Vibration test device for aviation fuel pipeline
By designing a vibration testing device for aviation fuel pipelines, and using a vibration table and sensors to simulate flight vibrations in a natural environment, the problem of high energy consumption in existing technologies has been solved, and efficient and accurate pipeline performance evaluation has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-10
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies require simulating the vibration environment of actual flight on the ground when conducting vibration tests on aviation fuel lines, resulting in high energy consumption.
Design a vibration testing device for aviation fuel pipelines, including a support base, a vibration table, a first fixed structure and a second fixed structure. The vibration table simulates vibration excitation, the vibration detection sensor collects the signal frequency, and an external data acquisition and analysis system generates a vibration test control curve to simulate actual flight vibration in a natural environment.
It reduces energy consumption, can accurately assess the vibration performance of aviation fuel lines in specific directions, provides reliable data support for flight safety, and can simultaneously test multiple lines, improving test efficiency and data comprehensiveness.
Smart Images
Figure CN224109017U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of aviation fuel pipeline reliability test, in particular to a vibration test device for aviation fuel pipeline. BACKGROUND
[0002] During the aviation flight, the fuel pipeline system is in a complex vibration environment for a long time, and the continuous mechanical vibration can cause fatigue stress accumulation of the pipeline structure, and further can cause safety hazards. In order to ensure flight safety, the mechanical behavior and the ability to resist damage of the aviation fuel pipeline in the vibration environment need to be studied, and the vibration test needs to be carried out.
[0003] In the related art, the vibration test of the aviation fuel pipeline includes vibration fatigue test and bending fatigue test, and the specific content is as follows: in the room temperature environment, first, a low-frequency sine sweep test is carried out, 5-8Hz, 7.81mm, 8-40Hz, 1g, 40-100Hz, 2g, each test is carried out along the specified direction once, and the sweep rate is 2.0oct / min; then, a high-frequency random vibration test is carried out, 20-350Hz, 0.14g² / Hz, 350-2000Hz, 0.8g² / Hz, the overall vibration root mean square is 37.0g, each test is carried out along the specified direction once, and the test time of each direction is 26min. During the test, the vibration detection sensor in the test device collects the corresponding physical quantity, and the data acquisition and analysis system is used to carry out fast Fourier transform, and the data is converted into vibration energy of different frequencies.
[0004] However, when the aviation fuel pipeline is subjected to the vibration test, the vibration environment generated in the actual flight needs to be simulated on the ground, and the energy consumption is large. CONTENT OF THE INVENTION
[0005] In order to provide a device for simulating the vibration environment generated in the actual flight when the aviation fuel pipeline is subjected to the vibration test, the present application provides a vibration test device for aviation fuel pipeline, one end of the aviation fuel pipeline is fixed and vibrated, and the other end of the aviation fuel pipeline is only fixed and collects corresponding test data.
[0006] The vibration test device for aviation fuel pipeline provided by the present application adopts the following technical scheme:
[0007] The utility model provides an aviation fuel pipeline vibration test device, including support base, vibration table, first fixed structure, second fixed structure and vibration detection sensor, vibration table fixedly installs one end of support base, first fixed structure is fixedly connected to the one end of vibration table far from support base, vibration table drives first fixed structure synchronous vibration, second fixed structure is fixedly connected to the one end of support base far from vibration table, and the both ends of aviation fuel pipeline are installed in first fixed structure and second fixed structure respectively, vibration detection sensor is equipped with two, two vibration detection sensors are arranged on first fixed structure and second fixed structure respectively, are used for gathering the signal frequency of vibration source and the signal frequency generated after aviation fuel pipeline is applied vibration, and cooperate with external data acquisition analysis system and obtain vibration test control curve.
[0008] Through the above technical scheme, during the test, one end of the aviation fuel pipeline is fixedly connected to the first fixed structure, and the other end is fixedly connected to the second fixed structure; the vibration table simulates vibration excitation, so that the aviation fuel pipeline in the first fixed structure vibrates, and the vibration is transmitted to the end of the aviation fuel pipeline in the second fixed structure through the aviation fuel pipeline; the signal frequency of the aviation fuel pipeline at one end of the first fixed structure and the signal frequency of the aviation fuel pipeline at one end of the second fixed structure are collected by the vibration detection sensor and transmitted to the external data acquisition analysis system for analysis, and finally the vibration test control curve is derived to complete the vibration test of the aviation fuel pipeline; the application can simulate the vibration environment during actual flight in the natural environment, reduce energy consumption compared with the prior art, and accurately evaluate the vibration performance of the aviation fuel pipeline in a specific direction to provide reliable data support for flight safety.
