Dual-input marine propulsion gear systems are susceptible to tooth separation-induced impact (TSI) because of power combining, asymmetric load sharing, and flexible coupling with the propeller shaft, potentially compromising dynamic stability and operational safety. Existing studies often examine extended speed ranges and simplify propeller shafting to an equivalent lumped inertia, leaving low-speed TSI insufficiently understood. Here, we develop a nonlinear dynamic model of a dual-input, two-stage herringbone gear transmission coupled with a flexible propeller shaft to characterize the TSI evolution, critical speed boundaries, and parameter effects. The results show that TSI is confined to a finite interval within the low-speed operating range and originates primarily in the second-stage gear pair on the low-load side. TSI is suppressed by increasing the low-side load share or propeller load and by moderately increasing mesh damping. Modeling distributed shaft flexibility markedly shifts the predicted separation boundary and impact intensity relative to an equivalent-inertia model, indicating that lumped-inertia reduction may be inadequate for dual-input propulsion systems. These findings support vibration and noise mitigation and the design of TSI-resistant marine propulsion transmissions.

The marine propulsion system with parallel engines is commonly employed in high-power ships. However, the manifestation of vibration instability and induced rattle phenomena of the main gear present significant challenges to the reliable operation of the propulsion system. This paper elucidates the underlying dynamic mechanism and proposes effective vibration control strategies for the primary components subjected to vibrational influences. To accomplish this, a nonlinear dynamic model that considers lateral-torsional-longitudinal coupling of the propulsion system is established, based on the analysis of both internal and external excitations. The effects of various combinations of dynamic parameters on the vibration response of the system are systematically examined through theoretical simulation and experimental investigations. Subsequently, a magnetorheological fluid (MRF) control unit is introduced to mitigate the torsional vibration of the main gear-rotor system. It is observed that when the MRF unit is positioned far away from the main engine, the vibration amplitude can be reduced to less than 50% of the value when MRF is not used, and the equilibrium position of the torsional vibration approaches zero. The research results are expected to provide a theoretical foundation for addressing the technical challenges associated with enhancing stability and reducing vibration in such systems.

In order to solve the problem of uneven pressure distribution in traditional water-lubricated bearings, a multi-layer composite structure water-lubricated bearing is proposed in this paper. Considering the fluid–structure interaction and journal misalignment effects, a mixed lubrication model of multi-layer composite structure water-lubricated bearing is established. Based on the aforementioned model, first, experimental tests are conducted to verify the accuracy of the model. Second, the lubrication characteristics of multi-layer bearing and single layer bearing are compared. Finally, the effects of external load, journal rotational speed, and aspect ratio on the pressure, film thickness, and friction coefficient of multi-layer composite structure water-lubricated bearing are investigated. The research results show that the multi-layer composite structure water-lubricated bearing can improve pressure distribution uniformity, enhance minimum film thickness, and reduce friction. By studying the lubrication characteristics of multi-layer composite structure water-lubricated bearing under different parameter conditions, it provides theoretical support for the structural optimization of water-lubricated stern bearings.

The stern shaft seal is crucial for maintaining the operational reliability and environmental integrity of ship propulsion systems. Friction-induced vibrations significantly affect the service life of these seals. This study develops a nonlinear dynamic model of the stern shaft seal, considering frictional contact, and investigates the dynamic characteristics of the seal, as well as the influence of key structural and operational parameters on friction-induced self-excited vibrations. The result shows that friction-induced torque in stern shaft seals triggers negative damping, leading to self-excited vibrations, and critical structural parameter thresholds within specific speed ranges are established. This study provides valuable reference for the optimal design of stern shaft seals in ships.

