A control method for periodic oscillation of a biomimetic hydrofoil

Abstract

The application belongs to the technical field of underwater propeller, and discloses a control method for periodic swing of bionic hydrofoil, which controls the hydrofoil to swing according to the following periodic swing rule: each swing period of the periodic swing rule is composed of two half periods which are mirror-symmetric about the center position; each half period is sequentially composed of a recovery stroke and a power stroke, wherein the ratio of the maximum angular velocity of the power stroke to the maximum angular velocity of the recovery stroke, i.e. the speed ratio, satisfies the application. Through the provided periodic motion rule, the rigid impact is eliminated, the residence time of the hydrofoil at the center position is prolonged, the propulsion efficiency and the forward distance are effectively improved, and reliable technical support is provided for the engineering propulsion of rigid hydrofoil.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underwater propeller, in particular to a control method of periodic oscillation of bionic hydrofoil. BACKGROUND

[0002] With the development of bionics, the concept of bionic propulsion is gradually applied to underwater propulsion research. People draw inspiration from the efficient propulsion mode of fish evolution, giving birth to bionic hydrofoil propulsion technology. This technology has become a research hotspot due to its small resistance, low noise, high efficiency, and good maneuverability. Domestic and foreign scholars have carried out extensive research around it. Due to the complexity and difficulty of controlling flexible hydrofoil movement, rigid hydrofoil with simple movement and easy control is often chosen as the research carrier in engineering practice. However, compared with mature propeller propulsion, hydrofoil propulsion research started relatively late, and a unified mathematical model has not yet been formed. The key factors affecting the propulsion performance and the rules are not clear.

[0003] At present, the oscillation law used for hydrofoil propulsion research is mostly based on the sine motion law control, that is, the angular displacement of the hydrofoil oscillation changes in the form of a sine function, and the angular velocity changes in the form of a cosine function. Although the sine oscillation law is simple in form and easy to implement, it cannot provide differentiated angular velocity and angular displacement control strategies for the functional requirements of the hydrofoil in different stages (such as the power stage for generating main propulsion force and the recovery stage for low resistance reset) during propulsion. This not only limits the improvement of propulsion efficiency, but also has problems such as rigid impact and excessive energy consumption. Therefore, there is an urgent need for a new control method of periodic oscillation of bionic hydrofoil to break through the bottleneck of existing technology. SUMMARY

[0004] The purpose of the present application is to provide a control method of periodic oscillation of bionic hydrofoil to solve the problems existing in the above-mentioned sine motion law.

[0005] The embodiments of the present application can be implemented by the following technical solutions:

[0006] A control method of periodic oscillation of bionic hydrofoil, the hydrofoil is controlled to oscillate according to the following periodic oscillation law:

[0007] Each oscillation period of the periodic oscillation law Composed of two half periods that are mirror symmetric about the center position;

[0008] Each of the half periods is composed of a recovery stroke and a power stroke in sequence, the recovery stroke refers to the process of the hydrofoil oscillating from the center position to the limit position to prepare for the next power stroke, and the power stroke refers to the process of the hydrofoil oscillating from the limit position to the center position to generate thrust;

[0009] Wherein, the maximum angular velocity of the power stroke is greater than the maximum angular velocity of the recovery stroke the ratio of the length of the recovery stroke to the length of the power stroke satisfies: .

[0010] Further, the periodic oscillation law is configured such that the absolute value of the angular velocity is 0 when the hydrofoil oscillates to the center position.

[0011] Further, the power stroke time and the recovery stroke time satisfy the following relationship: .

[0012] Further, the recovery stroke and the power stroke each include, in order, an acceleration phase, a constant speed phase, and a deceleration phase.

[0013] Further, the durations of the acceleration phase, the constant speed phase, and the deceleration phase in the recovery stroke and the power stroke are the same, and each is , and .

[0014] Further, the recovery stroke and the power stroke each include, in order, a uniform acceleration phase, a constant speed phase, and a uniform deceleration phase, and .

[0015] Further, the recovery stroke time satisfies: ; the angular acceleration of the recovery stroke satisfies: ; in the formula, is the oscillation amplitude.