[0009] Optionally, the first fixed structure includes a first connecting plate, a first bottom plate, and a first cover plate, the first connecting plate is detachably connected to the end of the vibration table away from the support base; the first bottom plate is fixedly connected to the end of the first connecting plate away from the vibration table; and the first cover plate is detachably fixed to the end of the first bottom plate away from the first connecting plate, and the aviation fuel pipeline is installed between the first cover plate and the first bottom plate.
[0010] Through the above technical scheme, the first connecting plate is detachably connected to the vibration table, so that the connection between the first fixed structure and the vibration table is flexible, facilitating installation and maintenance; the aviation fuel pipeline is installed between the first cover plate and the first bottom plate, which can stably fix one end of the aviation fuel pipeline and ensure that the end of the aviation fuel pipeline does not easily shake or shift during the vibration test, thereby ensuring the accuracy and reliability of the test data.
[0011] Optionally, first stiffening ribs are fixed to the two sides of the first bottom plate, respectively, and the first stiffening ribs are perpendicular to the length direction of the first bottom plate.
[0012] By adopting the technical scheme, the first stiffening rib can strengthen the structural strength of the first bottom plate and the first connecting plate, effectively resist stress generated due to vibration during the vibration test, prevent the first bottom plate from deforming, further guarantee the stability of the aviation fuel pipeline fixation, and avoid loosening of the pipeline due to deformation of the first bottom plate to affect the test result.
[0013] Optionally, the first connecting plate is provided with a plurality of first connecting holes for connection.
[0014] By adopting the technical scheme, different first connecting holes can be selected to be fixed with the vibration table according to actual test requirements, the flexibility and adaptability of installation of the first fixation structure are increased, the installation requirements under different specifications of vibration tables or different test conditions can be met, and the application range of the vibration test device is expanded.
[0015] Optionally, the second fixation structure comprises a second connecting plate, a stand plate, an adjusting plate, a second bottom plate and a second cover plate, the second connecting plate is installed on the support base, the stand plate is provided with two, and the two stand plates are vertically fixed on opposite ends of the second connecting plate; the adjusting plate is connected between the two stand plates, the adjusting plate can be vertically adjusted in height on the stand plate; the second bottom plate is fixedly connected to one end of the adjusting plate away from the support base, the second cover plate is detachably fixed to one end of the second bottom plate away from the second connecting plate, and the aviation fuel pipeline is installed between the second cover plate and the second bottom plate.
[0016] By adopting the technical scheme, the adjusting plate can be vertically adjusted in height on the stand plate, so that the two ends of the aviation fuel pipeline can be conveniently adjusted to the same horizontal direction, and uniform stress of the aviation fuel pipeline during the test is guaranteed; meanwhile, the second fixation structure can stably fix the other end of the aviation fuel pipeline, cooperates with the first fixation structure, so that the whole pipeline remains stable during the vibration test, and the test is ensured to be smoothly performed.
[0017] Optionally, the adjusting plate comprises a first fixed plate and a second fixed plate, the first fixed plate is installed on the side wall of the stand plate, the first fixed plate can be vertically adjusted in height; the second fixed plate is fixedly connected to one end of the first fixed plate away from the second connecting plate, the second fixed plate is horizontally arranged, and the second bottom plate is fixedly connected to one end of the second fixed plate away from the first fixed plate.
[0018] By adopting the technical scheme, the first fixing plate can be vertically adjusted in height, the second fixing plate is horizontally arranged and connected with the second bottom plate, the structure design can more accurately adjust the installation height and position of the aviation fuel pipeline, can not only make the two ends of the aviation fuel pipeline flush, but also can make the aviation fuel pipeline at one end of the second fixing structure curve through longitudinal adjustment, so as to detect the deflection of the aviation fuel pipeline, enrich the detection function of the test device, and obtain more comprehensive aviation fuel pipeline performance data.
