Structural Mechanics Model Research Articles

Study on the mechanism and control of strong ground pressure in the mining of shallow buried close-distance coal seam passing through the loess hilly region

Shallow buried close-distance coal seam (SBCCS) is widely found in northern Shaanxi, China. In the process of mining under the loess hilly area (LHA) in SBCCS, many accidents of strong ground pressure have occurred. Taking the in the Zhangjiamao Coal Mine as the background, this study revealed the mechanism of high ground pressure when the working face of lower coal seam passes through the surface loess hilly region. On-site measurements, physical similarity simulation, numerical calculation, and theoretical analysis were combined to study the mining process of SBCCS. The movement characteristics of the activated structure of the interval strata of the lower coal seam were analyzed. The dynamic load and the change pattern of the front abutment pressure (FAP) of the support during the loading stage of entering and exiting the loess hilly were determined. A coupled structural mechanics model of the overlying activated voussoir beam and the step voussoir beam rock beam of the interval strata was established, revealing the dynamic loading mechanism of strong ground pressure during passing through the LHA. The results showed that the dynamic load of the working face was the highest in areas affected by the load of the LHA, followed by the load while entering the LHA, the peak value of the FAP in the load-influenced LHA was high, which was approximately 1.12 times that after leaving the load-influenced LHA and 1.61 times that before entering this area. By establishing a mechanical model of the roof coupling structure when entering and exiting the load-influenced LHA, it was revealed that the dynamic load of the support while mining under the goaf in the LHA is mainly due to the synchronous movement of the activated structure of the collapsed roof of the upper coal seam and the interval rock structure. The load in the LHA was transmitted to the interval rock structure through the activated structure, resulting in a high dynamic load on the support. The study concluded that the determination of the support resistance of the working face should be based on the high-period compressive load of the synchronous movement of the roof structure in the LHA. Through the engineering practice of hydraulic fracturing, the roof structure of the interval strata is changed, which can effectively reduce the dynamic pressure disaster of the working face. The research provides a scientific basis for the safe and efficient mining of shallow coalfields, and it provides reference for similar mining.

Stabilization of loosely coupled schemes for 0D–3D fluid–structure interaction problems with application to cardiovascular modelling

In this paper we analyze the numerical oscillations affecting loosely coupled schemes for hybrid-dimensional 0D–3D fluid–structure interaction (FSI) problems, which arise e.g. in the field of cardiovascular modeling, and we propose a novel stabilized scheme that cures this issue. We study several loosely coupled schemes, including the Dirichlet–Neumann (DN) and Neumann–Dirichlet (ND) schemes. In the first one, the 0D fluid model prescribes the pressure to the 3D structural mechanics model and receives the flow. In the second one, on the contrary, the fluid model receives the pressure and prescribes the flow. The terms DN and ND, employed in the FSI literature, are borrowed from domain decomposition methods, although here a single iteration is performed before moving on to the next time step (that is, the coupling is treated explicitly). Should the fluid be enclosed in a cavity, the DN scheme is affected by non-physical oscillations whose origin lies in the balloon dilemma, for which we provide an algebraic interpretation. Moreover, we show that also the ND scheme can be unstable for a range of parameter choices. Surprisingly, increasing either the viscous dissipation or the inertia of the structure favours the onset of oscillations and, for certain parameter choices, the ND is unconditionally unstable. In the presence of inertial terms, by reducing the time step size below a certain threshold, the amplitude of the numerical oscillations is even amplified. We provide an explanation for these facts and establish sharp stability bounds on the time step size. Our analysis extends to Robin–Robin schemes, based on linear combinations of the conditions of pressure continuity and either volume or flux continuity. While appropriate choices of Robin coefficients can achieve numerical stability, tuning these coefficients can be challenging in practice. To address these issues, we propose a numerically consistent stabilization term for the Neumann–Dirichlet scheme, inspired by physical insight on the onset of oscillations. We prove that our proposed stabilized scheme is absolutely stable for any choice of time step size. Notably, the proposed scheme does not require parameter tuning. These results are verified by several numerical tests. Finally, we apply the proposed stabilized scheme to an important problem in cardiac electromechanics, namely the coupling between a 3D cardiac model and a closed-loop lumped-parameter model of blood circulation. In this setting, our proposed scheme successfully removes the non-physical oscillations that would otherwise affect the numerical solution.

