A method for designing the shape of a tail boom of a helicopter

Abstract

The application belongs to the field of helicopters and relates to a design method for the shape of a tail boom of a helicopter. The method comprises the following steps: determining the front end and the rear end of the tail boom, dividing the tail boom into a plurality of cross sections along the direction from the front end to the rear end; selecting several most severe load conditions from the main load conditions of the tail boom, which are hereinafter referred to as severe conditions; converting the load of each severe condition to each cross section to obtain the bending moment, the torque, the shear force and the axial force, and selecting the maximum bending moment, the maximum torque, the maximum shear force and the maximum axial force of each cross section; assuming that the cross section of the tail boom is a thin-walled circular ring, calculating the minimum circular radius of each cross section under the action of the maximum bending moment, the maximum torque, the maximum shear force and the maximum axial force of each cross section and the preset skin thickness and the preset allowable stress, so that the stress of the tail boom is less than or equal to the preset allowable stress; and assuming that the cross section of the tail boom is a thin-walled rectangle, calculating the horizontal width and the vertical height of the minimum rectangle of each cross section, so that the stress of the tail boom is less than or equal to the preset allowable stress.

Description

Technical Field

[0001] This invention belongs to the field of helicopters and relates to a method for designing the shape of a helicopter tail boom. Background Technology

[0002] Chinese invention patent CN201410424569.0 describes a method for designing the shape of a helicopter tail boom. This invention focuses on functionality and describes the design process of a helicopter tail boom. However, the tail boom is a load-bearing structure, and this design method does not consider the stress characteristics of the tail boom. Design involves a trade-off of various factors. Focusing solely on functionality is insufficient. Summary of the Invention

[0003] The purpose of this invention is to design the shape of the helicopter tail boom with a focus on mechanical performance, so as to achieve uniform stress, good stability, light weight, and at the same time take into account both functionality and aesthetic appearance.

[0004] The technical solution of the present invention:

[0005] A method for designing the shape of a helicopter tail boom, comprising:

[0006] Determine the front and rear ends of the tail beam, and divide the tail beam into several sections along the direction from the front to the rear end.

[0007] Among the main load conditions of the tail beam, the most severe load conditions were selected and will be referred to as severe load conditions.

[0008] The loads of each severe working condition are converted to each cross section to obtain bending moment, torque, shear force and axial force. The maximum bending moment, torque, shear force and axial force are selected on each cross section.

[0009] First, assume that the tail beam section is a thin-walled circular ring. Under the preset skin thickness, preset allowable stress, and the maximum bending moment, torque, shear force, and axial force on each selected section, calculate the minimum circle radius value of each section that makes the tail beam stress less than or equal to the preset allowable stress.

[0010] Assuming the tail beam section is a thin-walled rectangle, under the preset skin thickness, preset allowable stress, and the maximum bending moment, torque, shear force, and axial force on each selected section, calculate the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress.

[0011] With the front end of the tail beam as the origin, the direction from the front end to the rear end as the positive direction of the abscissa, the position of the centroid of each section as the abscissa L, and the minimum circle radius R of each section as the ordinate, fit the RL curve segment; connect the ends of the RL curve segment to obtain the line segment; determine the "upper boundary straight line of R" based on this line segment.

[0012] With the front end of the tail beam as the origin, the direction from the front end to the rear end as the positive direction of the abscissa, and the position of the centroid of each section as the abscissa L, and the horizontal width a and vertical height b of the smallest rectangle of each section as the ordinate, fit the aL curve segment and the bL curve segment; connect the ends of the aL curve segment to obtain the line segment; determine the "upper boundary line of a" based on this line segment; determine the "upper boundary line of b" based on the line segment obtained by connecting the ends of the bL curve segment.

[0013] Based on the "R upper bound line", "a upper bound line" and "b upper bound line", calculate the radius of the front circular section, the horizontal width and vertical height of the front rectangular section of the tail beam, and calculate the radius of the rear circular section, the horizontal width and vertical height of the rear rectangular section of the tail beam.

