Response Of Complex Structures Research Articles

The impact of extreme wind conditions and yaw misalignment on the aeroelastic responses of a parked offshore wind turbine

As global energy demands rise and the urgent need to reduce carbon emissions, offshore wind energy technology has evolved rapidly, becoming a vital component of the world’s energy portfolio. However, offshore wind turbines face new challenges due to complex marine environments. Under extreme conditions such as strong winds and yaw misalignment, parked wind turbines exhibit complex aerodynamic and structural responses that significantly differ from those in normal operating conditions. These responses, crucial to the integrity and safety of wind turbines, demand thorough analysis. This article presents an in-depth aeroelastic analysis of a parked 5 MW offshore wind turbine using a sophisticated and precise numerical model. It explores the impacts of incoming wind speed and yaw misalignment on the aerodynamic loads and structural behaviors of the wind turbine. The findings indicate that gravity plays a significant role in blade structural responses for a parked wind turbine. Additionally, higher wind speeds elevate aerodynamic forces, leading to more pronounced fluctuations in root forces and tip deflections. The increase in wind speed triggers and exacerbates high-frequency edgewise vibrations of the blade, further leading to fluctuations and instability in the loads. The study also reveals that yaw misalignment causes the AOA changes significantly over time, and generates intermittent fluctuations in lift and drag, leading to extra blade vibrations with the maximum amplitude exceeding 10% of the blade length. This research enhances the current understanding of the operational safety of offshore wind turbines, particularly under extreme conditions. It aims to provide valuable insights and guidance for researchers and developers in designing and monitoring the performance of offshore wind turbines, ensuring their resilience and efficiency in challenging environments.

Directional excitation of structural vibrations due to correlated sources

Dynamical Energy Analysis (DEA) is an approach used to compute the vibro-acoustic response of complex structures to externally applied high-frequency excitation. DEA tracks the global energy flow in a structure in terms of a local ray tracing approach implemented on meshes. Due to its in-built directional set-up, the approach is ideally suited for modelling the response of structures to directional excitation. Examples thereof are dipole sources or - more generally - correlated and distributed source excitation such as due to a Turbulent Boundary Layer (TBL) excitation across an aircraft wing during flight. We will demonstrate here how such directional sources are implemented in a DEA setting. TBL induced sources or general correlated sources can be described in terms of appropriate force or wave correlation functions (CF). Using Wigner-transformation, these CFs can be associated with a directional energy flow source. Vibrational energy field results are presented for a pair of phase-locked point forces. Results are also presented for 9 point-sources, which demonstrate the ability to channel the energy flow away from the sources by carefully choosing their relative phases. An implementation of this approach within DEA is also presented, with results demonstrating strong agreement with direct calculations.

Research on the response of underwater explosion side structure based on RKPM method

Abstract Based on smoothed particle hydrodynamics and reproducing kernel particle method, this paper establishes a fluid-structure interaction three-dimensional calculation model for the dynamic response of complex structures to underwater explosion shockwave, verifies the effectiveness, accuracy and progressiveness of SPH-RKPM coupling calculation, and establishes a control condition with detonation distance as a variable to determine the dynamic response characteristics of ship side under shockwave loads generated by underwater explosion at different detonation distances.

Treatment with Tinospora cordifolia ameliorates prenatal stress and maternal separation-induced memory deficits by restoring amygdaloid neuronal architecture

Introduction: Tinospora cordifolia (TC) possesses antioxidative properties and has been shown to improve cognition. In this study, the effects of TC were investigated on prenatal vibratory stress, maternal separation-induced amygdala plasticity, and memory retention in pregnant rats and their neonates. Methods: Four experimental animal groups of pregnant Wistar rats were employed in this research, including normal & vehicle controls, the stressed group, which received 3 hours of vibratory stress/day, and the TC-treated group, which received 6 mg/kg TC before vibratory stress. The neonates born to these mothers were then subjected to maternal separation, followed by postnatal TC treatment. After 6 weeks, the animals were assessed to evaluate memory retention, serum cortisol levels, and neuronal structural changes in the amygdala. Results: Neonates exposed to prenatal vibratory stress and maternal separation entered the dark compartment more quickly during the retention test (P<0.001), indicating reduced memory retention. In contrast, the TC-treated groups showed longer latencies (P<0.001), suggesting improved memory retention. The TC-treated mothers and neonates had longer dendrites with more branching points and intersections (P<0.001). However, these dendrites underwent pruning, indicating a complex structural response to stress and TC treatment. Conclusion: The results indicate that TC exerts neuroprotective effects against prenatal vibratory stress and maternal separation and aids memory retrieval in rats by restoring amygdala neuronal damage.

