تحليل ارتعاشات آزاد ديسك حلقوي به روش مدار معادل الكترومكانيكي

Vibration Analysis of Annular Disks by Equivalent Electro-mechanical Circuit Method

در اين نوشتار ارتعاشات پيچشي و شعاعي ديسك‌هاي حلقوي ايزوتروپيك با تغييرات خطي ضخامت در راستاي شعاعي و با استفاده از روش مدار الكترومكانيكي معادل و توابع بسل حل شده است. به‌كمك اين مدار، فركانس‌هاي طبيعي و روابط آن براي ارتعاشات پيچشي و شعاعي و همچنين ضرايب بزرگ‌نمايي (نسبت دامنه سرعت) آن به دست آمده است. سپس تغييرات فركانس‌هاي طبيعي و ضرايب بزرگ‌نمايي نسبت به تغييرات پارامتر هاي هندسي، از‌جمله شعاع داخلي و خارجي، مورد بحث قرار گرفته است. در ادامه، شكل مود‌ها و فركانس‌هاي طبيعي ديسك از نرم‌افزار اجزا محدود استخراج و با نتايج حاصل از روش مدار معادل مكانيكي مقايسه شده است. هم‌خواني خوبي بين اين نتايج مشاهده شده است. روش مطرح‌شده در اين نوشتار به‌عنوان يك الگوريتم حل براي بررسي ارتعاشات ديسك‌هاي با ضخامت متغير نيز قابل استفاده است.

In this paper, the vibration of an annular disk with a linearly varying cross-section is analyzed by means of Bessel’s functions and an equivalent electro-mechanical circuit method. By using the equivalent electrical equations, natural frequencies and magnification factors are obtained.This is done by writing the equations of motion for the disk vibration and rewriting the equation to make it similar to a three component Kirchhoff circuit.The method can be used to obtain the resonance frequency of an ultrasonic transducer as well as the resonance frequency of a circuit. In this method, the vibration of an annular disk is investigated separately in radial and torsional components.The results of the method were first verified for the cylindrical disks with uniform thickness and proved to be compatible with the previously developed methods for extracting natural frequencies of such shapes. Then, the effects of variations of geometrical parameters, namely; the ratio of the outer radius over the inner radius and the relation between the angular and radial displacement amplitude magnification on the natural frequencies, are studied. The results show that by fixing the inner radius, the torsional and radial resonance frequencies are decreased as the outer radius is increased. Although the inner radius affects the natural frequencies, it is observed that the primary factor is the outer radius. The relationship between the magnifications and the geometrical radius ratio is also analyzed, which shows a weak relationship between them. Correspondingly, the finite element method is used to analyze the modal shapes by ANSYS software. It is shown that the frequency values calculated by applying the presented theory are in good agreement with the simulation results by ANSYS. The method is also capable of providing benchmark values for researchers to validate other variable thickness annular plates. The drawback of this analysis is that it assumes a very thin annular disk. For thick disks, the vibrations are complex and the method of this paper is not applicable.