Engineering calculation method for water pressure load of water tank of fire-extinguishing aircraft

Abstract

The invention discloses a fire-extinguishing aircraft water tank water pressure load engineering calculation method. The method comprises the following steps: respectively treating water drawing and flying conditions for four combined water tanks of a fire extinguishing aircraft: during water drawing, firstly determining state parameters in the water drawing process of the water tanks, establishing a water drawing-overflow balance equation set, and calculating the water drawing-overflow pressure difference of each wall plate to obtain the maximum water pressure of the top / bottom of each wall plate of the water tanks under the water drawing condition; during flight, according to geometric parameters / angular point parameters of the water tank, typical maneuvering conditions and limited maneuvering load coefficients, determining the occurrence position of the maximum water pressure of each maneuvering condition, and by calculating the maximum water pressure of the wall plate of the water tank under each maneuvering condition, obtaining the maximum water pressure of the top / bottom of the wall plate of the water tank under the flight condition; and finally, establishing a water pressure distribution model by combining the maximum water pressure of the top / bottom of the water tank under water drawing and flight conditions for structural strength design of the water tank. The calculation method is simple and clear, and the design period of the water tank structure can be effectively shortened.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of load calculation, in particular to a fire-fighting aircraft water tank water pressure load engineering calculation method. BACKGROUND

[0002] In the field of aerial firefighting, fire-fighting aircraft has become a key equipment for emergency rescue of disasters such as forest fires due to its unique advantage of being able to quickly arrive at the fire scene to implement fire-fighting operations. At present, the mainstream fire-fighting aircraft is usually equipped with a water storage system composed of multiple water tanks, which can quickly draw water through a water suction port during water surface sliding or ground water injection on the airport, and then pour the water in the water tank down through a release mechanism above the fire scene to achieve the fire-fighting function. For example, a typical four-combined water tank structure, combined with the design of a water suction port and a water overflow port, greatly improves the water suction efficiency and water storage capacity of the aircraft.

[0003] However, during the water suction process and flight process of the aircraft, the water in the water tank will generate complex water pressure loads on the wall plates of the water tank due to the motion and attitude change of the aircraft and the inertia effect of the water. The existing water tank water pressure load calculation methods are mostly based on simplified models, empirical formulas or CFD fluid-structure coupling analysis. The simplified model and empirical formula method cannot accurately simulate the specific stress conditions of the four-combined water tank under dynamic working conditions such as water suction and flight attitude change, and cannot accurately calculate the maximum water pressure at key points such as the corner points of the water tank wall plates, which leads to the inability to establish a reliable water pressure distribution model during the design of the water tank structure. The CFD fluid-structure coupling analysis has high calculation cost, long time consumption and complex result interpretation, and needs to be combined with flow field mechanism analysis, which is easily affected by parameters such as grid quality and turbulence model. Therefore, there is an urgent need for an engineering calculation method that can quickly and reliably evaluate and calculate the water pressure load of the fire-fighting aircraft water tank during water suction and flight, in order to ensure the safety of the water tank structure and the efficient operation of the aircraft. SUMMARY

[0004] The purpose of the present application is to provide a fire-fighting aircraft water tank water pressure load engineering calculation method. The calculation method of the present application is simple and clear, and can effectively shorten the design cycle of the water tank structure.

[0005] The technical solution of the present application is: a fire-fighting aircraft water tank water pressure load engineering calculation method, comprising the following steps: S1: clearly define the typical geometric parameters of the water tank, and extract the typical state parameters of the water suction and flight process; S2: for water suction conditions, establish a water suction-overflow balance equation set under the full water state of the water tank, and calculate the water suction-overflow pressure difference of each wall plate; S3: for each maneuvering condition of the water tank during flight, determine the maximum load coefficient of each direction, and calculate the maximum water pressure of the water tank wall plate under each maneuvering condition; S4: Combining the calculation results of S2 and S3, determine the water pressure limit of each key part of the water tank, and establish the water pressure distribution model of each water tank.

