bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Control Strategy for Vehicle Semi-Active Suspension System
Authors: Zhang Yiming , Lin Ye
Published: April 2021

This paper investigates a reference control strategy for Vehicle semi-active suspension. The control is conducted by following the idea optimal active controller. The passive actuator is set to optimal whenever the active and passive actuators have the same signs; and set to zero output whenever the two signs are opposite. The simulation results of a 2DoF vehicle show that the semi -active suspension system can follow the ideal active system very well, both are superior to conventional passive systems. In this paper, a 2DoF vehicle model was also used to study a statistical optimal control strategy of the semi-active suspension system. The statistical optimal concept is the result of the combination of the nonlinear programming and controllable damper. A way of estimating statistical characteristics of road irregularities was also proposed.

Vehicle active, suspension, due to its perfect v i bra t i on isolation performance, gets moreand more attention. Active suspension can be generally divided into two categories, totally active suspension system and semi-active suspension system. From the published results it is known that active suspension can surpass the performance limit of conventional passive suspension and greatly improve the vehicle riding comfort and steering ability. But active suspension has a critical disadvantage of less applicability, due to its high cost and low reliability. Also it consumes large amount of energy as it works. The idea of semi-active suspension was put forward to overcome the shortcoming of active suspension. It is a compromise between active suspension and passive suspension. Semi-active suspension has approximately the same behavior as active suspension, and almost consumes no energy as it works. So semi-active suspension possesses a great potential in application. At. present, in the field of suspension research over the world, a great deal of attention is paied to semi-active suspension. At present, for the cotrol of semi-active suspension the widely studied strategy is “on off” control [1] [2], which is first put forward by Karnopp. “On-off” control can eliminate the phenomenon of vibration amplification for passive suspension, thus it can improve the suspension performance to certain extent. At present, no substantive result has been obtained yet in the field of optimal control of semi-active suspension. This paper will investigate a reference control strategy on the basis of linear optimal control. The control is conducted by following the optimal ctive controller. The referrence control result is optimal when the outputs of the active and semi-active force generators have the same signs.
A Transfer Matrix Technique for Evaluating the Natural Frequencies and Critical Speeds of a Rotor With Multiple Flexible Disks
Authors: Wu Fangsheng , Flowers George T.
Published: April 2021

Modern turbomachinery is used to provide power for a wide range of applications, from steam turbines for electrical power plants to the turbopumps used in the Space Shuttle Main Engine. Such devices are subject to a variety of dynamical problems, including vibration, rotordynamical instability, and shaft whirl. In order to properly design and evaluate the performance and stability of turbomachinery, It is important that appropriate analytical tools be available that allow for the study of potentially important dynamical effects. This research effort is concerned with developing a procedure to account for disk flexibility which can readily be used for investigating how such effects might influence the natural frequencies and critical speeds of practical rotor systems.

In the present work, a transfer matrix procedure is developed in which the disk flexibility effects are accounted for by means of additional terms included in the transfer matrix formulation. In this development, the shaft is treated as a discrete system while the disk is modelled as a continuous system using the governing partial differential equation. Based on this governing equation, an equivalent inertial moment Mk*, which is the generalized dynamic force coupling between shaft and disk, is then derived. Analysis shows that only the disk modes of one nodal diameter contribute to the inertial moment, Mk*, and thus influence the natural frequencies of the rotor system.

To determine the Mk*, the modal expansion method is employed and the governing partial differential equation of the disk is transformed to a set of decoupled forced vibration equations in the generalized coordinates. The Mk* are then calculated in terms of modal shapes, natural frequencies, and material and geometric parameters which can be found in the literature or can be obtained from experiments. Finally the Mk* are incorporated into the point transfer matrix. By so doing, the properties of quick computational speed and ease of use are retained and the complexity of solving partial differential equations is avoided. This allows the present procedure to be easily applied to practical engineering problems. This is especially true for multiple flexible disk rotor systems.

As an example, three different cases for a simplified model of the Space Shuttle Main Engine (SSME) High Pressure Oxygen Turbo-Pump (HPOTP) rotor have been studied using this procedure. Some of the more interesting results obtained in this example study are enumerated below.

1.) Disk flexibility can introduce additional natural frequency(s) to a rotor system.

2.) Disk flexibility can cause shifting of some of the natural frequencies.

3.) As disk flexibility is increased, lower natural frequencies of the rotor system will be influenced.

4.) At certain rotor speeds, disk flexibility may cause the disappearance of a natural frequency.

