Hydrostatic Force on Submerged Gate: Computer Based Program Analysis

Resultant force caused by the pressure loading of a liquid acting on submerged surfaces are known as Hydraulic force. Calculating the hydrostatic force is necessary to design a building that can resist forces due to its fluid. There are 2 conditions of the submerged surface, those are fully submerged and partly submerged. In this study, three scenarios will be used for developing computer-based program for calculating hydrostatic force and will be compared to manual calculation. The numerical analysis will be conducted using GNU Octave, version 6.2.0. The scenarios are fully submerged plane with 90°, fully submerged plane with inclination angle and partially submerged plane with inclination angle. Overall, from scenario one to three, the percentage differences are 0%, with the mean percentage difference of the program is 0%. Hence, it satisfies all the elements that need to be checked based on the hydrostatic force calculation in Fluid Mechanics.

Influence of Controller’s Parameters on Static Bifurcation of Magnetic-Liquid Double Suspension Bearing

Magnetic-Liquid Double Suspension Bearing (MLDSB) is composed of an electromagnetic supporting and a hydrostatic supporting system. Due to greater supporting capacity and static stiffness, it is appropriate for occasions of middle speed, overloading, and frequent starting. Because of the complicated structure of the supporting system, the probability and degree of static bifurcation of MLDSB can be increased by the coupling of hydrostatic force and electromagnetism force, and then the supporting capacity and operation stability are reduced. As the key part of MLDSB, the controller makes an important impact on its supporting capacity, operation stability, and reliability. Firstly, the mathematical model of MLDSB is established in the paper. Secondly, the static bifurcation point of MLDSB is determined, and the influence of parameters of the controller on singular point characteristics is analyzed. Finally, the influence of parameters of the controller on phase trajectories and basin of attraction is analyzed. The result showed that the pitchfork bifurcation will occur as proportional feedback coefficient Kp increases, and the static bifurcation point is Kp = −60.55. When Kp < −60.55, the supporting system only has one stable node (0, 0). When Kp > −60.55, the supporting system has one unstable saddle (0, 0) and two stable non-null focuses or nodes. The shape of the basin of attraction changed greatly as Kp increases from −60.55 to 30, while the outline of the basin of attraction is basically fixed as Kp increases from 30 to 80. Differential feedback coefficient Kd has no effect on the static bifurcation of MLDSB. The rotor phase trajectory obtained from theoretical simulation and experimental tests are basically consistent, and the error is due to the leakage and damping effect of the hydrostatic system within the allowable range of the engineering. The research in the paper can provide theoretical reference for static bifurcation analysis of MLDSB.

Heave Compensation Dynamics for Offshore Drilling Operation

In this study, dynamic response analysis of a heave compensation system for offshore drilling operations was conducted based on multibody dynamics. The efficiency of the heave compensation system was computed using simulation techniques and virtually confirmed before being applied to drilling operations. The heave compensation system was installed on a semi-submersible and comprises several interconnected bodies with various joints. Therefore, a dynamics kernel based on multibody dynamics was developed to perform dynamic response analysis. The recursive Newton–Euler formulation was adopted to construct the equations of motion for the multibody system. Functions of the developed dynamics kernel were verified by comparing them with those from other studies. Hydrostatic force, linearized hydrodynamic force, and pneumatic and hydraulic control forces were considered the external forces acting on the platform of the semi-submersible rig and the heave compensation system. The dynamic simulation was performed for the heave compensation system of the semi-submersible rig for drilling operations up to 3600 m water depth. From the results of the simulation, the efficiency of the heave compensation system was evaluated to be approximately 96.7%.

Numerical simulation of underwater cable laying with account of non-uniform hydrostatic force at Arctic basin condition

