Underwater EHA structure vibration control and stiffening optimization method based on multi-order modal characteristics

Abstract

The application relates to a kind of underwater EHA structure vibration control and stiffening optimization method based on multi-order modal characteristics, comprising establishing motor casing finite element model;Carrying out multi-order modal analysis, obtaining multiple order natural frequencies and corresponding modal vibration modes in the set frequency range;Each order modal vibration mode is analyzed, and the vibration mode antinode area, maximum relative displacement amplitude area and vibration energy concentration area of motor casing under different order modes are identified;Multiple annular ribs are arranged on the inner wall of motor casing along the axial direction and extend along the circumferential direction;Several axial stiffeners are arranged on the inner wall of motor casing along the axial direction;The optimized motor casing structure is verified.The application analyzes the structural dynamics characteristics of motor casing, identifies the key structural areas that affect the overall stiffness, local deformation and vibration response of the casing, and optimizes the design of the stiffening structure inside the casing under the premise of meeting the internal assembly space constraints.

Description

Technical Field

[0001] This invention belongs to the field of underwater electromechanical equipment structural design and vibration control technology. Specifically, it relates to a method for vibration control and stiffening optimization of underwater EHA structures based on multi-mode characteristics. In particular, it is a method that takes the underwater EHA motor housing as the object, identifies the multi-mode structural dynamic characteristics of the motor housing under axial overall bending mode and circumferential lobe-shaped shell mode, and coordinates the internal stiffening structure of the motor housing to achieve structural vibration control, overall stiffness improvement and service reliability enhancement. Background Technology

[0002] Underwater EHAs (electro-hydraulic actuators) are widely used in underwater robots, deep-sea operation equipment, subsea engineering devices, and underwater special operation tools. They typically integrate motors, hydraulic pumps, valve groups, and control units. The motor housing, as a key load-bearing and protective structure of the underwater EHA, not only serves for motor installation and positioning, protection and isolation, and pressure sealing, but also bears the functions of transmitting the overall structural load, maintaining assembly constraints, and transmitting operational vibration responses. Its structural stiffness and modal characteristics directly affect the vibration level, sealing reliability, and long-term service stability of the underwater EHA.

[0003] During actual operation, the underwater EHA (Electric Hydraulic Actuator) is subjected to multiple dynamic loads from various sources, including but not limited to electromagnetic force fluctuations, pressure pulsations, and external fluid disturbances, due to motor rotation, hydraulic pump operation, and external working loads. Under these loads, if the overall structural rigidity of the motor housing is insufficient, its structural dynamic characteristics are easily coupled with the excitation under operating conditions, leading to significant structural vibrations. This can further result in increased noise, exacerbated fatigue damage, and even seal failure and decreased structural reliability.

[0004] Currently, there is a relative lack of specialized methods for vibration control of underwater EHA motor housing structures. In engineering design, general thin-walled shell reinforcement methods are usually adopted, such as increasing wall thickness or empirically arranging reinforcing ribs. However, since underwater EHAs typically integrate high-power-density motors and various hydraulic and electrical components, their internal assembly space is limited. Simply increasing the overall thickness of the motor housing wall can easily lead to problems such as internal space compression, significant increase in mass, and reduced engineering feasibility. At the same time, empirical reinforcement methods lack systematic analysis of the multi-mode characteristics of the housing and the areas of concentrated vibration energy, making it difficult to take into account the synergistic optimization of different modes.

[0005] Therefore, there is an urgent need to propose a structural vibration control and stiffening optimization method based on multi-mode feature identification and with the direct goal of suppressing the vibration response of the motor housing. By identifying the displacement concentration area and vibration energy concentration area under different order modes, the method can guide the coordinated arrangement of circumferential ring ribs and axial stiffeners, thereby reducing the local vibration response of the housing and improving its structural stiffness, sealing reliability and long-term service stability. Summary of the Invention