5.) The axial position of the disk on the rotor shaft has a significant effect on the degree of this influence.
Suppression of Subsynchronous Vibration in the SSME HPFTP
Authors: Becht David G. , Hawkins Larry A. , Scharrer Joseph K. , Murphy Brian T.
Published: April 2021

SSME HPFTP hot-fire dynamic data evaluation and rotordynamic analysis both confirm that two of the most significant turbopump attributes in determining susceptibility to subsynchronous vibration are impeller interstage seal configuration and rotor sideload resulting from turbine turnaround duct configuration and hot gas manifold. Recent hot-fire testing has provided promising indications that the incorporation of roughened “damping” seals at the impeller interstages may further increase the stability margin of this machine. A summary of the analysis which led to the conclusion that roughened seals would enhance the stability margin is presented herein, along with a correlation of the analysis with recent test data.
Effect of Axial Vibrations on the Dynamics of a Helical Gear Pair
Authors: Kahraman Ahmet
Published: April 2021

In this paper, a linear dynamic model of a helical gear pair has. been developed. The model accounts for the shaft and bearing flexibilities, and the dynamic coupling among the transverse, torsional, axial and rotational motions because of the gear mesh. The natural frequencies and the mode shapes have been predicted, and the modes which are excited by the static transmission error have been identified. The forced response due to the static transmission error has also been predicted, including the dynamic mesh and bearing forces. A parametric study has been performed to investigate the effect of the helix angle on the free and forced vibrational characteristics of the gear pair. It has been shown that the helix angle can be neglected in predicting the natural frequencies and the dynamic mesh forces. An accurate prediction of dynamic bearing forces and moments requires inclusion of helix angle in the analysis.
Asymmetric Response of a Pneumatic Spring
Authors: Jettappa Richard Rodrigues
Published: April 2021

The exact equations of motion of a pneumatic spring are derived. Both single sided and double sided springs are considered. The enclosing walls are assumed to be perfectly rigid. It is shown that the single sided spring exhibits marked asymmetric response when set into motion by a non-zero initial displacement. The peaks are sharp and the troughs are flattened. The amplitude of motion is different in positive and negative directions. The two sided spring gives a symmetric response but the peaks and troughs show sharp corners indicating non-linear response. It is shown that the mounted frequency depends upon only two system parameters, namely, the initial volume and the spring area in contrast to the existing linear theory in which it depends upon two additional parameters, namely, the initial pressure and the mounted mass. The dependance of period of oscillation on the amplitude of initial displacement is demonstrated.
FE Meshing Tool for the Dynamic Analysis of Beam-Like Structures
Authors: De Smet M. , Van Brussel H. , Sas P.
Published: April 2021

This paper outlines a methodology for the automatic creation of finite element meshes used for calculating structural dynamic behaviour. Starting from the idealized geometry of the structure, the proposed Intelligent Meshing Tool determines a mesh density that a priori guarantees the resonant frequencies to be calculated within predetermined accuracy limits. Unlike most existing techniques for automatic meshing, this technique is not inherently adaptive, but does not exclude an extra adaptive mesh refinement step, either. Implementation of this methodology is discussed for structures composed of straight uniform, curved and tapered beam-like components. The feasibility of the meshing strategy is illustrated by means of an example.
Force Identification From Dynamic Response of Bi-Material Beams
Authors: Doyle James F.
Published: April 2021

The dynamic response due to impact of a 2-D bi-material system is described in terms of a waveguide model involving two displacements and a rotation. Coupled with spectral analysis, this allows measured signals to characterize the waves propagating in the system; this in turn, is used to predict responses at any locations. In particular, the impacting force can be reconstructed. The results are demonstrated on an aluminum/epoxy system.
Natural Frequencies and Mode Shapes of Elliptic Plates With Boundary Characteristic Orthogonal Polynomials As Assumed Shape Functions
Authors: Rajalingham C. , Bhat R. B. , Xistris G. D.
Published: April 2021

The natural frequencies and natural modes of vibration of uniform elliptic plates with clamped, simply supported and free boundaries are investigated using Rayleigh-Ritz method. A modified polar coordinate system is used to investigate the problem. Energy expressions in Cartesian coordinate system are transformed into the modified polar coordinate system. Boundary characteristic orthogonal polynomials in the radial direction, and trigonometric functions in the angular direction are used to express the deflection of the plate. These deflection shapes are classified into four basic categories, depending on its symmetrical or antisymmetrical property about the major and minor axes of the ellipse. The first six natural modes in each of the above categories are presented in the form of contour plots.
Circumferential Vibrations of Three Layered Sandwich Cylinders
Authors: Hamidzadeh H. R. , Chandler D. E.
Published: April 2021

The problem of forced lobar vibrations of three layered cylinders of infinite extent subjected to boundary stresses which do not vary along the axis is considered. Linear viscoelastic theory is employed and the lobar vibrations of a thick single cylinder is accurately formulated. The solution to the three constrained layer cylinders is developed by utilizing the stresses and displacement at all interfaces, and by complying with the compatibility requirements at each interface. Computed results are compared with an available approximate solution and satisfactory agreement is established. The reported solution is exact and it is not limited to thin cylinders.
Dynamic and Static Design of Engine Test Benches
Authors: Pol P. Santamarina
Published: April 2021