Multi-lane vehicle load measurement using bending and shear strains

Abstract Many load identification methods have been proposed, but most are affected by the basic axle parameters and lateral distribution of vehicles. To effectively measure traffic flow with lateral distribution information, this article presents an innovative method that employs a strain decoupling model (SDM) and a vehicle information identification model (VIDM) to measure multi-lane vehicle load depending on the bending strain and shear strain from long-gauge fiber bragg grating (FBG) sensors. The SDM decouples the measured coupling strain into the strain for a single lane load, thereby simplifying the complex structural response resulting from lateral distributed vehicles. By exploiting the distinct characteristics of different strain types that reflect various aspects of the structure, the VIDM establishes a sophisticated mapping relationship between bending, shear strain and axle parameters, which enables the accurate determination of axle parameters including axle speed and spacing. The real-time estimation of the multi-lane vehicle load is achieved by combining the obtained axle information with the decoupled bending strain. This method effectively solves the problem of large load estimation error caused by inaccurate identification of axle parameters, and enables accurate acquisition of vehicle load in lateral distribution using bending and shear strains near the bridge entrance. Both numerical studies and laboratory tests are carried out on a simply supported beam for conceptual verification. The results demonstrate that the proposed method successfully improves the measurement of multi-lane vehicle load.

Adaptive GN block-based model for seismic response prediction of train-bridge coupled systems

Deep learning (DL) methods has found extensive application in predicting structural responses. However, conventional neural networks often lack the capacity to effectively capture inter-data relationships, relying solely on training data for end-to-end prediction. Consequently, these methods may struggle with generalization, particularly when faced with new structural configurations absent from the training dataset. To overcome this limitation, this study adopts a graph-based framework, representing structures as graphs facilitates the transfer of features between different components, mimicking the transfer of forces in the real world. Subsequently, a Graph Neural Network Blocks (GN Blocks) model is introduced. Leveraging the holistic inference structure inherent in graph representations, the GN Block-based model as an adaptive model exhibits superior generalization performance in response analysis tasks involving unknown structural forms. Illustrated through the application to train-bridge coupled (TBC) systems, the GN Block-based model demonstrates high prediction accuracy and robust generalization performance, underscoring its suitability for tackling complex structural response prediction.

Residual deformation analysis of laser powder bed fusion-fabricated lattice structures

ABSTRACT Lattice structures are crucial for weight reduction, and laser powder bed fusion (LPBF) is an efficient fabrication method. However, there's a notable research gap in understanding the residual deformation of LPBF-fabricated lattice structures. This study investigates the residual deformation of three basic lattice structures, body centre cell (BCC), face centre cell (FCC), and diamond cell (DC), fabricated via LPBF to reveal their deformation mechanisms. Analysis covers horizontal direction, building direction, and total deformations, unveiling complex structural responses. Lower relative densities exhibit a prevalent structural deformation mode (SDM) causing significant deformations, while higher densities shift to an intrinsic deformation mode (IDM) dominated by contraction during fabrication. The FCC structure shows optimal stability with minimal residual deformation across most densities. This study offers insightful findings and a detailed mechanistic analysis of residual deformation in LPBF-fabricated lattice structures, applicable across various configurations, ensuring design process uniformity and reliability.

