Butt-joint structure for internally-connected pressure ball frame and machine body and design method of butt-joint structure

Abstract

The invention discloses a butt joint structure internally connected with a rear pressure ball frame and a fuselage and a design method of the butt joint structure, and belongs to the technical field of civil airliner fuselage structural design. The butt joint structure comprises an annular frame, annular supporting corner boxes, longitudinal supporting pieces, connecting joints and connecting corner pieces, and the annular frame is connected with the rear pressure ball frame and fuselage skin; the longitudinal supporting pieces are distributed at intervals in the circumferential direction in a pressurizing area of the front portion of the annular frame, the annular supporting corner boxes are arranged between the adjacent longitudinal supporting pieces and connected to the annular frame and the rear pressure ball frame, the longitudinal supporting pieces, the fuselage skin and the annular frame are fixed through the connecting joints, and the longitudinal supporting pieces, the annular frame, the annular supporting corner boxes and the rear pressure ball frame are fixed through the connecting corner pieces. By designing the configuration of the butt joint structure and designing the positions and the number of the longitudinal supporting pieces, the optimal butt joint structure is finally obtained. Rigidity matching of the annular frame and the fuselage structure is achieved, and the reverse transmission effect of bending loads is effectively restrained.

Description

Technical Field

[0001] The invention belongs to the technical field of civil passenger aircraft fuselage structure design, and relates to a docking structure of an inscribed rear pressure ball frame and a fuselage and a design method thereof. Background Art

[0002] In aircraft structures, the rear pressure ball frame is a key component that bears the airtight load of the fuselage and needs to efficiently transfer the load to the fuselage skin. The traditional internal connection solution has the following problems with the docking structure:

[0003] 1) The docking structure configuration easily causes the fuselage bending load to be transmitted back to the rear pressure ball frame through the ring frame, making the design of the rear pressure ball frame complicated.

[0004] 2) The rear pressure ball frame is first connected to a single flange of the Y-shaped connector, and the load is then transferred to the fuselage skin from the other two flanges. The load transfer is not direct, the Y-shaped structure has high manufacturing costs and the R zone is prone to fatigue.

[0005] 3) The longitudinal web has little design connection with the rear pressure ball frame and the fuselage curved surface, resulting in excessive local stress and affecting the structural life. Summary of the Invention

[0006] The present invention aims to improve the deficiencies of the prior art in the rigidity matching and load transfer of the docking structure, and provides a docking structure design scheme based on rigidity matching optimization and more direct load transfer.

[0007] The present invention adopts the following technical solutions:

[0008] A docking structure for an internally connected rear pressure ball frame and a fuselage comprises an annular frame 2, annular support angle boxes 3, longitudinal supports 4, connecting joints 5 and connecting angle pieces 6. The annular frame 2 is connected between the rear pressure ball frame 1 and the fuselage skin 8, and is used to transfer the normal and annular loads of the rear pressure ball frame 1 to the fuselage skin; a plurality of longitudinal supports 4 are circumferentially spaced in the pressurized area in front of the annular frame 2, and are used to transfer the radial load of the rear pressure ball frame 1 to the fuselage skin 8; the annular support angle boxes 3 are connected between adjacent longitudinal supports 4 and are connected to the annular frame 2 and the rear pressure ball frame 1, and are used to transfer loads to the annular frame 2 and the longitudinal supports 4; the connecting joints 5 achieve a fixed connection between the annular frame 2, the longitudinal supports 4 and the fuselage skin 8, and are used to enhance load transfer efficiency; the connecting angle pieces 6 achieve a fixed connection between the annular frame 2, the annular support angle boxes 3, the longitudinal supports 4 and the rear pressure ball frame 1, and are used to transfer loads to the longitudinal supports 4.

[0009] The ring frame 2 is annular and includes a fixedly connected ring frame web 21, a ring frame inner edge strip 22 and a ring frame outer edge strip 23. The ring frame inner edge strip 22 is a single-sided inner edge strip for fixing to the rear pressure ball frame 1, and the ring frame outer edge strip 23 is for fixing to the fuselage skin 8. It includes single-sided and double-sided configurations, which are selected according to design requirements and are designed in conjunction with the ring frame height H of the ring frame 2 to assist in achieving stiffness matching.