ObjectiveThe weak deformation signal generated by propeller thrust on a shaft system is easily overshadowed by interfering noise, making it challenging to accurately measure the thrust. Therefore, this study proposes a new method for accurately measuring the thrust of propellers under low signal-to-noise ratio conditions. MethodsBy taking into consideration the influence of measurement data errors and the underlying mechanical mechanisms, a thrust identification model is established based on a combination of Kalman filtering, and the thrust-displacement state equation. Thrust measurement research is conducted under three different operating conditions: constant rotational speed, variable rotational speed and low-frequency fluctuating rotational speed. The precision and robustness of the proposed method are then analyzed under different signal-to-noise ratios.ResultsThe results demonstrate that even at a signal-to-noise ratio of only 20 dB, the maxi-mum relative error in thrust identification is only 3.56%. Thus, the proposed method exhibits highly accurate and robust thrust identification performance under low signal-to-noise ratio conditions. Conclusion The findings of this study can provide valuable insights for the real-time and high-precision monitoring of propeller thrust and shaft system status in actual ship environments.

Pump-jet propulsors are inevitably affected by shafting vibrations in actual operating conditions, especially the longitudinal bearing force, which is the main inducing factor of hull acoustic radiation. In the present study, considering the working conditions of the uniform inflow and longitudinal vibration motion of the propulsion shafting, using the improved delay detached eddy simulation, the influence of the propulsion shafting longitudinal vibration on the excitation force and vortex dynamics characteristics of the pump-jet propulsor is investigated under design conditions. The results indicate that the longitudinal vibration modulates the excitation force characteristics of each component of the pump-jet propulsor. Within the calculated range of magnitudes and frequencies, the thrust and torque fluctuations are proportional to the longitudinal vibration magnitude, and their magnitudes have a quadratic relationship with the longitudinal vibration frequency. Additionally, longitudinal vibration directly affects the short-wave instability of the tip clearance vortex by changing the spiral-to-spiral distance, resulting in a more disordered shape of the wake field, especially at low longitudinal vibration frequencies. The wake field always exhibits characteristics of the longitudinal vibration frequency, indicating an energy generation mechanism for the longitudinal vibration frequencies induced by the propulsion shafting longitudinal vibration.

The stability of the marine propulsion system is significantly influenced by the load applied to the propeller and its own inertial effect. This paper focuses on the investigation of the propulsion system powered by double-cylinder turbines under unsymmetric input power, aiming to understand its dynamics through theoretical modeling, numerical simulation, and experimental verification. Firstly, a nonlinear dynamic model of the system is established considering the time-varying and nonlinear internal factors including meshing stiffness, tooth surface friction, tooth side clearance, and the unsymmetrical external input power. Subsequently, numerical methods are employed to explore the effects of the load on the propeller and its own rotational inertia on the stability and vibration characteristics of the propulsion system. The study describes the complex dynamic behavior that emerges due to these influencing parameters. Finally, the theoretical model is validated, and a comprehensive experimental platform for parallel propulsion systems is utilized to further investigate the impact of the load and rotational inertia on the vibro-acoustic characteristics of the system. The findings serve as valuable guidance for the design of power parameters and the optimization of propellers for the propulsion system characterized by parallel power configuration from the perspective of dynamics.

With the increasingly serious problems of international energy shortage and environmental degradation, the adoption of hybrid energy forms represents an effective solution to these challenges and has been widely implemented in the propulsion systems of aircraft, vehicles, and ships. For the hybrid propulsion system with parallel power configuration, a comprehensive investigation has been conducted to understand the system’s dynamic characteristics and the evolution laws associated with power parameters. By appropriately simplifying of the actual propulsion system, a nonlinear dynamic model with multi-factor and multi-degree-of-freedom (multi-DOF) coupling is established. The dynamic equations are solved by numerical method, and the motion state of the system under various rotating speeds is revealed through global and local characteristic analyses. The evolution laws of the dynamic characteristics are studies with respect to different combinations of key power parameters, including (λω, λf) and (fo, λf), and the impact of these parameters on the system stability is discussed. Finally, an experimental platform with a parallel drive system is established to quantitatively assess the effects of rotating speed and torque ratio on frequency response, dynamic characteristics, and power efficiency. The results indicate that low rotating speed, heavy load, and large torque ratio have positive implications for the stability of the propulsion system. However, an excessively low torque ratio can significantly compromise power efficiency. It is anticipated that this research will serve as a valuable reference for the design of dynamic stability and optimization of the power configuration in hybrid propulsion systems.