[0019] Optionally, the second stiffening rib is arranged between the first fixing plate and the second fixing plate.
[0020] By adopting the technical scheme, the second stiffening rib enhances the structural strength of the adjusting plate, ensures that the adjusting plate will not be deformed or damaged when adjusting the height and bearing the pipeline vibration stress, ensures the stability and reliability of the adjusting function, and further ensures the accuracy of the installation position of the aviation fuel pipeline, so that the test result is more persuasive.
[0021] Optionally, the second connecting plate is provided with a second connecting hole, and the second connecting hole is a waist-shaped hole.
[0022] By adopting the technical scheme, the waist-shaped hole makes the installation position of the second fixing structure on the second connecting plate adjustable, the position of the adjusting bolt in the waist-shaped hole can be adjusted to adapt to aviation fuel pipelines of different lengths, and the tension of the aviation fuel pipeline can be adjusted; in this way, the installation and fixation of pipelines of different specifications can be ensured, and the pipelines will not shake violently during the vibration test, thereby improving the applicability of the test device to different pipelines and the stability of the test process.
[0023] Optionally, a plurality of first bottom plates are arranged, a plurality of second fixing structures are arranged, and the number and position of the first bottom plates correspond to the number and position of the second fixing structures.
[0024] By adopting the technical scheme, the plurality of first bottom plates and the plurality of second fixing structures are arranged in one-to-one correspondence, so that the vibration test device can detect a plurality of aviation fuel pipelines at the same time, greatly improving the test efficiency and reducing the test time and cost; a plurality of data can be obtained in one test, improving the diversity and comprehensiveness of the data, and being more conducive to comprehensive evaluation of the vibration performance of the aviation fuel pipeline.
[0025] In summary, the present application has the following at least one beneficial technical effect:
[0026] 1. The present application can simulate the vibration environment in the natural environment during actual flight, reduce energy consumption compared with the prior art, and accurately evaluate the vibration performance of the aviation fuel pipeline in a specific direction, to provide reliable data support for ensuring flight safety;
[0027] 2. The adjusting plate in the second fixing structure can not only make the two ends of the aviation fuel pipeline flush, but also make the aviation fuel pipeline at one end of the second fixing structure bend through longitudinal adjustment to detect the deflection of the aviation fuel pipeline, thereby enriching the detection function of the test device and obtaining more comprehensive aviation fuel pipeline performance data.
[0028] 3. The vibration test device of the present application can simultaneously detect multiple aviation fuel pipelines, thereby greatly improving the test efficiency, reducing the test time and cost, obtaining multiple groups of data in one test, improving the diversity and comprehensiveness of the data, and being more conducive to comprehensive evaluation of the vibration performance of the aviation fuel pipeline. BRIEF DESCRIPTION OF DRAWINGS
[0029] Figure 1 is a schematic diagram of the overall structure of the embodiment of the present application;
[0030] Figure 2 is a top view of the embodiment of the present application;
[0031] Figure 3 is a side view of the first fixing structure in the present application;
[0032] Figure 4 is a structural schematic diagram of the second fixing structure in the present application.
[0033] Reference signs: 1, support base; 2, vibration table; 3, first fixing structure; 31, first connecting plate; 311, first connecting hole; 32, first bottom plate; 321, first fixing groove; 33, first cover plate; 331, second fixing groove; 34, first stiffening rib; 4, second fixing structure; 41, second connecting plate; 411, second connecting hole; 42, vertical plate; 421, fixing hole; 43, reinforcing plate; 44, adjusting plate; 441, first fixing plate; 442, second fixing plate; 443, mounting hole; 444, second stiffening rib; 45, second bottom plate; 46, second cover plate; 5, aviation fuel pipeline. DETAILED DESCRIPTION
[0034] The following will be described in detail in combination with the accompanying drawings Figures 1-4 The present application will be further described in detail.
