Loading Boundary Conditions Research Articles

Modeling high-resolution down-hole pressure transducer to achieve semi-distributed measurement in oil an d gas production wells

A full 3D computer model is developed to evaluate the performance impact of intrinsic loss and various geometrical features in high-resolution pressure transducer. The intrinsic loss is modeled as viscosity factors, which allows for a more efficient computer model. In this paper, the developed model is applied to yield an insight in the evolution of high-resolution down-hole pressure transducer, from Hewlett-Packard\texttrademark\, to Quartzdyne\texttrademark. As the quality factor is related to the inverse of the resolution, the transducing element optimization process to achieve the highest quality factor possible is investigated, considering the impact of crystal quality and geometrical features, such as: thickness, diameter and convexity (plano-convex and bi-convex). Temperature-dependent elastic constants are used to improve the model accuracy in modeling temperature effects on the vibrating resonator-type transducer. Boundary load conditions are used to simulate hydrostatic pressure. The simulations to extract the frequency shift are carried out in the range of $14\,psi$ ($96.5\,kPa$) to $20000\,psi$ ($137.89\,MPa$) and $0\,^oC$ to $200\,^oC$ for pressure and temperature, respectively, as such ranges are typically found in oil and gas wells. A discrepancy in the published temperature dependence has been found. A miniaturization path to achieve semi-distributed measurement in oil and gas production wells is presented.

Effect of Sediment Load Boundary Conditions in Predicting Sediment Delta of Tarbela Reservoir in Pakistan

Setting precise sediment load boundary conditions plays a central role in robust modeling of sedimentation in reservoirs. In the presented study, we modeled sediment transport in Tarbela Reservoir using sediment rating curves (SRC) and wavelet artificial neural networks (WA-ANNs) for setting sediment load boundary conditions in the HEC-RAS 1D numerical model. The reconstruction performance of SRC for finding the missing sediment sampling data was at R2 = 0.655 and NSE = 0.635. The same performance using WA-ANNs was at R2 = 0.771 and NSE = 0.771. As the WA-ANNs have better ability to model non-linear sediment transport behavior in the Upper Indus River, the reconstructed missing suspended sediment load data were more accurate. Therefore, using more accurately-reconstructed sediment load boundary conditions in HEC-RAS, the model was better morphodynamically calibrated with R2 = 0.980 and NSE = 0.979. Using SRC-based sediment load boundary conditions, the HEC-RAS model was calibrated with R2 = 0.959 and NSE = 0.943. Both models validated the delta movement in the Tarbela Reservoir with R2 = 0.968, NSE = 0.959 and R2 = 0.950, NSE = 0.893 using WA-ANN and SRC estimates, respectively. Unlike SRC, WA-ANN-based boundary conditions provided stable simulations in HEC-RAS. In addition, WA-ANN-predicted sediment load also suggested a decrease in supply of sediment significantly to the Tarbela Reservoir in the future due to intra-annual shifting of flows from summer to pre- and post-winter. Therefore, our future predictions also suggested the stability of the sediment delta. As the WA-ANN-based sediment load boundary conditions precisely represented the physics of sediment transport, the modeling concept could very likely be used to study bed level changes in reservoirs/rivers elsewhere in the world.

Characterization of giant magnetostrictive materials under static stress: influence of loading boundary conditions