[0014] The front circular cross section and the front rectangular cross section are enclosed as a smooth closed loop at the front end, and the rear circular cross section and the rear rectangular cross section are enclosed as a smooth closed loop at the rear end;

[0015] Enlarge the front smooth closed loop by a factor of N to a level suitable for docking with the body via the transition section; similarly enlarge the rear smooth closed loop by a factor of N; where N is a positive number.

[0016] The enlarged front-end smooth closed loop and the enlarged rear-end smooth closed loop are bridged together into a barrel according to the distance between the front and rear ends to obtain the tail beam shape.

[0017] The above preset values ​​are not to be used as a reference for subsequent designs. The allowable stress and thickness should be determined based on the actual materials used in the tail beam.

[0018] Calculate the minimum circle radius values ​​for each section that ensures the tail beam stress is less than or equal to the preset allowable stress, including:

[0019] The minimum circle radius value for each section is determined using the circle radius equation. The circle radius equation is as follows:

[0020]

[0021] In the above formula, M is the bending moment, T is the torque, Q is the shear force, F is the axial force, t and σ are the preset thickness and allowable stress, the x-axis is the length direction of the tail beam, the y-axis is the horizontal axis of the section, the z-axis is the vertical axis of the section, and R is the radius of the circle; the subscripts of the bending moment and torque indicate that the moment is about this axis, and the subscripts of the shear force and axial force indicate that the force is along this axis.

[0022] Calculate the R values ​​of the two equations above, and the larger one is the minimum circle radius that makes the tail beam stress less than or equal to the preset allowable stress under the single working condition of this section.

[0023] The same solution is applied to other working conditions. The larger of the obtained R values ​​is the minimum circle radius that makes the tail beam stress less than or equal to the preset allowable stress under all working conditions of this section.

[0024] Then, perform the above solution on all sections to obtain the minimum circle radius value of each section that makes the tail beam stress less than or equal to the preset allowable stress.

[0025] Calculate the horizontal width and vertical height of the minimum rectangle for each section that ensures the tail beam stress is less than or equal to the preset allowable stress, including:

[0026] The rectangular equation used, the minimum horizontal width and vertical height of the rectangle for each section, the rectangle equation is:

[0027]

[0028] In the above formula, M is the bending moment, T is the torque, Q is the shear force, F is the axial force, t and σ are the preset thickness and allowable stress, the x-axis is the length direction of the tail beam, the y-axis is the horizontal axis of the section, the z-axis is the vertical axis of the section, a is the horizontal width of the thin-walled rectangle, and b is the vertical height of the thin-walled rectangle. The subscripts of bending moment and torque indicate that the moment is about this axis, and the subscripts of shear force and axial force indicate that the force is along this axis.

[0029] Solve the equations to find the values ​​of a and b, which are the horizontal width and vertical height of the minimum rectangle for each section under a single working condition that makes the tail beam stress less than or equal to the preset allowable stress.

[0030] The same solution is applied to other working conditions. The larger of a and b is taken as the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress under all working conditions of this section.

[0031] Then, perform the above solution on all sections to obtain "the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress".

[0032] Based on this line segment, determine the "upper bound line of R", including:

[0033] If the line segment is not above the RL curve segment, translate the line segment to be above the RL curve segment and make an intersection with the RL curve segment. The translated line segment is taken as the "R upper bound line". If the line segment is above the RL curve segment, the line segment is taken as the "R upper bound line".

[0034] Based on this line segment, determine the "upper bound line of a", including:

[0035] If the line segment is not above the aL curve segment, translate the line segment to be above the aL curve segment and make an intersection with the aL curve segment. The translated line segment is taken as the "a upper bound line". If the line segment is above the aL curve segment, the line segment is taken as the "a upper bound line".

[0036] Based on this line segment, determine the "upper bound line of b", including:

[0037] If the line segment is not above the aL curve segment, translate the line segment to be above the bL curve segment, and make an intersection with the bL curve segment. The translated line segment is taken as the "upper bound line of b". If the line segment is above the bL curve segment, the line segment is taken as the "upper bound line of b".

