Lateral-torsional coupled vibration of a propulsion shaft with a diesel engine supported by a resilient mount

Lateral-torsional coupled vibration destabilizes a rotating system. The instability region of the rotating system is the speed range where the frequencies of the lateral and torsional modes intersect. In this study, the abnormally increased vibration of the typical diesel engine-reduction gear propulsion system for a naval vessel was examined in relation to the lateral-torsional coupled vibration under the assumption that it can be approximated by the Jeffcott rotor with three degrees of freedom. Through numerical and experimental investigation, a protection method was developed to avoid the unstable region of the diesel engine-reduction gear propulsion system.     

Dynamic modeling and analysis of axial vibration of a coupled propeller and shaft system

The dynamic and acoustic characteristics of a coupled propeller and shaft system which is modeled by the transfer matrix method are studied. The elasticity of the propeller is taken into consideration by employing the equivalent reduced modeling method. Thus the influence of the elastic propeller on the vibro-acoustic responses of the coupled system is investigated. To reduce the axial vibration of the coupled propeller-shaft system, the influence and location of the vibration isolator on the structural and acoustic responses is presented. Simulation results demonstrate that utilizing the relationship between the natural frequency of the propeller and the resonance frequency range of the shaft can control the vibration of the coupled system without other vibration control method. Utilizing a vibration isolator is another effective way to control vibration. The optimal position for the isolator installed between the shaft and the thrust bearing is investigated.     

Comparison of shear-thinning blood flow characteristics between longitudinal and transverse vibration

This article described the numerical investigation of shear-thinning blood flow characteristics when subjected to longitudinal and transverse vibrations and delineated the underlying mechanisms of the flow rate enhancements, respectively. In order to fully consider the mechanical vibrations of the capillary, a moving wall boundary condition was adopted. The present numerical results showed that the longitudinal vibration caused a significant increase of wall shear rates, which resulted in a decrease of viscosity and the subsequent increase of flow rates. However, the shear rate for the transverse vibration was slightly increased and the calculated flow rate was underestimated comparing with the previous experimental results.     

微细钻头超声轴向振动钻入横向偏移的有限元分析

利用有限元技术对微细钻头超声轴向振动钻入横向偏移过程进行深入分析。结果表明,超声轴向振动钻削从根本上改变了普通钻削的钻入机理,减小了横向偏移量,提高了钻入定心精度,特别适合硬脆材料上的微小孔的精密和超精密加工。     

Exact solutions for longitudinal vibration of rods coupled by translational springs

The objective of this paper is to present exact analytical solutions for longitudinal vibration of non-uniform rods with concentrated masses coupled by translational springs. Using appropriate transformation, the governing differential equation for longitudinal vibration of a rod with varying cross section is reduced to Bessel's equation or an ordinary differential equation with constant coefficients by selecting suitable expressions, such as power functions and exponential functions, for the area variation. The exact solutions for free longitudinal vibration of rods with varying cross-section are derived. The initial parameter method and the transfer matrix method are proposed to establish the frequency equation for the longitudinal vibration of two rods coupled by translational springs. The advantage of the proposed methods is that the frequency equation for two rods coupled by translational springs can be established in terms of a determinant of 2-order for any number of translational springs and concentrated masses. The proposed methods can be used to solve the problem of free longitudinal vibration of uniform and non-uniform rods with concentrated masses coupled by various translational springs, and thus to investigate the axial stiffness and mass distribution among the rods to alter the system's dynamic characteristics. A numerical example shows that the fundamental longitudinal natural frequency of two reaction towers coupled by a pipe calculated by the proposed methods is in good agreement with the full scale measured data, suggesting the proposed methods are applicable to engineering practices.     

Effects of a turbocharger cut out system on vibration characteristics of a propulsion shafting system and a large low speed marine diesel engine

To cope with the long term recession in the shipping industry due to oversupply of ships and high oil prices and due to reinforcement of environmental regulations to reduce greenhouse gas emission from ships, large container vessels built recently have ultra-long stroke engines with high propulsion efficiency. For these, de-rated engine and tuning technologies are used to reduce fuel oil consumption. However, previously built vessels were optimized for high ship speed. In these case, lowering ship speed to reduce ship operating cost does not provide similar benefits. Therefore, engine manufacturers have developed a turbocharger cut-out system to reduce fuel oil consumption at low speed. This has the advantage of reducing fuel consumption at low speeds, but also has the characteristic of producing higher torsional exciting force than is typical in existing engines for low load ranges. In this paper, the performance and dynamic characteristics of a marine diesel engine were reviewed after applying a turbocharger cut-out system. Then the effects on the engine body vibration and the torsional vibration were examined for a corresponding propulsion shafting system in a Panamax container-vessel equipped with a turbocharger cut-out system optimized for slow steaming. As a result, the torsional vibratory stress in shafts was increased. This had a larger effect on the X-mode shape of the engine body vibration and on the upper structure vibration, when one of three turbochargers was cut out.     