[0035] The embodiment of the present application discloses a vibration test device for an aviation fuel pipeline, which refers to Figure 1 and Figure 2, including a support base 1, a vibration table 2, a first fixed structure 3, a second fixed structure 4 and a vibration detection sensor, the vibration table 2 is fixedly installed at one end of the support base 1, the first fixed structure 3 is fixedly connected to the end of the vibration table 2 away from the support base 1, the vibration table 2 generates vibration to drive the first fixed structure 3 to vibrate synchronously, and the second fixed structure 4 is fixedly connected to the end of the support base 1 away from the vibration table 2; the vibration detection sensor is provided with two, the two vibration detection sensors are arranged on the first fixed structure 3 and the second fixed structure 4 respectively, and are respectively used for collecting the signal frequency of the vibration source and the signal frequency generated by the aviation fuel pipeline 5 after being subjected to vibration, and cooperating with an external data acquisition and analysis system to obtain a vibration test control curve.
[0036] During the test, one end of the aviation fuel pipeline 5 is fixedly connected to the first fixed structure 3, and the other end is fixedly connected to the second fixed structure 4; the vibration table 2 simulates vibration excitation, so that the aviation fuel pipeline 5 located in the first fixed structure 3 vibrates, and the vibration is transmitted to the end of the aviation fuel pipeline 5 located in the second fixed structure 4 through the aviation fuel pipeline 5; the signal frequency of the aviation fuel pipeline 5 at one end of the first fixed structure 3 and the signal frequency of the aviation fuel pipeline 5 at one end of the second fixed structure 4 are collected by the vibration detection sensor respectively and transmitted to the external data acquisition and analysis system for analysis, and finally a vibration test control curve is derived to complete the vibration test of the aviation fuel pipeline 5.
[0037] Referring to Figure 2 and Figure 3 , the first fixed structure 3 includes a first connecting plate 31, a first bottom plate 32 and a first cover plate 33, the first connecting plate 31 is detachably connected to the end of the vibration table 2 away from the support base 1; the first bottom plate 32 is fixedly connected to the end of the first connecting plate 31 away from the vibration table 2, the first cover plate 33 is arranged at the end of the first bottom plate 32 away from the first bottom plate 32, and threaded holes are formed at both ends of the first cover plate 33, and bolts are screwed into the first bottom plate 32 through the threaded holes to connect the first bottom plate 32 and the first cover plate 33. The first bottom plate 32 is integrally formed with a first stiffener 34 on each side, and the first stiffener 34 is perpendicular to the length direction of the first bottom plate 32.
[0038] A semicircular first fixed groove 321 is formed at one end of the first bottom plate 32 close to the first cover plate 33, the axis direction of the first fixed groove 321 is parallel to the axis direction of the aviation fuel pipeline 5, and the radius of the first fixed groove 321 matches the radius of the aviation fuel pipeline 5; a semicircular second fixed groove 331 is formed at one end of the first cover plate 33 close to the first bottom plate 32, and the radius of the second fixed groove 331 is equal to the radius of the first fixed groove 321, so that the aviation fuel pipeline 5 can be clamped between the first bottom plate 32 and the first cover plate 33.
[0039] During installation, first loosen the bolts, move the first cover plate 33 away from the first base plate 32 and insert the aviation fuel line 5 into the first fixing groove 321, then lower the first cover plate 33 so that the aviation fuel line 5 is located in the second fixing groove 331, tighten the bolts, and fix the aviation fuel line 5 between the first base plate 32 and the first cover plate 33 to ensure that one end of the aviation fuel line 5 in the first fixing structure 3 does not move significantly under vibration conditions.
[0040] The first connecting plate 31 is provided with multiple first connecting holes 311. The first connecting plate 31 can be selected with the appropriate first connecting holes 311 as needed and fixed to the vibration table 2. There are two first base plates 32, which are arranged in a direction perpendicular to the axis of the aviation fuel line 5. There are four first fixing grooves 321, which are evenly distributed along the length of the first base plate 32. There are four first cover plates 33, and the positions of the four first cover plates 33 correspond one-to-one with the positions of the four first fixing grooves 321, so that the vibration test device can test eight aviation fuel lines 5 at the same time.
[0041] Reference Figure 1 and Figure 4 The second fixing structure 4 includes a second connecting plate 41, a vertical plate 42, a reinforcing plate 43, and an adjusting plate 44. The second connecting plate 41 is horizontally installed on the support base 1. There are two vertical plates 42, which are vertically fixed to the opposite ends of the second connecting plate 41 and are fixedly connected to each other by the reinforcing plate 43. The vertical plate 42 is in the shape of a right triangle, with one right-angled side perpendicular to the plane of the second connecting plate 41 and a fixing hole 421 opened on the right-angled side.
