Growing energy demand is causing a significant decrease in the world’s hydrocarbon stock in addition to the pollution of our ecosystem. Based on this observation, the search for alternative sorts of energy to fossil fuels is being increasingly explored and exploited. Wind energy is experiencing a very important development, and it offers a very profitable opportunity for exploitation since the wind is always available and inexhaustible. Several technical solutions exist to exploit wind energy, such as floating vertical axis wind turbines (F-VAWTs), which provide an attractive and cost-effective solution for exploiting higher resources of offshore wind in deep water areas. Recently, the use of the Darrieus vertical axis wind turbine (VAWT) offshore has attracted increased interest because it offers significant advantages over horizontal axis wind turbines (HAWTs). In this context, this article presents a new concept of floating Darrieus-type straight-bladed turbine with three-stage rotors. A double-multiple stream tube (DMST) model is used for aerodynamic simulations to examine several critical parameters, including, solidity turbine, number of blades, rotor radius, aspect ratio, wind velocity, and rotor height. This study also allows to identify a low solidity turbine (σ = 0.3), offering the best aerodynamic performance, while a two-bladed design is recommended. Moreover, the results also indicate the interest of a variable radius rotor, as well as the variation of the height as a function of the wind speed on the aerodynamic efficiency.
Thermoset polymers offer great opportunities for mass production of fiber-reinforced composites and are being adopted across a large range of applications within the automotive, aerospace, construction and renewable energy sectors. They are usually chosen for marine engineering applications for their excellent mechanical behavior, including low density and low-cost compared to conventional materials. In the marine environment, these materials are confronted by severe conditions, thus there is the necessity to understand their mechanical behavior under critical loads. The high strain rate performance of bonded joints composite under hygrothermal aging has been studied in this paper. Initially, the bonded composite specimens were hygrothermal aged with the conditions of 50 °C and 80% in temperature and relative humidity, respectively. After that, gravimetric testing is used to describe the moisture diffusion properties for the adhesively bonded composite samples and exhibit lower weight gain for this material. Then, the in-plane dynamic compression experiments were carried out at different impact pressures ranging from 445 to 1240 s−1 using the SHPB (Split Hopkinson Pressure Bar) technique. The experimental results demonstrated that the dynamic behavior varies with the variation of strain rate. Buckling and delamination of fiber are the dominant damage criteria observed in the sample during in-plane compression tests.
The vertical axis wind turbine (VAWT) design has several advantages for offshore wind turbine installation. The VAWT provides omnidirectional wind power, and its mechanical rotating mechanisms can be installed near sea level. In this paper, the selection of a suitable composite material for floating H-Darrieus-type wind turbines with three-stage rotors and its properties are discussed. The centrifugal forces acting on the composite blades are compared to the values of these forces evaluated on the aluminum blades. Abaqus software is used for numerical simulations. The selection of appropriate laminations used to model the composite materials is discussed. The optimum combination of selected layers is determined to reduce the values of maximum bending stresses and displacements, resulting in a high strength-to-weight ratio. In the post-processor, a path is taken at the location of the application of the maximum load on the blade and the values of the displacements and stresses along this path are determined. These maximum values are compared to the unidirectional strength of the selected composite material to ensure a safe design.
This paper investigates the terminal sliding-mode control (TSMC) with predefined-time stability (PTS) for a disturbed quadrotor system (DQS). First, for both the rotational and translational subsystems of the DQS, a novel notion of predefined-time terminal sliding-mode manifold (PTTSMM) is created. Using the proposed PTTSMM method, the DQS state variables reach their origin in a predefined-time. The influence of disturbances is taken into consideration in the design of the suggested control to show its performance. A formal analysis technique is also provided, as well as the stability of the closed-loop DQS. The performance and effectiveness of the predefined-time method proposed in this work are illustrated by numerical simulations and also comparison study with other control techniques is presented.
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