Alfonso Fernandez Del Rincon

Effect of cracks and pitting defects on gear meshing

The development of vibration-based condition monitoring techniques, especially those focused on prognosis, requires the development of better computational models that enable the simulation of the vibratory behaviour of mechanical systems. Gear transmission vibrations are governed by the so-called gear mesh frequency and its harmonics, due to the variable stiffness of the meshing process. The fundamental frequency will be modulated by the appearance of defects which modify the meshing features. This study introduces an advanced model to assess the consequences of defects such as cracks and pitting on the meshing stiffness and other related parameters such as load transmission error or load sharing ratio. Meshing forces are computed by imposing the compatibility and complementarity conditions, leading to a non-linear equation system with inequality constraints. The calculation of deformations is subdivided into a global and a local type. The former is approached by a finite element model and the latter via a non-linear Herztian-based formulation. This procedure enables a reduced computational effort, in contrast to conventional finite element models with contact elements. The formulation used to include these defects is described in detail and their consequences are assessed by a quasi-static analysis of a transmission example.

Enhancement of Mechanical Engineering Degree through student design competition as added value. Considerations and viability

ABSTRACT This paper proposes using a student design competition as a learning tool in the Mechanical Engineering Degree for enhancing the general competences and motivation of the students, transferring theoretical knowledge to practical situations and bringing together all courses involved under a common framework. This constitutes an added value that the in-person universities should offer to their students as a consequence of the Bologna process and the raising of open online resources for self-learning. In order to assess the viability of this proposal, a pilot competition design activity (CDA) is presented using project-based learning methods during a Mechanism Theory course for sophomore students. Meanwhile, 27 participants of a 45-student course from a European university took part in the pilot CDA, which consisted of redesigning the motorbike rear suspension used in a student design competition. Participants also completed mid-term and final exams as well as a survey to get their perception of this activity. Based on the success of the pilot CDA, the authors are planning to implement the proposal, including similar CDAs in other Mechanical Engineering courses to use the competition as a link between them and to encourage students to participate on the competition.

Planetary gear profile modification design based on load sharing modelling

In order to satisfy the increasing demand on high performance planetary transmissions, an important line of research is focused on the understanding of some of the underlying phenomena involved in this mechanical system. Through the development of models capable of reproduce the system behavior, research in this area contributes to improve gear transmission insight, helping developing better maintenance practices and more efficient design processes. A planetary gear model used for the design of profile modifications ratio based on the levelling of the load sharing ratio is presented. The gear profile geometry definition, following a vectorial approach that mimics the real cutting process of gears, is thoroughly described. Teeth undercutting and hypotrochoid definition are implicitly considered, and a procedure for the incorporation of a rounding arc at the tooth tip in order to deal with corner contacts is described. A procedure for the modeling of profile deviations is presented, which can be used for the introduction of both manufacturing errors and designed profile modifications. An easy and flexible implementation of the profile deviation within the planetary model is accomplished based on the geometric overlapping. The contact force calculation and dynamic implementation used in the model are also introduced, and parameters from a real transmission for agricultural applications are presented for the application example. A set of reliefs is designed based on the levelling of the load sharing ratio for the example transmission, and finally some other important dynamic factors of the transmission are analyzed to assess the changes in the dynamic behavior with respect to the non-modified case. Thus, the main innovative aspect of the proposed planetary transmission model is the capacity of providing a simulated load sharing ratio which serves as design variable for the calculation of the tooth profile modifications.

Dynamic Analysis of an Offshore Wind Turbine Drivetrain on a Floating Support

This paper presents a multi-body model for the study of the non stationary dynamic behaviour of an off-shore wind turbine power train. The problem studied is an off-shore implementation with seafloor depths around a thousand metres, making it necessary to use a floating platform. Special attention is paid to combining the characteristics of the buoy’s off-shore support with a detailed model of the power train in order to assess the consequences of buoy movement in the forces that appear in gears and bearings. A multi-body analysis code was used to develop the model and a conventional wind turbine set up was implemented as an example. Gearbox dynamic behaviour is simulated for common manoeuvres of start-up and emergency stop and the results obtained are presented.

