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[Objective] Application of six-degree-of-freedom(DOF) robotic arms in industrial automation and intelligent manufacturing is rapidly expanding, especially in offshore operations, where high path planning accuracy and energy efficiency are critical. The complexity and uncertainty of offshore environments pose significant challenges to traditional path planning methods, making it difficult to achieve an effective balance between path precision and energy consumption. To address these challenges, this study proposes a path optimization method based on multi-objective optimization techniques, aimed at simultaneously improving path planning accuracy and energy efficiency for six-DOF robotic arms operating in offshore environments. Specifically, the proposed method seeks to minimize terminal error while reducing energy consumption, which is particularly important in applications where energy costs and precision are paramount. [Methods] First, a positive kinematic model of the robotic arm is developed using the Denavit–Hartenberg(D–H) parameter method, providing a foundation for minimizing terminal errors during path planning. To determine the optimal joint angle trajectories, a particle swarm optimization(PSO) algorithm is employed. The PSO algorithm is well-suited for solving nonlinear optimization problems, as it mimics the social behavior of birds flocking to efficiently search for global optimal solutions. Subsequently, the relation between energy consumption and terminal error is analyzed, focusing on gravitational potential energy and joint rotational motion, which are the primary contributors to energy usage during robotic arm movements. Based on this analysis, a multi-objective optimization model is developed, incorporating 0–1 binary decision variables to represent the selection of joint configurations. To make the problem tractable, the multi-objective model is converted into a single-objective optimization problem using an ε-constraint approach. This strategy simplifies the optimization process while maintaining an appropriate balance between path accuracy and energy efficiency. A genetic algorithm(GA), a powerful global search technique, is utilized to solve the resulting single-objective optimization problem, enabling efficient exploration of the solution space. For environments with obstacles, an obstacle avoidance path planning strategy based on the breadth-first search(BFS) algorithm is incorporated to ensure collision-free motion of the robotic arm along the optimized path. [Results] Simulation results demonstrate the effectiveness of the proposed multi-objective optimization method. Compared with traditional path planning approaches, the proposed method achieves a significant reduction in terminal error and energy consumption. Path planning accuracy is notably improved, and energy efficiency is enhanced, which is crucial for offshore operations where resources are often limited. The proposed method outperforms conventional methods in terms of path optimization and robustness, particularly in environments with obstacles and uncertainties. Furthermore, the method shows considerable improvements in energy efficiency without compromising the accuracy of the path. [Conclusions] By integrating advanced optimization and search techniques, such as PSO, GA, and BFS, this paper successfully addresses the challenges of path planning in offshore robotic applications. The proposed method enhances path-planning accuracy and significantly reduces energy consumption, providing an efficient solution for complex industrial automation tasks. These results highlight the great potential of the proposed approach for enhancing the performance of robotic arms across various applications, especially in offshore operations where energy efficiency and precision are of utmost importance.
[Objective] To implement the educational mechanism of scientific research feeding back into teaching, enhance the practical teaching quality in oil and gas storage and transportation engineering, and embody the engineering education philosophy of “virtual–real integration and research–education–industry collaboration,” a simulation teaching experiment was designed on “Impact characteristics on floating roofs impact by liquid during oil receiving in internal floating roof tanks based on Ansys Fluent.” [Methods] The simulation experiment comprised three-dimensional modeling, mesh generation, configuration of simulation parameters, transient solution computation, result post-processing, analysis of turbulent flow characteristics during oil impact on the floating roof, and evaluation of surface pressure distribution and impact forces on the floating roof. Students were required to research literature and textbooks to understand transient simulation methods, classifications, and the applicability of turbulence models and moving mesh techniques. They had to gain expertise in operating software such as Ansys SpaceClaim, Ansys Meshing, and Ansys Fluent, as well as in writing profile files, and were expected to utilize Tecplot to process simulation data. Additionally, a comprehensive assessment and evaluation system encompassing the entire process before, during, and after the simulation experiments was established. Through activities such as pre-simulation preparation, simulation operations, and problem-solving, the practical simulation abilities of the students were thoroughly evaluated. [Results] The numerical simulation of the oil-flow impact characteristics on the floating roof during normal oil receiving processes in internal floating roof tanks under different oil inlet velocities and initial liquid levels showed that at identical initial liquid levels, the turbulent kinetic energy and turbulent viscosity of the oil flow increased with rising inlet velocities. At constant oil inlet velocities, higher initial liquid levels reduced the pressure impact on the opposite tank wall of the inlet and the upper edge of the floating roof. Therefore, protection of these areas should be prioritized during low-level oil receiving processes to ensure tank safety and integrity and prevent fire and explosion incidents. Under identical oil inlet velocity conditions, when receiving oil at a low initial liquid level(1.8 m), the floating roof experiences greater impact forces. As the floating roof rose to 5 m and 9 m, the impact forces encountered during ascent changed relatively gradually over time, with the oil flow exerting comparatively smaller forces on the roof. When the oil inlet velocity increased from 2.5 m/s to 4 m/s, under identical initial liquid level conditions, the impact force peak gradually increased, and the time at which the peak is reached occurred earlier. [Conclusions] The instructional design of this simulation experiment reveals the flow field characteristics and response patterns of oil flow impacting a floating roof, providing a scientific basis for optimizing the structural design of floating roofs and the oil receiving and delivering process. Further, it sparks students' interest in inquiry, exercises their software operation skills, cultivates their scientific research and innovative thinking, enhances their engineering application capabilities, and lays a solid foundation for their graduation projects. Thus, it further strengthens the groundwork for their subsequent participation in storage tank safety research and engineering design work.