[0010] The longitudinal support member 4 includes a fixedly connected support member web 41, a support member inner edge strip 42 and a support member outer edge strip 43, and a total of several thereof are arranged in the pressurized area in the front part of the ring frame 2 and are distributed in a "finger" shape along the circumferential direction. The support member web 41 is designed to match the rear pressure ball frame 1 and the fuselage skin 8 through surface fitting, the support member inner edge strip 42 is a single-sided or double-sided inner edge strip, which is used to be connected to the rear pressure ball frame 1 through the connecting corner piece 6, and the support member outer edge strip 43 is a single-sided or double-sided outer edge strip, which is used to be connected to the fuselage skin 8 through the connecting joint 5; the longitudinal support member 4 disperses and transfers the radial load of the rear pressure ball frame 1 to the fuselage skin 8, and it has a variety of configurations through the combination design of the support member inner edge strip 42 and the support member outer edge strip 43 with different structures, which can be selected according to design needs.

[0011] The circumferential support corner box 3 is an integral structure, arranged between adjacent longitudinal support members 4, and includes a corner box web 31, a corner box inner edge strip 32 and a corner box end face 33. The corner box web 31 is fixedly connected to the side of the ring frame web 21 where the ring frame inner edge strip 22 is not provided, and the corner box inner edge strip 32 is fixedly connected to the rear pressure ball frame 1. Corner box end faces 33 are provided at the ends of the corner box web 31 and the corner box inner edge strip 32, which are respectively fixedly connected to the longitudinal support members 4 on both sides to form a circumferential load transfer path.

[0012] The connecting joint 5 includes a joint web 51 and a joint outer edge strip 52. The joint web 51 is fixedly connected to the support member web 41, and the joint outer edge strip 52 is fixedly connected to the support member outer edge strip 43 and the fuselage skin 8. The connecting joint 5 is arranged on one side or both sides of the support member web 41 according to design requirements.

[0013] One end of the connecting corner piece 6 is fixedly connected to the inner edge strip 42 of the support member, and the other end is fixedly connected to the rear pressure ball frame 1 and the inner edge strip 32 of the corner box.

[0014] If the docking structure is provided at the docking position of the fuselage skin 8 , a docking strip 7 is provided between the docking position of the ring frame outer edge strip 23 in the ring frame 2 and the fuselage skin 8 as a buffer structure.

[0015] A method for designing a docking structure between the aforementioned inscribed rear pressure ball frame and the fuselage comprises the following steps:

[0016] Step 1: Design the docking structure configuration:

[0017] Step 1.1: According to the load-bearing capacity of the rear pressure ball frame 1 and the load distribution of the fuselage, the range of the allowable transfer ratio of the fuselage bending load is set.

[0018] Step 1.2: To limit the transfer ratio of the fuselage bending load to the rear pressure ball frame, the docking structure configuration is designed, including:

[0019] a. Change the value of the ring frame height H;

[0020] b. Change the configuration of the ring frame 2 connected to the fuselage skin 8;

[0021] c. A docking strap 7 is provided between the docking structure and the fuselage skin 8 and its material and structural parameters are adjusted, and elastic materials or special connection designs are used to absorb and disperse bending loads.

[0022] Step 1.3: Select methods a, b, and c in step 1.2 individually or in combination. Establish a ring frame-load transfer ratio correlation model through finite element analysis, analyze the impact of different optimization schemes on load transfer, and select the structural configuration with the best force transmission performance and satisfactory load transfer ratio.

[0023] In step 1.4, based on the optimized configuration, plan experiments to verify the load transfer characteristics, and determine the optimal docking structure and ring frame height H value that meet the load transfer range based on the experimental data.

[0024] Step 2: Design the curved surface of the web 41 of a single longitudinal support member 4:

[0025] Step 2.1: Introduce the ring frame web datum plane and the rear pressure ball frame datum plane, obtain the intersection curve S1 of the two datum planes, cut the rear pressure ball frame surface with S1 as the boundary, and retain the pressure ball net surface M1; tangentially extend the M1 surface outward along the S1 curve to form a surface M2, and cut with S1 as the boundary to retain the net extension surface M3; introduce the center point Po of the rear pressure ball frame datum plane, create a straight line L1 perpendicular to the ring frame web datum plane through the center point Po, and obtain the intersection point P1 of the straight line L1 and the pressure ball net surface M1; select the longitudinal component station point P on the S1 curve Z1 , the intersection of a single fuselage long truss station plane and curve S1 is initially selected as P Z1 , establish the station point P through the center point Po and the intersection point P1 Z1 The plane T1 of three points, where plane T1 is preliminarily determined as the heading station of the reference plane; obtain the intersection S2 of the T1 plane and the net extension surface M3, and use S2 as the guide curve to establish the surface M4 with a 90° angle with the M2 surface as the initial reference plane.

