1,720,952 research outputs found
Nonlinear State and Parameter Estimation for Hopper Dredgers
No full textA Trailing Suction Hopper Dredger (TSHD) is a ship that excavates sediments from the sea bottom while sailing. In situ material is excavated with a special tool called the Drag-Head, then it is hydraulically transported through a pipe to the hopper where it is temporarily stored. After the dredging is completed the collected material is transported and discharged at a specified location. The efficiency of this process is highly dependent on the detailed knowledge of the excavated soil. The optimization of dredging operations is of vital importance for future improvement in efficiency, accuracy and from the viewpoint of labor saving. The automated onboard systems that have been developed to optimize the dredging performance require knowledge of several uncertain soil-dependent parameters. These cannot be directly measured but have to be estimated online from the available measurements. Such estimation is a challenging task due to lack of sufficient sensors, severe nonlinearities in models, and time-varying nature of the parameters of interest. In this thesis we focus on two of the most important TSHD-related models. These are: I. Drag-Head Model - describing the excavation process, II. Hopper Model - describing the sedimentation process occurring inside the hopper. They contain several uncertain soil-dependent parameters that need to be estimated. These are: I. horizontal cutting force coefficient kch (Drag-Head Model ), II. ratio kvh between the horizontal and vertical cutting forces (Drag-Head Model ), III. in situ permeability ksi (Drag-Head Model ), IV. average grain diameter dm (Hopper Model ). Both processes, together with the corresponding estimation problems, are discussed in detail in Chapter 2. The highly uncertain and time-varying nature of the soil-dependent parameters and the nonlinear dynamics of the models used to describe dredging process make the estimation a challenging task. The algorithms that are capable of tackling these type of problems are Nonlinear Bayesian Filters (NBF). In Chapter 3 we review several types of NBF, namely: I. parametric filters based on the Taylor series expansion (EKF, IEKF), II. parametric filters based on statistical approximations (UKF, GHF, CDF), III. parametric filters based on Gaussian Sum approximations (GSF), IV. nonparametric filters based on the importance sampling (BPF), V. nonparametric filters based on the mean-field control-oriented approach (FPF). In Chapter 4 we investigate the applicability of these nonlinear filters to the estimation problems that originate from the Drag-Head Model. The problems are: the Cutting Estimation Problem and the Cutting and Jetting Estimation Problem. The Cutting Estimation Problem applies for any cutting excavation tool whereas the Cutting and Jetting Estimation Problem is applicable only for tools equipped with cutting and jetting components. The former problem considers estimation of the ratio kvh between cutting forces and the horizontal cutting force coefficient kch, the latter problem deals with the estimation of the horizontal cutting force coefficient kch and the in situ permeability ksi. To solve the aforementioned estimation problems one needs to handle time-varying delay in the measurement of incoming density ?i, which is discussed separately. It is concluded that among the tested methods the best solution to the Cutting Estimation Problem is provided by the CDF and, in case of large uncertainty in the initial states, by the GSF. To solve the Cutting and Jetting Estimation Problem it is crucial to exploit the correlation between the horizontal cutting force coefficient kch and the in situ permeability ksi. This is done by a cascaded filter, which uses the PF to obtain an estimate of ksi, which will be further filtered by a Steady State Identification (SSI) filter, and finally by the BF to produce a final estimate of kch. In Chapter 5 we develop a novel class of nonlinear particle filters: the Saturated Particle Filter (SPF) that is used to solve the Hopper Estimation Problem. The SPF is a general method designed for Saturated Stochastic Dynamical Systems (SSDS), which are severely nonlinear systems often used in modeling real-life problems. They are characterized by a constrained probability distribution exhibiting singularity on the boundary of the saturation region. Such singularities make it difficult to estimate the states or the parameters of SSDSs by standard nonlinear filters. Our new method exploits the specific structure of the SSDS in order to design an importance sampling distribution that accounts for the most recent measurements in the prediction step of the filtering algorithm. Chapter 6 deals with the asymptotic properties of the SPF. We establish the conditions under which the SPF converges to the optimal theoretical filter. The convergence of our method is closely related to the appropriate resampling scheme. This led to the development of the improved Saturated Particle Filter (iSPF) which combines the importance sampling of the SPF with a novel resampling algorithm. In Chapter 7 the iSPF together with other nonparametric methods from Chapter 3 are used to estimate the average grain diameter dm, which solves the Hopper Estimation Problem. Because the sedimentation process is naturally divided into three regimes, to find the most efficient filtering method we considered each mode separately. We conclude that: I. for the No-Overflow loading phase the best estimate of dm is obtained by the FPF, II. for the Overflow loading phases with weak erosion, the recommended filtering method is the Reduced-Order PF, III. for the Overflow loading phases with strong erosion, the best estimation performance is achieved by the Reduced-Order PF when the excavated soil is fine and the Hybrid SPF when the excavated soil is coarse. The final solution to the Hopper Estimation Problem is obtained by integrating the filters designed for separate modes into a global estimator. Chapter 8 concludes the thesis.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Verification of Cascading Events in Interconnected Stochastic Systems: Using Adaptive Parametric Importance Sampling Methods
No full textVerification of rare cascading events in interconnected Markov processes are of high interest in energy grids, computer networks, and banking systems. Small defaults may lead to a global cascade of failures in the network. In this work, the rare events of contagious bankruptcies of the interconnected banking system are verified by three adaptive parametric importance sampling methods, belonging to Monte Carlo simulation based approaches. All three methods show comparable results in terms of the accuracy and the convergence speed on the medium sized benchmark example. Additionally, we claim that the adaptive parametric importance sampling methods scale linearly in time with respect to the sample size. The sensitivities of large or small size banks are clearly different; the larger, well connected banks have a significantly higher probability to trigger cascading; whereas for small, well connected banks this increase in probability is not found. The probability of triggering cascading is comparable between the larger sized, low connected banks and all small sized banks disregard its degree of connectivity. The results are in line with literature, which makes the adaptive parametric importance sampling methods suitable for verification of the network sensitivity.Systems and Control EngineeringDelft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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