Dynamic displacement estimation using data fusion

The paper describes a Kalman filtering technique for dynamic displacement estimation using accelerometer and laser sensor measurements. Data fusion of measurements from multiple sensors can give the more accurate results because of different advantages of sensors. Since the acceleration and displacement have different sampling rates, the multi-rate Kalman filter is applied. The filter is expanded with the fixed interval smoother to improve reconstruction accuracy of displacements. A modelled signal consisting of two sinus functions and Gaussian distributed noise is used to validate developed state-space model

Bridging Law Application to Fracture of Fiber Concrete Containing Oil Shale Ash

Concrete is a widely used material in various industries, including hazardous waste management. At the same time, its production creates a significant carbon footprint. Therefore, intensive research is being conducted to create more eco-friendly concrete, for example, partially replacing cement with by-products such as oil shale ash (OSA) or improving properties by adding dispersed fibers such as basalt fibers (BFs). The article consists of experimental testing of nine types of concrete and the modeling of crack propagation in bending. The basic trends of crack propagation in samples of concrete with OSA and BFs are simulated using a two-dimensional Finite Element (FE) model considering only material degradation on the opening crack surface and experimental data of three- and four-point bending tests. Crack propagation is modeled using the bridging law approach. A surrogate model for predicting the peak loading as a function of tensile strength and fracture work was created. An examination of the results of the FE model shows that the bilinear and nonlinear bridging law functions best describe the crack growth in the analyzed material. A comparison of experimental and modeled results showed that the length of the composite BF strongly affects the accuracy of the numerical model

Mechanics of composites with fiber bundle meso-structure

The presented thesis analyze mechanical phenomena in fibrous composites with fiber bundle sub-structure (woven composite sheet molding compounds (SMC) etc.). This sub-structure defines an intermediate meso-scale between the scale of individual fibers and macro-scale of the composite. The thesis consists of six papers dedicated to different mechanical aspects. Paper 1 contains an analysis of two analytical models for elastic properties of woven fabric composites. Predictions of these models are compared with results obtained using the method of reiterated homogenization and with experimental data for plain weave glass fiber- and carbon fiber polyester composites. Three different scales are identified in the analysis. It is shown that fiber bundle scale predictions are the most critical and the uncertainty there causes large differences in predictions. In Paper 2 the morphology of the ceramics C/PyC/SiC woven composite is studied and micro-damage mechanisms are revealed. Micromechanical fracture mechanics based models are proposed to describe the possible damage mechanisms. The significance of observed microdamage mechanisms for stiffness reduction is studied. The PyC core damage is suggested as the energy dissipation process. In contrast to most micromechanical models for stiffness prediction of woven composites, that assumes independence of the $Q$-matrix on the number of fabric layers in the composite, Paper 3 shows that it may not be true in some cases of woven composites. This paper contains experimental and theoretical investigations of plain weave carbon fiber/polyester composites with one single and eight layers of fabrics. The theoretical part of the paper consists of several micromechanical models which explain the main mechanisms. The last three papers: Paper 4 - Paper 6 are dedicated to the cohesive zone phenomenon which plays an important role in fracture of short fiber composites with fiber bundle structure. Paper 4 describes the finite element modeling (FEM) results of center-hole notched tensile specimens with different bridging-laws governing crack growth. Crack lengths, crack profiles and stress distributions are predicted. The results are compared with experimentally determined crack shapes from an earlier investigations. Only with softening bridging-laws, the experimental results can be matched. In Paper 5, fracture of SMC materials two double edge notched tensile (DENT) specimens with considerable difference in fracture characteristics is studied. Linear- and non-linear FEM were used to extract the true crack opening from measured displacements over the cracked region. The bridging laws of the two SMCs were estimated and the main physical mechanisms governing the fracture were recognized. Experimentally obtained load vs. displacement curves in compact tension tests (CT) of two different SMC materials are analyzed in Paper 6. Three different CT specimen geometries are considered. Progressive fracture is attained in all tests. By implementing bridging laws from Paper 5 and volumetric stiffness degradation of bulk SMC in an FEM model, the experimental results for two larger geometries were reproduced with high accuracy. Premature material degradation on the compressive side of the CT specimen precrack, was analyzed. The successful use of bridging laws strongly suggests that they are indiced intrinsic properties, governing the fracture behavior of SMC materials.Godkänd; 2002; 20061113 (haneit

Mechanical properties of a rapidly prototyped composite: numerical modeling and parametric analysis

Godkänd; 2012; 20120918 (joffe

Numerical analysis of large telescopes in terms of induced loads and resulting geometrical stability

Comprehensive numerical studies, involving structural and Computational Fluid Dynamics (CFD) analysis, have been carried out at the Engineering Research Institute “Ventspils International Radio Astronomy Center” (VIRAC) of the Ventspils University College to investigate the gravitational and wind load effects on large, ground-based radio telescopes RT-32 performance. Gravitational distortions appear to be the main limiting factor for the reflector performance in everyday operation. Random loads caused by wind gusts (unavoidable at zenith) contribute to the fatigue accumulation.Upprättat; 2013; 20130322 (joffe)</p

Characterization of Wind Loading of the Large Radio Telescope

This paper describes numerical simulations of windloads on the large parabolic reflector antenna RT-32 with a diameter of 32 m and a methodology of how calculated wind pressure can be transferred to beam-based digital model. The wind flow leads to a compressive load on the dish and thus to a deformation of the reflector. These deformations can cause a performance degradation of the input signal, or even loss of the observed or controlled object. The calculations show that the wind induced force is small in comparison with gravitational loads. Studies have been carried out at the Ventspils International Radio Astronomy Centre (VIRAC) to investigate the wind-loading effects on the radio telescope RT-32 structure. The wind loads are calculated with the help of an open sourced Computational Fluid Dynamics toolkit OpenFOAM

A comparison of different homogenization models and experimental results

Godkänd; 1999; 20080425 (ysko

Experimental studies of a single flexibly-mounted rod in a triangular rod bundle in cross-flow

Experiments on flow-induced vibrations using a closely-packed triangular rod array with a pitch-todiameter ratio of 1.1 in water cross-flow was carried out at Paul Scherrer Institute. The bundle consists of 21 row of five rods in each one. Single flexibly-mounted test rod (TR) is in the fourth row in an otherwise fixed array. The test rod can freely move in the transverse and in-line direction. Two accelerometer sensors were attached at both ends of the TR to measure the rod response on the fluid flow. The effect of flow rate on the stability of the flexibly-mounted TR has been analysed. During experiments, it reveals a set of conditions and tendencies for the flow-induced vibration in the closely-packed multi-rod system

Experimental studies of a single flexibly-mounted rod in a triangular rod bundle in cross-flow

Experiments on flow-induced vibrations using a closely-packed triangular rod array with a pitch-todiameter ratio of 1.1 in water cross-flow was carried out at Paul Scherrer Institute. The bundle consists of 21 row of five rods in each one. Single flexibly-mounted test rod (TR) is in the fourth row in an otherwise fixed array. The test rod can freely move in the transverse and in-line direction. Two accelerometer sensors were attached at both ends of the TR to measure the rod response on the fluid flow. The effect of flow rate on the stability of the flexibly-mounted TR has been analysed. During experiments, it reveals a set of conditions and tendencies for the flow-induced vibration in the closely-packed multi-rod system

Using reiterated homogenization for stiffness computation of woven composites

Godkänd; 1998; 20080425 (ysko