Analysis Of Surface Waves Method Research Articles

Aspects of cylindrical shell resonances in the Fourier diamond spaces. Use of surface wave analysis methods (SWAM) on experimental or numerical datas

For an attenuated surface wave (wave number K=K′+jK″), the resonant space-frequency S(x,ω) representation of a cylindrical shell is performed versus the angular position x. In this space, the MIIR properties are demonstrated. The resonant wave number-frequency representation Ksi(k,ω) is then obtained by spatial Fourier transform of S(x,ω). This two-dimensional second space clearly separates clockwise and anticlockwise propagating waves. The first ones are observed in the positive k values of Ksi, and the second ones in the negative k values of Ksi. The modulus of Ksi is maximum each time that the resonant condition is encountered [ω so that K′(ω) is integer]. As new results, the k cut of Ksi reveals the Sommerfeld Watson aspect of the problem and SWAM identify the complex K. On an ω cut of Ksi, SWAM identify the RST aspect of the target (and a little more): complex frequency resonances Ω=Ω′+jΩ″ for real modes n. SWAM is performed on experimental datas and on numerical form functions. The agreement with theoretical results obtained by RST is very good.

Aspects of a damped surface wave in the Fourier diamond spaces. New surface wave analysis method (SWAM)

A damped surface wave (complex wave number K=K′+jK″) is described by its space-frequency representation S(x,ω)=exp(jK(ω)x). The wave-number-frequency representation Ksi(k,ω) is the spatial Fourier transform of S(x,ω). A Ksi-cut versus k is a k-Breit Wigner form (square modulus maximum for k=K′,K″ half-width). A Ksi-cut versus ω is then shown to be an ω-Breit Wigner form (square modulus maximum for ω=Ω′, with an Ω″ half-width). New interesting properties are found: the phase velocity is Cp=Ω′/K′ and the group velocity is Cg=Ω″/K″. The wave-number-time representation N(k,t) is the inverse frequency Fourier transform of Ksi(k,ω). N(k,t) is then shown to be N(k,t)=exp(jΩ(k)t). The space-time representation s(x,t) is obtained by inverse frequency (respectively, wave number) Fourier transform of S(x,ω) [respectively of N(k,t)]. The four spaces s, S, Ksi, and N are the four Fourier diamond spaces. Used on s(x,t) experimental datas, the two cuts properties are the basis of the surface wave analysis methods (SWAM). Those methods identify the complex K (respectively, Ω) using k-ARMA (respectively ω-ARMA) models. Using SWAM on a cylindrical shell, the A-wave is experimentaly fully characterized. The agreement with theoretical results is excellent.

Quality Control of Portland Cement Concrete Slabs with Wave Propagation Techniques

Coring is normally done to monitor the thickness and quality of portland cement concrete (PCC) slabs during construction. Because this procedure requires a considerable amount of time, it is done at widely spaced intervals. As a result, the most critical points, in terms of strength or thickness, are sometimes not tested. Their repeatability and extreme sensitivity to the properties of surface layer enable wave propagation techniques to be used for quality control. The main advantage of these techniques is that they are nondestructive. Fortunately, these techniques have been automated in the last few years. Two seismic devices (seismic pavement analyzer and a portable version of it called the Lunch Box) have been used extensively for quality control. With them, slabs can be tested at closely spaced points and at a fraction of the cost and time of coring. The main tests used are the impact echo for determining the thickness of the slab, the ultrasonic body wave for determining the modulus, and the ultrasonic surface wave (an offshoot of the spectral analysis of surface waves method) also for determining the modulus. On the basis of extensive field testing on many types of base and subgrade, the techniques in general—and the two devices in particular—are suitable for many quality-control projects. It was found that the most robust method for determining the modulus is the ultrasonic surface wave. The impact echo also works well, as long as enough contrast exists between the properties of the PCC and the underlying materials.

Impact of Weight Falling onto the Ground

The application of some nondestructive testing procedures for soils and pavements, such as the spectral analysis of surface waves method, requires the use of dynamic sources at some point on the surface of the ground to create vibrations that can be recorded and related to the material characteristics of the medium. These sources are typically accomplished by means of falling weights of various sizes. This paper applies a simple mass‐spring‐dashpot model to assess the characteristics of the forces transmitted to the ground by the falling weight so as to be able to rationally decide on its size, mass, and dropping height. It is found that if inelastic effects are disregarded, a falling weight always rebounds; that the drop height affects only the impact velocity and amplitude of the contact force—not the duration of contact; and that increases in the drop weight lead to reductions in damping, increases in contact time, increases in contact force, and enhancement of the low‐frequency components in the Fourier spectrum of the contact force.