[0006] The purpose of this invention is to provide a vibration control and stiffening optimization method for underwater EHA structures based on multi-mode characteristics. Taking the motor housing as the optimization object, the invention systematically analyzes the structural dynamic characteristics of the motor housing at different modes, identifies key structural regions affecting the overall stiffness, local deformation, and vibration response of the housing, and, under the premise of meeting the internal assembly space constraints of the motor and related components, conducts targeted arrangement and optimization design of the internal stiffening structure of the housing. This effectively improves the overall structural stiffness, vibration control effect, and service reliability of the motor housing without significantly increasing the structural mass or using an overall increase in housing wall thickness, thereby solving the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A vibration control and stiffening optimization method for underwater EHA structures based on multi-mode characteristics includes the following steps: S1. Establish a three-dimensional structural model of the underwater EHA, extract the connection relationship, constraint features and load transfer relationship between the motor housing body and other components, and establish a finite element model of the motor housing. S2. Perform multi-mode analysis on the finite element model of the motor housing to obtain its multiple natural frequencies and corresponding mode shapes within a set frequency range; S3. Analyze the mode shapes of each order, identify the antinode regions, maximum relative displacement amplitude regions, and vibration energy concentration regions of the motor housing under different order modes, and determine the above regions as key candidate locations for structural stiffening optimization. S4. For the vibration mode distribution that exhibits the characteristics of an overall axial bending mode in the axial mode, multiple circumferential ring ribs are arranged on the inner wall of the motor housing at axial intervals and extending circumferentially. S5. For the vibration mode distribution that exhibits the characteristics of circumferential lobe-shaped shell modes in the circumferential mode, several axial reinforcing ribs are arranged along the axial direction on the inner wall of the motor housing. S6. Perform multi-modal analysis on the optimized motor housing structure again to verify the overall stiffness of the optimized motor housing structure. In step S2, the modal analysis includes the first and second modes in the axial vibration direction, and the first to fifth modes in the circumferential vibration direction. In step S6, the verification process includes: comparing the natural frequencies of each key mode and the maximum relative displacement amplitude of the motor housing structure before and after optimization. When the natural frequencies of the optimized structure are generally higher than those before optimization in multiple key modes, and the maximum relative displacement amplitude is lower than that before optimization, the stiffening optimization design of the motor housing structure is completed.

[0008] Furthermore, in step S1, during the finite element modeling process, structural features that are not significantly related to the overall structural dynamics are simplified.

[0009] Furthermore, in step S4, during the arrangement of the circumferential ribs, a reduction structure is set for some of the circumferential ribs according to the internal functional layout requirements of the underwater EHA.

[0010] Furthermore, in step S5, there are multiple axial reinforcing ribs, which are arranged at intervals along the circumference.

[0011] Furthermore, in step S5, during the arrangement of the axial stiffeners, a reduction structure is set for some of the axial stiffeners according to the internal functional layout requirements of the underwater EHA.

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention targets low-order overall modes that significantly affect overall stiffness and local modes that reflect local structural stability. It employs different types of structural stiffening components, such as circumferential ribs and axial stiffeners, to enable the structural stiffening design to simultaneously improve overall stiffness and local stability, which is beneficial for achieving synergistic optimization of modes with different physical meanings.

[0013] 2. While arranging stiffening components in key structural parts, this invention can also perform targeted optimization design on the stiffening components by notching, through holes or local reduction according to the functional layout requirements of the underwater EHA internal motor, wiring harness channel, electrical connector and sealing structure, thereby completing the structural stiffening while meeting the requirements of internal assembly, sealing and functional avoidance, and improving the engineering feasibility of the optimization scheme.

[0014] 3. This invention uses a built-in stiffening structure to improve the rigidity of the motor housing and control the vibration response. It does not rely on simply increasing the thickness of the housing wall, which can reduce the problems of increased mass, internal space compression and assembly restrictions caused by overall thickening. It is suitable for the structural design requirements of highly integrated underwater EHA with limited space.

[0015] 4. The structural stiffening optimization method based on modal characteristics proposed in this invention does not depend on specific motor housing size, shape or specific structural parameters. It can be adjusted according to the modal characteristics of different underwater EHA models and their key structural parts. It has good versatility and scalability, and is easy to promote and apply in underwater EHAs of different power levels, different sizes and different application scenarios.