Viscoelasticity of hydrating shotcrete as key to realistic tunnel shell stress assessment with the New Austrian Tunneling Method

The New Austrian Tunneling Method (NATM) essentially rests on observational information concerning displacements measured in selected positions at the inner surface of shotcrete tunnel shells. The combination of these measurements with advanced material and structural mechanics, in the course of so-called hybrid methods, have successfully delivered, for more than 20 years, practically relevant estimations of internal and external forces and corresponding degrees of utilization. The reliability of the latter, however, may crucially depend on the used material model. Based on a recently proposed analytical structural mechanics model [Acta Mech 233, 2989–3019 (2022)], and focusing on the benchmark example of measurement cross section MC1452 of the Sieberg tunnel, driven in the 1990s in Miocene clay marl, the present paper compares the estimations of forces and degrees of utilization arising from differently refined constitutive concepts, namely (i) aging elasticity, (ii) aging linear viscoelasticity, and (iii) aging nonlinear viscoelasticity. It turns out that only the consideration of aging nonlinear viscoelastic material behavior provides access to realistic values for the degree of utilization, being lower than one. Simpler material models would indicate local material failure, which was not observed in situ.

A Bayesian Multi-fidelity Neural Network to Predict Nonlinear Frequency Backbone Curves

Abstract The use of structural mechanics models during the design process often leads to the development of models of varying fidelity. Often low-fidelity models are efficient to simulate but lack accuracy, while the high-fidelity counterparts are accurate with less efficiency. This paper presents a multi-fidelity surrogate modeling approach that combines the accuracy of a high-fidelity finite element model with the efficiency of a low-fidelity model to train an even faster surrogate model that parameterizes the design space of interest. The objective of these models is to predict the nonlinear frequency backbone curves of the Tribomechadynamics Research Challenge benchmark structure which exhibits simultaneous nonlinearities from frictional contact and geometric nonlinearity. The surrogate model consists of an ensemble of neural networks that learn the mapping between low and high-fidelity data through nonlinear transformations. Bayesian neural networks are used to assess the surrogate model's uncertainty. Once trained, the multi-fidelity neural network is used to perform sensitivity analysis to assess the influence of the design parameters on the predicted backbone curves. Additionally, Bayesian calibration is performed to update the input parameter distributions to correlate the model parameters to the collection of experimentally measured backbone curves.

Stress Concentration Factor-Based Hot-Spot Stress Prediction Model for the Web-Gap Weld of Main Girder in Steel Truss Bridge

Fatigue cracking is one of the main diseases of steel bridges in operation stage. Scientific evaluation is of great significance to improve structural durability. However, obtaining the hot-spot stress (σHSS) extrapolation point is challenging due to limited space around certain structural details in steel bridges. To overcome this limitation, a HSS prediction method incorporating the stress concentration factor (SCF) was proposed. Additionally, a structural mechanics model based on the mechanical characteristics of the web gap in the main girder of a steel truss bridge was established to calculate its nominal stress. Experimental and numerical simulations have been conducted to investigate the effects of various geometric parameters of the web gap on the SCFs. On this basis, a formula for predicting the SCF in web-gap weld was developed using multiple linear stepwise regression analysis. A fatigue evaluation framework considering the SCF for the web-gap weld were proposed. The result shows the web gap is affected by the joint actions of rotation and displacement, with the web gap of the end floor beam being more prone to fatigue damage. Moreover, the structural mechanics model considering the joint actions of rotation and displacement aligns better with the actual stress characteristics. The proposed SCF prediction formula for the web-gap weld demonstrates an error of less than 5% compared to the FE results. The fatigue damage obtained by the proposed HSS prediction method is consistent with the traditional extrapolation method, hence validating the feasibility and reliability of the proposed approach.