[0006] In S1 of the aforementioned engineering calculation method of water tank water pressure load of fire-fighting aircraft, the typical geometric parameters of the water tank include: The Z-direction height from the highest point of the overflow port to the lowest point of the upper wall plate of the water tank h1; The Z-direction height from the highest point of the overflow port to the lowest point of the side wall plate of the water tank h2; The Z-direction height from the highest point of the overflow port to the lowest point of the water scoop h3; The Z-direction height from the highest point of the overflow port to the lowest point of the bottom h; The total water receiving area of the two water scoops S js , The total overflow area of the four overflow ports S ys ; The maximum water scooping speed V.

[0007] In S1 of the aforementioned engineering calculation method of water tank water pressure load of fire-fighting aircraft, the flight process includes water-carrying flight, water-carrying flight includes negative 1g symmetric maneuver, symmetric pitch maneuver, roll maneuver, water take-off, fire field flight and lateral sway.

[0008] In the aforementioned engineering calculation method of water tank water pressure load of fire-fighting aircraft, the fire field flight needs to be divided into four cases: one water tank carrying water, two water tanks carrying water, three water tanks carrying water and four water tanks carrying water, and each case is considered separately.

[0009] In the aforementioned engineering calculation method of water tank water pressure load of fire-fighting aircraft, for the flight process, the longitudinal, lateral and lateral limiting maneuver load coefficients are determined according to the characteristics of each maneuver, and the maximum water pressure appearing angle of each water tank is determined.

[0010] In S2 of the aforementioned engineering calculation method of water tank water pressure load of fire-fighting aircraft, according to the water scooping characteristics of the water tank, the entire water scooping process includes water scooping before the water tank is full and overflow after the four water tanks are full, and the water tank water pressure load when water scooping and overflow occur simultaneously after the water tank is full is calculated.

[0011] In the aforementioned engineering calculation method of water tank water pressure load of fire-fighting aircraft, the water tank water pressure load when water scooping and overflow occur simultaneously after the water tank is full is calculated as follows: Let the overflow speed be V2, the inflow speed be V3, and the following formulas hold:

[0012] The water flow pressure at the overflow port is

[0013] The pressure difference at the water scoop is

[0014] The pressure balance equation at the water scoop is

[0015] Combining the above formulas, we have:

[0016] According to the following three formulas, the pressure difference ΔP1 of the upper wall plate of the water tank, the pressure difference ΔP2 of the bottom of the side wall plate, and the pressure difference ΔP of the bottom of the middle partition plate during water absorption and overflow:

[0017]

[0018] ; n is the maximum maneuvering load coefficient.

[0019] In S3 of the aforementioned engineering calculation method for water tank water pressure load of fire-fighting aircraft, the calculation formula for the maximum water pressure of the water tank wall plate in each case of water-carrying flight is:

[0020] In the formula, P is the maximum water pressure of the water tank wall plate, ρ is the incoming flow density, n x , n y , n z are the maximum maneuvering load coefficients of the aircraft in the horizontal, lateral, and longitudinal directions, respectively, h x , h y , h z are the maximum heights of the liquid column in the x, y, and z directions, respectively, at the angle point where the maximum water pressure of the water tank occurs.

[0021] In S4 of the aforementioned engineering calculation method for water tank water pressure load of fire-fighting aircraft, the calculated water pressure load results of all key parts of the upper wall plate, side wall plate, and partition plate of the water tank are summarized, and the limiting water pressure results of each key part of the water tank are selected. When checking the static strength of each water tank, the pressure is considered to change linearly from the upper wall plate to the bottom of its partition plate, and a water pressure distribution model for each water tank is established.