含纵向裂纹提升机主轴数值模拟分析

用数值模拟技术工具，以含纵向裂纹的提升机主轴为研究对象，分别求出裂纹位于轴心和近表面的主轴应力分布状况，利用ANSYS中子模型技术探讨了提升机主轴裂纹尖端应力应变场强度和三维裂纹J积分、应力强度因子K的计算技术，为轴类零件完整性评价判据的建立提供了一定的理论基础。     

Numerical and experimental investigation of nonlinear vortex induced vibration energy converters

In this paper, effects of bi-stable stiffness and hardening stiffness on the performance of a Vortex induced vibration (VIV) energy converter are theoretically and experimentally studied through a wake oscillator model and a computer-based force-feedback testing platform. Based on the simulation and experimental results, it is found that the bi-stable stiffness is potential to allow the system to operate at low velocity water flows, while the hardening stiffness will extend the operating range at high velocity flows. Subsequently, in order to take the advantages of both types of stiffness, a combined nonlinear stiffness is proposed and verified experimentally to demonstrate its capability in improving the overall operating range of the VIV energy converter.     

Reduction of the sliding friction of metals by the application of longitudinal or transverse ultrasonic vibration

The influence on sliding friction of ultrasonic vibration both parallel and perpendicular to the sliding direction has been studied for samples of aluminium alloy, copper, brass and stainless steel sliding against tool steel. Experiments were performed at a mean sliding speed of 50 mm s⁻¹, and at mean contact pressures up to 0.7 MPa, with vibration amplitudes up to 10 μm at 20 kHz. Significant reduction in sliding friction was observed (up to >80%) and good agreement was found between the measured values and the predictions of two simple models for the effects of longitudinal and transverse vibrations. Longitudinal vibration produces greater reduction in friction than transverse vibration at the same amplitude and frequency. At high vibration amplitudes, the reduction in friction was less than that predicted by the models, because significant metallic transfer occurred from the softer metals to the tool steel counter surface.     

Design and experimental analysis of new industrial vibration dampers

Vibration dampers are the first line of defense against shock and impacts sustained by mechanical and structural systems. Consequently, for decades, new impact damping technologies have been developed and applied in several engineering fields to attenuate undesired vibrations. Linear particle chain (LPC) impact dampers are the latest category of impact dampers being developed for the mitigation of unwanted vibrations in many systems. However, the challenges associated with prototyping such devices made their application in practical systems very limited. This paper proposes five innovative designs for the LPC impact dampers satisfying a wide range of industry needs in terms of efficiency, cost, and sustainability. The proposed designs are fabricated and tested under the same conditions to assess their efficiency in attenuating the vibration of a simple structure. Each design showed consistent behavior, but some designs outperformed others depending on the geometry, physical characteristics, and type of structure. The detailed design, experimental study, and time response comparisons are presented here to provide an initial study towards the development of practical sustainable LPC vibration dampers for real engineering applications.     

基于热机耦合的机体主轴承壁性能数值模拟与实验研究

针对一款2.7 L高增压柴油机,采用有限元方法计算了机体的结构强度,分析了热载荷与机械载荷对机体主轴承壁区域的应变分布影响。设计了发动机台架实验,测取机体主轴承壁面的温度与动态应变,对计算结果进行验证并分析了产生误差的原因。研究结果表明:机体主轴承壁的工作应力由热应力与动载应力两部分组成,在额定工况下,热应力占主导地位。通过对比模拟与实验结果可以发现,基于第3类热载荷边界条件计算得到的壁面温度精度较高,但是该方法精度强烈依赖输入的换热系数精度。基于有限元方法获得的应变模拟值表现出良好的跟随性。有限元方法对最大动载荷模拟精度较高。最大工作应变计算误差主要来自于最大热应力的计算误差。计算模型的拓扑网格结构、测点当地材料属性与换热条件是造成计算误差的3个主要因素。     

带式输送机纵向振动的有限元分析法

通过对带式输送机的动力学现象、机理及运动规律的分析，建立了输送带的有限元力学模型，分析了系统的纵向动态特性，从而实现了对起动、制动等过程的控制和优化。     

Technology transfer of aircraft actuation to marine and propulsion

The most fundamental concept in designing multi-lane smart electromechanical actuation systems, besides meeting performance requirements, is the realization of high integrity. The main aim of this paper is to discuss fundamental consolidation designs and monitoring schemes in different architectures and to address threshold settings methodologies, inherent randomness, lane equalization, and control strategy. The analysis is based on a 4-lane actuation system capable of driving aerodynamic and inertial loads (with 2 lanes failed) of an aileron control surface similar to that of the Sea Harrier.     

