Hydrostatic Loading Research Articles

Use of interpolation methods for modeling the stress-strain state of operated oil storage tanks

The aim of the research is the comparison of two approaches for computer modeling of the stress-strain state of thin-walled shells of engineering structures, considering the imperfections of the geometric shapes arising due to their operation. The object of the study is the operated steel vertical cylindrical reservoir with imperfections of the geometric shape intended for storage of petroleum products. The first, so-called classical, approach provides geometric modeling of the surface of the tank's shell with the subsequent import of the geometric model into one of the systems of finite element analysis to calculate the stress-strain state of the structure and determine its technical condition, and the possibility of further operation. The geometric modeling of the shell surface with imperfections was performed using a two-dimensional interpolation method based on the 1st order smoothness outlines implemented in the point calculus. The calculation of the stress-strain state of the shell was carried out in the SCAD Office computer complex, taking into account geometric and structural non-linearity on the basis of the octahedral tangential stress theory. The second approach assumes modeling of an array of functions of vertical deflection of the tank wall by means of interpolation, solution of an array of differential equations of the elastic cylindrical shell under axisymmetric loading, improved by introduction of vertical deflection functions of the wall, followed by two-dimensional interpolation and analysis of the deformed state of the shell based on displacements arising in the tank wall from the hydrostatic load. As a result of the effective use of two-dimensional interpolation in the process of implementing the second approach, it was possible to achieve a significant increase in the speed of the numerical solution while maintaining sufficient accuracy for engineering calculations.

Impact of 3D collagen-based model and hydrostatic pressure on periodontal ligament fibroblast: A morpho-biochemical analysis

This study developed a customized hydrostatic pressure-based loading environment to investigate the effect of static hydrostatic pressure on the periodontal ligament fibroblasts (PDLf) in a three-dimensional (3D) collagen-based model. The cylindrical tissue constructs were comprised of PDL fibroblast cells seeded in type I collagen matrices and divided into three experimental groups: Control (no load), low-load (∼0.07 kPa), and high-load (∼60 kPa), all subjected to 24 h of experimental duration. Cells in the 3D construct were stained with fluorophore-conjugated antibodies for cytoskeletal protein F-actin and matricellular protein periostin. Cell culture supernatant was assessed for receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG) expression. Transmission electron microscopy examined the contact between the cells and the collagen matrix. Ultrastructural changes in the 3D collagen matrix were also analyzed using scanning electron microscopy. Experiments were performed in triplicates, and data was analyzed using one-way ANOVA (p < 0.05). The 3D PDLf constructs from the low-load group demonstrated the highest levels of homogeneous cell distribution and higher expression of F-actin and periostin with enhanced interaction with the matrix. The collagen matrix in this group showed more closely packed fibers forming thicker bundles when compared to the control and the high-load 3D PDLf constructs. Nonuniform cell distribution with decreased expression of F-actin and periostin was observed in the control and high-load PDLf constructs. The high-load group showed the highest RANKL/OPG expression. This study demonstrated low-level hydrostatic pressure's role in regulating PDLf functions and extracellular matrix response, while excessive hydrostatic pressure may be detrimental to PDL fibroblast cell function.

Effect of floater flexibility on global dynamic responses of a 15-MW semi-submersible floating wind turbine

Floater structural flexibility plays a significant role in accurate predictions of global dynamic responses of floating wind turbines (FWTs), especially for ultra-large wind turbines with increasing size and cost-effective floater design. The conventional analysis of FWTs often considers the floater as one rigid body, which cannot capture the correct resonant responses of the floater (especially the column that supports the tower). In this paper, a new approach where the floater is divided into multiple rigid bodies connected by flexible beams is developed for advanced modelling of flexible floaters in combination with coupled time-domain simulations. The hydrostatic and hydrodynmaic loads on each body from a one-body hydrodynamic analysis, together with gravitational loads and inertial loads, are implemented in the beam-based finite element model of the floater to carry out a time-domain analysis. The proposed approach is used to compare the responses of a 15-MW semi-submersible FWT considering a rigid and a flexible floater. The inclusion of floater flexibility reduces the tower natural frequency. It leads to larger bending moment amplitudes at the tower base close to the tower bending natural frequency, particularly in only-wind, irregular wave and wind-wave conditions, but smaller dynamic responses in regular wave conditions.

