Structural Control Devices Research Articles

Effect of scour on the fatigue life of offshore wind turbines and its prevention through passive structural control

Abstract. Offshore wind turbine (OWT) support structures are exposed to the risk of fatigue damage and scour, and this risk can be effectively mitigated by installing structural control devices such as tuned mass dampers (TMDs). However, time-varying scour altering OWTs' dynamic characteristics has an impact on the TMD design and fatigue life, which has rarely been studied before. In this paper, a simplified modal model is used to investigate the influence of scour and a TMD on the fatigue life evaluation of a 5 MW OWT's support structure, and a traditional method and a newly developed optimization technique are both presented to obtain TMD parameters. This optimization technique aims at finding optimal parameters of the TMD which maximize the fatigue life of a hotspot at the mudline, and the effect of time-varying scour can be considered. This study assumes that the TMD operates in the fore–aft (FA) direction, while the vibration in the side–side (SS) direction is uncontrolled. Results show that scour can decrease the fatigue life by about 24.1 % and that the TMD can effectively suppress vibration and increase the fatigue life. When the scour depth reaches 1.3 times the pile diameter, the TMD with a mass ratio of 1 % can increase the fatigue life of an OWT's support structure by about 64.6 %. Further, it is found that the fatigue life can be extended by 25 % with the TMD optimized by the proposed optimization technique rather than using a traditional design method which does not take the change in dynamic characteristics into account.

Fluid inerter-based vibration control of multi-modal structures subjected to vertical vibration

The so-called inerter is an attracting device that offers a solution to the goal of realizing or improving structural control devices with high mass ratios while avoiding the undesirable increase in dead load. The research presented here focuses on evaluating the performance of a fluid inerter in mitigating vertical vibrations of structures that exhibit multi-modal behavior, such as plates. First, a numerical study based on previous experimental data investigates the properties of the connection between the inerter and the structure to be controlled. Considering that a flexible connection has been shown to introduce a linearization effect, while a rigid connection of the inerter to the controlled structure can achieve significant displacement reductions, the influence of these two connection types over different inertance ratios is analyzed. To evaluate the practical suitability of the flexible connection to reduce the inherent nonlinear effects associated with the device, a novel application of the fluid inerter for vibration control in multi-modal structures is presented, exemplified by a cross-laminated timber panel, and compares its control performance with that of a conventional Tuned Mass Damper (TMD). This provides insight into the effectiveness of the inerter in controlling vertical vibrations. In addition, optimization procedures are employed to determine connection parameters that enhance the effectiveness of both the TMD and the inerter in mitigating vertical vibrations.

Magnetorheological Fluid Dampers: A Close Look at Efficient Parametric Models

The reasonable efficiency, high reliability, and minimal maintenance requirements of the semiactive control algorithms make this form of structural control the most successful method from a practical point of view. In addition, significant progress has been made in structural control devices. Magnetorheological (MR) dampers have been the subject of extensive research. In order to develop and implement a successful structural control algorithm, a deep understanding of their operation is required. Therefore, many efforts have been made to classify MR dampers as efficient tools; however, their complicated behavior has also been noted. Various relations have been proposed to describe the highly nonlinear behavior of MR dampers. To develop an efficient control algorithm, one must first properly understand the seismic behavior of the structure and the control device as well as its handling. The handling of the device will be efficient if there is a description for its control, a so-called inverse model. This model is an answer to the question of whether the proposed device model can be written in a form that practically brings the generated damping force as close as possible to the desired force. In the identification process, the selection of a basic mathematical model is critical. In this review article, we have compiled successful parametric models that accurately replicate the behavior of MR dampers. Since the primary functionality of the device is crucial for the development of a competent control algorithm, we have endeavored to investigate and present the reversibility of the proposed models. We also delved at the characteristics of the parameters that enable precise communication between the central control unit and the device. These parameters, which enable the dialog between the processing unit and the control devices, will play an important role in the development of the inverse model in its simplicity and efficiency.

