255 research outputs found
Assessment of reliability of multi-beam echo-sounder bathymetric uncertainty prediction models
No full textNowadays Multi-Beam Echo-Sounder (MBES) systems are used for obtaining information of the sea/river bed bathymetry and sediment composition. For the latter, use is usually made of the backscatter strength and depth derivatives, such as depth residuals. However, the depth derivatives are affected by the uncertainties inherent to the MBES varying with the sensors used, survey configuration and operational environment. Although models are available for the vertical uncertainty prediction, the question is how well these models can capture the estimated uncertainties of real observations. The present contribution addresses this issue by comparing the measured with modelled depth uncertainty accounting for the most recent insights of the error contributors. Data was acquired in water depths of around 2m, 10m and 30m with pulse lengths of 27 μs, 54 μs and 134 μs in the Oosterschelde estuary, the Netherlands, enabling the assessment of depth and pulse length dependence of the uncertainties. In general, the predicted and measured uncertainties are in the same order of magnitude. With increasing depth the discrepancy between the modelled and measured uncertainties increases. The effect of changing pulse length is found to be captured by the model, except for the angles close to nadir. The most dominant contributors to the vertical uncertainty are those induced by the angle of impact and range measurements. These contributors thus require further investigation to obtain a more realistic estimate of the vertical uncertainties.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aircraft Noise and Climate Effect
Guess What: Test Case Generation for Javascript with Unsupervised Probabilistic Type Inference
No full textSearch-based test case generation approaches make use of static type information to determine which data types should be used for the creation of new test cases. Dynamically typed languages like JavaScript, however, do not have this type information. In this paper, we propose an unsupervised probabilistic type inference approach to infer data types within the test case generation process. We evaluated the proposed approach on a benchmark of 98~units under test (i.e., exported classes and functions) compared to random type sampling w.r.t. branch coverage. Our results show that our type inference approach achieves a statistically significant increase in 56% of the test files with up to 71% of branch coverage compared to the baseline.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Software Engineerin
Underwater Noise Generated By Offshore Pile Driving: A Pile-Soil-Water Vibroacoustic Model Based On A Mode Matching Method
No full textIn this paper, a pile-water-soil model is developed for the prediction of sound generated due to impact piling. The complete model consists of two modules: i) a near-source module aiming at the accurate description of the pile-water-soil interaction together with the sound generation and propagation in the vicinity of the pile; and ii) a far-from-source module aiming at the propagation of the wave field at larger distances. The input to the far-from-source module is provided by the near-source module through a boundary integral formulation.Offshore EngineeringDynamics of StructuresEngineering Structure
Seafloor sediment characterization using multibeam echosounders without grab sampling: Opportunities and challenges
No full textIn the last two decades, the use of multibeam echosounders has been growing for seafloor mapping and characterization. The former uses bathymetry data whereas the latter makes use of backscatter data. The use of backscatter data has been the subject of intensive research to gain insight into seafloor composition using either empirical or model-based methods. Model-based methods employ the available physical models for predicting the backscatter strength and determine the seafloor geoacoustic parameters in an inversion algorithm using optimization methods. These methods allow for direct coupling between the backscatter curve and sediment characteristics. But the methods usually suffer from a shortcoming associated to uncalibrated sonars, which is referred to as calibration curve. Grab samples at reference areas are required to estimate the calibration curve. A question may arise as to whether, or to what extent, the calibration curve can be estimated without grab sampling. Knowing that the calibration curve is an unknown function of incident angle, in principle, one can approximate it using the available estimation and optimization theories. This is elaborated in this paper and its opportunities and challenges will be addressed. The potential benefit is twofold. 1) The huge amount of MBES backscatter currently available in many hydrographic organizations can directly be used for seafloor characterization. 2) The available multiple-frequency MBESs can further improve the performance of the inversion process. There are also challenges to be addressed. 1) Estimation of the calibration curve is an unstable process because it is merely based on observed backscatter data without using grab samples. 2) The physical models, and component parts thereof, are not usually wellbehaved functions, possibly due to their discontinuities or discontinuity of their derivatives. These issues will be elaborated in this paper.Aircraft Noise and Climate Effect
Numerical optimization of isolation systems for reciprocating engines
No full textThe use of numerical optimization methods to select reciprocating
engine anti-vibration characteristics is investigated. A rigid body
power train model coupled through an arbitrary array of vibration
isolators to a rigid supporting structure forms the basis of the
dynamic model. By calculating the forced response of the power train
to its internally generated excitation, the strain energy summed over
the isolators may be determined. This energy, which is indicative of
the efficiency of the vibration isolative mounts, is used as the
objective function in the optimization procedure. The method is
expected to be useful in preliminary design studies of front wheel
drive vehicles where traditional methods of mounting automotive
engines are not necessarily applicable. [Continues.
