A method for modeling and analyzing the reliability of a waterjet propulsion pump under cavitation conditions

Abstract

This invention belongs to the field of reliability modeling technology for waterjet propulsion pumps, specifically relating to a method for confident reliability modeling and analysis of waterjet propulsion pumps under cavitation conditions. The method includes: performing functional, performance, and margin analysis on the waterjet propulsion pump to determine key performance parameters and their thresholds; establishing interdisciplinary equations for performance and internal and external variables, and introducing cavitation-related loss terms to characterize the degradation effect of cavitation on head; establishing margin equations based on the types of key performance parameters, and constructing performance margin degradation equations; finally, considering the uncertainties of physical properties and external conditions, constructing a confident reliability model. This invention deeply couples the specific degradation mechanism under cavitation conditions with multi-source uncertainties, breaking the limitation of existing technologies that are only applicable to normal operating conditions. It achieves accurate assessment of the reliability of waterjet propulsion pumps under cavitation conditions, providing scientific guidance for anti-cavitation design, parameter optimization, and reliability improvement.

Description

Technical Field

[0001] This invention belongs to the field of reliability modeling technology for waterjet propulsion pumps, and specifically relates to a method for confirmatory reliability modeling and analysis of waterjet propulsion pumps under cavitation conditions. Background Technology

[0002] Waterjet propulsion and propeller propulsion, as two major technologies for ship propulsion, both have a history of development spanning hundreds of years. Compared to the widespread application of propeller propulsion, waterjet propulsion technology has only achieved breakthrough development and gradually matured in the last thirty years. This technology generates a high-speed jet through a propulsion pump, using the reaction force to drive the carrier's motion. Combined with a steering and reversing mechanism, it achieves vector thrust control, thus possessing both propulsion and maneuvering functions. This unique working principle gives it significant advantages in high-speed ships, amphibious vehicles, and special-purpose platforms.

[0003] While some progress has been made in the reliability research of waterjet propulsion pumps, many problems still exist in guiding their design. On the one hand, existing research often relies on overly idealistic theoretical models, failing to fully consider the complex and variable operating conditions faced by waterjet propulsion pumps in actual operation, especially the significant impact of cavitation. For example, in actual operation, factors such as seawater corrosion, water flow impact, and cavitation effects at different speeds interact and exert complex effects on pump materials and structures: high-frequency shock waves and microjets generated by cavitation can cause cavitation damage on blade surfaces, leading to material fatigue and spalling; cavitation-induced pressure pulsations and flow-induced vibrations can exacerbate structural stress and accelerate performance degradation. Current reliability research has failed to delve into the coupling mechanism between these dynamic factors and the cavitation process, resulting in a severe disconnect between theoretical models and actual operating scenarios. On the other hand, reliability research suffers from limitations in data collection and analysis. Real-time monitoring data related to cavitation (such as cavitation number, bubble distribution, and cavitation damage level) has long been lacking, making it difficult to accurately capture the impact of cavitation on the performance of waterjet propulsion pumps throughout their entire life cycle. For example, the dynamic evolution of key parameters such as head decay and vibration amplitude changes caused by cavitation lacks systematic recording. This results in reliability models built on limited data failing to accurately reflect the degradation path under cavitation conditions, lacking precision and failing to provide precise parameter support for design. Furthermore, current reliability studies lack comparative analyses of the cavitation resistance performance of different design schemes. For instance, for schemes involving blade materials (such as duplex stainless steel and titanium alloys), structural parameters (such as blade thickness distribution and relative flow angle), or cavitation suppression technologies (such as inducer design and supercavitation airfoils), there is a lack of systematic evaluation from dimensions such as cavitation sensitivity and cavitation lifetime. This fails to provide designers with clear guidance on cavitation resistance design from a reliability perspective, making it difficult to balance material cost, manufacturing precision, and cavitation resistance performance during the design process. Ultimately, this results in design outcomes that cannot meet the high reliability requirements of actual use under high cavitation risk conditions (such as high-speed mooring and foreign object ingestion). Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method for confident reliability modeling and analysis of waterjet propulsion pumps under cavitation conditions. Its unique design is based on performance margin as the core support, deeply coupling the specific degradation mechanism and multi-source uncertainty factors under cavitation conditions to construct a targeted confident reliability model. This breaks through the limitations of existing technologies that can only adapt to normal operating conditions and ignore the unique effects of cavitation. It can accurately assess the reliability level of waterjet propulsion pumps under cavitation conditions, ultimately providing important scientific guidance for targeted product design, parameter optimization, and reliability improvement, filling the gap in existing technologies in the field of reliability modeling under cavitation conditions.

