Parametric Study on the Axial Vibrations of Riser Suspended and Moored by Chains (RSAA) Configurations

2011 ◽  
Author(s):  
Claudio Marcio Silva Dantas ◽  
Marcos Queija de Siqueira ◽  
Victor Milanez da Silva Pereira ◽  
Fernando Jorge Mendes de Sousa ◽  
Gilberto Bruno Ellwanger ◽  
...  
Keyword(s):  
Parametric Study ◽  
Axial Stress ◽  
Flexible Structures ◽  
Mooring Line ◽  
Stress Variation ◽  
Line Segments ◽  
Deep Waters ◽  
Riser Design ◽  
Transversal Vibrations ◽  
High Level

Recently, in order to minimize the influence of the vertical motions in the risers and consequently allow the utilization of FPSOs in deep waters, a new riser configuration called RSAA (riser suspended and moored by chains - in Portuguese), composed of a rigid vertical riser, flexible structures and mooring line segments (top and bottom) was proposed. This configuration presents solutions to the most critical points in a riser design: the top tensions are dissociated from the bending moments at the top region, and the curvatures at the TDP are reduced by utilization of floaters. Feasibility analyses have shown that the vertical riser is the most critical part of the proposed system due to the FPSO high level of vertical motions. These motions are transmitted by the top chains, leading to high levels of axial stress variation due to dynamic tension. Faced with this, a parametric study is vital in order to understand the system’s behavior as well as to establish the main parameters which influence its structural behavior. Analytical methods may require some slight simplifications of the problem to be applicable, but they generally lead to compact formulas that do explain which parameters influence the results and why and how it does so. This work proposes an analytical model to determine axial stress and tension variations at the vertical riser, considering some simplifying hypotheses, like the flexible structures and mooring line segments at the bottom will be replaced by a mass and a spring. Neglecting some nonlinearities but considering the coupling between axial and transversal vibrations, a random dynamic analysis in the frequency domain can be performed to evaluate the maximum stresses and tensions levels with considerably lower computational costs.

Parametric Design of a Waterjet Pump by Means of Inverse Design, CFD Calculations and Experimental Analyses

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Duccio Bonaiuti ◽  
Mehrdad Zangeneh ◽  
Reima Aartojarvi ◽  
Jonas Eriksson
Keyword(s):  
Flow Field ◽  
Parametric Study ◽  
Parametric Design ◽  
Inverse Design ◽  
Design Parameters ◽  
Pump Design ◽  
Hydrodynamic Efficiency ◽  
Numerical Predictions ◽  
High Level ◽  
Suction Performance

The present paper describes the parametric design of a mixed-flow water-jet pump. The pump impeller and diffuser geometries were parameterized by means of an inverse design method, while CFD analyses were performed to assess the hydrodynamic and suction performance of the different design configurations that were investigated. An initial pump design was first generated and used as baseline for the parametric study. The effect of several design parameters was then analyzed in order to determine their effect on the pump performance. The use of a blade parameterization, based on inverse design, led to a major advantage in this study, because the three-dimensional blade shape is described by means of hydrodynamic parameters, such as blade loading, which has a direct impact on the hydrodynamic flow field. On the basis of this study, an optimal configuration was designed with the aim of maximizing the pump suction performance, while at the same time, guaranteeing a high level of hydrodynamic efficiency, together with the required mechanical and vibrational constraints. The final design was experimentally tested, and the good agreement between numerical predictions and experimental results validated the design process. This paper highlights the contrasting requirements in the pump design in order to achieve high hydrodynamic efficiency or good cavitation performance. The parametric study allowed us to determine design guidelines in order to find the optimal compromise in the pump design, in cases where both a high level of efficiency and suction performance must simultaneously be achieved. The design know-how developed in this study is based on flow field analyses and on hydrodynamic design parameters. It has therefore a general validity and can be used for similar design applications.