The elastic mechanical strength of the large and medium reciprocating engine test benches, is calculated for vertical and horizontal bendings and for torsion. The dynamic loads - horizontal vibrating forces and vertical vibrating couples (bending and torsion) and horizontal vibrating couple,- and the static loads, - distributed weight of the bench itself and the machinery and the motor torque (torsion), - are analyzed. It is pointed out that the bench body of reinforced concrete is submitted to bending moments and shearing forces and to torsion couples. This paper is the continuation of the paper “Dynamic Loads in Engine Test Benches” in 12th Biennial ASME Conference on Mechanical Vibration and Noise.
An Experimental Study of Cutting Noise Dynamics
Authors: Ya Wu , Shiqiu Ke , Shuzi Yang , Qilin Zhang , Shanxiang Xu , Yaozu Wen
Published: April 2021

Up to now little has been reported on the cutting noise in metal-cutting machine tools at home and abroad. Based on the research results available, tests on the cutting noise have been performed on three power lathes and a type Mx-4 crankshaft connecting rod neck lathe. The cutter material is hard alloy YT6x, workpiece material is nodular cast iron QT60-2, the cutting mode is broadedge plunge type turning. The influences of the cutter form, cutter angle, cutting speed, and feed on the cutting noise have been investigated using the test results. It is pointed out that the machine tool dynamic characteristics are one of the primary factors that influence the cutting noise, that there is a correlation between the cutting noise and cutting force and that the main spectral peak frequency of the cutting noise is close to the first-order modal frequency of the workpiece system. The importance of the two new discoveries lies in that a breach has been found for investigations on cutting noise dynamics.
Eigenvalue Inclusion Principles for Distributed Gyroscopic Systems
Authors: Yang B.
Published: April 2021

This paper presents several eigenvalue inclusion principles for a class of distributed gyroscopic systems under pointwise constraints. A transfer function formulation is proposed to describe the constrained system. Five types of non-dissipative constraints and their effects on the system natural frequencies are studied It is shown that the natural frequencies of the constrained gyroscopic system alternate with those of the unconstrained system.
A New Method of Time Series Analysis and its Application to Identifying Modal Parameters
Authors: He Yusheng , Deng Zhaoxiang
Published: April 2021

In the paper, the attention concentrates on the time domain modal analysis. A new method of time series analysis, which is formed mainly by an ideal modeling strategy and a new COR-IV method, is developed. In addition, an interesting parameter called as modal energy ratio, which is available for design reference, is defined and its identification algorithm is given. The new method presented in this paper and Frequency Domain Method (FDM) are performed on a frame of SG120 vehicle. It is shown by comparison between these two methods that the new method of time series analysis is practical.
Cyclic Transition Through Combination Resonances of Parametric Laminated Angle-Ply Composite Columns
Authors: Evan-lwanowski R. M. , Jia Hong-Yu , Lu Chu-Ho
Published: April 2021

Cyclic transitions through combination resonances of a laminated angle-ply, three-degrees-of-freedom column subjected to a parametric (periodic axial) load have been studied using the asymptotic method. The study included the effects of the coupling stiffnesses, fiber orientations, ply-angles, geometrical nonlinearities, load eccentricities, initial (stationary) conditions, types of the temporal modes.
Investigation of Parametric Resonance Instability in a Flexible Rod Slider Crank Mechanism
Authors: Beale David G. , Lee Shyr-Wen
Published: April 2021

A direct variational approach with a floating frame is presented to derive the ordinary differential equations of motion of a flexible rod, constant crank speed slider crank mechanism. Potential energy terms contained in the derivation include beam bending energy and energy in foreshortening of the rod tip (which were selected because of the importance of these terms in a pinned-pinned rod parametric resonance). A symbolic manipulator code is used to reduce the constrained equations of motion to unconstrained nonlinear equations. A linearized version of these equations is used to explore parametric resonance stability-instability zones at low crank speeds and small deflections by a monodromy matrix technique.
Static and Dynamic Analyses of Beam-Columns on Winkler Foundation
Authors: Lee T. W. , Cleghorn W. L. , Tabarrok B.
Published: April 2021

A finite element model is developed for static, free and forced vibration analyses of a compressed beam resting on a Winkler-type elastic foundation and subjected to transverse loads. The homogeneous solution of the governing differential equation of static equilibrium is used as shape functions when deriving the load vector, the stiffness and mass matrices. For the static case, a procedure is outlined for improving the internal distributions of deflections, rotations, bending moments and shear forces of the structure. In this procedure, exact results are obtained for concentrated, uniform and ramp distributed loads with a minimum number of elements. When considering free vibrations, natural frequencies converge rapidly with increasing numbers of elements, and are shown to agree with results obtained by other analytical methods. The effects of the axial load and elastic foundation on the natural frequencies are also illustrated. For forced vibrations, the Newmark β Method is employed for obtaining the time history response of a beam-column on an elastic foundation subjected to lateral time-dependent excitations and constant axial load.
Forced, Nonlinear, Nonplanar Oscillations of a Cantilevered Beam During Transition Through Resonance
Authors: Shyu In-Ming K. , Mook Dean T. , Plaut Raymond H.
Published: April 2021