[0026] Step 2.2, establish a straight line L2 with the two end points of the intersection line S2, measure the approximate angle β between the surface M4 and the fuselage surface, and set the surface angle Where n is the required number of surfaces; the sweep generates 2n candidate swept surfaces; the swept surface uses L2 as the reference curve and M4 as the reference surface and forms an integer multiple angle θ with them.

[0027] In step 2.3, finite element analysis is performed on the 2n curved surfaces at the four positions of a single longitudinal support member by applying pressure differential load and fuselage load, and the curved surface Mx with uniform stress distribution and optimal bearing capacity is selected.

[0028] In step 2.4, the optimized surface Mx is intersected with the fuselage surface to generate curve S3. The intersection line S4 between the Mx surface and the M3 surface is obtained. Multiple point sets are extracted at equal intervals on the S3 and S4 curves. The minimum multiplication method is used for fitting to generate plane T. Plane T is determined as the final reference plane of the longitudinal web of the single station.

[0029] Step 3: Determine the number N and configuration of the longitudinal supports 4:

[0030] Step 3.1: Build a model that correlates the number of longitudinal members with load transfer efficiency. Define load transfer efficiency η as (actual radial load transferred to the fuselage) / (theoretical maximum transferable load) * 100%. Through finite element parametric analysis, obtain a curve showing the relationship between η and N, as well as the minimum N value that satisfies the given η requirement. Extract the geometric features of the longitudinal support member 4 and use finite element parametric analysis to determine the load transfer efficiency η of the longitudinal support member 4.

[0031] Step 3.2, based on the Euler buckling theory, calculate the critical buckling load of a single longitudinal support member 4 according to the effective length L, section modulus E, moment of inertia I and end constraint coefficient K of the longitudinal support member 4.

[0032]

[0033] The overall stability safety factor S is set to require the total bearing capacity to meet the following requirements:

[0034] N.P. cr ≥S·F max (2)

[0035] Among them, F max is the maximum radial load borne by the rear pressure ball frame 1;

[0036] According to the N value calculated in step 3.1, the configuration of the longitudinal support member 4 is selected as the initial configuration, and the circumferential support angle box 3, the connecting joint 5 and the connecting angle piece 6 are set in combination.

[0037] Step 3.3, multi-objective optimization to solve the number N of longitudinal supports 4:

[0038] The minimum number N of longitudinal supports 4 must satisfy the following function:

[0039]

[0040] Among them, A is the required value of load transfer efficiency, B is the number of longitudinal supports 4 constrained by the process size of the circumferential support corner box 3, and the NSGA-Ⅱ genetic algorithm is used to perform integer programming on N to output the optimal solution set.

[0041] Step 3.4, engineering verification and correction, finite element verification is performed on the N value in the optimal solution set and the configuration of each longitudinal support 4, requiring the stress difference between the longitudinal supports 4 to be less than the required value, and the first-order buckling modal frequency to be greater than the required value. If the verification fails, increase the step size ΔN = 1 and adjust the configuration of each longitudinal support 4 respectively, and adjust the circumferential support angle box 3, connecting joint 5 and connecting angle piece 6 accordingly, and then re-verify until the conditions are met.

[0042] Beneficial effects of the present invention:

[0043] The present invention achieves stiffness matching between the ring frame and the fuselage structure by optimizing the ring frame height and its connection design with the fuselage buffer, and effectively suppresses the reverse transmission effect of the bending load. The docking structure achieves the load-bearing requirements of the rear pressure ball frame by arranging the buffer structure, adjusting the ring frame height, and its connection configuration with the fuselage skin; on this basis, an optimized docking form is introduced in which the longitudinal supports and the annular support corner box are directly connected to the rear pressure ball frame, constructing a multi-directional load transfer path, thereby achieving effective dispersion of radial and annular stresses and significantly improving the overall stability of the structure. In the design, the number of longitudinal supports is controlled, and the shape of the longitudinal supports is optimized and arranged using surface fitting technology, thereby increasing the load transfer efficiency and improving the fatigue performance of the docking structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is an assembly diagram of the docking structure of the present invention.

