Prediction Of Dynamic Response Research Articles

Prediction of dynamic response of semi-submersible floating offshore wind turbines by a novel hydrodynamic coefficient model

A novel hydrodynamic coefficients model is proposed for the components of floating offshore wind turbine (FOWT). First, the formulas for evaluation of the added mass and drag coefficient for the components of FOWT are proposed to consider the interaction effects between columns as well as the frequency and amplitude dependencies. The global matrices of hydrodynamic coefficients are then evaluated by the proposed formulas and validated by the experimental data from the forced oscillation test. The predicted dynamic response of FOWT is also validated by the water tank test. Finally, the improvement of dynamic behaviour of the platform by the skirts is investigated. The decrease of amplitude and the increase of natural period for the heave motion of the platform with skirts are successfully simulated by the proposed model.

Dynamic wind response of tall buildings using artificial neural network

SummaryThis paper presents an alternative approach for predicting the dynamic wind response of tall buildings using artificial neural network (ANN). The ANN model was developed, trained, and validated based on the data generated in the context of Indian Wind Code (IWC), IS 875 (Part 3):2015. According to the IWC, dynamic wind responses can be calculated for a specific configuration of buildings. The dynamic wind loads and their corresponding responses of structures other than the specified configurations in IWC have to be estimated by wind tunnel tests or computational techniques, which are expensive and time intensive. Alternatively, ANN is an efficient and economical computational analysis tool that can be implemented to estimate the dynamic wind response of a building. In this paper, ANN models were developed to predict base shear and base bending moment of a tall building in along‐ and across‐wind direction by giving the input as the configuration of the building, wind velocity, and terrain category. Multilayer perceptron ANN models with back‐propagation training algorithm was adopted. On comparison of results, it was found that the predicted values obtained from the ANN models and the calculated responses acquired using IWC standards are almost similar. Using the best fit model of ANN, an extensive parametric study was performed to predict the dynamic wind response of tall buildings for the configurations on which IWC is silent. Based on the results obtained from this study, design charts are developed for the prediction of dynamic wind response of tall buildings.

Multi-objective optimization for designing metallic corrugated core sandwich panels under air blast loading

This research aims to improve the blast performance of trapezoidal corrugated core sandwich panel under air blast loading. A finite element model for the prediction of dynamic responses of trapezoidal corrugated core sandwich panel was first proposed and validated by experiments. Based on the simulation results, kriging models were established to approximate the relationships between design variables and blast performances, and correlation analyses were carried out to investigate the effects of the design variables on the maximum back face deflection and specific energy absorption. It is found that any decrease in maximum back face deflection would always lead to undesirable deterioration in specific energy absorption, and the correlation relationships are associated with the stand-off distance. Using the developed kriging models, multi-objective design optimization was performed to seek trade-off solutions for the trapezoidal corrugated core sandwich panel under specific and variable stand-off distances. Results show that the design on Pareto fronts depended upon stand-off distance. Comparisons of the blast performance between optimized designs and initial designs turned out that there indeed existed a great potential in performance improvement. Importantly, careful examination of the responses of the optimized designs revealed some valuable design methods which should be useful for the engineering applications of trapezoidal corrugated core sandwich panel.

Determination of Corneal Biomechanical Behavior in-vivo for Healthy Eyes Using CorVis ST Tonometry: Stress-Strain Index.

Purpose: This study aims to introduce and clinically validate a new algorithm that can determine the biomechanical properties of the human cornea in vivo.Methods: A parametric study was conducted involving representative finite element models of human ocular globes with wide ranges of geometries and material biomechanical behavior. The models were subjected to different levels of intraocular pressure (IOP) and the action of external air puff produced by a non-contact tonometer. Predictions of dynamic corneal response under air pressure were analyzed to develop an algorithm that can predict the cornea's material behavior. The algorithm was assessed using clinical data obtained from 480 healthy participants where its predictions of material behavior were tested against variations in central corneal thickness (CCT), IOP and age, and compared against those obtained in earlier studies on ex-vivo human ocular tissue.Results: The algorithm produced a material stiffness parameter (Stress-Strain Index or SSI) that showed no significant correlation with both CCT (p > 0.05) and IOP (p > 0.05), but was significantly correlated with age (p < 0.01). The stiffness estimates and their variation with age were also significantly correlated (p < 0.01) with stiffness estimates obtained earlier in studies on ex-vivo human tissue.Conclusions: The study introduced and validated a new method for estimating the in vivo biomechanical behavior of healthy corneal tissue. The method can aid optimization of procedures that interfere mechanically with the cornea such as refractive surgeries and introduction of corneal implants.