A slender, elastic, inextensible, cantilevered beam is considered. The principal moments of inertia of the beam cross section are equal (e.g., the cross section may be circular or square). The beam is subjected to a uniformly distributed vertical force which has a static component (e.g., just the weight of the beam) and a dynamic component with constant amplitude and varying frequency Ω(t). Planar and nonplanar motions are analyzed.

The governing equations of motion are an extension of those derived by Crespo da Silva and Glynn [1,2], taking into account the static deflection. Nonlinear curvature, nonlinear inertia, torsional displacements, and viscous damping are included in the formulation. A perturbation method is applied, and quadratic and cubic terms are retained in the equations. Torsional inertia is neglected, and with the use of the inextensibility condition, the longitudinal motion is written in terms of the horizontal and vertical motions, which are then represented in terms of three vibration modes in the application of Galerkin’s method. In some cases, the time histories of the modal amplitudes are determined by numerical integration; in others, the method of multiple scales is used to obtain approximate solutions for the response.

When the forcing frequency Ω is fixed, the system exhibits primary resonance when Ω is close to a natural frequency of the beam, subharmonic resonance when Ω is close to twice or three times a natural frequency, and superharmonic resonance when Ω is close to one-half or one-third of a natural frequency. Under these resonance conditions, the planar (vertical) steady-state motion of the beam may be unstable and a non-planar (whirling) motion may occur. These stationary conditions have been examined previously [3]. Here, nonstationary conditions are studied, in which the forcing frequency Ω(t) either increases or decreases slowly through a resonance.

The time histories of the vertical and horizontal motions are determined. For the various resonances, the magnitude and form of the response depends on many factors, including the rate of change of Ω(t), the static component of the force, the amplitude of the dynamic component of the force, the amount of damping, and the initial conditions (at the beginning of the acceleration or deceleration). Attention is focused on cases that lead to nonplanar motions, and some interesting types of dynamic behavior are exhibited by the beam.
Simple Models for Periodic Lattices
Authors: Abrate Serge
Published: April 2021

In many applications, the dynamic behavior of large periodic structures must be modeled accurately, thus requiring the determination of a significant number of natural frequencies and mode shapes. In order to perform that task most efficiently, a continuum modeling approach can be adopted. The discrete structure is then replaced by a continuum model which can be analyzed more efficiently. Therefore, at the design stage many analyses can be performed while searching for the optimal solution.

Known structural models are usually used as continuum models, and several methods are available to determine the equivalent properties from the properties of the original structure. This task is usually cumbersome, and in addition, in certain cases, continuum models cannot represent all modes of deformation.

In this article, a simple approach to develop continuum models without explicit reference to an existing structural theory is presented. Very accurate results are obtained, and all vibration modes can now be handled easily.
A Method of On-Line Analysis for Mechanical Dynamic Characteristic
Authors: Wang Fengquan , Wu Huixin , Han Xiaolin , Fu Haomin
Published: April 2021

In this paper, a method of multipoint pseudorandom combined excitation with the orthogonal reciprocal repeated sequences (ORRS) is presented on the background of the on-line identification of the multivariate rotor system. The capacaty of the restraint to the identification error caused by the non-random D. C. drift of the multi-input excitation with the ORRS in the rotor system is also discussed. The validity of the method described in this paper is proved by the modelling tests of the multi-plate rotor system.
Identification of Viscously Damped Distributed Structural Dynamic Systems
Authors: Chander R. , Meyyappa M. , Hanagud S.
Published: April 2021

A frequency domain identification technique applicable to damped distributed structural dynamic systems is presented. The technique is developed for beams whose behavior can be modeled using the Euler-Bernoulli beam theory. External damping of the system is included by means of a linear viscous damping model. Parameters to be identified, mass, stiffness and damping distributions are assumed to be continuous functions over the beam. The response at a discrete number of points along the length of the beam for a given forcing function is used as the data for identification. The identification scheme involves approximating the infinite dimensional response and parameter spaces by using quintic B-splines and cubic cardinal splines, respectively. A Galerkin type weighted residual procedure, in conjunction with the least squares technique, is employed to determine the unknown parameters. Numerically simulated response data for an applied impulse load are utilized to validate the developed technique. Estimated values for the mass, stiffness and damping distributions are discussed.
The Principle of Cepstrum and its Application in Quantitative Fault Diagnostics of Gears
Authors: Tang He , Cha Jian-Zhong , Wang Yuanhui , Zhang Ce
Published: April 2021

