Drift Forces Research Articles

A Systematic Pipelaying Control Method Based on the Sliding Matrix for Dynamically Positioned Surface Vessels

A pipelaying control method is presented in this paper which includes path planning, path guidance, and path tracking controller for dynamically positioned (DP) surface vessels based on the characteristics of the predefined path in marine pipelaying operation. The pipelaying control method depends on path coding, path selection logic system, and a sliding matrix. The sliding matrix contains a vessel local path and its specified control requirements, which can be updated by sliding down the waypoint table line by line as the vessel is traveling from one path to the next. A line of sight (LOS) algorithm is developed to calculate the desired vessel position and heading on a circular arc path. The motion controller, which can simultaneously control the vessel speed at the directions of surge and sway, is designed by decomposing the desired inertial resulting velocity into the desired body velocity components. A DP simulator for pipelaying operation is developed, and in order to verify the proposed method, a pipelaying simulation is carried out. The simulation results show that the proposed method enables the vessel to move along the desired path while maintaining a set crab angle, a specified speed, and a turning radius. The pipeline can be laid onto the specified waypoints even when the vessel is subjected to drift forces caused by ocean currents, wind, and waves.

Seismic Response of Y-Shape Multi-Storey Building with Optimum Location of Shear Walls

Shear walls have extremely high in-plane strength and stiffness and also can counter heavy lateral loads making them quite advantageous in high-rise buildings. It is suggested to incorporate them in structures built in the places where there are chances of large intensity earthquakes or high winds. Positioning of the shear wall plays a very critical task in an asymmetric and irregular building subjected to earthquake forces. In our study, the main aim is to locate the advantageous position of the shear wall in Y-shaped asymmetric and irregular G+14 building in zone IV. The study is done by using a software package, CSI ETABS ver. 18.0.2. We have carried out Response Spectrum Analysis and Time History Analysis for this study. In this study, fourteen test models with unique location of shear wall are considered and parameters such as Time Period, Storey Displacement, Static Eccentricity, Storey Drift, Joint Displacement, Base Shear, and Base Force, are compared with the bare model. Thus, the best location of shear wall is suggested based on models having least static eccentricity, minimum displacement, Minimum drift, Minimum time period, Minimum joint displacement and Maximum base shear.

Numerical Researches of Rectangular Barge in Variable Bathymetry Based on Boussinesq‐Step Method

Wave responses of the rectangular barge in variable bathymetry are investigated by combining the Boussinesq‐type equations and the step method. The highly accurate Boussinesq‐type equations in terms of velocity potential are adopted for simulating the evolution of waves along the inclined beach. Hydrodynamic coefficients of a rectangular barge floating on the inclined bottom are calculated by the step method in the frequency domain. Based on the impulse response function method, the motions of the barge can be predicted in the time domain. The Haskind relation is used to reform the wave exciting forces, and the mean offset in the sway motion is also given based on the mean drift force. The wave responses of the barge at different locations along the inclined beach are measured in the experiments. Compared with experimental results, the solutions of the Boussinesq‐step method present an overall good agreement.

Research on a novel robot mooring system based on dual-parallel elastic under-actuated mechanisms

Parallel mechanisms have the advantages of a high carrying capacity, large stiffness and compact structure. To develop the theory and key technology of robot mooring systems, in this paper, focusing on a 266,000 m3 LNG ship model with a scale of 1:60, a novel robot mooring system based on dual-parallel elastic under-actuated mechanisms is proposed. The configuration, structure parameters and workspace of the system are determined by experiments and simulations of the ship model with conventional mooring arrangements. Based on the influence coefficient method, the global stiffness model of a parallel-robot mooring system (PRMS) is presented, yielding a stiffness matrix in tensor form. The boundary conditions for the PRMS-moored ship in an experimental basin are introduced and a dynamic equation is given considering the two work modes of the PRMS. Numerical simulations and experiments are carried out to obtain the motions of the PRMS-moored ship when encountering unidirectional irregular waves, and the results indicate that the system can reduce the frequency drift motions of ships in surge, sway and yaw induced by the second order wave drift force.

Excitonic transport driven by repulsive dipolar interaction in a van der Waals heterostructure.