[0038] The beneficial effects of this invention are: This method is designed from a stress perspective, resulting in a tail beam with uniform stress distribution, high material utilization, light weight, and good stability. It also balances functionality and aesthetic appeal. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a helicopter structure.

[0040] Figure 2 This is a schematic diagram of the RL curve and the "upper bound line of R".

[0041] Figure 3 This is a schematic diagram of curves aL and bL, the "upper bound line of a", and the "upper bound line of b".

[0042] Figure 4 This is a schematic diagram of a smooth closed loop of the front envelope.

[0043] Figure 5 This is a schematic diagram of the cylinder. Detailed Implementation

[0044] 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.

[0045] like Figure 1 As shown, the known conditions before design are: the centroid positions of the front and rear sections of the tail boom, the fuselage shape (excluding the tail boom and transition section), and the main load conditions on the tail boom. The transition section serves to connect the tail boom to the fuselage.

[0046] Design process:

[0047] 1. Preset a tail beam skin thickness t and a preset allowable stress σ for the tail beam skin material (both values ​​are determined empirically and their magnitude will not affect the final result). Divide the tail beam into several sections along its length.

[0048] 2. Select the most severe load conditions from the main load conditions of the tail beam, which will be referred to as severe load conditions in the following steps. Convert the load of the severe load conditions to each section. The load of each severe load condition converted to each section includes four components: bending moment, torque, shear force, and axial force.

[0049] 3. First, assume that the tail beam section is a thin-walled circular ring. Under the preset skin thickness, allowable stress, and severe working conditions, calculate the minimum circle radius value of each section that makes the tail beam stress less than or equal to the allowable stress.

[0050] 4. Assuming the tail beam section is a thin-walled rectangle, under the preset skin thickness, allowable stress, and severe working conditions, calculate the minimum rectangular horizontal width and vertical height values ​​for each section that make the tail beam stress less than or equal to the allowable stress.

[0051] 5. Using the position of each section along the length of the tail beam as the abscissa L, and the minimum circle radius of each section in step 0 as the ordinate R, draw the RL curve as shown below. Figure 2 As shown. Then draw the "upper bound line of R" for the RL curve.

[0052] 6. Using the position along the length of the tail beam of each section as the abscissa L, and the minimum rectangular horizontal width value a and vertical height value b of each section in step 0 as the ordinates, draw the aL curve and the bL curve respectively. Then draw... Figure 3 The "a upper bound line" and "b upper bound line" of the aL curve and bL curve.

[0053] 7. The value of the "upper bound line R" at the front end of the tail beam is the radius of the front circle of the tail beam, and the value of the "upper bound line R" at the rear end of the tail beam is the radius of the rear circle of the tail beam. The values ​​of the "upper bound line a" and "upper bound line b" at the front end of the tail beam are the horizontal width and vertical height of the rectangle, respectively.

[0054] The values ​​at the rear end of the tail beam are the horizontal width and vertical height of the rectangle.

[0055] 8. Enclose the front circle and the front rectangle into a front "ellipse", and enclose the rear circle and the smallest rear rectangle into another rear "ellipse". The "ellipse" here does not have to be a strict ellipse; it only needs to enclose the corresponding circle and rectangle. The shape details can take into account functionality.

[0056] 9. Enlarge the front ellipse to a size suitable for docking with the fuselage via a transition section. The enlargement ratio should take into account factors such as the functional requirements of the fuselage and the aesthetic and continuous shape of the fuselage. Enlarge the rear ellipse by the same ratio.

[0057] The enlarged front and rear ellipses are connected to form a cylinder, as shown below. Figure 5As shown, the tail boom shape is now obtained. Note that due to the enlargement in step 9, the preset values ​​in step 0 are no longer used as a reference for subsequent designs. Subsequent designs should determine the allowable stress and thickness based on the actual material used for the tail boom; either metal or composite materials can be used.

[0058] Example:

[0059] The front end of the tail boom of a helicopter is located at X=0, and the rear end is located at X=k. The X-axis represents the aircraft's heading, i.e., the length direction of the tail boom; the Y-axis represents the horizontal axis of the cross-section; and the Z-axis represents the vertical axis of the cross-section.

