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New computational models for better predictions of the soil-compression index
Ahmet Demir, 2015, original scientific article

Abstract: The compression index is one of the important soil parameters that are essential for geotechnical designs. Because laboratory and in-situ tests for determining the compression index (Cc) value are laborious, time consuming and costly, empirical formulas based on soil parameters are commonly used. Over the years a number of empirical formulas have been proposed to relate the compressibility to other soil parameters, such as the natural water content, the liquid limit, the plasticity index, the specific gravity. These empirical formulas provide good results for a specific test set, but cannot accurately or reliably predict the compression index from various test sets. The other disadvantage is that they tend to use a single parameter to estimate the compression index (Cc), even though Cc exhibits spatial characteristics depending on several soil parameters. This study presents the potential for Genetic Expression Programming (GEP) and the Adaptive Neuro-Fuzzy (ANFIS) computing paradigm to predict the compression index from soil parameters such as the natural water content, the liquid limit, the plastic index, the specific gravity and the void ratio. A total of 299 data sets collected from the literature were used to develop the models. The performance of the models was comprehensively evaluated using several statistical verification tools. The predicted results showed that the GEP and ANFIS models provided fairly promising approaches to the prediction of the compression index of soils and could provide a better performance than the empirical formulas.
Keywords: compression index, statistical analysis, genetic expression programming, adaptive neuro-fuzzy, empirical equations
Published: 14.06.2018; Views: 471; Downloads: 38
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Correlation between the point load index, $I_{s(50)}$, and the resistance to unconfined compression in limestone from the comunidad Valenciana, Spain
Manolo Galván, Jorge Preciado, Jose Serón, 2014, original scientific article

Abstract: The unconfined compression strength is one of the most important engineering parameters in rock mechanics; it is used to characterize and study the behaviour of solid rocks. A good correlation between the unconfined compression strength test (UCS) and the point load strength (PLS) can be very useful, because it allows for faster and cheaper testing than other methods with the same security to calculate the structures and performances of solid rocks. A preliminary step to implement the correlation is to have a good method to determine the resistance to a point load. This determination is correct if we have a sufficient number of tests on specimens of the same nature, but usually this does not occur, and it is necessary to apply a size-correction factor, F = (De/50)α, with α = 0.45. This paper is based on limestone from Comunidad Valenciana, Spain, because it represents a very high percentage of the rocks. The implementation was conducted over 700 field and laboratory tests, of which 255 are PLT tests, 45 are UCS tests, and the rest are other parameters, like porosity and specific weight, Slake Durability, and ultrasonic velocity.
Keywords: resistance to point load, point load strength, Franklin test, size correction factor, unconfined compression
Published: 14.06.2018; Views: 393; Downloads: 36
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A comparison between conventional triaxial and plane-strain compression on a particulate system using 3D DEM
Mahmud Sazzad, Kiichi Suzuki, 2012, original scientific article

Abstract: Granular materials such as sand are subjected to different stress paths depending on the in-situ conditions. For example, a granular system under the foundations experiences conventional triaxial compression (CTC), while it experiences plane-strain compression (PSC) in the case of the embankment of roads. Due to the difference in the stress paths, the behavior of granular materials also becomes different. This paper aims at comparing the behavior of granular materials under CTC and PSC conditions using the 3D discrete-element method (DEM). An isotropically compressed dense sample consisting of 8000 spheres was prepared numerically using periodic boundaries. The CTC and PSC tests were simulated using the same isotropically compressed dense sample to compare and explore the macro- and micro-mechanical responses of granular materials without any bias from the initial fabric of the numerical sample. Qualitatively, the simulated stress-strain responses are consistent with that observed in the experimental studies. The dilatancy index is found to be independent of the stress paths used in the present study. The b value (defined as b = (σ2 − σ3)/(σ1 − σ3) where σ1, σ2 and σ3 are the stresses in the x1 -, x2 - and x3 - directions, respectively) - axial strain curve has a close similarity with the stress ratio - axial strain curve for the PSC test. The evolution of the coordination number and the sliding contact fraction is independent of the stress paths. A link between the macro- and micro-quantities is observed and a unique macro-micro relationship is noticed, regardless of the stress paths applied in this study.
Keywords: conventional triaxial compression, plane-strain compression, micro response, DEM
Published: 13.06.2018; Views: 513; Downloads: 42
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Yielding in the isotropic compression of Porto silty sand
Miguel Ferreira Amaral, Sara Rios, António Viana da Fonseca, 2012, original scientific article

Abstract: The yielding locus of a well-graded silty sand was analysed by means of isotropic compression tests and scanning electron microscopy (SEM). The tests were performed with precise instrumentation, for internal and external strain measurements, and shear-wave velocity measurements by means of bender elements. Finally, aiming at an accurate evaluation of the yield stress, four different methods were applied – two quite well know and the other two being innovative – leading to interesting conclusions.
Keywords: silty sand, yield point, isotropic compression, high pressure, seismic waves
Published: 13.06.2018; Views: 319; Downloads: 52
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Lossless geometry compression through changing 3D coordinates into 1D
Yongkui Liu, Lijun He, Peng-jie Wang, Linghua Li, Borut Žalik, 2013, original scientific article