The parallel power propulsion system is the preferred option for large-scale ships. The improper configuration of multidimensional power parameters is a significant factor contributing to the vibration and noise generated by the system. This study examines the sensitivity and dependence of the vibro-acoustic characteristics of the system on various power parameters through theoretical and experimental methods, and reveals the evolution mechanism of the dynamic behaviors under the coupling effect of multidimensional power parameters. Firstly, the nonlinear dynamic model considering the lateral–torsional–axial coupling of the propulsion system is established and the effects of different combinations of power parameters on the vibration response and system stability are investigated. Secondly, an experimental platform of the parallel propulsion system is constructed, and the comprehensive description of the effects of multidimensional power parameters on the vibration and noise of the system under asymmetrical input power is further provided. Finally, the radial basis function (RBF) neural network is innovatively employed to predict and approximate the vibro-acoustic characteristics of the system under the combined influence of rotating speed, torque ratio, and drag current. The research results are of significant theoretical and practical importance in breaking through the technical bottleneck related to reducing the vibration and noise of such parallel propulsion systems.

The propulsion shafting whirling vibration causes non-uniform dynamic changes in the rotor tip clearance, which directly have a significant influence on the excitation force and vortex dynamic characteristics of the pump-jet propulsor. In the current study, based on improved delay detached eddy simulation, the influence of non-uniform blade tip clearance on the excitation force and vortex dynamics characteristics of the pump-jet propulsor is studied under design conditions. The results show that the application of propulsion shafting whirling vibration induces significant changes in the excitation force of the pump-jet propulsor. The rotor blades modulate the excitation forces of the stator blades and duct. The transverse and vertical excitation forces are more significant than the longitudinal excitation force. The magnitude change in the circular orbit shows a linear relationship with the excitation force magnitude. The characteristic frequency of the transverse and vertical excitation forces of each component is the shaft rotation frequency. In contrast, the characteristic frequency of the longitudinal excitation force is twice the shaft rotation frequency. In the elliptical orbit, the excitation force of each component is compressed or stretched in the time domain, and the dominant frequency is shifted in the frequency domain; there is no longer a linear relationship between the vibration magnitude change and the excitation force magnitude. Furthermore, an energy generation mechanism in the wake field of the pump-jet propulsor induces vortex frequency due to the whirling vibration of the propulsion shafting system.

Most vibrations in engineering are of low frequencies, so this study proposes a novel piezoelectric vibration energy harvester for low-frequency vibrations. The model consists of a piezoelectric stack, a vertical spring, and a negative stiffness structure (NSS). The NSS is introduced to reduce the resonance frequency of the piezoelectric stack, which consists of two horizontal springs and two connecting rods. The analytical expressions of optimal resistance load, optimal harvesting frequency, and harvesting power are derived. The results show that the NSS can dramatically decrease the optimal harvesting frequency and also greatly increase the energy harvesting efficiency near the optimal harvesting frequency. For the case considered in this study, the optimal harvesting frequency can be reduced from 70 Hz to 10.5 Hz and the maximum harvesting power is increased from 15.3 $\mu \mathrm{H}$ to 111.8 $\mu W$ .

螺旋桨纵向激励力是引起舰船艉部振动噪声的重要原因之一,对其研究有利于舰船艉部的振动噪声控制.通过面元法耦合有限元法建立螺旋桨双向流固耦合动力学模型,计算P438X系列螺旋桨在不均匀流场下的纵向激励力,研究桨叶弹性、侧斜角等因素对纵向激励力的影响.结果表明:当激励频率小于螺旋桨一阶固有频率一半时,桨叶弹性效应对纵向激励力影响很小,可对其按刚性螺旋桨处理;当激励频率接近螺旋桨一阶固有频率时,桨叶弹性对纵向激励力有显著放大效应;刚性螺旋桨侧斜角越大,纵向激励力越小,然而考虑桨叶弹性后,过大的侧斜角将降低桨叶各阶固有频率,从而恶化纵向激励力.因此需要结合激励频率、桨叶固有频率设计合适的侧斜角.