[Objective] Vehicle suspension systems are pivotal to the comfort, handling stability, and safety. Traditional passive suspensions are limited by fixed parameters that cannot adapt to varying road excitation, while fully active solutions remain prohibitively expensive and energy-intensive for mass-market adoption. Magnetorheological(MR) semi-active suspension systems offer a promising compromise because they can vary the damping force almost instantaneously with minimal power consumption. Despite a rich body of simulation studies, vehicle engineering education still lacks a low-cost, open-architecture experimental virtual instrumentation platform that exposes students to the entire “modeling–control–validation” workflow. This paper presents the design, implementation, and pedagogical deployment of an innovative quarter-car test bench that integrates measurement and control technology, embedded computing, and reproducible laboratory exercises. [Methods] The platform is based on a two-degree-of-freedom quarter-car rig consisting of sprung and unsprung masses connected by a coil spring, a tire-equivalent spring, and a commercially available MR damper whose force is continuously adjustable with currents ranging from 0 A to 1.5 A. A high-precision servo-electric cylinder generates vertical displacements that replicate random road profiles synthesized by a filtered-white-noise algorithm; profile severity is scaled to standard road classes A–D. Multi-modal sensing is achieved using IEPE accelerometers, magnetostrictive displacement transducers, and strain-gauge force sensors whose outputs are synchronously sampled at 1 kHz by a hybrid data-acquisition architecture that combines NI 9230 and ART USB-313 XA cards. A dual-core “STM32-LabVIEW” control backbone partitions tasks: an STM32H7 microcontroller executes real-time damping control algorithms at 1 kHz, while a LabVIEW host application provides supervisory control, data logging, and a graphical user interface. A hierarchical “three-layer” coupling(physical–algorithm–execution) and a “dual-loop” structure(outer excitation–response loop and inner damping-force loop) are introduced to guarantee microsecond-level synchronization and millisecond-level control latency. To support educational objectives, the system exposes all signals through open APIs. This allows students to implement and compare classical skyhook, groundhook, and hybrid skyhook–groundhook policies in MATLAB/Simulink before validating them on the rig. [Results] Extensive experimental campaigns demonstrated the component-level and system-level performances of the proposed test bench. At the component level, steady-state sinusoidal tests revealed that the MR damper force increased monotonically with applied current, rising from 60 N at 0 A to 220 N at 1.5 A, with a clear saturation trend beyond 1.2 A. This characteristic was well captured by an embedded hyperbolic–tangent model that was updated online to compensate for temperature drift. At the system level, C-class random-road experiments conducted at 36 km·h–1 showed that the hybrid skyhook–groundhook algorithm suppressed sprung-mass vertical acceleration, suspension deflection, and tire dynamic load remarkably better than the passive setup, although the exact percentage improvements are not reported herein. The results of five-run repeatability tests showed that the coefficient of variation was less than 5% for all key metrics, confirming the robustness of the test bench. Comparative tests across B-, C-, and D-class roads at 72 km·h–1 further demonstrated that despite intensified vehicle vibration on harsher road profiles, the semi-active controller consistently outperformed the passive configuration in mitigating these responses. Student feedback collected over two academic semesters implied that the “theory–simulation– experiment” workflow shortened the concept-to-validation cycle and significantly improved engagement. [Conclusions] The proposed magnetorheological semi-active suspension platform successfully bridges the gap between theoretical studies and hands-on experimentation. Its modular hardware and open-source virtual instrumentation platform make it affordable and extensible to other vehicle engineering topics. In addition, the embedded measurement and control framework equips students with industry-relevant skills. Future work will integrate energy-harvesting shock absorbers and cloud-based teleoperation to transform the rig into a cyber–physical learning factory.