Robustness Evaluation of Negative Stiffness Damper for Cable Vibration Mitigation Based on Interval Model with Experimental Validation

The negative stiffness damper (NSD) has emerged as a promising passive vibration control device for cable structures due to its simplicity and effectiveness. However, uncertainties stemming from both internal and external environmental factors can potentially compromise the NSD’s performance in real‐world applications, posing risks to cable safety. In response, this paper conducts a robustness evaluation on an integrated cable‐NSD system, taking into account various potential uncertainties. Specifically, the uncertain parameters are described by interval variables. Consequently, an interval model is constructed to delineate the boundaries of cable dynamic responses when subjected to these uncertainties. The model’s accuracy is validated against experimental results. Subsequent simulations involve assessing interval responses for both single‐ and multimode cable vibrations under varying uncertainties. Finally, the NSD’s robustness concerning cable vibration control is evaluated using the model, which incorporates the first‐passage theory. This analysis delves into the relationships among confidence levels, performance measures, and the variation range of uncertainties. The results indicate that for single‐mode vibration control, there is a 90% confidence level that the damping ratio reduction remains within 10%. As for multimode vibration control, a 90% confidence level is established that the amplification falls within 17%.

A Case Study of Magnetorheological Damper Models with Experimental Confirmation

This study aims to review and evaluate the performance of nonparametric and parametric models of magnetorheological (MR) dampers, which are commonly used as structural control devices. To do so, a comprehensive experimental investigation was conducted to examine the behavior of MR dampers to ascertain the performance of the control device while mimicking the alignment when it is used as a structural control device. A total of 156 performance tests were performed, and the results were compared with an optimal numerical Bouc-Wen model. The parameters obtained from performance testing were employed to define the coefficient of determination (R2), which reflects the accuracy of the damper model in predicting the performance of the control device subjected to different external forces. The findings suggest that the parameters of the MR damper obtained from testing the device in a horizontal orientation that simulates its position in practical structural control applications can be reliably predicted by the modified Bouc-Wen model. This study provides useful information on the efficiency and accuracy of MR damper models that can be utilized in the realm of structural vibration control.

Use of silicon rubber as a viscoelastic material in dampers

One of the most extensively utilized structural control devices is the viscoelastic damper (VD), and significant study has gone into enhancing their efficiency in structures. The mechanical response of a VD supplied with silicone rubber as viscoelastic material (SRD) under various loading conditions is investigated in this research. A conventional VD is the SRD, which is made up of dual layers of rubber mounted between three steel plates. A total of two specimens were produced. To evaluate the influence of strain amplitude and excitation frequency on the mechanical characteristics of SRD, each damper was exposed to harmonic loading with different values. Hysteretic loops for each loading case were extracted, and the variations of several mechanical parameters with the variated loading conditions were inspected. The results indicate that SRD has a high energy dissipation capacity, and has stable performance under different working conditions. Finally, a proper simplified element model was created using SAP2000 software to evaluate the dissipation characteristics and control impact of the SRD in structures, and then a time history analysis was executed on multi storey structure. Due to the obvious dampers’ extra stiffness and efficient damping property, the control impact of the SRD dampers on structural displacement is preferred and reflected on reducing the excessive displacement due to structure movement, according to data obtained.

Response of a building structure due to sloshing effect in an overhead water tank

Sloshing is a violent resonant fluid motion in a water tank or any other tank containing liquid. When a fluid moves and interacts with its container, the dynamic pressures of such interaction may cause large deformation in the container wall as well as the supporting structure, which results in failure of the tank. From the available literatures on water tank and sloshing effects on the tank, it was found that, an oscillation of the liquid, may result in negative effects such as deformations and ruptures of the tank walls due to impact. From the literatures, it has been observed that when the earthquake occurs, the tank moves dynamically creating a sloshing effect on the tank’s surface and creating impact loads over the structural parts of the tank, especially on the walls of the tank, generating more stresses and ultimately resulting in critical failure. But at the same time very less work was carried out on the response of the structure due to the sloshing effect in an overhead water tank for pure water inside condition for various a/H ratios (a-height of water inside tank and H-Height of the tank).In the literatures impact loading is not considered, It could be considered along with sloshing effect on structure. According to the various literatures that have been studied in this paper, the study for the creation of structural control devices to manage sloshing has received significant attention recently, particularly focused on reducing the effects of earthquake and wind actions, and it was found that Tuned Liquid Dampers are helpful in this regard. Few of the researchers analyzed various earthquakes, namely, El Centro earthquake, Bhuj earthquake, Washington earthquake, and values of deflections, bending moments, shear forces, base shear values, displacement values, etc., were studied and compared. Even few authors investigated soil-structure interaction and how the sloshing affects the behavior of tank concluding that in stiff soil, effect of sloshing on responses is more. This study is aimed at the gaps that have been made in literature and suggests carry out the analysis for checking the response of a building structure finding due to the sloshing effect in an overhead water tank. This work proposes that, the tank design must be carried out by considering and analyzing the dynamic response of a structure during sloshing, comparing the response of the structure against impact loads, temperature stresses, and other critical loads during sloshing of the water tank by using computational fluid dynamics and response spectrum method or time history method. Also, experimental analysis (shake table analysis) should be carried out to validate the simulation results with the theoretical calculations in terms of displacement, base shear, and the time period.