Giant magnetostrictive materials (GMM) can be integrated in actuator or sensor applications. The design of these systems is optimized based on a good knowledge of the material properties and conditions of use. Terfenol-D exhibits the greatest room temperature strain among commercially available GMM, however, its magneto-elastic behavior is very sensitive to pre-stress level. In this work, the design of an experimental setup dedicated to the characterization of GMM magneto-mechanical behavior under constant stress is described. A major difficulty is to master the mechanical boundary conditions while the sample is subjected to dynamic magnetic loading. The dynamic stress experienced by the sample is connected to the magnitude of the magnetostriction strain, the stiffness of the sample and the stiffness of the characterization setup. Results show that an appropriate setup is able to reduce the dynamic stress variations induced by magnetic excitation variations below 0.1 MPa, while this dynamic stress can reach up to 20 times the magnitude of the applied stress when the control system is not used. With the boundary conditions being controlled, magnetic and magnetostrictive behavior of Terfenol-D are characterized under various uniaxial compressive stress levels, from the stress-free conditions to 90 MPa. By comparing the results obtained under controlled and non-controlled stress conditions, it is shown that uncontrolled boundary conditions can be responsible for errors of several percent on the magnetic induction measurement. The measurement of strain is even more sensitive to the boundary conditions, with errors up to 40% and 30% on the longitudinal and transverse strains, respectively. This work highlights the utmost importance to control the boundary conditions in order to characterize the magneto-mechanical behavior of GMM.

Dynamical stability analysis of MDOF real-time hybrid system

Abstract Real-time hybrid simulation is an advanced testing methodology to evaluate structural responses under realistic operating conditions. Typically, the real-time hybrid system uses actuation and control system to apply load and motion boundary conditions on the experimental substructure. The inherent system dynamics present phase lags, in addition to the communication delays, that both cause negative damping in the real-time hybrid system. In this study, the dynamic equation of motion is derived for a generalized multiple-degree-of-freedom hybrid system. The negative damping effect is quantified, which depends not only on the actuator motion control performance, but also more importantly on the partition between the numerical and experimental substructures (i.e. how the stiffness and mass are assumed in both substructures). It is demonstrated the worst-case hybrid substructure partition may have very narrow stability margin in its tolerance of any system delay. The proposed equation of motion gains system level understanding of any arbitrary hybrid substructure partition; thus allow both frequency domain system analysis and time domain evaluation. The benchmark problem is studied to validate the proposed equation of motion compared with the virtual testing method, both approaches show excellent correlation. These pre-testing assessments could establish quantitative predictive measures about the system stability limit and performance criteria. Thus they are very important in the early design stage of a feasible real-time hybrid implementation, help reduce the risks of unintended physical testing responses.

Sequential finite element modelling of lightning arc plasma and composite specimen thermal-electric damage

Highly complex phenomena such as lightning strikes require simulation methods capable of capturing many different physics. However, completing this in one simulation is not always desired or possible. In such instances there can be a need for a methodology to transfer loading boundary conditions from one simulation to the next while accounting for the characteristic form of the loading and the dissimilar domain and mesh geometries. Herein, the objective is to combine two models to enable the automatic sequential simulation of a lightning arc and a composite test specimen. The approach is developed using Finite Element models, with a Magnetohydrodynamics model representing the lightning plasma and a thermal-electric model representing the specimen. The specimen mesh and loading boundary conditions are automatically generated based on the predicted output of the preceding plasma model. The precision, run-time and flexibility of the proposed approach is demonstrated, with thermal damage predictions generated in approximately 33 h. Resulting from the integrated modelling capability is the first time prediction of damage representing the test electric boundary conditions rather than assumed specimen boundary conditions (herein using test ‘Waveform B’).

Research on Hydraulic Speed Control System of Ship Crane Anti-Rolling Device

Ship cranes will be shaken sharply due to the influence of additional loads such as wind, waves and current during operation. Due to the influence of additional loads such as wind, waves and flow, the marine crane in operation will cause the cargo to shake sharply, which reduces the efficiency of the work greatly. In order to solve this problem, a three-rope traction type anti-rolling device is designed. In this paper, a hydraulic speed control system of the crane anti-rolling device is designed, the boundary conditions of the traction cable load are analysed, The boundary conditions of the traction cable load are analyzed, and the parameter matching of the main components such as hydraulic motor and hydraulic pump in the speed control system is studied.

