite large vibrations; when the number of pedestrians exceeds the critical number in consideration of nonlinear vibration, the vibration amplitude tends to be stable constant-amplitude vibration, and the amplitude of vibration response is unstable constant-amplitude vibration when only linear vibration is considered; the following factors have an impact on the response amplitude, including the number of pedestrians on footbridge per unit time, damping, initial conditions, and the number of pedestrians in synchronized adjustment. At last, when considering the lag of the pedestrian’s force on the footbridge, the time-lag effect has no effect on the amplitude but has an effect on the time needed to reach a stable amplitude.

Random vibration of pretensioned rectangular membrane structures under heavy rainfall excitation

This paper analytically and experimentally investigates the random vibration problem of pretensioned rectangular membrane structures under heavy rainfall. An analytical model is firstly proposed. In this model, the heavy rainfall is modeled as a series of discretized pulse load whose amplitude follows the non-Gaussian distribution; then, the nonlinear governing equation and corresponding Fokker Planck Kolmogorov (FPK) equation of membrane structures are derived and solved by the perturbation method, considering both the geometrical nonlinearity of structure and the non-Gaussian type of load; consequently, the analytical solutions of the probability density function (PDF), mean and standard deviation of displacement response can be obtained. An artificial heavy rainfall experimental system is then developed. This system is used to (i) verify the analytical model and (ii) evaluate the effects of rainfall intensity, pretension level, and material properties. The results show that the displacement follows the significant non-Gaussian distribution and proves strong nonlinear characteristics with increasing rainfall intensity and pretension. The proposed analytical model can guide engineers to design membrane structures from the perspective of probability.

Aeroelastic oscillations of a pitching flexible wing with structural geometric nonlinearities: Theory and numerical simulation

This paper focuses on the derivation of an analytical model of the aeroelastic dynamics of an elastically mounted flexible wing. The equations of motion obtained serve to help understand the behaviour of the aeroelastic wind tunnel setup in question, which consists of a rectangular wing with a uniform NACA 0012 airfoil profile, whose base is free to rotate rigidly about a longitudinal axis. Of particular interest are the structural geometric nonlinearities primarily introduced by the coupling between the rigid body pitch degree-of-freedom and the continuous system. A coupled system of partial differential equations (PDEs) coupled with an ordinary differential equation (ODE) describing axial-bending-bending-torsion-pitch motion is derived using Hamilton's principle. A finite dimensional approximation of the system of coupled differential equations is obtained using the Galerkin method, leading to a system of coupled nonlinear ODEs. Subsequently, these nonlinear ODEs are solved numerically using Houbolt's method. The results that are obtained are verified by comparison with the results obtained by direct integration of the equations of motion using a finite difference scheme. Adopting a linear unsteady aerodynamic model, it is observed that the system undergoes coalescence flutter due to coupling between the rigid body pitch rotation dominated mode and the first flapwise bending dominated mode. The behaviour of the limit cycle oscillations is primarily influenced by the structural geometric nonlinear terms in the coupled system of PDEs and ODE.

Response Reduction Factor for SMRF 3D Frame Buildings on Sloppy Ground

Lateral forces are key factors in the design of building structure and in general these forces are evaluated using linear static method with the incorporation of response reduction factor. The actual intensity of lateral force is minimized by response reduction factor. However IS Code 1893:2016 does not give information about the components of response reduction factor. The value mentioned in IS code may be based on expert engineering judgment without any scientific basis. The Present research work focus on the estimation of response reduction factor (R) of SMRF frames considering slope terrain without any impairment in slope in Zone V. Fifteen frame models are prepared according to the guideline of IS Code 456:2000 and lateral load on frame was assigned as per IS 1893:2016 (Part-1) for the research purposes. Evaluation of response Reduction Factor according to Applied Technical Council (ATC-19) is carried out which stated that response reduction factor is the product of Strength factor, Redundancy factor and Ductility factor. Pushover analysis also termed as nonlinear static analysis under displacement control method is performed on the analytical models by an integrated finite element software for structural analysis and design called ETABS 2017. P-delta governs the geometrical non-linearity of structure. It has been observed over strength of regular structure is more as compared to irregular geometrical model whereas the ductility reduction factor does not show any significant trend. Moreover, all the models are limited in 6 story only with same structural property additional research is needed considering wider set of parameters framework.

