Search

CN-115577461-B - Design and use method of indirect method-based dynamic stiffness measurement retarding mass block assembly

CN115577461BCN 115577461 BCN115577461 BCN 115577461BCN-115577461-B

Abstract

A design calculation and use method of a retarding mass block assembly for measuring the transfer dynamic stiffness of a multi-type flexible connecting pipe by an indirect method comprises the steps of designing the retarding mass block assembly according to basic parameters of the flexible connecting pipe to be measured and a required effective test frequency range (f min ,f max ), determining upper and lower mass limits of the retarding mass block, and selecting the retarding mass block assembly and a retarding mass block unit. The blocking mass block assembly mainly comprises a blocking mass block unit and a connecting fastener, wherein the blocking mass block assembly is connected with the transition element, the flexible connecting pipe to be tested and the excitation element by the connecting fastener respectively, and the axial measurement and the transverse measurement of the dynamic stiffness measured by an indirect method are completed. The combination of different blocking mass block unit components can meet the measurement requirement of the transmission dynamic stiffness of the multi-type flexible connecting pipe on the premise of not changing the overall structure of the measuring rack.

Inventors

  • GONG JINGFENG
  • YANG YANGYANG
  • XUAN LINGKUAN
  • LIU ZHEN

Assignees

  • 武汉科技大学
  • 武汉致工科技有限公司

Dates

Publication Date
20260512
Application Date
20220630

Claims (8)