Simultaneous Hydrostatic and Compressive Loading System for Mimicking the Mechanical Environment of Living Cartilage Tissue.

In vivo, articular cartilage tissue is surrounded by a cartilage membrane, and hydrostatic pressure (HP) and compressive strain increase simultaneously with the compressive stress. However, it has been impossible to investigate the effects of simultaneous loading in vitro. In this study, a bioreactor capable of applying compressive stress under HP was developed to reproduce ex vivo the same physical loading environment found in cartilage. First, a HP stimulation unit was constructed to apply a cyclic HP pressure-resistant chamber by controlling a pump and valve. A compression-loading mechanism that can apply compressive stress using an electromagnetic force was implemented in the chamber. The synchronization between the compression and HP units was evaluated, and the stimulation parameters were quantitatively evaluated. Physiological HP and compressive strain were applied to the chondrocytes encapsulated in alginate and gelatin gels after applying high HP at 25 MPa, which induced damage to the chondrocytes. It was found that compressive stimulation increased the expression of genes related to osteoarthritis. Furthermore, the simultaneous application of compressive strain and HP, which is similar to the physiological environment in cartilage, had an inhibitory effect on the expression of genes related to osteoarthritis. HP alone also suppressed the expression of osteoarthritis-related genes. Therefore, the simultaneous hydrostatic and compressive stress-loading device developed to simulate the mechanical environment in vivo may be an important tool for elucidating the mechanisms of disease onset and homeostasis in cartilage.

Water-Weakening and Time-Dependent Deformation of Organic-Rich Chalks

The Ghareb Formation is a shallowly buried porous chalk in southern Israel that is being considered as a host rock for a geologic nuclear waste repository. Setup and operation of a repository will induce significant mechanical, hydrological and chemical perturbations in the Ghareb. Developing a secure repository requires careful characterization of the rock behavior to different loads. To characterize hydromechanical behavior of the Ghareb, several short- and long-term deformation experiments were conducted. Hydrostatic loading tests were conducted both dry and water-saturated, using different setups to measure elastic properties, time-dependent behavior, and permeability. A set of triaxial tests were conducted to measure the elastic properties and rock strength under differential loading at dry and water-saturated conditions. The hydrostatic tests showed the Ghareb began to deform inelastically around 12–15 MPa, a relatively low effective pressure. Long-term permeability measurements demonstrated that permeability declined with increasing effective pressure and was permanently reduced by ~ 1 order of magnitude after unloading pressure. Triaxial tests showed that water saturation significantly degrades the rock properties of the Ghareb, indicating water-weakening is a significant risk during repository operation. Time-dependent deformation is observed during hold periods of both the hydrostatic and triaxial tests, with deformation being primarily visco-plastic. The rate of deformation and permeability loss is strongly controlled by the effective pressure as well. Additionally, during holds of both hydrostatic and triaxial tests, it is observed that when water-saturated, radial strain surpassed axial strain when above effective pressures of 13–20 MPa. Thus, deformation anisotropy may occur in situ during operations even if the stress conditions are hydrostatic when above this pressure range.

Investigation on radial fracturing around borehole under combined static stress and blasting

Blast-induced radial fracturing is generally subjected to geo-stress. This study experimentally, theoretically and numerically investigates the radial fracturing behaviours around a rock borehole under combined static stress and blast loading by combining blast testing, elastic mechanics analysis and finite element modelling. The study begins with 11 blast tests on 100 mm cubic granite samples under various uniaxial and biaxial stress states based on a biaxial hydrostatic loading system. The fracture networks are subsequently image-processed in ImageJ where the morphology and fractal characteristics of radial fracturing in the rock surface are examined. Then, the variations in fracture patterns are analyzed using elastic mechanics, and the corresponding crack extension is numerically simulated in LS-DYNA. The mechanisms of the influence of static pressure on blast-induced radial cracking are revealed. The results demonstrate that the static stress greatly suppresses the blast-induced radial fracturing, resulting in fewer and shorter radial cracks with lower propagation velocity. This leads to a reduction in the fractal dimension of fractures and rock damage, which is attributed to the initial stress offsetting the blast-formed tangential tensile stress. Meanwhile, uniaxial pressure governs the propagation direction of radial fractures, as the cracks initiate at the borehole wall where the maximum hoop tensile stress presents and propagate along a path with the smallest circumferential compression. At last, the implications of the current results for practical blasting are discussed. It is advisable to leverage the directional cracking advantage offered by blasting under anisotropic in-situ stress to achieve a smoother excavation profile.