Array of nanostrings electromagnetically interacting through repelling Lorentz forces

The collective stability behavior of a planar array of parallel nanostrings interacting through electromagnetic Lorentz forces is analyzed. The repelling coupling forces between the neighboring strings, organized in a snake-like arrangement and designed to deflect in a vertical, perpendicular to the array plane, direction, are generated solely by an electric current of alternating directions, which also results in the Joule heating of the strings. The analysis of the associated linearized eigenvalue problem provides the critical current corresponding to a push-out buckling with an intrinsic out-of-plane “zig-zag” mode. This bifurcation-type buckling is shown to precede the string loosening due to Joule heating, and to occur, in nano strings of realistic dimensions, at current density lower than the melting- or electromigration-related limits. The postbuckling behavior, governed by the inherent structural geometric and electromagnetic nonlinearities, is studied analytically and numerically. The results demonstrate the competing effects of the initial string tension and of the Joule heating on the array responses. In arrays constituting of finite numbers of strings, the critical buckling current is confined in a region bounded by the values obtained for the single string and infinite arrays.

Nonlinear Responses of a Slender Wing With a Store

The aeroelastic characteristics of the slender wing with store have been studied for several years. However, the nonlinear aeroelastic behaviors of the wing-store system have not been understood thoroughly. In this paper, the nonlinear aeroelastic model of a slender wing with a store is constructed. In the model, the geometric structural nonlinearity of the wing, and the kinematic nonlinearities of the wing and the store are considered. Two unsteady aerodynamic models are both employed to determine the aerodynamic loads. One is the linear unsteady aerodynamic model based on Wagner function, and the other is the nonlinear ONERA aerodynamic model. Simulation results are given to show that for the cases of employing the linear unsteady aerodynamic model based on Wagner function, the bifurcation diagrams are very complex and change with the variations of store position. For the cases of using the nonlinear ONERA model, the bifurcation diagrams are very simple and insensitive to the variations of the store position. Additionally, with the decrease of store spanwise coordinate, the system bending oscillation equilibrium position is reduced to zero, and the maximum absolute value of the bending response peak is also decreased. With the increase of the horizontal distance between the wing elastic center and the store mass center, the system response peak is decreased. Moreover, it is found that for the systems with the linear unsteady aerodynamic model based on Wagner function, the obtained response peak is larger and the nonlinear critical velocity is smaller than those with the ONERA model.

Study of seismic performance of super long-span partially earth-anchored cable-stayed bridges

To investigate the seismic performance of long-span partially earth-anchored cable-stayed bridge, a super long-span partially earth-anchored cable-stayed bridge scheme with main span of 1400m is taken as example, structural response of the bridge under E1 seismic action is investigated numerically by the multimode seismic response spectrum and time-history analysis, seismic behavior and also the effect of structural geometric nonlinearity on the seismic responses of super long-span partially earth-anchored cable-stayed bridges are revealed. The seismic responses are also compared to those of a fully self-anchored cable-stayed bridge with the same main span. The effects of structural parameters including the earth-anchored girder length, the girder width, the girder depth, the tower height to span ratio, the inclination of earth-anchored cables, the installation of auxiliary piers in the side spans and the connection between tower and girder on the seismic responses of partially ground-anchored cable-stayed bridges are investigated, and their reasonable values are also discussed in combination with static performance and structural stability. The results show that the horizontal seismic excitation produces significant seismic responses of the girder and tower, the seismic responses of the towers are greater than those of the girder, and thus the tower becomes the key structural member of seismic design, and more attentions should be paid to seismic design of these sections including the tower bottom, the tower and girder at the junction of tower and girder, the girder at the auxiliary piers in side spans; structural geometric nonlinearity has significant influence on the seismic responses of the bridge, and thus the nonlinear time history analysis is proposed to predict the seismic responses of super long-span partially earth-anchored cable-stayed bridges; as compared to the fully self-anchored cable-stayed bridge with the same main span, several stay cables in the side spans are changed to be earth-anchored, structural stiffness and natural frequency are both increased, the seismic responses of the towers and the longitudinal displacement of the girder are significantly reduced, structural seismic performance is improved, and therefore the partially earth-anchored cable-stayed bridge provides an ideal structural solution for super long-span cable-stayed bridges with kilometer-scale main span; under the case that the ratio of earth-anchored girder length to span is about 0.3, the wider and higher girder is employed, the tower height-to-span ratio is about 0.2, the larger inclination is set for the earth-anchored cables, 1 to 2 auxiliary piers are installed in each of the side spans and the fully floating system is employed, better overall structural performance is achieved for long-span partially earth-anchored cable-stayed bridges.