The influence of the hull-modulated inflow on the propulsion performance of the propeller is related to the matching design of the propeller–hull system. In the present study, considering the working conditions of the pump-jet propulsor in uniform inflow and two types of hull-modulated inflow, based on improved delay detached eddy simulation, the influence of hull-modulated inflow on unsteady force fluctuations and vortex dynamics of pump-jet propulsor under design conditions is carried out. The results show that the hull-modulated inflow increases the propulsion efficiency of the pump-jet propulsor to varying degrees within the range of the calculated advance coefficient and has a significant influence on the frequency characteristics of the unsteady force spectra characteristics of each component of the pump-jet propulsor. It also shows changes in the magnitude characteristics, that is, the energy transfer process of an individual rotor blade from the stator blade passing frequency to other harmonics of the shaft rotation frequency, and the thrust spectrum of an individual stator blade presents broad-spectrum characteristics in the high-frequency range. Furthermore, the application of hull-modulated inflow directly affects the shape of the stator shedding vortex, causing some of the stator blade shedding vortices to separate early and aggravating its short-wave instability. More secondary vortices are induced to accelerate the instability of the rotor blade tip clearance vortex. The energy transfer mechanism from the rotor blade passing frequency and its harmonics to the broadband spectra appears in the wake field of the pump-jet propulsor.

The propulsion system, as the crucial equipment to drive the ships, its stability is of great significance for the safe and reliable operation of the system. This study focuses on the propulsion system for large-scale ships with high- and low- integrated double-cylinder turbines, and carries out theoretical and experimental research on its dynamic characteristics and system stability. Firstly, based on comprehensively considering the key excitations and multi-state meshing of the system, a nonlinear dynamic model of the gear-rotor-bearing system including two power paths is established. Secondly, the influences of the load ratio between the unsymmetrical input power on the dynamic characteristics and motion stability are studied by global and local analysis methods. Finally, by establishing a comprehensive experimental platform for the parallel propulsion system, the in-depth experimental research on the vibration state, acoustic characteristics, and power loss of the system is carried out. The research results show that the increase of the load ratio has a positive effect on enhancing the system stability, reducing the vibration and noise, and improving the power efficiency. This research has the guiding significance for the power design and optimization of the marine propulsion system powered by double-cylinder turbines.

最小液膜厚度是判断轴承润滑状态的关键指标,提高最小膜厚有助于建立流体润滑状态、改善摩擦特性、保障轴系安全可靠运行.船用水润滑高分子轴承液膜极薄,常处于混合润滑状态,由于衬层弹性变形的作用,其最小名义膜厚常位于轴向端面.为改善轴承润滑特性,特别是为提高最小膜厚、减小摩擦,本文提出一种轴承设计方法,即增大轴向端面处的直径,也即将轴向端面设计为渐扩形,针对该端面渐扩型轴承建立混合润滑模型,并分别就轴颈倾斜、轴颈无倾斜两种情况分析渐扩形结构参数对轴承性能的影响.分析结果表明,适宜的端面渐扩形结构可显著提高最小膜厚,减少粗糙峰接触摩擦.在此基础上,总结出了可供广泛使用的端面渐扩形参数,以便于工程应用.

动力推进系统是舰船的心脏,其运行稳定性和可靠性直接关系到舰船的战斗力、生命力和高效机动航行的能力.为适应不同航行工况和高机动性要求,在较大转速范围内均能保证系统稳定运行并提供所需推力是舰船动力推进系统的一个重要特征,也是系统设计时的一个关键技术指标.如图1(a)所示,双缸汽轮(double-cylinder turbines,DCT)推进系统以其功率密度大、寿命长、结构紧凑、工作可靠、调速方便等优点,被多国作为大型、超大型舰船动力主机的主要选择[1].

