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This chapter contributes to the improvement of GPS-based travel surveying by introducing a combined method of GPS, GIS and web-based user interaction, which has been applied in large- scale fieldwork in the netherlands. With over 1000 participants, as far as we know, this is the first time that a GPS-based method that measures travel mode choice as well as the location and type of destinations that are visited has been used on such a large scale. The chapter focuses in particular on the identification of travel modes and destinations, which is still an under-researched issue. Our approach concentrates on the issue of deriving and validating the purpose of trip destinations and travel modes, while also allowing reliable multi-day data collection. The method consists of an interpretation process and a validation process. The interpretation process uses spatial data (e.g. railways, shops) and characteristics of the respondents (e.g. home address, possession of cars) to interpret data from the logs. The travel behaviour data that result from this interpretation round can be adjusted and added to by the respondents in a validation application. The link between both processes is interactive; when new individual characteristics (e.g. the address of a friend’s house) are entered by the respondents, these characteristics will be used for further interpretation of the data. The remainder of this chapter is structured as follows. The following section gives an overview of the advantages and drawbacks of current GPS-based data collection methods that are suitable for measuring choice of travel mode and/or trip destinations. The subsequent section describes the GPS-based method that we developed and in section four the value of our method is evaluated by presenting the results of the fieldwork we recently undertook. The results are compared with results from an internet survey that was carried out at an earlier date and also with the Dutch Travel Survey (DTS) that uses paper diaries. The chapter ends with conclusions on the use of GPS-based methods for the collection of travel behaviour data and a discussion of future possibilities., Research in Urbanism Series, Vol. 1 (2008): Urbanism on Track: Application of tracking technologies in urbanism

Linked data provide an alternative route for dissemination of spatial information as compared to the traditional SOA-based SDI approach. Where the latter is built on predefined structuring of semantics within domains, linked data is open to linking information to any data over the Web. In this respect both are complementary. The traditional approach providing a mechanism for a basis of standardized and structured data within domains, and linked data providing an open mechanism for sharing and combining. GML as the ISO standard for exchange of service based spatial data and RDF as the linked data format are therefore related. GML provides the format in which many spatial datasets are available and exchanged. This standardization process and effort has been realized on a large scale. Why not let the web of linked data take advantage of this effort? This article will focus on the use of GML structured data as a source for deriving RDF structured data. The first part of the paper focusses on deriving linked data from GML data. The first version of GML, v1.0, was based on RDF. From version 2.0 onwards GML was based on XML and XML Schema, but the object-property structure was retained. We describe a transformation for translating any correctly structured GML to RDFS/OWL automatically, using XSLT. Because GML’s object-property structure translates very well to triples, the transformation is straightforward. Well-known GML content elements such as names and descriptions are mapped to their RDF equivalent. However, any semantics specific to the input GML data (a.k.a. the application schema) are ignored in this translation. In the second part, we study how more meaningful RDF can be created from GML, given the underlying information model, by transforming it from UML to RDFS/OWL. There exists a straightforward mapping to convert a UML model into a RDFS/OWL vocabulary. However, the re-use of existing concepts in vocabularies takes a central role in RDFS/OWL while in UML the use of vocabularies is not supported. We describe how annotating the UML model could improve this translation.

FEMsimulation of large deformations as occur in metal forming processes is usually accompanied with highly distorted meshes. This leads first to a reduction of accuracy and later to loss of convergence when implicit solvers are used. Remeshing can be used to reduce element distortion, but repeated remeshing will result in smoothing of data like equivalent plastic strain, due to averaging and interpolation. A meshless method circumvents the problem of mesh distortion, but depending on the integration of the weak formulation of equilibrium mapping of data and hence smoothing of data still remains unless a nodal integration scheme is used. Starting with a LocalMaximum Entropy approach [1] with nodal integration, we end-up with a smoothed Finite Element formulation in the limit of local approximations [2]. It is straightforward to adapt the triangulation in every increment, yielding an Adaptive Smoothed Finite Element Method, in which large deformations can be modelled with a Lagrangian description without the necessity to map data from one step to the other. A cell based stabilized conforming nodal integration method (SCNI) [3] is used. Depending on the configuration of nodes, nodal integration can yield singular stiffness matrices, resulting in spurious displacement modes [4]. A stabilization is used, based on minimizing the difference between a ‘linear assumed’ and the consistent strain field. The cells are based on the Delaunay triangulation, connecting mid-sides and centres of gravity of the triangles (Figure 1). Especially at the outer boundary, this yields a simpler formulation than using the dual Voronoi tesselation

