Asymmetric Blade Research Articles

Investigation of Vertical-axis Tidal Turbine Mechanical Strength using FSI Analysis based on Blade Profile

Abstract Tidal energy, as a renewable energy source harnessed from the ocean, holds substantial promise owing to its heightened energy density, reliability, and longevity. An investigation encompassing the deployment of tidal stream electricity from 2003 through August 2020 revealed that blade malfunction was identified as the primary reason for system failures, with generator and monitoring system failures occurring subsequently. The majority of the research that has been done on the design of vertical-axis tidal turbine blades has focused on how well the blade performs in terms of power output without taking into account the generation of mechanical force. This force can potentially shorten the blade’s lifetime when implemented in a real-world scenario. By modelling a steady-state fluid-structure interaction (FSI) configuration, this study examines how the shape of the turbine blades affects the amount of mechanical force they generate, particularly in vertical-axis tidal turbines. The type of blade profile is the variable under consideration, and the stress levels experienced by a structure are influenced by the type of blade profile used. When comparing symmetrical and asymmetrical NACA straight blade types under similar climatic conditions, it has been found that the blade profile plays a significant role. Asymmetrical blade profiles, in particular, generate a higher lift force compared to symmetrical ones, thereby affecting stress levels more noticeably.

Fringe Projection Profilometry for Three-Dimensional Measurement of Aerospace Blades

The aero-engine serves as the “heart” of an aircraft and is a primary factor determining the aircraft’s performance. Among the crucial components in the core of aero-engines, aero-engine compressor blades stand out as extremely important. They are not only numerous but also characterized by a multitude of parameters, making them the most complex parts in an aero-engine. This paper aims to address the trade-off between accuracy and efficiency in the existing measurement methods for asymmetric blades. Non-contact measurements were conducted using a structured light system composed of a stereo camera and a DLC projector. The point cloud data of the blades are processed using methods such as the PCA (Principal Component Analysis) algorithm, binary search, and least squares fitting. This paper established a fringe-projection profilometry light sensor system for the multi-view measurement of the blades. High-precision rotary tables are utilized to rotate and extract complete spatial point cloud data of aviation blades. Finally, measurements and comparative experiments on the blade body are conducted. The obtained blade point cloud data undergo sorting and denoising processes, resulting in improved measurement accuracy. The measurement error of the blade chord length is 0.001%, the measurement error of blade maximum thickness is 0.895%, compared to CMM (Coordinate Measuring Machine), where the measurement error of chord is 0.06%.

The Influence of Angle of Attack on the Icing Distribution Characteristics of DU97 Blade Airfoil Surface for Wind Turbines

This study explores the influence of angle of attack (AOA) on the icing distribution characteristics of asymmetric blade airfoil (DU97) surfaces for wind turbines under icing conditions by numerical simulation. The findings demonstrate a consistence between the simulated ice shapes and experimental data. The ice thickness distribution on the lower surface of the leading edge exhibits a trend of first rising and then declining along the chord direction while showing a gradually decreasing trend on the upper surface. The ice distribution range on the upper surface of the trailing edge is broader than that on the lower surface. The peak ice thickness at the trailing edge rises significantly as AOA increases from 5° to 10°, and at the leading edge raises dramatically at droplet sizes of 30–40 μm and wind speeds of 5–10 m/s. The peak ice thickness is more significantly influenced by AOA than by ambient temperature due to the combined effect of airflow characteristics induced by AOA and latent heat (phase change) and sensible heat (thermal convection and thermal radiation) caused by ambient temperature. The findings offer valuable insights into the flow and heat transfer physics, and can operate as references for wind turbine anti/de-icing technology.

