Static structural analysis of S-lay pipe laying with a tensioner model based on the frictional contact

Static structural analysis of a pipe during laying is usually performed by use of finite element analysis tools specialized for this purpose. In this paper, Abaqus/CAE, which is a general purpose FEA software, was used for a static non-linear structural analysis of a pipe during pipe laying. The pipe is modeled as a geometrically non-linear elastic beam supported by a vessel and its stinger in the overbend region and by the seabed in the sagbend region. We propose a new method for tensioner modeling based on friction contacts between the pipe and the tensioner. Contact interactions between the pipe and rollers, as well as between the pipe and the seabed, are also considered. Basic static analysis is enhanced with floating stinger implementation, a non-flat seabed profile and buoyancy tanks application. The model results for various test cases of pipe laying are compared with an industry standard pipe laying modeling tool

Constrained multi-agent ergodic area surveying control based on finite element approximation of the potential field

Heat Equation Driven Area Coverage (HEDAC) is a state-of-the-art multi-agent ergodic motion control guided by a gradient of a potential field. A finite element method is hereby implemented to obtain a solution of Helmholtz partial differential equation, which models the potential field for surveying motion control. This allows us to survey arbitrarily shaped domains and to include obstacles in an elegant and robust manner intrinsic to HEDAC's fundamental idea. For a simple kinematic motion, the obstacles and boundary avoidance constraints are successfully handled by directing the agent motion with the gradient of the potential. However, including additional constraints, such as the minimal clearance dsitance from stationary and moving obstacles and the minimal path curvature radius, requires further alternations of the control algorithm. We introduce a relatively simple yet robust approach for handling these constraints by formulating a straightforward optimization problem based on collision-free escapes route maneuvers. This approach provides a guaranteed collision avoidance mechanism, while being computationally inexpensive as a result of the optimization problem partitioning. The proposed motion control is evaluated in three realistic surveying scenarios simulations, showing the effectiveness of the surveying and the robustness of the control algorithm. Furthermore, potential maneuvering difficulties due to improperly defined surveying scenarios are highlighted and we provide guidelines on how to overpass them. The results are promising and indiacate real-world applicability of proposed constrained multi-agent motion control for autonomous surveying and potentially other HEDAC utilizations.Comment: Revised manuscrip

Lagranževe koherentne strukture strujnog polja Riječkog zaljeva

Some of the major European oil supply routes pass through the Adriatic Sea representing a potential to endanger the whole basin with an oil spill. Particularly high ecological vulnerability of Rijeka Bay is due to its geospatial characteristics as semi-enclosed basin. The simulated onemonth sea surface velocity field of Rijeka Bay was analyzed using Lagrangian coherent structures (LCSs) to assess the diffusion and chaotic advection of passive pollutants (dye). LCSs were extracted by the Finite-Time Lyapunov Exponents (FTLE), hypergraphs, Lagrangian advection alone and advection-diffusion methods. Results show relatively complex nonstationary flow dynamics in Rijeka Bay. Areas of ridges and valleys of FTLE fields spread in north-south and northeast-southwest directions, and they move toward east. Similarly, the hypergraphs method shows areas of attraction and areas of mixing that can be observed in stripes that stretch in directions north-south and northeast-southwest. In addition, the stripes of mesohyperbolic area spread toward east. To assess the potential of passive pollutant spreading, Gaussian pollutant source was simulated at the middle of the bay. The pollutant spreads in the same direction (north-south and northeast-southwest) with lateral diffusion of material proportional to diffusion coefficient.Neke od glavnih europskih dobavnih ruta ulja prolaze kroz Jadransko more što predstavlja potencijalnu opasnost onečišćenje cijelog zaljeva uljnom mrljom. Posebno visoka ekološka ranjivost Riječkog zaljeva proizlazi iz njenih geoprostornih karakteristika poluzatvorenog zaljeva. Simulirano jednomjesečno površinsko strujno polje voda Riječkog zaljeva analizirano je primjenom Lagranževih koherentnih struktura (LKS) sa stanovišta difuzije i kaotične advekcije pasivnog onečišćenja (bojom). LKS su ekstrahirane metodom konačnih vremenskih Lijapunovih eksponenata (FTLE), hipergrafova, Lagranževe čiste advekcije i metodom advekcije-difuzije. Rezultati pokazujurelativno kompleksnu nestacionarnu dinamiku u Riječkom zaljevu. Dijelovi površine mora sa brijegovima i dolovima FTLE polja se protežu u smjeru sjever-jug i sjeveroistok-jugozapad.Također pruge mezohiperboliciteta šire se prema istoku. Da bi ispitali potencijal širenja pasivnog polutanta simuliran je utjecaj Gauss-ovog izvora onečišćenja u sredini zaljeva. Onečišćujuća tvar se širi u istom smjeru (sjever-jug i sjeveroistok-jugozapad) sa lateralnom difuzijom materijala proporcijonalnom koeficijentu difuzije