[0022] The beneficial effects of the present application: the present application gives a fire-fighting aircraft water tank water pressure load engineering calculation method, the calculation process is simple and clear, which can be used to guide the water tank water pressure load calculation of similar function, and is used for water tank static strength design to ensure the safety of the aircraft water tank structure. Compared with the rough calculation method relying on simplified model and empirical formula, the present application focuses on the structural characteristics of the four combined water tanks of the fire-fighting aircraft, completely simulates the specific stress conditions of the water tank under various working conditions such as water pumping and flight attitude change, further establishes a reliable water pressure distribution model, the function working condition is covered comprehensively, and the calculation precision is greatly improved; compared with the existing CFD fluid-structure coupling method which needs professional software and high-order computing power support, the present application does not need complex computing power resources, the calculation method is simple, the result is easy to understand, ordinary engineering and technical personnel can also quickly apply, and the manpower, time and economic investment are significantly saved, thereby providing reliable water load data support for the static strength checking of the water tank, solving the problems of insufficient accuracy of traditional algorithm and low efficiency of CFD, and ensuring the safety margin of the water tank structure. The water tank water pressure load calculation method of the present application has strong popularization, which is not only suitable for the four combined water tanks of the fire-fighting aircraft, but also can be adapted to other different combined water tanks through parameter adjustment, and has wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the position of the water tank in the fuselage in the invention example.

[0024] Figure 2 is the water tank number and each corner point in the invention example.

[0025] Figure 3 is the key height in the invention example.

[0026] Figure 4 is the four water tank water pressure distribution models established after the calculation in the invention example.

[0027] Figure 5 is the flowchart of the present application. DETAILED DESCRIPTION

[0028] In order to make the process of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below in combination with the drawings in the embodiments of the present application. In the drawings, the same or similar reference signs represent the same or similar elements or elements with the same or similar functions throughout. The described embodiments are part of the embodiments of the present application, not all embodiments, and the parts not described in detail are conventional technologies. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] Example 1. An engineering calculation method for the water pressure load of a fire-fighting aircraft water tank, see [link to example]. Figures 1-5 : like Figure 1 The diagram shown illustrates the specific locations of the water tanks within the fuselage of the firefighting aircraft according to the present invention. The four water tanks are symmetrical about the aircraft's plane of symmetry and are numbered as follows: Figure 2 As shown. The single-sided water tanks (I and III, II and IV) guide water flow to the front and rear water tanks through a water inlet and water pipe on that side. Each water tank has an overflow pipe with a cross-sectional area much larger than the water inlet / water outlet area, providing an overflow function when full.

[0030] The engineering calculation method for water pressure load on water tanks of firefighting aircraft provided by this invention is implemented as follows: Step 1: Prepare the geometric parameters of the water tank, including: like Figure 3 The Z-axis heights between the key points shown are: h1 from the highest point of the overflow outlet to the lowest point of the upper wall of the water tank; h2 from the highest point of the overflow outlet to the lowest point of the side wall of the water tank; h3 from the highest point of the overflow outlet to the lowest point of the water inlet; and h from the highest point of the overflow outlet to the lowest point of the bottom. The total water-facing area S of the two water-drawing buckets js The total overflow area of ​​the four overflow outlets is S. ys ; and such Figure 2 The coordinates of each corner point of the four water tanks shown are shown, and the maximum height of the liquid column at each corner point is shown in each direction.

[0031] Step 2: Identify the typical state parameters during the water-drawing process, including the maximum water-drawing speed V.

[0032] Step 3: Based on the law of conservation of mass for incompressible fluids, establish the flow balance equations at the intake and overflow points, and then establish the pressure balance equation at the intake point. Solve the system of equations to obtain the inflow velocity at the intake point, the flow velocity in the overflow pipe, and the dynamic pressure at the overflow point. The specific calculation method is as follows: Once the water tank is full, it's difficult to guarantee that the aircraft will immediately stop drawing water. Therefore, the calculation of the water tank pressure should consider the simultaneous occurrence of drawing and overflow. Let the overflow velocity be V2. At this time, the inflow at the draw port will also be subject to the back pressure of the overflow, changing the inflow velocity to V3 (neglecting pressure loss within the pipe). According to the law of conservation of mass for incompressible fluids, the following equation holds:

[0033] The water flow pressure at the overflow outlet is:

[0034] The pressure difference at the water inlet is:

[0035] The pressure balance equation at the water intake is:

[0036] Combining equations (2) to (5), we can obtain:

[0037] Step 4: Calculate the pressure difference ΔP1 at the top wall of the water tank during water intake and overflow, the pressure difference ΔP2 at the bottom of the side wall, and the pressure difference ΔP at the bottom of the middle partition plate, based on the calculation results in Step 3.

