BS ISO 21955 pdf free download

BS ISO 21955-2021 pdf free download.Acoustics一Experimental method for transposition of dynamic forces generated by an active component from a test bench to a receiving structure.
5 Operating mode
5.1 General
In this subclause, an operating mode to apply this document is proposed, as an example.
This procedure is based on the general Formula (2) allowing to transpose the dynamic forces generated by an active component from a test bench to a receiving structure. Depending on the assumptions on the different transfer functions, this operating mode allows the use of simplified versions of Formula (2).
The frequency range(s) for which the formulated hypotheses and steps presented below are considered as valid or invalid shall be mentioned.
5.2 Synopsis of procedure
The various special cases discussed below can be summarized in the form of a general diagram of the procedure (see Figure 2).
5.3 Tasks and preliminary operations
A number of tasks and processes shall be performed previous to the application o this procedure:
a) During the development of the product, the component will determine the active component transfer matrix at the connecting points. There are many cases for which the active component is not only connected to its fixation points, but interacts with its environment through cables, rotation axes, hoses, pipes, friction, which do not allow to measure the transfer matrix in free conditions for all degrees of freedom. In this case, different alternatives are proposed in the document.
b) During the development of the product, the component chooses the properties of the connecting device between the component and the receiving structure. It is remarked that this connecting device matrix properties are of first order influence on the final transmitted forces: the product shall ensure a perfect decoupling in order to minimize the vibration coupling between the component and the receiving structure. Some advices are given hereunder in this operating mode.
c) To apply the methodology to predict the forces transmitted to the receiving structure in order to check compliance with the specifications, a test bench is generally developed, transmitted forces to the bench are measured. Usually, in the field of noise and vibration, an infinitely rigid bench, such as a marble, is used, but this methodology is not mandatory. Therefore, the procedure covers the case of a not infinitely rigid test bench.
The operating mode starts with the analysis of the general equation IFormula (2)J and attempts to cover the different real cases that may be encountered in practice in the fields covered by the document. The choices in the flow chart not only depend on the possibilities offered by the product, but also on the relative order of scales of different transfer matrices in Formula (2). Three different examples are described in Annexes E and E to scan a wide range of applications.
5.4 Transfer matrices determination
5.4.1 General
Annex B is dedicated to frequency transfer functions measurement. These measurements are generally performed with accelerometers and force sensors, leading to accelerance measurements.
5.4.2 Final receiving structure transfer matrix determination Y
In Formula (2). the transfer matrix at the connecting points is required to predict the forces on the final structure; whenever there is a component integrator specification about the predicted forces, which means that the component integrator shall provide to the component supplier the transfer matrix values at the connecting points. These values are generally available at early stages of a project development via simulation tools.
In many cases, it is impossible to decouple the active component from the receiving structure to perform a measurement. Iso 20270 can be applied, with an indirect measurement of blocked forces.
5.4.3 Test bench transfer matrix determination,
At design stage for the test bench, it shall be considered to let some space to position the sensors for the
matrix determination.
5.4.4 Connecting device spring-like matrix properties determination, S1
The connecting device matrix is generally determined on its own on a specific bench. In this case only diagonal terms of the matrix are measured: ISO 10846 can be used.
Taking into account a connecting device is not adapted when:
— the active component is rigidly coupled to the receiving structure or test bench;
— the connecting devices are not a set spring-like point-like devices.
Taking into account a connecting device is not mandatory:
— the active component can be directly coupled to the receiving structure or test bench;
— the connecting device can be integrated in the Active component or in the Test Bench/ Receiving
structure part, whenever possible.
5.4.5 Active Component transfer matrix determination, AC
Whenever possible to position the active component in free boundary conditions, the frequency response functions of the transfer matrix shall be measured.
In many cases, the active component main function is to deliver a mechanical function to a system via connections which are not fixation points or fixation surfaces. In this case, it is not possible to test the active component in free boundary conditions.
Two options are possible to determine the active component transfer matrix:
a) Usage of a specific test bench called block sensor designed to measure indirect active component transfer matrix and indirect blocked force (see AnncxF);
b) Indirect determination of the active component transfer matrix associated with the connecting.BS ISO 21955 pdf download.