Water Structure Interaction Research Articles

A SUBSTRUCTURE MODEL FOR WATER-AXISYMMETRIC CYLINDER INTERACTION DURING EARTHQUAKES

A substructure analysis method for water-axisymmetric cylinder dynamic interaction problems is presented to simulate the seismic response of water-structure interactions. According to the wave equation and boundary conditions for the three-dimensional incompressible water and by applying the method of separation of variables, the model is transformed into a two-dimensional model, which is analytical in the circumferential direction and numerical in the vertical and radial directions. The dynamic stiffness equation of the infinity water at the truncated boundary is derived by using the scaled boundary finite element method, then the hydrodynamic pressure on the structure can be obtained by coupling the finite element equation of the near field water with the hydrodynamic on the truncated boundary. The finite element equation in time domain of a water-axisymmetric cylinder interaction system is developed by coupling the finite element equation of the structure with the hydrodynamic pressure. The numerical examples demonstrated that the proposed method is accurate and efficient. Numerical results show that the effect of the hydrodynamic pressure on the natural frequency and the dynamic response of the axisymmetric structure is increasing with the increase of the water depth in general.

Stochastic Response of a Coastal Cable-Stayed Bridge Subjected to Multi-Dimensional and Multi-Supported Earthquake and Waves

In this paper, a stochastic dynamic analysis method for cable-stayed bridges subjected to multi-dimensional and multi-supported earthquake and waves is established based on the pseudo-excitation method. The Monte Carlo method is used to analyze the influence of excitation nonlinearity on the bridge structure response, and the applicability of this method is verified. Stochastic response characteristic of coastal cable-stayed bridges subjected to multi-dimensional and multi-supported earthquake and waves is studied. The influence of water–structure interaction on the stochastic seismic response of main components of the cable-stayed bridge is described, and the influence of key parameters is analyzed. The results show that the influence of excitation nonlinearity on the response of the cable-stayed bridge can be neglected. A greater energy input caused by the rigid additional mass of the hydrodynamic pressure is the reason for the increasing of the seismic response. The influence of stochastic response of the underwater structure of the tower is changed with the site conditions. For the ground motion acceleration input energy being distributed in the high-frequency domain, the water–structure interaction has a greater effect on stochastic seismic response of the underwater structure of the tower. The influence of water–structure interaction on the stochastic seismic response of the underwater structure of the cable-stayed bridge increases with the increasing of the wave height and water depth.

Violent water-structure interaction: Overtopping features and vertical loads on a fixed structure due to broken incident flows

This paper presents an alternative experimental study of the interaction of broken flows with a fixed structure, concerning the overtopping features and vertical loads over its deck. Wet dam-break tests were carried out to generate incoming flows. Synchronized measurements provided by high-speed cameras, water elevation and force sensors, were used to investigate the influence of tank length in overtopping behaviour and the patterns and loads formed by wet dam-break flows generated by different conditions. During some of the overtopping events analysed, large scale plunging waves were observed, hitting the deck directly and forming large air cavities. These events generated violent interactions with the structure, causing significant loads and chaotic behaviour over the deck, due to the combination of air cavity collapse, reactive splash and run-down. The present approach could be employed as an alternative to study interactions of broken incident flows with different types of fixed structures, allowing the acquisition of detailed data to compare analytical or numerical models.

Soil–Water-Structure Interaction Algorithm in Smoothed Particle Hydrodynamics (SPH) with Application to Deep-Penetrating Problems

A fully coupled soil–water-structure interaction algorithm was presented in the framework of smoothed particle hydrodynamics (SPH). In this algorithm, soil–water interaction was simulated based on the two-phase mixture theory. Each phase of the mixture occupies part of the macroscopic mixture and satisfies its own conservation equations of mass and momentum. The Drucker–Prager model with nonassociated plastic flow rule was used to describe the constitutive behavior of soil. The water was treated as Newtonian fluid. Interaction between soil and water was modeled by the pore water pressure and the viscous drag force. The structure was considered as rigid and the interaction with soil/water was modeled by the frictional sliding contact algorithm. With this algorithm, it is possible to investigate pore water pressure, the effective stress and deformation of the soil undergoing large deformation. Moreover, the effect of the temporal and spatial evolution of soil porosity was taken into consideration. This study first examined the proposed algorithm for a U-tube seepage problem and a two-dimensional consolidation problem. Afterwards, the continuous deep penetrating process of the spudcan, which involved large soil deformation and complex soil–water-structure interaction, was simulated under axisymmetric conditions. The comparison with previous research indicates the robustness and applicability of the proposed algorithm. Furthermore, the proposed approach could be a potentially efficient tool helping to reveal the mechanism of soil failure in geotechnical, costal and ocean engineering.