[0038]

[0039]

[0040] n is the maximum maneuver load factor; This concludes the calculation of water tank pressure during the water intake and overflow process.

[0041] Step 5: Based on the aircraft's mission requirements and flight characteristics, identify the longitudinal, transverse, and lateral load coefficients of each water tank and the corner points where the maximum water pressure of each water tank occurs during the aircraft's maneuvers in the air, water takeoff after water intake, and lateral swaying.

[0042] Key aerial maneuvers to monitor include, but are not limited to: negative 1g symmetrical maneuvers, roll maneuvers, water takeoffs after water intake, flight over fire zones, and lateral swaying of water tanks.

[0043] When the aircraft performs a negative 1g symmetrical maneuver, without considering lateral and longitudinal load coefficients, the maximum water pressure in water tanks I / II occurs at corner point D3 / B1, and the maximum water pressure in water tanks III / IV occurs at corner point C4 / A2.

[0044] When the aircraft performs a symmetrical pitch maneuver, the normal load factor is the limiting load factor, there is a longitudinal load factor nx, and the lateral load factor is not considered. The maximum water pressure of water tanks I / II occurs at corner point b3 / d1, and the maximum water pressure of water tanks III / IV occurs at corner point b4 / d2.

[0045] When the aircraft performs a roll maneuver, the normal load factor is taken as 2 / 3n. zmax There is a lateral load factor, and the longitudinal load factor is assumed to be 0. The maximum water pressure in water tanks I and II occurs at corner points a3 / b3 / c1 / d1, and the maximum water pressure in water tanks III and IV occurs at corner point b4 / d2.

[0046] When the aircraft completes water intake and takes off from the water tank, it is assumed that the water level in the tank is at its maximum static height, reaching the highest point of the overflow outlet, with no back pressure from overflow. The normal load factor is taken as the normal inertial load factor for takeoff. There is a longitudinal load factor, but the lateral load factor is not considered. The maximum water pressure in tanks I / II occurs at corner point b3 / d1, and the maximum water pressure in tanks III / IV occurs at corner point b4 / d2.

[0047] When an aircraft is flying over a fire, four scenarios are considered: one water tank, two water tanks, three water tanks, and four water tanks. The maximum gust load factor under these four scenarios is taken as the normal load factor, while the longitudinal and lateral load factors are not considered.

[0048] For the lateral swaying of the water tank, the lateral overload is considered according to the lateral limit overload, without considering the longitudinal and normal load coefficients.

[0049] Step Six: Using the longitudinal and transverse load coefficients obtained in Step Five and the maximum height of the liquid column in each direction at the corner where the maximum water pressure occurs in each water tank, calculate the maximum water pressure in each water tank. The calculation formula is as follows:

[0050] Step 7: Summarize the water tank pressure load results during the water tank sump process, water-carrying flight, and lateral shaking, and extract the limiting water pressure of each key part of the water tank, including: the maximum limiting pressure of the upper wall plate of each water tank and the maximum limiting pressure of the bottom of the partition of each water tank.

[0051] Step 8: Linearize the maximum limiting pressure from the upper wall plate of each water tank to the maximum limiting pressure at the bottom of the water tank partition, and draw a diagram showing the water pressure distribution in each water tank, as shown below. Figure 4 As shown, this is applied to the static strength verification of water tanks.

[0052] Example 2. An engineering calculation method for the water pressure load of a fire-fighting aircraft water tank, see [link to example]. Figures 1-5 For the four-unit water tank of a firefighting aircraft, the following scenarios were addressed: water intake and flight. During water intake, the parameters of each state during the water intake process were first determined, and a water intake-overflow balance equation system was established. The water intake-overflow pressure difference of each wall panel was calculated to obtain the maximum water pressure at the top / bottom of each wall panel during water intake. During flight, based on the water tank's geometric parameters / corner parameters, typical maneuvering conditions, and limiting maneuvering load coefficients, the location of the maximum water pressure under each maneuvering condition was determined. By calculating the maximum water pressure of the water tank wall panels under each maneuvering condition, the maximum water pressure at the top / bottom of the water tank wall panels during flight was obtained. Finally, a water pressure distribution model was established by combining the maximum water pressure at the top / bottom of the water tank under both water intake and flight conditions for the structural strength design of the water tank.