  1. 1. A design method for measuring dynamic stiffness blocking mass block components by an indirect method comprises the steps of designing upper and lower mass limits of the blocking mass block components according to basic parameters of flexible connecting pipes to be measured and a required effective test frequency range (f min ,f max ), and is characterized in that a lowest resonance frequency method is adopted to determine first-order inherent frequency f 0 of the blocking mass block components according to the lowest resonance frequency f e of the flexible connecting pipes to be measured, then a limiting condition selection method is combined to determine lower-order mass of the axial and transverse measuring blocking mass block components, inherent frequency of the blocking mass block components in a free state is calculated by means of numerical simulation software to obtain first-order elastic modal frequency f t of the blocking mass block components, a relation diagram between upper-limit frequency of the blocking mass block components to be tested and upper-limit mass and size of the blocking mass block components is calculated by means of numerical simulation software, and the upper-limit mass and size of the blocking mass block components are determined, and the lower mass limit of the axial measuring blocking mass block components is determined by means of the lowest resonance frequency selection method, and the method comprises the following steps: ① Firstly, estimating the lowest resonance frequency of the flexible connecting pipe to be measured according to a formula (5), (5) Wherein: The axial low-frequency dynamic stiffness of the flexible connecting pipe to be tested is obtained; the mass of the elastic component is a flexible connecting pipe; ② Determination of The natural frequency of the mass/spring system of the flexible connection pipe to be tested, consisting of m 2z and auxiliary vibration isolation springs, can be used for simplifying the whole system into a two-degree-of-freedom system when the mass of the flexible connection pipe to be tested is considered to be non-negligible, and is required The first order axial natural frequency of the system can be considered, using equation (6): Calculation, in order to ensure the validity of the test, requires ; When the quality of the flexible connecting pipe to be measured is considered to be negligible, the whole system is simplified into a single-degree-of-freedom system, which is required Can be regarded as the first-order axial natural frequency of the system, using equation (7) Calculating; ③ Taking out Estimating the mass of m 2z : Equation (8) is used when two degrees of freedom are considered The calculation is performed such that, Wherein: to decouple spring rate; And (3) with The masses of the excitation element and the axial retarding mass respectively; equation (9) is used when considering single degree of freedom Calculating; the determination of the lower limit of the mass of the transverse measurement retarding mass block assembly adopts a lowest resonance frequency selection method, and comprises the following steps: ① According to mechanical vibration, determining the natural frequency of bending vibration of the two-end support flexible connecting pipe as formula (12) In the following For the length of the flexible connection pipe, In order to be the modulus of elasticity of the material, In order to resist the moment of inertia of the curved section, The mass of the elastic part of the flexible connecting pipe; The low-frequency bending rigidity of the flexible connecting pipe is represented by formula (13) Calculating, in For the flexural rigidity of the flexible connecting pipe at low frequency, the flexural rigidity can be approximately regarded as the static rigidity of the flexible connecting pipe at low frequency, and the unknown quantity in the formula (12) is calculated by the formula (13) And Replaced by a known quantity The natural frequency of the flexible pipe can thus be calculated, equation (14) ; ② Determination of The natural frequency of the mass/spring system of the flexible connection pipe to be tested, consisting of m 2h and auxiliary vibration isolation springs, i.e. equation (18) In the following In order to axially decouple the mass of the spring, For the mass of the vertical decoupling spring, m 2h is the transverse retarding mass, The bending stiffness of the axial decoupling spring and the axial stiffness of the vertical decoupling spring are respectively; ③ Estimation of the retarding mass m 2h The minimum mass of the transverse retarding mass is obtained from formulas (14) and (18), equation (19) 。
  2. 2. The method for designing an indirect measuring dynamic stiffness retarding mass assembly according to claim 1, wherein the determination of the lower mass limit of the axial and lateral measuring retarding mass assembly is performed by a constraint condition selection method, comprising the steps of: when the indirect method is adopted, the difference between the input end and the output end obtained by experimental measurement must satisfy the inequality DB constraint, then available (10) According to the following (4) And (10), the formula (11) can be deduced , In the formulas (4), (10) and (11) And (3) with The masses of the mass blocks are blocked axially and transversely respectively, For the transmission dynamic stiffness of the measured element, m 2 is the mass of the output end blocking mass, m f is the mass of the transition element and the flange mass of the output end of the measured elastic damping element, x 1 is the displacement of the input end of the measured elastic damping element, x 2 is the displacement of the output end of the measured elastic damping element, and f min is the lower limit frequency of measurement.
  3. 3. The method for designing an indirect measuring dynamic stiffness retarding mass assembly according to claim 1, wherein the determination of the lower limit of the mass of the axial measuring retarding mass assembly is determined by a minimum resonance frequency selection method and a limiting condition selection method, i.e., the lower limit of the mass of the axial measuring retarding mass assembly is determined by And (5) determining.
  4. 4. The method for designing an indirect measuring dynamic stiffness retarding mass assembly according to claim 1, wherein the determination of the lower mass limit of the transverse measuring retarding mass assembly is determined by a minimum resonance frequency selection method and a limiting condition selection method And (5) determining.
  5. 5. The method for designing an indirect measuring dynamic stiffness retarding mass assembly according to claim 1, wherein the determination of the lower mass limit of the transverse measuring retarding mass assembly is determined by a natural frequency formula (18), and the theoretical calculation result of the formula (18) is verified by the calculation result of numerical simulation software.
  6. 6. The method for designing an indirect measuring dynamic stiffness retarding mass assembly of claim 1, wherein the method comprises the steps of Determining an upper mass limit of the retarding mass, comprising the steps of: ① After a standard steel cube or steel cylinder blocking mass block is established by utilizing three-dimensional modeling software, the natural frequency of the standard steel cube or steel cylinder blocking mass block in a free state is calculated by utilizing numerical simulation software, and the first-order elastic modal frequency of the standard steel cube or steel cylinder blocking mass block is obtained Further obtaining the upper limit frequency of the retarding mass block I.e. ; ② And calculating by means of numerical simulation software to obtain a relation diagram of the upper limit frequency of the selected steel cube or equal-height cylinder block mass test and the upper limit of the block mass.
  7. 7. The method for designing the block mass component for measuring the dynamic stiffness through the indirect method according to claim 1, wherein the block mass component for measuring the dynamic stiffness through the flexible connecting pipe through the method for determining the lower limit of the axial blocking mass is m 2z.1 ～m 2z.2 in mass range, the block mass component for measuring the dynamic stiffness through the flexible connecting pipe through the method for determining the lower limit of the lateral blocking mass is m 2h.1 ～m 2h.2 in mass range, the block elements are combined in mass m ZH ≥max（m 2z.2 ,m 2h.2 , the block elements are split in mass m CF ≈min（m 2z.1 ,m 2h.1 , and the block mass can be split into n parts in theory, wherein n is more than or equal to 2.
  8. 8. The method for designing the blocking mass block assembly for measuring the dynamic stiffness by the indirect method according to claim 1, wherein the blocking mass block assembly is applied to the field of measuring the dynamic stiffness by the indirect method, the blocking mass block assembly is connected with the transition element, the flexible connecting tube to be measured and the excitation element by connecting fasteners respectively for axial measurement and transverse measurement of the dynamic stiffness, the blocking mass block assembly comprises a plurality of blocking mass block units and connecting fasteners, and the blocking mass block units are connected by the connecting fasteners.