Analysis of direct and inverse problems on transverse vibrations of a supported shaft

This study is devoted to direct and inverse spectral problems on transverse vibrations of a loaded multisupport shaft.     

Numerical and experimental analysis of a gear system with teeth defects

The modelling of a one-stage spur gear transmission by a two degrees of freedom system produces two modes: rigid body and elastic. The time varying meshing stiffness is the main internal excitation source for the transmission and governs the behaviour of the elastic mode. Deterioration of one or several teeth, which affects the gear mesh stiffness, is considered in this work. The beginning of crack or spalling are modelled respectively by tooth having localised and distributed defect and are taken into account in the model. Simulation results are analysed by cepstrum and spectrum techniques. It is found that cepstrum and spectrum techniques are very efficient for localised and distributed defects, respectively. Series of tests are made in the experimental setup. Spectrum and cepstrum analysis of the recorded responses, with and without defects, are compared with numerical results and confirms their usefulness in gear monitoring .     

Numerical and experimental analysis of a counter-rotating type horizontal-axis tidal turbine

In order to exploit renewable energies form tidal currents, a unique counter-rotating type horizontal-axis tidal turbine was proposed in this paper. Although a counter-rotating type horizontal-axis wind turbine can be taken as a reference in designing the proposed counterrotating tidal turbine, there are some different characteristics such as the effects of the free surface and the occurrence of cavitation. The unique tidal turbine in this paper was preliminarily designed on the basis of the in-house wind turbine, and then CFD analysis and experimental test were carried out to evaluate its performance. For the extreme conditions where severe flow separation and vortex exist, the comparison of the power coefficients generated by the turbine between the CFD predictions and the experimental data shows not so good. However, good agreement has been obtained for the comfortable blade pitch setting angles and over a range of tip speed ratios, which provides an evidence of validation of CFD analysis. Such results give sufficient confidence that the CFD model set up here is suitable for the further works.     

One-dimensional nonlinear vibration analysis and coupled thermoelasticity based on Green-Naghdi model

Journal of Mechanical Science and Technology - The present article reports on a study on nonlinear coupled thermoelasticity based on Green-Naghdi type III model in one-dimensional form. Unlike...     

船舶液压系统振动与噪声的分析与对策

1 引言 船舶采用液压传动这种传动方式日益增多,特别 在船舶辅机和特种机械,如舵机、锚机、起货机、减摇 鳍、可变距推进器等上用得更多,其原因是船舶要求辅 机具有较轻的重量指标和较好的控制品质。在现代超     

Dynamic analysis of propulsion mechanism directly driven by wave energy for marine mobile buoy

Marine mobile buoy(MMB) have many potential applications in the maritime industry and ocean science. Great progress has been made, however the technology in this area is far from maturity in theory and faced with many difficulties in application. A dynamic model of the propulsion mechanism is very necessary for optimizing the parameters of the MMB, especially with consideration of hydrodynamic force. The principle of wave-driven propulsion mechanism is briefly introduced. To set a theory foundation for study on the MMB, a dynamic model of the propulsion mechanism of the MMB is obtained. The responses of the motion of the platform and the hydrofoil are obtained by using a numerical integration method to solve the ordinary differential equations. A simplified form of the motion equations is reached by omitting terms with high order small values. The relationship among the heave motion of the buoy, stiffness of the elastic components, and the forward speed can be obtained by using these simplified equations. The dynamic analysis show the following:The angle of displacement of foil is fairly small with the biggest value around 0.3 rad;The speed of mobile buoy and the angle of hydrofoil increased gradually with the increase of heave motion of buoy; The relationship among heaven motion, stiffness and attack angle is that heave motion leads to the angle change of foil whereas the item of speed or push function is determined by vertical velocity and angle, therefore, the heave motion and stiffness can affect the motion of buoy significantly if the size of hydrofoil is kept constant. The proposed model is provided to optimize the parameters of the MMB and a foundation is laid for improving the performance of the MMB.     

Numerical and experimental analysis of spray atomization characteristics of a GDI injector

In this study, numerical and experimental analysis on the spray atomization characteristics of a GDI injector is performed. For numerical approach, four hybrid models that are composed of primary and secondary breakup model are considered. Concerning the primary breakup, a conical sheet disintegration model and LISA model are used. The secondary breakup models are made based on the DDB model and RT model. The global spray behavior is also visualized by the shadowgraph technique and local Sauter mean diameter and axial mean velocity are measured by using phase Doppler particle analyzer. Based on the comparison of numerical and experimental results, it is shown that good agreement is obtained in terms of spray developing process and spray tip penetration at the all hybrid models. However, the hybrid breakup models show different prediction of accuracy in the cases of local SMD and the spatial distribution of breakup.