[0016] Further, the angular velocity function of the Nth period (N = 1, 2, 3,...) of the periodic oscillation law satisfies:

[0017] When , in the uniform acceleration phase of the first half of the recovery stroke, the angular velocity linearly increases from 0 to at an angular acceleration of ;

[0018] When , in the constant speed phase of the first half of the recovery stroke, the angular velocity is kept constant at ;

[0019] When , in the uniform deceleration phase of the first half of the recovery stroke, the angular velocity linearly decreases from to 0 at an angular acceleration of ;

[0020] When , in the uniform acceleration phase of the first half of the power stroke, the angular velocity linearly increases from 0 to linearly increases from 0 to the maximum angular velocity of the power stroke ;

[0021] When , in the uniform speed stage of the first half of the power stroke, the angular velocity remains the maximum angular velocity of the power stroke uniform motion;

[0022] When , in the uniformly decelerating stage of the first half of the power stroke, the angular velocity linearly increases from to 0 at an angular acceleration of .

[0023] Further, the value of the speed ratio satisfies .

[0024] Further, the value of the swing amplitude satisfies ; the value of the maximum angular velocity of the power stroke satisfies .

[0025] The embodiment of the present application provides a control method for periodic swing of a bionic hydrofoil, which has at least the following beneficial effects:

[0026] By using the non-sine and segmented control swing law provided by the present application, the rigid impact during starting of the existing sine swing law can be completely eliminated; by setting the speed ratio > 1 and controlling the angular velocity at the end of the power stroke to be the lowest, the hydrofoil can be kept in the center position region with the minimum fluid resistance for a long time, and the effective propulsion time is significantly increased. Under the same period and swing amplitude, the average propulsion speed and forward distance per unit period of the present method can be effectively improved compared with the conventional sine swing law. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FIG. 1 is a schematic diagram of a wing propulsion device model;

[0028] Figure 2 FIG. 2 is a schematic diagram of swing of a hydrofoil;

[0029] Figure 3 FIG. 3 is a comparison schematic diagram of the swing law provided by the present application and the sine swing law of the prior art;

[0030] Figure 4 FIG. 4 is a comparison schematic diagram of the speed time history of the swing law of the embodiment 1 of the present application and the sine swing law of the comparative example 1;

[0031] Figure 5 FIG. 5 is a comparison schematic diagram of the displacement time history of the swing law of the embodiment 1 of the present application and the sine swing law of the comparative example 1; and

[0032] Figure 6 This is a schematic diagram of the vorticity cloud diagram of the oscillation law in Embodiment 1 of this application changing with time, where (a) is the initial t=0, (b) is t=0.75T, (c) is t=0.93T, (d) is t=1.00T, and (e) is t=1.15T;

[0033] Figure 7 The diagram shows the change of vorticity cloud over time for the sinusoidal oscillation law in Comparative Example 1. (a) is the initial time t=0, (b) is the time t=0.75T, (c) is the time t=0.93T, (d) is the time t=1.00T, and (e) is the time t=1.15T. Detailed Implementation

[0034] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0035] First, the oscillation law of biomimetic hydrofoils in existing technologies is introduced. In existing technologies, the oscillation of biomimetic hydrofoils is mostly controlled by sinusoidal motion law, such as... Figure 3 As shown by the dashed line, the angular displacement of the hydrofoil's oscillation changes according to the sine function law described in equation (1), and its angular velocity changes according to the cosine function law described in equation (2). As described in the background art, although the sine motion law is simple, it has obvious defects: First, an angular velocity is required when the sine oscillation starts, that is, the angular velocity changes abruptly when starting, which easily generates rigid impact and affects the service life of the hydrofoil; Second, the angular velocity at the center position during the sine oscillation is the largest in the entire cycle, so the hydrofoil stays at the center position for a very short time, and the resistance encountered by the hydrofoil's forward motion increases rapidly with the increase of the angle between the hydrofoil and the forward direction, thus greatly reducing the propulsion efficiency.

[0036] (1);

[0037] (2);

[0038] In the formula, The frequency of hydrofoil oscillation.

[0039] Therefore, this application provides a biomimetic hydrofoil periodic oscillation control method to solve the problems existing in the oscillation law of hydrofoils in the prior art.