Determination of Viscoelastic Properties of Soil and Prediction of Static and Dynamic Response

Determination of Viscoelastic Properties of Soil and Prediction of Static and Dynamic Response

Three-Dimensional Thermo-Elasto-Hydrodynamic Computational Fluid Dynamics Model of a Tilting Pad Journal Bearing—Part II: Dynamic Response

Abstract Part II presents a novel approach for predicting dynamic coefficients for a tilting pad journal bearing (TPJB) using computational fluid dynamics (CFD) and finite element method (FEM), including fully coupled elastic deflection, heat transfer, and fluid dynamics. Part I presented a similarly novel, high fidelity approach for TPJB static response prediction which is a prerequisite for the dynamic characteristic determination. The static response establishes the equilibrium operating point values for eccentricity, attitude angle, deflections, temperatures, pressures, etc. The stiffness and damping coefficients are obtained by perturbing the pad and journal motions about this operating point to determine changes in forces and moments. The stiffness and damping coefficients are presented in “synchronously reduced form” as required by American Petroleum Institute (API) vibration standards. Similar to Part I, an advanced three-dimensional thermal—Reynolds equation code validates the CFD code for the special case when flow Between Pad (BP) regions is ignored, and the CFD and Reynolds pad boundary conditions are made identical. The results show excellent agreement for this validation case. Similar to the static response case, the dynamic characteristics from the Reynolds model show large discrepancies compared with the CFD results, depending on the Reynolds mixing coefficient (MC). The discrepancies are a concern given the key role that stiffness and damping coefficients serve instability and response predictions in rotordynamics software. The uncertainty of the MC and its significant influence on static and dynamic response predictions emphasizes a need to utilize the CFD approach for TPJB simulation in critical machines.

Impact of aerodynamic modeling on seakeeping performance of a floating horizontal axis wind turbine

AbstractOver the last decade, several coupled simulation tools have been developed in order to design and optimize floating wind turbines (FWTs). In most of these tools, the aerodynamic modeling is based on quasi‐steady aerodynamic models such as the blade element momentum (BEM). It may not be accurate enough for FWTs as the motion of the platform induces highly unsteady phenomena around the rotor. To address this issue, a new design tool has been developed coupling a seakeeping solver with an unsteady aerodynamic solver based on the free vortex wake (FVW) theory. This tool is here compared with the reference code FAST, which is based on the BEM theory in order to characterize the impact of the aerodynamic model on the seakeeping of a floating horizontal axis wind turbine (HAWT). Aerodynamic solvers are compared for the case of the free floating NREL 5MW HAWT supported by the OC3Hywind SPAR. Differences obtained between the models have been analyzed through a study of the aerodynamic loads acting on the same turbine in imposed harmonic surge and pitch motions. This provides a better understanding of the intrinsic differences between the quasi‐steady and unsteady aerodynamic solvers. The study shows that differences can be observed between the three aerodynamic solvers, especially at high tip speed ratio (TSR) for which unsteady aerodynamic phenomena and complex wake dynamics occur. Observed discrepancies in the predictions of the FWT dynamic response can raise issues when designing such a system with a state‐of‐the‐art design tool.

Spectral formulated modelling of an electrodynamic shaker

Generally, dynamic and fatigue tests require complicated and time-consuming simulation to achieve good performance. However, to estimate a structure’s fatigue lifetime during a vibrational test, when the frequency response function is required, can be expensive or unsuitable. Thus, the coupling interaction between the electrodynamic shaker and the specimen is addressed, and an equivalent shaker spectral element model presented. In this context, the paper presents a study based on the spectral element approach to model the electrodynamic shaker. The spectral analysis is performed to predict the dynamic response of the specimen coupled with shaker by using the spectral element method. To validate the model it is compared with the experimental tests and numerical simulation obtained by using the Finite Element method. The dynamic response predictions using the presented model are similar to the experimental responses, showing the efficiency of this approach.