Dipolar bosonic gases are currently the focus of intensive research due to their interesting many-body physics in the quantum regime. Their experimental embodiments range from Rydberg atoms to GaAs double quantum wells and van der Waals heterostructures built from transition metal dichalcogenides. Although quantum gases are very dilute, mutual interactions between particles could lead to exotic many-body phenomena such as Bose-Einstein condensation and high-temperature superfluidity. Here, we report the effect of repulsive dipolar interactions on the dynamics of interlayer excitons in the dilute regime. By using spatial and time-resolved photoluminescence imaging, we observe the dynamics of exciton transport, enabling a direct estimation of the exciton mobility. The presence of interactions significantly modifies the diffusive transport of excitons, effectively acting as a source of drift force and enhancing the diffusion coefficient by one order of magnitude. The repulsive dipolar interactions combined with the electrical control of interlayer excitons opens up appealing new perspectives for excitonic devices.

A unified ship manoeuvring model with a nonlinear model predictive controller for path following in regular waves

In this paper, a nonlinear model predictive controller for path following of a surface vessel in the presence of regular waves is studied. A model predictive controller is developed for a 3DoF unified manoeuvring model of the KVLCC2 crude oil tanker. The surge, sway and yaw motions of the ship are influenced by the second order wave drift forces and moments calculated based on a potential flow solver. Propeller thrust, rudder and hydrodynamic forces and moments are computed using empirical formulas available in the literature. For path following purposes, waypoints are assigned in head and beam wave conditions and a line of sight algorithm computes the reference heading angle. The rudder control is exerted by a nonlinear model predictive controller and the effectiveness of the controller is studied. The performance of the nonlinear model predictive controller is compared against that of a basic PID controller.

A modified method for the singular spatial derivative of velocity potential at corners of 2D bodies and its application to second-order radiation problems

For the pressure integration over a body surface, the near-field method is convenient and versatile to calculate all of the wave force components but it is believed to be inferior to the far-field method in precision when calculating the second-order forces. Especially for moving structures with sharp corners, the velocity is singular at corners, which makes higher-order problems difficult. In this paper, analysis on a 2D structural corner is carried out by means of an analytic local solution. The spatial derivative of the velocity potential is modified and calculated to fine accuracy. Furthermore, singular integrations on the body surface are treated elaborately. The components of the second-order forces using the near-field method are presented to show the effect of a singularity. The results are compared with those of the conservative higher-order boundary element method and illustrate high precision. Moreover, the mean drift force obtained from the near-field method is also consistent with that obtained from the middle-field method.

Development and Calibration of a 3D Micromodel for Evaluation of Masonry Infilled RC Frame Structural Vulnerability to Earthquakes

Within the scope of literature, the influence of openings within the infill walls that are bounded by a reinforced concrete frame and excited by seismic drift forces in both in- and out-of-plane direction is still uncharted. Therefore, a 3D micromodel was developed and calibrated thereafter, to gain more insight in the topic. The micromodels were calibrated against their equivalent physical test specimens of in-plane, out-of-plane drift driven tests on frames with and without infill walls and openings, as well as out-of-plane bend test of masonry walls. Micromodels were rectified based on their behavior and damage states. As a result of the calibration process, it was found that micromodels were sensitive and insensitive to various parameters, regarding the model’s behavior and computational stability. It was found that, even within the same material model, some parameters had more effects when attributed to concrete rather than on masonry. Generally, the in-plane behavior of infilled frames was found to be largely governed by the interface material model. The out-of-plane masonry wall simulations were governed by the tensile strength of both the interface and masonry material model. Yet, the out-of-plane drift driven test was governed by the concrete material properties.

Analytical solution based on BEM to oblique waves scattering by thin arc-shaped permeable barrier applied for array of aquaculture cages

In this paper, linear oblique wave incident to a thin arc-shaped permeable barrier and an array of permeable circular cylinders was studied analytically. Two unique research objectives of this work include, considering the thickness for permeable material and the wavefield inside surrounded region by the permeable structure. The conventional boundary element method (BEM) is used to solve the governing equations of the problem. The mathematical relation between Bessel functions leads to representing the BEM-related integrals in the Fourier modes of Hankel function. This approach is useful as the singular integrals are accounted indirectly. Two basic geometries made by the permeable material are studied, including an arc-shaped and a circular geometry. The first geometry can represent a wave-breaking barrier in shallow water, while the latter can represent a floating fish farm in deep water. For the floating fish farm, the study is extended to the interaction between an array of cages. To quantify the amount of wave energy passed through the object, the Energy Transmission Index or ETI concept is introduced. ETI can be used as an indicator for permeable barriers performance.The results indicate that ETI is mostly a function of permeability rather than the wavenumber. In addition, the imaginary part of the permeability parameter plays an essential role in the problem of wave incident to permeable barrier, and it is necessary to be determined with enough accuracy. Furthermore, the shear force and bending moment on the base of the barrier and drift force and heeling moment on circular cylinders are studied. The results show, the drift force decreases as permeability and wavenumber increase. The results of this research are useful in the design of rigid circular offshore aquaculture fish cages and coastal barriers.