[0060] Two severe operating conditions were identified: Severe operating condition 1 is that the rear end of the tail beam is subjected to a vertically upward force F1, and the line of action of the force passes through the centroid of the tail beam; Severe operating condition 2 is that the rear end of the tail beam is subjected to a horizontal force F2, and the line of action of the force is offset by j relative to the centroid of the tail beam.

[0061] Divide the tail beam into sections every k / (m-1), resulting in a total of m sections.

[0062] Convert the forces of the two working conditions to each cross section. For example, working condition 1 converted to the front section yields bending moments My = F1·k, Mz = 0, Tx = 0, Qy = F1, Qz = 0, Fx = 0; working condition 2 converted to the front section yields bending moments My = 0, Mz = F2·k, Tx = F2·j, Qy = 0, Qz = F2, Fx = 0.

[0063] The skin thickness is preset to t, and the allowable stress is σ. First, assume the tail beam section is a thin-walled circular ring, and calculate the minimum radius of each section using the method described earlier. Then, assume the tail beam section is a thin-walled rectangle, and calculate the minimum horizontal width and vertical height of each section. For example, for the nth section, assume the minimum radius calculated for condition 1 is R. n1 The calculated minimum circle radius for working condition 2 is R. n2 And R n1 <R n2 The calculated minimum circle radius value for this section is taken as R. n =R n2 Assume the minimum horizontal width of the rectangle in working condition 1 is a. n1 The vertical height value is b n1 The minimum horizontal width of the rectangle in working condition 2 is a. n2 The vertical height value is b n2 , and a n1 n2 ,b n1 >b n2 Then the minimum horizontal width and vertical height of the rectangle in this section are taken as a. n =a n2 b n =b​n1 .

[0064] Find the minimum circle radius values ​​R1, R2, R3, ..., R for all m cross-sections. m Using the position of each section along the length of the tail beam as the abscissa L, and the minimum circle radius R1, R2, R3, ..., R of each section as the coordinates. m Draw the RL curve with R as the ordinate. Then draw the "upper bound line" of the RL curve. The ordinate of the "upper bound line" at the front end of the tail beam is the radius of the front circle of the tail beam, and the ordinate of the "upper bound line" at the rear end of the tail beam is R. m ' is the radius of the circle at the rear end of the tail beam.

[0065] Find the minimum horizontal width and vertical height values ​​a1, a2, a3, ..., a of all m cross-sections. m b1, b2, b3, ..., b m Using the position of each section along the length of the tail beam as the abscissa L, and the minimum rectangular horizontal width and vertical height values ​​a1, a2, a3, ..., a... of each section are respectively... m b1, b2, b3, ..., b m Using R as the ordinate, draw the aL and bL curves. Then, draw the "upper bound line" (a) and "upper bound line" (b) for the aL and bL curves respectively. The ordinate of the "upper bound line" at the front end of the tail beam represents the horizontal width of the front rectangle of the tail beam, and the ordinate of the "upper bound line" at the front end of the tail beam represents the vertical height of the front rectangle of the tail beam. The ordinate of the "upper bound line" at the rear end of the tail beam represents the horizontal width of the rear rectangle of the tail beam, and the ordinate of the "upper bound line" at the rear end of the tail beam represents the vertical height of the rear rectangle of the tail beam.

[0066] Enclose the front circle and front rectangle in a front "ellipse", and enclose the rear circle and smallest rear rectangle in another rear "ellipse". The "ellipse" here does not have to be a strict ellipse, as long as it encloses the corresponding circle and rectangle, the shape details can take into account functionality.

[0067] The front ellipse is enlarged to a size suitable for docking with the fuselage via a transition section. The enlargement ratio takes into account factors such as the functional requirements of the fuselage and the aesthetically pleasing and continuous shape of the fuselage. The rear ellipse is enlarged by the same ratio. The enlarged front and rear ellipses are then connected to form a cylindrical body, thus obtaining the tail boom shape.

