Determination of nonlinear forces of the second order arising from the interaction of waves and certain types of ship’s motions

В статье рассматривается определение нелинейных сил второго порядка, обусловленных взаимодействием набегающего, дифрагированного волнения и волнения, обусловленного различными видами колебаний на основании применения трехмерной потенциальной теории. Для их определения необходимо вычисление потенциалов второго порядка малости. Представленное решение в отечественной практике является новым. Решение задачи осуществляется на основании методов малого параметра и интегральных уравнений с учетом нелинейного граничного условия на свободной поверхностью жидкости. В работе расчет интегралов по свободной поверхности проводится напрямую за счет их сходимости на бесконечном удалении от судна. Нелинейные силы и моменты определяются в работе с использованием различных функций Грина: для бесконечно-глубокой жидкости и жидкости ограниченной глубины, когда . Полученные результаты практически полностью согласуются между собой. Приводятся результаты расчетов нелинейных сил и моментов для разных судов. Расчеты представлены в сравнении с расчетами по двумерной теории, выполненными также для случая бесконечно глубокой жидкости и жидкости ограниченной глубины при больших значениях отношения глубины к осадке H/T. Показано хорошее согласование результатов между собой в большинстве случаев. Показана возможность расчета нелинейных сил, возникающих при взаимодействии волнения и отдельных видов качки на произвольных курсовых углах. The article considers the definition of nonlinear second-order forces caused by the interaction of incoming, diffracted waves and waves caused by various types of motions based on the application of three-dimensional potential theory. To determine them, it is necessary to calculate the potentials of the second order of smallness. The presented solution is new in domestic practice. The problem is solved on the basis of small parameter methods and integral equations taking into account the nonlinear boundary condition on the free surface of the liquid. The paper shows the possibility of calculating the integrals over the free surface directly due to their convergence at an infinite distance from the ship. Nonlinear forces and moments are determined in the work using various Green's functions: for an infinitely deep fluid and a fluid of limited depth when H → ∞. The results obtained are in almost complete agreement with each other. The results of calculations of nonlinear forces and moments for different ships are presented. The calculations are presented in comparison with the calculations according to the two-dimensional theory, performed also for the case of an infinitely deep liquid and a liquid of limited depth at large values of ratio H / T. A good agreement of the results is shown among themselves in most cases. The possibility of calculating nonlinear forces arising from the interaction of waves and certain types of motions at arbitrary course angles is shown.

Remarks on the Boundary Conditions for a Serre-Type Model Extended to Intermediate-Waters

Numerical models are useful tools for studying complex wave–wave and wave–current interactions in coastal areas. They are also very useful for assessing the potential risks of flooding, hydrodynamic actions on coastal protection structures, bathymetric changes along the coast, and scour phenomena on structures’ foundations. In the coastal zone, there are shallow-water conditions where several nonlinear processes occur. These processes change the flow patterns and interact with the moving bottom. Only fully nonlinear models with the addition of dispersive terms have the potential to reproduce all phenomena with sufficient accuracy. The Boussinesq and Serre models have such characteristics. However, both standard versions of these models are weakly dispersive, being restricted to shallow-water conditions. The need to extend them to deeper waters has given rise to several works that, essentially, add more or fewer terms of dispersive origin. This approach is followed here, giving rise to a set of extended Serre equations up to kh ≈ π. Based on the wavemaker theory, it is also shown that for kh > π/10, the input boundary condition obtained for shallow-waters within the Airy wave theory for 2D waves is not valid. A better estimate for the input wave that satisfies a desired value of kh can be obtained considering a geometrical modification of the conventional shape of the classic piston wavemaker by a limited depth θh, with θ≤ 1.0.

Π-GISANS: probing lateral structures with a fan shaped beam

We have performed grazing incidence neutron small angle scattering using a fan shaped incident beam focused along one dimension. This allows significantly reduced counting times for measurements of lateral correlations parallel to an interface or in a thin film where limited depth resolution is required. We resolve the structure factor of iron inclusions in aluminium oxide and show that the ordering of silica particles deposited on a silicon substrate depends on their size. We report hexagonal packing for 50 nm but not for 200 nm silica spheres deposited by a modified Langmuir-Schaefer method on a silicon substrate. For the 200 nm particles we extract the particles shape from the form factor. Moreover, we report dense packing of the particles spread on a free water surface. We name this method π-GISANS to highlight that it differs from GISANS as it gives lateral information while averaging the in-depth structure.

Introducing k-lingo: a k-depth Bounded Version of ASP System Clingo

Depth-Bounded Boolean Logics (DBBL for short) are well-understood frameworks to model rational agents equipped with limited deductive capabilities. These Logics use a parameter k>=0 to limit the amount of virtual information, i.e., the information that the agent may temporarily assume throughout the deductive process. This restriction brings several advantageous properties over classical Propositional Logic, including polynomial decision procedures for deducibility and refutability. Inspired by DBBL, we propose a limited-depth version of the popular ASP system \clingo, tentatively dubbed k-lingo after the bound k on virtual information. We illustrate the connection between DBBL and ASP through examples involving both proof-theoretical and implementative aspects. The paper concludes with some comments on future work, which include a computational complexity characterization of the system, applications to multi-agent systems and feasible approximations of probability functions.