Seismic water-structure interaction analysis using a modified SBFEM and FEM coupling in a frequency domain

The seismic responses of offshore structures and dams can be affected by the water-structure interaction. The structures are commonly modelled by finite element method (FEM). If the infinite water layer is also modelled by FEM, then the computational costs are high. In this paper, an accurate and efficient substructure method is presented in a frequency domain for a 2D water-structure interaction analysis, in which the modified scaled boundary finite element method (SBFEM) is applied at a general shaped water-structure interface to replace the compressible water layer. Several numerical examples, including offshore structures and a typical-geometry gravity dam, are provided to demonstrate the computational efficiency and accuracy of the proposed substructure method. The effects of hydrodynamic pressure, water compressibility and structure geometry on the seismic responses of offshore structures are analysed based on the proposed method.

Molecular Order Affects Interfacial Water Structure and Temperature-Dependent Hydrophobic Interactions between Nonpolar Self-Assembled Monolayers.

Understanding how material properties affect hydrophobic interactions-the water-mediated interactions that drive the association of nonpolar materials-is vital to the design of materials in contact with water. Conventionally, the magnitude of the hydrophobic interactions between extended interfaces is attributed to interfacial chemical properties, such as the amount of nonpolar solvent-exposed surface area. However, recent experiments have demonstrated that the hydrophobic interactions between uniformly nonpolar self-assembled monolayers (SAMs) also depend on molecular-level SAM order. In this work, we use atomistic molecular dynamics simulations to investigate the relationship between SAM order, water structure, and hydrophobic interactions to explain these experimental observations. The SAM-SAM hydrophobic interactions calculated from the simulations increase in magnitude as SAM order increases, matching experimental observations. We explain this trend by showing that the molecular-level order of the SAM impacts the nanoscale structure of interfacial water molecules, leading to an increase in water structure near disordered SAMs. These findings are consistent with a decrease in the solvation entropy of disordered SAMs, which is confirmed by measuring the temperature dependence of hydrophobic interactions using both simulations and experiments. This study elucidates how hydrophobic interactions can be influenced by an interfacial physical property, which may guide the design of synthetic materials with fine-tuned interfacial hydrophobicity.

Dynamic monitoring of a concrete arch dam during the first filling of the reservoir

The Baixo Sabor dam is a concrete double-curvature arch dam, 123 m high, located in the north-east of Portugal, which is being monitored by a dynamic monitoring system that comprises 20 uniaxial accelerometers. The paper starts with the description of the structure and of the installed monitoring equipment, as well as the monitoring software used to process the data that is continuously retrieved from site through an internet connection. Then, the results obtained during the system’s first six months of operation are presented, which include the characterization of acceleration levels for major events, such as the opening of spillway gates after intense rain, and the evolution of the dam modal properties (natural frequencies, modal damping ratios and mode shapes) during the reservoir first filling. In particular, the continuous characterization of the dam modal properties during important variations of the water level is a very unique experimental result (up to the authors knowledge, this is the first journal paper describing the continuous tracking of the modal parameters of a dam during its first filling), which is particularly interesting for the calibration of numerical models that take into account water-structure interaction. Additionally, it should be noted that the accurate tracking of the modal properties, in quite demanding conditions motivated by the very low vibration levels, associated to the massive nature of the structure, and by the presence of harmonics induced by the turbines of the hydroelectric power plant, was only possible thanks to the use of a carefully designed installation and advanced processing methodologies. At the end of the paper, it is presented a comparison between the results estimated with ambient excitation and the ones obtained with a forced vibration test and also predicted by a numerical model that includes the water effect with the added mass technique.

Simplified evaluation of earthquake-induced hydrodynamic pressure on circular tapered cylinders surrounded by water

Dynamic response of offshore structures can be influenced due to the water-structure interaction. The water-structure interaction can be simply represented by added mass in earthquake response analysis. The added mass for a circular cylinder can be obtained by analytical method. However, the added mass for an arbitrary shape of structure is rather difficult to be solved by analytical method. In this study, a substructure method for analysis of the seismic response of an arbitrary shape of structure is presented. The finite element technique incorporating the exact artificial boundary condition presented for simulating the far field of the infinite water is applied to the evaluation of added mass for offshore structures, where the exact added mass matrix is fully populated and symmetrical. The structure is idealized as a three-dimensional finite element model system. Firstly, the presented method is to investigate the seismic response of circular tapered cylinder vibrating in water. Secondly, a lumped added mass matrix is adopted to replace the exact added mass matrix. Thirdly, a simplified formula is presented to evaluate the added mass of the circular tapered cylinder.