Hydrodynamics of a free-floating cylinder in front of an orthogonal vertical wall

ABSTRACT The paper deals with the analytical evaluation of the linearized exciting wave forces; hydrodynamic coefficients and wave drift forces acting on a free-floating vertical cylindrical body placed in front of a reflecting orthogonal vertical wall. Linear potential theory is assumed, and the associated diffraction and radiation problems are solved in the frequency domain. The hydrodynamic interactions among the body and the adjacent breakwater are taken into account by applying a theoretical model based on the method of images, considering the breakwater as a fully reflecting, bottom mounted and water surface piercing wall of infinite length. The theoretical approach is supplemented by a numerical model considering the orthogonal breakwater as a barrier of finite length. The results of both formulations are compared with the ones corresponding to an isolated cylindrical body demonstrating the amplified scattered and reflected waves at specific frequency ranges originating from the presence of the orthogonal breakwater.

A unified seakeeping and manoeuvring model with a PID controller for path following of a KVLCC2 tanker in regular waves

Heading control of ships in calm water has been investigated by several authors using different control techniques. However, the study on heading control of ships in actual sea conditions is very limited. This paper attempts to investigate the heading control in regular waves using a PID controller. A 6 DoF unified seakeeping and manoeuvring numerical model is integrated with a PID controller. A crude oil carrier (KVLCC2) prototype is used in the numerical study. The second order wave mean drift forces are calculated based on Salvesen’s method and affect the horizontal motions. The wave exciting forces/moments and the restoring forces in the vertical planes are calculated for the exact wetted surface area. Empirical relations available in the existing literature are used to compute the propeller thrust, control forces/moments and hydrodynamic forces. PID controller gains Kp,Kd and Ki changes for different sea states depending on the external wave force. Hence these gains are pre-calculated for different sea states by trial and error. The performance of the controller under the wave action is then studied for path-following application.

Mitigation of Earthquake Responses Using SMA Supplemented Base-Isolation Devices for Benchmark Building

The efficiency of traditional isolation bearings is doubted for near-field earthquakes because these bearings undergo large displacement. A comparative study of different base isolation systems of base-isolated benchmark building is carried out in the present study. The study is based on assumption that buildings are bi-directionally acted upon by near-field earthquakes for assessing their relative performance in seismic control of the benchmark building. The time history variations of important response parameters and evaluation criteria of the benchmark building has been studied for assessing the effectiveness of the isolation systems. The Shape Memory Alloy (SMA) is utilized with elastomeric bearings and friction bearings to study the effectiveness of SMA wires with different isolators. The benchmark building is modelled as a discrete linear elastic shear structure having three degrees of- freedom at each floor level. Time domain dynamic analysis of this building has been carried out with the help of constant average acceleration Newmark’s method and equilibrium of non-linear forces has been taken care by fourth order Runge-Kutta method. The comparative performance of various isolation systems has been studied with uniform and hybrid combinations. The hybrid combination of SMA supplemented bearings works out the better isolation system keeping in view of the percentage reduction in evaluation criteria for smart base-isolated benchmark building. Furthermore, it is shown that, the functionality of SMA wire is not efficient with Lead Rubber Bearing system, as it is able to control displacement but increases the acceleration, base shear, story drift and isolation forces.