[0042] The adjusting plate 44 includes a first fixing plate 441 and a second fixing plate 442. The first fixing plate 441 has a mounting hole 443. The first fixing plate 441 is fixed to the right-angle side of the upright plate 42 by bolts passing through both the mounting hole 443 and the fixing hole 421. The second fixing plate 442 is vertically connected to the end of the first fixing plate 441 away from the second connecting plate 41, and the second fixing plate 442 is horizontally arranged. A second stiffening rib 444 is provided between the first fixing plate 441 and the second fixing plate 442 to enhance the structural strength.
[0043] A second base plate 45 and a second cover plate 46 are horizontally arranged at the end of the second fixing plate 442 away from the first fixing plate 441. The second cover plate 46 is located at the end of the second base plate 45 away from the second fixing plate 442. The connection is achieved by bolts passing through the second cover plate 46, the second base plate 45 and the second fixing plate 442 in sequence and fixing them.
[0044] The second bottom plate 45 is provided with a semicircular third fixing groove near one end of the second cover plate, the axis direction of the second fixing groove 331 is parallel to the axis direction of the aviation fuel pipeline 5, and the radius of the second fixing groove 331 matches the radius of the aviation fuel pipeline 5; the second cover plate is provided with a semicircular fourth fixing groove near one end of the second bottom plate 45, and the radius of the fourth fixing groove is equal to the radius of the third fixing groove, so that the aviation fuel pipeline 5 can be clamped between the second bottom plate 45 and the second cover plate.
[0045] The fixing holes 421 are provided in multiple numbers and are uniformly distributed along the right-angle edges of the vertical plate 42. By installing the first fixing plate 441 in the fixing holes 421 at different heights, the two ends of the aviation fuel pipeline 5 are located in the same horizontal direction; at the same time, the aviation fuel pipeline 5 located at one end of the second fixing structure 4 can be adjusted longitudinally to bend to detect the deflection.
[0046] The second bottom plate 45 and the second cover plate 46 are provided with two groups in the horizontal direction, each second bottom plate 45 is provided with two third fixing grooves, that is, one second fixing structure 4 has four detection positions; the second fixing structure 4 is provided with two groups, and the eight third fixing grooves in the two groups of second fixing structures 4 correspond to the eight first fixing grooves 321 of the first fixing device respectively.
[0047] The second connecting plate 41 is provided with multiple second connecting holes 411, the second connecting holes 411 are waist-shaped holes, and the bolts are fixedly connected with the second connecting plate 41 through the second connecting holes 411. The second fixing structure 4 is fixed at different positions of the second connecting plate 41 to adapt to aviation fuel pipelines 5 of different lengths; the position of the bolt in the waist-shaped hole is adjusted to adjust the tension of the aviation fuel pipeline 5, so that it will not shake violently during the vibration experiment.
[0048] The vibration detection sensor can be an acceleration sensor, which is used to convert the collected physical quantity into an electrical signal and transmit it to an external data acquisition and analysis system; the external data acquisition and analysis system converts the frequency domain signal through fast Fourier transform, and finally generates a vibration test control curve.
[0049] The implementation principle of the vibration test device for the aviation fuel pipeline disclosed by the embodiment of the application is as follows: one end of the aviation fuel pipeline 5 is fixed between the first bottom plate 32 and the first cover plate 33 of the first fixing structure 3, and the other end of the aviation fuel pipeline 5 is fixed between the second bottom plate 45 and the second cover plate of the second fixing structure 4; the height of the adjusting plate 44 is adjusted so that the two ends of the aviation fuel pipeline 5 are located on the same horizontal direction; the vibration table 2 simulates vibration excitation, so that the aviation fuel pipeline 5 located in the first fixing structure 3 vibrates, and the vibration is transmitted to one end located in the second fixing structure 4 through the aviation fuel pipeline 5; the signal frequencies of the two ends of the aviation fuel pipeline 5 are collected by the vibration detection sensor respectively and transmitted to the external data acquisition and analysis system for analysis and conversion, and finally the vibration test control curve is derived, and the vibration test of the aviation fuel pipeline 5 is completed; the application can simulate the vibration environment in the actual flight in the natural environment, so as to test the vibration performance of the aviation fuel pipeline 5 in the specific direction.
