Abstract
Quasi-zero-stiffness (QZS) structures offer substantial practical benefits for facilitating the essential support and isolation of vibrational source loads aboard modern marine vessels. In order to design a compact QZS system of high bearing capacity, the article proposes a low stiffness air spring (LSAS) vibration-isolation mounting system composed of both vertical and lateral air springs. The vertical air springs support the load and isolate vibrations in the vertical direction, while the lateral air springs support the load and isolate transversal vibrations. Theoretical analyses based on a simple two-dimensional, single degree of freedom model demonstrate that the proposed novel LSAS design decreases the degree of stiffness in the support structure that would otherwise be induced by introducing lateral air springs and accordingly increases the vibration isolation effect. Moreover, optimization of the air spring parameters enables the lateral air springs to provide negative stiffness and thereby realize QZS characteristics. Experimental testing based on prototypes of a standard air spring mounting system and the proposed LSAS mounting system demonstrates that the stiffness of the proposed system is about 1/5 that of the standard system. Accordingly, the proposed structure design successfully alleviates the undesirable influence of lateral air springs on the stiffness of the mounting system.
Highlights
Vibration control is an essential operation in modern marine vessels for supporting numerous factors, such as the acoustic stealth of vessels, the living comfort of passengers, the working performance of on-board precision instruments, and the service life of the equipment
Vibration isolation has been the most widely adopted method for this purpose [1]. e general aim of vibration isolation systems is to reduce the level of vibrations transmitted to primary ship structures from vibration sources, such as marine propulsion units (MPUs), generators, ventilation units, and pumps. e most common vibration isolation systems employed in marine vessels include single-stage vibration isolation systems, double-stage vibration isolation systems, and floating raft vibration isolation systems [2]
The design of high-performance air springs has been the subject of intense interest for developing advanced vibration isolation systems. e development of air springs has greatly contributed to the effective isolation of vibrations arising from large-scale on-board equipment. ese efforts have been further supported by the development of a new type of air spring with numerous advantages, such as high working pressure, large load capacity, compact structure, and low natural oscillation frequency [3,4,5]
Summary
Vibration control is an essential operation in modern marine vessels for supporting numerous factors, such as the acoustic stealth of vessels, the living comfort of passengers, the working performance of on-board precision instruments, and the service life of the equipment. In addition to designing advanced air springs, efforts have been applied to developing more advanced vibration isolation systems, such as quasi-zero-stiffness (QZS) structures. Inspired by the nonlinear structures discussed above, this article proposes a novel low stiffness air spring (LSAS) vibration-isolation mounting system based on a standard air spring vibration isolation system to further improve the vibration isolation ability. While displacements in the horizontal direction can certainly affect the vibration transmissibility of the structure, the applied simplifications facilitate detailed theoretical analyses for determining the optimal air spring parameters that enable the lateral air springs to provide negative stiffness to the system and thereby realize QZS characteristics. Ese results demonstrate that the introduction of lateral air springs makes the natural oscillation frequency of the standard system (Ω2) 2 times greater than that of the single vertical air spring structure (Ω1) and reduces the vibration isolation effect of the system.
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