Статья посвящена моделированию динамического равновесия установившегося движения протяженной кабельной линии с учетом действия гидродинамических сил сопротивления и неоднородной гидростатической силы. Учитывая различные условия и глубины укладки, а также требования функционального назначения и защиты от враждебных факторов морского дна, необходимо рассмотреть широкий диапазон кабелей с различными механическими характеристиками: трехжильный кабель с одиночным бронированием 2XS2YRAA, одножильный кабель с одиночным бронированием ZS-YJQ41 и одножильный кабель с двойным бронированием – аналог GASLMLTV. Целью работы является развитие цифровой технологии по моделированию укладки подводных коммуникационных и силовых кабелей, позволяющей учитывать многочисленные физико-механические явления, имеющие место при проведении реальных морских работ. Для достижения поставленной цели работы используется программная среда Matlab Math Works с использованием разработанного комплекса программ для инженерной оценки формы и натяжения провисающего участка кабеля. Научная новизна состоит в апробации модели подводной укладки кабеля, учитывающей действие неоднородной гидростатической силы. Результаты моделирования представлены в виде формы и натяжения провисающей части кабеля при различных углах схода кабеля с движущегося судна при различных механических параметрах кабелей. Практическое значение работы состоит в повышении эффективности освоения перспективных месторождений, путем определения характеристик укладки кабеля в условиях Арктического бассейна: газовое месторождение Лудловское, газоконденсатное месторождение Ленинградское, нефтяное месторождение Медынское-море. This article studies the numerical simulation of underwater steady motion of the cable line with account of hydrodynamic water resistance forces and non-uniform hydrostatic force. It is necessary to consider distinctive types of cables due to various depths, laying conditions, functional requirements and protection requirements against adverse factors of seabed. Three-core single armoured cable 2XS2YRAA, one-core single armoured cable ZS-YJQ41 and one-core double armoured cable – analogue GASLMLTV are considered in this article. The aim of the research consists in digital technology development for underwater cable laying modeling, which allows taking into account numerous physical and mechanical features. These features occur during real marine operations for communication and power cables. Programming and numeric computing platform Matlab Math Works with developed software package is chosen as the research method. Simulation results are presented in dimensionless form for cable shape and tension for engineering purposes. The novelty of the work consists in approbation of underwater cable laying analytical model considering non-uniform hydrostatic force. Simulation results are presented for underwater cable laying during reeling from spool mounted on the vessel, moving with constant speed for distinctive types of cables. The influence of the cable run-off angle on the investigated characteristics was also considered. The practical value of the research consists in increasing of efficiency of exploration of oil, gas and condensate fields by determining underwater cable laying characteristics for perspective fields. At the end of the paper, the results of estimation of the shape and tension of the cable being laid undersea were presented for several fields at Arctic basin condition: gas field Ludlovskoe, condensate field Leningradskoe and oil field Medinskoe sea.

A Note on The Design of Seawall for Tsunami Disaster Mitigation

Many coastal structures or structures in coastal areas were destroyed by a tsunami attack. Such destructions were due primarily to the fact that such structures were not designed to withstand a tsunami. Those which were designed to withstand tsunami force may also have been destroyed due to some damaging factors which were not included in the design. The damage of the coastal structures is one of the important factors that have caused casualties. Especially, when the destroyed structures were originally aimed to mitigate the area against tsunami, they may cause higher fatalities. Examples of such structures are sea walls in many parts of Japan which were destroyed by the 2011 tsunami. This paper discusses the important factors relevant to the damage of seawall as tsunami mitigation structure such as impact force due to tsunami front, hydrostatic force, and hydrodynamic force, debris force and scour due tsunami. The study was carried out based on literature about the damages of seawall as tsunami protection structures and laboratory experiment reports. The destructions to the structures were divided into three classifications namely instantaneous direct destruction due to impact and drag forces, slowly direct destruction due to drag force, and slowly indirect destruction due to scour. Finally, important aspects to be considered in the design of seawall as tsunamis protection were proposed.

Double Closed-Loop Compound Control Strategy for Magnetic Liquid Double Suspension Bearing

As a new type of suspension bearing, the magnetic liquid double suspension bearing (MLDSB) is mainly supported by electromagnetic suspension and supplemented by hydrostatic support. At present, the MLDSB adopts the regulation strategy of “electromagnetic-position feedback closed-loop, hydrostatic constant-flow supply” (referred to as CFC mode). In the equilibrium position, the external load is carried by the electromagnetic system, and the hydrostatic system produces no supporting force. Thus, the carrying capacity and supporting stiffness of the MLDSB can be reduced. To solve this problem, the double closed-loop control strategy of “electromagnetic system-force feedback inner loop and hydrostatic-position feedback outer loop” (referred to as DCL mode) was proposed to improve the bearing performance and operation stability of the MLDSB. First, the mathematical models of CFC mode and DCL mode of the single DOF supporting system were established. Second, the real-time variation laws of rotor displacement, flow/hydrostatic force, and regulating current/electromagnetic force in the two control modes were plotted, compared, and analyzed. Finally, the influence law of initial current, flow, and controller parameters on the dynamic and static characteristic index were analyzed in detail. The results show that compared with that in CFC mode, the displacement in DCL mode is smaller, and the adjustment time is shorter. The hydrostatic force is equal to the electromagnetic force in DCL mode when the rotor returns to the balance position. Moreover, the system in DCL mode has better robustness, and the initial flow has a more obvious influence on the dynamic and static characteristic indexes. This study provides a theoretical basis for stable suspension control and the safe and reliable operation of the MLDSB.