Currently, the main tool for the simulation of forming processes is the finite element method. Unfortunately, for processes involving very large deformations, finite elements based on a Lagrangian formulation are problematic due to mesh distortion. Results become inaccurate and might even lose their physical meaning. In the 1980s, a new group of numerical methods emerged. This group is entitled meshless methods, and aims at avoiding problems related to the use of a mesh. The nodal-based approach of these methods does not restrict the relative motion of nodes by shape criteria related to elements. The goal of the research as presented in this thesis is to develop a meshless method for solving large deformations more efficiently than currently possible with finite elements. The first step in this research was to select a single meshless method for further developments. Therefore, three meshless shape functions and two numerical integration schemes were investigated in a comparative study. It can be concluded that diffuse meshless shape functions, like moving least squares and local maximum entropy approximations, are more accurate than simple linear interpolation upon a Delaunay triangle. However, the computational effort for these two diffuse functions is considerably higher. Concerning the numerical integration, a nodal integration scheme performs very well. Volumetric locking is absent and good accuracy is obtained. Therefore the linear triangle interpolation in combination with a nodal integration scheme was chosen for further development. For this combination, an extension to large deformations was presented. The new method, named Adaptive Smoothed Finite Elements (ASFEM), is based on a cloud of nodes following a Lagrangian description of motion and a triangulation algorithm that sets up the connectivity between nodes for each increment. The method was successfully tested on the simulation of a forging process and an extrusion process. No failure of the algorithm as a result of mesh distortion was encountered. Results compared accurately to reference solutions made with finite elements.

In this paper, the material flow around the pin during friction stir welding (FSW) is simulated using a 2D plane strain model. A pin rotates without translation in a disc with elasto-viscoplastic material properties and the outer boundary of the disc is clamped. Two numerical methods are used to solve this problem and an analytical solution is derived. The analytical model is complementary to validate the two numerical methods, i.e. the arbitrary Lagrangian-Eulerian (ALE) method and the adaptive smoothed finite elements method (ASFEM).

A successful simulation of a bulk forming process with finite elements can be difficult due to distortion of the finite elements. Nodal smoothed Finite Elements (NSFEM) are an interesting option for such a process since they show good distortion insensitivity and moreover have locking-free behavior and good computational efficiency. In this paper a method is proposed which takes advantage of the nodally smoothed field. This method, named adaptive smoothed finite elements (ASFEM), revises the mesh for every step of a simulation without mapping the history dependent material parameters. In this paper an updated-Lagrangian implementation is presented. Several examples are given to illustrate the method and to show its properties.

More and more public organizations publish their data in an open format to increase transparency and foster economic activity. In this modern gold rush, organizations strive to open up as many datasets as possible, without considering the strategic importance of open data. Especially linking data to other datasets can lead to the creation of innovative services. One issue that is often not explicitly addressed before opening up data is the format of the dataset. Central to open data is that the format is machine readable. But to allow for effortless linking of datasets, data being merely machine readable is not sufficient. Lifecycle models can uide the process of publishing linked open data. Current linked open data ifecycle models focus on the technical steps that need to be taken by the internal IT organization and often forget to include actions to be taken ater publication. The effectiveness of linked open data, however, depends n how much the data is used. Hence, this paper develops a linked open data lifecycle model that takes the multiple disciplines and stakeholders within and outside the organization into account as well as the steps to be taken after publication of the atasets. Firstly, using existing linked open data lifecycle models, this aper identifies generic phases of opening up linked data: identification, reparation, publication, re-use and evaluation. Secondly, investigating the rocess of opening up data in a semipublic oganization in the Netherlands, he lifecycle model is refined and detailed. his case study shows that the involvement of relevant stakeholders, both within and outside the organization and of various disciplines, is essential to realize the support for the process and stimulate re-use.