Analysis on seismic control strategies for structural control device: A comparative study

The paper explores various control strategies proposed by researchers from decades ago in controlling the building structural system. It focuses on hybrid mass dampers used by many researchers in their previous work because the implementation of this device needs an excellent control strategy to provide a better performance in suppressing building vibration. The suitable choice of control strategy in structural control is important in giving the best structure response to withstand an earthquake or strong wind. Based on previous structure and control strategies, a simulation for a two-storey building structure system equipped with a hybrid mass damper at the top building has been conducted. Fuzzy logic controller (FLC), Sliding mode controller (SMC) and fuzzy sliding mode controller (FSMC) are used to suppress the building structure vibration during an earthquake by giving input from seismic excitation taken from El Centro earthquake. The simulation result shows that FSMC technique provides better performance compared to FLC and SMC in suppressing the building vibration based on the displacement response and frequency response. This paper concludes with the problems left and recommendations for structural control improvement.

A Review Paper on Comparative Analysis on RCC Structure with Energy Dissipation Device and Composite Structure

Abstract: In recent years considerable attention has been paid to research and development of structural vibration control devices with particular emphasis on mitigation of wind and seismic response of buildings. Many vibration-control measures like passive, active, semi-active and hybrid vibration control methods have been developed. Base isolation is a passive vibration control system. The isolator partially reflects and partially absorbs input seismic energy before it gets transmitted to the superstructure. Lead rubber bearing isolators are placed between the superstructure and foundation, which reduces the horizontal stiffness of the system. It thereby increases the time period of the structure and decreases the spectral acceleration of the structure. The superstructure acts like a rigid body, thus inter storey drift is reduced. This study is concerned with the effects of various vertical irregularities on the seismic response of a structure and controls this response using base isolation. The objective of the study is to carry out response spectrum analysis. The predominant lateral loads acting upon building structures are earthquake and wind induced forces. If wind load is much greaterthan earthquake load, the lateral force resisting system required to tackle wind loading may be enough to resist the smaller earthquake load. In this situation, a seismic base isolator will not bring any benefit to the building system. Furthermore, if time period of a building without isolator is greater, incorporation of isolator will not bring much difference to the building behavior with respect to seismic load. Additionally, for buildings with lowerstructural time periods, incorporation of an isolator will greatly alter the seismic behavior

Mitigating Structural Vibrations due to Earthquake with Application of Slope Bottom Tuned Liquid Dampers

Earthquakes are one of man’s most feared natural phenomena, producing almost instantaneous destruction of buildings and other constructed facilities. In order to mitigate damage of structures and save the life, various measures are adopted and use of structural control devices is one of them . Structural control devices can enhance the integrity of structures without increasing the dimensions of structural members. In this study, an attempt has been made to systematically investigate the performance of structural control device namely, tuned liquid damper (TLD) for controlling the dynamic response of reinforced concrete (RC) framed structure. Dynamic analysis of a 10 story RC framed structure with both flat and slope (W or central slope) bottom rectangular TLDs, subjected to five earthquake time histories have been performed. Key results have been presented in the form of tuning ratio, liquid mass reduction and displacement response reduction due to slope at bottom TLD. For the case of TLDs with central slope, the analyses have been performed for slope angle ranging from 5-14º. Based on the study, it has been observed that, tuning ratio of TLD decreases with increase of central slope at the bottom of TLD, the variation of liquid mass reduction with slope angle has been observed to be linear and reduction in displacement of structure increases with increase in central slope angle.

Feasibility Study of Actively-Controlled Tuned Inertial Mass Electromagnetic Transducers for Seismic Protection

ABSTRACT This paper aims to investigate the effectiveness of actively controlled inerter-based structural control devices. As an example, a tuned inertial mass electromagnetic transducer (TIMET) consisting of an inerter, a tuning spring, and a motor is employed, and the performance when the motor is controlled actively is evaluated. Moreover, the energy generated and consumed by the motor during seismic events is examined, and the feasibility of the self-powered control scheme is discussed as well. Numerical studies carried out on the benchmark three-story building show that actively -controlled TIMETs work better than the passive system and that the self-powered system is highly feasible.