A high-speed precision micro-spindle use for mechanical micro-machining

Mechanical micro-machining has significant advantages in compassion with other machining techniques in terms of workpiece complexity, material diversity, energy consumption, and cost. The existing micro-spindles, as the key fundamental equipment, cannot simultaneously guarantee ultra-high rotational speed, high rotational accuracy, and compact structure. This study discussed the details in designing of high-speed precision micro-spindles, and a new micro-spindle was proposed, which is driven by an air turbine. To enhance its stiffness and rotational accuracy, the porous ceramic aerostatic bearings are used. The key structural parameters were selected based on theoretical calculation and simulation analysis. More importantly, the theoretical models for its static error and dynamic response predictions were established and combined to optimize the size of micro-spindle. The prototype micro-spindle has a radial motion error of approximately 6.0 μm and no heating problem. The micro-grinding experiment of micro-channel shows its good feasibility and potential application in mechanical micro-machining. And it has very simple and compact structure (28 mm in diameter × 45 mm in length) and low manufacturing difficulty and cost.

Observations of typhoon effects on a high-rise building and verification of wind tunnel predictions

This paper presents the analysis results of 18-h-long field measurement data collected at a 420-m-high building and four meteorological stations in Hong Kong during the passage of Typhoon Usagi (1319) which was the most intense tropical cyclone that attacked Hong Kong in 2013. In this paper, the wind characteristics during Typhoon Usagi over five different sites in Hong Kong are presented and discussed; the modal parameters of the monitored high-rise building are estimated by a probabilistic approach in a Bayesian framework (i.e., Bayesian spectral density approach) and a deterministic method (i.e., Random decrement technique), respectively; the serviceability of the high-rise building under typhoon condition is evaluated against four comfort criteria. Furthermore, the wind tunnel predictions of structural dynamic responses of the monitored building are validated by the field measurements. The goal of this study is to further the understanding of the effects of wind on high-rise buildings so as to provide useful information for the wind-resistant structural design in tropical cyclone-prone regions.

A Fully Coupled Computational Fluid Dynamics Method for Analysis of Semi-Submersible Floating Offshore Wind Turbines Under Wind-Wave Excitation Conditions Based on OC5 Data

Accurate prediction of the time-dependent system dynamic responses of floating offshore wind turbines (FOWTs) under aero-hydro-coupled conditions is a challenge. This paper presents a numerical modeling tool using commercial computational fluid dynamics software, STAR-CCM+(V12.02.010), to perform a fully coupled dynamic analysis of the DeepCwind semi-submersible floating platform with the National Renewable Engineering Lab (NREL) 5-MW baseline wind turbine model under combined wind–wave excitation environment conditions. Free-decay tests for rigid-body degrees of freedom (DOF) in still water and hydrodynamic tests for a regular wave are performed to validate the numerical model by inputting gross system parameters supported in the Offshore Code Comparison, Collaboration, Continued, with Correlations (OC5) project. A full-configuration FOWT simulation, with the simultaneous motion of the rotating blade due to 6-DOF platform dynamics, was performed. A relatively heavy load on the hub and blade was observed for the FOWT compared with the onshore wind turbine, leading to a 7.8% increase in the thrust curve; a 10% decrease in the power curve was also observed for the floating-type turbines, which could be attributed to the smaller project area and relative wind speed required for the rotor to receive wind power when the platform pitches. Finally, the tower-blade interference effects, blade-tip vortices, turbulent wakes, and shedding vortices in the fluid domain with relatively complex unsteady flow conditions were observed and investigated in detail.

A dynamic homogenization model for long-wavelength wave propagation in corrugated sandwich plates

In the present work, a new dynamic homogenization model is developed to investigate the long-wavelength wave propagation in a corrugated sandwich plate. With the harmonic motion assumption and using a shifting operator, the governing equations of the plate are firstly represented in a state-space form. Then, a dynamic homogenization model is developed via the two-scale homogenization method. Based on this model and considering the propagation of sinusoidal waves, the dispersion relations and corresponding wave modes can be easily obtained. In order to validate the developed homogenization model, the obtained dispersion relations are compared with those predicted by the spectral element method. It is found that the present method gives accurate results in low frequency range. Furthermore, the effects of some geometric and material parameters on the dispersion relations for the corrugated sandwich plate are also discussed. The developed homogenization model is expected to be helpful in the prediction and control of dynamic responses of corrugated or even lattice sandwich structures.