[Objective] Based on the ongoing global energy crisis and sustainable development goals, synthesizing highly efficient and stable composite photoanodes to achieve the efficient conversion of solar energy into green energy, such as H2, is essential in the photoelectrochemical(PEC) field. In this study, we design a comprehensive experiment centered on a composite photoanode—B:CoOx/BiVO4—for PEC water oxidation, grounded on the concept of integrating science and education as well as cutting-edge research findings of faculty members. Implementing such an experiment for undergraduate students not only helps bridge the gap between textbook knowledge and the related frontier of scientific research but also demonstrates the practical necessity for fostering high-level, energetic students equipped with innovative and creative capabilities. [Methods] Electrochemical deposition and solution impregnation were employed to fabricate an oxygen vacancy-rich B:CoOx/BiVO4 composite photoanode on an FTO substrate. By leveraging a large-scale instrument and equipment sharing platform from the state key laboratory of organic–inorganic composites, including scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy, the morphology, crystal structure, elemental composition, and oxygen vacancy of B:CoOx/BiVO4 were characterized, and the corresponding images and data were analyzed in detail. Further, the water oxidation performance of B:CoOx/BiVO4, including photocurrent density, stability, solar energy conversion efficiency, and charge separation/transfer efficiencies, was thoroughly investigated using linear sweep voltammetry, current–time curves, Mott–Schottky plot, polarization and surface charge transfer curves, and electrochemical impedance spectroscopy. In addition, the mechanism by which the oxygen vacancy-rich B:CoOx cocatalyst promotes the water oxidation performance of BiVO4 was explored. [Results] As revealed by the aforementioned characterizations, the oxygen vacancy-rich B:CoOx cocatalyst was successfully grown on the BiVO4 photoanode surface. Microscopic characterizations and electrochemical measurements manifest that the oxygen vacancy-rich B:CoOx cocatalyst decoration promotes photo-induced charge separation, provides rich surface catalytically active sites, accelerates charge transfer, and reduces the energy barrier for the water oxidation reaction, thereby boosting BiVO4's PEC activity. The optimized B:CoOx/BiVO4 composite photoanode exhibited an excellent PEC water oxidation performance, yielding a high photocurrent density of 3.20 mA cm-2 at 1.23 VRHE, and excellent stability for 5 h. Upon intermittent illumination for 180 min, the accumulation contents of O2 and H2 over the B:CoOx/BiVO4 photoanode and Pt cathode reached 104.5 and 53.4 µmol cm-2, respectively. [Conclusions] The comprehensive experiment conducted in this study is to develop a highly active oxygen vacancy-rich B:CoOx/BiVO4 composite photoanode via electrochemical deposition and solution impregnation. It was designed as a leading-edge scientific endeavor, integrating B:CoOx/BiVO4 synthesis, structural characterizations, electrochemical properties, PEC water oxidation assays, experimental data and result analysis, and possible reasons for the performance enhancement of the as-fabricated composite photoanode. This comprehensive experimental training helps students to understand the preparation and optimization of photoanodes and the PEC water oxidation theory, thereby cultivating comprehensive experimental skills, scientific exploration, and innovation consciousness.