Intelligent identification of moving forces based on visual perception

The task of identifying moving forces presents a challenging inverse problem for bridge health monitoring and condition assessment. Existing methods for identifying moving loads rely on complex structural response measurement equipment, resulting in inefficiency and elevated costs. To address these challenges, this study introduces an innovative intelligent identification method for moving forces on bridges using visual perception techniques. The proposed method utilizes cameras to capture displacement changes at specific points on the bridge surface to reconstruct moving forces in the time domain. Initially, numerical simulations were conducted to ascertain the feasibility and robustness of identifying moving forces based solely on the structural displacement response. This phase also investigates the influence of different measurement point combinations on identification accuracy. Subsequently, the accuracy of the proposed method in measuring the dynamic displacement response of the structure was carefully evaluated by an outdoor shaking table test. Furthermore, a meticulously designed simply supported beam model was fabricated, followed by the execution of precise vehicle-bridge coupling dynamic experiments. This phase rigorously validates the effectiveness and accuracy of the proposed moving force identification method at varying vehicle speeds. The obtained results substantiate the proposed approach's capability not only to comprehensively capture bridge response data for full-area monitoring but also to consistently and reliably identify information on moving vehicle forces. This study underscores a pioneering application of intelligent visual perception technology in the field of identifying moving forces. The introduced noncontact intelligent identification method is an effective solution for monitoring moving forces on bridges, which has a wide range of applications in the future.

Analysis Computational Fluid Dynamics in a State of Ballast Loading on a Passenger Ship Prototype

Indonesia, as the largest archipelagic country in the world, has a very favourable geographical position because it is located between the Indian Ocean and the Pacific Ocean. The background of this research stems from the critical importance of effectively managing ballast loading on passenger ships to ensure stability, safety, and operational efficiency during voyages. Traditionally, methods for assessing ballast loading have often relied on empirical formulas or simplified models, which may not fully capture the complex fluid dynamics and structural interactions inherent in modern ship designs. This gap highlights the need for advanced computational tools like computational fluid dynamics (CFD), which can provide a more detailed and accurate analysis of how ballast loading affects the ship’s behaviour. CFD simulations offer the capability to model and analyse complex flow patterns, pressure distributions, and structural responses under various ballasting scenarios. By leveraging CFD, this research aims to enhance understanding and optimize the management of ballast loading on passenger ships, thereby addressing the limitations of traditional methods and advancing the state-of-the-art in maritime engineering practices. The simulation was carried out at different speeds, namely 1 knot, 10 knots, and 20 knots. When moving at a speed of 1 knot, the obstacles encountered have a range of 30–40 cm/s and a maximum speed of 83.0971 cm/s. Likewise, when moving at a speed of 10 knots, the obstacle has a range of 200–400 cm/s and a maximum speed of 766.921 cm/s. Finally, at a speed of 20 knots, facing obstacles with speeds ranging from 400 to 800 cm/s and a maximum speed of 1504.56 cm/s, the ship’s hull remained unaffected in terms of damage. However, the fluid speed magnifies the occurrence of friction.

State-Space Approaches to Complex Structures in Aerospace

The state-space approach (SSA), traditionally utilized in modern control theory, has been successfully adopted over the last three decades to investigate the mechanical behaviors of complex structures composed of composite or smart materials. This is largely due to their increasing application across various fields, including aerospace, civil and marine engineering, and transportation vehicles. This paper provides a comprehensive review of the establishment of state-space formulations for structures of typical configurations, such as beams, plates, shells, and trusses, with a particular focus on their applications in the mechanical analyses of various complex aerospace or smart structures using the transfer matrix method. The paper first summarizes the three-dimensional SSAs applied to laminated structures without any assumptions on physical fields. By employing structural theories such as various beam, plate, and shell theories, simplified one-dimensional and two-dimensional SSAs for laminated structures are developed. The paper then outlines the advances in generating analytical solutions for the mechanical behaviors of laminated structures. For the sake of completeness, the paper also provides an account of SSAs applied to complex periodic structures, particularly in beam and truss forms. To overcome the limitations of conventional SSAs related to structures with specialized geometric configuration or under arbitrary boundary conditions, state-space based numerical methods have been proposed, for example, the state-space based differential quadrature method and state-space based finite-element method. The applications of these methods in the analyses of static and dynamic responses of complex structures are extensively reviewed. It is observed that there are still intriguing and potential research topics for the development of advanced SSAs with enhanced versatility and the studies on practical complex structures used in modern engineering, particularly in aerospace industry. Therefore, this review is expected to be beneficial for researchers in the fields of analytical and numerical methods, composite structures, aerospace, structural engineering, and more.