Plane Cascade Aerodynamic Performance Prediction Based on Metric Learning for Multi-Output Gaussian Process Regression

Multi-output Gaussian process regression measures the similarity between samples based on Euclidean distance and assigns the same weight to each feature. However, there are significant differences in the aerodynamic performance of plane cascades composed of symmetric and asymmetric blade shapes, and there are also significant differences between the geometry of the plane cascades formed by different blade shapes and the experimental working conditions. There are large differences in geometric and working condition parameters in the features, which makes it difficult to accurately measure the similarity between different samples when there are fewer samples. For this problem, a metric learning for the multi-output Gaussian process regression method (ML_MOGPR) for aerodynamic performance prediction of the plane cascade is proposed. It shares parameters between multiple output Gaussian distributions during training and measures the similarity between input samples in a new embedding space to reduce bias and improve overall prediction accuracy. For the analysis of ML_MOGPR prediction results, the overall prediction accuracy is significantly improved compared with multi-output Gaussian process regression (MOGPR), backpropagation neural network (BPNN), and multi-task learning neural network (MTLNN). The experimental results show that ML_MOGPR is effective in predicting the performance of the plane cascade, and it can quickly and accurately make a preliminary estimate of the aerodynamic performance and meet the performance parameter estimation accuracy requirements in the early stage.

Multimethod analysis of three rotary instruments produced by electric discharge machining technology.

This study aimed to compare three rotary instruments produced by the EDM process with the heat-treated ProTaper Gold system regarding design, metallurgy, mechanical properties and shaping ability. HyFlex EDM (25/~), Neoniti (25/.06), EDMax (25/.06) and ProTaper Gold (25/.08v) instruments (n = 58 per group) were compared regarding design, metallurgy and mechanical performance. Unprepared canal areas were calculated for each system after preparation of mesiobuccal, mesiolingual and distal canals of mandibular molars (15 canals per group) using micro-CT technology. Statistical analyses were performed using One-way anova post-hoc Tukey and Kruskal-Wallis post-hoc Dunn's tests (α = 5%). All instruments had asymmetrical blades, no radial lands, no major defects and almost equiatomic nickel/titanium ratios, but different cross-section designs, tip geometries and surface appearances. Although instruments had distinct transformation temperature curves, they showed crystallographic martensitic arrangement at 21°C and mixed austenite plus R-phase at body temperature. Neoniti and HyFlex EDM showed similar results in all mechanical tests (p > .05), while EDMax and ProTaper Gold had similar time to fracture (p = .841), maximum bending load (p = .729), and cutting ability (p = .985). ProTaper Gold showed the highest torque to failure (p < .001) and HyFlex EDM had the lowest buckling resistance (p < .001). Mean percentages of unprepared canal areas ranged from 20.4% to 25.7% in the mesial canals, and from 20.8% to 26.2% in the distal canal, with no statistical differences among systems (p > .05). Instruments' geometry and phase transformation temperatures influenced the results of the mechanical tests, but not their shaping ability.

Design, metallurgy, mechanical properties, and shaping ability of 3 heat-treated reciprocating systems: a multimethod investigation.

This study aimed to compare 3 reciprocating systems regarding design, metallurgy, mechanical properties, and shaping ability. New Reciproc Blue R25, WaveOne Gold Primary, and REX 25 instruments (n=41 per group) were analyzed regarding design, metallurgy, and mechanical performance, while shaping ability (untouched canal walls, volume of removed dentin, and hard tissue debris) was tested in 36 anatomically matched root canals of mandibular molars. Results were compared using one-way ANOVA post hoc Tukey and Kruskal-Wallis tests with a significant level set at 5%. All instruments showed symmetrical cross sections with asymmetrical blades, no radial lands, no major defects, and an almost equiatomic nickel and titanium ratio. The highest R-phase start temperatures were observed with WaveOne Gold (46.1°C) and REX (44.8°C), while Reciproc Blue had the lowest R-phase start (34.5°C) and finish (20°C) temperatures. WaveOne Gold had the lowest time to fracture (169 s) and the highest maximum load (301.6 gf) (P <0.05). The maximum torque of Reciproc Blue (2.2 N.cm) and WaveOne Gold (2.1 N.cm) were similar (P >0.05), but lower than REX (2.6 N.cm) (P <0.05). No statistical differences were observed among instruments in the angle of rotation (P >0.05) and in the shaping ability in both mesial and distal canals (P >0.05). Although the overall design, temperature transition phases and mechanical behavior parameters were different among tested instruments, they were similar in terms of shaping ability. All tested heat-treated NiTi reciprocating systems showed similar shaping ability, without clinically significant errors.

