A method for designing strength of a helicopter equipment mounting bracket considering vibration environment

Abstract

The application discloses a kind of helicopter equipment mounting bracket strength design method considering vibration environment, according to the equipment installation area on helicopter, determine the main excitation frequency and the maximum amplitude of vibration that equipment support is expected to withstand;Vibration load under the corresponding maximum amplitude is loaded to the center of gravity of equipment, the maximum static stress of equipment mounting bracket is calculated using finite element method, and then the equivalent dynamic stress of equipment mounting bracket under the vibration environment of helicopter is obtained;Obtain the total cycle number of fatigue by comparing the S-N curve of material, and the simplified high-cycle fatigue life of equipment mounting bracket is obtained according to frequency calculation.The application can make equipment mounting bracket better adapt to the vibration environment of helicopter, and avoid structural cracks.

Description

Technical Field

[0001] This invention relates to the field of helicopter structural strength design, and specifically to a method for designing the strength of helicopter equipment mounting brackets that takes into account vibration environments. Background Technology

[0002] Traditional strength design methods for helicopter equipment mounting brackets consider low-cycle fatigue and static strength, and strictly control the strength margin during the lightweight design process. However, this often leads to fatigue cracks in the equipment brackets under the harsh vibration environment of helicopters, which seriously affects the reliability of the equipment and the integrity of the helicopter equipment. Summary of the Invention

[0003] The purpose of this invention is to provide a strength design method for helicopter equipment mounting brackets that takes into account the vibration environment. This invention enables the equipment mounting brackets to better adapt to the vibration environment of helicopters and avoid structural cracks.

[0004] The technical solution of this invention is as follows: A strength design method for helicopter equipment mounting bracket considering vibration environment. Based on the installation area of ​​the equipment on the helicopter, the main excitation frequency and maximum amplitude of vibration expected to be experienced by the equipment bracket are determined; the vibration load at the corresponding maximum amplitude is applied to the center of gravity of the equipment, and the maximum static stress of the equipment mounting bracket is calculated using the finite element method, thereby obtaining the equivalent dynamic stress of the equipment bracket in the helicopter vibration environment; the total number of fatigue cycles is obtained by referring to the SN curve of the material, and the simplified high-cycle fatigue life of the equipment mounting bracket is calculated according to the frequency.

[0005] In the aforementioned method for designing the strength of helicopter equipment mounting brackets that takes into account vibration environments, the high-cycle fatigue life is compared with a preset life index; if the life index is met, the structural strength design of the bracket is completed.

[0006] In the aforementioned strength design method for helicopter equipment mounting brackets that consider vibration environment, if the life index is not met, the bracket structure is optimized, and the simplified high-cycle fatigue life of the optimized equipment mounting bracket is compared with the preset life index until the design requirements are met.

[0007] In the aforementioned method for designing the strength of helicopter equipment mounting brackets considering vibration environment, the determination methods for the main excitation frequency and vibration magnitude are as follows: The main vibration excitation source of the helicopter is the rotating components of the main rotor and tail rotor. Based on the main excitation source of the helicopter, the equipment installation area is divided into the main rotor influence area and the tail rotor influence area. Based on the area where the equipment is installed, the main excitation frequency f that is affected is determined. Based on empirical values ​​or flight measurement data, the maximum amplitude of vibration in this area is determined.

[0008] In the aforementioned strength design method for helicopter equipment mounting brackets considering vibration environment, the calculation method for equivalent dynamic stress is as follows:

[0009] Establish a finite element model of the equipment installation, apply a vibration load corresponding to the maximum amplitude of the vibration at the center of gravity of the equipment, and calculate the maximum static stress σ under this vibration load. s Then, use the following formula to calculate the equivalent dynamic stress σ. eq :

[0010]

[0011] Where, σ 0，2 This represents the conditional yield strength of the material.

[0012] In the aforementioned strength design method for helicopter equipment mounting brackets considering vibration environment, the calculation method for high-cycle fatigue life is as follows:

[0013] Using equivalent dynamic stress and based on the material's SN curve, determine the total number of fatigue cycles c under the equivalent stress. total ;

[0014] Based on the primary excitation frequency f of the area where the equipment is located, the number of cycles per hour c0 under this frequency is calculated using the following formula:

[0015] c0 = f × 3600

[0016] The high-cycle fatigue life of the mounting bracket for this equipment is calculated using the following formula:

[0017]

[0018] Where ε is the proportion of the entire flight spectrum in the state corresponding to the largest amplitude value.