[0068] The minimum circle radius is calculated as follows:

[0069] The minimum circle radius value for each section is determined using the circle radius equation. The circle radius equation is as follows:

[0070]

[0071] In the above formula, M is the bending moment, T is the torque, Q is the shear force, F is the axial force, t and σ are the preset thickness and allowable stress, the x-axis is the length direction of the tail beam, the y-axis is the horizontal axis of the section, the z-axis is the vertical axis of the section, and R is the radius of the circle; the subscripts of the bending moment and torque indicate that the moment is about this axis, and the subscripts of the shear force and axial force indicate that the force is along this axis.

[0072] Calculate the R values ​​of the two equations above, and the larger one is the minimum circle radius that makes the tail beam stress less than or equal to the preset allowable stress under the single working condition of this section.

[0073] The same solution is applied to other working conditions. The larger of the obtained R values ​​is the minimum circle radius that makes the tail beam stress less than or equal to the preset allowable stress under all working conditions of this section.

[0074] Then, perform the above solution on all sections to obtain the minimum circle radius value of each section that makes the tail beam stress less than or equal to the preset allowable stress.

[0075] like Figure 4 As shown, the horizontal width and vertical height of the minimum rectangle are calculated as follows:

[0076] The rectangular equation used, the minimum horizontal width and vertical height of the rectangle for each section, the rectangle equation is:

[0077]

[0078] In the above formula, M is the bending moment, T is the torque, Q is the shear force, F is the axial force, t and σ are the preset thickness and allowable stress, the x-axis is the length direction of the tail beam, the y-axis is the horizontal axis of the section, the z-axis is the vertical axis of the section, a is the horizontal width of the thin-walled rectangle, and b is the vertical height of the thin-walled rectangle. The subscripts of bending moment and torque indicate that the moment is about this axis, and the subscripts of shear force and axial force indicate that the force is along this axis.

[0079] Solve the equations to find the values ​​of a and b, which are the horizontal width and vertical height of the minimum rectangle for each section under a single working condition that makes the tail beam stress less than or equal to the preset allowable stress.

[0080] The same solution is applied to other working conditions. The larger of a and b is taken as the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress under all working conditions of this section.

[0081] 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 shape of a helicopter tail boom, characterized in that, include: Determine the front and rear ends of the tail beam, and divide the tail beam into several sections along the direction from the front to the rear end. Among the load conditions of the tail beam, the most severe load conditions were selected, which will be referred to as severe load conditions from now on. The loads of each severe working condition are converted to each cross section to obtain bending moment, torque, shear force and axial force. The maximum bending moment, torque, shear force and axial force are selected on each cross section. First, assume that the tail beam section is a thin-walled circular ring. Under the preset skin thickness, preset allowable stress, and the maximum bending moment, torque, shear force, and axial force on each selected section, calculate the minimum circle radius value of each section that makes the tail beam stress less than or equal to the preset allowable stress. Assuming the tail beam section is a thin-walled rectangle, under the preset skin thickness, preset allowable stress, and the maximum bending moment, torque, shear force, and axial force on each selected section, calculate the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress. With the front end of the tail beam as the origin, the direction from the front end to the rear end as the positive direction of the abscissa, the position of the centroid of each section as the abscissa L, and the minimum circle radius R of each section as the ordinate, fit the RL curve segment; connect the ends of the RL curve segment to obtain the line segment; determine the "upper boundary straight line of R" based on the line segment. With the front end of the tail beam as the origin, the direction from the front end to the rear end as the positive direction of the abscissa, and the position of the centroid of each section as the abscissa L, and the horizontal width a and vertical height b of the smallest rectangle of each section as the ordinate, fit the aL curve segment and the bL curve segment; connect the ends of the aL curve segment to obtain the line segment; determine the "upper boundary line of a" based on this line segment; determine the "upper boundary line of b" based on the line segment obtained by connecting the ends of the bL curve segment. Based on the "R upper bound line", "a upper bound line" and "b upper bound line", calculate the radius of the front circular section, the horizontal width and vertical height of the front rectangular section of the tail beam, and calculate the radius of the rear circular section, the horizontal width and vertical height of the rear rectangular section of the tail beam. The front circular cross section and the front rectangular cross section are enclosed as a smooth closed loop at the front end, and the rear circular cross section and the rear rectangular cross section are enclosed as a smooth closed loop at the rear end; Enlarge the front smooth closed loop by a factor of N to a level suitable for docking with the body via the transition section; similarly enlarge the rear smooth closed loop by a factor of N; where N is a positive number. The enlarged front-end smooth closed loop and the enlarged rear-end smooth closed loop are bridged together into a barrel according to the distance between the front and rear ends to obtain the tail beam shape.