Electro-dynamic analysis of smart nanoclay-reinforced plates with integrated piezoelectric layers

• Static and dynamic behaviors of smart sandwich plates are investigated. • Sandwich plates consist a nanoclay/polymer core and two piezoelectric layers. • A mesh-free method based on MLS shape function and FSDT is developed and implemented. • Two morphologies of intercalated stacks and exfoliated nanoclays are considered. Integrating engineering structures with piezoelectric layers as actuator and/or sensor offers smart sandwich structures with controllable static and dynamic deflections. In this paper, a smart sandwich plate consisting of a light nanoclay-reinforced composite core and two piezoelectric face sheets is considered. The static and dynamic behaviors of the proposed smart plate are obtained using their governing coupled electro-mechanical system of equations. In order to facilitate the governing equations, a mesh-free method based on moving least square (MLS) shape function and first order shear deformation (FSDT) is developed and implemented. Two morphologies of intercalated stack and exfoliated nanoclay dispersions are considered in the distribution of the nanoclay into the polymeric matrix. The effects of morphology and volume fraction of the nanoclay, time-dependent loading, and essential boundary condition on the static and dynamic behavior of the smart piezoelectric-integrated nanocomposite plates are examined. In the dynamic analysis, resonance and amplitude modulation phenomena are studied. It is observed that the use of nanoclay, especially with exfoliated morphology, improves the static and the free vibration responses of the smart sandwich plates. Moreover, the frequency of the applied mechanical load has a significant effect on the electro-dynamic response of the proposed smart sandwich plates.

Lateral behavior of panelized CLT walls: A pushover analysis based on minimal resistance assumption

A new simplified mechanistic model was developed in this study to predict the rocking and sliding lateral response of a CLT panel wall under monotonic pushover with different boundary and gravity loading conditions based on an approximation of the principle of virtual work. Namely, for a given forced lateral displacement increment, the CLT wall will engage in a combination of rocking and sliding motion that will minimize the total work needed to go through that displacement increment. The proposed model was compared to the existing test results to illustrate its ability to capture the two types of wall behavior. Being a simplified mechanistic model, a number of material nonlinear characteristics such as the local crush of wood and the biaxial interaction of the connectors were not captured, resulting in a backbone characterization accuracy not as good as some existing well-calibrated models. However, the contribution of the study is to provide a mechanistic approach to address the switching between rocking and sliding behavior of CLT panelized walls under different boundary conditions. Using the model, a sensitivity analysis was conducted to investigate the effect of wall configurations and boundary conditions on the behavior of CLT shear walls.

Static analysis of four-parameter functionally graded plates with general boundary conditions

In this study, the Ritz variational method is used to analyze and solve the bending problem of rectangular functionally graded material plate with general boundary conditions and subject to some types of load distribution over the entire plate domain. Based on the Kirchoff plate theory, the equilibrium equations are obtained by minimizing the total potential energy. The material properties are assumed to be graded through the thickness of the plates according to a power law with four parameters. The accuracy of the solution has been checked and validated through different comparisons to that available literature. A wide variety of examples have been carried out to reveal the influences of different geometrical parameters, FGM power law index, type of load distribution and boundary conditions on the bending responses of the plates. The results show that the gradients in material properties play an important role in determining the response of the FGM plates.Keywords: FGM; Kirchhoff plate; Ritz method; boundary conditions.

The flexural response of large scale steel-framed composite glazing panels

Novel composite glazing panels provide an opportunity to significantly reduce the weight and depth of glazed facades and simultaneously minimize the visual and spatial bulkiness of conventional facade framing systems. However the mechanical response of these novel composite glazing panels is poorly understood and there is no published data on the flexural response of large scale panels. In this research, medium scale (700-mm long and 300-mm wide) and large scale (3500-mm long and 1500-mm wide) composite glazing panels were fabricated and tested in bending up to failure. Recently developed analytical model for composite sandwich panels was also implemented on the medium and large scale panels. The experimental test data shows that shear-lag effects can be significant in large scale panels and can reduce their effective widths by about 40%. The analytical model provided a good fit of experimental results when the effective width was reduced according to strain gauge measurements. Neglecting shear-lag effect is unsafe and would underestimate deflections and stresses by approximately 40%. Further research is required to quantify the shear-lag effects, and the corresponding variation of effective widths, along the length of composite glazing panels and the influence of load distribution and boundary conditions on the effective thickness of the glass panels.