An investigation of rotor aeroacoustics with unsteady motions and uncertainty factors

The aeroacoustic characteristics of flying vehicles with pitch-fixed rotors differ from traditional helicopters with pitch-controlled rotor blades. Accurate predictions of rotor noise are still challenging because many uncertainty factors and unsteadinesses exist. This work investigates the aeroacoustic effects of rotational speed deviation, rotation speed fluctuation, blade vibration and blade geometric asymmetry. The analysis is based on the efficient computation of rotor noise under different working conditions. The mean aerodynamic variables are computed using the blade element moment theory, while small-amplitude fluctuations are introduced to account for the unsteadiness and uncertainty factors. It is shown that periodic rotation speed fluctuations and blade vibrations can produce significant extra tones. By contrast, if the fluctuations and vibrations are random, the noise level in a wide frequency range is increased. The intriguing result reminds us of the need to revisit the rotor broadband noise sources commonly attributed to turbulent flows. The influences are observer angle dependent, and the extra noise production is more significant in the upstream and downstream directions. The asymmetric blade geometry can cause extra tonal noise at the harmonics of the blade shaft frequency. The noise features of dual rotors are also investigated. Usually, the noise is sensitive to the initial phase difference and rotation directions due to the interference effect. However, the noise features are vastly altered if there are slight differences in the rotation speeds. Although the influences of some factors on rotor noise were already known, the present study provides a more comprehensive analysis of the problem. The results also highlight the need to consider these practical factors for accurate noise prediction of multi-rotor flying vehicles.

Identification of the wood species in the wooden sheath of Indonesian kris by synchrotron X-ray microtomography

A kris is a traditional dagger that originated in Indonesia. A kris is distinguished by its asymmetrical blade, which has layers of different metals bonded on its surface. Wood is the main material used to make the kris sheath. To preserve the knowledge about wood selection of the sheath, wood identification is a crucial first step. In the present study, we identified the wood species used to make the kris sheath. We performed synchrotron X-ray microtomography, which allows microscopic observation with minimum sample availability. Seven wooden kris sheaths were investigated. The results showed that synchrotron X-ray microtomography is suitable for observing the important microscopic anatomical features of the wood species in kris sheaths. We found that Dysoxylum spp., Tamarindus indica, and Kleinhovia hospita were used as sheath materials. We also visualized the spatial distribution of the prismatic crystals inside the T. indica and K. hospita xylem cells. Abundant crystals were present in T. indica arranged in longitudinal alignment inside the chambered axial parenchyma cells. The crystals were arranged in radial alignment inside the ray cells of K. hospita. The existence of abundant crystals in series may be important for the mechanical support of certain xylem cells.

Validation of a procedure for the numerical simulations of gas–liquid stirred tanks by means of a computational fluid dynamics approach

AbstractImpellers with concave and vertically asymmetric blades proved superior gas dispersion capabilities and power consumption characteristics under gassed turbulent conditions with respect to traditional flat‐blade turbines in aerated fermenters. In this study, a pilot‐size gas–liquid tank stirred with an asymmetric blade disk impeller is numerically investigated by means of a Reynolds averaged two‐fluid model combined with a simplified population balance model without adjustable parameters. This work aims at increasing the predictive capabilities of computational fluid dynamics multiphase modelling by validating a computational approach for the realistic simulation of industrial aerated fermenters and thus allowing for a more reliable scale‐up. A methodology for achieving fully predictive results on fundamental variables for gas–liquid stirred tanks such as gassed power consumption, overall gas hold‐up, and volumetric mass transfer coefficient, with affordable computational requirements at pilot and industrial scale is presented. Two‐phase results are compared with the experimental data collected in a geometry matching the computational domain equipped with 3 planes of 16 sensors to enable electro‐resistance tomography measurements and with suitable correlations from the literature. The limits and strength of the numerical procedure are discussed, starting from the comparison between computational predictions and experimental measurements.

