A method for compiling wave taxiing load spectrum for seaplanes

Abstract

This invention discloses a method for compiling a wave taxiing load spectrum for seaplanes: The method involves determining the center of gravity acceleration data from the water tank test data for each mission segment based on the overall and structural parameters of the aircraft; comparing the time history curve of the center of gravity acceleration data with the time history curve of the aircraft's pitch angle to extract the stable segment data for each mission segment; performing power spectral density analysis on the acceleration overload / overload increment in the stable segment data to obtain the acceleration characteristic frequency band; determining the cutoff frequency based on the acceleration characteristic frequency band and filtering the stable segment data; performing cumulative exceedance statistics on the filtered stable segment data to obtain the cumulative exceedance curve for each mission segment; obtaining the cumulative exceedance curve for each mission segment in actual aircraft water surface operations based on the time ratio of each mission segment and similarity criteria; and forming the aircraft wave taxiing equivalent spectrum according to the damage equivalence criterion. This invention solves the technical problem of compiling and verifying the fatigue load spectrum for seaplanes during water skidding.

Description

Technical Field

[0001] This invention belongs to the field of fatigue strength analysis technology for aircraft structures, and relates to a method for compiling wave taxiing load spectrum for seaplanes. Background Technology

[0002] Seaplanes not only have to bear the inherent aerodynamic loads of ordinary land-based aircraft, but also the hydrodynamic loads brought about by the aircraft taking off, landing and sailing on the water. The load conditions are diverse and the load distribution is complex. In particular, the pressure on the bottom of the ship is different from the tensile load on the surface of the land-based aircraft.

[0003] Currently, the compilation of surface load spectra is in the theoretical exploration stage and has not been experimentally verified. Therefore, the compilation of surface load spectra for seaplanes faces problems such as a lack of design theory and research methods. The surface load spectrum is the main load input for fatigue and damage tolerance assessment of seaplanes, and the accuracy of compiling the surface load spectrum directly affects the accuracy and reliability of aircraft structural fatigue life prediction. Summary of the Invention

[0004] The purpose of this invention is to propose a method for compiling wave taxiing load spectra for seaplanes. This invention solves the technical challenge of compiling and verifying fatigue load spectra for seaplanes by conducting research on water surface load spectra.

[0005] The technical solution of this invention is: a method for compiling wave taxiing load spectra of seaplanes, comprising:

[0006] Step 1: Determine the center of gravity acceleration data for each mission segment's water tank test data based on the overall and structural parameters of the aircraft;

[0007] Step 2: Compare the time history curve of the center of gravity acceleration data with the time history curve of the body pitch angle, and extract the stable segment data of each mission segment.

[0008] Step 3: Perform power spectral density analysis on the acceleration overload / overload increment in the stable segment data to obtain the acceleration characteristic frequency band;

[0009] Step 4: Determine the cutoff frequency based on the acceleration characteristic frequency band, and filter the stable segment data;

[0010] Step 5: Calculate the cumulative exceedance count for the filtered stable segment data to obtain the cumulative exceedance curve for each task segment;

[0011] Step 6: Based on the time ratio of each task segment and the similarity criterion, obtain the cumulative overtaking curve for each task segment of the actual aircraft surface operation;

[0012] Step 7: Generate the equivalent spectrum of body wave gliding according to the damage equivalence criterion.

[0013] In step one of the aforementioned method for compiling the wave taxiing load spectrum of a seaplane, the overall and structural parameters of the aircraft include: the speed, pitch angle, weight, expected duration of action, and overload / overload increment data of the test model's center of gravity for each wave taxiing mission segment.

[0014] In step one of the aforementioned method for compiling the wave gliding load spectrum of seaplanes, for firefighting missions, after landing on the water, the mission segments are as follows: water landing gliding → water scooping gliding → takeoff water gliding.

[0015] In step one of the aforementioned method for compiling the wave gliding load spectrum of seaplanes, for a rescue mission, after landing on the water, the mission segments are as follows: water landing gliding → water surface rescue → takeoff gliding.

[0016] In the aforementioned method for compiling the wave taxiing load spectrum of seaplanes, step one is as follows:

[0017] Based on the weight and center of gravity state of the waterborne mission segment in a typical seaplane mission profile, the corresponding model's center of gravity overload data and pitch angle data for the water tank test are determined. The similarity relationship between the model and the actual aircraft follows the principle that the corresponding lengths of the model and the actual aircraft are proportional; at corresponding instants, the velocities at corresponding points have the same direction and are proportional in magnitude, and during flow around the object, the streamlines and acceleration distributions are similar; at corresponding instants, the forces at corresponding points have the same direction and are proportional in magnitude; inertial forces, mass forces, pressure surface forces, and viscous surface forces are based on the Froude similarity criterion. Calculate, where: For model speed, Model length.