Lane Marking Detection Based on Segments with Upper and Lower Structure

2019 ◽  
Vol 34 (02) ◽  
pp. 2055005
Author(s):  
Junjie Huang ◽  
Zhiling Wang ◽  
Huawei Liang ◽  
Linglong Lin ◽  
Biao Yu ◽  
...  
Keyword(s):  
Detection Algorithm ◽  
Urban Traffic ◽  
Middle Level ◽  
Threshold Method ◽  
Line Segments ◽  
Lane Marking ◽  
Lane Departure ◽  
Lower Structure ◽  
Multiple Disturbance ◽  
High Level

An effective and accurate lane marking detection algorithm is a fundamental element of the intelligent vehicle system and the advanced driver assistant system, which can provide important information to ensure the vehicle runs in the lane or warn the driver in case of lane departure. However, in the complex urban environment, lane markings are always affected by illumination, shadow, rut, water, other vehicles, abandoned old lane markings and non-lane markings, etc. Meanwhile, the lane markings are weak caused by hard use over time. The dash and curve lane marking detection is also a challenge. In this paper, a new lane marking detection algorithm for urban traffic is proposed. In the low-level phase, an iterative adaptive threshold method is used for image segmentation, which is especially suitable for the blurred and weakened lane markings caused by low illumination or wear. In the middle-level phase, the algorithm clusters the candidate pixels into line segments, and the upper and lower structure is used to cluster the line segments into candidate lanes, which is more suitable for curve and dashed lane markings. In the high-level phase, we compute the highest scores to get the two optimal lane markings. The optimal strategy can exclude interference similar to lane markings. We test our algorithm on Future Challenge TSD-Lane dataset and KITTI UM dataset. The results show our algorithm can effectively detect lane markings under multiple disturbance, occlusions and sharp curves.

Modeling and linear analysis of sound generation mechanism in sonic soot blowers

2019 ◽  
Vol 25 (17) ◽  
pp. 2305-2315
Author(s):  
A. Najafi ◽  
M. Asayesh ◽  
A. Siami
Keyword(s):  
Sound Wave ◽  
Parametric Study ◽  
Low Frequency ◽  
Linear Analysis ◽  
Generation Mechanism ◽  
Frequency Content ◽  
Sound Generation ◽  
Governing Equations ◽  
High Level ◽  
Frequency Sound Wave

Sonic soot blowers (SSBs) are nondestructive tools to prevent ashes and particle build-up on the surfaces of boilers or other similar instruments. For higher performance, sonic soot cleaners should generate a high level-low frequency sound wave. In this article, the sound generation mechanism in these tools has been modeled. Firstly, the governing equations of the diaphragm and the horn and coupling between them are derived. By linearization, a parametric study is performed to find the optimum design points. Based on the eigenvalue analysis, it is shown that the sound generation in sonic soot cleaners is due to instability of the interaction between the diaphragm and the horn. Moreover, it is found that the sound wave frequency is approximately equal to the lowest fundamental frequency of the horn or diaphragm. Finally, the frequency content of an SSB voice is investigated.

Computational Study for Inventory Estimation of Se-79, Tc-99, Sn-126, and Cs-135 in High-Level Radioactive Wastes From Spent Nuclear Fuels of Light Water Reactors

2011 ◽  
Author(s):  
Keisuke Okumura ◽  
Shiho Asai ◽  
Yukiko Hanzawa ◽  
Tsutomu Okamoto ◽  
Hideya Suzuki ◽  
...  
Keyword(s):  
Parametric Study ◽  
Computational Study ◽  
Estimation Method ◽  
Fission Products ◽  
Radioactive Wastes ◽  
Light Water Reactors ◽  
Nuclear Fuels ◽  
Light Water ◽  
Water Reactors ◽  
High Level

Inventory estimation of long-lived fission products (LLFPs) in high-level radioactive wastes (HLW) from spent nuclear fuels of light water reactors is important for a safety assessment of their disposal. In order to develop an inventory estimation method of difficult-to-measure LLFPs (Se-79, Tc-99, Sn-126, and Cs-135), a parametric study was carried out by using a sophisticated burnup calculation code and data. In the parametric study, fuel specifications and irradiation conditions are changed in the conceivable range. The considered parameters are fuel assembly types (PWR / BWR), U-235 enrichment, moderator temperature, void fraction, power density, and so on. From the calculated results, we clarify the burnup characteristics of the target LLFPs and their possible ranges of generations. Finally, candidates of the key nuclide are proposed for the scaling factor method of HLW.