A Multimethod Assessment of a New Customized Heat-Treated Nickel-Titanium Rotary File System.

This study aimed to compare three endodontic rotary systems. The new Genius Proflex (25/0.04), Vortex Blue (25/0.04), and TruNatomy (26/0.04v) instruments (n = 41 per group) were analyzed regarding design, metallurgy, and mechanical performance, while shaping ability (untouched canal walls, volume of removed dentin and hard tissue debris) was tested in 36 anatomically matched root canals of mandibular molars. The results were compared using one-way ANOVA, post hoc Tukey, and Kruskal–Wallis tests, with a significance level set at 5%. All instruments showed symmetrical cross-sections, with asymmetrical blades, no radial lands, no major defects, and almost equiatomic nickel–titanium ratios. Differences were noted in the number of blades, helical angles, cross-sectional design, and tip geometry. The Genius Proflex and the TruNatomy instruments had the highest and lowest R-phase start and finish temperatures, as well as the highest and lowest time and cycles to fracture (p < 0.05), respectively. The TruNatomy had the highest flexibility (p < 0.05), while no differences were observed between the Genius Proflex and the Vortex Blue (p > 0.05). No differences among tested systems were observed regarding the maximum torque, angle of rotation prior to fracture, and shaping ability (p > 0.05). The instruments showed similarities and differences in their design, metallurgy, and mechanical properties. However, their shaping ability was similar, without any clinically significant errors. Understanding these characteristics may help clinicians to make decisions regarding which instrument to choose for a particular clinical situation.

Vertical tail sizing of propeller-driven aircraft considering the asymmetric blade effect

An engineering approach is presented to analyse the asymmetric blade thrust effect with the help of analytical and semi-empirical methods. It is shown that the contribution of the asymmetric blade thrust effect in the lateral-directional stability of multi-engine propeller-driven aircraft is significant particularly in critical flight conditions with one engine out of service. Also, in some cases where the engines are rotating in one direction, the asymmetric blade effect has substantial effects on the handling qualities of the aircraft even in normal flight conditions. Overall, due to the significant contribution of this phenomenon in the lateral-directional stability of propeller-driven airplanes, it is important to consider it in the design of the vertical stabilizer and rudder. The resulting analytical method has been used to determine the vertical tail incident angle and desired rudder deflection in accordance with the most critical flight condition for two different cases and validated to ensure the accuracy of the result. In this work, the aerodynamic coefficients as well as the stability and control derivatives have been predicted using analytical and semi-empirical methods validated for light aircraft.

Wave attenuation by suspended canopies with cultivated kelp (Saccharina latissima)