Hydrodynamic Sensitivity of Moored and Articulated Multibody Offshore Structures in Waves

Within the framework of Space@Sea project, an articulated modular floating structure was developed to serve as building blocks for artificial islands. The modularity was one of the key elements, intended to provide the desired flexibility of additional deck space at sea. Consequently, the layout of a modular floating concept may change, depending on its functionality and environmental condition. Employing a potential-flow-based numerical model (i.e., weakly nonlinear Green function solver AQWA), this paper studied the hydrodynamic sensitivity of such multibody structures to the number of modules, to the arrangement of these modules, and to the incident wave angle. Results showed that for most wave frequencies, their hydrodynamic characteristics were similar although the floating platforms consisted of a different number of modules. Only translational horizontal motions, i.e., surge and sway, were sensitive to the incident wave angle. The most critical phenomenon occurred at head seas, where waves traveled perpendicularly to the rotation axes of hinged joints, and the hinge forces were largest. Hydrodynamic characteristics of modules attached behind the forth module hardly changed. The highest mooring line tensions arose at low wave frequencies, and they were caused by second-order mean drift forces. First-order forces acting on the mooring lines were relatively small. Apart from the motion responses and mooring tensions, forces acting on the hinge joints governed the system’s design. The associated results contribute to design of optimal configurations of moored and articulated multibody floating islands.

Identification of wave drift force QTFs for the INO WINDMOOR floating wind turbine based on model test data and comparison with potential flow predictions

The paper presents a comparison between empirical and numerical quadratic transfer functions (QTFs) of the horizontal wave drift loads on the INO WINDMOOR floating wind turbine. The empirical QTFs are determined from cross bi-spectral analysis of model test data obtained in an ocean basin. Validation of the identified QTF is provided by comparing low frequency motions reconstructed from the empirical QTF with measurements. The numerical QTFs are calculated by a panel code that solves the wave-structure potential flow problem up to the second order. Systematic comparisons between numerical and empirical QTFs allows identification of tendencies of empirical QTFs and limitations of the second order potential flow predictions. The study is limited to hydrodynamic loads from waves only, i.e. without current. For small seastates, the results indicate that the second order potential flow predictions of the surge QTFs agree quite well with the wave drift coefficients identified empirically from the model test data. For moderate and high seastates, second order predictions underestimate the surge wave drift coefficients for all compared diagonals of the QTFs. The discrepancies between predictions and empirical coefficients are not small, especially at the lower frequency range (below around 0.10 Hz) where the potential flow wave drift forces tend to zero.

Estimation of drift force by real ship using multiple regression a nalysis

Estimation of drift force by real ship using multiple regression a nalysis

Study on steel slit shear walls with different characteristics of hysteretic behavior

To study the contributing factors for the hysteretic behavior of the steel slit shear wall (SSSW), four SSSW specimens are designed, with design parameters of link configuration (flat and twisted) and steel property (mild carbon steel and low yield steel). Subjected to quasi-static cyclic loading, four patterns of shear force-drift curves are obtained: pinched, pinched but without cyclic degradation, plump and combined. Macro models are developed to simulate their different hysteretic behaviors, which agree well with the tested data. Finally, to investigate the influence of hysteretic pattern on the overall structural response, steel frame structure models equipped with SSSWs having different patterns of hysteretic behavior respectively are built. Structural responses in terms of maximum inter-story drift, residual inter-story drift and story shear force distribution are comparatively investigated.

A modified simplified analysis method to evaluate seismic responses of subway stations considering the inertial interaction effect of adjacent buildings

A modified simplified analysis method is proposed in this paper to evaluate seismic responses of subway stations in dense urban environments. Based on the dynamic analysis of the underground structure-soil-adjacent building interaction (SSSI) model, the seismic response of subway station was distinguished as the kinematic interaction (KI) effect (induced by the free-field movement) and the inertial interaction (II) effect (induced by the vibration of adjacent building). In order to comprehensively and simply consider the KI and II effects, a modified model was established after simplifying the analytical solution of underground structural seismic response. Owing to acquiring the dynamic response via static modelling and calculation, the method proposed herein requires a shorter analysis time and incurs a lower cost. In addition, a typical subway station-soil-ground building system in an east city in China was selected as the case-history to verify the modified method and further evaluate its computational accuracy. The traditional response displacement method and dynamic time history analysis method were also conducted in simulation as a comparison method and standard method, respectively. The case study demonstrates that referencing the results obtained by the dynamic time history analysis method (D-M), the maximum story drift and maximum internal force (including bending moment, axial force and shear force) errors of the traditional response displacement method (T-M) reached −28% and −48%, respectively. Obviously, this method is dangerous in designing due to its smaller computing results. In contrast, the modified method (M-M) which can accurately reflect the impacts of adjacent buildings, is a more accurate and safer analysis method (two seismic response indexes of the modified method generally exceeded the actual values, and more gratifying is that the errors were less than 12%). Therefore, the modified simplified analysis method proposed is a higher accuracy, safer design, less time consumed, and faster analysis process method, which can be used to substitute the traditional method in the aseismic performance and dynamic response analysis of subway stations in dense urban environments.

