First, based on the modified Hamiltonian principle, the nonlinear dynamic control equation of the deep-sea coarse-grained ore vertical lifting pipeline system was established. Then, the equation was discretized using the Galerkin method, converting the partial differential equation into a system of ordinary differential equations. Finally, numerical solutions were obtained for the stability characteristics of the pipeline using the eigenvalue method and Newton-Raphson iteration method. The system analyzed the influence of four key dimensionless parameters, namely the particle feed concentration, terminal lumped mass, gravity coefficient of the pipeline, and fluid velocity, on the critical flow velocity of the structure. Results show that when the feed concentration is C_v is 0.1, Hopf bifurcations occur only in the first three modes. When the feed concentration increases to C_v = 0.3, a Hopf bifurcation also occurs in the fourth mode, and the minimum critical flow velocity u_cr decreases significantly. When the internal flow velocity is below the critical value, the imaginary parts of the complex eigenfrequencies remain positive, indicating decaying structural vibrations. Once the internal flow velocity exceeds the critical threshold, the imaginary part of the first complex eigenfrequency becomes negative, signifying flutter instability. When the gravity coefficient α is held constantly, the critical flow velocity u_cr increases progressively with the dimensionless terminal mass κ₅. Conversely, with fixed κ₅, an increase in the gravity coefficient leads to a significant rise in critical flow velocity, exhibiting an approximately parabolic growth trend.

To address the insufficient analytical accuracy of traditional turbulence models in simulating ship maneuvering flow characteristics, this study proposesd a hydrodynamic derivative identification method based on the Elliptic Blending (EB) turbulence model, aiming to improve the prediction accuracy of ship motion under complex maneuvering conditions. Taking the KCS ship as the object, the performance of the k-ε turbulence model, Shear Stress Transport (SST) k-ω turbulence model and EB turbulence model was compared in terms of flow stability and vortex-resolving capability. Based on the EB turbulence model, static drift and pure yaw simulations were conducted to identify hydrodynamic derivatives, which were then input into the MMG model to predict turning motions. The EB turbulence model significantly improves the resolution of flow with strong pressure gradients near the wall by reconstructing the Reynolds stress transport equations. It accurately captures the evolution of bilge vortex clusters and asymmetric stern vortices in static drift conditions. In pure yaw motion, it effectively represents the dynamic coupling between vortex intensity and free-surface fluctuations. For the 35° rudder angle turning prediction, the average deviations of tactical diameter and steady turning diameter are only 3.34% and 1.55%, respectively, representing a maximum accuracy improvement of over 30% compared to the k-ε turbulence model. The EB turbulence model demonstrates high fidelity in simulating ship maneuvering flow characteristics, enables accurate identification of hydrodynamic derivatives, provides reliable prediction of maneuvering motions, and offers a reliable tool for the safety assessment of actual ship navigation.

Based on the 10 MW semi-submersible floating wind turbine foundation OO-Star, this study investigates the influence of wave spectrum characteristics on the dynamic behavior of floating wind turbines. A hydrodynamic analysis model of the floating wind turbine is established in ANSYS/AQWA, and hydrodynamic loads are calculated using Morison’s equation and potential-flow theory. Under identical incident wave height and peak period conditions, the effects of wave spectrum bandwidth on the hydrodynamic performance of the floating platform are analyzed. The surge and pitch responses of the turbine increase significantly with broader wave spectra, with peak amplitudes increasing by over 50%. Meanwhile, surge and pitch motions are distributed over a wider displacement range, indicating greater variability in motion response. Statistical values for heave response show little variation across different spectral bandwidths, suggesting a limited influence of spectrum width on heave motion. As spectral bandwidth increases, mooring line tension rises markedly and exhibits greater variation, potentially, exacerbating fatigue damage in the mooring system.

