The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Anayet U. Patwari

Waleed F. Faris

A. K. M. Nurul Amin

S. K. Loh

Dynamic Modal Analysis of Vertical Machining Centre Components

Yehia A. Bahei-El-Din

Mohammad Tawfik

Advanced Materials for Applications in Acoustics and Vibration

Reducing ground borne vibrations in urban areas is a very challenging task in railway transportation. Many mitigation measures can be considered and applied; among these open trenches are very effective.
This paper deals with the study of the effect, in terms of reduction of vertical and horizontal displacements and velocities, of the open trenches. 2D FEM simulations have been performed and several open trench configurations have been analysed varying the main geometric features such as   width and depth, distance from the rail, thickness of the soil layer over the rigid bedrock, type of the ground, ratio between the depth of the trench,  and the thickness of the soil layer. For quantifying the influence of the above specified parameters in reducing ground-borne vibrations an analysis using artificial neural networks (ANNs) has been carried out. Results show that among the geometric parameters the role of the depth of the trench is very significant; however the influence of the depth must be also evaluated in relation to the thickness of the soil layer.

Gaetano Di Mino

Marinella Giunta

Ciro Maurizio Di Liberto

Assessing the Open Trenches in Screening Railway Ground-Borne Vibrations by Means of Artificial Neural Network

The load acting on a cylindrical shell, with added periodic stiffeners,
under a transient pressure pulse propelling a pullet (gun case) has been experimentally
studied. This study is based on two modes of velocities, the first is subcritical mode and
the second is supercritical mode. The stiffeners are added to the gun tube of an
experimental gun facility, of 14 mm bore diameter. The radial strains are measured by
using high-frequency strain gage system in phase with a laser beam detection system.
Time-resolved strain measurement of the wall response is obtained and both precursor
and transverse hoop strains have been resolved. The time domain analysis has been done
  using “wavelet transform package” in order to determine the frequency domain
modes of vibrations and detect the critical frequency mode. A complete comparison
of the dynamic behavior of the shell tube before and after adding periodic stiffeners has 
been done, which indicated that a significant damping effect reaches   values between 61.5
and 38% for subcritical and critical modes. The critical frequency of the stiffened shell
is increased, so the supercritical mode is changed to subcritical mode. The amplification
and dispersion factors are determined and constructed; there is a reduction in the
corresponding speed frequencies by about 10%. Also the radial-bending vibrations and
tube muzzle motions are detected at muzzle velocity ratio of 0.99%, the results indicated
that there is a significant improvement in increasing the number of rounds per second by
about 36% and increasing the pointing precision by about 47%.

Khaled M. Saadeldin Eldalil

Amr M. S. Baz

Dynamic Stability of Cylindrical Shells under Moving Loads by Applying Advanced Controlling Techniques Part  I—Using Periodic Stiffeners

The load acting on the actively controlled cylindrical shell under a transient pressure pulse propelling a moving mass (gun case) has been experimentally studied. The concept of using piezoelectric stack and stiffener combination is utilized for damping the tube wall radial and circumferential deforming vibrations, in the correct meeting location timing of the moving mass. The experiment was carried out by using the same stiffened shell tube of the experimental 14&#x2009;mm gun tube facility which is used in part 1. Using single and double stacks is tried at two pressure levels of low-speed modes, which have response frequencies adapted with the used piezoelectric stacks characteristics. The maximum active damping ratio is occurred at high-pressure level. The radial circumferential strains are measured by using high-frequency strain gage system in phase with laser beam detection system similar to which used in part 1. Time resolved strain measurements of the wall response were obtained, and both precursor and transverse hoop strains have been resolved. A complete comparison had been made between the effect of active controlled and stepped structure cases, which indicate a significant attenuation ratio especially at higher operating pressures.