Vibration Control of Coupled Wind Tower–Nacelle–Blade System

Wind turbines are slender and flexible structures which can undergo large amplitude vibrations when subjected to external loads and, an important way to reduce these excessive vibrations is to apply structural control. In this work, the vibration control of the coupled wind tower–blade system subjected to external lateral loads and rotating blade is studied. To model the tower and blade, the nonlinear Euler–Bernoulli beam theory was applied, and the structural control device considered is a nonlinear inverted tuned mass damper pendulum (ITMDP), located at the top of the tower. The Rayleigh–Ritz method, together with Hamilton’s principle, is applied to obtain a set of coupled nonlinear ordinary differential equations of motion which are in turn solved by the Runge–Kutta method. First, the dynamic instability of the system is studied by considering the variation of the natural frequencies of the tower, as a function of the speed of rotation of the blade and the veering phenomenon is observed. The optimum parameters for the ITMDP are obtained and, a nonlinear dynamic analysis is performed to evaluate the influence of the tuned mass damper (TMD) in the nonlinear regime, by obtaining the time responses, resonance curves, Poincaré maps and basins of attraction. The obtained results show the importance of considering the coupled system and the good performance of the structural control in the dynamic behavior of the system.

Numerical study of a point absorber wave energy converter with tuned variable inerter

This paper introduces a novel point absorber wave energy converter (WEC) with tuned variable inerter (TVI). Originally, the tuned inerter (TI), consisting of a tuning spring, an inerter, and a dashpot element, was introduced in the field of civil engineering as a control device for structures subjected to seismic loadings. Moreover, a point absorber WEC equipped with TI, in which a motor is used for the dashpot element, has been proposed and its effectiveness has been shown. However, since the TI mechanism takes advantage of the resonance of the inerter to absorb energy from vibrating buoys, it has been pointed out that the TI could not respond well to the dominant period changes of ocean waves. Thus, for further improvement, a system to control the inerter is developed because the effective period is determined by the tuning spring stiffness and the inerter. In this system, the dominant wave period is calculated by the Fast Fourier Transform using the wave amplitude and the inerter and the motor current are adjusted accordingly. Numerical results obtained from the WEC-Sim showed that the proposed TVI system responded appropriately to the wave period changes and works better than the TI system.

Design Method of Tuned Mass Damper by Linear-Matrix-Inequality-Based Robust Control Theory for Seismic Excitation

AbstractThis paper presents a new design method based on a robust-control strategy in the form of a linear matrix inequality (LMI) approach for a passive tuned mass damper (TMD), which is one of the common passive-control devices for structural vibration control. To apply the robust control theory, we first present an equivalent expression that describes a passive TMD as an active TMD. Then, some LMI-based condition is derived that not only guarantees robust stability but also allows us to adjust the robust H∞ performance. In particular, this paper considers the transfer function from a seismic-wave input to structural responses. Unlike other methods, this method formulates the problem to be a convex optimization problem that ensures a global optimal solution and considers uncertainties of mass, damping, and stiffness of a structure for designing a TMD. Numerical example uses both a single-degree-of-freedom (SDOF) and 10DOF models and seismic waves. The simulation results demonstrated that the TMD that is designed by the presented method has good control performance even if the structural model includes uncertainties, which are the modeling errors.

TMD stroke limiting influence on barge-type floating wind turbines

In this paper, passive structural control techniques are applied to a barge-type Floating Offshore Wind Turbine (FOWT) to mitigate the impact of pendulum effect loads. The passive structural control device, a tuned mass damper (TMD) installed in the nacelle, is analyzed on a reduced dynamics FOWT model. Genetic algorithms are used for the optimization process, taking the tower fatigue as the fitness function, implemented as the standard deviation of the fore-aft tower top displacement. The optimization of the TMD shows that its resulting stroke is unfeasible in terms of space needed for installation. Therefore, the addition of stroke-limiting stops to the TMD should be considered. A new optimization, including stops, yields a clear improvement of the device performance while limiting the stroke to the nacelle dimensions. It is observed that the stops allow to mitigate the second collective platform pitch-tower bending mode in addition to the first one. Finally, a third case is presented, considering the whole stops configuration as additional variables in the optimization loop. This last case improved the TMD performance in terms of vibration suppression rate, proving the effectiveness of optimizing stops for mass and space constrained applications.