[0050] The above are preferred embodiments of the application, and do not limit the protection scope of the application, so: any equivalent changes made on the structure, shape, principle of the application should be covered in the protection scope of the application.
Claims
1. A vibration testing device for aviation fuel pipelines, characterized in that, The utility model provides a kind of aviation fuel pipeline vibration test device, including support base (1), vibration table (2), first fixed structure (3), second fixed structure (4) and vibration detection sensor, the vibration table (2) is fixedly installed in support base (1) one end, the first fixed structure (3) is fixedly connected in vibration table (2) one end away from support base (1), the vibration table (2) drives first fixed structure (3) synchronous vibration, the second fixed structure (4) is fixedly connected in support base (1) one end away from vibration table (2), and the both ends of aviation fuel pipeline (5) are installed in first fixed structure (3) and second fixed structure (4) respectively;The vibration detection sensor is equipped with two, two vibration detection sensors are respectively arranged on first fixed structure (3) and second fixed structure (4), for collecting the signal frequency of vibration source and the signal frequency generated after aviation fuel pipeline (5) is applied vibration, and cooperation external data acquisition analysis system obtains vibration test control curve.
2. A vibration testing apparatus for an aircraft fuel line as defined in claim 1, wherein The first fixed structure (3) includes first connecting plate (31), first bottom plate (32) and first cover plate (33), the first connecting plate (31) is detachably connected to the one end of vibration table (2) away from support base (1);The first bottom plate (32) is fixedly connected to the one end of first connecting plate (31) away from vibration table (2), and the first cover plate (33) is detachably fixed to the one end of first bottom plate (32) away from first connecting plate (31), and the aviation fuel pipeline (5) is installed between the first cover plate (33) and the first bottom plate (32).
3. A vibration testing apparatus for an aircraft fuel line as defined in claim 2, wherein The both sides of the first bottom plate (32) are fixed with first stiffeners (34) respectively, and the first stiffeners (34) are perpendicular to the length direction of the first bottom plate (32).
4. The vibration testing apparatus for an aircraft fuel line according to claim 2, wherein A plurality of first connecting holes (311) for connection are arranged on the first connecting plate (31).
5. The vibration testing apparatus for an aircraft fuel line according to claim 2, wherein The second fixed structure (4) includes second connecting plate (41), stand (42), adjusting plate (44), second bottom plate (45) and second cover plate (46), the second connecting plate (41) is installed on support base (1), the stand (42) is provided with two, and the two stands (42) are vertically fixed on the opposite ends of second connecting plate (41);The adjusting plate (44) is connected between the two stands (42), and the adjusting plate (44) can be vertically adjusted in height on the stand (42);The second bottom plate (45) is fixedly connected to the one end of adjusting plate (44) away from support base (1), and the second cover plate (46) is detachably fixed to the one end of second bottom plate (45) away from second connecting plate (41), and the aviation fuel pipeline (5) is installed between the second cover plate (46) and the second bottom plate (45).
6. A vibration testing apparatus for an aircraft fuel line as defined in claim 5, wherein The adjusting plate (44) comprises a first fixed plate (441) and a second fixed plate (442), the first fixed plate (441) is installed on the side wall of the vertical plate (42), and the first fixed plate (441) can be vertically adjusted in height; the second fixed plate (442) is fixedly connected to one end of the first fixed plate (441) away from the second connecting plate (41), the second fixed plate (442) is horizontally arranged, and the second bottom plate (45) is fixedly connected to one end of the second fixed plate (442) away from the first fixed plate (441).
7. A vibration testing apparatus for an aircraft fuel line as defined in claim 6, wherein Second stiffening ribs (444) are arranged between the first fixed plate (441) and the second fixed plate (442).
8. The vibration testing apparatus for an aircraft fuel line according to claim 6, wherein The second connecting plate (41) is provided with a second connecting hole (411), and the second connecting hole (411) is a waist-shaped hole.
9. The vibration test apparatus for an aircraft fuel line according to claim 6, wherein The first bottom plate (32) is provided with a plurality of second fixed structures (4), and the number and position of the first bottom plate (32) correspond to the number and position of the second fixed structure (4) one by one.