[0005] This invention discloses a reliable modeling method for waterjet propulsion pumps under cavitation conditions, comprising the following steps: S1: For the cavitation operation state of the waterjet propulsion pump, perform functional, performance and margin analysis on the waterjet propulsion pump, and determine the key performance parameters and their thresholds. S2: Based on the internal physical property parameters of the relative liquid flow angle and blade thickness at the impeller blade inlet of the waterjet propulsion pump and the external stress condition parameters of cavitation number, flow velocity and pressure, establish the interdisciplinary equations of the key performance parameters and internal and external variables. The key performance parameter is the operating head, which is determined by the pressure difference between the pump inlet and outlet, the square difference of the fluid velocity at the pump inlet and outlet, and the height difference between the inlet and outlet. S3: Establish the corresponding margin equation based on the type of the key performance parameters; S4: Based on the margin equation, introduce a cavitation additional loss term that characterizes the performance degradation caused by cavitation into the interdisciplinary equation to construct a performance margin degradation equation. S5: Based on the aforementioned performance margin degradation equation, and taking into account the uncertainties of physical property parameters and external stress condition parameters, a reliable assurance model is constructed.

[0006] Optionally, in the performance margin degradation equation after introducing the cavitation additional loss term in step S4, the operating head is jointly determined by the pressure difference between the pump inlet pressure and the fluid saturated vapor pressure, the velocity difference between the square of the pump inlet velocity and the square of the average absolute velocity at the impeller inlet, the inlet and outlet height difference, and the cavitation additional loss term, which is a function of the cavitation number.

[0007] Optionally, the cavitation additional loss term is positively correlated with the difference between the critical cavitation number and the actual cavitation number.

[0008] Optionally, the margin equation characterizes the performance margin in the current state by taking the smaller value between the key performance parameter and its threshold; the performance margin degradation equation compares the difference between the zero-time head and the cumulative head change with the operating head threshold and takes the smaller value.

[0009] Optionally, in step S5, the uncertainty of the physical property parameters includes the uncertainty of the relative flow angle slightly in front of the streamline blade inlet of the front cover plate, the blade inlet thickness, and the maximum blade thickness; the uncertainty of the external stress condition parameters includes the uncertainty of the cavitation number.

[0010] Another aspect of the present invention discloses a method for confident reliability analysis of a waterjet propulsion pump under cavitation conditions. Using the aforementioned confident reliability model, the confident reliability of the waterjet propulsion pump under cavitation conditions is analyzed, specifically including the following steps: S101: Determine the model parameters of the waterjet propulsion pump; S102: Based on the model parameters, obtain the performance degradation curve and confidence interval curve of the waterjet propulsion pump; S103: Obtain reliability using a certainty reliability model; S104: Perform sensitivity analysis to determine sensitivity parameters.

[0011] Compared with the prior art, the present invention has at least the following beneficial effects: (1) In view of the fact that the existing research on water jet propulsion pumps mainly adopts the "black box" reliability modeling method, which cannot reveal the inherent relationship between the reliability of water jet propulsion pumps and internal physical properties and external environmental factors, this invention adopts the "white box" performance modeling method based on the parameter information of internal components, which successfully breaks through this limitation and can clearly analyze the inherent mechanism of the relationship between the reliability of water jet propulsion pumps and internal component parameters and external environment, making it more scientific and interpretable.

[0012] (2) In the prior art, the reliability modeling of waterjet propulsion pumps has not achieved a unified integration of physical degradation mechanism and parameter uncertainty, and has not fully considered the combined effects of internal factors of pump mechanical structure and external factors of operating conditions, resulting in insufficient accuracy of evaluation results. Based on the theory of certainty reliability, this invention integrates the physical degradation mechanism and parameter uncertainty of waterjet propulsion pumps into the modeling framework. It establishes a dedicated certainty reliability model specifically for internal factors of pump mechanical structure such as relative flow angle and blade thickness, as well as external factors of operating conditions such as flow velocity, pressure, and cavitation number. This model can achieve quantitative reliability assessment of key performance parameters throughout their entire life cycle, solving the problems of low accuracy and poor adaptability of the prior art.

[0013] (3) Existing technologies make it difficult to quantitatively analyze the sensitivity and contribution of each component parameter to the reliability of the water jet propulsion pump system, resulting in designers being unable to accurately locate weak links, leading to low R&D efficiency and serious cost waste. This invention can achieve quantitative analysis of the sensitivity and contribution of each component parameter to the system reliability, directly guiding designers to prioritize the improvement of weak components and parameters, effectively improving R&D efficiency, reducing R&D costs, and significantly improving cost-effectiveness.