A topology-change model of multi-speed transmissions in electric vehicles during gear-shifting

Recent developments in electric vehicles incorporate multi-speed transmissions to improve the electric vehicle range and performance. Similar to transmissions for fossil-fuel vehicles, those for their electric counterparts undergo topology changes during gear-shifting. However, this important phenomenon has been overlooked in the development of transmission mathematical models, which results in unrealistic prediction of the transmission dynamic response. In this study, a topology-change model based on the impulse-momentum relation is developed to address the topology change of multi-speed transmissions in electric vehicles during gear-shifting. An orthogonal complement is introduced to eliminate the non-working constraint forces. The velocity jump brought about by topology changes is given due attention. A case study is included, whereby the model is applied to a novel modular multi-speed transmission for electric vehicles. First, tests are conducted on the transmission experimental testbed; then, the test results are reproduced in simulation using the model developed herein. Moreover, the velocity jump of the gear-shifting is computed by means of the model. Subsequently, simulation of the transmission gear-shifting incorporating the velocity jump is conducted. By means of the model developed in this paper, a more realistic prediction of the transmission dynamic response can be achieved. Moreover, this model can be applied to any vehicle transmissions with gear-shifting, such as dual-clutch transmissions (DCTs).

VibronRotor, an opensource rotordynamic code: Development and benchmarking

Precise prediction of dynamic response is an important first step in the design and troubleshooting of rotating machinery. Utility of the finite element (FE) method in rotordynamics is well entrenched and has translated into many specialized codes for rotor response prediction. Most specialized codes are propriety software with expensive subscriptions which restrict the access for small-scale rotating machinery manufacturers and researchers to these codes and employed algorithms. In contrast, this paper presents the detailed algorithm and benchmarking of an open-source FE code VibronRotor for rotordynamic analysis. FE formulation in code is based on the work of Nelson and McVaugh (1976). Functionalities of the code include Campbell diagram, critical speed map, mode shapes, imbalance response, orbit plots, and instability threshold analysis. An important capability to analyze the stability of closed-loop electromechanical levitation systems is also explained. These analysis tools are described with design insights to enable selection of rotor design parameters for stable operation and failure prevention. VibronRotor is verified with results from an established rotordynamic software and validated with an inhouse-developed rotor test-rig. Open-source development is primarily aimed to support rotating machinery manufacturers and start-ups to design and troubleshoot rotors without expensive reliance on commercial software. VibronRotor is written to run on a free scientific programming language GNU Octave.

Prediction of dynamic response of semi-submersible floating offshore wind turbine using augmented Morison's equation with frequency dependent hydrodynamic coefficients

Abstract A fully coupled nonlinear simulation tool using Morison's equation is developed to predict the dynamic response of floating offshore wind turbine (FOWT) system. Water tank tests are conducted to investigate hydrodynamic coefficients and the performance of the simulation tool under different sea states. Three issues are discussed in this paper. First, correction factors for the added mass and drag coefficients are proposed to account for the effects of frequency dependent hydrodynamic coefficients, and the effects of these correction factors on the global matrices are validated by the forced oscillation tests. Then, the effects of the frequency dependent hydrodynamic coefficients and the axial Froude-Krylov force on slender members are clarified by the free decay tests and water tank tests with regular and irregular waves. Finally, the dynamic behavior of mooring system on the fairlead tension is investigated by using quasi-static and dynamic models, respectively. The dynamic responses of FOWT with improved hydrodynamic models agree well with those measured in the water tank tests.

ASSESSMENT OF CONCRETE ANISOTROPY IN RELATION TO THE DIRECTION OF CASTING

In numerical predictions of both static and dynamic response of concrete structures, the usual assumption of global isotropic behavior is usually accepted, constituting standard practice in structural analysis and design. It has been recognized, however, that in situ concrete compressive strength of drilled cores in the direction normal to the direction of casting is somewhat smaller than the strength in the vertical direction. Since the consideration of this factor may reduce model error in numerical schemes that assume isotropic behavior, experimental studies were conducted in order to quantify the degree of anisotropy that may be expected in concrete structures. These initial studies suggest that the effect may result in errors as high as 10% in the estimated carrying capacity, deserving in consequence additional research.

The modelling and prediction of dynamic responses of slender continua deployed in tall structures under long-period seismic excitations

Tall building structures are susceptible to large sway motions when subjected to earthquake excitations. They are particularly affected by long period earthquake ground motions. These low frequency seismic waves resonate with the fundamental mode of the building structure which in turn causes resonance interactions with long slender continua deployed in modular non-structural installations, such as lifts. Damage due to large resonance motions of suspension/compensating ropes and cables during earthquake are one of the most common modes of failure in high-rise lift installations. In this paper an analytical model to predict the dynamic responses of a suspension rope system installed in a tall host structure under seismic conditions is presented. The model is then used to predict the dynamic performance of the system under earthquake excitations. The predictions can then be used to develop suitable mitigating strategies and protective measures to minimize the earthquake damage.