Many kelp aquaculture farms consist of moored arrays of long horizontal lines that grow kelp near the water surface. Most kelp farms are deployed in the same direction of wave propagation. However, with numerous longlines of densely grown kelp, these farms may have the potential to attenuate waves if installed perpendicular to the direction of wave propagation. In this application, the kelp farm may serve as a form of nature-based coastal protection. To assess this potential, a set of 1:10 scale physical model experiments were conducted to measure the wave attenuation of a suspended kelp model. The model was scaled based on the morphological and mechanical properties of the cultivated Saccharina latissima (sugar kelp) from Saco Bay, Maine, USA. Experimental results demonstrated that suspended blades have asymmetric oscillatory motions with more bending in the opposite direction of wave propagation. Due to severe asymmetric blade motion in large waves, the suspended blade could roll over the attached line following the wave orbital motion. The results also showed that suspended kelp farms in the designed configuration with 20 longlines of 1-m-long blades and 100 blades/m have the potential attenuating wave energy by up to 33.7% under the experimental wave conditions. Based on the experimental data, empirical formulas were developed for the bulk drag coefficient (CDB) and effective blade length (le) of suspended kelp canopies for wave attenuation. To predict wave attenuation under a wider range of conditions and to identify the key parameters affecting wave attenuation, a numerical model was developed that could resolve blade motion. The benefits of resolving blade motion were to improve the model accuracy and reduce the number of experiments needed for obtaining CDB or le, which is required in the conventional wave attenuation models based on the rigid blade assumption. The results indicate that (i) the wave energy dissipation ratio (EDR defined as the ratio of the dissipated wave energy to the incident wave energy) of suspended kelp farms decreases with increased water depth, (ii) EDR is not sensitive to wave height, (iii) EDR first increases and then decreases with wavelength, and (iv) EDR increases with blade size, kelp vertical position, plant density, and the number of longlines. Therefore, the technique to improve the wave attenuation capacity of suspended kelp farms for nature-based coastal defense is to install the kelp farms in shallower water, expand the farm size by adding more longlines, locate the kelp in a higher position of the water column, grow the kelp more densely, and choose the kelp species with more rigid, wider, and longer blades/biomass.

Analytical grid generation and numerical assessment of tip leakage flows in sliding vane rotary machines

The research presents a new analytical grid generation methodology for computational fluid dynamics studies in positive displacement sliding vane rotary machines based on the user defined nodal displacement approach. This method is more inclusive than state of the art ones since it enables the investigation of a broader range of design configurations, such as single, double and multiple-acting vane machines with non-circular housing, slanted blade and asymmetric blade tip profiles. Node number and radial divisions of blade tip are the parameters that affect most the mesh quality. The method was validated against indicated pressure measurements on a rotary vane expander resulting in a confidence interval within 4.31%. The benchmark analysis showed that the proposed method is as accurate as the manual ANSYS ICEM one but more than 1500 times faster (111s instead of 48h to generate 360 grids). The paper further proposes a novel method to track the leakage flows at the blade tip gaps of vane machines through a post-processing routine in ANSYS CFD-Post based on rotating monitoring planes. The leakage assessment on the vane expander case study showed that a 10 μm gap between blade tip and the 76 mm stator led to a 0.06 unit increase of the expander filling factor.

Begonia xishuangbannaensis (Begoniaceae), a New Tuberous Species from Yunnan, China

Begonia xishuangbannaensis W.G. Wang & L.J. Jiang (Begoniaceae), a new tuberous species from Yunnan, China, is described and illustrated. It belongs to Begonia sect. Diploclinium. Morphologically, it is similar to B. fimbristipula and B. exposita in its tuberous habit and pubescent leaves, but can be distinguished from both by its asymmetrical leaf blade, 16–18 stamens, filaments that are free at base, and pistillate flowers having five tepals.

Effect of blade attachments on the performance of an asymmetric blade H-Darrieus turbine at low wind speed

