Balancing of Flexible Rotors Supported on Fluid Film Bearings by Means of Influence Coefficients Calculated by the Numerical Assembly Technique

In this paper, a new method for the balancing of rotor-bearing systems supported on fluid film bearings is proposed. The influence coefficients necessary for balancing are calculated using a novel simulation method called the Numerical Assembly Technique. The advantages of this approach are quasi-analytical solutions for the equations of motion of complex rotor-bearing systems and very low computation times. The Numerical Assembly Technique is extended by speed-dependent stiffness and damping coefficients approximated by the short-bearing theory to model the behavior of rotor systems supported on fluid film bearings. The rotating circular shaft is modeled according to the Rayleigh beam theory. The Numerical Assembly Technique is used to calculate the steady-state harmonic response, influence coefficients, eigenvalues, and the Campbell diagram of the rotor. These values are compared to simulations with the Finite Element Method to show the accuracy of the procedure. Two numerical examples of rotor-bearing systems are successfully balanced by the proposed balancing method

Fault Detection in Offshore Structures: Influence of Sensor Number, Placement and Quality

Within the Space@Sea project floating offshore islands, designed as an assembly of platforms, are used to create space in offshore environments. Offshore structures are exposed to harsh environment conditions. High wind speeds, heavy rainfall, ice and wave forces lead to highly stressed structures. The platforms at the Space@Sea project are connected by ropes and fenders. There exists the risk of a rope failing which is therefore investigated subsequently. To ensure the safety of the structure, the rope parameters are monitored by the Extended Kalman Filter (EKF). For platform arrangements, a large number of sensors is required for accurate fault diagnosis of these ropes, leading to high investment costs. This paper presents a strategy to optimize the number and placement of acceleration sensors attached to the floating platforms. There are also high demands on the sensors due to the harsh offshore conditions. Material deterioration and overloading may lead to decayed sensor performance or sensor defects. Maintenance of offshore sensors is difficult, expensive and often not feasible within a short time. Therefore, sensor measurement deviations must not affect reliable structure fault detection. The influence of defect sensors on the rope fault detection is examined in this study: Types, intensities, number, place of occurrence of defect sensors and the distance between defect sensors and rope faults are varied

SIRM 2017

This volume contains selected papers presented at the 12th International Conference on vibrations in rotating machines, SIRM, which took place February 15-17, 2017 at the campus of the Graz University of Technology. By all meaningful measures, SIRM was a great success, attracting about 120 participants (ranging from senior colleagues to graduate students) from 14 countries. Latest trends in theoretical research, development, design and machine maintenance have been discussed between machine manufacturers, machine operators and scientific representatives in the field of rotor dynamics. SIRM 2017 included thematic sessions on the following topics: Rotordynamics, Stability, Friction, Monitoring, Electrical Machines, Torsional Vibrations, Blade Vibrations, Balancing, Parametric Excitation, and Bearings. The papers struck an admirable balance between theory, analysis, computation and experiment, thus contributing a richly diverse set of perspectives and methods to the audience of the conference

Investigaciones en las operaciones de transferencia de carga offshore, desafíos, desarrollos y nuevas fronteras

Currently, offshore operations are considered activities with high impact on the economy, which standsin direct relation to the products of great importance and value for diverse economic sectors. Thus, itbecomes necessary to implement new technologies that make the manipulation of these products fasterand easier. In this work, the authors introduce the problem in offshore cargo transfer operations. Thisproblem involves different kinds of areas: logistics, dynamics, and control are some of them. The authorspresent an approach for the last two. In the dynamic problem is presented a study on the dynamics of asuspended load connected to a crane via a mechanism with two prismatic degrees of freedom. The studiesshow the complex large-amplitude motion of the load given the visibly nonlinear behavior of the ship.Therefore, the development of a fuzzy controller was necessary to decrease oscillations and position theload in one definitive point of interest. The work presents the test results, demonstrating that this typeof manipulator in combination with an effective control strategy allows for the reduction of oscillationsin offshore activities.En la actualidad, las operaciones en alta mar se consideran actividades con alto impacto en la economía, lo cual se encuentra en relación directa con los productos de gran importancia y valor para diversos sectores económicos. Así entonces, se hace necesario implementar nuevas tecnologías que permitan más rápida y fácil manipulación de estos productos. En este trabajo, los autores presentan el problema en operaciones de transferencia de carga en alta mar. Este problema involucra diferentes tipos de áreas: logística, dinámica y control, son algunos de ellos. Los autores presentan un acercamiento para las últimas dos. En el problema de dinámica se presenta un estudio sobre la dinámica de una carga suspendida conectada a una grúa mediante un mecanismo con dos grados prismáticos de libertad. Los estudios demuestran el movimiento complejo de gran amplitud de la carga dada el comportamiento visiblemente no-lineal de la embarcación. Entonces, el desarrollo de un controlador de lógica difusa fue necesario para disminuir las oscilacionesy posicionar la carga en un punto de interés definitivo. El trabajo presenta los resultados de pruebas, demostrando que este tipo de manipulador en combinación con una estrategia efectiva de control permite la reducción de oscilaciones en actividades en alta mar