[0014] (4) In view of the shortcomings of existing technologies that cannot adapt to different application scenarios and are difficult to balance reliability, cost and performance, this invention supports customized reliability design for different application scenarios. It can optimize product cost and performance while ensuring that the water jet propulsion pump meets reliability requirements, taking into account practicality and economy, and adapting to the application needs of multiple scenarios. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly introduced below. The features and advantages of the present invention can be more clearly understood by referring to the accompanying drawings. The accompanying drawings are schematic and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the water jet propulsion pump device of the present invention; Figure 2 This is a schematic diagram illustrating the variation of NPSHA and NPSHR with flow rate according to the present invention; Figure 3 Typical of the present invention H-σ image; Figure 4 This invention illustrates the degradation law of the head under different cavitation levels. Figure 5 The control cavitation number after the present invention Ht image; Figure 6 The performance margin of the waterjet propulsion pump of the present invention has degraded. image; Figure 7 To ensure the reliability of the water jet propulsion pump of the present invention image ； Figure 8 For the sensitivity parameter changes of the present invention The impact; Figure 9 For the sensitivity parameter changes of the present invention The impact. Detailed Implementation

[0017] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0018] A specific embodiment of the present invention, such as Figure 1-9 A method for confident reliability modeling of a waterjet propulsion pump under cavitation conditions is disclosed, the specific steps of which include: S1 performs functional, performance, and margin analysis on the waterjet propulsion pump to determine the key performance parameters and thresholds of the waterjet propulsion pump; and determines the type of key performance parameters by combining the thresholds of key performance parameters with product design specifications.

[0019] Furthermore, the types of key performance parameters include whether the target is large-scale, small-scale, or target-oriented.

[0020] Preferably, the water jet propulsion pump is a new type of special power device. Its main function is to generate a high-speed jet through the propulsion pump, use the reaction force to drive the carrier to move, and cooperate with the steering and reversing mechanism to achieve vector thrust control, thus having both propulsion and control functions.

[0021] Further, (1) functional analysis is used to determine the effects of the impeller, guide vane, shaft system, inlet flow channel, grid base and nozzle of the waterjet propulsion pump on the waterjet propulsion pump.

[0022] Specifically, for a waterjet propulsion pump, the pump receives mechanical energy transmitted from the shaft, draws water from the hull bottom through the inlet channel, pressurizes and accelerates the water flow, and then ejects a high-speed water jet through the nozzle to generate thrust that propels the vessel forward. The lower flange of the inlet base is welded to the hull bottom plate, and the upper flange connects to the lower flange of the waterjet propulsion device's inlet channel, ensuring that water flows smoothly from the hull bottom into the propulsion pump. A grating prevents floating debris from entering the propulsion pump, thus protecting it.

[0023] The hydraulic system's navigation control module drives the steering and reversing hydraulic cylinder groups to achieve directional adjustment and reverse maneuvering functions. The port and starboard reversing mechanisms can perform symmetrical or asymmetrical coordinated operations. In addition, the hydraulic system lubricates the bearing assemblies in the waterjet propulsion system.

[0024] During this process, when the propulsion pump is in a cavitation state, due to the low local pressure at the impeller suction surface, a large number of cavitation bubbles are precipitated and develop with the flow. Subsequently, as the flow field pressure recovers, the cavitation bubbles collapse and deform, forming cavitation bubbles with high velocity and high impact pressure. Some cavitation bubbles collapse near the guide vane blades, leading to the formation of pits on the blade surface. Over a long timescale, such repeated cavitation impacts cause fatigue failure of the guide vane material, resulting in cracks, a decrease in head, an increase in strain, and a significant increase in vibration acceleration. Ultimately, blades or even the casing may fracture, causing a sharp drop in head and a sharp increase in vibration, significantly affecting the speed of ship equipment and threatening navigation safety. If severe cavitation occurs, the cavitation bubbles eroding the guide vane are stronger and more numerous, and transient high-intensity impacts may cause rapid damage to the guide vane material, resulting in a decline in the performance of the waterjet propulsion pump. The functional analysis of the waterjet propulsion pump includes the operating head.

[0025] (2) Performance analysis: The hydraulic performance indicators of water jet propulsion pumps include flow rate, head, speed, power, efficiency and specific speed. Among them, the working head fully considers the pump's usage requirements and can directly characterize the energy conversion efficiency of a unit weight of liquid through the pump. It is the core indicator for measuring the hydraulic performance of water jet propulsion devices. Therefore, the working head is selected as the key performance parameter.

[0026] (3) Margin analysis: Based on the key performance parameters obtained from the performance analysis and combined with the product design specifications, determine the types and thresholds of the key performance parameters of the water jet propulsion pump, in order to prepare for the subsequent construction of the margin equation.

[0027] For example, the product design specification requires that the difference between the working head and the initial head be less than 0.4m, and the key performance parameter type is the minimum requirement parameter.

[0028] S2 establishes interdisciplinary equations relating performance to internal and external variables for key performance parameters of waterjet propulsion pumps.

[0029] S21 establishes a key performance parameter model for water jet propulsion pumps based on their working principle and structural composition. S211 defines the working principle and structural composition of the waterjet propulsion pump.

