Multibody Models for Tower Vibrations With an Unbalanced Rotor

This paper compares different models that can be used to analyze the vibrations of an unbalanced rotor with horizontal axis over a flexible tower. Model results are compared with experimental results. The modeled system is equivalent to a wind turbine with perfectly rigid blades. The selected models are the linear elastic model that is obtained using the linear theory of vibrations and two multibody models. The first multibody model uses Component Mode Synthesis for the description of the tower flexibility while the second multibody model used a lumped properties approach. Experimental results validate with reasonable agreement the resonance speeds of an unbalanced rotor. Furthermore, the models, while low degrees of freedom, give valuable insight of inertial loads on drivetrain components based on tower top dynamic motion. The work presented in this paper showed the use of 3 low-degrees of freedom models to predict resonance and tower top displacements. All simulation models did exhibit slightly higher resonance frequencies than the experimental results. The results showed that the tower top motion for the rectangular tower resembles a figure eight type motion, while the square tower top shows an elliptical motion.

Distance Between Two Circles In Any Number Of Dimensions Is A Vector Ellipse

Based on measured astronomical position data of heavenly objects in the Solar System and other planetary systems, all bodies in space seem to move in some kind of elliptical motion with respect to each other, whereas objects follow parabolic escape orbits while moving away from Earth and bodies asserting a gravitational pull, and some comets move in near-hyperbolic orbits when they approach the Sun. In this article, it is first mathematically proven that the “distance between points on any two different circles in three-dimensional space” is equivalent to the “distance of points on a vector ellipse from another fixed or moving point, as in two-dimensional space.” Then, it is further mathematically demonstrated that “distance between points on any two different circles in any number of multiple dimensions” is equivalent to “distance of points on a vector ellipse from another fixed or moving point”. Finally, two special cases when the “distance between points on two different circles in multi-dimensional space” become mathematically equivalent to distances in “parabolic” or “near-hyperbolic” trajectories are investigated. Concepts of “vector ellipse”, “vector hyperbola”, and “vector parabola” are also mathematically defined. The mathematical basis derived in this Article is utilized in the book “Everyhing Is A Circle: A New Model For Orbits Of Bodies In The Universe” in asserting a new Circular Orbital Model for moving bodies in the Universe, leading to further insights in Astrophysics.

Capture Rate of Weakly Interacting Massive Particles (WIMPs) In Binary Star Systems

The distribution of dark matter (DM) inside galaxies is not uniform. Near the central regions, its density is the highest. Then, it is logical to suppose that, inside galaxies, DM affects the physics of stars in central regions more than outer regions. Besides, current stellar evolutionary models did not consider DM effects in their assumptions. To consider DM effects, at first one must estimate how much DM a star contains. The capture rate (CR) of DM particles by individual stars was investigated already in the literature. In this work, we discuss how CR can be affected when stars are members of binary star systems (BSS) (instead of studying them individually). When a star is a member of a BSS, its speed changes periodically due to the elliptical motion around its companion star. In this work, we investigated CR by BSSs in different BSS configurations. In the end, we discussed observational signatures that can be attributed to the DM effects in BSSs.

A Dumbbell Shaped Piezoelectric Motor Driven by the First-Order Torsional and the First-Order Flexural Vibrations

A piezoelectric motor driven by the first-order torsional and first-order flexural (T/F) vibrations is designed, fabricated, and tested in this study. The actuating force is generated by the torsional vibration of the dumbbell-shaped vibrator, while the elliptical motion shape is adjusted with the flexural vibration. The rotor, pressed onto the vibrator’s lateral surface, is frictionally driven with the vibrator. Here, the torsional vibration, the shear modes of piezoelectric ceramics, and the driving method may contribute to high torque and high output power. To test the feasibility of our proposal, first, a prototype of the T/F vibrator is built and its vibration properties are explored. As predicted, the torsional and flexural vibrations are excited on the vibrator. Then, the load characteristics of the piezoelectric motor are investigated. The maximal torque, the no-load rotation speed, and maximal output power are 4.3 Nm, 125 r/min, and 16.9 W, respectively. The results imply that using the first-order torsional and the first-order flexural vibrations is a feasible method to achieve high torque and high output power of piezoelectric motors.

A Novel Self-Moving Framed Piezoelectric Actuator

Utilizing the inherent advantages of the piezoelectric driving technology, such as good adaptability to vacuum environment and no electromagnetic interference, a novel self-moving framed piezoelectric actuator is proposed, simulated, and tested in this study, holding a potential application for magnetic confinement fusion. Four piezoelectric composite beams form a framed piezoelectric actuator. Two orthogonal vibration modes are excited and coupled in the framed piezoelectric actuator, producing a microscopic elliptical motion at its driving feet. Due to the friction, the framed piezoelectric actuator can move on a rail, thereby constructing the railed carrying system. Numerical simulation is carried out to confirm the operation principle and to conduct the dimensional optimization of the proposed framed piezoelectric actuator. A prototype of the proposed framed piezoelectric actuator with a weight of 83.8 g is manufactured, assembled, and tested, to verify the piezoelectric actuation concept. The optimal driving frequency of 20.75 kHz is obtained for the proposed actuator prototype, and at the excitation voltage of 400 Vpp its maximum mean velocity of 384.9 mm/s is measured. Additionally, the maximum load weight to self-weight of the proposed actuator prototype reached up to 10.74 at the excitation voltage of 300 Vpp. These experimental results validate the feasibility of the piezoelectric actuation concept on the railed carrying system.

Discrete Element Modeling of Railway Ballast for Studying Railroad Tamping Operation

The dynamic behavior of ballast particles during track tamping is studied by developing a computer simulation model using the Discrete Element Model (DEM) method. The simulation model is developed in a commercially available DEM software called PFC3D (Particle Flow Code 3D). The study primarily evaluates a complete tamping cycle as defined by insertion, squeeze, hold, and withdrawal. Using a Taguchi approach, the effect of Tine motion’s frequency and amplitude, insertion velocity, and squeeze velocity are evaluated on tamping effectiveness. The compactness of the ballast particles, as defined by the average number of contacts per particle (referred to “Coordination Number”) is used as a measure of the effectiveness of tamping. Setting up the DEM model and important elements such as selection and calibration of particle shapes, ballast mechanical properties, contact model, and parameters governing the contact force models are described in detail. The tamping process is evaluated using a half-track layout with a highly modular code that enables a high degree of adjustability to allow control of all parameters for improved simulation flexibility. A parametric study is performed to find the best values of tine motion parameters for improving tamping efficiency. A performance comparison is made between linear and elliptical tamping. The results indicate that smaller squeeze and release velocities of the tines yield better compaction. Of course, reducing the velocities would result in increased tamping time. Additionally, the results indicate that the linear motion of the tines potentially result in better compaction than elliptical motion, although the latter may require less insertion force (power) and cause less ballast damage.

Motion Control of a Two-Degree-of-Freedom Linear Resonant Actuator without a Mechanical Spring

This study aims to present a new two-degree-of-freedom (DOF) linear resonant actuator (LRA) and its motion control method without a position sensor. The design method of 2-DOF LRA which resonates with only detent force without a mechanical spring is proposed. Since the information of displacement and direction is required to control 2-DOF LRA, a sensor or an estimator is needed. Therefore, we proposed a position estimator and a motion controller for 2-DOF LRA. This paper proved that reciprocating motion, elliptical motion, and scrolling motion can be controlled without a position sensor. Finite element analysis (FEA) and dynamic simulation results validated the proposed method as well.