Operational Vibration Analysis of Naval Platforms for System Integration

In this study, the operational vibration analysis and evaluation of the pedestal mounted missile system, BORA, which was developed for air defense of naval platforms, are performed. The main mission of BORA is the low level air defense of naval platforms such as frigates and fast attack boats. The gyro stabilized turret of BORA enables automatic target tracking and firing capabilities without being effected from the disturbances due to the waves and maneuvers of the ship. The location of the systems depends on many operational conditions in the platforms and is generally fixed. Therefore it is meaningless to perform operational modal analysis and obtain mode shapes; resonance frequencies etc. of the boat itself and locate system to the suitable regions. Solving vibration problems with signal analysis that is the process of analyzing the response of a system, due to some generally unknown excitation, are carried out in this work. 1.0 INTRODUCTION ASELSAN Pedestal Mounted Stinger (PMS) System is a highly capable very short range low level air defense system. It is equipped with several sensors for target detection and tracking and all the functions are controlled by the fire control computer. At night and bad weather conditions fire control functions enable target detection, tracking and identification. The system is armed with four/eight ready to fire Stinger missiles and one 12.7 mm automatic machine gun. While integrating PMS BORA System to attack boats, measurement of rotational velocity and linear acceleration reactions which will affect the system was aimed. Being able to determine the mechanical vibration magnitudes and frequencies during the lifetime of the system is of great importance in checking the stabilization with respect to the inputs from the boat and the strength of mechanical pedestal structure. In this study, data acquisition from the accelerometers and the frequency responses are reported. The BORA system incorporating electronics and electro-optical subsystems can be tested in the laboratory after obtaining the operational vibration tests data of the boat. For this purpose integrated circuit piezoelectric (ICP) accelerometers are located at points of interest for testing vibration on the system. Power Spectrum Density (PSD) analysis is performed to define the vibration profile that the electronic equipments should withstand. It is also intended to obtain required stabilization during operation of the platform. The aim of the environmental tests is to ensure that the production equipment meets the specified requirements over the full range of the specified environmental conditions. Mechanical shock and vibration are the most complicated type of the environments because of the importance of their spectral characteristics, but it must still be dealt with simple terms. Many vibration and shock specifications related to the conditions at the locations of the usage so that they provide design and development incentives for Paper presented at the RTO AVT Symposium on “Habitability of Combat and Transport Vehicles: Noise, Vibration and Motion”, held in Prague, Czech Republic, 4-7 October 2004, and published in RTO-MP-AVT-110. RTO-MP-AVT-110 21 1 UNCLASSIFIED/UNLIMITED UNCLASSIFIED/UNLIMITED Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 01 OCT 2004 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Operational Vibration Analysis of Naval Platforms for System Integration 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) MST-MTM Aselsan Inc. 06172 Yenimahalle-Ankara /TURKEY 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited 13. SUPPLEMENTARY NOTES See also ADM201923, Habitability of Combat and Transport Vehicles: Noise, Vibration and Motion (L’habitabilite des vehicules de combat et de transport: le bruit, les vibrations et le mouvement). , The original document contains color images. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF PAGES 12 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 Operational Vibration Analysis of Naval Platforms for System Integration survival and operation of the product in such conditions. Usually these specifications attempt to require the environmental tests to simulate such conditions. The specifications lead to developmental tests guiding the designers in revealing features which might require redesign [1, 2]. Figure 1: PMS Bora system on an attack boat. For many electronic systems, shock and vibration are a part of the qualification test requirements. Military Standards proposes limited approximate (empirical) values for various military platforms. These values can be used when there is no opportunity of measurement. The PSD graph for shipboards is given in vibration section of MIL STD 810F [3] (Figure 2). The standard particularly stresses the requirement of performing test at the installation region of the systems. In naval platforms structural effects of the platform to the equipments are more critical than the effects of the equipments to the platforms, as expected. Products which are analyzed experimentally and/or numerically will have less production time and costs, also higher quality and reliability. There are several solutions the vibration problem during design stage. 