Introducing languid particle dynamics to a selection of PSO variants

Previous research showed that conditioning a PSO agent's movement based on its personal fitness improvement enhances the standard PSO method. In this article, languid particle dynamics (LPD) technique is used on five adequate and widely used PSO variants. Five unmodified PSO variants were tested against their LPD-implemented counterparts on three search space dimensionalities (10, 20, and 50 dimensions) and 30 test functions of the CEC 2014 benchmark test. In the preliminary phase of the testing four of the five tested PSO variants showed improvement in accuracy. The worst and best-achieving variants from preliminary test went through detailed investigation on 220 and 770 combinations of method parameters, where both variants showed overall gains in accuracy when enhanced with LPD. Finally, the results obtained with best achieving PSO parameters were subject to statistical analysis which showed that the two variants give statistically significant improvements in accuracy for 13-50% of the test functions.Comment: 13 pages, 10 tables, 1 figure. Egyptian Informatics Journal, 201

Multi-UAV trajectory planning for 3D visual inspection of complex structures

This paper presents a new trajectory planning algorithm for 3D autonomous UAV volume coverage and visual inspection. The algorithm is an extension of a state-of-the-art Heat Equation Driven Area Coverage (HEDAC) multi-agent area coverage algorithm for 3D domains. With a given target exploration density field, the algorithm designs a potential field and directs UAVs to the regions of higher potential, i.e., higher values of remaining density. Collisions between the agents and agents with domain boundaries are prevented by implementing the distance field and correcting the agent's directional vector when the distance threshold is reached. A unit cube test case is considered to evaluate this trajectory planning strategy for volume coverage. For visual inspection applications, the algorithm is supplemented with camera direction control. A field containing the nearest distance from any point in the domain to the structure surface is designed. The gradient of this field is calculated to obtain the camera orientation throughout the trajectory. Three different test cases of varying complexities are considered to validate the proposed method for visual inspection. The simplest scenario is a synthetic portal-like structure inspected using three UAVs. The other two inspection scenarios are based on realistic structures where UAVs are commonly utilized: a wind turbine and a bridge. When deployed to a wind turbine inspection, two simulated UAVs traversing smooth spiral trajectories have successfully explored the entire turbine structure while cameras are directed to the curved surfaces of the turbine's blades. In the bridge test case an efficacious visual inspection of a complex structure is demonstrated by employing a single UAV and five UAVs. The proposed methodology is successful, flexible and applicable in real-world UAV inspection tasks.Comment: 14 page

Modeling and optimization of submarine pipe laying

U doktorskoj disertaciji obrađena je tema modeliranja i optimizacije polaganja podmorskih cjevovoda. Razmatran je model polaganja temeljen na nelinearnom elastičnom modelu grede uz elastične kontaktne interakcije s krutim strukturama valjkastih oslonaca i morskog dna. Osnovni model polaganja podmorskih cjevovoda te proširenja modela implementirani su i rješavani u softveru Abaqus za različite primjere polaganja cjevovoda. Formuliran je optimizacijski problem određivanja parametara polaganja, za koji je razvijena hibridna specijalizirana optimizacijska metoda temeljena na metodi optimizacije rojem čestica. Razvijeni optimizacijski postupak je testiran i analiziran na više različitih slučajeva polaganja podmorskih cjevovoda.The doctoral thesis deals with the topic of modeling and optimization of the submarine pipe laying. Considered laying model is based on a nonlinear elastic beam model with elastic contact interactions with rigid structures of roller supports and the seabed. The basic model of the submarine pipe laying and its extensions are implemented and solved in the Abaqus software for various pipe laying cases. The optimization problem is formulated to determine the parameters of pipe laying, for which a specialized hybrid optimization method is developed based on a particle swarm optimization method. Developed optimization method was tested and analyzed in several different cases of submarine pipe laying

Modeling and optimization of submarine pipe laying

U doktorskoj disertaciji obrađena je tema modeliranja i optimizacije polaganja podmorskih cjevovoda. Razmatran je model polaganja temeljen na nelinearnom elastičnom modelu grede uz elastične kontaktne interakcije s krutim strukturama valjkastih oslonaca i morskog dna. Osnovni model polaganja podmorskih cjevovoda te proširenja modela implementirani su i rješavani u softveru Abaqus za različite primjere polaganja cjevovoda. Formuliran je optimizacijski problem određivanja parametara polaganja, za koji je razvijena hibridna specijalizirana optimizacijska metoda temeljena na metodi optimizacije rojem čestica. Razvijeni optimizacijski postupak je testiran i analiziran na više različitih slučajeva polaganja podmorskih cjevovoda.The doctoral thesis deals with the topic of modeling and optimization of the submarine pipe laying. Considered laying model is based on a nonlinear elastic beam model with elastic contact interactions with rigid structures of roller supports and the seabed. The basic model of the submarine pipe laying and its extensions are implemented and solved in the Abaqus software for various pipe laying cases. The optimization problem is formulated to determine the parameters of pipe laying, for which a specialized hybrid optimization method is developed based on a particle swarm optimization method. Developed optimization method was tested and analyzed in several different cases of submarine pipe laying