This paper has studied the principle of cepstrum and introduced a new method which can be used to quantitatively diagnose gear-wear through cepstrum analysis of gear noise. The amplitude value of the peak in cepstrum, which represents gear mesh-harmonics in spectrum, is independent of the intensity of gear noise signal. The value can indicate quantitatively the existence of gear-wear. In the paper, the further interpretation on physical meanings of other peaks in cepstrum has been done. Based on analysing the results of experiments with gearboxes, the thresholds of the gear wear by cepstrum diagnosis have been obtained. The theoretical analysis has agreed with the experimental results very well.
Trouble Diagnosis of Diesel Valves by Sound Intensity and Vibration Signals
Authors: Sun Zhonglang , Wang Hong , Xu Xiaoling
Published: April 2021

In this paper, we study the trouble diagnosis of diesel valve train by sound intensity, especially by the technique of the Gated Spectrum Analysis. To check the efficiency and reliability of our sound intensity measurement, we record vibration signals and sound intensity simultaneously to diagnose the valve train troubles of the 290-QN diesel. Some typical troubles with the valve train are analogued, the frequency spectrum plots of the vibration signals and sound intensity signals are gotten with the help of the tape recorder which record the signals in situ, so we could identify the troubles of the valve train from these frequency spectrum plots directly.
Optimum Design of Structure by Sensitivity Analysis
Authors: Kajiwara I. , Nagamatsu A.
Published: April 2021

A series of researches by the authors on structural optimum design by sensitivity analysis is introduced. First, the sensitivity of the anti-resonance frequency is defined, and an approach to eliminate the resonance peak from the frequency response function is proposed using this sensitivity. Next, an experimental approach for structural optimization based on a vibration test is introduced. An approach for optimum design combined with substructure synthesis method is proposed, in which the objective function is an impulse response function. The proposed methods are illustrated by some examples.
An Active Vibration Control Approach for Isolating General Base Vibration
Authors: Chen Anning , Batta George R.
Published: April 2021

This paper presents an approach for active vibration control in which translational vibration and rotational vibration can be controlled jointly or separately. By doing so, the flexibility of either partially isolating or totally isolating the vibration is achieved; this flexibility can be useful in a variety of engineering applications. A generic two degree-of-freedom vibration system is analyzed and modelled as a multivariable system. The control (isolation) approach is based on multivariable feedback decoupling design. The design scheme and simulation results are presented.
Quantification of the Eigenfrequency Extraction Advantages of the Riccati Transfer Matrix Method Over the Standard Transfer Matrix Method
Authors: Zeng Xiandi , Mitchell Larry D. , Li William Xinzuo
Published: April 2021

In this paper the Riccati transfer matrix method is implemented with a goal of studying its ability to expand eigenextraction capability. A pin-pin uniform beam is used as a numerical example to demonstrate the numerical stability of the Riccati transfer matrix method in finding higher natural frequencies. The results are compared with those from analytical solution and those from the standard transfer matrix method. It is shown that the number of frequency that can be found with the Riccati transfer matrix method is dependent on the number of segments into which the beam is evenly divided. It is also shown that the Riccati transfer matrix method exhibits the infinite wrap problem, i.e, the determinant has a number of infinite wrap points, where the determinant goes from +∞ to −∞. A simple method is suggested to take care of this problem when determinant search is used to find the natural frequencies. The mathematical demonstration of the numerical stability and infinite wrap associated with the Riccati transfer matrix method is provided.
Noninvasive Evaluation of the Prosthetic Hip Joint Using the Acousto-Ultrasonic Technique
Authors: Vaidya U. K. , Raju P. K.
Published: April 2021

The need to identify the bond quality between the implant material and the bone is crucial in prosthetic orthopedic applications. When in service, there is a likelihood of loosening of the implant-bone interface which can result in loss of mechanical rigidity and stress concentration in the vicinity of the bone and the implant. Hence, noninvasive techniques are necessary to assess the bond quality in orthopedic implants. The purpose of the present work was to investigate the bond quality in a hip bone with a steel implant, using the acousto-ultrasonics technique in which two methods — acoustic emission and ultrasonics are used in combination. The acousto-ultrasonic technique was found to be sensitive to a loose joint when compared to a good one, indicating variation in terms of the ringdown counts and energy content of the acoustic emission events.
Two-Dimensional Velocity Data Smoothing and Structural Angular Velocity Extraction Using a DFT-IDFT Technique
Authors: Sun F. P. , Mitchell Larry D.
Published: April 2021