[Objective] Mode-locked fiber lasers are extensively employed in a variety of fields, such as ultrafast spectroscopy, optical communication, precision machining, precision metrology, and biomedical science, because of their compact design, narrow pulse duration, high peak power, and excellent beam quality. Saturable absorbers with desirable nonlinear optical properties are essential to achieve stable mode-locking operation. Graphene oxide(GO) has several advantages, including a low saturation intensity, substantial modulation depth, high damage threshold, and rapid recovery time. Additionally, gold nanorods(GNRs) have a high third-order nonlinear coefficient and an ultrafast response time. Hence, they are exceptionally promising for applications in both saturable absorption and reverse saturable absorption. The synergistic integration of GO and GNRs can amalgamate the strengths of these two materials, producing state-of-the-art saturable absorbers with enhanced performance. To meet the experimental teaching requirements of the course “Nonlinear Optics: Principles and Applications,” with a focus on the nonlinear saturable absorption effects of materials and their applications in fiber lasers, we propose a comprehensive experiment on high-order harmonic mode-locked fiber lasers based on a graphene oxide–gold nanorod(GO-GNRs) composite material. [Methods] In this study, the GO was synthesized from natural graphite powder by a modified Hummers method, while the GNRs were fabricated through a seed-mediated growth technique. Subsequently, the GO-GNRs composite was fabricated by an ex situ hybridization method, ensuring a uniform and stable combination of these two components. The GO-GNRs were characterized and analyzed to evaluate their material properties and saturable absorption behavior. To fabricate a fiber device, the GO-GNRs were deposited onto the cross-section of a D-shaped optical fiber to serve as a saturable absorber(SA). Thereafter, the fabricated GO-GNRs were integrated into an Er3+-doped fiber laser cavity, enabling ultrashort pulse generation via their SA property. [Results] By adjusting the pump power and polarization controller(PC), the fundamental mode-locked pulse was obtained with a central wavelength of 1 559.65 nm and a repetition rate of approximately 20.555 7 MHz. The mode-locking operation exhibited excellent long-term stability. When the pump power was increased to 600 mW, the 34th-order harmonic mode-locked pulse was obtained by suitably adjusting the PC orientation, corresponding to a repetition frequency of 699.301 MHz and a signal-to-noise ratio(SNR) of 68.2 dB. The results demonstrated that GO-GNRs effectively enhanced nonlinear optical modulation, promoting the formation and stabilization of high-order harmonic mode-locking. [Conclusions] This comprehensive experiment effectively enhances students' abilities to apply theoretical knowledge to practical analysis and operations. Through the synthesis and characterization of low-dimensional materials, students can gain practical experience in nanomaterial fabrication and optical measurement techniques. In the mode-locked Er3+-doped fiber laser experiment, students can understand the working principles, structural design, and output characteristics of fiber lasers. By combining theoretical teaching with experiment, this work stimulates students' research interest, broadens their innovative thinking, and strengthens their ability to solve complex problems independently.
[Objective] The growing national and societal demand for talent in the field of polymorphic networks has highlighted the relevance of advancing network education in universities. As the primary institutions for cultivating network professionals, universities are placing increasing emphasis on the development of practical, forward-looking network curricula. Given the inherently hands-on nature of networking, designing polymorphic network experiments enables students to broaden their knowledge base, gain a deeper understanding of polymorphic network theory, and strengthen their innovative capabilities. However, traditional network teaching experiments are often limited by rigid protocols, which lack flexibility, programmability, and support for innovation. Although emerging experiments based on software-defined networking(SDM) and programmable data plane(PDP) offer improvements, they largely remain confined to single-modality scenarios. Therefore, overcoming the constraints of traditional methods and creating innovative experiments that support polymorphic network design has become an urgent and valuable research focus. [Methods] Inspired by the strong correlation between key modality processing technologies in polymorphic networks and the capabilities of the P4-based PDP, the flexible forwarding advantages of the PDP are leveraged to redesign the original programming network experiments. By integrating cutting-edge research achievements in PNs, we developed a comprehensive experimental project—PDP-based polymorphic network—and introduced it into undergraduate teaching. Three major challenges were addressed during the design process: redefining the experimental objectives, optimizing the design and content of the experiment, and implementing effective instructional guidance. The overall goal of the designed experiment is to construct and implement a polymorphic network topology based on P4 PDP. The experiment includes multiple progressive stages, namely, single-modality network implementation, dual-modality network implementation, polymorphic network implementation, modality scheduling, and arbitration verification, as well as supporting flexible adjustment of difficulty levels. In terms of instructional support, instructors are expected to provide continuous progress tracking and comprehensive guidance throughout the experimental process. [Results] Topology and link state correctness are validated using the Mininet platform's command-line interface. Connectivity tests confirm that hosts on both sides of the polymorphic network can communicate, and packets sent from one host are encapsulated into different modalities and forwarded to the other host using distinct addressing and routing methods. In the security test, an ARP spoofing attack is launched from a server based on CENI, confirming that the polymorphic network provides greater security than traditional single-modality networks when facing network threats. Simulated packet transmission and reception experiments verify that the polymorphic network introduces some overhead. Finally, the experiment is validated through actual implementation in an educational setting. [Conclusions] This experiment is derived from cutting-edge research in polymorphic networking. By leveraging the PDP capabilities, the experiment designs and implements multiple network forwarding modalities and supports flexible adjustment of difficulty levels. As verified through actual teaching practice, the experiment can effectively help students broaden their knowledge in the field of networking, deepen their understanding of polymorphic networks, enhance their skills in network programming, and strengthen their capacity for polymorphic network innovation.
