Down-sampling of large lidar dataset in the context of off-road objects extraction

Nowadays, LiDAR (Light Detection and Ranging) is used in many fields, such as transportation. Thanks to the recent technological improvements, the current generation of LiDAR mapping instruments available on the market allows to acquire up to millions of three-dimensional (3D) points per second. On the one hand, such improvements allowed the development of LiDAR-based systems with increased productivity, enabling the quick acquisition of detailed 3D descriptions of the objects of interest. However, on the other hand, the extraction of the information of interest from such huge amount of acquired data can be quite challenging and time demanding. Motivated by such observation, this paper proposes the use of the Optimum Dataset method in order to ease and speed up the information extraction phase by significantly reducing the size of the acquired dataset while preserving (retain) the information of interest. This paper focuses on the data reduction of LiDAR datasets acquired on roads, with the goal of extraction the off-road objects. Mostly motivated by the need of mapping roads and quickly determining car position along a road, the development of efficient methods for the extraction of such kind of information is becoming a hot topic in the research community

On the use of the OptD method for building diagnostics

Terrestrial laser scanner (TLS) measurements can be used to assess the technical condition of buildings and structures; in particular, high-resolution TLS measurements should be taken in order to detect defects in building walls. This consequently results in the creation of a huge amount of data in a very short time. Despite high-resolution measurements typically being needed in certain areas of interest, e.g., to detect cracks, reducing redundant information on regions of low interest is of fundamental importance in order to enable computationally efficient and effective analysis of the dataset. In this work, data reduction is made by using the Optimum Dataset (OptD) method, which allows to significantly reduce the amount of data while preserving the geometrical information of the region of interest. As a result, more points are retained on areas corresponding to cracks and cavities than on flat and homogeneous surfaces. This approach allows for a thorough analysis of the surface discontinuity in building walls. In this investigation, the TLS dataset was acquired by means of the time-of-flight scanners Riegl VZ-400i and Leica ScanStation C10. The results obtained by reducing the TLS dataset by means of OptD show that this method is a viable solution for data reduction in building and structure diagnostics, thus enabling the implementation of computationally more efficient diagnostic strategies

Investigation of the strain-rate-dependent mechanical behavior of a photopolymer matrix composite with fumed nano-silica filler

With the evolution of additive manufacturing, there is an increasing demand to produce high strength and stiffness polymers. Photopolymers are very commonly used in stereolithography and fused deposition modeling processes, but their application is limited due to their low strength and stiffness values. Nano‐sized fibers or particles are generally embedded in the polymer matrix to enhance their properties. In this study, we have studied the effect of fumed nano‐sized silica filler on the elastic and viscoelastic properties of the photopolymer. The uniaxial testing coupons with different concentrations of silica filler have been fabricated via casting. We observed improvement in mechanical properties by the addition of the nano‐sized filler. As polymers exhibit time‐dependent mechanical response, we have conducted tensile tests at different strain rates as it is one of the most common modes of deformation, and is commonly used to characterize the parameters of the rate‐dependent material. We noticed significant dependence of the mechanical properties on the strain rate. quasi‐linear viscoelastic (QLV) model, which combines hyperelastic and viscoelastic phenomena, has been employed to capture the response of the material at different strain rates. We found out that the QLV model with Yeoh strain energy density function adequately describes the rate‐dependent behavior of the material and has reasonable agreement with the experimental results

Numerical implementation of finite strain elasto-plasticity without yield surface

In the present study, the finite element (FE) implementation of elasto-plasticity without a yield surface is discussed. For that purpose, the method of perturbing the deformation gradient tensor is employed to calculate approximate tangent moduli. The development of a user subroutine that enables one to use the proposed model within the FE program ABAQUS is covered. A number of exemplary numerical simulations is conducted in order to check the performance of this subroutine. Material parameter values determined for different materials are utilized. Finally, the presented constitutive equation is examined upon its ability to capture the shear-softening process

Finite element implementation of slightly compressible and incompressible first invariant-based hyperelasticity: theory, coding, exemplary problems

The present study is concerned with the finite element (FE) implementation of slightly compressible hyperelastic material models. A class of constitutive equations is considered where the isochoric potential functions are based on the first invariant of the right Cauchy-Green (C-G) deformation tensor. Special attention is paid to the most recently developed model formulations. The incremental form of hyperelasticity and its numerical implementation into both commercial and non-commercial FE software are discussed. A Fortran 77 UMAT code is attached which allows for a simple implementation of arbitrary first invariant-based constitutive models into Abaqus and Salome-Meca FE packages. Several exemplary problems are considered