[0053] The engineering calculation method for water pressure load on the water tank of the fire-fighting aircraft includes the following steps: Step 1: Determine the typical geometric parameters of the water tank and extract the typical state parameters for water intake, flight process, and lateral swaying. Step 2: For the water intake situation, establish a set of water intake-overflow balance equations when the water tank is full, and calculate the water intake-overflow pressure difference of each wall panel; Step 3: For each maneuver involving water flight, determine the maximum load coefficient of each water tank in each direction, and calculate the maximum water pressure on the water tank wall for each maneuver. Step 4: Combining the calculation results from Step 2 and Step 3, determine the limiting water pressure of each key part of the water tank and establish a water pressure distribution model for each water tank.

[0054] In step 1, the geometric parameters of the water tank include: The Z-axis height h1 from the highest point of the overflow outlet to the lowest point of the upper wall panel of the water tank; the Z-axis height h2 from the highest point of the overflow outlet to the lowest point of the side wall panel of the water tank; the Z-axis height h3 from the highest point of the overflow outlet to the lowest point of the water intake outlet; the Z-axis height h from the highest point of the overflow outlet to the lowest point of the bottom; the total water-facing area S of the two water intake hoppers. js The total overflow area of ​​the four overflow outlets is S. ys V represents the maximum water-drawing speed.

[0055] It is necessary to define each corner point of the water tank's exterior and obtain the parameters of each corner point of the four water tank exteriors to facilitate pressure difference calculation.

[0056] In step 1, the flight process includes flight with water, which includes but is not limited to negative 1g symmetrical maneuvers, symmetrical pitch maneuvers, roll maneuvers, takeoff from water, flight over fire, and lateral swaying.

[0057] When flying over a fire, it is necessary to distinguish between four scenarios: one water tank, two water tanks, three water tanks, and four water tanks, and to consider each scenario separately.

[0058] For the flight process, the longitudinal, lateral, and side limiting maneuver load coefficients and the corner points where the maximum water pressure of each water tank occurs are determined based on the characteristics of each maneuver. In step 2, based on the water-drawing characteristics of the water tank, the entire water-drawing process includes the water-drawing situation before the water tank is full and the overflow situation after the four water tanks are full. The main consideration is to calculate the water pressure load of the water tank when water-drawing and overflow occur simultaneously after the water tank is full.

[0059] After the water tank is full, it is difficult to guarantee that the aircraft will stop drawing water immediately. Therefore, the simultaneous occurrence of drawing and overflow should be considered when calculating the water pressure in the tank. Let the overflow velocity be V2. At this time, the inflow at the water inlet will also be subject to the back pressure of the overflow, and the inflow velocity will become V3 (ignoring the pressure loss in the pipe). According to the law of conservation of mass of incompressible fluids, the following equation (1) holds. (1) The water flow pressure at the overflow outlet is (2) The pressure difference at the water inlet is (3) The pressure balance equation at the water intake is: (4) Combining equations (2) to (5), we can obtain: (5) According to the following formulas (6) to (8), the pressure difference ΔP1 of the upper wall plate, the pressure difference ΔP2 of the bottom of the side wall plate, and the pressure difference ΔP of the bottom of the middle partition plate during water intake and overflow are calculated.

[0060] (6) (7) (8) n is the maximum maneuver load factor; In step 3, the formula for calculating the maximum water pressure on the tank wall panel under each case of water-borne flight is as follows: (9) In equation (9), P is the maximum water pressure on the tank wall, ρ is the incoming flow density, and n x n y n z These are the maximum maneuver load factors for the aircraft's lateral, longitudinal, and horizontal directions, respectively, h. x h y h z The maximum height of the liquid column along the x, y, and z directions is the point where the maximum water pressure in the water tank occurs.