Indirect measurement method for high frequency response of complex structure based on statistical energy analysis

The harsh working environments often make it difficult to measure high frequency responses of complex structures in the fields such as aerospace and aeronautic, which severely hinders the evaluation of structural performance and safety. An indirect measurement method is proposed to estimate the high frequency responses of non-measurable subsystems using a statistical energy analysis (SEA) framework. Whether or not the non-measurable subsystem includes input load, two indirect measurement approaches are developed by constructing an overdetermined problem and a well-posed problem respectively. Both utilize only the power flow balance equations of unexcited subsystems to solve the problems and thus do not require solving for input loads. The approaches are validated numerically and experimentally through case study of a rocket engine structure. Furthermore, the interval error analyses indicate that the approaches are robust against SEA modeling errors and response measuring errors.

Seismic response of deep circular tunnels subjected to P-waves: Axial and transverse compression-extension

Body waves can intersect a tunnel at various angles and thus induce complex structural responses that, at a minimum, require a comprehensive understanding of all modes of tunnel deformation due to both P- and S-waves. The majority of studies in this field have focused on a single S-wave mode, ovaling or racking (where the waves impinge on a tunnel transversely with the direction of particle movement perpendicular to the tunnel axis). Significantly less work has been devoted to the other modes. This study introduces two sets of new analytical solutions, using the soil-structure interaction approach, to predict the P-wave modes of tunnel deformation: axial compression-extension and transverse compression-extension. The solutions account for both drained and undrained loading conditions, with both no-slip and full-slip interface conditions between the tunnel lining and the ground. 2-D and 3-D numerical simulations, both static and dynamic analyses, are performed to verify the analytical solutions and determine their applicable limits. The numerical analyses also provide insights into the effects of dynamic amplification on the tunnel cross section.

Detailed Structural Analysis of Cylindrical Steel Tank Subjected to Various Seismic Peak Ground Values Using FSI Approach

The seismic analysis of ground-supported cylindrical steel tanks subjected to lateral harmonic displacement loadings has been carried out. This paper numerically evaluates the structural response of various tank geometries due to resonant seismic sloshing. The numerical investigation is performed using a two-way fluid structural interaction approach that couples computational fluid dynamics analysis with finite element transient structural analysis. The results of the analysis have been validated using Seismic Design Code (Eurocode 8, part 4). Regarding tank aspect ratio (H/D), five geometries covering slender, medium, and broad structures are analyzed under ten harmonic base excitations. All the geometries are excited at their first convective frequency, whose shape and magnitude are evaluated using modal analysis. The seismic response curves have been developed for each tank model, which reveal the complex and peculiar structural response. It is observed from the tanks’ seismic response that they undergo three transitional stress zones named safe, yielding, and failure zones. The critical loadings and failure duration have also been evaluated for each tank model. This will help to avoid future structural damage by designing liquid-containing structures based on evaluated seismic failure loads.

A machine learning-based hybrid seismic analysis of a lead rubber bearing isolated building specimen

This paper presents the first experimental validation of the hybrid seismic analysis, previously developed by the authors, by simulating the structural behavior of a full-scale base-isolated building specimen tested at the E-Defense. The two-dimensional structural behavior of the lead rubber bearings (LRBs) is predicted by a machine learning model (MLM) previously developed by the authors, whereas analytical models describe the response of the superstructure. A Python script has been developed to incorporate both analytical models and MLMs into an explicit time integration method to perform three-dimensional hybrid seismic analyses. Moreover, conventional time history analyses have been carried out using a bilinear model for the isolation devices. Experimental, ML-based, and conventional analysis responses of 14 shake table motions are processed and compared in terms of hysteresis curves of the isolation layer, roof displacement and peak floor acceleration. Overall, hybrid seismic analysis showed better results than conventional one in terms of capturing the energy dissipation capacity of the isolation layer (maximum a20-index of 0.859 for the drift and 0.720 for the shear with respect to experiment). Similarly, roof displacement was predicted with a maximum a20-index value of 0.832. Besides, the maximum average computation time of hybrid seismic analysis was 1.78 s per integration time-step. Therefore, the efficiency of the hybrid seismic analysis is experimentally proven in this paper in terms of both accuracy and applicability. This machine learning-based analysis method is strongly recommended to simulate time-history response of complex structures.