ABSTRACT Wind energy is a significant source of renewable energy and vertical axis wind turbine (VAWT) is one of the advanced wind energy harvesters. Maximum extraction of energy from wind harvesters is a major goal. Researchers are faced with the challenge of enhancing the performance of VAWTs in low wind speed conditions. To this end, researchers have contributed substantially by doing research on the blade design parameters thereby generating innovative and improved VAWT designs. However, there is hardly any work on the performance augmentation of H-Darrieus VAWT with blade attachments on asymmetric blades, which is the main objective of this work. Further, this work investigates the combined effect of turbulence intensity and flow dissimilarity on turbine performance for low wind speed condition. In this paper, blade attachment of length 20 cm (equal to 1/2.5 times blade span) is attached to asymmetric NACA 63–415 blade turbine having fixed blade pitch angle (+5°). NACA 63–415 blade profile is one of the prominent asymmetric series of NACA blades; hence it is considered in this work. The performances of seven different configurations of the turbine with blade attachments have been investigated experimentally at 5.0 m/s and 6.0 m/s using wind tunnel testing. The performance of the VAWT design is systematically improved by changing the number and position of these attachments on the turbine blades. The result shows that both side attachments on turbine blade on its top position have maximum power coefficient (Cp) of 0.13 at tip speed ratio (TSR) 1.8 at wind speed 6.0 m/s among all the turbine configurations tested. There is an improvement of power coefficient by 4.34% when attachments are placed at top of the turbine blade compared to turbine blade without attachment at wind speed 6.0 m/s. Further, maximum power coefficient is increased by 3.28% when turbine is operated from 5.0 m/s to 6.0 m/s for both side attachments at top of the turbine blade. Moreover, due to the combined effect of turbulence intensity and flow dissimilarity, the power coefficient of the turbine configuration having both side attachments has also improved a little. In this case, an improvement of 0.6% in power coefficient of turbine having both side attachments on top of the blade is achieved. As the turbine is a prototype having smaller size hence the effect of turbulence intensity and flow dissimilarity is less, in case of actual turbine of bigger size the effect of turbulence intensity and flow dissimilarity will be more and hence the percentage enhancement of power coefficient will also be more. Hence, it can be concluded that a turbine blade with higher degree of thickness (by using blade attachments) at top portion will increase the performance of an asymmetric blade H-Darrieus VAWT.

Repetitive Individual Pitch Control for Load Alleviation at Variable Rotor Speed

In recent years, wind turbines have been growing in size and became more lightweight and thus more flexible. Spatial variation in the wind speed results in asymmetrical blade loads, which include a periodic component increasing with growing wind turbine size. Asymmetrical blade loads can be reduced by individual blade pitch control in general and repetitive control can reduce especially the periodical parts of the loads. We investigate, how a repetitive control based individual blade pitch controller as extension to an existing collective pitch controller can reduce periodical loads resulting from unsteady non-uniform wind conditions under consideration of variable rotor speeds. As plant, we use a simulation model of a 3 MW wind turbine, developed by W2E Wind to Energy GmbH, and control it with a model predictive collective pitch controller. This controller is extended with the proposed repetitive individual pitch control scheme. This study shows, that the presented repetitive controller reduces especially the tower yaw moments by up to 65% and higher harmonics of the blade root moments by up to 30% at the cost of increased pitch activity. Hence, for the use of this controller one has to balance the load reduction of blades and tower with increased loads of the pitch actuators.

Low wind speed aerodynamics of asymmetric blade H-Darrieus wind turbine-its desired blade pitch for performance improvement in the built environment

An asymmetric blade vertical-axis wind turbine (VAWT) is one of the emerging technologies for harvesting power in the built environment, which has low wind speed. Although asymmetric blade improves VAWT’s performance, the effect of blade pitch angle on its design is hardly ascertained. In this paper, unsteady 2D Reynolds-averaged Navier–Stokes CFD simulations are carried out to investigate the effect of blade pitch angle on the aerodynamic performance of a NACA 63-415 asymmetric blade H-Darrieus VAWT at a low wind speed of 6.0 m/s. Its detailed flow physics at different operating and pitch angle conditions is investigated, and important performance insights are obtained to elucidate its desired blade pitch for performance improvement. The present study shows that positive pitch angle (+ 5°) improves the turbine performance in upwind position, whereas negative pitch angle (− 5°) augments the turbine performance in downwind position as well as causes less wake effect than positive pitch angle. Further, optimal pitch angle (+ 5°) is found out at which the maximum power coefficient of 0.271 is obtained for an operating tip speed ratio 2.4. The present study delineates how desired blade pitch improves the performance of asymmetric blade VAWT for sustainable power generation in the built environment.