Abstract: A method of lossless geometry compression on the coordinates of the vertexes for grid model is presented. First, the 3D coordinates are pre-processed to be transformed into a specific form. Then these 3D coordinates are changed into 1D data by making the three coordinates of a vertex represented by only a position number, which is made of a large integer. To minimize the integers, they are sorted and the differences between two adjacent vertexes are stored in a vertex table. In addition to the technique of geometry compression on coordinates, an improved method for storing the compressed topological data in a facet table is proposed to make the method more complete and efficient. The experimental results show that the proposed method has a better compression rate than the latest method of lossless geometry compression, the Isenburg-Lindstrom-Snoeyink method. The theoretical analysis and the experiment results also show that the important decompression time of the new method is short. Though the new method is explained in the case of a triangular grid, it can also be used in other forms of grid model.
Keywords: triangular mesh, model, lossless, compression
Published: 12.07.2017; Views: 899; Downloads: 239
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Experimental and numerical evaluation of the mechanical behavior of strongly anisotropic light-weight metallic fiber structures under static and dynamic compressive loading
Olaf Andersen, Matej Vesenjak, Thomas Fiedler, Jehring, Lovre Krstulović-Opara, original scientific article

Abstract: Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.
Keywords: aluminum fiber, fiber structure, orthotropy, sintering, compression, static loading, dynamic loading, energy absorption, numerical simulation
Published: 21.06.2017; Views: 475; Downloads: 351
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Percutaneous trigeminal ganglion balloon compression rhizotomy: experience in 27 patients
Tadej Strojnik, Tomaž Šmigoc, 2012, original scientific article

Abstract: Purpose. Percutaneous ganglion balloon compression (PBC) is a minimally invasive procedure for treatment of trigeminal neuralgia. Materials and Methods. Twenty-seven (19 female and 8 male) patients, who presented with classical symptoms of trigeminal neuralgia, were included. Age ranged from34 to 91 years (median 62 years), 33 procedures were performed. Duration of the symptoms ranged from 1 year to 30 years (median 5 years). Results. After the procedure, pain relief was reported in 25 (93%) patients. In two patients, the pain remained the same. The pain free period ranged from 2 to 74 months (median 15 months). A mean duration of analgesia was longer in patients with ideal pear shape of balloon at the time of the procedure compared to nonideal shape (P = 0.01). No major complications occurred in our group of patients. Conclusions. Percutaneous trigeminal ganglion balloon compression is a safe, simple, and effective method for temporary pain relief in a selective group of trigeminal neuralgia patients.
Keywords: balloon compression
Published: 15.06.2017; Views: 468; Downloads: 325
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An efficient eigenspace updating scheme for high-dimensional systems
Simon Gangl, Domen Mongus, Borut Žalik, 2014, original scientific article

Abstract: Systems based on principal component analysis have developed from exploratory data analysis in the past to current data processing applications which encode and decode vectors of data using a changing projection space (eigenspace). Linear systems, which need to be solved to obtain a constantly updated eigenspace, have increased significantly in their dimensions during this evolution. The basic scheme used for updating the eigenspace, however, has remained basically the same: (re)computing the eigenspace whenever the error exceeds a predefined threshold. In this paper we propose a computationally efficient eigenspace updating scheme, which specifically supports high-dimensional systems from any domain. The key principle is a prior selection of the vectors used to update the eigenspace in combination with an optimized eigenspace computation. The presented theoretical analysis proves the superior reconstruction capability of the introduced scheme, and further provides an estimate of the achievable compression ratios.
Keywords: eigenspace, projection space, data compression, principal component analysis
Published: 10.07.2015; Views: 746; Downloads: 71
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The wavelet transform for BEM computational fluid dynamics
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, original scientific article

Abstract: A wavelet matrix compression technique was used to solve systems of linear equations resulting from BEM applied to fluid dynamics. The governing equations were written in velocity-vorticity formulation and solutions of the resulting systems of equations were obtained with and without wavelet matrix compression. A modification of the Haar wavelet transform, which can transformvectors of any size, is proposed. The threshold, used for making fully populated matrices sparse, was written as a product of a user defined factor and the average value of absolute matrix elements values. Numerical tests were performed to assert, that the error caused by wavelet compression depends linearly on the factor , while the dependence of the error on the share of thresholded elements in the system matrix is highly non-linear. The results also showed that the increasing non-linearity (higher Ra and Re numbervalues) limits the extent of compression. On the other hand, higher meshdensity enables higher compression ratios.
Keywords: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression
Published: 01.06.2012; Views: 1476; Downloads: 70
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