[0018] In the aforementioned method for compiling the wave taxiing load spectrum of seaplanes, step five is as follows: the time history curve of the center of gravity overload increment of the response generated by performing a single seaplane mission is divided by the 0g horizontal line to form 2n or 2n-1 closed loops of the center of gravity overload response; the maximum positive overload increment and the maximum negative overload increment in each closed loop are statistically analyzed.

[0019] In step six of the aforementioned method for compiling the wave taxiing load spectrum of seaplanes, the cumulative exceedance curve is as follows:

[0020] ,

[0021] in, For overload increment, The cumulative number of exceedances is represented by a and b, which are both fitting parameters.

[0022] In step seven of the aforementioned method for compiling the wave taxiing load spectrum of seaplanes, the equivalent load in the equivalent spectrum... Equivalent load cycle count Specifically as follows:

[0023] Equivalent load

[0024] Equivalent load cycle number , ,

[0025] a and b are the fitting parameters; S is the slope parameter of the stress-life curve; K is the number of flights.

[0026] Beneficial Effects: This invention decomposes the typical mission profile of seaplanes into four characteristic mission segments: water taxiing, water scooping taxiing, takeoff water taxiing, and water rescue, establishing a multi-condition load mapping system. It employs a collaborative analysis method combining scaled-down model pool test data and real aircraft similarity criteria to generate overload / overload increment cumulative exceedance curves for each level of the real aircraft's water taxiing, water scooping taxiing, takeoff water taxiing, and water rescue mission segments. Multi-condition data fusion is performed using flight mission time weighting to construct a weighted comprehensive load spectrum. The equivalent spectrum for each mission segment of seaplane operations is generated using the principle of damage equivalent conversion. Compared to traditional theoretical calculation methods, this invention, driven by physical test data, effectively solves the problem of characterizing the random characteristics of water surface loads, significantly improving the engineering reliability of the load spectrum. Attached Figure Description

[0027] Figure 1 This is an overall framework diagram of a method for compiling wave taxiing load spectra for seaplanes;

[0028] Figure 2 This is a method for compiling wave taxiing load spectrum for seaplanes - a comparison chart of the time history curve of the center of gravity overload of a seaplane model at 20 km / h and 0.5 m wave height with the time history curve of the body pitch angle;

[0029] Figure 3 This is a method for compiling wave taxiing load spectrum of a seaplane - power spectral density analysis diagram of the center of gravity overload of a seaplane at a speed of 20 km / h and a wave height of 0.5 m;

[0030] Figure 4 This is a schematic diagram of a method for compiling wave taxiing load spectrum of a seaplane - extracting the maximum and minimum values ​​of the closed loop of the center of gravity overload incremental response;

[0031] Figure 5 This is a method for compiling wave taxiing load spectrum for seaplanes - a schematic diagram of the cumulative overtaking curve of a seaplane at a speed of 20 km / h and a wave height of 0.5 m. Detailed Implementation

[0032] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific design details are set forth in the following detailed description to provide a more complete understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setup and method set forth below, but covers any improvements, substitutions, and modifications to the structures, methods, and devices without departing from the spirit of the invention. In the drawings and the following description, any parts not exhaustively described are considered to be common knowledge or conventional practices in the art.

[0033] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0034] Example 1. A method for compiling wave taxiing load spectrum of a seaplane, comprising the following steps:

[0035] Step 1: Determine the center of gravity overload data for each mission segment based on the overall and structural parameters of the aircraft;

[0036] Step 2: By comparing the center of gravity overload time history curve with the body pitch angle time history curve, the center of gravity overload data of the stable section of the test hydroplaning section is obtained.

[0037] Step 3: Perform power spectral density analysis on the centroid overload / overload increment data in the stable segment to obtain the characteristic frequency band of centroid acceleration;

[0038] Step 4: Determine the cutoff frequency based on the obtained center of gravity overload / overload increment characteristic frequency band, and filter the stable segment data;

[0039] Step 5: Calculate the cumulative exceedance count for the filtered stable segment data to obtain the cumulative exceedance curve for each task segment;

[0040] Step Six: Based on the time proportions of each task segment and the similarity criteria, obtain the cumulative overtaking curves for each task segment of the actual water surface operation. Perform linear fitting on the curve data to obtain the curves for each task segment of the water skiing operation. ,in For overload increment, This represents the cumulative number of times the ...