[0045] Figure 2 This is an example diagram of a docking structure based on the AA section of the present invention.

[0046] Figure 3 This is another example diagram of a docking structure based on the AA section of the present invention.

[0047] Figure 4 This is a flow chart of the docking structure design of the present invention.

[0048] Among them, 1-rear pressure ball frame, 2-ring frame, 3-annular support corner box, 4-longitudinal support, 5-connecting joint, 6-connecting corner piece, 7-docking plate, 8-fuselage skin, 21-ring frame web, 22-ring frame inner edge strip, 23-ring frame outer edge strip, 31-corner box web, 32-corner box inner edge strip, 33-corner box end face, 41-support member web, 42-support member inner edge strip, 43-support member outer edge strip, 51-joint web, 52-joint outer edge strip, H-ring frame height. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention more clear, the specific implementation methods of the present invention will be described in detail below based on the technical solutions.

[0050] Figure 1 and Figure 2 A docking structure between an inboard rear pressure ball frame and a fuselage includes a ring frame 2, a ring support corner box 3, a longitudinal support member 4, a connecting joint 5, and a connecting corner piece 6.

[0051] The ring frame 2 is annular and is used to transfer the normal and hoop loads of the rear pressure ball frame 1 to the fuselage skin. It includes a fixedly connected ring frame web 21, a ring frame inner edge strip 22 and a ring frame outer edge strip 23. The ring frame inner edge strip 22 is a single-sided inner edge strip for fixing with the rear pressure ball frame 1, and the ring frame outer edge strip 23 is used for fixing with the fuselage skin 8, which includes a single side (such as Figure 3 ) and bilateral (e.g. Figure 2 ) two configurations, which can be selected according to design requirements, and the ring frame height H of the ring frame 2 is designed to assist in achieving stiffness matching.

[0052] The longitudinal support member 4 is used to transfer the radial load of the rear pressure ball frame 1 to the fuselage skin 8, including a fixedly connected support member web 41, a support member inner edge strip 42 and a support member outer edge strip 43. A total of several support members are distributed in a "finger" shape in the pressurized area in front of the ring frame 2, and are initially arranged at the long stringer station of the fuselage in the pressurized area. The support member web 41 is designed to be triangular by surface fitting to match the rear pressure ball frame 1 and the fuselage skin 8. The support member inner edge strip 42 is a single-sided or double-sided inner edge strip, which is used to be connected to the rear pressure ball frame 1 through the connecting corner piece 6. The support member outer edge strip 43 is a single-sided or double-sided outer edge strip, which is used to be connected to the fuselage skin 8 through the connecting joint 5; the longitudinal support member 4 disperses the radial load of the rear pressure ball frame 1 to the fuselage skin 8, and it has a variety of configurations through the combination of support member inner edge strips 42 and support member outer edge strips 43 with different structures, such as C-shaped, Z-shaped, I-shaped, J-shaped, etc. cross-sections, which can be selected according to design needs.

[0053] The circumferential support corner box 3 is an integral structure, arranged between adjacent longitudinal support members 4, and includes a corner box web 31, a corner box inner edge strip 32 and a corner box end face 33. The corner box web 31 is fixedly connected to the side of the ring frame web 21 where the ring frame inner edge strip 22 is not provided. The corner box inner edge strip 32 is fixedly connected to the rear pressure ball frame 1 and the connecting corner piece 6 in three layers. Corner box end faces 33 are provided at the ends of the corner box web 31 and the corner box inner edge strip 32, which are respectively fixed to the longitudinal support members 4 on both sides to form an circumferential load transfer path for transferring load to the ring frame 2 and the longitudinal support members 4.

[0054] The connecting joint 5 includes a joint web 51 and a joint outer edge strip 52. The joint web 51 is fixedly connected to the support member web 41, and the joint outer edge strip 52 is fixedly connected to the support member outer edge strip 43 and the fuselage skin 8. The connecting joint 5 is arranged on one side or both sides of the support member web 41 according to design requirements to enhance the load transfer efficiency.

[0055] One end of the connecting corner piece 6 is fixedly connected to the inner edge strip 42 of the support member, and the other end is fixedly connected to the rear pressure ball frame 1 and the inner edge strip 32 of the corner box, so as to transfer the load to the longitudinal support member 4 .