[0019] In the aforementioned method for designing the strength of helicopter equipment mounting brackets that takes into account vibration environment, ε is estimated based on the flight spectrum.

[0020] In the aforementioned method for designing the strength of helicopter equipment mounting brackets that takes into account vibration environment, the main excitation frequency f = 21.5 Hz.

[0021] The beneficial effects of this invention are as follows: Based on conventional strength design, this invention additionally considers the vibration environment of helicopters, forming a simplified high-cycle fatigue design method for equipment mounting brackets. This allows the equipment mounting brackets to better adapt to the helicopter's vibration environment, significantly reducing the risk of cracks appearing within the helicopter's lifespan and improving reliability. Related application examples show that, after strength design according to this invention, the mounting brackets can achieve safe and reliable service throughout the helicopter's lifespan (9000 Fh), proving that this invention provides an effective means for equipment mounting brackets and has high versatility. Attached Figure Description

[0022] Figure 1 This is a flowchart of the present invention;

[0023] Figure 2 The maximum stress is the mounting bracket designed according to the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1. Taking a certain model as an example, see... Figure 1 The steps are as follows:

[0026] S1: Determine the bracket installation area

[0027] The equipment is mounted on the flange of the equipment bracket at the nose of the forward fuselage and is connected by bolts, located in the influence zone of the main rotor.

[0028] S2: Vibration frequency and amplitude

[0029] According to the vibration level statistics of the test flight, the maximum vertical vibration of 1.0g at the center of gravity of the equipment is at the frequency of 5Q of the main rotor.

[0030] S3: Maximum static stress

[0031] Using the finite element method and considering the vibration environment, calculate the maximum static stress of the equipment mounting bracket and the stress distribution of the equipment mounting bracket. Figure 2 As shown, the maximum static stress of the mounting bracket is 104 MPa.

[0032] S4: Calculate equivalent dynamic stress

[0033] Calculate equivalent dynamic stress

[0034] When the equivalent stress σ eq =59.3MPa

[0035] S5: Check the materials manual to get the total number of cycles.

[0036] The total number of fatigue cycles c under this equivalent stress was found. total =1.0E+30

[0037] S6: Main excitation frequency and cycle number

[0038] Based on the primary excitation frequency f = 21.5Hz in the area where the equipment is located, the number of cycles per hour c0 under this frequency is calculated using the following formula:

[0039] c0 = 21.5 × 3600 = 77400

[0040] S7: High-cycle fatigue life

[0041] Based on the flight spectrum, it is estimated that the state corresponding to the maximum amplitude accounts for ε = 20% of the total flight spectrum time. Considering the vibration environment, the mounting bracket designed according to this invention...

[0042] The high-cycle fatigue life of the mounting bracket for this equipment is calculated using the following formula:

[0043]

[0044] The high-cycle fatigue life is greater than 9000 Fh, which meets the usage requirements.

[0045] Example 2. A strength design method for helicopter equipment mounting brackets considering vibration environment, see [link to example]. Figure 1 Based on the installation area of ​​the equipment on the helicopter, the expected main excitation frequency and vibration magnitude of the equipment support are determined. A vibration load of the corresponding magnitude is applied to the center of gravity of the equipment. Using the finite element method, the maximum static stress of the equipment mounting support is calculated, yielding the equivalent dynamic stress of the support under helicopter vibration conditions. The number of fatigue cycles is obtained by referring to the SN curve of the material, and the simplified high-cycle fatigue life of the support is calculated according to the frequency.

[0046] Design steps:

[0047] The main vibration excitation sources of a helicopter are rotating components such as the main rotor and tail rotor. Based on these main excitation sources, the equipment installation area is divided into the main rotor influence zone and the tail rotor influence zone. The dominant excitation frequency in the main rotor influence zone is NQ, and the dominant excitation frequency in the tail rotor influence zone is NQ. t Where n is the number of blades, Q, Q' t To correspond to the blade rotation frequency, the main excitation frequency affected by the equipment is determined based on the area where the equipment is installed; the maximum amplitude of vibration in that area is determined based on empirical values ​​or flight measurement data.

