基于PDCA的船舶设计质量管理

为提高船舶设计质量管理水平,以某满足《协调共同结构规范》(Harmonized Common Structure Rule,HCSR)的巴拿马型散货船为研究对象,利用计划、执行、检查、处理(Plan,Do,Check,Act,PDCA)循环法基本原则对设计质量进行管控,并建立同一船型设计质量管理体系。此外,对船舶能效指数(Energy Efficiency Design Index,EEDI)提升和结构轻量化设计的研讨方法进行分析。研究成果可为船舶设计质量管理提供一定参考。

Operational Modal Analysis of a Ship Model in the Presence of Harmonic Excitation

A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm （NExT-ERA） is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.

The Non-Degeneracy of Harmonic Structures on Planar Sierpinski Gaskets

We present a direct and short proof of the non-degeneracy of the harmonic structures on the level-n Sierpinski gaskets for any n≥2,which was conjectured by Hino in[1,2]and confirmed to be true by Tsougkas[8]very recently using Tutte’s spring theorem.

Analysis of generation of cumulative second harmonics of Lamb modes in a layered planar structure

A technique for analyzing the nonlinear generation of the cumulative second har-monics of generalized Lamb modes in a layered planar structure is developed. A theoretical model for nonlinear generalized Lamb mode propagation in a layered planar structure has been established, based on a partial plane wave approach. The nonlinearity is treated as a second-order perturbation of the linear elastic response. This model reveals some interesting features of the physics of the cumulative second harmonic generation. Although Lamb mode propagation is dispersive in a layered structure, the results of this analysis show that the amplitudes of the second harmonics do accumulate with propagation distance under certain special conditions. On the basis of the boundary and initial conditions of excitation, the formal solution of the cumulative second harmonic has been derived. Using the formal solution, we have performed some numerical simulations and obtained the cumulative second harmonic field patterns, illus-trating the distortion effect along the propagation distance, as well as the dependence of the field patterns on the position of the excitation source.

Multi-harmonic forced vibration and resonance of simple beams to moving vehicles

This study modeled the moving-vehicle-induced forcing excitation on a single-span prismatic bridge as a multiple frequency-multiplication harmonic load on the modal coordinates of a linear elastic simple Euler–Bernoulli beam,and investigated the forced modal oscillation and resonance behavior of this type of dynamic system.The forced modal responses consist of multiple frequency-multiplication steady-state harmonics and one damped mono-frequency complementary harmonic.The analysis revealed that a moving load induces high-harmonic forced resonance amplification when the moving speed is low.To verify the occurrence of high-harmonic forced resonance,numerical tests were conducted on single-span simple beams based on structural modeling using the finite element method(FEM)and a moving sprung-mass oscillator vehicle model.The forced resonance amplification characteristics of the fundamental mode for beam response estimation are presented with consideration to different end restraint conditions.The results reveal that the high-harmonic forced resonance may be significant for the investigated beams subjected to vehicle loads moving at specific low speeds.For the investigated single-span simple beams,the moving vehicle carriage heaving oscillation modulates the beam modal frequency,but does not induce notable variation of the modal oscillation harmonic structure for the cases that vehicle of small mass moves in low speed.