Incam 2015

Indian Conference on Applied Mechanics (INCAM)

IIT Delhi, 12-15 July 2015Indian Conference on Applied Mechanics (INCAM), IIT Delhi, 13-15 July 2015

Study of a Shock Isolation Satellite Transportation FixtureSrinivasa Prasad K. S1, Rajeev Chaturvedi2,Shree Niwas Sahu3, A. Sekar4 , K. V. Govinda51 Student, Bangalore Institute of Technology, Bangalore, Karnataka, 560 004. 2 Engineer SD, MDMD, ISRO Satellite Centre (ISAC), Bangalore, Karnataka, 560 017.

3 Engineer SG, MDMD, ISAC, Bangalore, Karnataka, 560 017 4 Head, Design and Development Section, MDMD, ISAC, Bangalore, Karnataka, 560 017

5 Deputy Director, ICA, ISAC, Bangalore, Karnataka, 560 017Presenting authors email: rajeevc@isac.gov.inAbstractISRO satellite centre (ISAC) builds the state of art satellites for communication, remote sensing, scientific experiments, weather forecasting and interplanetary missions. The satellite assembly consists of a number of detachable payload/equipment panels that provide housing for sensitive and delicate bus elements viz. power distribution package, IRU package, TTC package, Solar Array Drive Assembly (SADA) etc. and payload elements. Often the satellite assembly is transported to other centers for assembly and integration activities. In-house designed Four Bar Linkage Tilting System (FLTS) is used for transporting the satellite assembly. The transportation of the satellite assembly by road and air is always a challenge and requires adequate protection system to counter attack the effects of shock and vibration. Metallic wire rope isolators are used for isolating the FLTS from the destructive effects of shock and vibration. These isolators exhibit nonlinear force deflection characteristics in order to absorb the shock energy. This paper discusses the dynamic behavior of the FLTS with the isolators, when subjected to shock excitation originating during the transportation environment. The finite element model as well as an equivalent two degree of freedom model were developed and correlated with each other. The wire rope isolators were modeled as nonlinear springs in the FE model by using pseudo force method available in MSC Nastran finite element structural code. Theoretical and numerical results obtained from FEA were found to be in good agreement with each other.1. IntroductionThe Four bar linkage tilting system (FLTS) is one of the mechanical ground support equipments, which is used for orienting the satellite at any angle during assembly, integration and testing activities. Apart from assembly, integration and testing activities, it also serves as a rigid platform for the satellite during the transportation. The complete FLTS along with the satellite is placed in Satellite Transportation and Storage System (STSS). The FE model of the FLTS is shown in Figure 1. The structural response of the FLTS along with the satellite to the shock pulse excitation in the vertical direction (Z Axis as shown in Figure 1) should be properly assessed in order to determine the clearance space available between the satellite and the top surface of the STSS. Further, proper assessment of the above mentioned structural response helps in avoiding collision and subsequent damage of the satellite and its components.

The FLTS along with the satellite is mounted on metallic wire rope isolators. These wire rope isolators possess properties like low natural frequency, ability to deflect in controlled and repeatable way to absorb the impact loadings and good damping characteristics, which make them suitable for shock and vibration isolation purposes [1]. In order to meet the requirements of effective absorption of shock energy, they exhibit nonlinear force deflection characteristics. In the isolation of steady-state vibration, displacement amplitude is usually small, and nonlinearity of the isolator tends to be unimportant but in the isolation of shock, nonlinearity tends to be more important because large deflections prevail. The degree of isolation is substantially affected by the ability of the isolator to accommodate the required deflection in the case of shock isolation.

Figure 1. Four bar linkage tilting system

2. General DescriptionThe FE model as well an equivalent two degree of freedom model of the FLTS with the isolators was developed. In order to mathematically model the nonlinear force deflection characteristics of the wire rope isolator, curve fitting techniques were used and the cubic polynomial which best fits with the static load deflection data of the isolator was determined. Figure 2 shows the force deflection characteristics of the isolator used.

Figure 2. Force deflection characteristics of the wire rope isolator

In order to model the nonlinearity of the isolators for the case of shock pulse excitation, an efficient method called pseudo force method which is available in MSC Nastran[2] is used. In this method, localized nonlinearities are treated so that they require no additional computer time when compared to a purely linear analysis. In this method, deviations from linearity are treated as additional applied loads.3. Summary

A study of dynamic behavior of the FLTS with the isolators, when subjected to shock pulse excitation was made. Both theoretical and FE methods were used and the results were correlated. They were found to be in good agreement with each other.4. References[1] William T Thomson, Marie Dillon Dahleh, Chandramouli Padmanabhan, 1998, Theory of Vibrations with Applications, Pearson Education, Inc., New York.

[2] MSC Software, 2011, MSC NASTRAN 2012 Dynamic Analysis User's Guide, MacNeal - Schwendler Corporation, Los Angeles, CAPage 2 of 2Page 1 of 2