Impact of the ground clearance on the annual energy production and tower cost of an offshore wind turbine

This article analyzes the impact of the ground clearance on the Annual Energy Production (AEP) and tower cost of a 20 MW offshore wind turbine. In addition, the influence of the rated wind speed on the analysis result will be considered. The AEP is computed by considering wind speed variation over the swept area of the rotor blades. The tapered tubular steel tower is considered for mass and cost calculation. The tower is considered as a fixed-free cantilever beam with concentrated mass at the free end. The analysis shows that the ground clearance only has a minor impact on the AEP but it has a remarkable impact on the tower mass. Specifically, when the ground clearance reaches 50 meters, the AEP only increases by roughly 3% while tower mass is nearly doubled compared to the case with no ground clearance. The results also reveal the significant impact of the rated speed on both the AEP and tower mass.

Analysis of Changes in Parameters of Free Vibration of Single and Multi-span Girders with Semi-rigid Joints

This study presents the analysis carried out for changes in parameters of free vibrations of single-span corrugated web girders with a semi-rigid joint at midspan and multi-span girders with spans connected by semi-rigid joints. Based on the experimental tests and the theoretical analysis, the behavior of six simply supported girders with the semi-rigid joint at midspan was analyzed. They were straight and double-slope girders with a span of 6.02 m, made of corrugated web sections WTA 500/300x15 with different types of semi-rigid end plate joints. It was demonstrated that the variable rotational stiffness Sj of the joint affected the equivalent concentrated mass of the girder mz, the frequency of damped free vibrations α, damping ρ, and the frequency of free vibrations ω. The theoretical analysis was conducted for a change in the equivalent concentrated mass of the single-span girders fixed at both ends and of the multi-span girders. It was described how the change in the support stiffness in the single-span girders fixed at both ends and the change in joint stiffness of spans affected the equivalent concentrated mass mz as a function of non-dimensional stiffness k. The equivalent concentrated mass mz of the girder was found to affect the values of maximum vibrations in the structure. A continuous change in the rotational stiffness of joints was taken into account from the pinned to the rigid joint.

Fuzzy Adaptive Controller Design for Double-pendulum Tower Crane with Distribute Mass Payload

As a kind of high-efficiency transportation tools, tower cranes are widely used in construction site. With the increasing volume and mass of payload being transported, the researches of distributed mass payload (DMP) problems have been paid more and more attentions. However, most of the existing control algorithms designed for the concentrated mass payload (CMP) are not enough to meet the needs of actual production. The difference between DMP and CMP is mainly manifested in that the remaining payload swing caused by inertial torque of DMP cannot be effectively suppressed, which leads to safety hazards. In addition, due to the different working environment, accurate system parameters (such as mechanical frictions, air frictions ) are hard to obtain, which leads to errors in their positioning. To solve the above issues, first, we establish mathematical model of a double-pendulum tower crane with distributed mass payload (DTCDMP) and carry out dynamic analysis. Then we propose a fuzzy adaptive control method, which has a good tracking effect against external disturbances and parameter uncertainties, and the method can achieve accurate positioning and effective anti-swing. Then, the Lyapunov technology and LaSalle's invariance principle are used to rigorously prove the stability of the system. Finally, on the basis of tracking the S-shaped trajectories, the effectiveness and robustness of the proposed controller are verified through multi-group comparative experiments.

Self- concentrated mass-transfer during deformation treatments of organic-inorganic compositions

This paper prolongs the series of our previous papers where we found super-fast and super-deep introduction of foreign substances in crystalline materials by means of the ball rolling. A set of new experimental results was used to justify the new version of the mechanism of this introduction with the record speed and depth. The main process which determines this phenomena is connected with the sequence of openings and closings of nanocracks at the surface subjected to the rolling and the capture of the substance introduced from the surface by these cracks. The process of this introduction with the record parameters is supported by the intense chemical interactions between the matrix and the substance being introduced. This chemical interaction is intensified by several times with the deformation treatments. The analogous super-fast mass transfer is observed in the situation of the pulling out of the polystyrene fibers from the solution of polystyrene in benzene when the interaction of the organic components with cesium iodide nanoparticles was activated by the deformation treatment of the solution during its pulling out resulting in the formation of big amounts of nano-channels promising for effective utilization of hazardous radioactive wastes.