A Modified Fractional-Order Derivative Zener Model for Rubber-Like Devices for Structural Control

AbstractFractional-order derivative (FD) models are widely used to describe the dynamic behavior of rubber-like materials. However, experiments have shown that FD models cannot reproduce the amplit...

Analysis of the Effects of the Location of Passive Control Devices on the Platform of a Floating Wind Turbine

Floating offshore wind turbines (FOWT) are subjected to strong loads, mainly due to wind and waves. These disturbances cause undesirable vibrations that affect the structure of these devices, increasing the fatigue and reducing its energy efficiency. Among others, a possible way to enhance the performance of these wind energy devices installed in deep waters is to combine them with other marine energy systems, which may, in addition, improve its stability. The purpose of this work is to analyze the effects that installing some devices on the platform of a barge-type wind turbine have on the vibrations of the structure. To do so, two passive control devices, TMD (Tuned Mass Damper), have been installed on the platform of the floating device, with different positions and orientations. TMDs are usually installed in the nacelle or in the tower, which imposes space, weight, and size hard constraints. An analysis has been carried out, using the FAST software model of the NREL-5MW FOWT. The results of the suppression rate of the tower top displacement and the platform pitch have been obtained for different locations of the structural control devices. They have been compared with the system without TMD. As a conclusion, it is possible to say that these passive devices can improve the stability of the FOWT and reduce the vibrations of the marine turbine. However, it is indispensable to carry out a previous analysis to find the optimal orientation and position of the TMDs on the platform.

Adaptation of a Deep Liquid-Containing Tank into an Effective Structural Vibration Control Device by a Submerged Cylindrical Pendulum Appendage

Due to a high proportion of impulsive liquid mass and low inherent damping, liquid-containing deep tanks, such as conventional overhead water tanks, are generally not considered for design as tuned liquid dampers (TLDs) for passive vibration control of structures under lateral excitation. This paper presents a novel concept to convert deep tanks into effective vibration control systems through the incorporation of a submerged cylindrical pendulum appendage (CPA). The CPA is placed in the impulsive liquid zone of the tank and its oscillating frequency is tuned to the dominant frequency of the primary structure. When laterally excited, the primary structure transfers vibrational energy to the CPA, thereby setting it into oscillation. The motion of the CPA is opposed by the drag exerted by the surrounding liquid on it, which leads to dissipation of the vibrational energy. This particular design utilizes impulsive liquid mass in the energy dissipation mechanism, while allowing fluctuation in the liquid level in the upper region of the tank, thereby fulfilling the functional requirements of the tank. In this paper, the mathematical model and working principle of the deep tank with CPA (DT-CPA) damper are developed. The equations of motion of a two degree-of-freedom (2-DOF) structure-damper system are derived. The design of the DT-CPA damper is illustrated considering an example structure and the performance of the damper is examined by subjecting the structure-damper system to pre-recorded seismic base excitations. The sensitivity of the performance of the proposed damper to tuning ratio is further studied. Results indicate that the DT-CPA damper is effective in controlling structural vibrations and its performance is comparable to that of a conventional tuned mass damper (TMD) and even slightly superior to that of a conventional TLD system of the shallow tank configuration. The proposed concept thus holds potential for the utilization of deep tanks as energy dissipation devices with minimal interference to their usual functionality.

Numerical evaluation of a two-body point absorber wave energy converter with a tuned inerter

To increase the amount of energy captured from a vibrating buoy in the ocean with a simple mechanism, this paper proposes a two-body point absorber wave energy converter (WEC) with a tuned inerter. The tuned inerter mechanism consists of a spring, a linear damping element, and a component called inerter. This mechanism was originally proposed in the field of civil engineering as a structural control device which can absorb energy from vibrating structures effectively by taking advantage of the resonance effect of the inerter part. In addition to this mechanism where a generator is used as the linear damping element, the current of the generator for the power take-off system is controlled based on the algorithms proposed in literature to achieve further improvement of the power generation capability. In this research, a detailed analytical model of the proposed WEC is introduced and developed. Then the power generation performances of full-scale WEC models are assessed through numerical simulation studies using WAMIT software and it is shown that the current-controlled WEC with the proposed mechanism achieves an 88% increase compared to the conventional one for the JONSWAP spectrum with 6 s peak period and 1 m significant wave height.

Development of a Structural Control and Power Generation Device Employing an Inerter Mechanism for Floating Offshore Wind Turbines

Development of a Structural Control and Power Generation Device Employing an Inerter Mechanism for Floating Offshore Wind Turbines