本文在传统轴承动力学分析模型的基础上考虑了水润滑轴承轴瓦的刚度、阻尼和轴承质量以及可能存在的接触刚度、阻尼,推导了考虑表面粗糙度和轴瓦变形的扰动压力雷诺方程,对比了混合润滑模型与动力润滑模型、弹流润滑模型的轴承动力特性系数并分析其差异,研究了倾角、粗糙度等参数综合作用下水润滑轴承动力特性系数的变化规律.结果表明,最小膜厚比大于某一阈值时粗糙度增加可提高水膜动力特性系数,轴瓦变形会使动力特性系数减小,同时也会扩大使水膜刚度、阻尼获得增幅的粗糙度范围,但削弱了粗糙度对承载方向刚度、阻尼的增幅效果.此外,在承受载荷一定的条件下,粗糙轴承的动力特性系数在倾角较大时明显小于光滑轴承的对应值.

船舶螺旋桨工作时,除了不均匀流场会产生轴承力外,推进轴系振动同样会使螺旋桨产生轴承力.目前针对这类轴承力的研究非常少,因此本文利用面元法结合转子动力学理论构建了考虑不均匀流场与轴系振动同时作用下的螺旋桨轴承力预报模型,基于该模型探讨了轴系纵向振动与其诱发的螺旋桨纵向轴承力间的相互关系.通过对一系列半径、叶数、螺距比和盘面比不同的螺旋桨进行计算,拟合得到了螺旋桨纵向轴承力的估算公式,最后进行了实验验证.研究表明:轴系纵向振动诱发的螺旋桨纵向轴承力与轴系纵振幅值成正比关系,与纵振频率成平方关系.本文的研究有助于人们进一步加深对螺旋桨轴承力特性的认识.

At present, although there are a large number of studies on the hydroelastic analysis of ship propellers, almost all of them neglect the shaft, thus ignoring the influence of the structural coupling effect between the propeller and the shaft. Therefore, considering this coupling effect, a new hydrodynamic analysis model of propellers is established by using the boundary element method (BEM) coupled finite element method (FEM). And then the model is verified by some experiments on the water tunnel test bench. Finally, based on this model, the influence of the structural coupling effect on propellers' hydroelastic performance is mainly studied. The results show that when the structural coupling effect is ignored, the relative errors of the first-order jellyfish mode of the blade, the dynamic stress at the blade root, and the longitudinal bearing force of the propeller are as high as 22.78%, 28.04%, and 20.37% respectively. Therefore, the structural coupling effect between the propeller and the shaft should be considered when analyzing the propellers’ hydroelastic response. Further, when designing the propeller-shaft system, this coupling effect can also be fully utilized to reasonably match the parameters of the propeller and the shaft to optimize the hydroelastic performance of propellers.

Background DI-SO (Double inputs and single output) helical gears are the key components of many propulsion systems and the phenomenon of nonlinear instability caused by multiple time-varying parameters and unsymmetrical input loads cannot be ignored. Methods The nonlinear dynamic model of the DI-SO helical gear system was studied considering multiple nonlinear factors, and the evolution laws of the dynamic characteristics with load and structural parameters were discovered by numerical analysis methods. Results Abundant dynamic behaviors of periodic, quasi-periodic, harmonic, sub-harmonic, multi-harmonic, and chaotic responses are revealed with the variation of the system parameters. The increases of the load parameters, such as the excitation frequency, the load ratio, and the load value, are beneficial to improve the stability of the system. With the increasing structural parameters of the helix angle and the face width, the dynamic response of the system changes in fluctuation. Conclusion This study puts forward the importance of appropriate rotate speed, heavy load, and high contact ratio for the stability of the system and provides a theoretical reference for the design and optimization of the propulsion system with DI-SO helical gears.