Branched dicationically-charged phosphodicholine (PdC) modified chitosan with specific associated water structure and unique interactions with biocomponents

Cationic polymers possess significant potential in various biomedical applications due to their favorable interactions with biocomponents in aqueous media, which is related to their inherent structure and associated water structure. This work presents the development of a novel biodegradable cationic polymer with specific associated water structure and unique interactions with biocomponents. Bioinspired branched dicationically-charged phosphodicholine-chitosan (PdCCs) with different substitute degree were synthesized via Atherton-Todd reaction. As compared with monocationically charged N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC), thermal analysis confirmed the existence of the freezing bound water surrounding PdCCs due to the introduction of branched dicationically-charged PdC moiety. Fluorescence spectra revealed that PdCCs induced much less conformational change of bovine serum albumin than HTCC. Antibacterial and hemolysis assay showed that PdCCs and HTCC displayed high antibacterial activities against Escherichia coli and Staphylococcus aureus with different bacterial-type selectivity, and PdCCs showed higher selectivity to kill bacteria over red blood cell than HTCC. Furthermore, PdCCs-immobilized antibacterial surfaces exhibited better hydrophilicity and less protein adsorption than HTCC-immobilized antibacterial surfaces. These results indicated that branched dicationic PdC with capacity to restrain the freezing bound water may provide a good choice for developing cationic polymers for therapeutic applications.

Marine composite sandwich plates under air and water blasts

Fluid-structure interaction solutions for the air and water blast response of marine composite sandwich panels with crushable foam cores are presented in this paper. Reflected and radiated acoustic pressure waves were introduced using Taylor's FSI method into Lagrange's equations of motion for the sandwich plate. In comparison to air blast, water-structure interactions diminished deflection and slowed down the response of the sandwich panel for a given pressure pulse loading. The predicted elastic-plastic transient response of the sandwich panel from the analytical model was shown to be fairly consistent results with ABAQUS Explicit. Pressure amplitudes to initiate damage in a sandwich panel with E-glass/Vinyl Ester facesheets and PVC H250 foam core were calculated under water blast/air back, water blast/water back, and air blast/air back conditions. It took significantly higher pressures to initiate damage in the panels under water blast/air back and water blast/water back conditions than in the air blast/air back plate because of fluid damping and higher plastic work dissipation in the core. A parametric study showed that on a per unit areal weight basis, panels with softer, more ductile foams were more blast resistant than panels with strong and stiff cores because of work dissipation during core plasticity. In the water blast cases, foam yielding was affected by transverse compression and not only transverse shear, as is usually case in air blast-loaded sandwich panels.

PAMAM dendrimers-mediated specific targeting and intracellular apoptosis with aptamer and Bcl-2 converting peptide conjugation

Cationic polymers possess significant potential in various biomedical applications due to their favorable interactions with biocomponents in aqueous media, which is related to their inherent structure and associated water structure. This work presents the development of a novel biodegradable cationic polymer with specific associated water structure and unique interactions with biocomponents. Bioinspired branched dicationically-charged phosphodicholine-chitosan (PdCCs) with different substitute degree were synthesized via Atherton-Todd reaction. As compared with monocationically charged N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC), thermal analysis confirmed the existence of the freezing bound water surrounding PdCCs due to the introduction of branched dicationically-charged PdC moiety. Fluorescence spectra revealed that PdCCs induced much less conformational change of bovine serum albumin than HTCC. Antibacterial and hemolysis assay showed that PdCCs and HTCC displayed high antibacterial activities against Escherichia coli and Staphylococcus aureus with different bacterial-type selectivity, and PdCCs showed higher selectivity to kill bacteria over red blood cell than HTCC. Furthermore, PdCCs-immobilized antibacterial surfaces exhibited better hydrophilicity and less protein adsorption than HTCC-immobilized antibacterial surfaces. These results indicated that branched dicationic PdC with capacity to restrain the freezing bound water may provide a good choice for developing cationic polymers for therapeutic applications.

Modelling large deformation and soil–water–structure interaction with material point method: Briefing on MPM2017 conference

The 1st International Conference on the Material Point Method for “Modelling Large Deformation and Soil–Water– Structure Interaction” (MPM2017) was held in Delft, The Netherlands on 10–13 January 2017. This is the first conference organised by the Anura3D MPM Research Community, following a series of international workshops and symposia previously held in The Netherlands, UK, Spain and Italy, as part of the European Commission FP7 Marie-Curie project MPM-DREDGE. We are delighted to present seven contributions in this Special Column of the Journal of Hydrodynamics, and take this opportunity to announce that the 2nd conference, MPM2019, will be held in Cambridge, UK in January 2019.

