A method for indirect measurement of low-frequency longitudinal bearing forces of a ship propeller

Abstract

The embodiment of the present application provides a kind of indirect measurement method of ship propeller low-frequency longitudinal bearing force, including air propeller-shaft longitudinal vibration transfer function prediction model construction, in-dock propeller shaft system vibration measurement and transfer function prediction model correction, real ship vibration measurement and transfer function model correction, propeller low-frequency longitudinal bearing force identification method.The longitudinal vibration transfer prediction model of propeller shaft system is improved by simulation and test correction, combined with the vibration response measurement result of the inboard shaft section of real ship, the low-frequency longitudinal bearing force of real ship propeller is obtained based on excitation force identification technology, engineering is strong in implementability, measurement is simple, and certain prediction accuracy can be maintained.

Description

Technical Field

[0001] This invention belongs to the field of ship vibration reduction and noise reduction technology, and relates to an indirect method for measuring the low-frequency longitudinal bearing force of a ship propeller. Background Technology

[0002] Structural vibration and underwater radiated noise control of naval vessels and research vessels are among the key issues that need to be addressed in the overall design. When a propeller operates in a non-uniform flow at the stern of a ship, it generates pulsating pressure and bearing forces, which in turn excite structural vibration and radiated noise. Understanding the characteristics of propeller pulsating pressure and bearing forces is crucial for the acoustic optimization and improvement design of similar vessels. During actual ship navigation, propeller pulsating pressure can be directly measured using pressure sensors placed above the propeller, but propeller bearing forces are difficult to measure directly. Bearing forces consist of three force components (longitudinal, transverse, and vertical) and three torque components, with the longitudinal force component being the most important. Its energy is mainly concentrated in the low-frequency range below 100Hz, which can excite longitudinal vibration modes in the propulsion shaft system, causing strong structural vibration and radiated noise. Currently, computational fluid dynamics (CFD) simulation technology or scaled-down model testing technology is commonly used to predict propeller bearing forces, but their accuracy and effectiveness need to be verified. Therefore, the measurement of low-frequency axial bearing forces of propellers on actual ships is very important.

[0003] Based on the formation mechanism of propeller bearing force, this excitation force originates in the propeller blades. Since the propeller blades operate in seawater, it is difficult to directly place sensors on the blades for measurement; moreover, measuring dynamic force inherently presents technical challenges compared to measuring strain, displacement, velocity, and acceleration. However, based on vibration response measurement and force and vibration transfer function measurement, excitation force identification technology can be used to indirectly measure dynamic force. Therefore, a study on the characteristics of excitation force in actual ship propellers and the feasibility of testing is needed to propose an indirect measurement method for low-frequency dynamic bearing force of propellers. Summary of the Invention

[0004] The purpose of this invention is to provide an indirect method for measuring low-frequency longitudinal bearing force of a ship propeller, characterized by comprising the following steps:

[0005] Step 1: Establish a prediction model for the longitudinal excitation force of the propeller in the air and the transfer function of the shaft segment response:

[0006] Step 2: Verify and correct the transfer function prediction model through in-dock vibration measurements;

[0007] Step 3: Verify and revise the transfer function prediction model based on the actual ship vibration measurement results;

[0008] Step 4: Predict the low-frequency longitudinal bearing force of the propeller.

[0009] Preferably, step 1 includes:

[0010] Based on the design drawings of the ship's propulsion shafting system, a prediction model M1 for the longitudinal vibration transfer function of the propeller-shafting system is established.

[0011] The propeller model should take into account the low-order bending vibration characteristics of the blades and the propeller mass; the shaft section adopts a beam model, and the thrust bearing adopts an equivalent stiffness model; the transfer function H1(ω) is calculated using the propeller-shaft longitudinal vibration transfer function prediction model M1.

[0012] Preferably, step 2 includes:

[0013] In accordance with the excitation force and vibration response point location in step 1, the transfer function and low-order vibration modes of the propeller longitudinal excitation force-shaft section response of typical parts are measured in the dock state;

[0014] The transfer function H1(ω) was verified and corrected by measuring the longitudinal excitation force of the propeller and the response of typical parts of the shaft section under dock conditions.