[0016] 5. This invention uses modal analysis as a means of structural dynamics analysis and weak area identification to reveal the mode shape distribution, displacement concentration and deformation characteristics of the motor housing at different orders. Its role is to provide quantitative basis and spatial guidance for structural stiffening design. Unlike the optimization method in the prior art that aims to increase the frequency of a single mode, this invention does not simply pursue changes in the modal frequency value. Instead, it combines the characteristics of multiple mode shapes to coordinate the arrangement of circumferential ribs and axial stiffeners inside the housing, thereby improving the overall stiffness of the motor housing and effectively suppressing the vibration response from the structural level. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the motor housing, used to show the overall structure of the motor housing before simplification. Figure 2 This is a simplified model diagram of a motor housing used for modal analysis. It shows the overall structure of the motor housing after simplification. The model retains the main outline, wall thickness distribution and connection / constraint areas of the motor housing, while removing threads, chamfers, small fillets and other small structural features that are not related to the structural dynamics. Figure 3 This is a structural diagram of the motor housing without reinforcement, i.e., the structure before optimization, used to compare and illustrate the structural form of the motor housing without structural reinforcement. Figure 4 This is a schematic diagram of the structure after arranging circumferential ribs and axial stiffeners on the inner wall of the motor housing based on multi-mode characteristics, i.e., the optimized structure, used to show the overall arrangement of the spatial stiffening skeleton structure proposed in this invention. Figure 5 This is a schematic diagram of the internal structure of the optimized motor housing, used to further illustrate the overall arrangement of the spatial stiffening frame structure proposed in this invention; Figure 6 This is a schematic diagram comparing the first-order axial mode shape of the motor housing before optimization (left side) and after optimization (right side); Figure 7 This is a schematic diagram comparing the axial second-order mode shape of the motor housing before optimization (left side) and after optimization (right side); Figure 8This is a comparative diagram showing the circumferential second-order mode shape of the motor housing before optimization (left side) and after optimization (right side); Figure 9 This is a comparative diagram showing the circumferential third-order mode shape of the motor housing before optimization (left side) and after optimization (right side); Figure 10 This is a comparative diagram of the fourth-order circumferential mode shape of the motor housing before optimization (left side) and after optimization (right side) (the fourth-order circumferential mode and the first-order axial mode have the same frequency). Detailed Implementation

[0018] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0019] For easier understanding, please refer to Figures 1 to 10 This embodiment provides a method for vibration control and stiffening optimization of underwater EHA structures based on multi-mode characteristics. According to the structural function and load transfer characteristics of the motor housing, it is identified as the object of structural vibration control and stiffening optimization. This method is applicable to underwater EHA motor housings of different outer diameters and power ratings. The stiffening position is determined based on the modal analysis results of the corresponding motor housing. This embodiment takes the motor housing of a certain type of underwater EHA as the research object. The motor housing is a thin-walled cylindrical structure, with one end connected to a connecting flange by bolts and the other end connected to the motor end cover. The interior of the motor housing is an assembly cavity for installing the motor. The motor housing material is selected as 316L stainless steel according to engineering requirements, and the outer surface is treated with anti-corrosion and anti-biofouling to meet the requirements of deep-sea service. The method specifically includes the following steps: S1. Establish the finite element model of the motor housing.

[0020] Based on the actual structural dimensions and assembly relationships or forms of this type of underwater EHA, a complete three-dimensional structural model of the underwater EHA is established. On this basis, the connection positions (connection relationships), constraint areas (constraint features), and load transfer relationships between the motor housing body and its components such as end covers and connecting flanges are extracted, and a finite element model of the motor housing is established for multi-order structural modal dynamics analysis and structural stiffening optimization.