ОПРЕДЕЛЕНИЕ ГРАНИЧНЫХ УСЛОВИЙ ДЛЯ РАСЧЁТА ТЕРМОНАПРЯЖЕННОГО СОСТОЯНИЯ ПОРШНЯ

The paper deals with the study of the influence of the working process parameters of the two-stroke opposed piston engine like D100 (20.7/2×25.4), especially the heat exchange between the working substance and the wall of the combustion chamber (CC) – cylinder and pistons on temperature and stress-strain state of the piston. To make an estimation of the effect of a working process on the boundary condition we considered the internal heat balance and specific features of gas dynamic loading of main parts of the cylinder-piston group. To calculate the temperature fields, the actual boundary conditions of non-stationary thermal loading were replaced with the equivalent steady-state ones, obtained from the condition that the amount of heat perceived by the piston surface in real and conditionally equivalent processes are equal. Equivalent parameters of heat transfer are calculated by the condition of conservation of the amount of heat passing through the walls of the CS. It was performed the validation of the calculation of equivalent heat exchange parameters. It is shown that in case of an error in specifying the initial conditions, for example, temperature per 100K, the temperature of the piston CC surface may change by 5K in the first 5 operating cycles. It is shown that the developed model of the workflow can be adjusted according to the available experimental data and used to model the boundary conditions. The authors made corrections to the dependence obtained by prof. Rosenblit, to determine the current heat transfer coefficient from the working fluid to the walls of the CC by the total heat removal for the cycle, equal to 20%. It was obtained the average coefficient of heat transfers from the working fluid to the piston and the temperature of the cycle for the nominal mode, which are 3500 W/(m2•K) and 835 K respectively. It was carried out the simulation of the thermal properties of the gap between the piston ring and the groove filled with combustion products. It is shown that the conditions of heat transfer through annular grooves and rings require clarification in modeling, which is associated with the conditions of heat transfer in the gaps, and the gap can be replaced by a gasket with appropriate thermal properties.

Performances Analysis of a Novel Electromagnetic-Frictional Integrated Brake Based on Multi-Physical Fields Coupling

In this article, a novel electromagnetic-frictional integrated brake is proposed, and its structure and working principle are introduced. The geometric model and mathematical models of integrated brake were established, and the multi-field coupling mechanism of integrated brake were analyzed. With BYD Qin as a reference vehicle, the boundary conditions of thermal load and force load of integrated brake were determined according to its structure and performance parameters. Based on the COMSOL software, numerical coupling calculations of electric, magnetic, thermal, and solid fields of integrated brake were carried out respectively in the emergency and downhill braking at a constant speed. The axial, circumferential, and radial temperature distributions of integrated brake disc were analyzed respectively, and they were compared with those of the traditional friction brake disc. The analysis results show that the proposed integrated brake can effectively improve the heat fading resistance of automotive brake during emergency and continuous braking. Under the two braking conditions, the temperature rise of friction brake was faster than that of an electromagnetic brake, and the effect of the electromagnetic brake on temperature rise of integrated brake was small.

Insights into the micromechanics of stress-relaxation and creep behaviours in the aortic valve