Wprowadzenie funkcji energii potencjalnej typu Knowlesa do systemu metody elementów skończonych: teoria, kodowanie i zastosowania

This paper contains the full way of implementing a user-defined hyperelastic constitutive model into the finite element method (FEM) through defining an appropriate elasticity tensor. The Knowles stored-energy potential has been chosen to illustrate the implementation, as this particular potential function proved to be very effective in modeling nonlinear elasticity within moderate deformations. Thus, the Knowles stored-energy potential allows for appropriate modeling of thermoplastics, resins, polymeric composites and living tissues, such as bone for example. The decoupling of volumetric and isochoric behavior within a hyperelastic constitutive equation has been extensively discussed. An analytical elasticity tensor, corresponding to the Knowles stored-energy potential, has been derived. To the best of author's knowledge, this tensor has not been presented in the literature yet. The way of deriving analytical elasticity tensors for hyperelastic materials has been discussed in detail. The analytical elasticity tensor may be further used to develop visco-hyperelastic, nonlinear viscoelastic or viscoplastic constitutive models. A FORTRAN 77 code has been written in order to implement the Knowles hyperelastic model into a FEM system. The performace of the developed code is examined using an exemplary problem.Praca przedstawia pełną drogę wprowadzania do systemu metody elementów skończonych (MES) równania konstytutywnego hipersprężystości zdefiniowanego przez użytkownika przy użyciu odpowiedniego tensora sztywności. Aby zilustrować metodykę wprowadzania równania konstytutywnego do MES posłużono się modelem materiału hipersprężystego typu Knowlesa, gdyż model ten dobrze opisuje nieliniową sprężystość w zakresie średnich deformacji. Stąd model Knowlesa pozwala na poprawny opis własności mechanicznych polimerów termoplastycznych, żywic, kompozytów polimerowych i niektórych tkanek biologicznych, jak np. tkanka kostna. Przedstawiono podział równania konstytutywnego na część izochoryczną i objętościową. Wyprowadzono analitycznie tensor sztywności odpowiadający modelowi Knowlesa. Tensor ten nie był dotąd prezentowany w literaturze. Omówiono szczegółowo sposób wyprowadzania analitycznych tensorów sztywności dla materiałów hipersprężystych. Wyznaczony tensor sztywności może dalej posłużyć do budowy równań konstytutywnych nieliniowej lepkosprężystości lub lepkoplastyczności. W celu wprowadzenia modelu do systemu MES napisany został program w języku FORTRAN 77. W pracy przedstawiono wyniki z prostej symulacji MES wykonanej z wykorzystaniem napisanego programu

Conception of monitoring of cliff shores

Cliff shores are those objects which due to their dynamics should be subject to periodic measurements in order to determine their displacement. These measurements need to be cyclically performed in an established time interval according to specific criteria. In this article, the methodology developed to monitor cliff shores is presented, which defines the rules to carry out measurements and the manner of data processing aimed at building the Digital Cliff Model. A number of partial investigations, whose results were published in the studies by (Suchocki et al. 2008, Suchocki 2009a, Suchocki 2009b, Suchocki and Wasilewski 2009a, Suchocki and Wasilewski 2009b, Suchocki 2010, Suchocki and Wasilewski 2010) were performed to develop this methodology. This paper constitutes a summary of several years’ research, whose effect is an extensive methodology developed to monitor cliff shores with an application of terrestrial laser scanning technology