[0021] During the finite element modeling process, geometric features and connection areas that significantly influence the overall mass distribution, stiffness distribution, and modal characteristics of the motor housing are fully preserved. These include the main outline of the housing, wall thickness distribution and variation areas, end connection areas (structures), and flange transition areas, ensuring that the established finite element model can be used for subsequent multi-order modal analysis and structural optimization design. Simultaneously, to ensure that the modal analysis results accurately reflect the overall structural dynamics of the motor housing while considering computational efficiency and result stability, the finite element modeling process follows the principles of equivalent modeling and structural simplification. Specifically, local fine structural features with low (no significant) correlation to the overall structural dynamics, such as threads, chamfers, small fillets, and small hole arrays, are reasonably simplified or equivalently processed (deleted) to weaken the influence of fine structures on local stiffness distribution and avoid generating local high-frequency modes unrelated to the overall structural dynamics, thereby improving the reliability and stability of the modal analysis results. Furthermore, appropriate material parameters and boundary conditions are set according to the material properties, connection forms, and actual assembly conditions of the motor housing.

[0022] S2. Perform multi-mode analysis on the finite element model.

[0023] After establishing the finite element model, based on the underwater EHA operating excitation frequency band, the structural form of the motor housing, and connection constraints, multi-order modal analysis was performed on the finite element model of the motor housing. Multiple natural frequencies and corresponding mode shapes within a set frequency range were obtained. Based on the relative displacement amplitude and vibration energy distribution characteristics in the mode shapes, the modes were identified and classified, determining the low-order global modes that significantly affect the overall stiffness and the local modes that reflect the stability of the local structure. Modal analysis included: (1) The first and second modes in the axial vibration direction are used to identify the main axial bending deformation and antinode regions that affect the overall stiffness; (2) The first to fifth modes in the circumferential vibration direction are used to identify the circumferential lobe deformation and vibration energy concentration areas that affect the stability of the local structure.

[0024] S3. Identify key modal vibration regions.

[0025] By comparing and analyzing the contour maps of different modes (e.g.) Figures 6-10 As shown in the figure, the antinode regions, maximum relative displacement amplitude regions, and vibration energy concentration regions of the motor housing under different order modes were identified, and these regions were used as key reference (candidate) locations for subsequent structural stiffening design. Modal analysis results show that the motor housing mainly exhibits structural modal characteristics dominated by axial overall bending mode in low-order modes, while gradually showing vibration morphology dominated by circumferential lobe shell mode in mid-to-high-order modes.

[0026] S4. Circumferential ring rib arrangement based on axial overall bending mode.

[0027] For mode distributions exhibiting axial overall bending characteristics, i.e., mode morphology primarily characterized by axial overall bending, multiple circumferential ribs are arranged at intervals along the axial direction on the inner wall of the motor housing. These axial ribs correspond to the regions of maximum relative displacement amplitude or antinodes in the axial mode, thereby improving the local stiffness of the housing at critical axial positions and enhancing the overall structural stiffness. Furthermore, during the arrangement of the circumferential ribs, notches, through-holes, or partial reduction structures are incorporated into some stiffening structures according to the internal functional layout requirements of the underwater EHA. This avoids passageways for the motor, circuit boards, wiring harnesses, electrical connectors, plugs, and sealing structures, thus improving the overall stiffness and structural stability of the motor housing at critical axial positions without affecting the internal functional layout, ensuring the engineering feasibility of the structural optimization scheme.

[0028] Specifically, the circumferential ribs extend circumferentially along the motor housing and adopt a segmented structure. The circumferential coverage angle is controlled within the range of 180° to 350°, preferably approximately 270°.

[0029] More specifically, combining the mode shape distribution results of the first-order axial mode and the second-order axial mode (e.g.) Figure 6 and Figure 7 As shown (in the diagram), it can be observed that the motor housing forms the region of maximum relative displacement response at the midpoint of the axial direction in the first-order axial mode, exhibiting obvious overall bending vibration characteristics. In the second-order axial mode, two main mode antinodes are formed at approximately one-third and two-thirds of the axial length of the housing, respectively, representing regions of peak displacement response and concentrated vibration energy. Based on the above modal characteristic analysis results, this embodiment arranges three circumferential ribs at intervals along the axial direction on the inner wall of the motor housing, with their axial positions corresponding to the region of maximum displacement response in the first-order axial mode and the two main mode antinodes formed in the second-order axial mode, respectively. Given the integrated motor and related components inside the underwater EHA, the internal assembly space of the motor housing is limited. To ensure motor assembly clearance and operational safety, the three circumferential ribs all adopt a thin, internally reinforced structure, with a rib thickness controlled within approximately 3 mm. This effectively improves the overall stiffness of the motor housing while meeting the internal assembly space constraints.

