Transmission Of Transient Waves Research Articles

Analysis of the Transient Impact Performance of Alternating Pneumatic Impact Hammer

Based on the method of characteristics, the impact system of alternating pneumatic impact hammer is analyzed theoretically. The transient wave's transmission between different impact parts and the variation of the force of the impact contact interface is studied. The impact system model of pneumatic impact hammer is simulated by nonlinear FEM program, LS-DANA, and the numerical model is verified very effectively by theoretic analysis. The effects of the piston's initial impacting velocity and the nature of working medium on the force of the impact contact interface and the rebound velocity of the piston are analyzed and calculated, respectively. The results show that, there is a corresponding relationship between the nature of working medium and the transient dynamic characteristics of the pneumatic impact hammer. The final conclusions provide reference for further studying of using the hammer rebound to carry out a real time measurement of the nature of working medium.

A closed-form solution for reflection and transmission of transient waves in multilayers

The reflection–transmission problem for a multilayer is examined in the time domain. The layers are linearly elastic, possibly anisotropic, but homogeneous. The multilayer is sandwiched between two homogeneous half-spaces and the incident wave propagates along the normal to the layers. By applying repeatedly the continuity of displacement and traction, the outgoing waves at each interface are evaluated in terms of the incoming ones. As a result, a system of equations is established which eventually determines the reflected and transmitted waves and the waves inside the layers, in terms of the incident wave. A few simple cases are examined in detail to show, e.g., the distortion of a rectangular incident pulse, originated by multiple reflections, and the occurrence of resonance effects.

Reflection and Transmission of Transient Waves in Anisotropic Elastic Multilayers

The reflection-transmission process, originated by a planar multilayer sandwiched between two homogeneous half-spaces, is investigated within the time domain. The half-spaces and the multilayer consist of anisotropic elastic materials. The single layers are axially inhomogeneous in that the material properties vary in the direction orthogonal to the interfaces. Two new results are established for normal incidence. First, the uniqueness of the solution in the whole space domain is proved by means of an energy method. Secondly, a closed-form solution is determined, for a homogeneous layer, where the reflected and transmitted displacement is given in terms of the incident displacement.

NEAR FIELD TRANSIENT AXISYMMETRIC WAVES IN LAYERED STRUCTURES: EFFECTS OF WEAK COUPLING

Axisymmetric stress wave transmission through the leading layers of layered structures of infinite radial but finite axial extent is numerically studied by employing two different computational approaches: a technique based on the numerical inversion of Double Integral Transformations (DIT), and a Finite Element (FE) analysis. Considering the first approach, careful selections of the limits of the numerical inversions and the sampling rates are required in order to overcome inherent numerical instabilities associated with exponential dichotomy. This type of numerical instability is more evident in layered media with weak coupling. In such systems, direct multiplications of layer transfer matrices are avoided by employing a global scheme to assemble well-conditioned global transfer matrices. Moreover, the specific structure of the propagation and attenuation zones of the structure are taken into account for increasing the efficiency and effectiveness of the transfer matrix manipulations. Satisfactory agreement between the DIT and FE numerical results is observed, at least for early times. Close to the region of application of the external pressure, the FE simulations suffer from the discretization of the applied load, node-to-node oscillations and reflections from ‘infinite’ elements (‘silent boundaries’). Using the aforementioned numerical techniques, transient wave transmission in two-layered systems (one with weak and one with strong interlayer coupling) is considered, and the effects of weak coupling on the wave transmission is studied. We show that at early times, weak coupling results in stress localization in the region close to the applied pressure, a result which can have potential application in the use of layered media as shock isolators. © 1997 by John Wiley & Sons, Ltd.

Research on Wave Phenomena in Hydraulic Lines : 6th Report, Transient Properties of Non-linear Elements

A new method is presented which gives complete plots of transient waves in hydraulic pipes with non-linear boundaries. The numerical procedure of the Laplace inversion plays an effective role there. The availability of the method is confirmed in the experiment to observe dispersions of pressure pulses by an air bubble placed in an oil pipe. This method also makes it possible to experimentally investigate transient flows in a pipe with a circular orifice. The results show that the characteristics of an orifice placed in a transient wave transmission line are approximated by the steady-state ones, if there is no reserve flow at the orifice. Moreover transient variations of flow-rate are measured by a modified "impedance tube" method which is realized by virtue of the present analytical technique. The measurement reveals the hysteresis in the relation between the instantaneous pressure drop across, and flow-rate through, the orifice.

Some results of a numerical analysis of transient waves in gas suspensions

Special aspects of the transmission of transient waves through gas mixtures carrying suspended solid particles of chemically inert substances are examined. The influence of the parameters of the gas suspension on the conditions governing the occurrence of transient processes is discussed. The interaction of shock waves with a dust-laden half-space is considered. The results of calculations relating to the decay of an arbitrary discontinuity during the reflection of a shock wave from a wall are presented.