Comparison and Validation of Hydrodynamic Theories for Wave Energy Converter Modelling

Dynamic Wave Energy Converter (WEC) models utilize a wide variety of fundamental hydrodynamic theories. When incorporating novel hydrodynamic theories into numerical models, there are distinct impacts on WEC rigid body motions, cable dynamics, and final power production. This paper focuses on developing an understanding of the influence several refined hydrodynamic theories have on WEC dynamics, including weakly nonlinear Froude-Krylov and hydrostatic forces, body-to-body interactions, and dynamic cable modelling. All theories have evolved from simpler approaches and are of importance to a wide array of WEC archetypes. This study quantifies the impact these theories have on modelling accuracy through a WEC case study. Theoretical differences are first explored in a regular sea state. Subsequently, numerical validation efforts are performed against field data following wave reconstruction techniques. Comparisons of significance are WEC motion and cable tension. It is shown that weakly nonlinear Froude-Krylov and hydrostatic force calculations and dynamic cable modelling both significantly improve simulated WEC dynamics. However, body-to-body interactions are not found to impact simulated WEC dynamics.

TINJAUAN GAYA TSUNAMI PADA JEMBATAN KRUENG RABA

Aceh Province is located in one of the earth's fault lines in Indonesia, which is an area prone to earthquakes and the potential for a tsunami disaster. Therefore, any planning of structures located on the coast must consider the potential for a tsunami to obtain a strong structure to withstand the forces affected by the tsunami. During the 2004 tsunami, many bridges were carried away by the tsunami. Both bridges made of concrete, as well as steel frame bridges, such as the Krueng Raba steel frame bridge, Lhoknga, the Krueng No bridge, the Meunasah Kulam bridge, and several other bridges. This study aims to analyze and calculate the force and load effects of the tsunami on the structure of one of these bridges, namely the Krueng Raba steel frame bridge, Lhoknga. The force and load of the tsunami effect (Ts) will be analyzed by adopting the Guidelines for Design of Structures for Vertical Evacuation from Tsunamis, 2012, namely: (1) hydrostatic force; (2) buoyant forces; (3) hydrodynamic forces; (4) impulsive forces; (5) debris impact forces; (6) debris damming forces; (7) lift force; and (8) additional gravity load from water retained on the bridge floor. From the results of this study, it is shown that each of the tsunami forces acting on the crew-raba Lhoknga bridge at the minimum tsunami height variable, 11 meters, which is the initial height of the tsunami touching the bridge's superstructure are: 94.866 KN hydrodynamic force; 142,299 KN thrust; 133,810 KN debris impact force; 14,244 KN debris dam force, and 34,018 KN lift force. Meanwhile, the maximum tsunami height variable, 25 meters, is 24634.934 KN hydrodynamic force; 36952,400 KN thrust; 720,591 KN collision force; 3698,939 KN debris blocking force; and 986,519 KN lift styles. The results of the analysis using computational methods, by inputting the magnitude of the tsunami forces to the bridge model, it can be seen that the ability of the Krueng Raba, Lhoknga steel frame bridge to withstand the forces and loads caused by the tsunami only up to a height of 14 meters.

Traversable wormhole modelling with exponential and hyperbolic shape functions in F(R,T) framework

The concept of traversable wormhole, a hypothetical tunnel-like structure is initially proposed by Morris and Thorne (Am. J. Phys. 56, 395 (1988)) by using Einstein’s general relativity theory. Harko et al. (Phys. Rev. D 84, 024020 (2011)) defined [Formula: see text] gravity as an extended gravitational theory having terms [Formula: see text] and [Formula: see text] as Ricci scalar and trace of energy momentum respectively. In this article, we explore wormhole models for the framework of [Formula: see text] gravity by using two different shape functions. The first shape function is [Formula: see text], [Formula: see text] (proposed by Mishra and Sharma, arXiv:2003.00298v1 , 2020) and second is a hyperbolic shape function which is of the form [Formula: see text]. Geometrical behavior of wormholes are discussed in anisotropic scenario by using equation of state [Formula: see text]. The stability of models are analyzed by using equilibrium condition and determining gravitational force, anisotropic force, hydrostatic force and force due to modified gravity. For the validation of null energy condition and weak energy condition, significant role of shape function is illustrated for the presence of nonexotic matter.

Genetic Optimization of Shape and Control of Non-Linear Wave Energy Converters

This paper presents an optimization approach to design ax-isymmetric wave energy converters (WECs) based on a nonlinear hydrodynamic model. This paper shows optimal nonlinear shapes of buoy can be generated by combing basic shapes in an optimal sense. The time domain non-linear Froude-Krylov force can be computed for a complex buoy shape, by adopting analytical formulas of its basic shape components. The time domain Forude-Krylov force is decomposed into its dynamic and static components, and then contribute to the calculation of the excitation force and the hydrostatic force. A non-linear control is assumed in the form of the combination of linear and nonlinear damping terms. A variable size genetic algorithm (GA) optimization tool is developed to search for the optimal buoy shape along with the optimal control coefficients simultaneously. Chromosome of the GA tool is designed to improve computational efficiency and to leverage variable size genes to search for the optimal non-linear buoy shape. Different criteria of wave energy conversion can be implemented by the variable size GA tool. Simulation results presented in this paper show that it is possible to find non-linear buoy shapes and non-linear controllers that take advantage of non-linear hydrodynamics to improve energy harvesting efficiency with out adding reactive terms to the system.