Structure dynamic imaging using a scanning Laser Doppler Velocimeter provides a feasible and efficient means for high-resolution rotational velocity extraction. It shifts the experimentalists’ ground from physical measurement of rotations to mathematical data manipulation and the differentiation of the experimental translational velocity. Consequently, the differentiability of velocity data becomes a major issue since such data are sequences of discrete numbers and are usually noise contaminated. This paper presents an effective method for two-dimensional data set smoothing using one-dimensional Discrete Fourier Transform-Inverse Discrete Fourier Transform (DFT-IDFT) process as a lowpass spatial filter. The angular velocities can then be defined analytically by differentiation in the spatial frequency domain. The technique is prototyped with several real experimental data sets from a steel plate excited at its resonance modes. Special attention is paid to the efforts on making 2-D data set periodic in the data frame as well as to the related error analysis. A preliminary criterion is suggested for determination of “spatial frequency truncation” in IDFT.
On Object-Oriented Databases, Materialized Views, and Concurrent Engineering
Authors: Hardwick Martin , Downie Blair R.
Published: April 2021

Concurrent engineering seeks to reduce the length of the design life cycle by allowing multiple engineers to work on a design concurrently using their different design tools. A major stumbling block in achieving this goal is that most design tools use different file formats. Emerging standards such as STEP/PDES/EXPRESS reduce this barrier, but conformance to standards is not enough. One reason design tools have different file formats is because each tool requires a different perspective or view of the design. Engineering databases must provide designers with the ability to define application specific views of design data, and the ability to propagate changes among those related views. In this paper, we examine how an object-oriented database system can support the definition of application views using a class hierarchy and multiple inheritance.
Numerical Research on the Interaction of Multidirectional Random Waves With a Large-Scale Offshore Wind Turbine Foundation
Authors: Ji Xinran , Wang Daoru
Published: April 2021

Real sea waves are multidirectional, but most of researches are focused on the unidirectional wave. Special to the numerical wave basin based on OpenFOAM to simulate the propagation of multidirectional random wave and its interaction with structure has the insufficient of large amount of calculation, to overcome this problem, a one-way coupling model is established based on the potential theory and OpenFOAM wave basin, and the amount of calculation is reduced and the computational efficiency is improved. Base on the coupling model, the multidirectional random waves and its interaction with a large-scale offshore wind turbine foundation are simulated. In the outer domain, the multidirectional random wave is generated by the potential theory quickly. The interaction of multidirectional waves with the offshore wind turbine foundation is simulated in the inner domain by solving the Navier-Stokes equation. The result shows that the wave directionality has a significant effect on the interaction of multidirectional irregular waves with cylinder.
A Reduced-Order Mathematical Model for the Current-Induced Motion of a Floating Offshore Wind Turbine
Authors: de Oliveira Éverton L. , Pesce Celso P. , Mendes Bruno , Orsino Renato M. M. , Franzini Guilherme R.
Published: April 2021

Floating offshore platforms motions induced by currents are quite complex phenomena, in general. In particular, VIM, Vortex-Induced Motion, is a type often encountered in platforms with circular columns. Recently, VIM has been observed in towing tank tests with a small-scale model of a Floating Offshore Wind Turbine (FOWT), the OC4 Phase II floater, a 3+1 columns platform. The present paper proposes a reduced-order mathematical model (ROM) to assess VIM of a FOWT. The ROM is derived on the horizontal plane, including yaw motions and nonlinear mooring forces. Current forces are represented through ‘wake variables’, adapting phenomenological models firstly used for VIM of mono-column platforms. The ROM is built upon a set of eleven generalized coordinates, three for the rigid body motion on the horizontal plane and a pair of wake variables for each column, resulting in a system of eleven nonlinear second-order ODEs. The pairs of wake variables obey van der Pol equations, and use hydrodynamic coefficients and parameters obtained from previous experiments with small draught cylinders. Hydro-dynamic interferences among columns or heave plates effects on the flow are not considered, for simplicity. The validity of the proposed model is assessed having the mentioned small-scale experimental campaign as a case study. The simulations are carried out at three different current incidence angles, 0, 90 and 180 degrees, spanning a large range of reduced velocities. The simulations reproduce well the oscillations observed in the experimental tests. A good agreement in transverse oscillations is found, including lock-in regions. The simulations also depict a possibly important phenomenon: a resonant yaw motion emerging at high reduced velocities.
Experimental Validation of a Wave Elevation Observer on a Floating Wind Turbine Model
Authors: Di Carlo Simone , Fontanella Alessandro , Facchinetti Alan , Muggiasca Sara , Taruffi Federico , Belloli Marco
Published: April 2021

The scope of this work is to investigate if and how it is possible to estimate the incident wave elevation on a floating wind turbine, with the purpose of improved control strategies. A Kalman based algorithm is proposed, which receives as input the rigid motions of the floater and estimates the wave elevation hitting the floating platform. The structure of the observer is described and the estimator is tested numerically on the OC3-Hywind platform coupled with the 5-MW reference wind turbine from NREL. Limitations to the estimation procedure are discussed. Finally the algorithm is tested on experimental data coming from a wave basin experimental campaign on a floating wind turbine model. The algorithm still needs improvements, but results are encouraging in the development of this technology.
Study of Motion Performance of a Floating System With Four Moonpools and a VAWT
Authors: Tan Lei , Moritsu Satsuya , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi
Published: April 2021

