Two-stage Mounting Research Articles

Dynamic analysis and design of novel distributed lump-parameters mounting system for marine power devices

Marine power devices (MPD) are one of the dominant vibration and noise sources on board marine vessel. Its vibration can be attenuated effectively through floating raft mounting system. But this becomes unsuitable to implement due to a more stringent light-weighting request. In this paper, a novel distributed lump-parameters mounting system (NDLMS) for MPD is proposed consisting of two-stage mounting subsystem, attitude monitoring and controlling subsystem, and emergency protection subsystem. A theoretical model under multiple excitations is presented to estimate the vibration isolation effectiveness (VIE) using equivalent mobility matrix methods. To improve the VIE of NDLMS, distributed dynamic vibration absorbers (DDVA) are introduced. Compared with the equally weighted rigid mass blocks, DDVA has a qualitative improvement in the attenuation ability of the characteristic spectrum. Replacing part of the mass of mounting system with finely tuned DDVA can greatly reduce the vibration transmitted from vibratory MPD to the foundation. DDVA are validated to compensate for the vibration transmission loss by light-weighting. A scaled and a practical NDLMS prototypes are manufactured and tested. Experimental results validate the effectiveness of theoretical models and show that the performance of NDLMS satisfies the operation requirements of MPD.

Model-based design of a novel modular mounting system: Light, compact, and efficient

Two-stage mounting systems applied in ships are expected to be light in weight, compact in installation space, and efficient in vibration isolation performance at the same time, which largely increases the engineering complexity. In this paper, analytical models of a two-stage mounting system with flexible and rigid intermediate mass are proposed to compare the vibration isolation effectiveness (VIE) performance and the influences of system parameters with the rigid intermediate mass on VIE are introduced. Based on the analysis results, an integrated adjustable two-stage mounting module is designed. Compared to the traditional floating raft mounting system with flexible intermediate mass, this two-stage mounting module can be arranged in a more compact structure space with greatly reduced size and weight. Furthermore, a novel modular mounting system prototype is proposed and manufactured based on several two-stage mounting modules and real-time behavior monitoring and controlling subsystem. The testing results verify the compatibility of the module design and the behavior monitoring and controlling system. The modular mounting system also exhibits excellent VIE performance combined with the advantage of compact intermediate mass size, lightweight, and automatic behavior monitoring and controlling.

Study on two-stage mounting systems having distributed intermediate mass

Nowadays, two-stage mounting system having integral intermediate mass is widely applied and researched to attenuate vibration of marine machinery equipment, while two stage mounting system having distributed intermediate mass which has the feature of lightweight and installation dimension is rarely used and studied. The theoretical models of two types of mounting systems are set up and force transmissibility rate of the two mounting systems are deduced through four-pole parameters method. A scale experimental prototype is established to test the isolation efficiency of the two-stage mounting system having distributed intermediate mass. FEMs of the two systems are established to make a comparison ascertaining the difference between the two about vibration isolation efficiency at the different frequency. The result shows that two stage mounting system having distributed intermediate mass achieve better vibration isolation efficiency and take less space than two-stage mounting system having integral intermediate mass if with equivalent intermediate mass. Two-stage mounting system having distributed intermediate mass can meet the requirements of practical projects and provides a new way for engineer to refer to when meet with machinery equipment vibration problems.

The Influence of Internal Resonances From Machinery Mounts on Radiated Noise From Ships

Machinery vibration is a significant source of noise from marine vessels. Consequently, problematic machinery is often decoupled from the hull using resilient mounts. When radiated noise is a priority, two-stage mounting arrangements can be used which provide superior performance. This improvement, however, comes at a much higher weight and cost. A commonly overlooked issue with isolation systems is that the individual mounts suffer from internal resonances which reduce their effectiveness. This paper broadly evaluates the influence of these on the underwater noise levels from a typical ship diesel. The effect of nonrigid structural components, that is, the supported machine, the machine foundation, and the intermediate mass in two-stage mounting arrangements, is also discussed. The structureborne and airborne transmission paths are resolved individually using approximate analytical methods, and the source levels are estimated from empirical relationships for typical marine diesels. It is shown that, by mitigating the internal resonances of the mounts, a two-stage mounting arrangement may be unnecessary because of the contribution to the underwater noise by airborne transmission.