[0030] The waterjet propulsion pump has a complex structure with various components working in tandem. The core components include the inlet channel, impeller assembly, guide vanes, shaft assembly, sealing structure, and nozzle assembly. The inlet channel, consisting of an inlet bell and a flow guide, guides the fluid smoothly into the pump body; its structural dimensions and inlet angle directly affect the fluid flow. The impeller assembly, as the core of energy conversion, consists of a hub, impeller disc, and multiple blades. Key parameters such as blade thickness, number of blades, and relative flow angle determine the pump's head, flow rate, and cavitation resistance. The guide vanes are located on the impeller. Downstream, consisting of guide vanes and flow channels, its main function is to eliminate the rotational kinetic energy of the fluid and guide the fluid to flow smoothly. The vane angle and flow channel size affect the fluid pressure transmission efficiency. The shaft system assembly includes the pump shaft, bearings, and seals. The pump shaft is used to transmit power to drive the impeller to rotate, the bearings ensure the stable operation of the shaft system, and the seals prevent fluid leakage. The nozzle assembly serves as the fluid discharge terminal. Its outlet cross-sectional area and outlet angle directly determine the thrust of the water jet propulsion. All components cooperate with each other to complete the entire process of water flow intake, pressurization, rectification, and jet propulsion.

[0031] Furthermore, the working principle of the waterjet propulsion pump is as follows: the propulsion pump receives mechanical energy transmitted from the shaft, draws water from the hull bottom through the inlet channel, pressurizes and accelerates the water flow, and ejects a high-speed water jet through the nozzle. The reaction force drives the carrier to move, thus generating thrust to propel the vessel forward. The lower flange of the inlet base is welded to the hull bottom plate, and the upper flange is connected to the lower flange of the inlet channel of the waterjet propulsion device, ensuring that water flows smoothly from the hull bottom into the propulsion pump. The grating prevents floating debris from entering the propulsion pump, protecting it. The hydraulic system's navigation control module drives the steering and reversing hydraulic cylinder groups to achieve directional adjustment and reverse maneuvering functions. The port and starboard reversing mechanisms can perform symmetrical or asymmetrical coordinated operations.

[0032] Based on the working principle and structural composition of the waterjet propulsion pump, S212 establishes a key performance parameter model for the waterjet propulsion pump.

[0033] Key performance parameters of waterjet propulsion pump: operating head The expression is: (1) In the formula, To advance the work journey; , These are the pump inlet and outlet pressures, respectively. , The fluid velocity at the pump inlet and outlet; The height difference between import and export; The density of the liquid; This is the acceleration due to gravity.

[0034] S22 analyzes and quantifies the influence of internal physical property parameters (relative flow angle slightly in front of the streamline blade inlet, blade inlet thickness and maximum blade thickness and pump inlet height difference, etc.) and external stress conditions (cavitation number, pump inlet velocity, pump inlet pressure, characteristic velocity, velocity at the inlet flange, etc.) on the key performance parameters of the waterjet propulsion pump.

[0035] S221 Obtains the basic equation for cavitation in a waterjet propulsion pump; Figure 1 In this context, the point at the impeller inlet that lies on the same streamline as the impeller inlet reference point (point 0) is defined as the pump inlet reference point (point c); the impeller inlet blade characteristic point (point K) is the blade flow channel characteristic point at the impeller inlet immediately adjacent to point 0. Both are flow field characteristic points selected for analyzing the cavitation characteristics of the waterjet propulsion pump: point 0 characterizes the fluid motion state of the main flow channel at the impeller inlet, and point K reflects the local hydrodynamic characteristics at the leading edge of the impeller blades. The hydrodynamic conditions for cavitation can be quantified by deriving the Bernoulli equation for these two points. Therefore, the absolute motion Bernoulli equation from point c to point 0 is: (2) in, The water head (unit: m) indicates the position of the reference point (point c) at the pump inlet. The hydrostatic pressure at point c is expressed in Pa. Indicates fluid density (unit: kg / m3); This represents the acceleration due to gravity (unit: m / s²). The absolute velocity of the fluid at point c (unit: m / s); The head (unit: m) indicates the position of the impeller inlet reference point (0 point); The hydrostatic pressure at point 0 (unit: Pa); The absolute velocity of the fluid at point 0 (unit: m / s); This represents the head loss along the route from point c to point 0 (unit: m).

[0036] Furthermore, the Bernoulli equation for the relative motion from point 0 to point K is: (3) in, The fluid relative velocity at point 0 (unit: m / s); The impeller circumferential velocity at point 0 (unit: m / s); The head (unit: m) indicates the position of the characteristic point (K point) of the impeller inlet blades. The hydrostatic pressure at point K is expressed in Pa. The fluid relative velocity at point K (unit: m / s); The impeller circumferential velocity at point K (unit: m / s); This represents the local head loss from point 0 to point K (unit: m). Furthermore, based on the above two equations, the common terms are eliminated. get: (4) Further rewritten as: (5) Because point K and point 0 are very close in the circumferential direction, The above formula can be rewritten as: (6) make The above formula can be rewritten as: (7) Furthermore, the average absolute velocity at the impeller blade inlet is used. and average relative velocity In the substitution formula (7) and Add velocity non-uniformity coefficients respectively and The following correction is made: Equation (7) is rewritten as follows: (8) Subtract one term from the left side of equation (8) Then add and define the right side The formula can then be rewritten as: (9) in, The saturated vapor pressure of a fluid is expressed in Pa. In the formula, , .