[0040] To facilitate a better understanding of this invention, the following settings and definitions are first established:

[0041] Combination Figure 1 Schematic diagram of the wing propulsion device model and Figure 2Fig. 1 is a schematic diagram of the oscillation of a hydrofoil, with the forward direction of the propulsion device as the negative direction of the x-axis, the horizontal direction perpendicular to the x-axis as the y-axis, and the vertical direction perpendicular to the xy plane as the z-axis;

[0042] The degrees of freedom of the hydrofoil in a specific motion plane are divided into two categories: the overall translation of the propulsion device and the relative rotation around a specific axis. Taking the xz plane as an example, the degrees of freedom of the hydrofoil include the movement of the propulsion device along the x-axis direction (the positive direction of translation is consistent with the forward direction of the propulsion device, i.e., the negative direction of the x-axis) and the rotation around the y-axis (when looking from the negative direction of the y-axis to the positive direction, the counterclockwise rotation of the hydrofoil is the positive direction of rotation). Figure 2 Similarly, when the motion plane is the xy plane, the degrees of freedom of the hydrofoil include the movement of the propulsion device along the x-axis direction (the positive direction of translation is consistent with the overall forward direction) and the rotation around the z-axis (when looking from the positive direction of the z-axis to the negative direction, the counterclockwise rotation of the hydrofoil is the positive direction of rotation).

[0043] The center position is defined as the reference position of the angular displacement of the hydrofoil, at which the chord direction of the hydrofoil is parallel to the forward direction of the carrier.

[0044] The limit position is defined as the maximum angular displacement position reached by the hydrofoil when it swings from the center position (angular displacement ) to both sides (clockwise or counterclockwise direction), at which the absolute value of the angular displacement of the hydrofoil is defined as the swing amplitude .

[0045] The power stroke refers to the process of the hydrofoil swinging from the limit position to the center position, which is the stage of generating propulsion force.

[0046] The recovery stroke refers to the process of the hydrofoil swinging from the center position to the limit position away from the center, which aims to reduce resistance and prepare for the next power stroke.

[0047] The initial condition is set as and , i.e., the periodic swing of the hydrofoil starts from the initial time , at which the initial angular velocity is 0, the initial angular displacement is 0, and the hydrofoil is at the center position.

[0048] The mirror symmetry of the motion law refers to the center symmetry of the motion law about the midpoint of the half cycle , i.e., in one cycle , the curve of the motion law (angular velocity function curve and angular displacement function curve) of the hydrofoil in the first half cycle ( to ) is centrally symmetric with the curve in the second half cycle ( to ).​​

[0049] The core of the present application is to provide a specific periodic swing rule different from the sine rule, combined with Figure 3 The specific periodic swing rule is shown by the solid line in the figure, which is: each swing period contains two mirror-symmetric push processes, and each push process is composed of a recovery stroke and a power stroke in turn, that is, it satisfies , wherein is the power stroke time, is the recovery stroke time.

[0050] Further, the maximum angular velocity of the power stroke and the maximum angular velocity of the recovery stroke The ratio of the speed ratio satisfies: By setting , the power stroke completes the propulsion action at a faster speed, improving the propulsion force output efficiency, while the recovery stroke completes the reset action at a slower speed, reducing water flow resistance and energy consumption.

[0051] Further, the swing rule is configured so that when the hydrofoil swings to the center position (θ ), the absolute value of the angular velocity is significantly reduced to 0, and by this means, the effective residence time of the hydrofoil at the center position can be significantly prolonged, at which time the hydrofoil chord length is parallel to the forward direction, and the disturbance resistance is reduced to the lowest. It should be noted that due to the existence of control errors in the actual driving system (such as motor response delay, sensor precision limitation), the angular velocity at the center position may not be strictly 0, but the case where the absolute value of the angular velocity tends to 0 still meets the design goal of the swing rule and belongs to the protection scope.