Recent &lt;i&gt;In Situ&lt;/i&gt; Experimental and Theoretical Advances in Severe Plastic Deformations, Strain-Induced Phase Transformations, and Microstructure Evolution under High Pressure

Severe plastic deformations (SPD) under high pressure, mostly by high-pressure torsion, are employed for producing nanostructured materials and stable or metastable high-pressure phases. However, they were studied postmortem after pressure release. Here, we review recent in situ experimental and theoretical studies of coupled SPD, strain-induced phase transformations (PTs), and microstructure evolution under high pressure obtained under compression in diamond anvil cell or compression and torsion in rotational diamond anvil cell. The utilization of x-ray diffraction with synchrotron radiation allows one to determine the radial distribution of volume fraction of phases, pressure, dislocation density, and crystallite size in each phase and find the main laws of their evolution and interaction. Coupling with the finite element simulations of the sample behavior allows the determination of fields of all components of the stress and plastic strain tensors and volume fraction of high-pressure phase and provides a better understanding of ways to control occurring processes. Atomistic, nanoscale and scale-free phase-field simulations allow elucidation of the main physical mechanisms of the plastic strain-induced drastic reduction in phase transformation pressure (by one to two orders of magnitude), the appearance of new phases, and strain-controlled PT kinetics in comparison with hydrostatic loading. Combining in situ experiments with multiscale theory potentially leads to the formulation of methods to control strain-induced PT and microstructure evolution and designing economic synthetic paths for the defect-induced synthesis of desired high-pressure phases, nanostructures, and nanocomposites.

Numerical Simulation of PMMA Impact Based on the J–C Constitutive and Damage Models under Hydrostatic Pressure Loading

Polymethyl methacrylate (PMMA) polymer is widely used in various fields today. In order to reveal the structural impact performance of PMMA materials in underwater engineering thoroughly, this paper firstly proposed a simplified plate model for a spherical shell hull under concentrative impact loading. Then, to simulate the hyper-elastic material properties of PMMA in the impact process, the Johnson–Cook constitutive model and damage failure model were adopted. And the least squares method was used to confirm accurately the J–C constitutive and damage failure model parameters of PMMA through material test data. Moreover, the dynamic process of the steel bullet impacting the PMMA plate structure was analyzed by the finite element software ABAQUS. The calculation results show that the numerical simulation results in this paper have a good convergence, and the residual velocities at different initial velocities and thicknesses of plates are in good agreement with the experimental test data. Therefore, the feasibility and accuracy of the impact analysis of PMMA structures based on J–C constitutive and damage failure models in this paper are verified accordingly. Finally, based on the presented finite element model, the structure response and the variation of residual velocity of the bullet with the PMMA plate thickness was analyzed in depth; that is, the results show that the residual velocity of the bullet has a certain linear relationship with the thickness, even in an underwater environment, and even in an underwater environment will increase both with a thicker structure or a higher pressure.

Напряженно-деформированное состояние плотины Юмагузинского гидроузла

Introduction. The stone-and-earth dam of the Yumaguzinskiy hydroelectric complex on the Belaya river is constructed in complicated geological conditions on heterogeneous foundation. The results of computational research of stress-strain state (SSS) of the dam, carried out for the variant of an earth dam with the central core are presented. When calculating the deflected mode of dams, the real structure of ground characterized by its relation of elastic and plastic bonds should be taken into account. The change of this structure takes place along with the change in stresses and is reflected in the values of coefficient of relative strength and coefficients of reliability. The values of the safety coefficients can be used to judge the strength state of the dam. Materials and methods. The stress-strain state of the dam was determined on the basis of the energy model of the developed by L.N. Rasskazov. The area of the selected fragment of the dam has been divided into single-type elements; a triangular grid of the finite element method has been adopted, by means of which the structure of the soil dam and the foundation have been described. Results. Numerical calculations have shown that when water level in the reservoir rises to the level of the forced retaining level the character of stress distribution σxx changes. At the base of uppermost buttress prism at the boundary with the core there appears an area with small positive values, the largest of which is obtained in the transition zone. The entire hydrostatic load is transferred to the pressure face of the core and, consequently, the entire work of external forces is transferred to the internal deformation energy of this element, causing a stress concentration in it. The transition zone material is forced to follow the deformations of the core, resulting in the development of tensile stresses in the core. Therefore, increasing the stiffness of the core results in less deformation of the core and correspondingly less tensile stress in the transition zone. The nature of stress distribution σyy is symmetrical. Conclusions. Increasing the rigidity of the core entails elimination of the arch effect, which is particularly noticeable at lower reservoir levels. For this reason the use of skeleton material in the core of the dam is desirable.