[0056] If the docking structure is set at the docking position of the fuselage skin 8, a docking strip 7 is set between the outer edge strip 23 of the ring frame 2 and the docking position of the fuselage skin 8 as a buffer structure. Figure 2 .

[0057] A design method for the docking structure of the above-mentioned inscribed rear pressure ball frame and the fuselage, the process is as follows Figure 4 As shown, the following steps are included:

[0058] Step 1: Design the docking structure configuration:

[0059] Step 1.1: According to the load capacity of the rear pressure ball frame 1 and the load distribution of the fuselage, the allowable transfer ratio of the fuselage bending load is set to 10%.

[0060] Step 1.2: To limit the transfer ratio of the fuselage bending load to the rear pressure ball frame, the docking structure configuration is designed, including:

[0061] a. Change the value of the ring frame height H;

[0062] b. Change the configuration of the ring frame 2 connected to the fuselage skin 8;

[0063] c. Set a docking strap 7 between the docking structure and the fuselage skin 8 and adjust its material and thickness parameters, using elastic materials or special connection design to absorb and disperse bending loads.

[0064] Step 1.3: Establish a ring frame-load transfer ratio correlation model through finite element analysis, analyze the impact of different optimization schemes on load transfer, and adjust the docking structure configuration by using the above methods a, b, and c individually or in combination. Finally, select the structural configuration with the best force transmission performance and satisfactory load transfer ratio:

[0065] The pressure differential load is added to the finite element analysis to obtain the maximum stress σ1 of the rear pressure ball frame connection area; the pressure differential load and fuselage bending load are added to the docking structure by finite element analysis to obtain the maximum stress σ1 of the rear pressure ball frame connection area. σ2-σ1σ2-σ1

[0066] Force σ2; calculate the value of σ1. When σ1 is greater than 10%, give priority to adjusting the ring frame height H parameter. Use finite element analysis tools to simulate different ring frame height combinations to evaluate their impact on the transfer ratio of the fuselage bending load to the rear pressure ball frame. When the frame height is increased to the upper limit (the upper limit is limited by the minimum space requirement in the pressurized cabin and is a set value) and the transfer ratio still does not meet the requirements, use method b in step 1.2 to change the connection configuration of ring frame 2 and the fuselage skin. For example, change the ring frame 2 configuration from 2 to Figure 3 If the transfer ratio result still does not meet the requirements after the change, the docking strip 7 can be added as a buffer structure, and its selected material and thickness value can be changed.

[0067] In step 1.4, based on the optimized configuration, plan experiments to evaluate and verify the load reverse transfer effect, and determine the optimal docking structure and ring frame height H value that meet the load transfer range based on experimental data.

[0068] Step 2: Design the curved surface of the web 41 of a single longitudinal support member 4:

[0069] Step 2.1: Introduce the ring frame web datum plane and the rear pressure ball frame datum plane, obtain the intersection curve S1 of the two datum planes, cut the rear pressure ball frame surface with S1 as the boundary, and retain the pressure ball net surface M1; tangentially extend the M1 surface outward along the S1 curve to form a surface M2, and cut with S1 as the boundary to retain the net extension surface M3; introduce the center point Po of the rear pressure ball frame datum plane, create a straight line L1 perpendicular to the ring frame web datum plane through the center point Po, and obtain the intersection point P1 of the straight line L1 and the pressure ball net surface M1; select the longitudinal component station point P on the S1 curve Z1 , the intersection of a single fuselage long truss station plane and curve S1 is initially selected as P Z1 , establish the station point P through the center point Po and the intersection point P1 Z1 The plane T1 of three points, where plane T1 is preliminarily determined as the heading station of the reference plane; obtain the intersection S2 of the T1 plane and the net extension surface M3, and use S2 as the guide curve to establish the surface M4 with a 90° angle with the M2 surface as the initial reference plane.

[0070] Step 2.2, establish a straight line L2 with the two end points of the intersection line S2, measure the approximate angle β between the surface M4 and the fuselage surface, and set the surface angle Sweep to generate 10 candidate swept surfaces; the swept surface uses L2 as the reference curve and M4 as the reference surface and forms an integer multiple angle θ with them.

[0071] In step 2.3, finite element analysis is performed on the 10 curved surfaces at the four positions of a single longitudinal support member by applying pressure differential load and fuselage load, and the curved surface Mx with uniform stress distribution and optimal load-bearing capacity is selected.

