Mid-frequency band gap performance of sandwich composites with unconventional core geometries

In this work novel unconventional core architectures are presented which are able to induce flexural band gaps while not being detrimental for structural bending stiffness of the sandwich structures. Two different core schemes are examined with both of them exhibiting low-frequency stop bands. While unconventional, the designs of the core offer a novel solution which can be easily manufactured in high volume parts using two-dimensional automated cutting machine. A hybrid finite element and periodic structure theory scheme is employed for the calculation of the stiffness and mass matrices, and periodic structure theory is used to obtain the wave propagation of the beams. Having acquired the wave dispersion curves and the finite element analysis' results, two specimens are manufactured using carbon fibre cured plates and commercially available PVC foam as core material. Experimental measurements of the dynamic performance of the structures are conducted using a laser vibrometer and electrodynamic shaker setup

Optimal Dynamic Motion Sequence Generation for Multiple Harvesters

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 9 (2007): Optimal Dynamic Motion Sequence Generation for Multiple Harvesters. Manuscript ATOE 07 001. Vol. IX. July, 2007

THE VALIDATION OF THE TRANSFORMATION BETWEEN AN OLD GEODETIC REFERENCE FRAME AND A MODERN REFERENCE FRAME, BY USING EXTERNAL SPACE TECHNIQUES SITES: THE CASE STUDY OF THE HELLENIC GEODETIC REFERENCE SYSTEM OF 1987

Many of the old geodetic reference frames which realized in the previous decades using classical observations carry biases. These biases are mainly caused due to the problematic observations and/or the tectonic motion. That is the case of the official Greek geodetic reference frame which consists of classical and satellite observations. Herein, we present a rigorous approach of the reconstruction of the Greek official reference frame based on the modern geodetic reference frames and their ability to express the spatial position and the dynamic change of the stations. We applied the rigorous approach to ninety stations located in Greece and we compare it with the officially accepted procedure. We found a consistency at 59.4cm between the rigorous and the officially accepted approaches, respectively. The associated mean bias estimation was estimated at 51.4 cm, indicating the resistance of a rather large amount of systematic effects. In addition, the observed discrepancies between the two approaches show great inhomogeneity all over the country

Field Operation Planning for Agricultural Vehicles: A Hierarchical Modeling Framework

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 9 (2007): Field Operation Planning for Agricultural Vehicles: A Hierarchical Modeling Framework. Manuscript PM 06 021. Vol. IX. February, 2007

Prediction of temperature dependent wave dispersion and interaction properties in composite structures

Composite structures are widely used for aerospace and automotive applications. These operate within a broad temperature range varying between -100_C to 200_C for launch vehicles and -60_C to +50_C for aircraft and automotive vehicles. Hereby, the sensitivity of the wave propagation and interaction properties of a composite structure to the ambient flight temperature is investigated. A wave finite element (WFE) and finite element (FE) based computational method is presented by which the temperature dependent wave dispersion characteristics and interaction phenomenon in a composite structures can be predicted. Initially, the temperature dependent mechanical properties of the panel in the range of -100_C to 150_C are measured experimentally using the Thermal Mechanical Analysis (TMA). Temperature dependent wave dispersion characteristics of each waveguide of the structural system, which is discretised as a system of a number of waveguides joined by a coupling element, is calculated using the WFE approach. The wave scattering properties, as a function of temperature, is determined by coupling the WFE wave characteristics models of the waveguides with the full FE modelling of the coupling element on which defect is included. Numerical case studies are exhibited for two waveguides coupled through a coupling element

Acoustic transmission properties of pressurised and pre-stressed composite structures

this work was focused on the examination of the effect of the pre-stress, namely tension and pressure, on the wave propagation and acoustic behaviour of composite laminates. The dispersion characteristics of two dimensional layered and sandwich structures were predicted using Wave Finite Element Method (WFEM). The structures were examined in non-stressed and pre-stressed scenarios. After extracting the mass and stiffness matrix of a small periodic segment of the structure using commercially available Finite Elements software, a polynomial eigenvalue problem was formed, the solutions of which consisted of the propagation constants of the waves of the structure. This way the wavenumbers and eigenvectors of the out of plane structural displacements were extracted. These wave propagation magnitudes were then used to calculate important Statistical Energy Analysis (SEA) quantities, such as modal density and radiation efficiency. The effect of pre-stress on these quantities, along with its effect on loss factor of the structure were examined

Band gap behavior of optimal one-dimensional composite structures with an additive manufactured stiffener

In this work, the banded behaviour of composite one-dimensional structures with an additive manufactured stiffener is examined. A finite element method is used to calculate the stiffness, mass and damping matrices, and periodic structure theory is used to obtain the wave propagation of one-dimensional structures. A multi-disciplinary design optimisation scheme is developed to achieve optimal banded behaviour and structural characteristics of the structures under investigation. Having acquired the optimal solution of the case study, a representative specimen is manufactured using a carbon fibre cured plate and additive manufactured nylon-based material structure. Experimental measurements of the dynamic performance of the hybrid composite structure are conducted using a laser vibrometer and electrodynamic shaker setup to validate the finite element model

The SLR observations to GNSS satellites: Preliminary results and open questions

In the present study, we show the results of the multi-year processing of SLR observations to GNSS satellites (both for GPS and GLONASS satellites), using the Bernese GNSS Software. The aim of the study is to investigate the associated SLR range residuals, defined as the differences between: (a) the observed SLR ranges and (b) the computed spatial distances between the ground stations and the GNSS (precise) orbits, respectively. The residuals are estimated on daily basis, taking into account inter alia, the Non Tidal Atmospheric Loading (NTAL) and the Atmospheric Ocean De-aliasing (AOD) effect. The results indicate different biases for the GPS and GLONASS satellites and show remarkable variability among the ground stations