Aerodynamic stability analysis of geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction

This paper studies the aerodynamic stability of a tensioned, geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction. Considering flow separation, the wind field around membrane structure is simulated as the superposition of a uniform flow and a continuous vortex layer. By the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics, aerodynamic pressure acting on membrane surface can be determined. And based on the large amplitude theory of membrane and D\'Alembert\'s principle, interaction governing equations of wind-structure are established. Then, under the circumstance of single-mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction governing equations into a system of second-order nonlinear differential equation with constant coefficients. Through judging the frequency characteristic of the system characteristic equation, the critical velocity of divergence instability is determined. Different parameter analysis shows that the orthotropy, geometrical nonlinearity and scantling of structure is significant for preventing destructive aerodynamic instability in membrane structures. Compared to the model without considering flow separation, it\'s basically consistent about the divergence instability regularities in the flow separation model.

Nonlinear aeroelastic analysis of high-aspect-ratio wings using indicial aerodynamics

A new approach for calculating the unsteady aerodynamic loads based upon the indicial functions concept in combination with a fully third-order nonlinear structural model has been developed to analyze the aeroelastic behavior of high-aspect-ratio wings over the entire range of subsonic flow. The resulting aeroelastic equations including all structural geometric nonlinearities associated with large deformations and mass distributions, along with nonlinear terms due to mass imbalance at wing’s cross section, are then rewritten in the state-space form, introducing an efficient and appropriate approach to use in both eigenvalue and time response analysis. To validate the developed aeroelastic equations, the linear and nonlinear aeroelastic behaviors of a specified wing are compared with those presented for an incompressible aerodynamic case. Quantitative and qualitative agreement between the present results and available ones confirms the unsteady indicial aerodynamics, nonlinear structural modeling, and, consequently, the developed nonlinear aeroelastic model. By changing the wing model and applying the unsteady compressible aerodynamic loads, the nonlinear aeroelastic behavior of Goland wing is then investigated, including the flutter boundary, limit cycle oscillations, pre-flutter, flutter, and post-flutter time responses, phase plane diagrams, and also the effect of flight conditions such as altitude and air speed on the aeroelastic behavior. The results represent the necessity of applying appropriate Mach-dependent aerodynamic loads to provide reasonable description of the aeroelastic analysis in the compressible flight speed regime.

Effects of Externally Mounted Store on the Nonlinear Response of Slender Wings

The nonlinear characteristics of slender wings have been studied for many years, and the influences of the geometric structural nonlinearity on the postflutter responses of the wing have been received significant attention. In this paper, the effects of the external store on the nonlinear responses of the slender wing will be discussed. Based on the Hodges–Dowell beam model, the dynamical equations of the wing which include the geometric structural nonlinearity and store effects are constructed. The unsteady aerodynamic loading of the wing will be calculated by employing Wagner function and strip theory. The slender body theory is adopted to get the aerodynamic forces of the store. The Galerkin method is used to obtain the state equations of the system and the appropriate mode combination is obtained for the cases studied in this paper. Numerical simulations are given to show that the store spanwise position and the distance between the store mass center and the elastic center of the wing are two important factors which will affect the nonlinear characteristics of the wing. These two parameters will induce the occurrence of quasi-periodic motion and branch structure in bifurcation diagrams to the system. The peak of postflutter response is also related to these parameters and the lower response peak can be obtained when the store mass center is in front of the elastic center. The models and results are helpful to the design procedure of the slender wing with store in the preliminary stage.

Compliant assembly variation analysis of thin-walled structures based on the absolute nodal coordinate formulation

PurposeThin-walled structures inevitably always have manufacturing deviations, which affects the assembly quality of mechanical products. The assembly quality directly determines the performances, reliability and service life of the products. To achieve the automatic assembly of large-scale thin-walled structures, the sizing force of the structures with deviations should be calculated, and its assembling ability should be studied before assembly process. The purpose of this study is to establish a precise model to describe the deviations of structures and to study the variation propagation during assembly process.Design/methodology/approachCurved thin-walled structures are modeled by using the shell element via the absolute nodal coordinate formulation. Two typical deviation modes of the structure are defined. The generalized elastic force of shell elements with anisotropic materials is deduced based on a continuum mechanics approach to account for the geometric non-linearity. The quasi-static method is introduced to describe the assembly process. The effects of the deviation forms, geometrical parameters of the thin-walled structures and material properties on assembly quality are investigated numerically.FindingsThe geometric non-linearity of structure and anisotropy of materials strongly affect the variation propagation and the assembly quality. The transformation and accumulation effects of the deviations are apparent in the multiple assembly process. The constraints on the structures during assembly can reduce assembly deviation.Originality/valueThe plate element via the absolute nodal coordinate formulation is first introduced to the variation propagation analysis. Two typical shape deviation modes are defined. The elastic force of structures with anisotropic materials is deduced. The variation propagation during the assembly of structures with various geometrical and material parameters is investigated.