[0052] In some preferred embodiments, the speed ratio is in the range of 2-8, when is too large, as can be seen from , the maximum angular velocity of the power stroke will increase significantly, and the power stroke time will be greatly shortened, and combined with the acceleration derivation relationship (the power stroke angular acceleration is proportional to ), therefore, too large will cause the power stroke angular acceleration to rise sharply, exceeding the rated output capacity of the driving motor; when it is too small, the speed difference between the power stroke and the recovery stroke is not enough, and are close, and The gap is narrowed, and the power stroke cannot form a concentrated propulsion force output stage, the hydrofoil stays in the center position for a short time, and the performance difference with the traditional sinusoidal swing rule is not significant.

[0053] Further, the swing amplitude is preferably selected as follows: When the swing amplitude is too small, the angular acceleration generally increases, which is difficult to achieve in engineering; and when the angle is too large, a reverse phenomenon may occur in stable propulsion.

[0054] Further, the maximum angular velocity of the power stroke is preferably selected as follows: When the value is too large, it is difficult to achieve in engineering; and when the value is less than 80, the contribution of the power stroke to the thrust is insufficient to compensate for the loss of thrust due to the increase in the maximum angular velocity of the recovery stroke, in other words, the contribution of the power stroke to the thrust is decreasing, and the efficiency is also low at this time.

[0055] Further, in some preferred embodiments, the recovery stroke and the power stroke each include an acceleration, constant speed, and deceleration phase, and the time distribution and angular velocity change characteristics of each phase are as follows:

[0056] Recovery stroke: the duration ratio of the acceleration phase is (i.e., the duration is ), the angular velocity starts from 0 and rises to the maximum angular velocity according to a linear law (or a preset acceleration curve); the duration ratio of the constant speed phase is (i.e., the duration is ), the angular velocity remains stable; the duration ratio of the deceleration phase is (i.e., the duration is ), the angular velocity decreases from according to a linear law (or a preset acceleration curve) to 0, and when decreases to 0, the hydrofoil stops at the limit position.

[0057] The time distribution of each phase of the power stroke and the recovery stroke is the same: the duration ratio of the acceleration phase is , the angular velocity starts from 0 and rapidly rises to the maximum angular velocity (because > 1, the angular acceleration in this phase is greater than that in the acceleration phase of the recovery stroke); the duration ratio of the constant speed phase is , the angular velocity remains at a high swing with an angular velocity of to concentrate the propulsion force; the duration ratio of the deceleration phase is , the angular velocity decreases from to 0, and when When the temperature drops to 0, the hydrofoil returns to its center position.

[0058] Furthermore, the time allocation ratios for the above stages satisfy... and Preferably, If this value is too large, the angular acceleration will also be too large, making it difficult to implement in engineering.

[0059] Furthermore, in some preferred embodiments, both the recovery stroke and the power stroke sequentially include three stages: uniform acceleration, uniform speed, and uniform deceleration. In this case, when given... , , and The following relationships can be derived from the above motion laws;

[0060] ; ;

[0061] ; .

[0062] Specifically, the angular velocity function of the Nth period (N=1,2,3…) of the periodic oscillation law satisfies:

[0063] when During the uniform acceleration phase of the recovery stroke in the first half of the cycle, the angular velocity is as follows: The angular acceleration increases linearly from 0 to ;

[0064] when It is in the uniform speed phase of the recovery process in the first half of the cycle, maintaining... It moves at a constant angular velocity;

[0065] when During the uniform deceleration phase of the recovery stroke in the first half of the cycle, the angular velocity is... angular acceleration from Linearly decreasing to 0;

[0066] when During the uniform acceleration phase of the first half of the cycle, the angular velocity is... The angular acceleration increases linearly from 0 to the maximum angular velocity of the power stroke. ;

[0067] when During the uniform velocity phase of the first half of the power stroke, the angular velocity remains at the maximum angular velocity of the power stroke. Uniform motion;

[0068] when During the uniform deceleration phase of the first half of the power stroke, the angular velocity is... angular acceleration from 0 linearly to ;

[0069] The motion law of the second half cycle is mirror-symmetric with the first half cycle about the time point , and the angular velocity variation process is a repetition of the first half cycle but with opposite signs, which is specifically shown as:

[0070] When , the uniform acceleration phase of the recovery stroke in the second half cycle, the angular velocity increases from 0 to with an angular acceleration of ;

[0071] When , the uniform speed phase of the recovery stroke in the second half cycle, the angular velocity keeps a uniform motion with ;