Can Liquid Lenses Increase Depth of Field in Head Mounted Video See-Through Devices?

Wearable Video See-Through (VST) devices for Augmented Reality (AR) and for obtaining a Magnified View are taking hold in the medical and surgical fields. However, these devices are not yet usable in daily clinical practice, due to focusing problems and a limited depth of field. This study investigates the use of liquid-lens optics to create an autofocus system for wearable VST visors. The autofocus system is based on a Time of Flight (TOF) distance sensor and an active autofocus control system. The integrated autofocus system in the wearable VST viewers showed good potential in terms of providing rapid focus at various distances and a magnified view.

The Determination of nonlinear second-order diffraction forces acting on a ship based on three-dimensional theory

В статье рассматривается определение нелинейных дифракционных сил второго порядка, на основании применения трехмерной потенциальной теории. Для их определения необходимо вычисление потенциалов второго порядка малости. Представленное решение в отечественной практике является новым. Решение задачи осуществляется на основании методов малого параметра и интегральных уравнений с учетом нелинейного граничного условия на свободной поверхностью жидкости. В работе показана возможность расчета интегралов по свободной поверхности напрямую за счет их сходимости на бесконечном удалении от судна. Нелинейные дифракционные силы и моменты определяются в работе с использованием различных функций Грина: для бесконечно-глубокой жидкости и жидкости ограниченной глубины, когда H→∞. Полученные результаты практически полностью согласуются между собой. Приводятся результаты расчетов дифракционных сил и моментов для четырех разных судов. Расчеты представлены в сравнении с расчетами по двумерной теории, выполненными также для случая бесконечно глубокой жидкости и жидкости ограниченной глубины при больших значениях отношения глубины к осадке H/T. Показано хорошее согласование результатов между собой. Показана возможность расчета нелинейных дифракционных сил на произвольных курсовых углах. The article discusses the definition of nonlinear diffraction forces of the second order, based on the application of three-dimensional potential theory. To determine them, it is necessary to calculate the potentials of the second order of smallness. The presented solution is new in domestic practice. The problem is solved on the basis of small parameter methods and integral equations taking into account the nonlinear boundary condition on the free surface of the liquid. The paper shows the possibility of calculating the integrals over the free surface directly due to their convergence at an infinite distance from the ship. Nonlinear diffraction forces and moments are determined in the work using various Green's functions: for an infinitely deep fluid and a fluid of limited depth when H → ∞. The results obtained are in almost complete agreement with each other. The results of calculations of diffraction forces and moments for four different ships are presented. The calculations are presented in comparison with the calculations according to the two-dimensional theory, performed also for the case of an infinitely deep liquid and a liquid of limited depth at large values of ratio H / T. Good agreement of the results with each other is shown. The possibility of calculating nonlinear diffraction forces at arbitrary heading angles is shown.

Semantic Web and Knowledge Graphs for Industry 4.0

In recent years, due to technological advancements, the concept of Industry 4.0 (I4.0) is gaining popularity, while presenting several technical challenges being tackled by both the industrial and academic research communities. Semantic Web including Knowledge Graphs is a promising technology that can play a significant role in realizing I4.0 implementations. This paper surveys the use of the Semantic Web and Knowledge Graphs for I4.0 from different perspectives such as managing information related to equipment maintenance, resource optimization, and the provision of on-time and on-demand production and services. Moreover, to solve the challenges of limited depth and expressiveness in the current ontologies, we have proposed an enhanced reference generalized ontological model (RGOM) based on Reference Architecture Model for I4.0 (RAMI 4.0). RGOM can facilitate a range of I4.0 concepts including improved asset monitoring, production enhancement, reconfiguration of resources, process optimizations, product orders and deliveries, and the life cycle of products. Our proposed RGOM can be used to generate a knowledge graph capable of providing answers in response to any real-time query.

Methodology for optimising the hull shape of a vessel with restricted draft

Increasing transport volumes on Europe's inland waterways is a major reason for improving the quality and reliability of internationally important waterways. Continued navigation restrictions due to restricted draft (draught) led to the search for new design solutions. Such solutions enable navigation even under critical navigation conditions. Restricted draft is one of the most important limitations that hinder navigation, especially in the summer. The main objective of the construction of an inland vessel is to obtain a shape that will achieve optimum performance with as little resistance as possible. A shape that will be able to navigate at a limited depth. Presently, there is no clearly defined methodology as a procedure for optimising the hull. When solving theoretical problems of shipbuilding character and ship calculations, it is necessary to consider the basic theory of the ship with special regard to the latest methodological procedures of related scientific disciplines. This paper presents a methodology that considers all the basic aspects of optimisation tasks in ship design and construction.