1) Decreasing the power of the vibration source (removing unbalance and misalignment, maintenance etc.), 2) Manipulating frequency band by geometric modifications (modal design) in the system, 3) Isolating regions that might fall in resonance by the source, 4) Increasing energy absorption ability of the regions that are possibly in excessive vibration. 21 2 RTO-MP-AVT-110 UNCLASSIFIED/UNLIMITED UNCLASSIFIED/UNLIMITED Operational Vibration Analysis of Naval Platforms for System Integration Figure 2: MIL-STD-810F, Ship vibration PSD profile. Ruggedization of the systems are handled with reinforcement of the components that are located inside the structure and/or external protection of the systems by isolators for minimizing disturbing force and/or modal design of the equipments and their mounting points. Initially, shock and vibration are caused by some types of sources such as tracks and engine of the vehicle, firing of a projectile etc., which are unavoidable during the operation. In this case, the path of the energy which is transmitted to the target system should include isolators and/or should be modified according to the target sensitivities by optimizing the stiffness and the mass of the structure [4, 5, and 6]. 2.0 SIGNAL AND SYSTEM ANALYSIS IN MECHANICAL STRUCTURES Signal Analysis is the vibration analysis for determining the response of a system due to generally unknown excitation and presenting it in a manner which is easy to interpret [7]. In the analysis under operational conditions the loads which are input to the system are unknown. But the data obtained from the test results give the behavior (operational deflection shapes) of the system under operational conditions. In Signal Analysis time signal does not give too much information. Converting signal to frequency domain forms acceleration spectrum information. This spectrum can show the energy intensity concentrated around one or more of the frequencies. By the knowledge and experience of the system mechanics, relation between these frequencies and special mechanic components are defined so that the source of the vibration can be determined. As an example the magnitude of frequency in one spectrum might coincide with a specific rotational speed of a particular shaft in the transmission system. This analysis is a strong evidence to identify the source of the vibration. As the source is identified new questions arising should be examined like; does the source has enough dynamic energy to vibrate the structure, or is the response of the structure extremely high when the structure is weak and insufficient? Determining the vibration properties of the path between source and sink shows dynamic structural characteristic of the whole system. All the peak points in the graph can not be termed as resonance points. Since the excitation function is unknown and modal analysis must be done to understand whether the reason is structural or excitation. RTO-MP-AVT-110 21 3 UNCLASSIFIED/UNLIMITED UNCLASSIFIED/UNLIMITED Operational Vibration Analysis of Naval Platforms for System Integration System (Modal) Analysis is the vibration analysis that deals with techniques for determining the inherent properties (modes, resonances, damping etc.) of a system and constructing mathematical model of the system. This can be done by stimulating the system with measurable forces and studying the response/force ratio (receptance). For linear systems this ratio is independent, inherent property which remains same whether the system is excited or at rest. Modal analysis is performed by numerical and experimental techniques. Structure’s vibration modes and frequencies give structure’s dynamic properties. When obtained results and excitation frequencies coincide then some precautions must be taken. After the outputs are evaluated adding stiffness to the system might be a solution. Much of the effort is expended for making mounting supports rigid and less is spent for damping them. This stiffness shifts the natural frequencies to higher values. Structure could be taken out from excitation range by modifying the structural design. The amount of this modification is based on proper mathematical models and iterations in modal analysis software’s [8] or engineering background. The modifications will be easier after the numerical model confirmed with the experimental results [9]. In some cases isolating the structure (free-free) from external forces or applying enough vibration forces to excite the system (tank, bridge etc.) is not possible when performing the modal analysis. Then operational modal analysis should be applied and only response function might be necessary to analyze the system [10]. It is an important approach in vibration analysis since the modal analysis method could be applicable to both the equipments and the platforms. In this study operational vibration analysis is performed by using signal analysis on naval platform for system integration. Modal analysis is applied to BORA structure to analyze possible effects coming from the platform to the PMS system before the integration. And also environmental qualification tests could be performed to the electronic equipments by using PSD vibration profile obtained from operational tests. 3.0 OPERATIONAL MEASUREMENTS OF THE BOAT STRUCTURE The three dimensional rotation and translational movement inputs are collected during design stage of the PMS system that will be mounted on the battleship (Figure 3).