Planet Load Sharing Behavior During Run Up

The objective of this paper is to study the effects of meshing phase between planets and the planet position error on the load sharing behavior in planetary gear set during run up regime. These effects will be studied numerically and will be validated experimentally through a back-to-back planetary gear test bench by comparing strains in the pinhole of each planet.

Experimental Investigation on the Influence of Relative Density on the Compressive Behaviour of Metal Mesh Isolator

Vibrations, considered one of the major problems in the engineering applications, are analyzed to predict their detrimental effects on the equipment and structures. The metal mesh isolator, named also metal rubber, has become widely applied to mitigate the disturbing vibration due to its special production techniques. Metal rubber is a kind of novel style porous damping material that is manufactured via a process of wire-drawing, weaving and compression moulding. This paper investigates the influence on the compression and dissipative behaviour of the metal mesh isolator provided by the relative density. The mechanical properties of five metal mesh samples with cylindrical geometry and with different relative density are obtained from a quasi-static cyclic compression test. The loading-unloading results of the five samples, subjected to a constant compression level, show the strong dependence exerted by the relative density over the compressive properties. Experimental analysis indicated that the porosity affects the stiffness but has an opposite effect regarding the loss factor. By increasing the ratio between the isolator’s and wire’s densities, the nominal stiffness increases, but the reduction of loss factor is obvious.

Effect of Gravity of Carrier on the Dynamic Behavior of Planetary Gears

This work investigates the effect of gravity of carrier on the dynamic behavior of back to back planetary gears in a stationary condition. A tridimensional lumped parameter model is developed in order to study this phenomenon. The gravity of carriers has an effect on the distance between gears and it is included in the model through sun-planets and ring-planets mesh stiffness which influence on the dynamic response of gear. Numerical results are correlated with the experimental results obtained from a back-to-back planetary gear test bench, this test bench is composed of two identical planetary gears sets: reaction gear, where the ring is free and test gear where the ring is fixed. They are connected through two rigid shafts. A fix external load was applied through an arm attached to the free reaction ring. Data Acquisition System acquired signals from accelerometers mounted on the carrier and the ring. The signal processing was achieved using LMS Test.Lab software.

Load Sharing Behavior in Planetary Gear Set

The objective of this paper is to study the effects of meshing phase between planets, the effects of the gravity of carrier and the planet position error on the load sharing behavior in planetary gear set. These effects will be studied numerically under the stationary condition and will be validated experimentally by a back-to-back planetary gear test bench. In this test bench, strain gauges are installed on each planet’s pin hole in order to compare strains in the pinhole of each planet.

An Experimental Investigation of the Dynamic Behavior of Planetary Gear Set

In this paper an experimental planetary gear set rig is developed for dynamic analysis purposes. This bench is composed by two identical planetary gears connected by a common shaft. Two tri axial accelerometers are mounted in both rings. Series of mmeasurements were achieved to study the influence of speeds as well as loads on the dynamic behaviour of the system. Time histories are characterized by a periodic fluctuation. Spectra showed sidebands around the mesh frequency and its harmonics. In order to identify the natural frequencies of the bench, series of run up are done. Influence of load on natural frequencies values is also investigated.

Dynamic Behavior of Back to Back Planetary Gear in Presence of Pitting Defects

The diagnosis of rotating machinery such as planetary gearbox running under operating condition is a complex task. Depending on their nature, the defects can be classified into teeth, geometrical or bearing defects. This paper studies the dynamic behavior of a back-to-back spur planetary gear running in stationary condition in the presence of teeth defects. This damage is the pitting and it is located in one tooth of the sun gear. An experimental test is performed by the measurement of the instantaneous accelerations on a test gear. The tests are carried out under a fixed load and speed. The presence of the tooth pitting defect activates repeated-like transient in ring’s vibration displacement because of phase change and amplitude reduction of the mesh stiffness when the damage tooth comes into contact. The Fast Fourier Transform (FFT) is used to transform the time signal into the frequency domain for signature analysis. The acceleration spectra show the influence of damage both in frequency and amplitude. The frequency of pitting which is the frequency of rotation of the test sun and the frequency of rotation of the motor appears along of frequency bandwidth. Moreover, the impulses of the defect tooth with the planets become important in amplitude.