Introduction: Finite element simulations of bulk forming processes, like extrusion or forging, can fail due to element distortion. Simulating a forming process requires either many re-meshing steps or an Eulerian formulation to avoid this problem. This re-meshing or usage of an Eulerian formulation, requires the mapping or convection of state variables. This causes inaccuracies for history dependent materials, for instance in hardening plasticity. In this research, a new method is examined which avoids the problems mentioned above. - Methods: The method will be divided in three main components and treated seperately below. The first component of the method is a linear triangular element formulation. It is cost effective and easy to generate on a cloud of nodes by means of Delaunay triangulation. For every increment of a forming process, the old triangulation is deleted and a new Delaunay triangulation is performed. Thereby, the nodal connectivity is changing in time during the process, hence avoiding the problem of mesh distortion. The method of alpha shapes is used to retrieve the boundary of the cloud of nodes. The second component is a nodal integration scheme of the weak form. Nodal integration avoids the problem of mapping state variables in case of triangulations. Furthermore the nodal integration scheme gives good results in incompressibility whereas ‘Gaussian’ integrated linear triangular elements will show locking behavior in the incompressible limit. The third componenent is an updated Lagrangian formulation. A Jaumann rate is used to account for stress rotation and a rate of deformation as a measure of strain was chosen. The formulation allows history dependent materials to be used in an adaptive strategy. - Results: To examine the performance of the method, two tests were performed. The first is the non-proportional loading of a piece of metal. The second test is the elasto-plastic deformation of a tapered bar. The tests show that indeed it is possible to use history dependent material models in an adaptive strategy without resorting to mapping or convection algorithms. Secondly the artefact of volumetric locking is absent and to conclude, the computation times for this method are found to be comparable to those of finite elements. Current point of research is resolving an oscillation related to the case of near incompressibility. Though volumetric locking was not found in the current research, the pressure was found to be oscillating spuriously in certain cases. Future research will focuss on resolving this pressure mode.

Meshless methods offer interesting properties for the simulation of bulk forming processes. This research concerns the investigation of the stabilized conforming nodal integration scheme (SCNI) for use in metal-forming processes. Two tests are carried out. Firstly, the performance of SCNI is compared to a standard integration scheme. The performance seems problem specific. Secondly the footing of a piece of nearly incompressible material is used for testing the locking behavior of the method. No volumetric locking was found.

In this work we review the opportunities given by the use of local maximum- entropy approximants (LME) for the simulation of forming processes. This approximation can be considered as a meshless approximation scheme, and thus presents some appealing features for the numerical simulation of forming processes in a Galerkin framework. Especially the behavior of these shape functions at the boundary is interesting. At nodes on the boundary, the functions possess a weak Kronecker-delta property, hence simplifying the prescription of boundary conditions. Shape functions at the boundary do not overlap internal nodes, nor do internal shape functions overlap nodes at the boundary. Boundary integrals can be computed easily and efficiently compared to for instance moving least-squares approximations. Furthermore, LME shapes also present a controllable degree of smoothness. To test the performance of the LME shapes, an elastic and a elasto-plastic problem was analyzed. The results were compared with a meshless method based on a moving least-squares approximation.

Database applications using large vector data are often supported by spatial index structures to locate spatially related objects. An important query class deals with finding related object pairs under a distance function. %, i.e. those %spatially close to a given point. , like nearest neighbors. In this paper we demonstrate that a light-weight indexing structure, based on the metric properties derived from the distance function, is often sufficient to support this important class. It is of particular importance as a temporary search accelerator while processing complex queries. Moreover, it can be used to speed up point and region queries for low selectivities and, presumably, highly-skewed spaces.