Earthquake response of solitary slender freestanding intake towers

Earthquake response of solitary slender intake towers is investigated considering an idealized hollow intake tower with its circular footing submerged in water. The tower is studied in anchored (fixed base) and unanchored (freestanding) states placed on undeformable soil foundation. The water-structure interaction is modeled by the Eulerian-Lagrangian approach, using the pressure-based elements for the water and the displacement-based elements for the structure. The only source of nonlinearity is the contact at the base joint between the tower's footing and the ground. This contact is modeled using Coulomb friction model which allows the tower to slide and uplift. The system is three-dimensionally analyzed using finite element method under static and dynamic earthquake loads. A detailed parametric study is conducted to assess the importance of system characteristics including surrounding and inside water levels, ratio of tower height to footing radius, base joint friction coefficient, water compressibility, footing flexibility, and vertical ground motion.

Unstructured finite volume method for water impact on a rigid body

A new method is presented for the water impact simulation, in which the air-water two phase flow is solved using the pressure-based computational fluid dynamics method. Theoretically, the air effects can be taken into account in the water structure interaction. The key point of this method is the air-water interface capture, which is treated as a physical discontinuity and can be captured by a well-designed high order scheme. According to a normalized variable diagram, a high order discrete scheme on unstructured grids is realised, so a numerical method for the free surface flow on a fixed grid can be established. This method is implemented using an in-house code, the General Transport Equation Analyzer, which is an unstructured grid finite volume solver. The method is verified with the wedge water and structure interaction problem.

A framework for soil-water modeling using the pedostructure and Structural Representative Elementary Volume (SREV) concepts

Current soil water models do not take into account the internal organization of the soil medium and consequently ignore the physical interaction between the water film at the surface of solids that form the soil structure and the structure itself. In this sense, current models deal empirically with the physical soil properties, which are all generated from this soil water and soil structure interaction. As a result, the thermodynamic state of the soil water medium, which constitutes the local physical conditions of development for all biological and geochemical processes within the soil medium, is still not well defined and characterized. This situation limits modeling and coupling the different processes in the soil medium since they all thermodynamically linked to the soil water cycle. The objective of this article is to present a complete framework for characterizing and modeling the internal soil organization and its hydrostructural properties resulting from interaction of its structure with the soil water dynamics. The paper builds on the pedostructure concept, which allowed the integration of the soil structure into equations of water equilibrium and movement in soils. The paper completes the earlier framework by introducing notions of soil-water thermodynamics that were developed in application to the concept of the Structural Representative Elementary Volume (SREV). Simulation of drainage after infiltration in the Yolo loam soil profile, as compared to measured moisture profile using the measured soil characteristic parameters, showed a high degree of agreement. This new modeling framework opens up new prospects in coupling agro-environmental models with the soil medium, recognizing that the soil organization, hydro-structural, and thermodynamic properties are the foundation for such coupling.

Investigation of the shock wave propagation characteristics and cavitation effects of underwater explosion near boundaries

The shock wave propagation characteristics of underwater explosion have been of great interest to researchers. While the physical processes during an underwater explosion near boundaries are extremely complex, which involve lots of complex issues such as the explosion, shock wave propagation, water–air or water–structure interaction, etc. After the underwater detonation of an explosive, the shock wave may approach two main types of boundaries: the free surface of the water and the fluid–structure interface. The presence of these boundaries will significantly affect the wave propagation phenomena, and lead to bulk cavitation near the free surface or the structure surface. This paper deals with the behavior of shock wave propagation and cavitation from underwater explosion near different boundaries. A coupled numerical approach with combined Lagrangian and Eulerian methods is used to simulate the water–air interface and shock wave–structure interaction. A numerical model of free-field explosion in water is established, and the results have been compared with the published empirical formulas to verify the results of numerical solutions. The shock wave propagation characteristics from explosions in water near different boundaries are simulated and compared. In addition, the unsteady cavitations just near the free surface and the structure surface are described and captured. The water–air and water–structure interaction effects are examined. The results show that the free surface and structure surface boundaries have significant influence on the shock wave propagation characteristics.