[0072] In step 2.4, the optimized surface Mx is intersected with the fuselage surface to generate curve S3. The intersection line S4 between the Mx surface and the M3 surface is obtained. Multiple point sets are extracted at equal intervals on the S3 and S4 curves. The minimum multiplication method is used for fitting to generate plane T. Plane T is determined as the final reference plane of the longitudinal web of the single station.

[0073] Step 3: Determine the number N and configuration of longitudinal supports 4:

[0074] Step 3.1: Build a model that correlates the number of longitudinal members with load transfer efficiency. Define load transfer efficiency η as (actual radial load transferred to the fuselage) / (theoretical maximum transferable load) * 100%. Through finite element parametric analysis, obtain a curve showing the relationship between η and N, as well as the minimum N value that satisfies the given η requirement. Extract the geometric features of the longitudinal support member 4 and use finite element parametric analysis to determine the load transfer efficiency η of the longitudinal support member 4.

[0075] Step 3.2: Based on the Euler buckling theory, calculate the critical buckling load of the longitudinal support 4 according to its effective length L, section modulus E, moment of inertia I, and end constraint coefficient K:

[0076]

[0077] According to the overall stability calculation formula N·P cr ≥S·F max Calculate the overall stability safety factor S.

[0078] According to the N value calculated in step 3.1, a Z-shaped longitudinal support 4 is selected as the initial configuration, initially arranged at the long stringer position of the pressurized area fuselage, and is coordinated with the circumferential support corner box 3, the connecting joint 5 and the connecting corner piece 6, wherein the connecting joint 5 is arranged on one side of the longitudinal support 4.

[0079] Step 3.3, multi-objective optimization to solve the number N of longitudinal supports 4:

[0080] The minimum number N of longitudinal supports 4 must satisfy the following function:

[0081]

[0082] Among them, A is the required value of load transfer efficiency, B is the number of longitudinal supports 4 constrained by the process size of the circumferential support corner box 3, and the NSGA-Ⅱ genetic algorithm is used to perform integer programming on N to output the optimal solution set.

[0083] Step 3.4, engineering verification and correction, finite element verification is performed on the N value in the optimal solution set and the configuration of each longitudinal support 4, requiring the stress difference between the longitudinal supports 4 to be less than the required value, and the first-order buckling modal frequency to be greater than the required value. If the verification fails, increase the step size ΔN = 1 and adjust the configuration of each longitudinal support 4 respectively, and adjust the circumferential support angle box 3, connecting joint 5 and connecting angle piece 6 accordingly, and then re-verify until the conditions are met.

[0084] In this embodiment, when the load transfer efficiency η of the longitudinal support members 4 at a certain girder station is less than 50% and the safety factor S is greater than or equal to 2, the longitudinal support members 4 in this area are deleted and the thickness of the longitudinal support members 4 in the adjacent area is increased; when the load transfer efficiency η of the longitudinal support members 4 at a certain girder station is greater than 150% and the safety factor S is less than or equal to 0.2, the longitudinal support members 4 at this station are deleted and two longitudinal support members 4 with even spacing are added between the two adjacent longitudinal support members 4 to the deleted longitudinal support member 4.

[0085] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A docking structure between an inscribed rear pressure ball frame and a fuselage, characterized in that: The invention comprises an annular frame (2), an annular support angle box (3), longitudinal support members (4), a connecting joint (5) and a connecting angle piece (6); the annular frame (2) is connected between the rear pressure ball frame (1) and the fuselage skin (8) and is used to transmit the normal and annular loads of the rear pressure ball frame (1) to the fuselage skin; a plurality of longitudinal support members (4) are distributed in the pressurized area in front of the annular frame (2) at intervals along the circumference and are used to transmit the radial load of the rear pressure ball frame (1) to the fuselage skin (8); the annular support angle box (3) is connected to the corresponding The connecting joint (5) is connected between the adjacent longitudinal support members (4) and is connected to the ring frame (2) and the rear pressure ball frame (1), and is used to transfer the load to the ring frame (2) and the longitudinal support member (4); the connecting joint (5) realizes the fixed connection between the ring frame (2), the longitudinal support member (4) and the fuselage skin (8), and is used to enhance the load transfer efficiency; the connecting corner piece (6) realizes the fixed connection between the ring frame (2), the annular support corner box (3), the longitudinal support member (4) and the rear pressure ball frame (1), and is used to transfer the load to the longitudinal support member (4).