NUMERICAL INVESTIGATION OF THE INFLUENCE OF THE DOUBLY CURVED BLADE PROFILES ON THE REVERSIBLE AXIAL FAN CHARACTERISTICS

Abstract. In reversible axial fans a change in the direction of the impeller rotation is accompanied with a change in the direction of the working fluid flow. To satisfy the flow reversibility, the impeller blades are usually designed with straight symmetrical profiles. The flow reversibility may also be achieved by using asymmetrical blade profiles in which, to satisfy the equality of the leading and trailing angle of the profiles, the mean line of the profile has to have a double curvature in the shape of the stretched letter 'S'. The paper numerically investigates the influence of the doubly curved blade profiles on the reversible axial fan characteristics. Numerical simulations are carried out on an axial fan only with the impeller, with the blades that have double-curved mean line profiles for different values of the angles at the profile ends. For numerical simulation the ANSYS CFX software package is used. Results of the numerical simulation are shown in diagrams Δp(Q), h(Q) and P(Q) at different angles of the profile ends. On the basis of the simulation and analysis of the characteristics, appropriate conclusions are proposed, along with the most advantageous profile of the blades.

Wind turbine asymmetrical load reduction with pitch sensor fault compensation

AbstractOffshore wind turbines suffer from asymmetrical loading (blades, tower, etc), leading to enhanced structural fatigue. As well as asymmetrical loading different faults (pitch system faults etc.) can occur simultaneously, causing degradation of load mitigation performance. Individual pitch control (IPC) can achieve rotor asymmetric loads mitigation, but this is accompanied by an enhancement of pitch movements leading to the increased possibility of pitch system faults, which exerts negative effects on the IPC performance. The combined effects of asymmetrical blade and tower bending together with pitch sensor faults are considered as a “co‐design” problem to minimize performance deterioration and enhance wind turbine sustainability. The essential concept is to attempt to account for all the “fault effects” in the rotor and tower systems, which can weaken the load reduction performance through IPC. Pitch sensor faults are compensated by the proposed fault‐tolerant control (FTC) strategy to attenuate the fault effects acting in the control system. The work thus constitutes a combination of IPC‐based load mitigation and FTC acting at the pitch system level. A linear quadratic regulator (LQR)‐based IPC strategy for simultaneous blade and tower loading mitigation is proposed in which the robust fault estimation is achieved using an unknown input observer (UIO), considering four different pitch sensor faults. The analysis of the combined UIO‐based FTC scheme with the LQR‐based IPC is shown to verify the robustness and effectiveness of these two systems acting together and separately.

Mechanisms for the Asymmetric Motion of Submerged Aquatic Vegetation in Waves: A Consistent‐Mass Cable Model

AbstractSubmerged aquatic vegetation (SAV) provides primary products for the food web, as well as shelter and nursery for many juvenile species. SAV can also attenuate waves, stabilize the seabed, and improve water quality. These environmental services are influenced by the dynamic motion of SAV. In this paper, a consistent‐mass cable model was developed to investigate flow interaction with a flexible vegetation blade. Compared with previous vegetation models, the cable model showed improvements in simulating blade motions in waves with and without currents, especially for “second‐normal‐mode‐like” blade motion. Wave asymmetry would cause blade motion to be asymmetric. However, asymmetric blade motion may also occur in symmetric waves. Results indicate that the asymmetric blade motion in symmetric waves is induced by two major mechanisms: (i) the spatial asymmetry of the encountered wave orbital velocities (wave motion relative to blade) due to blade displacements and (ii) the asymmetric action on the blade by vertical wave orbital velocities. Consequently, the blade motion is asymmetric even underneath symmetric waves unless (i) blade length ( ) is much smaller than the wavelength ( ), (ii) blade length is much smaller than the water depth ( ) in finite water depth waves, or (iii) water depth is much smaller than the wavelength ( ). Peak asymmetric blade motion occurs as increases to a critical value. The peak asymmetry increases with wave height and blade length but decreases with increasing blade flexural rigidity. Blade motion characteristics play an important role in wave‐vegetation interaction, wave‐driven currents, wave‐attenuation capacity, breakage of vegetation and ecosystem services.