[0015] Preferably, step 2 includes: correcting the thrust bearing equivalent stiffness parameter, system damping parameter, and propeller effect model parameter in the calculation model to obtain the corrected transfer function prediction model M2 and transfer function H2(ω).

[0016] Preferably, step 3 includes: maintaining the same vibration response position as in step 1, determining the first two longitudinal vibration modes of the propeller shaft system by measuring the vibration response at different rotational speeds;

[0017] By comparing the first two longitudinal vibration modes obtained from the model calculation in step 2, two key parameters, the blade water attachment coefficient and the thrust bearing stiffness coefficient, are obtained.

[0018] Substituting the two key correction parameters into the transfer function prediction model M2, we obtain the propeller longitudinal excitation force-shaft segment response transfer function H(ω) under actual ship operating conditions.

[0019] Preferably, step 4 includes: calculating the low-frequency longitudinal bearing force F(ω) of the propeller using excitation force identification technology based on the longitudinal vibration response A(ω) of the shaft section measured under actual ship operating conditions and the corrected transfer function H(ω).

[0020] Preferably, the specific method for obtaining the low-frequency longitudinal bearing force F(ω) of the propeller in step 4 includes:

[0021] F(ω)=[H T (ω)H(ω)+λ 2 ] -1 H T (ω)A(ω)

[0022] In the formula, λ is the regularization coefficient.

[0023] The method used in this invention has the following advantages and benefits: the measurement is relatively simple and the engineering implementation is highly operable; the low-frequency longitudinal bearing force of the propeller is indirectly predicted by using the modified transfer function and the actual ship vibration response measurement results, and the results are relatively accurate and can be used for acoustic optimization design of similar ships. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the indirect measurement process of low-frequency longitudinal bearing force of a ship propeller according to an embodiment of the present invention.

[0025] Figure 2 This is a finite element model for calculating the longitudinal vibration of the propeller-shaft system according to an embodiment of the present invention. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The indirect measurement method for low-frequency longitudinal bearing force of a ship propeller according to the present invention includes the following steps in its specific implementation.

[0027] Step 1: Establish a prediction model of the longitudinal excitation force-shaft segment response transfer function of the propeller in the air.

[0028] Based on the design drawings of the propulsion shaft system and propeller, a low-frequency longitudinal vibration model of the propeller-shaft system was established, see... Figure 2 The propeller blades are simplified into an equivalent variable cross-section beam model to ensure that the low-order bending vibration modes below 100Hz are basically consistent with the actual propeller blade modes; the hub is simplified into a lumped mass model; the shaft section is simplified into a beam model; and the thrust bearing is simplified into an equivalent spring model. The system damping characteristics are considered using complex stiffness or complex elastic modulus. This model is used to calculate the longitudinal vibration modes of the propeller-shaft system, determining the natural frequencies, mode shapes, and node locations below 100Hz.

[0029] A unit force is applied at 0.7 times the radius of the blade. The vibration response monitoring point is a non-mode node on the inner shaft section that is convenient for arranging vibration acceleration sensors. The longitudinal excitation force and the vibration transfer function H1(ω) at the monitoring point on the shaft section are calculated.

[0030] Step 2: Verify and correct the transfer function model through in-dock vibration measurement.

[0031] After the ship is built and the propulsion shaft system is installed, it is in dry dock. Excitation force is applied at 0.7 times the radius of the blade using a vibrator. Vibration response monitoring points at typical locations of the blade and shaft section (including at least the monitoring points in the calculation model in step one) are measured. The blade bending vibration mode, the longitudinal vibration mode of the propeller shaft system, and the vibration transfer function are obtained through test data analysis.

[0032] Using the equivalent stiffness of the thrust bearing, system damping, and propeller equivalent model parameters as correction values, the calculation model in step one is corrected using test data to obtain the corrected vibration transfer function model and transfer function H2(ω).

[0033] Step 3: Further verify and revise the transfer function model based on the actual ship vibration measurement results.