Seismic Performance of Building Structures Using Structural Integral Mechanics Model under the Guidance of Fluid Mechanics

The purpose is to study the core causes of serious collapse of buildings damaged in the earthquake and improve the seismic performance of buildings to reduce casualties. First, the theoretical overview of seismic engineering and related form and requirements of the building structure are deeply studied. Next, the building node structure is deeply analyzed according to the knowledge of fluid mechanics and the basic idea of the finite element method of integral structure. The seismic performance of building structures and the principles and requirements of seismic engineering are analyzed and summarized. It is found that the concrete analysis and description of seismic performance in the research method of fluid mechanics is a steel structure’s bending resistance, deformation and displacement degree, and the bearing degree of external impact force. Further, the model design of the integral structure is carried out through the finite element idea of fluid mechanics. Then, the model simulation experiment is conducted to obtain the curve of the impact force on the building structure, the ultimate bearing capacity of the steel beam joint and the skeleton displacement under the impact. Meanwhile, the degradation of stiffness and strength of node structure during an earthquake is analyzed. Finally, through the simulation results, it is concluded that the maximum displacement between node members under the action of impact force is no more than 300mm, so the model has high impact bearing capacity and strong seismic capacity, and can meet the requirements of seismic fortification. This exploration will be of great significance to the development of building seismic engineering under the guidance of fluid mechanics.

Computational fluid–structure interaction framework for passive feathering and cambering in flapping insect wings

AbstractIn flapping insect wings, veins support flexible wing membranes such that the wings form feathering and cambering motions passively from large elastic deformations. These motions are essentially important in unsteady aerodynamics of insect flapping flight. Hence, the underlying mechanism of this phenomenon is an important issue in studies on insect flight. Systematic parametric studies on strong coupling between a model wing describing these elastic deformations and the surrounding fluid, which is a direct formulation of this phenomenon, will be effective for solving this issue. The purpose of this study is to develop a robust numerical framework for these systematic parametric studies. The proposed framework consists of two novel numerical methods: (1) A fully parallelized solution method using both algebraic splitting and semi‐implicit scheme for monolithic fluid–structure interaction (FSI) equation systems, which is numerically stable for a wide range of properties such as solid‐to‐fluid mass ratios and large body motions, and large elastic deformations. (2) A structural mechanics model for insect flapping wings using pixel modeling (pixel model wing), which is combined with explicit node‐positioning to reduce computational costs significantly in controlling fluid meshes. The validity of the proposed framework is demonstrated for some benchmark problems and a dynamically scaled model incorporating actual insect data. Finally, from a parametric study for the pixel model wing flapped in fluid with a wide range of solid‐to‐fluid mass ratios, we find a FSI mechanism of feathering and cambering motions in flapping insect wings.

Spiral Chiral Metamaterial Structure Shape for Optical Activity Improvements.

We report on a spiral structure suitable for obtaining a large optical response. We constructed a structural mechanics model of the shape of the planar spiral structure when deformed and verified the effectiveness of the model. As a verification structure, we fabricated a large-scale spiral structure that operates in the GHz band by laser processing. Based on the GHz radio wave experiments, a more uniform deformation structure exhibited a higher cross-polarization component. This result suggests that uniform deformation structures can improve circular dichroism. Since large-scale devices enable speedy prototype verification, the obtained knowledge can be exported to miniaturized-scale devices, such as MEMS terahertz metamaterials.

Different effects on thermal conductivity of Ca-based thermochemical energy storage materials for a concentrated solar power plant

Concentrated solar power plant with calcium looping (CSP-CaL) is a promising candidate to overcome the intermittency of solar energy owing to its numerous advantages, such as high energy density, low cost, and widespread availability. The reliable effective thermal conductivity of CaCO3 and CaO particles is crucial on designing reactors and gas–solid heat exchangers for a CSP-CaL plant. This paper investigates the different effects of pore structure, temperature and thermal expansion on effective thermal conductivities of CaCO3 and CaO particles using a reasonable mathematical model which combines the heat transfer and structural mechanics models. The results show that the pore structure has a negative effect on the effective thermal conductivities of both CaCO3 and CaO particles, especially for the large theoretical effective thermal conductivity of particles. In addition, the effective thermal conductivities of both CaCO3 and CaO particles at a low temperature is less than that with the same pore structure at a high temperature owing to their different thermos-physical properties at various temperature. This might lead to a more terrible heat transfer performance during heating process of energy charging process. Finally, the effective thermal conductivities of CaCO3 and CaO particles are also affected by thermal expansion arising from high temperature which can change the pore structure, and result in a 37.65 % and 52.69 % reduction in effective thermal conductivities of both CaCO3 and CaO particles, respectively, during heating process of energy charging process.