Analytical and Parametric Optimization of Force Transmissibility by Taguchi Method for Double Stage Engine Mountings

It is essential to design a warship to avoid detection by submarines or enemy ships. One of the recent techniques used is to mount all vibrant machinery on a double stage vibration isolation system. For high structure-borne noise attenuation there is requirement of two-stage mounting system. The main goal of current research work is to reduce vibration levels from machinery to foundation, and thereby to reduce radiate noise levels from ship hull. The present work deals with the mathematical modeling and parametric optimization of force transmissibility (Ftr) for design of engine foundation system. The vertical vibrations of the system are assumed to be most predominant, and other types of vibrations are neglected. The research work is carried out for finding parameters of mounts and optimizing the same. The analysis is based on discrete system modeling. Taguchi method is used for finding optimal combination of process parameters based on S/N ratio and analysis of variance (ANOVA) is statistical technique to investigate contribution of each process parameters on the performance characteristic. The result shows that spring stiffness is most affecting process parameter.

Vibration and noise control of structural systems using squeeze mode ER mounts

This paper presents vibration and noise control of flexible structures using squeeze mode electro-rheological mounts. After verifying that the damping force of the ER mount can be controlled by the intensity of the electric fild, two different types of ER squeeze mounts have been devised. Firstly, a small size ER mount to support 3 kg is manufactured and applied to the frame structure to control the vibration. An optimal controller which consists of the velocity and the transmitted force feedback signals is designed and implemented to attenuate both the vibration and the transmitted forces. Secondly, a large size of ER mount to support 200 kg is devised and applied to the shell structure to reduce the radiated noise. Dynamic modeling and controller design are undertaken in order to evaluate noise control performance as well as isolation performance of the transmitted force. The radiated noise from the cylindrical shell is calculated by SYSNOISE using forces which are transmitted to the cylindrical shell through two-stage mounting system.

OPTIMAL DESIGN OF A TWO-STAGE MOUNTING ISOLATION SYSTEM BY THE MAXIMUM ENTROPY APPROACH

In this paper, the optimization of the parameters for two-stage mounting isolation system is studied. The maximum entropy approach is applied to deal with the non-differentiable optimization problems. Results of numerical examples confirm the efficiency and accuracy of the proposed method, which is also suitable for the optimization of other kind of isolation system, such as Ruzicka isolation system (Ding wen-jing 1988 Theory on Vibration Reduction, Tsinghua University Publishing House, Ruzicka 1967 Journal of Engineering and Industries ASME 89), etc

Vibration isolation: Use and characterization

The results of a search and critical evaluation of the literature pertinent to both the use and the characterization of the performance of antivibration mountings for the control of noise and vibration are described. First to be discussed are the static and dynamic properties of rubberlike materials that are suited for use in antivibration mountings. This is followed by analyses of the simple (one-stage) mounting system and its subsequent, impaired performance when second-order resonances occur either in the isolator (wave effects) or in the structure of the mounted item itself (nonrigid supporting feet). A discussion is then given of the performance of the compound or two-stage mounting system which possesses superior isolation properties for high frequencies. Next, the four-pole parameter technique of analysis is described and applied, in general terms, to the characterization of the performance of an antivibration mounting with wave effects for the cases where either the supporting foundation or mounted item are nonrigid. The methods adopted for the direct measurement of antivibration-mounting performance are described, followed by an explanation of how this same experimental determination of transmissibility can also be made using an indirect measurement technique based upon four-pole parameter analysis considerations.