[0030] S5. Arrangement of axial stiffeners based on the circumferential lobe-shaped shell mode.

[0031] To address the mode shape distribution exhibiting circumferential wavelobe-shaped shell mode characteristics in the circumferential modes—that is, mode shapes primarily characterized by circumferential wavelobe-shaped shell modes—several axial stiffeners are installed on the inner wall of the motor housing. These axial stiffeners are continuously arranged along the axial direction of the motor housing and extend throughout its entire length. During their extension and penetration, the axial stiffeners connect with the circumferential ring ribs on the inner wall of the motor housing, forming a spatial skeletal stiffening structure. This improves the circumferential stability and deformation resistance of the motor housing and raises the natural frequency of the circumferential wavelobe-shaped shell mode. Furthermore, during the arrangement of the axial stiffeners, notches, through holes, or localized reduction structures are incorporated into some of the stiffening structures according to the internal functional layout requirements of the underwater EHA. This avoids obstructing the passageways of the motor, circuit boards, wiring harnesses, electrical connectors, plugs, and sealing structures. Thus, without affecting the internal functional layout, the overall stiffness and structural stability of the motor housing at key circumferential locations are improved, ensuring the engineering feasibility of the structural optimization scheme.

[0032] Specifically, by comparing and analyzing the first to fifth circumferential modes, it can be found that the overall displacement response of the motor housing is relatively small under the first circumferential mode. However, in the second to fifth circumferential modes, the motor housing exhibits obvious vibration energy concentration and large circumferential lobe deformation characteristics at multiple circumferential positions, which are key modes that have a significant impact on structural reliability.

[0033] Based on the above analysis, the arrangement of the axial stiffeners in this embodiment is mainly determined according to the mode shape distribution characteristics of the second to fifth circumferential modes. Five axial stiffeners are ultimately arranged at intervals in the circumferential direction on the inner wall of the motor housing, all extending along the axial direction. Their circumferential positions are determined by comprehensively considering the overlapping positions of the vibration energy concentration areas in multiple circumferential mode shapes, in order to achieve coordinated control of multiple circumferential modes. The axial stiffeners adopt a rectangular cross-section, and their height and width are adjustable design parameters to improve the circumferential stiffness and overall stability of the motor housing under limited space conditions. Simultaneously, considering the limited internal assembly space, the thickness of the axial stiffeners in the radial direction is controlled within approximately 3mm to achieve effective structural stiffening while meeting assembly requirements. The final structural layout is as follows: Figure 5 and Figure 6 As shown.

[0034] S6. Optimization effect verification.

[0035] After arranging multiple circumferential ribs and several axial stiffeners, the optimized motor housing structure is re-analyzed (i.e., steps S1 to S2 are repeated). Under the same material parameters, boundary conditions, and corresponding modes with similar or identical vibration characteristics, the natural frequencies and maximum relative displacement amplitudes of the key modes of the motor housing structure before and after optimization are compared to verify whether the overall structural stiffness has been effectively improved. When the natural frequencies of the optimized structure are generally higher in multiple modes and the maximum relative displacement amplitude is lower than before optimization, the optimized design of the motor housing structure is complete.

[0036] Specifically, in this embodiment, comparative analysis results show that the axial first-order modal natural frequency of the optimized structure increased from 1614.8Hz to 2027.3Hz, an increase of approximately 25.5%; the axial second-order modal natural frequency increased from 2044.5Hz to 3488.7Hz, an increase of approximately 70.6%; and the circumferential first to fifth-order modal natural frequencies increased from 834.12Hz, 1143.3Hz, 1580.9Hz, 1614.8Hz, and 1903.1Hz to 985.03Hz, 1254.7Hz, 1739.9Hz, 2027.3Hz, and 3212.7Hz, respectively, with corresponding increases of approximately 18.1%, 9.7%, 10.1%, 25.5%, and 68.8%.