Description

Design and use method of indirect method-based dynamic stiffness measurement retarding mass block assembly Technical Field The invention relates to a method for measuring dynamic stiffness by an indirect method, in particular to a design and use of a blocking mass block in the dynamic stiffness measuring method. Background In order to isolate and attenuate structural vibration noise transmitted along channels such as equipment legs, pipelines, supporting structures and the like, vibration reduction components such as flexible connecting pipes, vibration isolators and the like are widely applied in the fields of ships, automobiles, aviation and the like. Dynamic stiffness is an important index for evaluating vibration isolation performance of vibration reduction components and reflects dynamic characteristics of the vibration reduction components. Dynamic stiffness refers to dynamic exciting force required to be applied by a vibration reduction component to generate unit displacement under the action of dynamic load. Dynamic stiffness of the vibration damping component plays a decisive role in the performance of the vibration isolation system in engineering, and the ideal vibration isolation effect cannot be achieved due to the fact that the dynamic stiffness is too large, and fatigue damage and instability can be caused due to overlarge structural deformation although the vibration isolation performance can be improved due to the fact that the dynamic stiffness is too small. The method for measuring the dynamic stiffness of the elastic vibration reduction element mainly comprises a direct method and an indirect method. The direct method is a method for measuring the transmission rate of vibration (displacement, speed or acceleration) when the output end of the elastic vibration damping element is provided with a rigid mass block with large mass. The direct method can accurately measure the low-frequency dynamic stiffness below 10Hz, but the upper limit frequency of the test is about 300Hz due to the influence of the fundamental frequency of the basic test frame mode, the test frequency range is low, and the dynamic characteristics of the elastic vibration reduction component in the middle-high frequency range can not be reflected. The indirect method indirectly obtains the retarding force of the output end by measuring the displacement (speed or acceleration) of the rigid body of the output end of the elastic element, and the upper limit frequency of the test can reach 5kHz. When the dynamic stiffness test is carried out on the elastic damping element, the longitudinal excitation does not cause the problem of torsion of the elastic damping element, and the transverse excitation always couples the transverse translation and the torsion. The experimental bench for measuring the axial dynamic stiffness of the flexible connecting pipe is different from the experimental bench for measuring the transverse stiffness in arrangement. . The transverse dynamic stiffness test can enhance unidirectional vibration of the input end through the symmetrical arrangement structure, so that the influence of torsional vibration of the input end on the test precision can be reduced, and the test result is more accurate. The indirect method is used for measuring the dynamic stiffness axially and referring to fig. 4, and the indirect method is used for measuring the dynamic stiffness transversely and referring to fig. 5. The indirect method for measuring the transmission dynamic stiffness of the elastic vibration reduction element theoretically considers that the output force of the receiving end of the test bed is approximately equal to the retarding force of the output end of the elastic element, namely: F2≈F2,b＝k2,1u1 (1) Wherein k 2.1 is the transmission dynamic stiffness of the tested element, F 2 is the excitation force of the output end of the tested elastic damping element, F 2.b is the blocking force of the output end of the tested elastic damping element, and x 1 is the displacement of the input end of the tested elastic damping element. From newton's second law: F2,b＝(m2+mf)ü2 (2) Then: Wherein m 2 is the mass of the output end blocking mass block, m f is the mass of the transition element and the flange mass of the output end of the elastic vibration reduction element to be measured, x 2 is the displacement of the output end of the elastic vibration reduction element to be measured, and x 2/x1 is defined as the vibration (displacement) transmissibility and is also equal to the corresponding speed ratio and acceleration ratio. Therefore, the transmission dynamic stiffness of the element to be measured can be obtained by measuring the vibration transmission rate of the input end and the output end, combining the frequency and the selection of the retarding mass block and then utilizing the formula (4). 1. Frequency application range The test device can only obtain valid measurement data over a range of frequencies, one o