Loading–shape interaction analysis of membrane structures subjected to deformation dependent hydrostatic loadings

Due to their flexibility, membrane structures loaded and/or supported by gas and/or fluid undergo large deformations when subjected to external loads, for example when a relatively flat membrane deflects under accumulative ponding. The most noteworthy feature during the deformation process is the loading–shape interaction since changes in the form of the structure induce changes in the loading profiles, and vice versa. Description of the hydrostatic loading is complex since the discontinuity of structural domain and fluid domain occurs with the deformation of membrane. In this paper, an interactive model dealing with accurate hydrostatic load description and nonlinear finite element analysis is employed to analysis the structural response. The hydrostatic loading is described in vectors by fluid level and loading direction in current mesh of the membrane. In case to conserve a specific volume, the free surface height is calculated with a Newton algorithm. Equivalent nodal forces evaluation on different elements are deduced especially when they are partially or fully loaded by judging the spatial relation between the element and the fluid domain, and integrating with shape functions and area coordinates in a local coordinate system. In case of multiple fluid domains, the hydrostatic load description procedure is proposed to be conducted for each fluid domain with care in identifying respective loading direction and then sum them up to get the total hydrostatic loading forces. Two numerical examples, (a) single fluid domain case: a flat membrane subjected to accumulative water loading, and (b) multiple fluid domains case: an air-inflated dam partially filled with water and loaded by lateral pressures of water, are presented to demonstrate correctness, performance and effectiveness of the proposed method in large displacement analysis of flexible membrane structures subjected to deformation dependent hydrostatic loading.

Hull Girder Ultimate Strength Analysis of 17500 LTDW Oil Tanker under the Combined Global and Local Load using Explicit Finite Element Analysis

This study investigates the hull girder’s ultimate strength of 17500 LTDW Oil Tanker. The explicit finite element analysis is carried out to estimate the hull girder longitudinal strength of the Oil Tanker. The numerical analysis starts with the longitudinal strength analyses that examine the ship’s structural response behavior due to sagging and hogging bending moment load. The structural strength analyses were conducted to determine the maximum structural response behavior for withstanding the operational load. Afterward, the hull girder’s ultimate strength is undertaken to reflect the progressive collapse behavior of the oil tanker structure under the combined global bending moment and local hydrostatic pressure load. The explicit finite element analysis is performed to estimate the ultimate strength behavior, considering the effect of the hydrostatic pressure load and the material nonlinearities. The typical 17500 LTDW oil tanker represents Indonesia’s common oil vessel that supports national fuel oil distribution. Furthermore, this study can recognize the oil tanker’s ultimate hull girder strength characteristics.

Structural design evaluation for Underwater Remotely Operated Vehicle (ROV), case study: Madura Straits

Using Remotely Operated Vehicles (ROV) is very important, especially in underwater investigations. The Madura Strait, located between the Java islands and Madura, is used as an industrial area, especially for oil and gas sources. Therefore, the ROV structure must be designed in such a way that it can withstand the hydrostatic loads it receives during operations in the deep sea. The study was conducted to determine the ROV’s ability to withstand hydrostatic loads using materials such as steel, aluminium, and HDPE. The pre-designed ROV is converted and modeled in 3D. The model formed and detailed as the basic form of the ROV is imported to the Finite Element Analysis tools to obtain the value of the stress and deformation of the ROV. Therefore, the load is adjusted to the hydrostatic pressure, with the seawater depth up to 200 m. The study structural design evaluation is able used as a reference for selecting materials used in the ROV.