Steady-state linear harmonic vibrations of multiple-stepped Euler-Bernoulli beams under arbitrarily distributed loads carrying any number of concentrated elements

In this paper, general beam vibration problems with several attachments under arbitrarily distributed harmonic loading are solved. A multiple-stepped beam is modelled by the Euler-Bernoulli beam theory and an extension of an efficient numerical method called Numerical Assembly Technique (NAT) is used to calculate the steady-state harmonic response of the beam to an arbitrarily distributed force or moment loading. All classical boundary conditions are considered and several types of concentrated elements (springs, dampers, lumped masses and rotatory inertias) are included. Analytical solutions for point forces and moments and polynomially distributed loads are presented. The Fourier extension method is used to approximate generally distributed loads, which is very efficient for non-periodic loadings, since the method is not suffering from the Gibbs phenomenon compared to a Fourier series expansion. The Numerical Assembly Technique is extended to include distributed external loadings and a modified formulation of the solution functions is used to enhance the stability of the method at higher frequencies. The method can take distributed loads into account without the need for a modal expansion of the load, which increases the computational efficiency. A numerical example shows the efficiency and accuracy of the proposed method in comparison to the Finite Element Method

OMAE2009-79604 STATISTICAL INVESTIGATION OF THE NONLINEAR BEHAVIOR OF STRUCTURES OPERATING OFFSHORE

ABSTRACT Due to the increasing amount of ship and offshore operations taking place in the ocean environment, the amount of reports concerning damage, loss of cargo or even loss of human lives increases, too. The reasons for these incidents have been a subject of intensive research for many years. Recently, the aim of some research concentrated on extreme wave phenomena such as 'rogue waves' or 'the three sisters'. These phenomena are a severe danger, but they do not play a decisive role for most of the incidents happening at sea. More often, the reason for endangerment of structures in the environment is a fluid-structureinteraction that leads to unstable dynamical system behaviour. Including nonlinear effects in the calculations, through statistical investigation of structures in waves, it can be shown that critical behaviour of ships and structures can occur without the absolute necessity of heavy sea conditions or the occurrence of dangerous sea phenomena. The reason that many of these incidents do not lead to severe accidents lies in the experience of the master and his crew and their ability to change system parameters in a way that prevents the catastrophe. The aim of this paper is to show the current state of development of a program that uses a Monte-Carlo-Simulation technique based on a common panel-method for the creation of added masses and added damping with hydrodynamic coupling to predict the behaviour of the structure in several wave conditions. NOMENCLATURE A(ω) Added mass matrix, coefficients INTRODUCTION The dynamic behaviour of offshore structures depends on design properties and operating conditions, mainly external forces induced by wind and waves. For appropriate motion investigation of floating systems, adequate theoretical models and mathematical techniques are needed. In our models, we account for hydrodynamic effects, nonlinear forces, and multiple body interaction. Depending on the complexity of the used model, especially with nonlinearities in the equations, this easily leads to extensive sets of equations and results in time-consuming computer analyses. For statistical analysis, large datasets have to b

Quasi-analytical solutions for the whirling motion of multi-stepped rotors with arbitrarily distributed mass unbalance running in anisotropic linear bearings

Vibration in rotating machinery leads to a series of undesired effects, e.g. noise, reduced service life or even machine failure. Even though there are many sources of vibrations in a rotating machine, the most common one is mass unbalance. Therefore, a detailed knowledge of the system behavior due to mass unbalance is crucial in the design phase of a rotor-bearing system. The modelling of the rotor and mass unbalance as a lumped system is a widely used approach to calculate the whirling motion of a rotor-bearing system. A more accurate representation of the real system can be found by a continuous model, especially if the mass unbalance is not constant and arbitrarily oriented in space. Therefore, a quasi-analytical method called Numerical Assembly Technique is extended in this paper, which allows for an efficient and accurate simulation of the unbalance response of a rotor-bearing system. The rotor shaft is modelled by the Rayleigh beam theory including rotatory inertia and gyroscopic effects. Rigid discs can be mounted onto the rotor and the bearings are modeled by linear translational/rotational springs/dampers, including cross-coupling effects. The effect of a constant axial force or torque on the system response is also examined in the simulation

Steady-State Harmonic Vibrations of Viscoelastic Timoshenko Beams with Fractional Derivative Damping Models

Due to growing demands on newly developed products concerning their weight, sound emission, etc., advanced materials are introduced in the product designs. The modeling of these materials is an important task, and a very promising approach to capture the viscoelastic behavior of a broad class of materials are fractional time derivative operators, since only a small number of parameters is required to fit measurement data. The fractional differential operator in the constitutive equations introduces additional challenges in the solution process of structural models, e.g., beams or plates. Therefore, a highly efficient computational method called Numerical Assembly Technique is proposed in this paper to tackle general beam vibration problems governed by the Timoshenko beam theory and the fractional Zener material model. A general framework is presented, which allows for the modeling of multi-span beams with general linear supports, rigid attachments, and arbitrarily distributed force and moment loading. The efficiency and accuracy of the method is shown in comparison to the Finite Element Method. Additionally, a validation with experimental results for beam systems made of steel and polyvinyl chloride is presented, to illustrate the advantages of the proposed method and the material model