Identification of Volterra kernels for improved predictions of nonlinear aeroelastic vibration responses and flutter

Aeroelastic structural systems are intrinsically nonlinear and accurate predictions of dynamic responses of nonlinear aeroelastic systems have become of paramount importance since these directly affect the accuracy and reliability of subsequent stability analyses. Such nonlinear systems can be generally represented with Volterra series whose kernels have been found to be effective in their dynamic characterizations. This paper examines how first- and second-order Volterra kernels of nonlinear aeroelastic systems can be accurately identified and then incorporated into the theoretical models of aeroelastic analyses such as predictions of dynamic response and onset of aeroelastic flutter. A novel identification method based on correlation analysis to extract frequency components has been developed which can be applied to general nonlinear aeroelastic systems to obtain accurately the required Volterra transfer functions. The method is very accurate and extremely robust against measurement noise contaminations in both input and output signals, due to the correlation scheme which effectively filters uncorrelated signal components. Detailed aeroelastic behavior of a representative pitch-plunge airfoil dynamic model with nonlinear pitch stiffness has been examined. Its Volterra transfer functions are then identified which are found to be close to their exact analytical counterparts, though interaction between kernels becomes apparent as input level increases. Once inverse Fourier transformed, these identified Volterra kernels are then included in the modeling of the dynamics of aeroelastic systems for vibration response and flutter. Extensive numerical simulation results have demonstrated that the proposed method is very accurate and resilient to measurement errors when applied to the identification of second-order Volterra kernels, and the improvement in predictions of vibration response and flutter become significant when the contributions of these second-order Volterra kernels are included in the overall aeroelastic system dynamics. The identification and subsequent inclusion of second-order Volterra kernels into system dynamics model offer improved design capabilities of nonlinear aeroelastic structural systems.

Neural networks for displacement analysis in an advanced gas cooled reactor core model

This paper presents a Neural Network (NN) approach for displacement analysis with applications in modelling the seismic response of the UK’s Advanced Gas Cooled Reactors (AGRs). A quarter sized physical model of a reactor core was developed at the University of Bristol to provide experimental validation to the existing numerical models that support the seismic resilience assessments of the AGRs. The physical model outputs include displacement and acceleration datasets of considerable size and complexity, collected for a range of seismic inputs and postulated component damage scenarios. Rich sets of displacement data were employed in training two NN models that can predict displacement at user-defined locations in the core physical model and can map the correlation between the component relative displacements. Understanding component displacements is particularly important, as such displacements may affect the channel shapes and can cause local and general distortion of the core. This paper presents the development, testing and performance of the NN models. The NNs yield predictions that compare well with the experimentally obtained parameters. As more experimental test data become available, the NN’s prediction capability will benefit from accumulated training. In the future, the NNs will be incorporated into a multi-layered framework for dynamic response prediction and analysis.

Validación del Modelo de un Regulador Automático de Voltaje basado en Optimización de Mapeo Media-Varianza y Pruebas de Campo

La operación y planificación de los sistemas de potencia son en gran medida basadas en una serie de análisis que involucran el uso de simulaciones dinámicas y en estado estacionario. En este contexto, el modelado a detalle de un sistema de potencia es un requerimiento básico para las aplicaciones que se basan en una predicción precisa de la respuesta dinámica del sistema, como el diseño de estrategias de protección y esquemas de control. La mayoría de los modelos únicamente corresponden a una representación matemática, cuyos parámetros deben ser, en primera instancia, ajustados o identificados con base en un proceso racional de validación de modelos que emplea frecuentemente datos experimentales. Este trabajo propone un método de estimación paramétrica para lograr la validación de modelos en sistemas de potencia a través de una simulación software-in-the-loop (SIL) implementada mediante la optimización de mapeo media-varianza (MVMO) en DIgSILENT PowerFactory, la cual permite comparar los resultados de las simulaciones con registros obtenidos de pruebas de campo. El método propuesto es luego utilizado para realizar la validación del regulador automático de voltaje (AVR) de Coca Codo Sinclair, la planta de generación hidroeléctrica más grande de Ecuador. Los resultados obtenidos son finalmente comparados con dos enfoques similares: i) el objeto “Model Parameter Identification” de PowerFactory y ii) la herramienta “Parameter Estimation” de Matlab-Simulink. Las comparaciones muestran las bondades de la propuesta para sobrellevar limitaciones de las otras dos metodologías, como precisión, restricciones y capacidad de simulación en SIL.