Torsional effects through mass asymmetry : A state-of-the-art review

Asymmetric distribution of mass over the floor slabs can cause torsional effects in buildings, even when it is symmetric in strength and stiffness. Such systems are referred to as mass eccentric or mass asymmetric buildings. Eccentricity in mass can result in building rotation in addition to its normal translation modes, which can further cause unpredictable deformation and even failure of the building under seismic loads. Irregularity in mass is found in buildings having concentrated mass elements in certain floors such as water tanks, machinery, etc. Many researchers have attempted to study the behavior of asymmetric buildings in general, but very few on the specific topic of mass asymmetry. This paper attempts to review and consolidate the literature written on the topic of mass asymmetry to the author’s knowledge.

Nonlocal Vibration Analysis of a Nonuniform Carbon Nanotube with Elastic Constraints and an Attached Mass

Here, we consider the free vibration of a tapered beam modeling nonuniform single-walled carbon nanotubes, i.e., nanocones. The beam is clamped at one end and elastically restrained at the other, where a concentrated mass is also located. The equation of motion and relevant boundary conditions are written considering nonlocal effects. To compute the natural frequencies, the differential quadrature method (DQM) is applied. The influence of the small-scale parameter, taper ratio coefficient, and added mass on the first natural frequency is investigated and discussed. Some numerical examples are provided to verify the accuracy and validity of the proposed method, and numerical results are compared to those obtained from exact solution. Since the numerical results are in excellent agreement with the exact solution, we argue that DQM provides a simple and powerful tool that can also be used for the free vibration analysis of carbon nanocones with general boundary conditions for which closed-form solutions are not available in the literature.

A General Fourier Formulation for In-Plane and Out-of-Plane Vibration Analysis of Curved Beams

Based on the principle of energy variation, an improved Fourier series is introduced as an allowable displacement function. This paper constructs a calculation model that can study the in-plane and out-of-plane free and forced vibrations of curved beam structures under different boundary conditions. Firstly, based on the generalized shell theory, considering the shear and inertial effects of curved beam structures, as well as the coupling effects of displacement components, the kinetic energy and strain potential energy of the curved beam are obtained. Subsequently, an artificial spring system is introduced to satisfy the constraint condition of the displacement at the boundary of the curved beam, obtain its elastic potential energy, and add it to the system energy functional. Any concentrated mass point or concentrated external load can also be added to the energy function of the entire system with a corresponding energy term. In various situations including classical boundary conditions, the accuracy and efficiency of the method in this paper are proved by comparing with the calculation results of FEM. Besides, by accurately calculating the vibration characteristics of common engineering structures like slow curvature (whirl line), the wide application prospects of this method are shown.

Active Loading Control Design for a Wearable Exoskeleton with a Bowden Cable for Transmission

Exoskeletons with a Bowden cable for power transmission have the advantages of a concentrated mass and flexible movement. However, their integrated motor is disturbed by the Bowden cable’s friction, which limits the performance of the force loading response. In this paper, we solve this problem by designing an outer-loop feedforward-feedback proportion-differentiation controller based on an inner loop disturbance observer. Firstly, the inner loop’s dynamic performance is equivalent to the designed nominal model using the proposed disturbance observer, which effectively compensates for the parameter perturbation and friction disturbance. Secondly, based on an analysis of the stability of the inner loop controller, we obtain the stability condition and discuss the influence of modeling errors on the inner loop’s dynamic performance. Thirdly, to avoid excessive noise from the force sensors being introduced into the designed disturbance observer, we propose the feedforward-feedback proportion-differentiation controller based on the nominal model and pole configuration, which improves the outer loop’s force loading performance. Experiments are conducted, which verify the effectiveness of the proposed methods.

Analysis of Two-Dimensional Nonlinear Sloshing in a Rectangular Tank by Using a Concentrated Mass Model

Major problems can occur when liquid sloshes in a tank, such as occurs in liquid storage tanks during an earthquake, and this is an important engineering problem to address. To analyze this phenomenon, semi-analytical methods such as the perturbation method, the multimodal method, and the finiteelement method are generally used. However, semi-analytical methods involve quite complicated equations, and the finite-element method involves many degrees of freedom when the tank is large. In this paper, a nonlinear numerical model with relatively few degrees of freedom is established for vertical and horizontal two-dimensional nonlinear sloshing in a rectangular tank excited horizontally. The model comprises concentrated masses of liquid connected by nonlinear springs and dampers. The connecting springs have characteristics based on the static and dynamic pressures of the liquid. In addition, a method is proposed for reducing the number of degrees of freedom in the two-dimensional model. The natural frequencies, modes, and frequency responses are then compared among the concentrated-mass model, theoretical calculations, and experimental results. Good agreement was achieved among them, thus demonstrating the validity of the model.