[Objective] Ultrahigh-temperature ceramics(UHTCs) are essential materials for aerospace thermal protection systems, including nose caps and wing leading edges, due to their excellent high-temperature mechanical properties, resistance to antioxidant ablation, and appropriate thermal expansion coefficients. However, their inherent brittleness results in low fracture toughness and poor thermal shock resistance, which limits their widespread use. Fabricating ceramic matrix composites through continuous fiber reinforcement and the precursor infiltration and pyrolysis method offers an effective solution, with ceramic precursors playing a key role in defining the final composite properties. [Methods] This study provides a comprehensive experiment on synthesizing and optimizing SiZrBC ceramic precursors, combining cutting-edge UHTC research with educational practices to address the high costs and low yields associated with traditional precursors. The experiment utilized a one-pot polymerization method with zirconium tetrachloride, tetraethyl orthosilicate(TEOS), boric acid, and boron phenol resin(BPR) as raw materials. It systematically examined the effects of precursor preparation temperature(80 ℃-120 ℃), Si source(TEOS), B source(boric acid), and C source(BPR), along with the influence of different pyrolysis atmospheres on the properties of the resulting ceramics. Characterization techniques included Fourier Transform Infrared Spectroscopy(FTIR), X-ray diffraction(XRD), scanning electron microscopy(SEM), and energy dispersive spectroscopy(EDS). [Results] The results showed that the best overall properties were achieved at a synthesis temperature of 80 ℃, with the addition sequence starting with the Si source, then the B source, followed by the C source. Pyrolysis was performed at 1 550 ℃ in an argon atmosphere. This addition order significantly affected ceramic yield and microstructure. Specifically, initial addition of the Si source helped form a Si–O–Zr network, providing stable attachment sites for subsequent components, while early B source addition facilitated B–O bonds in the polymer backbone, acting as strong cross-linking points. The precursor was pyrolyzed at 1 550 ℃ in an argon atmosphere to produce composite ceramic powder with optimal properties. After pyrolysis at 1 000 ℃ in argon, the ceramic achieved a high yield of 64.7%, with fine grains averaging approximately 65.61 nm, and exhibited relatively low toxicity and low raw material costs. The pyrolysis atmosphere greatly influenced the final product: argon favored higher ceramic yields and finer grains by slowing gas diffusion and promoting network formation, while a vacuum atmosphere encouraged complete oxide reduction but accelerated boron loss via B_2O3 evaporation and grain growth beyond 106 nm. Vacuum pyrolysis removed ZrO2 impurities but resulted in lower ceramic yields and larger grains. [Conclusions] This experimental approach effectively integrates core materials science concepts with practical laboratory work, covering all stages from material synthesis and structural characterization to performance analysis. By systematically exploring processing-structure-property relationships, students develop a deeper understanding of ceramic precursor chemistry, pyrolysis mechanisms, and advanced characterization methods such as FTIR, XRD, SEM, and EDS. The use of low-toxicity, cost-effective raw materials ensures safety and accessibility in educational settings. This experiment improves the quality of materials chemistry education, enhances students' practical skills in data analysis and problem-solving, and promotes innovative thinking vital for scientific research. Through project-based learning, students acquire critical research skills, recognize the importance of parameter optimization, and understand the connection between laboratory experiments and real-world aerospace applications, preparing them for careers in materials science and engineering.
