EuroWire July 2016

Technical article

Design Analysis of a Large Planetary Strander using CAE tools By Giorgio Pirovano, MFL Group, and Fabiano Maggio, EnginSoft SpA

Introduction The design of a stranding and closing planetary machine with back-twist is not a simple project, due to the “planetary” rotation of the parts: that introduces dynamic effects that are difficult to estimate; in particular if the performance is extreme due to large spool mass, load configurations and rotation speed. In order to avoid any possible risk and to obtain the most precise design input, MFL involves EnginSoft and its simulation capabilities as reliable partner in this project. For this specific project, EnginSoft is in charge of carrying out the whole dynamical assessment of the planetary machine. In order to achieve reliable and precise results, it is necessary to use a powerful and versatile multi-body software: RecurDyn®. On the other hand, MFL has to complete the design of all parts in order to meet structural requirement in terms of strength and lifetime. This colossal planetary machine will be used to produce cable with different diameters and strand combinations, so that the spools loaded on the machine can be different in size and position on the main rotor. In addition, the spools are naturally unbalanced due to winding errors. This results in various load scenarios to be analysed. The goal is the identification of the worst case in terms of power required to the motors and stress on parts. Methods and problem definition

defined in the RecurDyn® environment. The result is an accurate model with more than 100 bodies. Most of the inertial proprieties are derived automatically from CAD, but several bodies are parametrised inside the multi-body software. Obviously, the connection between the different bodies perfectly simulates the real kinematic link (gear, shafts, and so on) in order to obtain a model which is the closest as possible to the real machine in terms of degrees of freedom. Gear elements are special features of the RecurDyn® library, designed to simulate both kinematics (transmission ratio) and dynamics (reciprocal loading) occurring at any gear couple. Figure 4 shows the gears back-twist system. It is easy to see that the “gear feature” of RecurDyn® has been massively used due to the conformation of the transmission chain.

EnginSoft’s engineers are in charge of finding out such worst conditions through dynamic simulation. The approach starts with a single cage, and an analysis defines the worst configuration. After that, together with MFL, finite load scenarios are defined. The next step is the dynamic simulation of the different load scenarios by applying the worst cage condition previously defined. At the end it is possible to obtain the worst working condition of the whole machine. In other words, this activity is the scientific and precise application of the design of experiment (DOE). ▲ ▲ Figure 1 : Rotations on a planetary stranding machine

▼ ▼ Figure 2 : Single cage of planetary machine

Single cage

Rigid body dynamics model

Single cage

Single cage

▼ ▼ Figure 3 : Method and DOE approach

A rigid body dynamic analysis is performed; internal loads and motor power torques mainly depend on accele- ration and inertias of moving parts, so that there is not a clear need of introducing flexibilities into the model (which would significantly increase the computational effort). Starting from the MFL 3D CAD geometry of the machine, the dynamic model is

Spool dimension

Spool combination

DOE

Spool unbalance

Motor’s power

Load on parts

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July 2016