[0041] Step 7: Calculate the equivalent damage curves for each task segment of the actual aircraft's surface operation using the damage equivalence criterion to form the aircraft's wave gliding equivalent spectrum; the derivation process is as follows:

[0042] Equivalent load Δg eqThe size selection represents the payload that occurs once per flight. It is determined by accumulating the payloads of each level that occur once per flight, and then calculating their weighted average value using the probability of occurrence as the weight:

[0043] ………………………………………(1)

[0044] The number of cycles N of the equivalent load eq This is the ratio of the total damage under one flight load spectrum to the damage under one equivalent load in this situation:

[0045] ……………………………………(2)

[0046] In the formula, S is the slope parameter of the stress-life curve;

[0047] Linear equation for the load spectrum of flight K:

[0048] ……………………………………………(3)

[0049] In the formula: a and b are constants of the load spectrum line of flight K;

[0050] Then we have:

[0051] Equivalent load Δg eq :

[0052] …………………………………(4)

[0053] Equivalent load cycle number N eq :

[0054] ……………………………(5)

[0055] ……………………………………(6).

[0056] Example 2. A method for compiling wave taxiing load spectrum of a seaplane, comprising the following steps:

[0057] Step 1: Determine the center of gravity overload data (i.e., center of gravity acceleration data) for each mission segment's water tank test based on the overall and structural parameters of the aircraft.

[0058] Based on the weight and center of gravity of the seaplane in the typical mission profile, the overload data and pitch angle data of the corresponding model in the water tank test are determined. The similarity relationship between the model and the actual aircraft follows that the corresponding lengths of the model and the actual aircraft are proportional; at corresponding instants, the velocities at corresponding points have the same direction and are proportional in magnitude, and the streamlines and acceleration distributions are similar during flow around the object; at corresponding instants, the forces at corresponding points have the same direction and are proportional in magnitude, and the inertial force, mass force, pressure surface force, and viscous surface force are similar according to the Froude similarity criterion. In the formula: For model speed, Model length.

[0059] Step 2: Based on the comparison between the center of gravity overload time history curve and the body pitch angle time history curve, extract the center of gravity overload / overload increment data of the stable section of the test hydroplaning section;

[0060] Figure 2 A comparison graph is presented of the time history curves of center of gravity overload and body roll angle of a seaplane at a speed of 20 km / h and a wave height of 0.5 m. The overload / overload increment data of the center of gravity are extracted during the time when the roll angle is stable at around 0.5°.

[0061] Step 3: Perform power spectral density analysis on the acceleration overload increment of the stable segment data to obtain the characteristic frequency band of centroid overload / overload increment;

[0062] Figure 3 The power spectral density analysis diagram of the center of gravity overload of a seaplane at a speed of 20 km / h and a wave height of 0.5 m is given.

[0063] Step 4: Determine the cutoff frequency based on the center of gravity overload / overload increment characteristic frequency bands with different rates and wave heights under each task segment obtained in Step 3, and filter the stable segment data.

[0064] Step 5: Calculate the cumulative exceedance count for the filtered stable segment data to obtain the cumulative exceedance curve for each task segment;

[0065] The response generated from a single waterborne mission is divided into 2n or 2n-1 closed loops of center of gravity overload response by dividing the time history curve of the center of gravity overload increment by the 0g horizontal line. The maximum and minimum values ​​in each closed loop are extracted, namely the maximum positive overload increment and the maximum negative overload increment, resulting in n positive overloads and n or n-1 negative overloads.

[0066] Figure 4 A schematic diagram is provided for extracting the maximum and minimum values ​​of the closed loop of the centroid overload incremental response;

[0067] By observing these 2n or 2n-1 overload increment data, the range of overload increment is determined, that is, the maximum possible positive / negative overload increment. The overload is divided into several small segments, and the corresponding occurrence frequency is counted.

[0068] Table 1 illustrates the number of times the statistical center of gravity overload increment exceeded the limit;

[0069] Table 1

[0070]

[0071] A cumulative overload increment overload curve with symmetrical positive and negative overload overload response is formed;

[0072] Figure 5 A schematic diagram of the cumulative overtaking curve of a seaplane at a speed of 20 km / h and a wave height of 0.5 m is given.