Long-Term Radioactivity Release from Solidified High-Level Waste - Part II Parametric Study of Waste form Properties, Temperature and Time

1982 ◽  
Vol 15 ◽  
Author(s):  
Friedrich K. Altenhein ◽  
Werner Lutze ◽  
Rodney C. Ewing
Keyword(s):  
Parametric Study ◽  
Computer Code ◽  
Salt Dome ◽  
Waste Form ◽  
Glass Block ◽  
High Level Waste ◽  
Surface Layers ◽  
History Of ◽  
High Level

The computer code QTERM has been used to calculate the total released activity from a single glass block when in contact with brine in a salt dome repository as a function of: (1) waste form properties, (2) leaching mechanisms, (3) retention or precipitation of specific radionuclides in surface layers, (4) thermal history of the repository and (5) decreasing activity as a function of time.

An improved method of mooring damping estimation considering mooring line segments contribution

2021 ◽  
Vol 239 ◽  
pp. 109887
Author(s):  
Jun Yan ◽  
Dongsheng Qiao ◽  
Binbin Li ◽  
Bin Wang ◽  
Haizhi Liang ◽  
...  
Keyword(s):  
Mooring Line ◽  
Improved Method ◽  
Line Segments ◽  
Damping Estimation

Fatigue Testing and Analysis of a Deep Water Steel Tube Umbilical

2008 ◽  
Author(s):  
Alan Dobson ◽  
Dave Fogg
Keyword(s):  
Mathematical Model ◽  
Fatigue Testing ◽  
Steel Tube ◽  
Steel Tubes ◽  
Stick Slip ◽  
Stress Variation ◽  
Slip Mechanism ◽  
Deep Waters ◽  
Bending Loads ◽  
The Mathematical Model

Rapid analysis of dynamic umbilical structures during the design phase requires a robust mathematical model of the component stresses due to static and alternating loads. The following discusses the validation of a model, through full scale testing, used to assess the stresses and strains present within steel tubes, in umbilical structures typically used in dynamic service in deep waters, such as found in the Gulf of Mexico and offshore West Coast of Africa. The validation focuses upon the complexity of the mathematical model and the influence of tension magnitude the stick-slip mechanism and the stress variation around the circumference of the tubes when under the influence of bending loads.

scholarly journals Large-Scale LiDAR SLAM with Factor Graph Optimization on High-Level Geometric Features

Sensors ◽  
2021 ◽  
Vol 21 (10) ◽  
pp. 3445
Author(s):  
Krzysztof Ćwian ◽  
Michał R. Nowicki ◽  
Jan Wietrzykowski ◽  
Piotr Skrzypczyński
Keyword(s):  
Large Scale ◽  
Point Clouds ◽  
Factor Graph ◽  
Optimization Approach ◽  
Geometric Features ◽  
Visual Slam ◽  
Loop Closure ◽  
Line Segments ◽  
Graph Optimization ◽  
High Level

Although visual SLAM (simultaneous localization and mapping) methods obtain very accurate results using optimization of residual errors defined with respect to the matching features, the SLAM systems based on 3-D laser (LiDAR) data commonly employ variants of the iterative closest points algorithm and raw point clouds as the map representation. However, it is possible to extract from point clouds features that are more spatially extended and more meaningful than points: line segments and/or planar patches. In particular, such features provide a natural way to represent human-made environments, such as urban and mixed indoor/outdoor scenes. In this paper, we perform an analysis of the advantages of a LiDAR-based SLAM that employs high-level geometric features in large-scale urban environments. We present a new approach to the LiDAR SLAM that uses planar patches and line segments for map representation and employs factor graph optimization typical to state-of-the-art visual SLAM for the final map and trajectory optimization. The new map structure and matching of features make it possible to implement in our system an efficient loop closure method, which exploits learned descriptors for place recognition and factor graph for optimization. With these improvements, the overall software structure is based on the proven LOAM concept to ensure real-time operation. A series of experiments were performed to compare the proposed solution to the open-source LOAM, considering different approaches to loop closure computation. The results are compared using standard metrics of trajectory accuracy, focusing on the final quality of the estimated trajectory and the consistency of the environment map. With some well-discussed reservations, our results demonstrate the gains due to using the high-level features in the full-optimization approach in the large-scale LiDAR SLAM.