[0061] In step 4, the water pressure load results of the key parts of the water tank upper wall panel, side wall panel and partition obtained in steps 2 and 3 are summarized, and the water pressure results of each key part of the water tank are selected to limit the water pressure.

[0062] When checking the static strength of each water tank, a water pressure distribution model for each water tank is established, taking into account the linear change of pressure from the upper wall plate to the bottom of its partition.

[0063] The above description is merely a specific embodiment of the present invention, but 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 technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for engineering calculation of water ballast load of a water tank of a fire-fighting aircraft, characterized in that, The method comprises the following steps: S1: determining typical geometric parameters of the water tank and extracting typical state parameters of the water tank in the process of water pumping and flight; S2: establishing a water pumping-overflowing balance equation set of the water tank in a full water state for water pumping, and calculating water pressure differences of each wall plate in water pumping-overflowing; S3: determining maximum load coefficients of each water tank in each direction for each flight condition, and calculating maximum water pressure of the water tank in each flight condition; S4: combining calculation results of S2 and S3, determining limiting water pressure of each key position of the water tank, and establishing a water pressure distribution model of each water tank.

2. The method according to claim 1, wherein, In S1, the typical geometric parameters of the water tank include: Z-direction height h1 from the highest point of the overflow port to the lowest point of the upper wall plate of the water tank; Z-direction height h2 from the highest point of the overflow port to the lowest point of the side wall plate of the water tank; Z-direction height h3 from the highest point of the overflow port to the lowest point of the water scooping port; Z-direction height h from the highest point of the overflow port to the lowest point of the bottom; total water receiving area S of the two water scooping buckets js total overflow area S of the four overflow ports ys ; maximum water scooping speed V.

3. The method according to claim 2, wherein, In S1, the flight process includes water flight, and the water flight includes negative 1g symmetrical maneuver, symmetrical pitching maneuver, rolling maneuver, water take-off, fire field flight and lateral swing.

4. The method according to claim 3, wherein, The fire field flight needs to be considered in four conditions of one water tank with water, two water tanks with water, three water tanks with water and four water tanks with water.

5. The method according to claim 3, wherein, For the flight process, longitudinal, lateral and lateral limiting maneuver load coefficients and the maximum water pressure appearing angle point of each water tank are determined according to the characteristics of each maneuver.

6. The method of claim 2, wherein, In S2, according to the characteristics of the water tank, the whole water pumping process includes water pumping before the water tank is full and overflowing after four water tanks are full, and water tank water pressure load when water pumping and overflowing occur at the same time after the water tank is full is calculated.

7. The method according to claim 6, wherein, The water tank water pressure load when water pumping and overflowing occur at the same time after the water tank is full is calculated as follows: Let the overflowing speed be V2, the inflow speed be V3, and the following formulas be established: The water flow dynamic pressure at the overflowing port is The pressure difference at the water pumping port is The pressure balance equation at the water pumping port is By combining the above formulas, the following is obtained: According to the following three formulas, the pressure difference ΔP1 of the upper wall plate of the water tank, the pressure difference ΔP2 of the bottom of the side wall plate and the pressure difference ΔP of the bottom of the middle partition plate during water pumping-overflowing are: ； n is the maximum maneuver load coefficient.

8. The method of claim 1, wherein, In S3, the calculation formula of the maximum water pressure of the water tank wall plate in each water flight condition is: Where P is the maximum water pressure of the tank wall, p is the incoming flow density, n x , n y , n z are the maximum maneuver load coefficients of the aircraft in the lateral, lateral, and longitudinal directions, h x , h y , h z are the maximum heights of the liquid column in the x, y, and z directions at the angle point where the maximum water pressure of the tank occurs.

9. The method of claim 1, wherein, In S4, all water pressure load results of the key positions of the upper wall plate, the side wall plate and the partition plate of the water tank are summarized, and the limiting water pressure results of each key position of the water tank are selected; When the static strength of each water tank is checked, the pressure is considered to change linearly from the upper wall plate to the bottom of the corresponding partition plate, and a water pressure distribution model of each water tank is established.

Images