Vibration Isolation: Use and Characterization

Abstract This article is concerned with vibration isolation, with antivibration mountings (resilient isolators), and with the static and dynamic properties of rubberlike materials that are suited for use in antivibration mountings. The design of practical antivibration mounts incorporating rubber or coiled-steel springs is described in Refs. 1–27; pneumatic isolators (air mounts, etc.) are described in Refs. 5, 28–35. Throughout the literature, as here, attention is focussed predominantly on the translational (vertical) effectiveness of antivibration mountings. However, the two- and three-dimensional vibration of one- or two-stage mounting systems is addressed in Refs. 4, 10, 12, 36–56. Following a description of the static and dynamic properties of rubberlike materials, the performance of the simple or one-stage mounting system is analyzed, account being taken of the occurrence of second-order resonances in the isolator and in the mounted item. In the latter case, as likely in practice, the bulk of the mounted item is assumed to remain masslike, whereas the feet of the item are assumed to be nonrigid (multiresonant). Discussion is then given to the two-stage or compound mounting system, which affords superior vibration isolation at high frequencies. Subsequently, the powerful four-pole parameter technique is employed to analyze, in general terms, the performance of an antivibration mounting with second-order resonances (wave effects) when both the foundation that supports the mounting system and the machine are nonrigid. The universally adopted method of measuring mount transmissibility is then described, followed by an explanation of how transmissibility can also be determined by four-pole parameter techniques based on an apparatus used by Schloss. The four-pole measurement approach has not been exploited hitherto, but it is apparently feasible and valuable because it enables mounts to be tested under compressive loads equal to those routinely encountered in service.

Compound Mounting Systems That Incorporate Dynamic Vibration Absorbers

The transmissibility across novel compound or two-stage mounting systems is discussed, and representative calculations of transmissibility are compared for systems with intermediate stages that comprise either (1) a rigid mass plus a dynamic vibration absorber, (2) dual beams loaded symmetrically by equal lumped masses, or (3) dual beams to which multiple dynamic vibration absorbers are attached. In the first case, the undesirable secondary resonance of the compound system can be suppressed effectively by the dynamic vibration absorber, for which appropriate design data are given. In the latter two cases, lumped masses or dynamic vibration absorbers are applied to each intermediate beam of the compound system at the locations of the four upper mounts that support the vibrating item from below. In turn, the beams are supported at each end by single antivibration mounts on a rigid foundation. The “secondary” resonance of the compound system that incorporates the multiple dynamic absorbers can be suppressed heavily by them; and it is shown how the excitation of a high-frequency resonance of the intermediate beams can be avoided, at the same time, by judicious choice of upper mount location. Design data for the multiple absorbers, which have relatively small mass, are tabulated.

Isolation from Vibration with a Mounting Utilizing Low- and High-Damping Rubberlike Materials

Abstract This paper describes a theoretical investigation of the performance of an antivibration mounting utilizing elements of low- and high-damping rubberlike materials in parallel, arranged such that both materials experience the same strain. Knowledge of the dynamic mechanical properties of natural rubber and a high-damping synthetic rubber has enabled the behavior of the so-called parallel mounting to be estimated realistically. General expressions have been derived from which the response ratio of a parallel mounting employed in one- and two-stage mounting systems may be determined, once the variation with frequency of the mechanical impedance Zω of the foundation of the mounting system is known. The mounting systems have been assumed throughout to possess natural frequencies of 5 cps. To compare the response ratios of the mounting systems, a specific nonrigid foundation has been considered, namely, a simply supported beam possessing damping of the solid type. The beam possesses a “springlike” impedance at frequencies below its fundamental resonance, which is assumed to occur/at 50 cps. The ratio of the mechanical impedance of the beam to the value it takes at low frequencies is plotted in Figure 3 of Reference 1, through the frequency range 1–1000 cps. The mounted item is supposed to behave purely as a lumped mass. “Wave effects” that may occur in the rubberlike mount materials are disregarded. These materials are always assumed to behave in a linear manner.

Isolation from Vibration with a Mounting Utilizing Low- and High-Damping Rubberlike Materials

The dynamic mechanical properties of rubberlike materials have been briefly reviewed. The value of a mounting composed of a low- and a high-damping rubber in parallel is in this way made apparent. Expressions have been derived from which the ability of the so-called parallel mounting to isolate vibration from any nonrigid foundation may be determined, if the mechanical impedance of the foundation is known. One- and two-stage mounting systems have been considered. To compare their performance, the mechanical impedance of a damped beam has been employed to simulate the behavior of a nonrigid foundation. It is shown that the parallel mounting suppresses resonant motion at the natural frequencies of the foundation and the mounting systems with similar effectiveness to the high-damping rubber, yet provides the greater isolation at other frequencies. The isolation afforded by the mounting is, in fact, often comparable to that which the low-damping rubber affords.