Vertical Gravity Gradient Modeling by 3-D Least Squares Collocation and its impact on quasigeoid-geoid separation term

<p>For the quasi-geoid determination by 3-D Least Squares Collocation (LSC) in the context of Molodensky’s approach, there is no need to measured or modelled vertical gravity gradient (VGG) as the 3-D LSC takes the varying heights of the gravity observation points into account. However, the use of measured or modelled VGG instead of the thereotical value is expected to improve the quasigeoid-geoid separation term particularly in mountainous areas. The VGG measurements are found to be different from the theoretical value in the range of - % 25 and + % 39 in western Turkey. Previously there has been no study using modelled VGGs for gravimetric geoid modelling in Turkey. VGGs are modelled by 3-D Least Squares Collocation (LSC) in remove-restore approach and validated by terrestrial VGG measurements in western Turkey. The effect of using modelled VGG instead of the theoretical one in quasigeoid-to-geoid separation term is found to be significant. The quasi-geoid computed by 3-D LSC in western Turkey is converted to geoids using theoretical or modelled VGG values and compared with GPS/levelling geoid-undulations.</p><p> </p>

Measure of Nonlocal Response in Multiscale Gradient Modeling

Realistic description of heterogeneous material behavior demands more accurate modeling at multiple scales. Multiscale scheme employing second-order homogenization requires C1 continuity at the macrolevel, while classical continuum is usually kept at the microlevel (C1-C0 homogenization). However, due to C1-C0 transition, consistency of macroscale variables is violated. This research proposes a new second-order homogenization scheme employing C1 continuity at both scales. Discretization is performed by the C1 finite element and Aifantis gradient elasticity theory. A new gradient boundary conditions are derived. The relation between the Aifantis length scale and the RVE size has been found. The new procedure is tested on a benchmark example. After successful development of the C1-C1 multiscale scheme, the next step is an extension to consistent scaling of the microscale strain localization towards a macroscopic fracture.