Wing Deformation of an Airborne Wind Energy System in Crosswind Flight Using High-Fidelity Fluid–Structure Interaction

Airborne wind energy (AWE) is an emerging technology for the conversion of wind energy into electricity. There are many types of AWE systems, and one of them flies crosswind patterns with a tethered aircraft connected to a generator. The objective is to gain a proper understanding of the unsteady interaction of air and this flexible and dynamic system during operation, which is key to developing viable, large AWE systems. In this work, the effect of wing deformation on an AWE system performing a crosswind flight maneuver was assessed using high-fidelity time-varying fluid–structure interaction simulations. This was performed using a partitioned and explicit approach. A computational structural mechanics (CSM) model of the wing structure was coupled with a computational fluid dynamics (CFD) model of the wing aerodynamics. The Chimera/overset technique combined with an arbitrary Lagrangian–Eulerian (ALE) formulation for mesh deformation has been proven to be a robust approach to simulating the motion and deformation of an airborne wind energy system in CFD simulations. The main finding is that wing deformation in crosswind flights increases the symmetry of the spanwise loading. This property could be used in future designs to increase the efficiency of airborne wind energy systems.

Evaluation of global sensitivity analysis methods for computational structural mechanics problems

Abstract The curse of dimensionality confounds the comprehensive evaluation of computational structural mechanics problems. Adequately capturing complex material behavior and interacting physics phenomenon in models can lead to long run times and memory requirements resulting in the need for substantial computational resources to analyze one scenario for a single set of input parameters. The computational requirements are then compounded when considering the number and range of input parameters spanning material properties, loading, boundary conditions, and model geometry that must be evaluated to characterize behavior, identify dominant parameters, perform uncertainty quantification, and optimize performance. To reduce model dimensionality, global sensitivity analysis (GSA) enables the identification of dominant input parameters for a specific structural performance output. However, many distinct types of GSA methods are available, presenting a challenge when selecting the optimal approach for a specific problem. While substantial documentation is available in the literature providing details on the methodology and derivation of GSA methods, application-based case studies focus on fields such as finance, chemistry, and environmental science. To inform the selection and implementation of a GSA method for structural mechanics problems for a nonexpert user, this article investigates five of the most widespread GSA methods with commonly used structural mechanics methods and models of varying dimensionality and complexity. It is concluded that all methods can identify the most dominant parameters, although with significantly different computational costs and quantitative capabilities. Therefore, method selection is dependent on computational resources, information required from the GSA, and available data.

Mechanics Principle and Implementation Technology of Surrounding Rock Pressure Release in Gob-Side Entry Retaining by Roof Cutting

Improving coal resource mining rates has long been a focus of coal industry research. The gob-side entry retaining by roof cutting (GERRC) is a new coal mining technology that has gained popularity in China due to its high mining rate and safety. Based on the GERRC technology, the precise technical procedure is elaborated, and the fundamental idea of pressure relief is explored through creating a structural mechanics model of the surrounding rock in this paper. The results of mechanical analysis show that the primary mechanism of roof pressure release is to weaken the integrity of the roof, thereby reducing the ultimate bending moment of the rock stratum. In addition, an additional strategy for pressure release is suggested in this research, involving the weakening of the roof rock by the creation of dense pressure-released holes. The results of the engineering field experimentation demonstrate that the dense pressure-released holes can completely replace the conventional blasting technology of the past to achieve the effect of releasing the roof pressure, thus avoiding the use of hazardous and challenging-to-obtain explosives and demonstrating safety, reliability, and feasibility.