Experimental investigation of a closed vertical cylinder-shaped fish cage in waves

Wave-induced response of a closed floating fish cage consisting of a vertical circular cylinder with an external toroidal floater is studied theoretically and experimentally. A main purpose was to investigate how the internal sloshing would influence the global response of the cage, the interior wave elevation and also the mean drift loads. An ocean basin laboratory was used in order to minimize tank wall effects. An optical system involving eight markers was used to obtain experimental values for radial elastic deformations of the cylindrical part. The closer a coupled natural period between body motions and sloshing is to a corresponding natural sloshing period, the more nonlinear sloshing can be. In the examined case, the highest coupled natural period between surge, pitch and sloshing is 0.8 times the highest natural sloshing period. Linear potential flow theory can, in general, explain experimental transfer functions of rigid-body motions and sloshing due to rigid-body motions obtained by both regular wave and truncated white noise tests. Theoretical second order mean wave drift forces based on a rigid body and potential flow agree also well with experimental results. Resonant 3D sloshing was excited due to ovalizing hydroelastic structural modes in both regular waves and white-noise tests. The closeness between the corresponding structural and sloshing frequencies caused large response. A linear hydroelastic analysis based on WAMIT and LS-DYNA could partly explain the response. Parametric resonant pitch response occurred experimentally at large wave periods partially due to in and out of water motion of portions of the floater and was explained by treating the pitch as uncoupled motion modeled by the Mathieu equation. The pitch motion predicted by linear potential flow theory was, in general, unsatisfactory when the floater was partly out of the water occasionally.

Effect of hydrodynamic coupling of floating offshore wind turbine and offshore support vessel

The hydrodynamic coupling of Semi-submersible floating wind turbine and offshore support vessel during walk-to-work operation is studied, which is aimed at investigating the interaction of seakeeping and stationkeeping on both floating structures. The complex multi-body hydrodynamic problem is analyzed by 3-D diffraction and radiation computation in the frequency domain. To identify and evaluate coupling effects, three strategies are proposed in the modeling of the time domain simulation i.e. fully-coupling, no-coupling, and semi-coupling which ignores the interactive wave damping terms between the wind turbine and support vessel. The dynamic and mechanical properties of the wind turbine such as nonlinear mooring tension and damping are validated and reach a good agreement with existing measurements. A series of sea-state that combining different wave conditions and wave headings are taken into account in the study. By analyzing the maximum and spectrum of dynamic response, the surge and sway of support vessel show over-predicted motion due to the overestimate of drift force if hydrodynamic interaction was ignored. Under the following sea, the apparent ’splitting’ phenomenon can be observed that makes both structures drift towards opposite directions. The sway and roll of the wind turbine reduce significantly by up to 40% because of the ’shielding effect’ that ’cut down’ both linear and nonlinear wave forces in the entire frequency range. Sway and heave of support vessel present behavior of ’gap resonance’ where different modes of peak or trough are observed whose occurrence is however opposite to sway and heave.

Comparison of seismic load calculation based on SNI 1726-2012 and SNI 1726-2019 to capacity of elements on low level building

Buildings are designed to resist earthquake loads. After an earthquake occurs, it is expected that buildings will suffer minimal non-structural and structural damage. In designing earthquake loads on buildings, the regulations used in Indonesia refer to SNI 1726-2012. In 2019, the national standardization body (BSN) issued a new standard in carrying out earthquake load planning on building structures. In this standard there is an update on the latest earthquake map based on past earthquake event data. This paper aims to compare those twostandards on low level building in terms of capacity of beams and columns using SAP 2000. The parameter of design spectral response at short periods, SDS anddesign spectral response at one seconds periods, SD1 has been increased as well in SNI 1726-2019 especially in Jakarta area, which resulted in greater base shear, story drift, and internal forces on the beam and columns. The analysis result showed that base shear of low-level building has increased by 4,98% in x-axis and 7,21% in y-axis. The internal forces caused by the earthquake load are compared with the cross-sectional capacities of the beams and columns. Since there are not significant changes inSDS andSD1 of Jakarta area, the impact on internal forces are minor which leads to result that all beams and columns still below the cross-sectional capacity of the beam and column.