[0048] Based on the flight spectrum, estimate the proportion ε of the entire flight spectrum corresponding to the state with the maximum amplitude. Establish a finite element model of the equipment installation, apply the vibration load corresponding to the maximum amplitude at the equipment's center of gravity, and calculate the maximum static stress σ under this vibration load. s The equivalent dynamic stress σ is calculated using the following formula. eq :

[0049]

[0050] Where, σ 0，2 This represents the conditional yield strength of the material.

[0051] Using the equivalent dynamic stress obtained in the previous step, and based on the material's SN curve, determine the total number of fatigue cycles c under this equivalent stress. total .

[0052] Based on the primary excitation frequency f of the area where the equipment is located, the number of cycles per hour c0 under this frequency is calculated using the following formula:

[0053] c0 = f × 3600

[0054] The high-cycle fatigue life of the mounting bracket for this equipment is calculated using the following formula:

[0055]

[0056] The simplified high-cycle fatigue life of the equipment mounting bracket is calculated using the above steps and compared with the required life index. If the life index is not met, the bracket structure is optimized, and the above steps are repeated.

[0057] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for designing the strength of a helicopter equipment mounting bracket considering vibration environment, characterized in that, Based on the installation area of ​​the equipment on the helicopter, the main excitation frequency and the maximum amplitude of vibration expected to be experienced by the equipment support are determined; the vibration load at the corresponding maximum amplitude is applied to the center of gravity of the equipment, and the maximum static stress of the equipment mounting support is calculated using the finite element method, thereby obtaining the equivalent dynamic stress of the equipment support in the helicopter vibration environment; the total number of fatigue cycles is obtained by referring to the SN curve of the material, and the simplified high-cycle fatigue life of the equipment mounting support is calculated according to the frequency. The equivalent dynamic stress is calculated as follows: Establish a finite element model of the equipment installation, apply a vibration load corresponding to the maximum amplitude of the vibration at the center of gravity of the equipment, and calculate the maximum static stress σ under this vibration load. s Then, use the following formula to calculate the equivalent dynamic stress σ. eq : ， Where, σ 0.2 The conditional yield strength of the material; The high-cycle fatigue life is calculated as follows: Using equivalent dynamic stress and based on the material's SN curve, determine the total number of fatigue cycles c under the equivalent stress. total ; Based on the primary excitation frequency f of the area where the equipment is located, the number of cycles per hour c0 under this frequency is calculated using the following formula: c0 = f × 3600, The high-cycle fatigue life of the mounting bracket for this equipment is calculated using the following formula: ， Where ε is the proportion of the entire flight spectrum in the state corresponding to the largest amplitude value.

2. The strength design method for helicopter equipment mounting bracket considering vibration environment according to claim 1, characterized in that, The high-cycle fatigue life is compared with the preset life index; if the life index is met, the strength design of the support structure is completed.

3. The strength design method for helicopter equipment mounting bracket considering vibration environment according to claim 2, characterized in that, If the lifespan index is not met, the support structure will be optimized, and the simplified high-cycle fatigue life of the optimized equipment mounting support will be compared with the preset lifespan index until the design requirements are met.

4. The strength design method for helicopter equipment mounting bracket considering vibration environment according to any one of claims 1-3, characterized in that, The methods for determining the main excitation frequency and vibration magnitude are as follows: The main vibration excitation source of the helicopter is the rotating components of the main rotor and tail rotor. Based on the main excitation source of the helicopter, the equipment installation area is divided into the main rotor influence area and the tail rotor influence area. Based on the area where the equipment is installed, the main excitation frequency f that is affected is determined. Based on empirical values ​​or flight measurement data, the maximum amplitude of vibration in this area is determined.

5. The strength design method for helicopter equipment mounting bracket considering vibration environment according to claim 1, characterized in that, The ε mentioned is estimated based on the flight spectrum.

6. The strength design method for helicopter equipment mounting bracket considering vibration environment according to claim 1, characterized in that, The main excitation frequency is f = 21.5 Hz.

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