Grasping the little things: Modeling and simulation of the electromechanical behavior of individual carbon nanotubes and nanotweezers

Nanotweezers are electromechanical nanosized devices with versatile applications. Due to the challenges for experiments on the nanoscale, the support of models and simulations is crucial to get a better insight into the operational mode of nanotweezers. In the current work, armchair and zigzag individual carbon nanotubes (CNTs) as well as nanotweezers are investigated with regard to their behavior under various prescribed electrostatic loads. The applied model is a combination of the model by Cox and Hill for the geometry, the modified molecular structural mechanics (MSM) model for the covalent bonds and the charge-dipole-model by Mayer for the electric field. Compared to the models based on the solution of the Schrdinger equation, the computational cost of the MSM model is much lower. A weak coupling is given between the mechanical and the electrical field through the application of the Coulomb forces on the mechanical model. The finite element software ABAQUS was used for the numerical simulation. It was shown that (i) the resulting strains and closing gaps are nearly identical for armchair and zigzag CNTs with the same diameter and that (ii) an increase in CNT length leads to greater strains for individual CNT and narrower closing gaps between the arms of the nanotweezers.

Overburden Deformation Rule in Super High Seam Fully Mechanized Caving Mining of Thick Unconsolidated Stratum

It is urgent for westward coal mine development to control surrounding rock of thick unconsolidated stratum, thin basement rock, and super high seam under geological conditions. Studying surrounding rock deformation control mechanism under special geological conditions in western regions is of practical guiding significance for the implementation of China’s energy strategy in western regions, with special mining geological conditions of the experimental mine as the background, deformation rule, failure characteristic, and stress distribution characteristic of surrounding rock in fully mechanized caving mining of thick unconsolidated stratum. By establishing the structural mechanics model of “sidestepped rock beam,” the stability criterion is determined. The horizontal displacement of surrounding rock in the middle of the working face is small, and the displacement at both ends is large. After the mining of the working face, an “O” ring appears on the main roof. The ring extends outward with the excavation, reaches the maximum at the initial weighting, and its displacement decreases from inside to outside. Finally, through theoretical analysis, experimental research, numerical calculation, and field observation, the thin bedrock and ultra-high coal seam are systematically analyzed, and its deformation and failure mechanism is revealed. Relevant research findings are successfully implemented on the scene and effectively ensured safety, high yield, and high efficiency of the mine.

Multi-scale modeling of an atomic force microscope tip for the study of frictional properties and oscillation behavior

In this paper, the vibrational behavior of the atomic force microscope (AFM) on a graphene sheet sample was analyzed using a multi-scale model. The cantilever and silicone tip base were simulated using continuum mechanics and finite element modeling, while the tip apex was modeled using Tersoff potential and structural mechanics modeling. The modified Morse potential was used to model the single-layer graphene, and the Lennard-jones potential was employed as nonlinear springs to model the interactions between the graphene layers and the tip-sample. In addition, the contact behavior between the tip and graphene was investigated by measuring the friction force during the movement of the tip on the graphene sheet, and the results were compared to those obtained from a molecular dynamics simulation and an experimental test. The friction force between the tip and graphene increased by enhancing the tip radius and the contact surface between the tip and the sample. With the initial distance displacement of the tip from the sample, two curves of the tip oscillation amplitude variations and the tip oscillation and excitation vibration phase shift were plotted. In conclusion, the results of the present multi-scale model are compared with those of the MD simulation and demonstrate the strong correlation between the proposed model and the MD model.

Mechanics Informed Neutron Noise Monitoring to Perform Remote Condition Assessment for Reactor Vessel Internals

Abstract The use of neutron noise analysis in pressurized water reactors to detect and diagnose degradation represents the practice of pro-active structural health monitoring for reactor vessel internals. Recent enhancements to this remote condition monitoring and diagnostic computational framework quantify the sensitivity of the structural dynamics to different degradation scenarios. This methodology leverages benchmarked computational structural mechanics models and machine learning methods to enhance the interpretability of neutron noise measurement results. The novelty of the methodology lies not in the particular technologies and algorithms but our amalgamation into a holistic computational framework for structural health monitoring. Recent experience revealed the successful deployment of this methodology to pro-actively diagnose different degradation scenarios, thus enabling prognostic asset management for reactor structures.