[0037] The term within the square brackets on the left side of equation (9) is determined by the device and is expressed in terms of the effective net positive suction head (NPSHA), i.e.: (10) Understandably, the size of the NPSHA is related to the parameters of the device. The device refers to the external supporting facilities of the entire waterjet propulsion system, including the pump's suction pipe, the hull's water inlet channel, the suction inlet's height, the fluid temperature and pressure environment, etc. The device encompasses the pump's external operating environment and supporting systems. The pump is the core working component of the device (impeller, guide vanes, pump body, etc.), and due to hydraulic losses... It is proportional to the square of the flow rate; therefore, as the flow rate increases, NPSHA gradually decreases, and the NPSHA-Q curve declines (e.g., ...). Figure 2 (As shown).

[0038] S221 derives the fundamental cavitation equations using Bernoulli's equations, clarifying the hydrodynamic principles of cavitation. This provides a theoretical basis for quantifying NPSHA (System Cavitation Resistance Measure) and NPSHR (Pump Cavitation Resistance Requirement), serving as the core theoretical source for "cavitation failure mechanism analysis" in reliability modeling. The NPSHA and NPSHR calculation formulas derived from the fundamental cavitation equations in S221 are key parameter inputs for constructing a reliable model. By calculating the difference between NPSHA and NPSHR (cavitation margin), the performance margin of the pump under cavitation conditions can be quantified. Furthermore, by combining degradation mechanisms and uncertainties, a reliability model under cavitation conditions can be established.

[0039] The two terms on the right side of equation (9) are determined by the flow within the pump and are expressed in terms of the required net positive suction head (NPSHR), namely: (11) According to statistical laws Usually, take directly Therefore, equation (11) is often rewritten as: (12) Among them, the impeller inlet cavitation correction coefficient The value is related to the shape of the pump impeller blade inlet (number of blades, angle of attack, blade thickness and distribution, etc.).

[0040] Preferably, .

[0041] Specific speed of the pump pump, The value can be approximated using the following empirical formula: (13) In the formula, The relative fluid flow angle is located slightly in front of the streamline blade inlet of the front cover plate (without considering displacement). , These are the blade inlet thickness and the blade maximum thickness, respectively.

[0042] Just like the pump's operating head, the pump's net positive suction head (NPSHR) is essentially a performance parameter of the pump itself, and its value is only related to the flow parameters at the pump impeller blade inlet. and The decision is independent of external devices. As long as the velocity distribution flowing through the pump inlet is the same, the NPSHR value remains unchanged.

[0043] because and As the flow rate increases, according to equation (11), we know that NPSHR increases with the flow rate Q (see [reference]). Figure 2 However, the mechanism of pump cavitation involves the coupling of multiple parameters. When the flow rate decreases within the pump, the change in the liquid flow angle triggers a change in the angle of attack, and the resulting flow separation exacerbates the generation and spread of cavitation. When the negative effects of the angle of attack change outweigh the positive effects of the reduced flow rate, the NPSHR actually increases with the decrease in flow rate. Therefore, when the pump flow rate is greater than the design flow rate, the NPSHR increases; and when the flow rate continuously decreases from the design point, the NPSHR first decreases and then increases.

[0044] From equations (9), (10), and (11), the basic equation for pump cavitation is obtained, and its expression is: (14) Right now: (15) The basic equation for pump cavitation in this invention is the relationship between the device's clean suction head and the pump's clean suction head.

[0045] The physical meaning of the pump's net positive suction head can be further understood based on equation (15). First, the pump's net suction head... NPSHR It's an inherent property of the pump itself; once the pump design is complete, NPSHR It is only related to the rotational speed and flow rate. In addition, from the perspective of the basic equation of the pump, in order to prevent cavitation during pump operation, the head energy provided by the device must not be lower than that required. NPSHR This is also the positive suction head of the pump. NPSHR This is also known as "the suction head must be cleaned".

[0046] S222 Acquisition Device Clean Positive Suction Head NPSHA ; The formula for calculating the net positive suction head of the device is equation (10). See also... Figure 1 According to the Bernoulli equation between the pump inlet flange and reference point c: (16) in, The position head (unit: m) indicates the pump inlet reference surface (point s). This indicates the static pressure of the fluid at the pump inlet reference surface (point S) (unit: Pa). This represents the absolute velocity of the fluid at the pump inlet reference surface (point s) (unit: m / s). This represents the total head loss (in meters) from the pump inlet reference point (point c) to the pump inlet reference surface (point s). Converting equation (10) to the pump inlet reference plane, the expression is: (17) And ignore and The difference (depending on whether the pump is installed horizontally or vertically) and The differences are different (the difference is more significant for large pumps), that is, they can be considered as: (18) Then we have: (19) In the formula, This refers to the loss from the pump inlet flange to point K.

[0047] S223 obtains the pump cavitation number; First, the vacuolation number is defined as: (20) in, This refers to the pump inlet pressure. denoted as fluid vaporization pressure; u is the characteristic flow velocity, typically taken as the impeller inlet velocity.