Generalization of the Singum Model for the Elasticity Prediction of Lattice Metamaterials and Composites

The recently developed singum model was extended to lattice metamaterials and composites for prediction of the effective elasticity based on the stiffness of the lattice components and the structure of the lattice, in which the load is transferred through the lattice network represented by unit cells that can contain one or more singums. The equilibrium of the singums was considered under a displacement variation, and the relation between the variations of averaged stress and strain can be evaluated to predict the elasticity. It was proved that the stiffness of any unit cells is the same as that of the primitive cell. A generalized formulation was developed to calculate the effective elasticity of lattice metamaterials and composites, which reflects the symmetry and anisotropic feature of the lattice more accurately. A hydrostatic load does not change the shape of the singum but changes its elasticity, although the bonds are linear elastic. The formulation shows the prestress-dependent elasticity for lattice metamaterials. When a large uniform biaxial tension is applied, a honeycomb lattice can exhibit a negative Poisson’s ratio under a pre-tension. Case studies of auxetic and body-centered cubic lattices were conducted to demonstrate the negative Poisson’s ratio and anisotropic elasticity, respectively.

Buckling and strength failure for unstiffened and ring-stiffened composite shells

An experimental method was applied to study the buckling pressure and failure strength for the unstiffened and ring-stiffened fiber reinforced composite cylindrical shells under the external hydrostatic pressure. Both the strain and pressure data are collected and discussed. The FE simulation models are also analyzed as comparison to investigate the relation among the critical buckling pressure, failure strength and the final structure failure strength. The results indicate that the ring-stiffened structure can improve the buckling pressure more significantly than increasing the failure pressure. The experimental burst pressure of the ring-stiffened cylindrical shell is increased by 23.2%. The buckling mode is changed and the buckling behavior can be improved and eliminated by the ring-stiffened structure before the cylinder bursts under the hydrostatic pressure load.

Improved Singum Model Based on Finite Deformation of Crystals with the Thermodynamic Equation of State

The recently published simplified singum model has been improved by using the thermodynamics-based equation of state (EOS) of solids to derive a new interatomic potential based on elastic constants. The finite deformation formulation under hydrostatic load has been used to evaluate the pressure-volume (p-v) relationship for the EOS of a solid. Using the bulk modulus and its derivatives at the free-stress state, one can construct the EOS, from which a new form of interatomic potential is derived for the singum, which exhibits much higher accuracy than the previous one obtained from the Fermi energy and provides a general approach to construct the interatomic potential. The long-range atomic interactions are approximated to be proportional to the pressure. This improved singum model is demonstrated for the face-centered cubic (FCC) lattice of single-crystalline aluminum. The elastic properties at different pressures are subsequently predicted through the bond length change and compared with the available experimental data. The model can be straightforwardly extended to higher-order terms of EOS with better accuracy and other types of lattices.

Physics of molecular deformation mechanism in 6H-SiC

Even though there have been several studies in literature of 6H SiC, a proper physics based understanding of the molecular deformation mechanisms of the material under different loading conditions is still lacking. Experimentally, the brittle nature of the material leads to difficulties associated with in-situ determination of molecular deformation mechanisms of the material under an applied load; whereas, the complex material structure along with the bonding environment prevents proper computational identification of different types of inelasticity mechanisms within the material. Molecular dynamics study (on successful verification of the interatomic potential with experimental results) of pristine single crystals of 6H SiC have been used to probe the physics of molecular deformation mechanisms of the material along with its inherent orientational anisotropy. The study elucidates the experimentally observed mechanisms of defect nucleation and evolution through a detailed analysis of radial distribution functions, x-ray diffraction as well as phonon vibrational studies of the single crystal. Studies have been presented at room temperature, initial high temperature and different types of confinement effects of the material (including hydrostatic and different biaxial loading cases). The confinement resulted in an increase in stress and stiffness whereas increase in initial temperature resulted in a decrease compared to uniaxial stress loading conditions at room temperature.