Aeroelastic effect on modal interaction and dynamic behavior of acoustically excited metallic panels

This paper details the study of the aeroelastic effect on modal interaction and dynamic behavior of acoustically excited square metallic panels with fully clamped edges using finite element method. The first-order shear deformation plate theory and von Karman nonlinear strain–displacement relationships are employed to consider the structural geometric nonlinearity caused by large vibration deflections. Piston aerodynamic theory and Gaussian white noise are used to simulate the aerodynamic load and the acoustic load, respectively. Motion equations are derived by the principle of virtual work in the physical coordinates and then transformed into the truncated modal coordinates with reduced orders. Runge–Kutta method is employed to obtain the system response, and the modal interaction mechanism is quantitatively valued by the modal participation distribution. Results show that in the pre-/near-flutter regions, in addition to the dominant fundamental resonant mode, the first twin companion antisymmetric modes can be largely excited by the aeroelastic coupling mechanism; thus, aeroelastic modal participation distribution and the spectrum response can be altered, while the dynamic behavior still exhibits linear random vibrations. In the post-flutter region, the dominant flutter motion can be enriched by highly ordered odd order super-harmonic motion occurs due to 1:1 internal resonances. Correspondingly, the panel dynamic behavior changes from random vibration to highly ordered motions in the fashion of diffused limit-cycle oscillations (LCOs). However, this LCOs motion can be affected by the intensifying acoustic excitation through changing the aeroelastic modal interaction mechanism. Accompanied with these changes, the panel can experience various stochastic bifurcations.

Member Discrete Element Method for Static and Dynamic Responses Analysis of Steel Frames with Semi-Rigid Joints

In this paper, a simple and effective numerical approach is presented on the basis of the Member Discrete Element Method (MDEM) to investigate static and dynamic responses of steel frames with semi-rigid joints. In the MDEM, structures are discretized into a set of finite rigid particles. The motion equation of each particle is solved by the central difference method and two adjacent arbitrarily particles are connected by the contact constitutive model. The above characteristics means that the MDEM is able to naturally handle structural geometric nonlinearity and fracture. Meanwhile, the computational framework of static analysis is consistent with that of dynamic analysis, except the determination of damping. A virtual spring element with two particles but without actual mass and length is used to simulate the mechanical behaviors of semi-rigid joints. The spring element is not directly involved in the calculation, but is employed only to modify the stiffness coefficients of contact elements at the semi-rigid connections. Based on the above-mentioned concept, the modified formula of the contact element stiffness with consideration of semi-rigid connections is deduced. The Richard-Abbort four-parameter model and independent hardening model are further introduced accordingly to accurately capture the nonlinearity and hysteresis performance of semi-rigid connections. Finally, the numerical approach proposed is verified by complex behaviors of steel frames with semi-rigid connections such as geometric nonlinearity, snap-through buckling, dynamic responses and fracture. The comparison of static and dynamic responses obtained using the modified MDEM and those of the published studies illustrates that the modified MDEM can simulate the mechanical behaviors of semi-rigid connections simply and directly, and can accurately effectively capture the linear and nonlinear behaviors of semi-rigid connections under static and dynamic loading. Some conclusions, as expected, are drawn that structural bearing capacity under static loading will be overestimated if semi-rigid connections are ignored; when the frequency of dynamic load applied is close to structural fundamental frequency, hysteresis damping of nonlinear semi-rigid connections can cause energy dissipation compared to rigid and linear semi-rigid connections, thus avoiding the occurrence of resonance. Additionally, fracture analysis also indicates that semi-rigid steel frames possess more anti-collapse capacity than that with rigid steel frames.

Suppression of two-dimensional vortex-induced vibration with active velocity feedback controller

Vortex-induced vibrations (VIV) establish key design parameters for offshore and subsea structures subject to current flows. Understanding and predicting VIV phenomena have been improved in recent years. Further, there is a need to determine how to effectively and economically mitigate VIV effects. In this study, linear and nonlinear velocity feedback controllers are applied to actively suppress the combined cross-flow and in-line VIV of an elastically-mounted rigid circular cylinder. The strongly coupled fluid-structure interactions are numerically modelled and investigated using a calibrated reduced-order wake oscillator derived from the vortex strength concept. The importance of structural geometrical nonlinearities is studied which highlights the model ability in matching experimental results. The effectiveness of linear vs nonlinear controllers are analysed with regard to the control direction, gain and power. Parametric studies are carried out which allow us to choose the linear vs nonlinear control, depending on the target controlled amplitudes and associated power requirements.