[0048] Substituting this into equation (19), we obtain the quantitative correlation expression between the net positive suction head (NPSHA) and the cavitation number σ: (twenty one) In other words, the cavitation number σ has the same meaning as the net positive suction head of the device. This step aims to establish a direct relationship between the system's energy margin and the degree of cavitation by defining the cavitation number, and to clarify the physical nature of the cavitation number σ as an evaluation index of the device's anti-cavitation capability. That is, σ reflects the energy margin in the device's net positive suction head used to offset the fluid vaporization pressure and ensure fluid stability.

[0049] Furthermore, as the degree of cavitation increases, the cavitation number gradually decreases, and at this time, parameters related to pump performance, such as the operating head, also decrease.

[0050] Based on the impact analysis of the key performance parameters of the waterjet propulsion pump in step S22, S23 adds a cavitation additional loss term to the model of the key performance parameters of the waterjet propulsion pump to obtain an interdisciplinary model of the key performance parameters of the waterjet propulsion pump.

[0051] Based on the static calculation formula (1) for head and the definition of cavitation number (20), we can obtain (twenty two) But this and The statement that a decrease in pressure corresponds to a decrease in H does not hold true. This is because during cavitation, the collapse of air bubbles leads to a decrease in outlet pressure. It decreases due to local energy loss. Experiments show that when the cavitation number σ is below the critical value, The sudden drop in head is the main reason for the sharp decrease in lift. Therefore, an additional cavitation loss term is introduced.

[0052] Specifically, based on the static calculation formula (1) for the working head and the definition of cavitation number (20), and introducing the cavitation additional loss term. We can obtain: (twenty three) in, Indicates the saturated vapor pressure of the fluid; Indicates characteristic flow velocity; This indicates the geometric height difference at the pump inlet, which is the vertical height difference between the pump suction inlet reference point and the impeller inlet reference surface. Represents the vacuolation number.

[0053] Furthermore, cavitation-related additional losses The expression is: (twenty four) in, The critical cavitation number is the threshold number at which cavitation just occurs in a waterjet propulsion pump. .

[0054] From equations (12), (13), (15), and (21), we obtain and NPSHR The relationship, among which, The expression is: (25) and (26) in, This indicates the relative fluid flow angle slightly in front of the streamline blade inlet of the front cover; This indicates the thickness at the inlet section of the impeller blade's leading edge, i.e., the thickness of the section at the very tip of the blade. This indicates the maximum cross-sectional thickness of the impeller blades along the flow channel direction.

[0055] visible, It is a parameter that is related to both internal and external factors. The final H-value is... The relationship also reflects that the degradation of head is the result of a combination of internal and external factors.

[0056] Substituting equations (24), (25), and (26) into equation (23) yields the interdisciplinary equation for the head of the water jet propulsion pump under cavitation conditions.

[0057] (27) in, Indicates the pump inlet velocity. Indicates the pump inlet pressure. Indicates characteristic flow velocity, This indicates the flow rate at the inlet flange. This represents the average absolute velocity at the impeller blade inlet. These represent average relative speeds, which are related to ship speed and engine speed.

[0058] S3 establishes the corresponding margin equation based on the type of key performance parameters, with the expression as follows: (28) In the formula, Indicates performance margin; This represents the margin equation; H represents the operating head; This indicates the operating head threshold.

[0059] S4 constructs a performance margin degradation equation based on the margin equation; S41 analyzes the degradation mechanism and causes of the waterjet propulsion pump, identifies the performance parameters that are degraded, and obtains the degradation equations corresponding to the degraded performance parameters; Specifically, the relative flow angle slightly in front of the streamlined blade inlet of the front cover plate The tangent value increases uniformly with time, satisfying the following equation: (29) In the formula, The relative flow angle at time t The tangent value; The relative flow angle at time 0 The tangent value; h represents the rate of change. -1 ; The time is indicated by h.

[0060] Substituting equation (29) into equation (26), we get: (30) Substituting (30) into equation (27) yields the working head function. That is, when all other parameters are determined, the head is a time-dependent variable. and vacuolation number The function that has an effect.

[0061] Furthermore, the cumulative change in head The calculation formula is: (31) In the formula, For the 0-hour head, This is the head function.

[0062] S42 combines the threshold values ​​of key performance parameters and substitutes the degradation equation into the margin equation to obtain the performance margin degradation equation, which is expressed as: (32) In the formula, The margin equation representing the operating head; For the operating head threshold, This represents the cumulative change in head.

[0063] S5 constructs a certainty reliability model based on the performance margin degradation equation and considering internal and external uncertainties. Specifically, the uncertainties in the performance margin degradation equation of the waterjet propulsion pump are analyzed from two aspects: physical properties and external conditions. These uncertainties are then quantified, and a reliable model of the waterjet propulsion pump is constructed.

[0064] S51 determines the internal and external parameters with uncertainties and their distribution.