scholarly journals SIMPLIFIED MODELLING OF CIRCULAR CFST MEMBERS WITH A CONCENTRATED PLASTICITY APPROACH

2018 ◽  
Author(s):  
Yadong Jiang ◽  
António Silva ◽  
Luís Macedo ◽  
José Miguel Castro ◽  
Ricardo Monteiro ◽  
...  
Keyword(s):  
Numerical Models ◽  
Axial Stress ◽  
Local Buckling ◽  
Experimental Tests ◽  
Elastic Stiffness ◽  
Steel Tube ◽  
Deterioration Model ◽  
Cyclic Behaviour ◽  
Flexural Loading ◽  
High Level

The research reported herein aims to propose an accurate and efficient simplified numerical modelling approach for circular Concrete-Filled Steel Tubes (CFST) under flexural loading. Experimental tests were carried out to characterize the monotonic and cyclic behaviour of CFST members under bending. To assess the seismic performance of a composite structure with CFST members, both Distributed Plasticity (DP) and Concentrated Plasticity (CP) models were considered as potential simplified models for CFST members. The DP model was developed on the basis of a fibre discretization of the composite cross-section and displacement-based beam-column finite element. It was concluded that one could not accurately capture the development of local buckling of the steel tube and the development of multi-axial stress state effects (e.g. concrete confinement). Thus the DP model was found to be unsuitable for modelling of CFST members under cyclic flexural loading. Regarding the CP modelling, the modified Ibarra-Medina-Krawinkler deterioration model (with peak-oriented hysteretic response) was selected to define the behaviour of the plasticity spring associated with the plastic hinging region of the member. In order to accurately simulate the cyclic behaviour of the CFST section within the response of the spring, the deterioration model was calibrated, within a parameter-optimization framework, on the basis of 3D comprehensive numerical models in ABAQUS. The CP model was found to capture well the deterioration in both strength and stiffness of the hysteretic loops of the CFST members, which may be mostly associated with the development of local buckling phenomena. Furthermore, the elastic stiffness, the ultimate strength and the pinching effects of the hysteretic loops were also well simulated. Thus, the proposed CP model, coupled with the advanced calibration framework, was concluded to have a high level of accuracy in terms of simulating the cyclic flexural response of CFST members.

Designing a High Energy Rockfall Kit

2011 ◽  
Vol 82 ◽  
pp. 692-697
Author(s):  
Benoit Boutillier ◽  
Alice Clarke ◽  
Denis Huber
Keyword(s):  
Flexible Structures ◽  
High Energy ◽  
Full Scale ◽  
European Standard ◽  
Full Scale Tests ◽  
Main Component ◽  
High Level ◽  
Flexible Barriers ◽  
The Impact ◽  
Best Parameters

The present study deals with flexible structures which protect human lives and buildings against falling rocks with a high energy, up to 5 000 kJ. These rockfall kits have to match the new European standard ETAG 027 which requires different specific full scale tests. To reach high level of performance, these flexible barriers have to be studied in details. First, each main component such as net sets and dissipating devices, have been studied separately. The Anti Sub Marine net was then chosen for its elasticity and isotropic behavior. The best parameters for braking systems have been defined by different tests. Then, the complete design of the structure was performed according to several criteria such as the position of brakes, the post height, the easy repair, the independence of modules and the final cost (kit with its global installation). Finally, the design which fit the best of our criteria was used to perform full scale tests. After some trials, the so-called HC RP® 3 000 kJ and 5 000 kJ kits matched the ETAG 027 requirements. All kits need lateral anchors to stabilize lateral posts during the impact. All the posts are H-shaped and a central net brake is used.

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