In this paper the hydrodynamic performance of a barge-type floating foundation installed with four moonpools and a VAWT was investigated through model tests and theoretical calculations. The characteristics of wave-induced motion responses and tether tensions and the effects of turbine rotations were examined. Physical model tests were conducted in a wave tank using regular waves with the wave period ranging from 0.6 to 1.6 seconds and 0.01 or 0.02 meters in amplitude. A 2-MW-class VAWT was modelled with a scale ratio of 1/100 in the experiments. By varying the mass and the rotational speed of the turbine, gyroscopic moment effects were studied. In addition, numerical calculations based on the linear potential theory and Green function method were carried out to estimate motion responses and tether tensions.

The present results indicate that the gyroscopic effect due to turbine rotations can be profound. It was found that the first-order motions of the floating system were substantially reduced by the gyroscopic effect, while the second-order motions and tether tensions may be significantly increased. Moreover, the viscous damping of water motions in moonpools was found not negligible. As a result, theoretical models based on linear potential theory should be used with care in hydrodynamic analysis with regard to the floating systems with VAWT rotations. In addition, the present in-house program code was validated against WAMIT through comparing hydrodynamic predictions of a floating foundation with four moonpools, with reasonable agreement.
A CFD Study for Floating Offshore Wind Turbine Aerodynamics in Turbulent Wind Field
Authors: Zhou Yang , Xiao Qing , Liu Yuanchuan , Incecik Atilla , Peyrard Christophe , Wan Decheng , Li Sunwei
Published: April 2021

The present study is aimed at investigating the turbulent wind effect on FOWT through the usage of a high-fidelity computational fluid dynamics (CFD) method. This method is believed to resolve the wind field, giving us a more in-depth examination into the aerodynamics of FOWT. The work is built upon our previous studies on the modelling of a coupled aero-hydro-mooring FOWT system under regular wave and uniform wind. In the present study, we replaced the previously uniform wind with a temporal and spatial variable turbulent wind field using a time-varying spectrum. The turbulent wind is generated with Mann’s wind turbulence model while the Von Karman wind spectrum is used to represent wind turbulence. The present study shows that when turbulent wind is present, there may be fluctuations of the rotor thrust and power outputs, causing the non-uniform wake region. Despite this, both the dynamic motions and the mooring tensions of the floater are not significantly influenced by the wind turbulence under the present inflow wind conditions.
Prevention of Offshore Wind Power Cable Incidents by Employing Offshore Oil/Gas Common Practices
Authors: McLaurin David , Aston Alan , Brand John
Published: April 2021

It has been observed that, although submarine power cables have a critical role to wind power arrays and power export to shore, they are often overlooked at early stages of projects and oversimplified during late stages. This leads to lack of attention given during cable design and planning, as well as pressured schedules during manufacturing, testing and installation. The significant number of incidents attributed to offshore submarine cables during construction has increased overall project risk, lowered system average power availability and increased insurance costs. Lack of proper routing can also result in an inability to maintain asset integrity for the project design life. Despite the attention that submarine power cables have received over the past few years, the number and cost of incidents does not appear to be decreasing.

A comparison can be made between offshore HVAC and HVDC cables used for wind power and offshore umbilicals and MV cables used in the oil and gas sector. These umbilicals are often similar in weight, size and bending stiffness, and have similar design, manufacturing, routing and installation challenges, but with a fraction of the incidents observed with offshore wind array and export cables. An additional caveat is that the offshore oil and gas sector has achieved a reliable track record while installing and maintaining these umbilicals and cables in fully dynamic conditions (ultra-deep water) as well static conditions. One primary difference between how the oil and gas sector executes these systems are design, planning and specification from an early stage of the project. Significant attention is given at an early stage to quality control, including offshore routing and umbilical testing specifically to avoid incidents resulting in umbilical damage due to the tension and crushing forces during installation as well as ambient seawater and seabed interaction. Management of these risks are documented, and optimal mitigation strategies are implemented early in the design phase.

