Vibration isolation using open or filled trenches
ABSTRACT The problem of structural isolation from ground transmitted vibrations by open or infilled trenches under conditions of plane strain is numerically studied. The soil medium is assumed to be linear elastic or viscoelastic, homogeneous and isotropic. Horizontally propagating Rayleigh waves or waves generated by the motion of a rigid foundation or by surface blasting are considered in this work. The formulation and solution of the problem is accomplished by the boundary element method in the frequency domain for harmonic disturbances or in conjunction with Laplace transform for transient disturbances. The proposed method, which requires a discretisation of only the trench perimeter, the soil-foundation interface and some portion of the free soil surface on either side of the trench appears to be better than either finite element or finite difference techniques. Some parametric studies are also conducted to assess the importance of the various geometrical, material and dynamic input parameters and provide useful guidelines to the design engineer.
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ABSTRACT: Near-field scattering of surface waves by a single surface-breaking crack in solid medium has been well investigated by prior researchers. However, there have been few studies for more realistic problems involving near scattering of surface waves by distributed surface-breaking cracks. One possible reason is complexity caused by the interaction of surface waves between multiple cracks. In this study, interaction of surface waves between two surface-breaking cracks with various crack spacing was investigated. The experimental study was performed on Plexiglas specimens with non-contact sensors (air-coupled sensors, and a laser vibrometer), and compared with numerical simulation results. The effects of crack depth h, spacing a, and the number of cracks N on surface wave transmission were studied. Analyses show that for the very small crack spacing (a/h<0.2), the distributed cracks can be regarded as a single surface-breaking crack. However, for a/h ranging between approximately 1 and 6, transmission coefficient of surface waves is significantly affected by interaction between cracks. The transmission coefficients have the lowest value when a/h is between 2 and 3. When a/h is large (a/h>6), transmission coefficients obtained from experiments, and numerical simulations agree with the theoretical results based on non-interaction crack assumption.Journal of Sound and Vibration. 06/2011;
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ABSTRACT: Field vibration tests were carried out at a proposed site for the vibration testing room, and 2D numerical analysis using finite difference tool FLAC 5.0 was performed to suggest effective vibration isolation systems. In the analysis, the numerical model is first calibrated with respect to material properties, damping value, and boundary conditions to obtain the output comparable to the field test results. The calibrated model was further used to perform a parametric study by (1) providing vibrating input motions from vibrating machines to be operated; (2) using two depths of cutoff trench; and (3) providing gravel bed, gravel bed with rubber pad, and gravel bed with rubber pad and cutoff trench to study the isolation effects. Comparing the results from the parametric studies with the human perception level of vibration, a decision on the isolation system was determined.International Journal of Geomechanics 10/2010; 11:364-369.
- Proceedings of the 11th International Workshop on Railway Noise IWRN11; 09/2013