2. The method according to claim 1, characterized in that, The above preset values ​​are not to be used as a reference for subsequent designs. The allowable stress and thickness should be determined based on the actual materials used in the tail beam.

3. The method according to claim 1, characterized in that, Calculate the minimum circle radius values ​​for each section that ensures the tail beam stress is less than or equal to the preset allowable stress, including: The minimum circle radius value for each section is determined using the circle radius equation. The circle radius equation is as follows: ； ； In the above formula, M is the bending moment, T is the torque, Q is the shear force, F is the axial force, and t and The thickness and allowable stress are preset. The x-axis is the length direction of the tail beam, the y-axis is the horizontal axis of the section, the z-axis is the vertical axis of the section, and R is the radius of the circle. The subscripts of bending moment and torque indicate that the moment is about this axis, and the subscripts of shear force and axial force indicate that the force is along this axis. Calculate the R values ​​of the two equations above, and the larger one is the minimum circle radius that makes the tail beam stress less than or equal to the preset allowable stress under the single working condition of this section. The same solution is applied to other working conditions. The larger of the obtained R values ​​is the minimum circle radius that makes the tail beam stress less than or equal to the preset allowable stress under all working conditions of this section. Then, perform the above solution on all sections to obtain the minimum circle radius value of each section that makes the tail beam stress less than or equal to the preset allowable stress.

4. The method according to claim 1, characterized in that, Calculate the horizontal width and vertical height of the minimum rectangle for each section that ensures the tail beam stress is less than or equal to the preset allowable stress, including: The rectangular equation used, the minimum horizontal width and vertical height of the rectangle for each section, the rectangle equation is: ； In the above formula, M is the bending moment, T is the torque, Q is the shear force, F is the axial force, and t and Given the preset thickness and allowable stress, the x-axis is the length direction of the tail beam, the y-axis is the horizontal axis of the section, the z-axis is the vertical axis of the section, a is the horizontal width of the thin-walled rectangle, and b is the vertical height of the thin-walled rectangle; the subscripts of bending moment and torque indicate the moment about this axis, and the subscripts of shear force and axial force indicate the force along this axis; Solve the equations to find the values ​​of a and b, which are the horizontal width and vertical height of the minimum rectangle for each section under a single working condition that makes the tail beam stress less than or equal to the preset allowable stress. The same solution is applied to other working conditions. The larger of a and b is taken as the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress under all working conditions of this section. Then, perform the above solution on all sections to obtain "the horizontal width and vertical height of the minimum rectangle of each section that makes the tail beam stress less than or equal to the preset allowable stress".

5. The method according to claim 1, characterized in that, Based on this line segment, determine the "upper bound line of R", including: If the line segment is not above the RL curve segment, translate the line segment to be above the RL curve segment and make an intersection with the RL curve segment. The translated line segment is taken as the "R upper bound line". If the line segment is above the RL curve segment, the line segment is taken as the "R upper bound line".

6. The method according to claim 1, characterized in that, Based on this line segment, determine the "upper bound line of a", including: If the line segment is not above the aL curve segment, translate the line segment to be above the aL curve segment and make an intersection with the aL curve segment. The translated line segment is taken as the "a upper bound line". If the line segment is above the aL curve segment, the line segment is taken as the "a upper bound line".

7. The method according to claim 1, characterized in that, Based on this line segment, determine the "upper bound line of b", including: If the line segment is not above the aL curve segment, translate the line segment to be above the bL curve segment, and make an intersection with the bL curve segment. The translated line segment is taken as the "upper bound line of b". If the line segment is above the bL curve segment, the line segment is taken as the "upper bound line of b".

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-7.

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