[Objective] To enhance the energy consumption capacity and assembly efficiency of precast concrete structures, a novel design of cantilever-supported beam-end precast joints is proposed. In this study, we elucidate the force transmission mechanism of such joints and identify potential failure issues at the structural interface connection formed by embedded reinforced concrete and structural steel. [Methods] Cantilever-supported beam-end assembly node specimens were fabricated according to the requirements of the current national standard drawings and specifications, such as the Concrete Structure Design Code and Steel Structure Design Code. Various analysis methods, including low-cycle cyclic testing, simulation modeling, and theoretical analysis, were employed. Node damage patterns were observed throughout the process, and high-density strain data from the entire beam section(reinforcing bars and structural steel) were collected for comparative analysis. The low-cycle fatigue testing employed interlayer displacement angle control for loading using an MTS servo actuator. Simulation methods were based on rapid building information modeling of precast special-shaped components and CAE finite element analysis. Theoretical analysis primarily focused on node failure patterns, reinforcement stress, and structural steel stress. [Results] Novel design of cantilever-supported beam-end precast joints avoids the structurally complex and installation-restricted core zone at beam-column junctions. This approach enhances construction efficiency, minimizes impact on the core zone, and effectively uses steel to achieve plastic energy dissipation. In this study, we analyzed and summarized the stress distribution patterns in cantilever-supported beam-end precast joints, along with how changes in the strength ratio between beam segments and structural steel sections affect joint load-bearing capacity. We also reveal the interaction mechanism between embedded structural steel and concrete interfaces. [Conclusions] Cantilever-supported beam-end precast joints transfer forces through concrete compression by the steel section. Bending moments and shear forces are transmitted from the reinforced concrete main beam section to the steel section. Bolted connections then distribute these forces to the steel flange(bending moment) and web(shear force) of the cantilever-supported beam section. Subsequently, the forces are transferred to the reinforced concrete via the compression of the embedded zone within the steel section, ultimately reaching the core joint region. Node failure primarily occurs when the embedded depth is too shallow or the reinforced concrete section's flexural strength is insufficient, causing excessive concrete compression by the steel section. This compression exceeds the cube compressive strength, leading to premature failure. Increasing the embedded depth or enhancing the reinforced concrete section's strength can effectively prevent premature node failure. The load-bearing capacity of a node primarily relies on the reinforced concrete beam segment's sectional strength. When the beam segment's sectional strength is lower than that of the structural steel, the beam segment's longitudinal reinforcement will reach its yield strength before the structural steel, thereby reducing the load-bearing capacity. When the beam segment's sectional strength exceeds that of the structural steel, the structural steel reaches its flexural yield strength first but has not yet reached its shear yield strength, thereby increasing the load-bearing capacity. When both strengths are equal, the beam segment's longitudinal reinforcement and the structural steel's weakened section simultaneously reach their flexural yield strength.
[Objective] Cross-medium impact dynamics is a core compulsory course for ship and ocean engineering, aerospace engineering, and related majors. It deals with complex physical phenomena such as underwater ejection of navigating bodies, cavitating multiphase flow, and water-exit impact. Traditional theoretical teaching relies primarily on formula derivation and lacks effective visualization tools, making it difficult for students to understand the intricate ice–flow–solid coupling mechanisms and cavitation evolution laws involved in the process. Although cross-medium experimental teaching has been explored domestically and internationally, research on experimental teaching with a focus on cavitation morphology evolution during the high-speed water-exit icebreaking process of a navigating body is lacking. This study aims to fill this gap by integrating the high-speed water-exit icebreaking experiment of navigating bodies with course teaching: systematically observing the entire experimental process; analyzing key characteristics, including changes in the velocity of the navigating body, wake cavitation morphology evolution, and ice layer fragmentation rules; and developing an intuitive experimental teaching case to overcome the insufficiency of intuitiveness of traditional teaching and improve the experimental operation skills and scientific thinking ability of students. [Methods] An integrated experimental and teaching system was constructed. The experimental system comprised a high-speed water-exit icebreaking system, a data acquisition system, and an ice-making device. A transparent acrylic water tank(80 × 80 × 120 cm) was filled with tap water to a depth of 80 cm; prefabricated ice layers(8 layers in all, each 40 × 40 × 1.5 cm, prepared 2 days in advance) were placed on the water surface. The navigating body(length: 257 mm, diameter: 38 mm) was ejected by 150 kPa high-pressure air from a gas tank(controlled by a PLC panel and solenoid valve). Two Phantom VEO 710L high-speed cameras(10,000 frames/s, 448 × 800 resolution, and 50 μs exposure) and two 2000 W thermal headlamps captured images at horizontal and oblique overhead