[0034] During ship navigation, the propulsion shaft system's rotational speed is adjusted at certain intervals, and the longitudinal vibration response of the inboard shaft section (the measuring point is the same as the monitoring point in step one) is measured. A vibration response waterfall diagram is plotted, and the first two natural frequencies of the shaft system's longitudinal vibration, ωn1 and ωn2, are analyzed and determined. Based on the vibration transfer function model obtained in step two, a series of blade attachment water coefficients and thrust bearing equivalent stiffness coefficients are assumed, and the first two natural frequencies of the propeller shaft system's longitudinal vibration are calculated. A graph showing the relationship between the correction coefficients and the natural frequencies is plotted. Based on the natural frequency test results ωn1 and ωn2, the blade attachment water coefficient and thrust bearing equivalent stiffness coefficient are determined, and the transfer function prediction model in step two is corrected to obtain the longitudinal excitation force and shaft section vibration response transfer function H(ω) of the actual ship.

[0035] Step 4: Predict the low-frequency longitudinal bearing force of the propeller based on excitation force identification technology.

[0036] Based on the longitudinal vibration response A(ω) of the shaft section measured under actual ship operating conditions and the corrected transfer function H(ω), the low-frequency longitudinal bearing force F(ω) of the propeller is calculated using excitation force identification technology. To reduce the influence of noise in the test data, a regularization method can be used, and its calculation formula can be expressed as:

[0037] F(ω)=[H T (ω)H(ω)+λ 2 ] -1 H T (ω)A(ω) (1)

[0038] In the formula, λ is the regularization coefficient.

[0039] The method used in this invention has the following advantages and benefits: the measurement is relatively simple and the engineering implementation is highly operable; the low-frequency longitudinal bearing force of the propeller is indirectly predicted by using the modified transfer function and the actual ship vibration response measurement results, and the results are relatively accurate and can be used for acoustic optimization design of similar ships.

[0040] Obviously, those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for indirect measurement of low-frequency longitudinal bearing force in a ship propeller, characterized in that, Including steps: Step 1: Establish a prediction model for the longitudinal excitation force of the propeller in the air and the transfer function of the shaft segment response: Step 2: Verify and correct the transfer function prediction model through in-dock vibration measurements; Step 3: Verify and revise the transfer function prediction model based on the actual ship vibration measurement results; Step 4: Predict the low-frequency longitudinal bearing force of the propeller; Step 1 includes: Based on the design drawings of the ship's propulsion shafting system, a prediction model M1 for the longitudinal vibration transfer function of the propeller-shafting system is established. The propeller model should take into account the low-order bending vibration characteristics of the blades and the propeller mass; the shaft section adopts a beam model, and the thrust bearing adopts an equivalent stiffness model; the transfer function H1(ω) is calculated using the propeller-shaft longitudinal vibration transfer function prediction model M1. Step 2 includes: In accordance with the excitation force and vibration response point location in step 1, the transfer function and low-order vibration modes of the propeller longitudinal excitation force-shaft section response at typical locations are measured under dock conditions. The transfer function H1(ω) was verified and corrected using the transfer function of the longitudinal excitation force of the propeller and the response of typical parts of the shaft section, as well as the low-order vibration modes, measured in the dock. By correcting the thrust bearing equivalent stiffness parameters, system damping parameters, and propeller model parameters in the propeller-shaft longitudinal vibration transfer function prediction model M1, the corrected transfer function prediction model M2 and the transfer function H2(ω) are obtained. Step 3 includes: maintaining the same vibration response position as in step 1, determining the first two longitudinal vibration modes of the propeller shaft system by measuring the vibration response at different rotational speeds; By comparing the first two longitudinal vibration modes calculated with the transfer function prediction model M2 in step 2, two key parameters, the blade water attachment coefficient and the thrust bearing stiffness coefficient, are obtained. Substituting the two key parameters into the transfer function prediction model M2, we obtain the propeller longitudinal excitation force-shaft segment response transfer function H(ω) under actual ship operating conditions. Step 4 includes: calculating the low-frequency longitudinal bearing force F(ω) of the propeller using excitation force identification technology based on the longitudinal vibration response A(ω) of the shaft section measured under actual ship operating conditions and the corrected transfer function H(ω).

2. The indirect measurement method for low-frequency longitudinal bearing force of a ship propeller as described in claim 1, characterized in that, The specific method for obtaining the low-frequency longitudinal bearing force F(ω) of the propeller in step 4 includes: In the formula, λ is the regularization coefficient.

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