Viscoelastic attributes of the aortic valve (AV) tissue are, in part, reflected in stress-relaxation and creep behaviours observed in vitro. While the extent of AV time-dependent behaviour under physiological conditions is not yet fully understood, in vitro the tissue exhibits clear stress-relaxation but minimal creep under equi-biaxial loading, in contrast to uniaxial loading where creep is evidently exhibited. Tissue-level stress-relaxation behaviour follows the form of (single and double) Maxwell-type exponential decay relaxation modes, and creep occurs in the form of exponential primary followed by linear secondary creep modes. This paper aims to provide an explanation for these behaviours based on the AV microstructural (i.e. fibre-level) mechanics. The kinematics of AV microstructural reorganisation is investigated experimentally using confocal microscopy to track the interstitial cell nuclei as markers of AV microstructural reorganisation under uniaxial loading. A theoretical framework is then applied to describe the experimentally observed kinematics in mathematical terms. Using this framework it is shown that at the microstructural level, AV stress-relaxation and creep behaviours both stem from the same dissipative kinematics of fibre-fibre and fibre-matrix interactions, that occur as a consequence of microstructural reorganisation due to the applied tissue-level loads. It is additionally shown that the proposed dissipative kinematics correctly predict the nature of relaxation and creep behaviours, i.e. the type and the number of modes involved. Further analysis is presented to demonstrate that the origin of the minimal creep behaviour under equi-biaxial loading can be explained to stem from tissue-level loading boundary conditions. These key findings help to better understand the underlying causes of AV stress-relaxation and creep behaviours in vivo, and why these may differ from the behaviours observed under non-physiological in vitro loading.

Nonlinear consolidation of multilayer soil under cyclic loadings

This paper proposes a uniform approach for modelling one-dimensional nonlinear consolidation of multilayer soil under various cyclic loadings based on the differential quadrature method. Various cyclic loading forms and boundary conditions are readily treated. The current differential quadrature formulation using harmonic function coefficients (HDQM) is proven more efficient in solving the consolidation problem of multilayer soil under cyclic loadings than conventional differential quadrature formulation using Lagrangian interpolation polynomial. The computation indicates that the pore pressure and average consolidation degree of a multilayer soil are highly dependent on the loading form and the length of the loading period in each loading–unloading cycle. The influence of the various boundary conditions on the distribution of the pore pressure in soil layers and consolidation rate is also discussed. An analysis on field measurements in Ningbo subway line 1 is presented to demonstrate the application of the proposed method. Analysis reveals that at the initial stage of the subway services, the main settlement is contributed by the consolidation settlement, which is quite considerable, about 0.5 mm per month. When the Up reach 50%, the consolidation settlement tends to stable state, then, the accumulative settlement becomes noticeable.

Fixed-grid hole-shape optimization for opening structures using smoothly deformable implicit curve

Hole-shape optimization for opening structures can effectively alleviate the hole-edge stress concentration; however, it requires high precision of stress analysis and high geometrical deformation capacity of the hole-edge curves. Therefore, the finite cell method is adopted in this work for high-precision numerical analysis within the fixed mesh, and the smoothly deformable implicit curve is proposed to describe the boundary to be optimized. After deriving analytical sensitivity analysis formulas, we built a hole-shape optimization design framework having high precision and high efficiency. Through hole-shape optimization in opening structures under different load boundary conditions, the proposed framework exhibited several advantages such as no mesh updating, simple sensitivity derivation, high analytical precision, and large design space.

Simulation and Sensitivity Analysis of Microtubule-Based Biomechanical Mass Detector.

The microtubule is biologically the most rigid filament that is so critical to the cytoskeleton system. It is significant to study the mass sensitivity of microtubule in order to understand biophysical behaviors, such as the influence of kinesin and dynein moving along microtubules. In this research, the sensitivity of mass detector using individual microtubule is first studied. The frequency shifting of the detector due to mass loads is simulated. The influences of mass load positions and boundary conditions on the mass sensitivity are evaluated. It is predicted in this research that the mass sensitivity of a 1 μm microtubules-based mass detector could reach 10-17 g. Results also show that the resonant frequency decreases logarithmic linearly with the increase of the attached mass regardless of the microtubule length and the position of mass load. Moreover, the sensitivity of resonant frequency shift to the microtubule length is also analyzed.