[0072] When , the uniform deceleration phase of the recovery stroke in the second half cycle, the angular velocity decreases from to 0 linearly with an angular acceleration of ;

[0073] When , the uniform acceleration phase of the dynamic stroke in the second half cycle, the angular velocity increases from 0 to with an angular acceleration of ;

[0074] When , the uniform speed phase of the dynamic stroke in the second half cycle, the angular velocity keeps a uniform motion with the maximum angular velocity of the dynamic stroke ;

[0075] When , the uniform deceleration phase of the dynamic stroke in the second half cycle, the angular velocity decreases from to 0 linearly with an angular acceleration of .

[0076] In some specific embodiments, the values of the above-mentioned , , and parameters can be further optimized by the following method: first, preset initial values; then calculate the remaining parameters according to the relationship; then substitute the parameters into the determined angular velocity function for calculation; finally, analyze the thrust, efficiency, average speed, displacement, etc. through CFD simulation, and iteratively optimize the above-mentioned preset parameters until satisfactory results are obtained.

[0077] Embodiment 1

[0078] This embodiment gives a specific operation step of a preferred bionic hydrofoil periodic swing control method, and the specific steps are as follows:

[0079] S1, set the basic periodic oscillation law:

[0080] Each oscillation period Contains two mirror-symmetric push processes, and each push process is composed of a recovery stroke and a power stroke in turn, that is, ;

[0081] Set the maximum angular velocity of the power stroke The ratio of the maximum angular velocity of the recovery stroke The speed ratio Satisfies: ;

[0082] Set the absolute value of the angular velocity of the hydrofoil when it oscillates to the center position (θ ) during the power stroke phase to be 0;

[0083] Set the angular velocity functions of the recovery stroke and the power stroke to each include a uniform acceleration phase (the duration ratio is ), a uniform speed phase (the duration ratio is ), and a uniform deceleration phase (the duration ratio is );

[0084] S2, take , , and as preset parameter values, and calculate other related parameters, the specific calculation process is as follows:

[0085] Take the recovery stroke as an example:

[0086] From ,

[0087] It can be obtained: ;

[0088] Further: ;

[0089] Correspondingly, in the power stroke:

[0090] ; ;

[0091] When , the specific angular velocity function expression is as follows, where N indicates the Nth period (N=1, 2, 3…):

[0092] ,

[0093] When , , The simulation results of the propulsive performance of the hydrofoil are as follows:

[0094] Figure 4 The solid line part shows the time history curve of the advancing speed of the hydrofoil along the x-axis direction when the hydrofoil swings according to the periodic swing rule provided in the present embodiment 1; Figure 5 The solid line part shows the time history curve of the advancing displacement of the hydrofoil along the x-axis direction when the hydrofoil swings according to the periodic swing rule provided in the present embodiment 1; Figure 6 The vortex cloud changes in the advancing process of the hydrofoil when the hydrofoil swings according to the periodic swing rule provided in the present embodiment 1 are shown.

[0095] Comparative Example 1

[0096] The present comparative example 1 adopts the existing sinusoidal motion rule, and keeps the same period and the same swing amplitude as the embodiment 1 The angular velocity function of the swing of the hydrofoil is:

[0097] (unit );

[0098] Figure 4 The solid line part shows the time history curve of the advancing speed of the hydrofoil along the x-axis direction when the hydrofoil swings according to the periodic swing rule provided in the present comparative example 1; Figure 5 The solid line part shows the time history curve of the advancing displacement of the hydrofoil along the x-axis direction when the hydrofoil swings according to the periodic swing rule provided in the present comparative example 1; Figure 7 The vortex cloud changes in the advancing process of the hydrofoil when the hydrofoil swings according to the periodic swing rule provided in the present comparative example 1 are shown.