This paper will discuss the types of incidents which have been observed during construction and installation of submarine HVAC/HVDC cables in the wind power sector and how they could have been prevented by normal practices of the offshore oil/gas sector from early design and planning all the way to installation and commissioning.
A Multidimensional FEA Approach for Determination of Hot Spot Stresses in Offshore Jacket Structures
Authors: Hectors Kris , Saeed Hasan , De Waele Wim
Published: April 2021

A new fatigue lifetime assessment approach for offshore jacket structures is presented. It combines a previously developed numerical framework for automated determination of stress concentration factors in tubular joints and a multidimensional finite element modelling approach. The approach is explained based on a case study of an OC4 type offshore jacket. To determine the fatigue life, a directional wave spectrum is combined with the JONSWAP spectrum. The fatigue life of the jacket is assessed for two different sea states. Based on the fatigue analysis the most fatigue critical wave direction is identified. The hot spot stresses in one of the most critical joints are determined and compared to stresses obtained with the Efthymiou equations. The shortcomings of these equations are highlighted and it is shown how the numerical framework can be used to improve the current fatigue design philosophy for offshore jackets which relies on the Efthymiou equations for stress concentration factors in the welded tubular joints.
Investigation of the Capacity Factor of Weather-Routed Energy Ships Deployed in the Near-Shore
Authors: Abd Jamil Roshamida , Gilloteaux Jean-Christophe , Lelong Philippe , Babarit Aurélien
Published: April 2021

The energy ship concept has been proposed as an alternative wind power conversion system to harvest offshore wind energy. Energy ships are ships propelled by the wind and which generate electricity by means of water turbines attached underneath their hull, The generated electricity is stored on-board (batteries, hydrogen, etc.) It has been shown that energy ships deployed far-offshore in the North Atlantic Ocean may achieve capacity factors over 80% using weather-routing. The present paper complements this research by investigating the capacity factors of energy ships harvesting wind power in the near-shore. Two case studies are considered: the French islands of Saint-Pierre et-Miquelon, near Canada, and Ile de Sein, near metropolitan France.

The methodology is as follows. First, the design of the energy ship considered in this study is presented. It was developed using an in-house Velocity, and Power Performance Program (VPPP) developed at LHEEA. The velocity and power production polar plots of the ship were used as input to a modified version of the weather-routing software QtVlm. This software was then used for capacity factor optimization using 10m altitude wind data analysis which was extracted from the ERA-Interim dataset provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Three years (2015, 2016, and 2017) data are considered. The results show that average capacity factors of approximately 40% and 40% can be achieved at Ile de Sein and Saint-Pierre-et-Miquelon with considered energy ship design.
Concept for a Wind-Yawing Shallow-Draft Floating Turbine
Authors: Papadopoulos J. M. , Qiao C. , Myers A. T.
Published: April 2021

Offshore wind turbines are poised to become a vital part of the global energy landscape — particularly the floating types which give access to a much greater wind power resource. The design possibilities for floating turbines are so different from onshore and offshore fixed-bottom turbines, that a cost-reducing re-imagining may be justified. Apart from the expense of an offshore transmission cable and substation, the costs of hardware for offshore bottom-fixed wind turbines (CAPEX) are roughly twice as much as for onshore. Much of the extra cost can be attributed to the mass of the above- and underwater support and expensive installation. In this paper, we reconsider two aspects of present-day offshore turbines: (a) maintaining a land-turbine architecture (a slender tower with the rotor cantilevered from a yawing, equipment-filled nacelle); (b) seeking to minimize wave-induced motion and loads of the above-water plant. Our aim is an offshore floating design that is potentially less expensive than offshore fixed-bottom units. We outline the preliminary structural analyses that underlie a design focused on weight, cost reduction, and ease of manufacturing. This includes lattice towers, tubular hub and axle, and needle-roller bearings. The biggest concerns about the proposed lightweight system involve motions and forces induced by waves. Shallow-draft floats will follow the waves, leading to greater rotor translation and precession; and lattice towers may be subject to impact loads, ice buildup, and fouling. We present analysis of some of these motions and forces, along with resulting estimates for required structural weight as a preliminary investigation into the feasibility of this lightweight concept.
Implementation and Verification of Cable Bending Stiffness in MoorDyn
Authors: Hall Matthew , Sirnivas Senu , Yu Yi-Hsiang
Published: April 2021

The relatively large motions experienced by floating wind turbines and wave energy converters pose a challenge for power cables, whose internal components provide significant bending resistance and are sensitive to deformation. The behavior and associated design considerations of power cables in these highly dynamic applications make coupled analysis relevant for design.

Bending stiffness capabilities have recently been added to the lumped-mass mooring dynamics model MoorDyn to enable simulation of dynamic power cables. MoorDyn is a common modeling choice for floating wind energy simulation (often coupled with OpenFAST) and floating wave energy converter simulation (often coupled with WEC-Sim) but the model’s previous line elasticity formulation only considered axial stiffness. To properly capture the dynamics of power cables, a bending stiffness model has been added that approximates cable curvature based on the difference in tangent vectors of adjacent elements. The resulting bending moment is realized by applying forces on adjacent nodes, enabling cable modeling while leaving the underlying lumped-mass formulation unchanged.

In this paper, the new bending stiffness implementation is verified in static conditions against analytical solutions and then in a dynamic power cable scenario in comparison with the commercial simulator OrcaFlex. The dynamic scenario uses prescribed motions and includes wave loadings on the cable. Results indicate correct implementation of bending stiffness and show close agreement with OrcaFlex.