Application of terrestrial laser scanner in cliff shores monitoring

Łączna długość brzegów klifowych na polskim wybrzeżu wynosi ponad 100 kilometrów. Klify są jednym z najbardziej widowiskowych i ciekawych rodzajów brzegów morskich, charakteryzujących się znacznymi wysokościami oraz dużą stromizną. Walory te często sprzyjały w podejmowaniu decyzji budowania obiektów mieszkalnych w bliskim sąsiedztwie zbocza klifu. W wyniku działania czynników erozyjnych następuje niszczenie, a następnie cofanie się zboczy klifowych o średnią wielkość około 0,5 m rocznie [1, 8], co stanowizagrożenie dla obiektów znajdujących się w ich bezpośrednim zapleczu.Zaplanowanie działań ochronnych dotyczących brzegów klifowych wymaga wykonywania okresowych obserwacji w celu zarejestrowania zachodzących zmian. Do tej pory geodezyjne pomiary brzegów klifowych polegały jedynie na pomiarze górnej i dolnej krawędzi skarpy klifu ze względu na niedostępność pozostałej części klifu [4]. Takie obserwacje są niewystarczające do monitorowania szczegółowych zmian zachodzących na klifie. Wykorzystanie metod fotogrametrycznych w badaniu przemieszczeń brzegów klifowych jest trudne. Wąska plaża, która zazwyczaj występuje przy zboczach klifu częstouniemożliwia zastosowanie fotogrametrii naziemnej. Zdjęcia lotnicze stosowanesą najczęściej do zaobserwowania zmian linii brzegowej morza, rzadziej do badania zmian powierzchni klifu. Rozwój techniki pozwolił na wprowadzenie do geodezji nowoczesnych technologii i systemów pomiarowych, które dzięki bezlustrowemu pomiarowi odległości dają możliwość obserwacji całej powierzchni klifu, w tym również obszarów niedostępnych. Wykonywanie pomiarów tymi instrumentami jest szybsze, dokładniejsze i w większym stopniu zautomatyzowane niż metodami klasycznymi. Zdaniem autora rozwiązania problemu monitorowania zmian zachodzących w obiektach geotechnicznych, jakim jest klif, należy upatrywać właśnie w metodzie polegającej na skanowaniu laserowym.The coastline in Poland is around 500 km long, including around 110 km of shore cliff. Cliffs belong to the most interesting types of sea coast, and enjoy a great interest on the part of scientists dealing with their protection, geological structure, and monitoring. Up to this time, the geodetic surveys of shore cliff have been conducted by means of classical methods, namely establishing the location of top edge and the bottom of the cliff slope. Such observation is not sufficient to monitor detailed changes taking place on the shore cliff. Application of ground photogrammetry to examine cliff retreat proves difficult because of narrow beach. Aerial photography can be unsuitable due to long vertical sections of a cliff or tree branches protruding over cliffs. Over the last few years, ground laser scanners, one of the major technological achievements in geodesy, developed significantly. Application of these instruments throws new light on cliff shore monitoring. Reflectorless technology allows safe surveying of a cliff slope, which can oftentimes be difficult to access. The use of this technology allows automatisation of surveys with high accuracy and short time of observations. This paper presents the application of the terrestrial laser scanner to monitoring of cliff shores. The object of study is situated on the Baltic Sea in the vicinity of Pleśnia village, between 314 and 315 km of the coastline, according to the Polish coastline kilometric marking. This cliff is 150 m long, 5 to 10 m high and is located in the area of water waves activity. It was decided to conduct the surveying of this particular object, because dynamic changes taking place on this cliff were observed. The scanner used in the survey (ScanStation 2 Leica Geosystem company) is equipped with impulse laser with surveying range of up to 300 m. This instrument can obtain data with the speed of 50 thousand points per second and can save it as a cloud of points of sub millimeter resolution. During the scanner survey, not only the object itself is being observed, but certain additional elements such as bushes or tree branches. In this paper was proposed a way of elimination irrelevant observations from the measurements data. It also presents the results of four-year observations in the form of vertical cross sections conducted along the same line. Thus it is possible to observe the changes caused by the erosion

An internal-state-variable based viscoelastic-plastic model for polymers

In this study, a new viscoelastic-plastic constitutive model which has been formulated by utilizing the formalism of stress-like internal state variables is introduced. The developed constitutive equation allows for a good description of the inelastic material response of polymeric materials over a wide range of strain rates. An algorithm for numerical integration of the model equations has been derived. The FE implementation of the constitutive equation is widely discussed and the results of solving several exemplary problems are presented

Model reologiczny quasi-liniowej lepkosprężystości dla termoplastów i żywic

A new rheological model for polymeric materials has been proposed. The model is based on the concept of utilizing the Knowles stored-energy potential within the framework of quasi-linear viscoelasticity theory. The quasi-linear viscoelastic constitutive equation in its general form has been formulated using the formalism of the internal state variables. The developed constitutive equation allows for capturing the nonlinear-viscoelastic behavior of many polymeric materials such as thermoplastics or resins. The model has been implemented into a FE system. An application of the developed constitutive equation to modeling of the short-term, dissipative response of polyethylene has been presented.Zaproponowano nowy model reologiczny dla materiałów polimerowych. Model bazuje na koncepcji wykorzystania funkcji potencjalnej energii akumulowanej typu Knowlesa w ramach teorii quasi-liniowej lepkosprężystości. Równanie konstytutywne quasi-liniowej lepkosprężystości w ogólnej postaci sformułowano, wykorzystując formalizm wewnętrznych zmiennych stanu. Opracowane równanie konstytutywne pozwala na opis nieliniowo lepkosprężystych własności wielu materiałów polimerowych, takich jak termoplasty czy żywice. Model wprowadzono do systemu MES. W pracy zaprezentowano zastosowanie opracowanego równania konstytutywnego do modelowania krótkookresowej i dyssypatywnej odpowiedzi polietylenu