Insights on Phytohormonal Crosstalk in Plant Response to Nitrogen Stress: A Focus on Plant Root Growth and Development.

Nitrogen (N) is a vital mineral component that can restrict the growth and development of plants if supplied inappropriately. In order to benefit their growth and development, plants have complex physiological and structural responses to changes in their nitrogen supply. As higher plants have multiple organs with varying functions and nutritional requirements, they coordinate their responses at the whole-plant level based on local and long-distance signaling pathways. It has been suggested that phytohormones are signaling substances in such pathways. The nitrogen signaling pathway is closely associated with phytohormones such as auxin (AUX), abscisic acid (ABA), cytokinins (CKs), ethylene (ETH), brassinosteroid (BR), strigolactones (SLs), jasmonic acid (JA), and salicylic acid (SA). Recent research has shed light on how nitrogen and phytohormones interact to modulate physiology and morphology. This review provides a summary of the research on how phytohormone signaling affects root system architecture (RSA) in response to nitrogen availability. Overall, this review contributes to identifying recent developments in the interaction between phytohormones and N, as well as serving as a foundation for further study.

Characterisation of extreme load responses of a 10-MW floating semi-submersible type wind turbine

The global average size of offshore wind turbines has increased steadily from 1.5 MW to 6 MW from 2000 to 2020. With this backdrop, the research community has recently looked at huge 10–15 MW class floating offshore wind turbines (FOWTs). The larger rotor, nacelle structure and tower have more significant structural flexibility. The larger structural flexibility, controller dynamics, aerodynamics, hydrodynamics, and various environmental conditions result in complex structural responses. The structural load effects of a very large FOWT could be more severe than that of the lower MW classes. Accurate quantification of the extreme dynamic responses of FOWT systems is essential in the design of the Ultimate Limit State (ULS) due to the fully-coupled interaction between the FOWT system and environmental conditions. Motivated by this, extreme responses of the 10 MW semi-submersible type FOWT are investigated using the average conditional exceedance rate (ACER) and Gumbel methods. Three operating conditions representing below-rated (U = 8 m/s), rated (U = 12 m/s) and above-rated (U = 16 m/s) regions were considered. The aim is to guide future research on large FOWTs by indicating the expected ULS loads.

The porous cantilever beam as a model for spinal implants: Experimental, analytical and finite element analysis of dynamic properties.

Investigation of the dynamic properties of implants is essential to ensure safety and compatibility with the host's natural spinal tissue. This paper presents a simplified model of a cantilever beam to investigate the effects of holes/pores on the structures. Free vibration test is one of the most effective methods to measure the dynamic response of a cantilever beam, such as natural frequency and damping ratio. In this study, the natural frequencies of cantilever beams made of polycarbonate (PC) containing various circular open holes were investigated numerically, analytically, and experimentally. The experimental data confirmed the accuracy of the natural frequencies of the cantilever beam with open holes calculated by finite element and analytical models. In addition, two finite element simulation methods, the dynamic explicit and modal dynamic methods, were applied to determine the damping ratios of cantilever beams with open holes. Finite element analysis accurately simulated the damped vibration behavior of cantilever beams with open holes when known material damping properties were applied. The damping behavior of cantilever beams with random pores was simulated, highlighting a completely different relationship between porosity, natural frequency and damping response. The latter highlights the potential of finite element methods to analyze the dynamic response of arbitrary and complex structures, towards improved implant design.

