Estimation of Frequency Response Function on Rotational Degrees of Freedom of Structures

1999 ◽  
Author(s):  
Naoki Hosoya ◽  
Takuya Yoshimura
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Structural Dynamics ◽  
Frequency Response Function ◽  
Degrees Of Freedom ◽  
Estimation Procedure ◽  
Rigid Block ◽  
Measurement Point ◽  
Beam Structure ◽  
Rotational Degrees Of Freedom

Abstract In conventional vibration testing, measurement of frequency response function (FRF) has been limited to translational degrees of freedom (DOF). Rotational DOFs have not been treated in experimental analysis. However, the rotational DOF is indispensable in further analysis, such as substructure synthesis, prediction of structural dynamics modification, etc. Hence, measurement of FRFs on rotational DOF is essential for expanding applicability of experimental modal analysis. This paper proposes a new method for FRF estimation on rotational DOF of structures. The following is the estimation procedure: A rigid block is fixed on the measurement point of the structure; the block is excited by conventional impact hammer; the inner force and the response of the connection point including rotational DOFs are estimated; and lastly, the FRF including rotational DOF at the connection point of the structure is obtained. The feasibility of the method is investigated experimentally by applying it to a beam structure.

scholarly journals Modal Mass and Length of Mode Shapes in Structural Dynamics

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
M. Aenlle ◽  
Martin Juul ◽  
R. Brincker
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Structural Dynamics ◽  
Mode Shape ◽  
Physical Meaning ◽  
Frequency Response Function ◽  
Degrees Of Freedom ◽  
Mode Shapes ◽  
Length Measure ◽  
Modal Mass

The literature about the mass associated with a certain mode, usually denoted as the modal mass, is sparse. Moreover, the units of the modal mass depend on the technique which is used to normalize the mode shapes, and its magnitude depends on the number of degrees of freedom (DOFs) which is used to discretize the model. This has led to a situation where the meaning of the modal mass and the length of the associated mode shape is not well understood. As a result, normally, both the modal mass and the length measure have no meaning as individual quantities but only when they are combined in the frequency response function. In this paper, the problems of defining the modal mass and mode shape length are discussed, and solutions are found to define the quantities in such a way that they have individual physical meaning and can be estimated in an objective way.

scholarly journals Corrigendum to “Modal Mass and Length of Mode Shapes in Structural Dynamics”

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
M. Aenlle ◽  
Martin Juul ◽  
R. Brincker
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Structural Dynamics ◽  
Mode Shape ◽  
Physical Meaning ◽  
Frequency Response Function ◽  
Degrees Of Freedom ◽  
Mode Shapes ◽  
Length Measure ◽  
Modal Mass

The literature about the mass associated with a certain mode, usually denoted as the modal mass, is sparse. Moreover, the units of the modal mass depend on the technique used to normalize the mode shapes, and its magnitude depends on the number of degrees of freedom (DOFs) used to discretize the model. This has led to a situation where the meaning of the modal mass and the length of the associated mode shape is not well understood. As a result, normally, both the modal mass and the length measure have no meaning as individual quantities, but only when they are combined in the frequency response function. In this paper, the problems of defining the modal mass and mode shape length are discussed, and solutions are found to define the quantities in such a way that they have individual physical meaning and can be estimated in an objective way.

Analytical Passive Time Reversal Method Combined With Equivalent Source Method for Sound Source Localization in an Enclosure

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Chuan-Xing Bi ◽  
Yong-Chang Li ◽  
Yong-Bin Zhang ◽  
Rong Zhou
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Source Localization ◽  
Time Reversal ◽  
Arbitrary Shape ◽  
Frequency Response Function ◽  
Sound Source Localization ◽  
Measurement Point ◽  
Sound Sources ◽  
Equivalent Source

The analytical passive time reversal method (APTRM) is a powerful technique for sound source localization. In that technique, it generally requires that the frequency response function relating the measurement point to the focusing point should be known in advance. However, inside an enclosure of arbitrary shape, there is no theoretical formulation of this frequency response function, and using the APTRM with the free-field Green's function might lead to inaccurate localization of sound sources. This paper proposes a method combining the APTRM with the equivalent source method (ESM) to locate sound sources in an enclosure of arbitrary shape. In this method, the frequency response function relating the measurement point to the focusing point inside the enclosure is first calculated numerically using the ESM, and then the APTRM with this numerical frequency response function is used to realize the localization of sound sources. Numerical simulations in a rectangular enclosure and an enclosure of arbitrary shape as well as an experiment in a rectangular wooden cabinet are performed to verify the validity of the proposed method. The results demonstrate that the frequency response function in an enclosure can be accurately calculated using the ESM; based on measurements with a spherical array composed of 48 microphones, the proposed method can effectively locate the sound sources in enclosures of different shapes and work stably under the situation of low signal-to-noise ratio.

scholarly journals Frequency Response Function Measurement on Simplified Disc Brake Model

2018 ◽  
Vol 68 (3) ◽  
pp. 225-230
Author(s):  
Úradníček Juraj ◽  
Miloš Musil ◽  
Michal Bachratý
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Degrees Of Freedom ◽  
Disc Brake ◽  
Damping Properties ◽  
Function Measurement ◽  
Two Degrees Of Freedom ◽  
Frequency Response Function Measurement

AbstractThe paper describes role of non-proportional damping in flutter type instability, demonstrated on simplified disc brake model. The discrete two degrees of freedom system is considered to imply damping induced instability through a system eigenvalues evaluation. The Frequency Response Function (FRF) is further calculated from measurements on the physical disc brake model. From FRF, damping properties are estimated and discussed. Several different loading states of the pad versus disc are considered to show loading impact on FRF and thus damping of the system.

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