[0073] Step Six: Based on the time proportions of each task segment and the similarity criteria, obtain the cumulative overtaking curves for each task segment of the actual water surface operation. Perform linear fitting on the curve data to obtain the curves for each task segment of the water skiing operation. ,in For overload increment, This represents the cumulative number of times the number of times the limit has been exceeded.

[0074] Step 7: Calculate the equivalent damage curves for each task segment of the actual aircraft's surface operation according to the damage equivalence criterion to form the aircraft's wave gliding equivalent spectrum.

[0075] Equivalent load

[0076] Equivalent load cycle number , ,

[0077] a and b are the fitting parameters;

[0078] Equivalent load;

[0079] The equivalent load cycle count.

[0080] This invention decomposes typical seaplane mission profiles into four characteristic mission segments: water taxiing, water scooping taxiing, takeoff water taxiing, and water rescue, establishing a multi-condition load mapping system. It employs a collaborative analysis method combining scaled-down model tank test data with real-aircraft similarity criteria to generate overload / overload increment cumulative exceedance curves for each level of the real-aircraft water taxiing, water scooping taxiing, takeoff water taxiing, and water rescue mission segments. Multi-condition data fusion is performed using flight mission time weighting to construct a weighted comprehensive load spectrum. The equivalent spectrum for each mission segment of seaplane operations is generated using the damage equivalent conversion principle. Compared to traditional theoretical calculation methods, this invention, driven by physical test data, effectively solves the problem of characterizing the stochastic characteristics of water surface loads, significantly improving the engineering reliability of the load spectrum.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for compiling wave taxiing load spectra of seaplanes, characterized in that, include: Step 1: Determine the center of gravity acceleration data for each mission segment's water tank test data based on the overall and structural parameters of the aircraft; Step 2: Compare the time history curve of the center of gravity acceleration data with the time history curve of the body pitch angle to extract the stable segment data of each mission segment. Step 3: Perform power spectral density analysis on the acceleration overload or overload increment in the stable segment data to obtain the acceleration characteristic frequency band; Step 4: Determine the cutoff frequency based on the acceleration characteristic frequency band, and filter the stable segment data; Step 5: Calculate the cumulative exceedance count for the filtered stable segment data to obtain the cumulative exceedance curve for each task segment; Step 6: Based on the time ratio of each task segment and the similarity criterion, obtain the cumulative overtaking curve for each task segment of the actual aircraft surface operation; Step 7: Generate the equivalent spectrum of body wave gliding according to the damage equivalence criterion.

2. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, In step one, the overall and structural parameters of the aircraft include: the speed, pitch angle, weight, expected duration of action, and overload or overload increment data of the test model's center of gravity during each wave taxiing mission.

3. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, In step one, for firefighting missions, after landing on the water, the mission segments are as follows: water landing and gliding → water scooping and gliding → takeoff and water skiing.

4. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, In step one, for the rescue mission, after landing on the water, the mission segments are as follows: water landing and gliding → water rescue → take-off and water skiing.

5. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, Step one is as follows: Based on the weight and center of gravity of the waterborne mission section of a typical seaplane mission profile, determine the corresponding model water tank test center of gravity overload data and pitch angle data. The similarity relationship between the model and the real aircraft follows that the corresponding length of the model and the real aircraft are in the same proportion; at the corresponding instant, the velocity directions at the corresponding points are the same, the magnitudes are in the same proportion, and the streamlines and acceleration distributions are similar when flowing around the object. At the corresponding instant, the forces acting at the corresponding points are in the same direction and have the same magnitude proportion; Inertial forces, mass forces, pressure surface forces, and viscous surface forces are based on the Froude similarity criterion. Calculate, where: For model speed, Model length.

6. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, Step 5 is as follows: Divide the time history curve of the center of gravity overload increment of the response generated by performing a water mission by the 0g horizontal line to form 2n or 2n-1 closed loops of the center of gravity overload response; count the maximum positive overload increment and the maximum negative overload increment in each closed loop.

7. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, In step six, the cumulative exceedance curve is as follows: ， in, For overload increment, The cumulative number of exceedances is represented by a and b, which are both fitting parameters.

8. The method for compiling the wave taxiing load spectrum of a seaplane according to claim 1, characterized in that, In step seven, the equivalent loading in the equivalent spectrum Equivalent load cycle count Specifically as follows: Equivalent load , Equivalent load cycle number , , a and b are fitting parameters; S is the slope parameter of the stress-life curve; K is the number of flights; This is an overload increment.

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