Khaled M. Saadeldin  Eldalil

Dynamic Stability of Cylindrical Shells under Moving Loads by Applying Advanced Controlling Techniques&#8212;Part II: Using Piezo-Stack Control

Phononic crystals (PCs) can be used as acoustic frequency selective insulators and filters. In a two-dimensional (2D) PC, cylindrical scatterers with a common axis direction are located periodically in a host medium. In the present paper, the layer multiple-scattering (LMS) computational method for wave propagation through 2D PC slabs is formulated and implemented for general 3D incident-wave directions and polarizations. Extensions are made to slabs with cylindrical scatterers of different types within each layer. As an application, the problem is considered to design such a slab with small sound transmittance within a given frequency band and solid angle region for the direction of the incident plane wave. The design problem, with variable parameters characterizing the scatterer geometry and material, is solved by differential evolution, a global optimization algorithm for efficiently navigating parameter landscapes. The efficacy of the procedure is illustrated by comparison to a direct Monte Carlo method.

Sven M. Ivansson

Designing 2D Phononic Crystal Slabs with Transmission Gaps for Solid Angle as well as Frequency Variation

Production of carbon fibre reinforced polymers is an elaborate process unfree from faults and problems. Problems during the manufacturing, such as plies&#39; overlapping, can cause flaws in the resulting material, so compromising its integrity. Compared with metallic materials, carbon epoxy composites show a number of advantages. Within this framework, ultrasonic tests are effective to identify the presence of defects. In this paper a Finite Element Method approach is proposed for evaluating the most effective incidence angle of an ultrasonic probe with regard to defects&#39; identification. According to our goal, the analysis has been carried out considering a single-line plane emitting source varying the probe angle of inclination. The proposed model looks promising to specially emphasize the presence of delaminations as well as massive breaking in a specimen of multilayer carbon fibre epoxy. Subsequently, simulation parameters and results have been exploited and compared, respectively, for a preliminary experimental in-lab campaign of measurements with encouraging results.

M.  Buonsanti

M. Cacciola

S. Calcagno

G. Megali

F. C. Morabito

D. Pellican&#242;

M. Versaci

Evaluation of Defects in Multilayer Carbon Fibre Epoxy for Aeronautics Applications

In this paper, the problem of vibrations induced by trains and their propagation through the soil is studied. Particular attention is focused on the vibration induced by trains in motion and on the effects of such vibrations on the foundations of buildings in proximity of the tracks. The interaction between propagating waves induced by trains in motion and buildings foundations is a problem which does not admit a straightforward analytical solution; thus a solution is given by the use of a model based on the finite elements method. Firstly, we analyze the theoretical aspects of the problem by considering constant or harmonic loads moving along a straight railway track; then, we define a transfer function soil-railway and the response function of the entire system. The study aims to address the wave propagation in an elastic semi-space and the presence in the ground of a discontinuity element, such as a barrier of a given depth is considered. The efficiency variation of barriers is analyzed in function of the different materials used, and different numerical simulations are analyzed in order to study how the wave propagation and the track-soil interaction are influenced by the membrane, seen as damping barrier.

Michele  Buonsanti

Francis Cirianni

Giovanni Leonardi

Adolfo Santini

Francesco Scopelliti

Mitigation of Railway Traffic Induced Vibrations: The Influence of Barriers in Elastic Half-Space

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Advances in Acoustics and Vibration acts as a forum for the dissemination of innovative and original research and development work in the area of acoustics and vibration.

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Advances in Acoustics and Vibration

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Advances in Acoustics and Vibration

Advanced Materials for Applications in Acoustics and Vibration

Advanced Materials for Applications in Acoustics and Vibration

Articles

Dynamic Modal Analysis of Vertical Machining Centre Components

Advanced Materials for Applications in Acoustics and Vibration

Assessing the Open Trenches in Screening Railway Ground-Borne Vibrations by Means of Artificial Neural Network

Dynamic Stability of Cylindrical Shells under Moving Loads by Applying Advanced Controlling Techniques Part I—Using Periodic Stiffeners

Dynamic Stability of Cylindrical Shells under Moving Loads by Applying Advanced Controlling Techniques—Part II: Using Piezo-Stack Control

Designing 2D Phononic Crystal Slabs with Transmission Gaps for Solid Angle as well as Frequency Variation

Evaluation of Defects in Multilayer Carbon Fibre Epoxy for Aeronautics Applications

Mitigation of Railway Traffic Induced Vibrations: The Influence of Barriers in Elastic Half-Space