2. The docking structure of the internally connected rear pressure ball frame and the fuselage according to claim 1, characterized in that: Specifically: The ring frame (2) is annular and comprises a ring frame web (21), a ring frame inner edge strip (22) and a ring frame outer edge strip (23) which are fixedly connected. The ring frame inner edge strip (22) is fixedly connected to the rear pressure ball frame (1), and the ring frame outer edge strip (23) is fixedly connected to the fuselage skin (8). The longitudinal support member (4) comprises a fixedly connected support member web (41), a support member inner edge strip (42) and a support member outer edge strip (43); the support member web (41) is designed to match the rear pressure ball frame (1) and the fuselage skin (8) through curved surface fitting, and is connected to the rear pressure ball frame (1) through a connecting corner piece (6); and the support member outer edge strip (43) is connected to the fuselage skin (8) through a connecting joint (5); The annular support corner box (3) is an integrated structure, comprising a corner box web (31), a corner box inner edge strip (32) and a corner box end face (33). The corner box web (31) is fixedly connected to the ring frame web (21), the corner box inner edge strip (32) is fixedly connected to the rear pressure ball frame (1), and the ends of the corner box web (31) and the corner box inner edge strip (32) are both provided with corner box end faces (33), which are respectively fixedly connected to the longitudinal support members (4) on both sides. The connecting joint (5) comprises a joint web (51) and a joint outer edge strip (52), wherein the joint web (51) is fixedly connected to the supporting member web (41), and the joint outer edge strip (52) is fixedly connected to the supporting member outer edge strip (43) and the fuselage skin (8); One end of the connecting corner piece (6) is fixedly connected to the inner edge strip (42) of the support member, and the other end is fixedly connected to the rear pressure ball frame (1) and the inner edge strip (32) of the corner box.

3. The docking structure of the internally connected rear pressure ball frame and the fuselage according to claim 2, characterized in that: The inner edge strip (22) of the ring frame is a single-sided inner edge strip, and the outer edge strip (23) of the ring frame is a single-sided or double-sided outer edge strip, which can be selected according to design requirements.

4. The docking structure of the internally connected rear pressure ball frame and the fuselage according to claim 2, characterized in that: The inner edge strip (42) of the support member is a single-sided or double-sided inner edge strip, and the outer edge strip (43) of the support member is a single-sided or double-sided outer edge strip. The longitudinal support member (4) has a variety of configurations through the combination design of the inner edge strip (42) and the outer edge strip (43) of the support member with different structures, which can be selected according to design requirements.

5. The docking structure of the internally connected rear pressure ball frame and the fuselage according to claim 2, characterized in that: The connection joint (5) is arranged on one side or both sides of the support member web (41) according to design requirements.

6. The docking structure of the inscribed rear pressure ball frame and the fuselage according to claim 2, characterized in that: If the docking structure is provided at the docking position of the fuselage skin (8), a docking strip (7) is provided between the docking position of the ring frame (2) and the fuselage skin (8) as a buffer structure.