To establish an intelligent prediction method for internal shock environments of shipboard cabinet-type equipment, this study conducted shock tests on typical shipboard electrical cabinets to verify the reliability of numerical calculation methods. Based on industry survey data, a parametric simplified model of cabinet-type equipment was established. Using Abaqus secondary development, a batch finite element analysis platform was constructed, successfully obtaining 1000 complete datasets containing structural parameters, shock loads, and dynamic responses. To address the limitations of traditional regression models, an innovative deep neural network (DNN) shock response prediction model was developed, creating dedicated prediction networks for spectral acceleration, spectral velocity and spectral displacement. Through grid search algorithm optimization of network topology, a coefficient of determination R² > 0.9 was achieved, with the mean absolute error of spectral acceleration prediction being 0.14, while spectral velocity and spectral displacement prediction errors were both below 0.1. The SHAP (SHapley Additive exPlanations) interpretability analysis method was introduced, revealing that installation frequency, spectral velocity of foundation shock environment and plate thickness are dominant factors in shock responses, clarifying the coupling mechanism between structural parameters and shock loads. The research results provide efficient analysis tools and theoretical support for shock-resistant design of shipboard equipment.

At present, submarine propulsion shafts are gradually developing towards shorter shafts, and they have features such as multi-segment, variable cross-section, and variable bearing oil-film stiffness. The existing analytical methods are mostly based on uniform beam theory, which has limitations in solving multi-segment and variable cross-section shaft systems. To address this issue, this paper proposes an analytical calculation method for the modal and vibration transmission of multi-segment, variable cross-section, and variable stiffness-supported propulsion shaft systems based on the Timoshenko beam vibration theory. This method has high solution efficiency and good agreement with finite element results. Based on this theoretical model and calculation method, the paper studies the influence of bearing stiffness variation, bearing simulation methods and bearing span on the vibration characteristics of complex propulsion shaft systems. The results show that this analytical method is highly practical and can effectively consider the influence of the variation in bearing oil film stiffness on the vibration of the shafting system. The main manifestation is that as the bearing speed and frequency increase, the bearing stiffness decreases and the natural frequency of the propeller shaft reduces. In addition, when modeling the shafting system, it is recommended that the number of simulated springs for the bearing be more than two, and the bearing span should not be too large. It should be selected based on the effective length of the actual bearing; otherwise, the deviation of each natural frequency will increase.

Deepwater mooring systems are critical infrastructure for semi-submersible platforms, directly influencing their operational safety and stable operation. Traditional steel-chain mooring systems are increasingly inadequate for meeting the urgent demands of deepwater and ultra-deepwater marine resource development, primarily due to their inherent limitations such as high self-weight and susceptibility to corrosion. Carbon fiber reinforced polymer (CFRP) composites, which possess exceptional properties including light weight, high strength, high-temperature resistance, corrosion resistance, fatigue resistance and durability, provide a new solution for the configuration design and engineering application of mooring systems for deepwater semi-submersible platforms. Taking a deepwater semi-submersible platform in the South China Sea as the research object, this study proposes a novel three-segment mooring configuration consisting of steel chain–CFRP cable–steel chain, and further constructs two three-segment mooring systems, namely steel chain–CFRP cable–steel chain and steel chain–polyester cable–steel chain. A coupled hydrodynamic analysis model of the large floating platform–mooring system was established, and the dynamic response characteristics of the two mooring configurations including mooring tension, fatigue damage and platform motions were comparatively investigated through numerical simulations. The results indicate that compared with the polyester cable mooring configuration, the CFRP cable mooring configuration exhibits higher overall stiffness and lower natural periods in surge, sway, roll, pitch, and yaw. Under extreme wave conditions, it shows better performance in restraining platform motions, thereby leading to higher platform stability and operational reliability. Notably, the fatigue damage of the CFRP mooring cable is much lower than that of the polyester cable; however, the use of CFRP cable increases the fatigue damage of the steel chains at both ends, especially that of the bottom steel chain. These findings reveal the dynamic response characteristics of a deepwater semi-submersible platform under a CFRP mooring system, preliminarily verify the feasibility and superior performance of CFRP cables in deepwater semi-submersible platform mooring systems, and provide important data support and reference for innovative mooring scheme design and engineering applications.