Green water loading on a floating structure with degree of freedom effects

The aim of the present work is to investigate whether the degree of freedom (DOF) of a floating body has a notable effect on the maximum impact pressure due to green water on deck. The analysis is carried out for a box-shaped floating structure with a deckhouse, using experimental and numerical means to model the green water load. Green water on deck and impact on the deckhouse is generated by the impingement of a focusing wave group on a floating structure. Computations are performed using a two-dimensional constrained interpolation profile-based model solving the Navier–Stokes (N–S) equations with free surface boundary condition to deal with nonlinear water–structure interactions. The free surface is captured by a volume of fluid (VOF)-type tangent of hyperbola for interface capturing/slope weighting (THINC/SW), which is more accurate than the original THINC scheme. The verifications of the simulation through a series of model-to-model comparisons are performed in a two-dimensional glass-wall wave tank. Experimental water surface elevations, body motions and impact pressure are compared satisfactorily with the computed results for different DOFs cases. As a result, the peak impact pressure due to green water decreases rapidly with the increasing DOF.

Optimum geometry of tuned liquid column-gas damper for control of offshore jacket platform vibrations under seismic excitation

In this study, the effectiveness of a tuned liquid column-gas damper, TLCGD, on the suppression of seismicinduced vibrations of steel jacket platforms is evaluated. TLCGD is an interesting choice in the case of jacket platforms because it is possible to use the structural elements as the horizontal column of the TLCGD. The objective here is to find the optimum geometric parameters, namely orientation and configuration of vertical columns, length ratio, and area ratio of the TLCGD, considering nonlinear damping of the TLCGD and water-structure interaction between the jacket platform and sea water. The effects of different characteristics of ground motion such as PGA and frequency content on the optimum geometry are also investigated and it is observed that these features have some influence on the optimum area ratio. Finally it is observed that pulse arrangement of ground acceleration is one of the most important parameters affecting the efficiency of a TLCGD. In other words, it is found that the TLCGD’s capability to reduce the RMS responses depends only on the frequency content of the ground acceleration, but its capability to reduce the maximum responses depends on both the frequency content and the pulse arrangement of the ground acceleration.

Effect of trimethylamine-N-oxide on pressure-induced dissolution of hydrophobic solute

Molecular dynamics simulations are performed to study the effects of increasing trimethylamine-N-oxide (TMAO) concentration on the pressure-induced dissolution of hydrophobic solutes immersed in water. Such systems are of interest mainly because pressure increases the dissolution of hydrophobic protein interior causing protein denaturation and TMAO acts to offset the protein denaturing effect of high hydrostatic pressures. In view of this, in this study, methane molecules are considered as model hydrophobic molecules and simulations are performed for four independent TMAO solutions each at four different pressures ranging from 2 to 8 kbar. From potentials of mean force calculations, it is found that application of pressure reduces the free energy difference between contact minimum (CM) and solvent-separated (SSM) minimum of hydrophobic solute, suggesting dissolution at high pressures. TMAO, on the other hand, increases the relative stability of CM state of methane molecules relative to its SSM state. High packing efficiency of water molecules around the hydrophobic solute at high pressure is observed. Also observed are TMAO-induced enhancement of water structure and direct hydrogen-bonding interaction between TMAO and water and the correlated dehydration of hydrophobic solute. From hydrogen bond properties and dynamics calculations, it is observed that pressure increases average number of water-water hydrogen bonds while reduces their life-times. In contrast, TMAO reduces water-water hydrogen bonding but enhances their life-times. These results suggest that TMAO can reduce water penetration into the protein interior by enhancing water structure and also forming hydrogen bonds with water and hence counteracts protein unfolding.

Observations of dynamic and non-dynamic interactions between a quay wall and partially stabilised backfill

The dynamic and non-dynamic interactions between a gravity-type quay wall and a backfill ground were investigated by centrifuge model testing, considering cases in which a rigidly cement-stabilised ground existed at varying distances from the quay wall. In conducting the centrifuge tests, the performance of the instrumentation applied to measure the pressure from granular soils was critically assessed. At non-dynamic states, the backfill confined between the quay wall and the rigidly stabilised soil block exerted smaller earth pressure at deeper locations, at both apparently active and transient states. The calculation, based on perfect plasticity and considering friction arching, was useful in explaining these results. A similar feature was also observed during the steady-state oscillations, in the case of dry sand backfill, and was associated with the system’s increased seismic stability. In underwater cases, the pore water fluctuations in the backfill dominated the total earth pressure behaviour, with the active pressure being smaller again from a confined fill than from a fully extending one. Despite the reduced active pressure, placing the stabilised soil in the proximity of the quay wall increased the wall’s permanent seaward movement, unless the two bodies were in direct contact. This ostensible association of smaller active pressure with greater instability in the underwater cases cannot be explained by the conventional, simplified conception of the active earth pressure as a unilateral cause of instability. The evaluation of such unconventional backfill conditions seems to require rigorous consideration of the simultaneous soil–water-structure interactions.