The Ramification and Qualification Problems in Temporal Databases
No full textThe ramification and qualification problems are two infamous, hard and ever present problems in databases and, more generally, in systems exhibiting a dynamic behavior. The ramification problem refers to determining the indirect effects of actions, whereas the qualification problem refers to determining the preconditions which must hold prior to the execution of an action. A solution to these problems in database systems permits reasoning about the dynamics of databases and allows proving consistency properties. These two problems become increasingly complex in temporal databases and no satisfactory solution has been proposed as of yet. In this paper, we describe these twoproblems in the context of temporal databases and we propose a solution of polynomial complexity based on the language of the Situation Calculus
Numerical optimization of isolation systems for reciprocating engines
No full textThe use of numerical optimization methods to select reciprocating
engine anti-vibration characteristics is investigated. A rigid body
power train model coupled through an arbitrary array of vibration
isolators to a rigid supporting structure forms the basis of the
dynamic model. By calculating the forced response of the power train
to its internally generated excitation, the strain energy summed over
the isolators may be determined. This energy, which is indicative of
the efficiency of the vibration isolative mounts, is used as the
objective function in the optimization procedure. The method is
expected to be useful in preliminary design studies of front wheel
drive vehicles where traditional methods of mounting automotive
engines are not necessarily applicable. [Continues.
Αλγόριθμοι τοπικής Αναζήτησης με Απαγόρευση Κινήσεων και Παραλληλοποίηση της Αναζήτησης για την Επίλυση του Προβλήματος Ροϊκής Παραγωγής
No full textDuring the last decades, the flowshop sequencing problem has held the attention of many researchers. The flowshop sequencing problem is a production scheduling problem in which each one of N jobs must be processed in the same sequence on each one of M machines. Since Johnson proposed optimal two and three-stage production schedules, many heuristics have been suggested to solve this problem. Complete enumeration, branch and bound techniques or integer programming determine the optimal sequence for very small problems, but efficient heuristics are necessary in order to solve larger ones. In this thesis two cases of the flowshop problem were dealt with. In the first case the objective was to minimize the maximum completion time of the jobs C_max, whereas in the second case each job was assigned a due date and the objective was to minimize primarily the maximum tardiness and secondary the maximum completion time of the jobs. The computational complexity of the flowshop sequencing problem does not allow the development of computationally fast algorithms which could optimally solve it. In this thesis taboo search techniques were studied and heuristic algorithms were developed to suboptimally solve the flowshop sequencing problem. Taboo search is a simple and flexible method for obtaining good solutions quickly and has been successfully applied to NP-complete problems such as the flowshop problem. The efficience of the method depends on the size of neighborhoods in the search space which are iteratively examined in order to obtain local optimums. In case that the optimum in a neighborhood is not unique the method can not determine the best path to continue the search. To overcome the weaknesses of taboo search, a pruning path mechanism was developed which proved effective for both the problems of flowshop that were studied. In the case of the flowshop problem with the unique criteria of minimizing the maximum completion time of the jobs, a tree search technique was developed which allows the evaluation of equivalent search paths. Finally, the process of taboo search was parallelized which drastically improved its running time
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