[0099] By Figure 4 and Figure 5 comparing the embodiment 1 with the comparative example 1, it can be seen that the maximum speed of the hydrofoil advancing under the two swing rules occurs when the hydrofoil swings to the central position, and the average speed of the embodiment 1 reaches 1.40 m / s, which is much higher than the average speed ​The water wing of Example 1 also has a significantly higher forward distance along the x-axis direction than that of Comparative Example 1; it is analyzed that this is due to the fact that the swing law adopted by Example 1 has a very small angular velocity at the central position, and the water wing can stay at the central position for a longer time, at which time the fluid resistance to the forward movement of the water wing is also the smallest, thus the water wing of Example 1 has a larger velocity and displacement distance along the x-axis direction; while the water wing of Comparative Example 1 has a sine swing law with the largest angular velocity at the central position, and the water wing stays at the central position for a very short time, thus the fluid resistance to the forward movement of the water wing increases rapidly as the angle between the water wing and the forward direction increases, thus the water wing of Comparative Example 1 has a limited velocity and displacement distance along the x-axis direction.

[0100] By Figure 6 and Figure 7 Comparing the vortex cloud changes of Example 1 and Comparative Example 1, it can also be seen that according to the two swing laws of Example 1 and Comparative Example 1, the water wing of Example 1 swings to the maximum position at 0.93T, while the water wing of Comparative Example 1 swings to the maximum position at 0.75T; at 1.00T, the water wings of Example 1 and Comparative Example 1 both swing to the central position, at which time the fluid resistance becomes the smallest; at 1.15T, the water wing of Example 1 still stays near the central position, while the water wing of Comparative Example 1 has obviously deviated from the central position, and the fluid resistance to its forward movement also increases significantly due to the deviation, which is consistent with the above Figure 4 and Figure 5 The comparative results are consistent.

[0101] The above detailed description of the specific embodiments of the present application is provided, and those skilled in the art can make some improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also belong to the protection scope of the claims of the present application.

Claims

1. A method for controlling the periodic oscillation of a biomimetic hydrofoil, characterized in that, The hydrofoil is controlled to oscillate according to the following periodic oscillation pattern: Each oscillation cycle of the periodic oscillation pattern It consists of two half-cycles whose motion laws are mirror-symmetric about the central position; Each half-cycle consists of a recovery stroke and a power stroke in sequence. The recovery stroke refers to the process by which the hydrofoil swings from the center position to the extreme position to prepare for the next power stroke. The power stroke refers to the process by which the hydrofoil swings from the extreme position to the center position to generate thrust. Among them, the maximum angular velocity of the power stroke Maximum angular velocity of the recovery stroke ratio satisfy: ; The periodic oscillation pattern is configured such that the absolute value of the angular velocity when the hydrofoil oscillates to the center position is 0. The power stroke time and resumption time The following relationship must be satisfied: ； Both the recovery stroke and the power stroke include three stages in sequence: acceleration, constant speed, and deceleration. The duration of the acceleration, constant speed, and deceleration phases in both the recovery stroke and the power stroke is the same, accounting for the same percentage. , and ; Both the recovery stroke and the power stroke include three stages in sequence: uniform acceleration, uniform speed, and uniform deceleration. ; Resumption of travel time satisfy: ; Angular acceleration for restoring the stroke satisfy: ; In the formula, This represents the amplitude of the swing.

2. The control method according to claim 1, characterized in that, The angular velocity function of the Nth period (N=1,2,3…) of the periodic oscillation law satisfies: when During the uniform acceleration phase of the recovery stroke in the first half of the cycle, the angular velocity is as follows: The angular acceleration increases linearly from 0 to ; when It is in the uniform speed phase of the recovery process in the first half of the cycle, maintaining... It moves at a constant angular velocity; when During the uniform deceleration phase of the recovery stroke in the first half of the cycle, the angular velocity is... angular acceleration from Linearly decreasing to 0; when During the uniform acceleration phase of the first half of the cycle, the angular velocity is... The angular acceleration changes linearly from 0 to the maximum angular velocity of the power stroke. ; when During the uniform velocity phase of the first half of the power stroke, the angular velocity remains at the maximum angular velocity of the power stroke. Uniform motion; when During the uniform deceleration phase of the first half of the power stroke, the angular velocity is... angular acceleration from Linear change to 0.

3. The control method according to claim 1, characterized in that, speed ratio The value of satisfies .

4. The control method according to claim 1, characterized in that, Swing amplitude The value satisfies ; Maximum angular velocity of power stroke The value satisfies .

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