Influence of combined imperfections on lateral-torsional buckling behaviour of pultruded FRP beams

By way of computational analyses using Finite Element (FE) software this paper presents, by way of sensitivity studies, lateral-torsional buckling resistances of I-beams made of pultruded fibre reinforced polymer. Parameters changed in the studies are the geometric imperfections, the vertical load position and the load eccentricity. Measured geometrical and material imperfections are incorporated into the geometrical nonlinear FE simulations. Constants in the FE work are three-point bending loading and the imperfection condition from having different elastic constants in the four flange outstands. Numerical results from the sensitivity studies are verified by comparing them with equivalent buckling load results from a series of physical tests conducted previously. It is found that the influence of combined geometrical and material imperfections on LTB failure can be significant, such that an imperfect beam can be put into a near ‘perfect imperfection’ condition, in which it possesses a higher buckling resistance. The opposite can happen for a ‘more severe imperfection’ with poorer beam response under loading. The load eccentricity on I-beams confirms a complex structural response. To be able to have a recognised design procedure for pultruded I-beam members the influence of combined imperfections on lateral-torsional buckling resistance needs to be reliably quantified.

Decomposition of the structural response of the Francis-99 runner during resonance.

In this work, the complex structural response of the Francis-99 turbine runner is further investigated by decomposition of the output signal from previous Laser Doppler Vibrometry (LDV) measurements into the motion of each nodal diameter. During the structural measurements, the non-rotating runner was installed in the turbine pit, submerged in a non-flowing water, and excited with piezoelectric patches mounted on the hub. The patches were excited with phase shifted sinusoidal voltage to create overall excitation of the runner with a desired number of nodal diameters. The deflection of selected locations on the trailing edges were scanned with LDV, one point at a time, and the global movement was reconstructed by combining the data for all points.The Francis-99 runner has its blades bolted to an over-dimensioned hub and shroud, where the hub is not fully axi-symmetrical and has several hollows in it. This, together with the fact that one patch was found to be non-functional, is believed to have excited other ND patterns in addition to the one that was intentionally excited, therefore contaminating the movement of the trailing edges with movements that does not belongs to the excited ND. To mitigate this and create a better representation of the movement of the trailing edge, which is not affected by the bleed from other ND, the LDV signal for each excited frequency of a particular ND is post-processed using discreet Fourier transformation to decompose the motion of each nodal diameter in the range ND0 to ND7. This unveils the contribution of each nodal diameter within the output signal where a spike is seen for the excited ND in all measurements. Influence from other nodal diameters were found, where the failed patched is believed to cause a ND1 like movement. In addition the clustering of multiple eigenmodes with differing nodal diameters previously found in narrow frequency bands were also found as interfering contribution when exciting at the relevant frequencies.

Effect of cracks on dynamical responses of double-variable-edge plates made of graphene nanoplatelets-reinforced porous matrix and sur-bonded by piezoelectric layers subjected to thermo-mechanical loads

This paper presents free vibration analyses and nonlinear dynamic responses of new complex edge contour non-rectangular plate structures with a part-through surface crack which the authors name as temporarily double-variable-edge (DVE) plates. The analytical results and numerical simulation are investigated in the Part I and it is expected that the experimental approach will be shown in Part II. The cracked plate made of a functionally graded porous (FGP) matrix structure and reinforced by graphene nano-platelets (GNPs) is covered by two piezoelectric layers and rested on a Winker-Pasternak elastic foundation. The material properties are determined by using the Halpin-Tsai micro-mechanical model, Gaussian Random Field (GRF) proposal, and the rules of mixtures. The governing equations are established based on the classical plate theory (CPT) and Galerkin's method which are convenient in analyzing the behaviors of complex edge contour plates. The obtained results are compared with those obtained from the existing Finite Element Method (FEM) to ensure the reliability and accuracy. In addition, the effects of geometrical shapes, crack parameters, applied voltages of piezoelectric layers, elastic foundations as well as thermal impacts are scrutinized. The obtained outcomes in the paper are promising for applications in the fields of aerospace, civil, and electronic engineering.