Dynamic Amplification Factor of Shear Force on Bridge Columns under Impact Load

Shear failure is a common mode for bridge column collapse during a vehicle‐column collision. In current design codes, an equivalent static load value is usually employed to specify the shear capacity of bridge columns subject to vehicle collisions. But how to consider the dynamic effect on bridge columns induced by impact load needs further research. The dynamic amplification factor (DAF) is generally used in the analysis and design to include the dynamic effect, which is usually determined using the equivalent single degree of freedom (SDOF) method. However, SDOF method neglects the effect of the higher‐order modes, leading to big difference between the calculated results and the real induced forces. Therefore, a novel method to obtain dynamic response under concentrated impact load including the effect of higher‐order modes is proposed in the paper, which is based on the modified Timoshenko beam theory (MTB) and the classical Timoshenko beam theory (CTB). Finite element models are conducted to validate the proposed method. The result comparisons show that the results from the proposed method have more accuracy compared with the results from the CTB theory. Additionally, the proposed method is employed to calculate the maximum DAF of shear forces for bridge columns under impact load. Parametric studies are conducted to investigate the effect on the DAF of shear forces including slenderness ratio, boundary condition, and shape and position of impact load. Finally, a simplified formula for calculating the maximum DAF of shear force is proposed for bridge column design.

Stability and vibration analysis of CNT-Reinforced functionally graded laminated composite cylindrical shell panels using semi-analytical approach

The present paper examined the buckling, postbuckling and vibration characteristics of pre-buckled and post-buckled laminated CNT reinforced composite (CNTRC) cylindrical shell panel made up of single walled carbon nanotubes (SWCNTs) and isotropic matrix. The effective material properties of CNTRC panel are computed using extended rule-of mixture (ROM) method. Higher order shear deformation theory (HSDT) with von Kármán type of nonlinearity is adopted to model the CNTRC cylindrical shell panel. Four different boundary conditions are considered. Besides uniform loading, different types of non-uniform in-plane load distribution such as triangular, trapezoidal, parabolic and partial edge loadings are considered. The internal stress distribution within the shell panel due to applied non-uniform loadings is evaluated by prebuckling analysis. Subsequently, via Hamilton's principle the governing partial differential equations of CNTRC laminated cylindrical shell panel are derived. Employing Galerkin's method and by neglecting the inertia terms the partial differential equations are reduced to a set of non-linear algebraic equation for the static problem. However, for dynamic problem the partial differential equations are converted to a set of ordinary differential equations. Beside parametric study the obtained numerical results from the present semi-analytical study illustrates the effects of CNT volume fraction, CNT dispersion profile, non-uniform load distribution and boundary conditions on the stability and vibration characteristics of CNTRC cylindrical panel.

Thermoelastic behaviour of FGM rotating cylinder resting on friction bed subjected to a thermal gradient and an external torque

ABSTRACT Thermoelastic behaviour of a functionally graded rotating cylinder with short length subjected to thermal and mechanical loads is studied in this article. It is assumed that the cylinder is located on a friction bed and is rotating due to an external torque. The material property is assumed to be variable along radius according to a power law distribution. Thermal conductivity equation is solved to obtain temperature distribution in terms of thermal boundary conditions and the material grading index. First-order shear deformation theory is used to derive kinematic relations. The governing equations are derived using minimum total potential energy theory and Euler relations. These governing equations are solved using method of eigenvalue and eigenvector. The physical and loading boundary conditions are applied to obtain unknown coefficients. The numerical results including stresses, strains and displacements are presented to show the influence of in-homogeneity index in longitudinal direction of the cylinder. The numerical results show that the longitudinal distributions of stresses, strains and displacements experience sharp and sudden changes at the end of the cylinder where the torsional moment is applied.

One dimensional consolidation of multi-layered unsaturated soil under partially permeable boundary conditions and time-dependent loading

In the present study the numerical Incremental Differential Quadrature Method (IDQM) was utilized in order to produce a general solution for one-dimensional consolidation of layered unsaturated soil under two different states: (i) constant loading and exponentially time growing drainage, and (ii) time-dependent loading and semi-permeable boundary conditions. A comparison between the results of this study and those of an available analytical solution for a single-layered unsaturated soil indicated high precision of the applied numerical method. A variety of instances were solved to study the impact of boundary conditions on the consolidation phenomenon.