A unified method for in-plane vibration analysis of double-beam systems with translational springs

Double-beam structures with many translational springs are a class of significant engineering structures, which have been widely used in civil, aerospace, and mechanical engineering. The dynamic characteristics of such structures is significant to their structural design, vibration abatement and condition assessment. Since the motion differential equation of a double-beam system is a system of complex fourth-order variable coefficient partial differential equations. The existing analytical methods either need to simplify the structural mechanics model or make some prior assumptions about the form of the solution of the equation, which is convenient for the simplification and solution of the equation, and finally reduces the universality of the whole analysis process, and has many limitations in the practical application. An alternative solution is the finite element method, but it can only give an approximate solution to distributed parameter systems. In view of this, this article developed a unified approach for the free vibration of the double-beam structures by employing the dynamic stiffness method (DSM), which has no restrictions on the geometric characteristics and boundary conditions of the structure, and can obtain the exact dynamic characteristics of the system without any approximation. The correctness of the proposed method is validated by comparison with literatures and the finite element solutions. Finally, a comprehensive parametric study is performed to investigate the influence of key parameters on modal frequencies and mode shapes.

Control Techniques for Gob-Side Entry Driving in an Extra-Thick Coal Seam with the Influence of Upper Residual Coal Pillar: A Case Study

In multi-seam mining, the residual coal pillar (RCP) in the upper gob has an important influence on the layout of the roadway in the lower coal seam. At present, few papers have studied the characteristics of the surrounding rock of gob-side entry driving (GED) with different coal pillar widths under the influence of RCP. This research contributes to improving the recovery rate of the extra-thick coal seam under this condition. The main research contents were as follows: (1) The mechanical parameters of the rock and coal mass were obtained using laboratory experiments coupled with Roclab software. These parameters were substituted into the established main roof structure mechanics model to derive the breakage position of the main roof with the influence of RCP, and the rationality of the calculation results was verified by borehole-scoping. (2) Based on numerical simulation, the evolution laws of the lateral abutment stress in the lower working face at different relative distances to the RCP were studied. FLAC3D was used to study the whole space-time evolution law of deviatoric stress and plastic zone of GED during driving and retreating periods with various coal pillar widths under the influence of RCP. (3) The plasticization factor P was introduced to quantify the evolution of the plastic zone in different subdivisions of the roadway surrounding rock, so as to better evaluate the bearing performance of the surrounding rock, which enabled a more effective determination of the reasonable coal pillar width. The field application results showed that it was feasible to set up the gob-side entry with an 8 m coal pillar below the RCP. The targeted support techniques with an 8 m coal pillar could effectively control the surrounding rock deformation.

Design and modeling of a graphene-based composite structure optical pressure sensor.

In this paper, a novel graphene-based composite structure optical pressure sensor is designed and built with the aid of modeling. A PDMS force-sensitive structural mechanics model is established to optimize the size of the pyramid array distributed on the PDMS layer so that to support high levels of sensitivity and stability. Meanwhile, a graphene waveguide optical model is established to obtain the optimized interference length (L), arm spacing (H) and core width (W), with the objectives of advanced sensitivity, low propagation loss, high resolution. The experimental results show that the pressure sensitivity of the proposed sensor is 17.86 nm/kPa and the maximum pressure that can be detected is 3.40 kPa, which is consistent with the theoretical analysis and verifies the feasibility of the design, also the modeling methods of the graphene-based composite structure optical pressure sensor.

Intelligent structural design of shear wall residence using physics‐enhanced generative adversarial networks

AbstractIntelligent structural design using generative adversarial networks (GANs) is a revolutionary design approach for building structures. Despite its far‐reaching capability, the data quantity and quality may have limited the performance of such a data‐driven network. This study proposes to enhance the objectiveness of training processes by innovatively introducing a surrogate model, Physics Estimator, that informs the generator by appraising the physical behavior of the generated design. Dual loss functions evaluated by a traditional data‐driven discriminator and the Physics Estimator collaboratively foster the physics‐enhanced GAN architecture. We further develop a structural mechanics model to train and optimize the inherent accuracy of the Physics Estimator. The comparative study suggests that the proposed physics‐enhanced GAN can generate structural designs from architectural drawings and specified design conditions 44% better than a data‐driven design method and 90 times faster than a competent engineer.