7. A method for designing a docking structure between an inscribed rear pressure ball frame and a fuselage according to any one of claims 1 to 6, characterized in that: The steps include: Step 1: Design the docking structure configuration: Step 1.1, according to the load-bearing capacity of the rear pressure ball frame (1) and the load distribution of the fuselage, setting the range of the allowable transfer ratio of the fuselage bending load; Step 1.2: Design the docking structure to limit the transfer ratio of the fuselage bending load to the rear pressure ball frame. Step 1.3: Establish a ring frame-load transfer ratio correlation model through finite element analysis, analyze the impact of different optimization schemes on load transfer, and select the structural configuration with the best force transmission performance and satisfactory load transfer ratio; Step 1.4: Based on the optimized configuration, plan a test to verify the load transfer characteristics and determine the optimal docking structure and ring frame height H value that meet the load transfer range based on the experimental data; Step 2: Design the curved surface of the web (41) of the single longitudinal support member (4): Step 2.1: Introduce the ring frame web datum plane and the rear pressure ball frame datum plane, obtain the intersection curve S1 of the two datum planes, cut the rear pressure ball frame surface with S1 as the boundary, and retain the pressure ball net surface M1; tangentially extend the M1 surface outward along the S1 curve to form a surface M2, and cut with S1 as the boundary to retain the net extension surface M3; introduce the center point Po of the rear pressure ball frame datum plane, create a straight line L1 perpendicular to the ring frame web datum plane through the center point Po, and obtain the intersection point P1 of the straight line L1 and the pressure ball net surface M1; select the longitudinal component station point P on the S1 curve Z1 , the intersection of a single fuselage long truss station plane and curve S1 is initially selected as P Z1 , establish the station point P through the center point Po and the intersection point P1 Z1 The plane T1 of the three points is initially determined as the heading position of the reference plane; the intersection S2 of the plane T1 and the net extension plane M3 is obtained, and the surface M4 with a 90° angle with the surface M2 is established as the initial reference plane using S2 as the guide curve; Step 2.2, establish a straight line L2 with the two end points of the intersection line S2, measure the approximate angle β between the surface M4 and the fuselage surface, and set the surface angle Where n is the number of surfaces required; Sweep generates 2n candidate sweep surfaces; The slightly curved surface takes L2 as the reference curve and M4 as the reference surface and forms an integral multiple angle θ with them; Step 2.3, applying pressure differential load and fuselage load to the 2n curved surfaces of a single longitudinal support (4) to perform finite element analysis, and selecting the curved surface Mx with uniform stress distribution and optimal load-bearing capacity; Step 2.4: Intersect the optimized surface Mx with the fuselage surface to generate curve S3. Obtain the intersection line S4 between the Mx surface and the M3 surface. Extract multiple point sets at equal intervals on the S3 and S4 curves. Use the minimum multiplication method to fit the points to generate plane T. Determine plane T as the final reference plane of the longitudinal member web at this single station. Step 3, determine the number N and configuration of longitudinal supports (4): Step 3.1, establish a longitudinal component number-load transfer efficiency correlation model, define the load transfer efficiency η = (actual radial load transferred to the fuselage) / (theoretical maximum transferable load) * 100%, and obtain the relationship curve between η and N and the minimum N value corresponding to the given requirement of η through finite element parametric analysis; extract the geometric characteristics of the longitudinal support member (4), and obtain the load transfer efficiency η of the longitudinal support member (4) through finite element parametric analysis; Step 3.2, based on Euler buckling theory, calculate the critical buckling load P of a single longitudinal support (4) cr ; The overall stability safety factor S is set to require the total bearing capacity to meet the following requirements: N·P cr ≥S·F max (2) Among them, F max is the maximum radial load borne by the rear pressure ball frame (1); According to the N value calculated in step 3.1, the configuration of the longitudinal support member (4) is selected as the initial configuration, and the circumferential support angle box (3), the connecting joint (5) and the connecting angle piece (6) are arranged in conjunction; Step 3.3, multi-objective optimization solution for the number N of longitudinal supports (4): The minimum number N of longitudinal supports (4) must satisfy the following function: Among them, A is the required value of load transfer efficiency, B is the number of longitudinal supports (4) constrained by the process size of the hoop support corner box (3), and the NSGA-Ⅱ genetic algorithm is used to perform integer programming on N to output the optimal solution set; Step 3.4, perform finite element verification on the N value in the optimal solution set and the configuration of each longitudinal support member (4), requiring that the stress difference between the longitudinal supports (4) is less than the required value and the first-order buckling modal frequency is greater than the required value. If the verification fails, increase the step size ΔN=1 and adjust the configuration of each longitudinal support member (4) and the corresponding adjustment of the circumferential support angle box (3), the connecting joint (5) and the connecting angle piece (6) and re-verify until the conditions are met.

8. The method for designing a docking structure between an inscribed rear pressure ball frame and a fuselage according to claim 7, characterized in that: In step 1.2, designing the docking structure configuration includes: a. Change the value of the ring frame height H; b. Change the configuration of the ring frame (2) connected to the fuselage skin (8); c. Arrange a docking strap (7) between the docking structure and the fuselage skin (8) and adjust its material and structural parameters.

9. The method for designing a docking structure between an inscribed rear pressure ball frame and a fuselage according to claim 7, characterized in that: In step 3.2, the critical buckling load is calculated according to the following formula: Wherein, L, E, I and K are the effective length, section modulus, moment of inertia and end restraint coefficient of the longitudinal support (4), respectively.

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