To address the severe shock protection requirements of marine heavy equipment, this paper proposes a metal rubber impact isolator featuring both high-temperature resistance and corrosion resistance, capable of meeting operational requirements in complex marine environments. The isolator adopts a series-parallel combination of multiple metal rubber components as its cushioning and energy-absorbing elements, which ensures a high load-bearing capacity while achieving a favorable linear elastic working range. Additionally, the stiffness and damping characteristics are adjusted by means of parallel linear springs. A dynamic model of the impact isolator is established to analyze the influence of stiffness and damping on its shock isolation performance. The mechanical properties and impact resistance of the isolator are verified through experimental tests. Experimental results demonstrate that the isolator exhibits excellent linear elasticity within a stroke of ±9 mm, with an average stiffness of 7.45×10⁶ N/m, an equivalent damping ratio of approximately 0.43, and a limit load capacity of 6.5 t. Under the impact of a 2.2 t drop hammer falling freely from a height of 8.6 mm, the impact loss factor reaches 1.03 and the shock transmissibility is 0.0038, indicating excellent impact resistance performance. This study will provide a reference for the design of impact isolators for marine heavy equipment.

Aiming at the ultimate bearing capacity problem of I-type metal sandwich panels under in-plane compressive loads, a series of nonlinear finite element calculations were carried out for I-type metal sandwich panels examples. The typical failure modes and ultimate bearing capacity were analyzed. The calculation results show that the main failure modes are yielding or overall collapse caused by local panel buckling. The compressive ultimate strength is highly correlated with the flexibility of the face plates and core plates. Based on this, a simplified method for calculating the ultimate stress by superimposing the stresses of the face sheets and core plates is proposed. Compared with the nonlinear finite element results, the simplified method yields a mean relative error of −5.53%, and a deviation of 5.45% from published model test data, indicating good accuracy. This method can provide technical support for the rapid prediction of the ultimate strength and the design of configuration parameters of I-type metal sandwich panels.

The prediction accuracy and control effectiveness of hydrodynamic noise for underwater vehicles directly impact their overall performance. Accurately grasping the distribution characteristics of pulsating pressure is the fundamental and critical basis for assessing hydrodynamic noise levels and conducting low-noise design. This study takes an axisymmetric underwater structure as the research object, conducts numerical simulations of pulsating pressures based on Large Eddy Simulation (LES), and analyzes their distribution patterns in different regions. Using the Q-criterion, the vortex structures in various typical regions of the axisymmetric structure are captured and the characteristics of pulsating pressures in each region are analyzed in conjunction with vorticity distribution. By comparing the simulated pulsating pressure results with experimental data, the accuracy of the simulation method was verified. Based on this, research on pulsating pressure control methods in the flank array region of an underwater vehicle was conducted, and it proposes adding a guide fillet at the transition position between the front end of the flank array and the hull. The study shows that this measure can effectively suppress the horseshoe vortex induced by the geometric discontinuity of the flank array, reducing the overall pulsating pressure level at typical locations by over 5 dB.

Accurate determination of the mechanical properties of Arctic sea ice during the melting season is essential for navigation safety assessment in Arctic routes, prediction of ship icebreaking resistance, and ice-load design of polar engineering structures. In this study, uniaxial compression, three-point bending, temperature-salinity-density testing, and microstructural observations were conducted based on laboratory experiments, field trials, and ice-crystal image analysis. The results indicate that, under laboratory conditions, the uniaxial compressive strength of sea ice exhibits a pronounced ductile-to-brittle transition with varying strain rates, and reaches a peak value of 2.41 MPa at approximately 4.8×10⁻⁴ s⁻¹. The field results of three-point bending tests revealed a marked layered strength profile along the ice thickness; the central columnar ice exhibited relatively higher strength, whereas the lower layer showed significantly reduced bending strength due to seawater melting and compromised structural integrity. Differences between laboratory and field test results are consistent with the difference in temperature conditions; under the test conditions of this study, ice strength obtained in the low-temperature laboratory environment (−10 ℃) was generally higher than that of field tests. Observations of ice crystals and pores indicated distinct layered microstructural variations within melting-season sea ice, offering microstructural evidence for interpreting the variability of mechanical properties, crack initiation paths, and mechanisms of structural weakening. This study may provide a reference for the selection of mechanical parameters of Arctic sea ice during the melting season and for the cross-validation of laboratory and field test results.