[0037] Combination Figures 6 to 10 The modal shape contour plots show that the optimized structure exhibits a general reduction in the maximum relative displacement amplitude under both the axial overall bending mode and the circumferential lobe-shaped shell mode, weakening the localized displacement concentration areas. Specifically, the maximum relative displacement amplitude of the axial first-order mode decreased from approximately 1.7578 to approximately 1.2802, a reduction of approximately 27.2%; the maximum relative displacement amplitude of the circumferential third-order mode decreased from approximately 2.1043 to approximately 1.1287, a reduction of approximately 46.4%. These results indicate that the optimized motor housing exhibits an overall increase in the natural frequencies under both axial and circumferential modes, with the modal frequency distribution shifting towards the higher frequency range. Simultaneously, under the same modal conditions, the maximum relative displacement amplitude corresponding to each mode decreases, effectively suppressing the previously localized axial overall deformation response and circumferential lobe-shaped shell deformation.

[0038] The comparison results of the natural frequency and the maximum relative displacement amplitude show that this embodiment, by recognizing multi-mode features, coordinates the circumferential ribs and axial stiffeners inside the motor housing. Under the premise of not significantly increasing the structural mass and meeting the assembly space constraints of the internal motor and related components, it effectively improves the overall stiffness and structural stability of the motor housing and reduces the structural vibration response. This provides a strong guarantee for the structural reliability, acoustic concealment and long-term service safety of the underwater EHA.

[0039] Although the present invention has been described using the above preferred embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by those skilled in the art to the above embodiments without departing from the spirit and scope of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A vibration control and stiffening optimization method for underwater EHA structures based on multi-mode characteristics, characterized in that, Includes the following steps: S1. Establish a three-dimensional structural model of the underwater EHA, extract the connection relationship, constraint features and load transfer relationship between the motor housing body and other components, and establish a finite element model of the motor housing. S2. Perform multi-mode analysis on the finite element model of the motor housing to obtain its multiple natural frequencies and corresponding mode shapes within a set frequency range; S3. Analyze the mode shapes of each order, identify the antinode regions, maximum relative displacement amplitude regions, and vibration energy concentration regions of the motor housing under different order modes, and determine the above regions as key candidate locations for structural stiffening optimization. S4. For the vibration mode distribution that exhibits the characteristics of an overall axial bending mode in the axial mode, multiple circumferential ring ribs are arranged on the inner wall of the motor housing at axial intervals and extending circumferentially. S5. For the vibration mode distribution that exhibits the characteristics of circumferential lobe-shaped shell modes in the circumferential mode, several axial reinforcing ribs are arranged along the axial direction on the inner wall of the motor housing. S6. Perform multi-modal analysis on the optimized motor housing structure again to verify the overall stiffness of the optimized motor housing structure. In step S2, the modal analysis includes the first and second modes in the axial vibration direction, and the first to fifth modes in the circumferential vibration direction. In step S6, the verification process includes: comparing the natural frequencies of each key mode and the maximum relative displacement amplitude of the motor housing structure before and after optimization. When the natural frequencies of the optimized structure are generally higher than those before optimization in multiple key modes, and the maximum relative displacement amplitude is lower than that before optimization, the stiffening optimization design of the motor housing structure is completed.

2. The underwater EHA structure vibration control and stiffening optimization method based on multi-mode characteristics according to claim 1, characterized in that, In step S1, during the finite element modeling process, structural features that are not significantly related to the overall structural dynamics are simplified.

3. The underwater EHA structure vibration control and stiffening optimization method based on multi-mode characteristics according to claim 1, characterized in that, In step S4, during the arrangement of the circumferential ribs, a reduction structure is set for some of the circumferential ribs according to the internal functional layout requirements of the underwater EHA.

4. The underwater EHA structure vibration control and stiffening optimization method based on multi-mode characteristics according to claim 1, characterized in that, In step S5, there are multiple axial reinforcing ribs, which are arranged at intervals along the circumference.

5. The underwater EHA structure vibration control and stiffening optimization method based on multi-mode characteristics according to claim 1 or 4, characterized in that, In step S5, during the arrangement of axial stiffeners, a reduction structure is set for some axial stiffeners according to the internal functional layout requirements of the underwater EHA.

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