angles; the data were processed by PCC software. The experiment followed 10 standardized steps, and teaching adopted a three-stage model: pre-class preparation(teachers prepared equipment/outlines; students previewed), in-class group experiments(role rotation for camera operation, PLC control, and phenomenon observation), and post-class assignments. Velocity was calculated as displacement divided by the time interval using high-speed camera frame data. [Results] The experiment accurately reproduced the underwater movement, ice collision, penetration, and water–air interface crossing of the navigating body. Velocity increased initially and then decreased, rising from 7.41 m/s(head exit) to 8.15 m/s(tail exit), then dropping to 7.41 m/s(ice collision), 5.13 m/s(ice penetration, a 31% decrease), and finally 4.76 m/s(tail water-exit). Cavitation evolved in five stages: stable aggregation(pre-collision), irregular mushroom-shaped disturbance(collision), intense fragmentation with vacuum zones(icebreaking), asymmetric elongation/shedding(penetration), and gradual dissipation(water-exit). Ice cracks developed from intact surfaces(pre-collision) to microcracks(initial collision), reticulated main cracks(icebreaking), expanded networks with shedding(penetration), and complete fragmentation into small pieces(post-water-exit). In the teaching process, visualization substantially improved students' understanding, and group rotation ensured mastery of all key equipment operations. [Conclusions] This study successfully established an innovative experimental teaching method for the free-ejection high-speed water-exit icebreaking movement of navigating bodies. Experimental results revealed complex multiphase flow coupling characteristics, providing important data for polar underwater vehicle design. Integrating experiments with teaching overcomes the poor intuitiveness of traditional theoretical teaching, improves students' grasp of cross-medium dynamics principles(e.g., cavitation evolution and ice–flow–solid coupling), and cultivates practical skills in equipment operation, data processing, and error analysis. Standardized procedures and interactive design make the teaching method applicable to ship and ocean engineering, aerospace engineering, and other majors. Post-class open questions stimulate students' innovative thinking, enrich cross-medium experimental teaching resources, and lay a solid foundation for talent cultivation in related disciplines.
[Objective] A grid-shaped steel box girder structure serves as the core load-bearing component of ground support systems in a specific engineering project. It bears static support, fuel filling, and gas flow impact loads during service. Owing to the extensive number of structural welds and their concealed locations, weld cracks are inevitable during manufacturing, assembly, and usage. During actual inspection and maintenance, cracks are detected in various weld locations within the structural load-bearing core area. This core area comprises a two-way grid pattern of girders with complex stress conditions, making it difficult to assess crack propagation under high-intensity service conditions. Existing studies primarily employ an analytic hierarchy process or a finite element method to analyze the impact of cracks on structural reliability and service life. However, these studies did not investigate the propagation behavior of cracks under repeated operational loads, and their findings were not sufficiently validated by experimental data. [Methods] To assess the crack propagation behavior at critical weld joints under high-intensity service demands and ensure structural service safety, an experimental research approach was adopted. A 1:10 scaled-down model of a load-bearing core structure was designed based on similitude relationships. Six artificial defects were prefabricated at different weld locations within the load-bearing core area by introducing artificially created flaws, with two and four located in the compression and tension zones, respectively. Then, fatigue loading was applied by progressively increasing the load magnitude, resulting in the initiation of four initial cracks. Subsequently, crack propagation tests were conducted on the scaled-down model with these cracks under equivalent service loads.[Results] Test results indicate the following.(1) When the fatigue peak load was increased to three times the equivalent service load, fatigue cracks initiated from all prefabricated defects in the tension zone, whereas no cracks were observed in the compression zone throughout the process.(2) With twice the equivalent service fatigue loading, the cracks in base and vertical plates at support points #2 and #4 of the scaled-down model exhibited similar evolution characteristics. The crack growth rates in the lower sections of the vertical plates were consistently higher than those in the base plates, which aligns with the strain patterns measured during the prefabricated crack tests.(3) The propagation direction of all cracks was essentially perpendicular to the beam's longitudinal direction(i.e., the tensile stress direction), indicating that the cracks were primarily in the opening mode.(4) The a–N curves of all propagating cracks demonstrated relatively stable linear characteristics, with the maximum growth rate recorded at 0.945 mm/10³ cycles. [Conclusions] We proposed and validated the feasibility of using artificially prefabricated defects combined with stepwise increased fatigue loading to generate initial cracks in structural testing. The test results elucidated the propagation behavior of cracked structures at critical weld locations under equivalent service loads. This provides an experimental data reference for technicians to assess the service condition of the load-bearing core structure and forms a basis for optimizing structural inspection and maintenance strategies.