[0065] In practical applications, the performance margin of waterjet propulsion pumps may be affected by various uncertainties during their operation. This invention analyzes and quantifies the uncertainties in the performance margin degradation equation of waterjet propulsion pumps from two aspects: physical properties and external conditions. This allows for the determination of uncertain internal and external parameters and their distribution, ultimately leading to the construction of a reliable model for the waterjet propulsion pump.

[0066] Step S511: Obtain the internal and external parameters of the model based on the performance margin degradation model of the waterjet propulsion pump, including physical properties and external conditions.

[0067] Specifically, physical properties (Internal parameter), the expression is: ; External conditions (External parameter), the expression is: ; S512 determines the uncertainty of physical properties; Due to uncertainties in the manufacturing and assembly process, the blade inlet thickness of the waterjet propulsion pump blades... Maximum blade thickness and relative flow angle It has uncertainty, and its uncertainty is quantified as follows: (33) in, express The mean; express Standard deviation; express The mean; express Standard deviation; express The mean; express Standard deviation; S513 defines the uncertainty of external conditions; Furthermore, the quantification results of the uncertainty of the cavitation number are shown in Table 1: Table 1. Cavitation Numbers σ Correspondence with cavitation status

[0068] S52 establishes a certainty reliability model based on the uncertainty of physical properties and external conditions.

[0069] (35) In the formula, Indicates a high degree of certainty regarding reliability; Represents a probability measure; This indicates a performance margin that takes into account uncertainties; Indicates the internal variable; This represents an external variable.

[0070] Another embodiment of the present invention discloses a method for analyzing the certainty reliability of a waterjet propulsion pump under cavitation conditions. Using the certainty reliability model described in the foregoing claims, the method analyzes the certainty reliability of the waterjet propulsion pump under cavitation conditions. The specific steps are as follows: S101 determines the model parameters of the waterjet propulsion pump; The distributions of deterministic and uncertain parameters, as well as their distribution parameters, of the degradation model of a waterjet propulsion pump were obtained. The model parameter values ​​for a certain type of waterjet propulsion pump were derived from product design specifications and experimental data.

[0071] S102 obtains the performance degradation curve and confidence interval curve of the waterjet propulsion pump based on the model parameters; Furthermore, the 95% confidence interval curve of the waterjet propulsion pump was obtained.

[0072] S103 uses the confidence reliability model obtained in step S5 to obtain the reliability; S104 sensitivity analysis; Based on the degradation model parameter information of the waterjet propulsion pump, the sensitivity of each parameter of the waterjet propulsion pump is analyzed, the sensitivity parameters are determined, and suggestions are provided for product design and use.

[0073] Taking a certain type of waterjet propulsion pump as an example, we model its key performance parameters and analyze the performance degradation and degradation range to complete the reliability analysis of the waterjet propulsion pump.

[0074] First, a model-based reliability analysis of the waterjet propulsion pump; The parameter values ​​for the degradation model of the waterjet propulsion pump are shown in Table 2.

[0075] Table 2 Parameters of the Waterjet Propulsion Pump Performance Degradation Model

[0076] It should be noted that the above list of the types and quantities of parameters in this invention is only a hypothetical example. In actual implementation, the corresponding parameters can be set as needed.

[0077] Then, the deterministic law of degradation; Under the parameter conditions of the waterjet propulsion pump performance degradation model in Table 2, the relationship between head and cavitation number and time was obtained according to the performance margin degradation model of the waterjet propulsion pump (Equation (32)). The cavitation number is between 0 and 1, and the time is between 0 and 200 h. The results are shown in [see table]. Figure 4 , where cavitation number The degradation curves for values ​​of 0.2, 0.15, and 0.1 are as follows: Figure 5 As shown, it can be seen that with the cavitation number As the cavitation level decreases (i.e., the cavitation intensity increases), the head degradation slope gradually increases. This phenomenon indicates that if the cavitation number... If cavitation is not properly controlled (i.e., the degree of cavitation is aggravated), the performance life of the pump will be significantly shortened, further verifying the necessity of cavitation suppression in engineering practice.

[0078] Next, we will quantify the uncertainty; The results of uncertainty quantification are shown in Table 3.

[0079] Table 3 Uncertainty Quantification Parameters

[0080] It should be noted that the above list of the types and quantities of parameters in this invention is only a hypothetical example. In actual implementation, the corresponding parameters can be set as needed.

[0081] Then, determine the performance degradation range of the waterjet propulsion pump; Under the parameters of the waterjet propulsion pump performance degradation model in Table 2, based on the performance margin degradation model of the waterjet propulsion pump and its uncertainty quantification results, the relationship between the performance degradation of the waterjet propulsion pump and time can be calculated. After Monte Carlo simulation, the 95% confidence interval of the waterjet propulsion pump head performance margin degradation during the mission period can be statistically obtained, such as... Figure 6 As shown.