Leakage Threshold of a Saddle Point

The threshold condition for leakage inception is of great interest to many engineering applications, and it is essential for seal design. In the current study, the leakage threshold is studied by means of a numerical method for a mechanical contact problem between an elastic bi-sinusoidal surface and a rigid flat surface. The coalesce process of the contact patches is first investigated, and a generalized form of solution for the relation between the contact area ratio and the average applied pressure is acquired. The current study shows that the critical value of the average applied pressure and the corresponding contact area required to close the percolation path can be represented as a power law of a shape parameter, if the effect of the hydrostatic load from the pressurized fluid is ignored. With contact patches merged under a constant applied load, the contact breakup process is investigated with elevated sealed fluid pressure condition, and it is shown that the leakage threshold is a function of the excess pressure, which is defined as a ratio between the average applied pressure and the critical pressure under dry contact conditions.Graphical abstract

Small-Scale Modeling of Flexible Barriers. I: Mechanical Similitude of the Structure

Flexible barriers can be used to trap woody debris or debris flows. However, their small scale modelling is challenging because of their possible deformation. This article addresses how to meet the partial mechanical similitude of manufactured flexible barriers. Relevant dimensionless parameters are defined from flow velocity, barrier geometry, and component mechanical properties. These similitude criteria are validated using numerical simulations of barriers exposed to a hydrodynamic loading at various scales. The simulations also confirm the importance of accounting for the mechanical characteristics of the barrier components when designing model barriers in view of achieving realistic deformations. Next, a real barrier with complex features is scaled to conduct flume experiments. This scaled barrier is 3D-printed with material selected to achieve the mechanical similitude criterion. Another validation of this approach is performed considering hydrostatic loading and checking that simulated and measured deformations are similar. As an application case, the deformations measured during the experiments performed with woody debris are also compared to the hydrostatic loading.

Small-Scale Modeling of Flexible Barriers. II: Interactions with Large Wood

During strong floods, rivers often carry significant amounts of sediment and pieces of large wood (LW). When bridges and hydraulic structures are unable to allow LW to pass through, it becomes necessary to trap LW through specific wood retention structures (e.g., flexible barriers). This paper presents a comprehensive analysis of the interactions between LW and flexible barriers using small scale models. A dimensionless criterion is first proposed to compute blockage probability of single logs. It is based on experiments varying log size and shape, channel slope (2%, 4%, and 6%), water discharge, and barrier bottom clearance. Based on runs using six mixtures of hundreds of logs, an equation is secondly provided to compute flow depth at a barrier accounting for the head losses related to large numbers of logs. Conditions leading to the release of LW when the barrier is severely overwhelmed are also studied. The deformation measured on the barrier proves to be lower with LW-laden flows than under full hydrostatic loading of a barrier obstructed by a plastic sheet. Overall, we demonstrate that flexible barriers are very relevant structures to trap LW. A companion paper shows how to design and manufacture a small scale flexible barrier in mechanical similitude with the prototype scale.

A deep-learning approach for predicting water absorption in composite pipes by extracting the material’s dielectric features

Monitoring the mass of liquid absorption in laminated composite structures, that have a direct contact surface with working liquid-like pipes, is very important in order to prevent the sudden collapse of the structures because of the degradations in strength and mechanical properties over time. An electrical capacitance sensor technique has been applied for monitoring the mass of liquid absorption, over the time, in laminated composite pipelines by measuring the change of dielectric characteristics of composite pipelines subjected to an internal hydrostatic pressure load of water and thermal effect. Results show the technique is very effective. However, a major difficulty in utilizing this technique is that it is highly time consuming to be used for monitoring, in addition to the detection efforts that it requires to calculate the mass of liquid absorption that exerts high cost and loss of additional time in monitoring. In this paper, a deep neural network model is used to estimate the mass of liquid absorption in glass fiber reinforced epoxy laminated composite pipelines by extracting the features from datasets from experimental and numerical measurements of the electrical capacitance sensor. The experimental and numerical data used in this paper to train and test the new deep neural network model are collected from the literature and the finite element model of the electrical capacitance sensor system respectively. The results show an excellent agreement between the finite element model data, available experimental data, and those predicted by a deep neural network with an average error of 0.067%, and show that the proposed method achieves satisfactory performance with 86.34% accuracy, 82.83% regression rate and 83.74% F-score. The proposed approach overcomes the difficult problem of saving time and effort to accurately detect the mass of liquid absorption over the time, and provides a promising approach for a wider application of this intelligent model.