[0082] Next, reliability assessment; Based on the waterjet propulsion pump metric model, the parameters in Table 3 are substituted into the certainty reliability model. Monte Carlo simulation is used for random sampling to calculate the probability of a margin greater than 0. The reliability change curve of the waterjet propulsion pump after 200 hours is calculated, and the certainty reliability assessment results are obtained. The results are as follows: Figure 7 As shown.

[0083] The results above show that, due to environmental factors and error accumulation, the head performance margin will gradually degrade over time, especially in the later stages, where the degradation rate accelerates and the impact on the overall reliability of the waterjet propulsion pump becomes more significant in the later stages.

[0084] Finally, sensitivity analysis; Based on the degradation model parameters of the waterjet propulsion pump, the internal physical properties of the waterjet propulsion pump, including the relative flow angle slightly in front of the streamlined blade inlet of the front cover, are analyzed. Blade inlet thickness and the maximum thickness of the blade Sensitivity analysis of the parameters was conducted to study their changes on the head H0 at time 0 and the cumulative head change over 200 hours. The influence of H(t). First, take all three parameters as 1.0, and calculate the head H0 at time 0 and the cumulative head change over 200 hours. H(t) is calculated, and two of the parameters are set to their original values ​​(1.0 times), while the third parameter is set to either 0.9 times or 1.1 times. The head H0 at time 0 and the cumulative head change over 200 hours are then calculated. H(t) is compared to provide suggestions for product design and use.

[0085] Figure 8 The effect of changes in the sensitivity parameter on the head H0 at time 0. Figure 9 The change in cumulative head over 200 hours is the effect of changes in sensitivity parameters. The influence of H(t) can be seen from the above analysis results: the order of influence on the head at time 0 from largest to smallest is: relative flow angle. Maximum blade thickness >Blade inlet thickness Therefore, more attention needs to be paid to the relative flow angle during processing. The impact on cumulative head variation, ranked from largest to smallest: maximum blade thickness. >Blade inlet thickness Relative flow angle Therefore, more attention needs to be paid to the maximum thickness of the blades during use.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A reliable modeling method for a waterjet propulsion pump under cavitation conditions, characterized in that, Includes the following steps: S1: For the cavitation operation state of the waterjet propulsion pump, perform functional, performance and margin analysis on the waterjet propulsion pump, and determine the key performance parameters and their thresholds. S2: Based on the internal physical property parameters of the relative liquid flow angle and blade thickness at the impeller blade inlet of the waterjet propulsion pump and the external stress condition parameters of cavitation number, flow velocity and pressure, establish the interdisciplinary equations of the key performance parameters and internal and external variables. The key performance parameter is the operating head, which is determined by the pressure difference between the pump inlet and outlet, the square difference of the fluid velocity at the pump inlet and outlet, and the height difference between the inlet and outlet. S3: Establish the corresponding margin equation based on the type of the key performance parameters; S4: Based on the margin equation, introduce a cavitation additional loss term that characterizes the performance degradation caused by cavitation into the interdisciplinary equation to construct a performance margin degradation equation. S5: Based on the aforementioned performance margin degradation equation, and taking into account the uncertainties of physical property parameters and external stress condition parameters, a reliable assurance model is constructed.

2. The reliable modeling method for a waterjet propulsion pump under cavitation conditions according to claim 1, characterized in that, In the performance margin degradation equation after introducing the cavitation additional loss term in step S4, the operating head is determined by the pressure difference between the pump inlet pressure and the fluid saturated vapor pressure, the velocity difference between the square of the pump inlet velocity and the square of the average absolute velocity at the impeller inlet, the inlet and outlet height difference, and the cavitation additional loss term, which is a function of the cavitation number.

3. The reliable modeling method for a waterjet propulsion pump under cavitation conditions according to claim 1, characterized in that, The cavitation-related loss term is positively correlated with the difference between the critical cavitation number and the actual cavitation number.

4. The method for confident reliability modeling of a waterjet propulsion pump under cavitation conditions according to claim 1, characterized in that, The margin equation characterizes the performance margin in the current state by taking the smaller value between the key performance parameter and its threshold; the performance margin degradation equation compares the difference between the zero-time head and the cumulative head change with the working head threshold and takes the smaller value.

5. The method for confident reliability modeling of a waterjet propulsion pump under cavitation conditions according to claim 1, characterized in that, In step S5, the uncertainty of the physical property parameters includes the uncertainty of the relative flow angle slightly in front of the streamline blade inlet of the front cover plate, the blade inlet thickness, and the maximum blade thickness; the uncertainty of the external stress condition parameters includes the uncertainty of the cavitation number.

6. A reliable analysis method for a waterjet propulsion pump under cavitation conditions, characterized in that, Using the certainty reliability model described in any one of claims 1-5, the certainty reliability of the waterjet propulsion pump under cavitation conditions is analyzed, specifically including the following steps: S101: Determine the model parameters of the waterjet propulsion pump; S102: Based on the model parameters, obtain the performance degradation curve and confidence interval curve of the waterjet propulsion pump; S103: Obtain reliability using a certainty reliability model; S104: Perform sensitivity analysis to determine sensitivity parameters.

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