Stress Calculation Method Research Articles

Data reconstruction at surface in immersed-boundary methods

This work compares interpolation techniques for data reconstruction at the surface in an immersed-boundary method. Three different methods of surface pressure reconstruction based on inverse distances are presented, which are christened as: Inverse Distance Weight (IDW) method, Inverse Distance Weight at Interpolation Point method (IDW-IP) and Inverse Distance Weight based on Upwinding (IDW-Upwind) method. Additionally, shear stress at the immersed surface is determined using two approaches: direct interpolation of velocity gradient at the surface using IDW method, and interpolation of velocity at a point along the surface normal using IDW-IP method. The interpolation methods are verified against analytic solutions of ideal flow past a circular cylinder and subsonic-supersonic inviscid flow in a convergent-divergent nozzle, and validated against laminar flow simulations of Mach 0.5 flow past a NACA0012 airfoil, Mach 2.0 flow past a circular cylinder, and Mach 3.0 flow past a 10∘ ramp. The verification cases show that while the pressure values reconstructed at the surface by the three interpolation methods are very similar for the incompressible flow, the IDW-Upwind method produces the sharpest pressure rise across the normal shock in the convergent-divergent nozzle. Comparisons of the reconstructed surface pressure coefficient (Cp) and skin-friction coefficient (Cf) with values available from literature or ANSYS-Fluent simulations conducted as part of the validation study show good match, but indicate that the reconstructed pressure and shear stress values at the immersed surface has noise, which, however, reduces with grid refinement. Further, the IDW and IDW-Upwind method for pressure reconstruction, and the gradient reconstruction based method for shear stress calculation are shown to produce less noise in computed values. Integrated drag and lift values using the reconstructed surface pressure and shear stress indicate that while the different methods used for pressure reconstruction result in similar values of aerodynamic loads, the gradient-based shear stress calculations result in more accurate load estimation. Finally, one of the interpolation methods (IDW-Upwind) is used to investigate the variation of the surface pressure coefficient with time for a NACA0012 airfoil undergoing non-periodic plunge motion in a Mach 0.2 flow. The computed surface pressure coefficients are correlated with the leading and trailing edge vortices in the flow field.

A rapid stress calculation method for short flexspline harmonic drive

PurposeBecause of the compact structure, short flexspline (FS) harmonic drive (HD) is increasingly used. The stress calculation of FS is very important in design and optimization of HD system. This paper aims to study the stress calculation methods for short FS, based on mechanics analysis and finite element method (FEM).Design/methodology/approachA rapid stress calculation method, based on mechanics analysis, is proposed for the short FS of HD. To verify the stress calculation precision of short FS, a complete finite element model of HD is established. The results of stress and deformation of short FS in different lengths are solved by FEM.FindingsThrough the rapid calculation method, the analytical relationship between circumferential stress and length of cylinder was obtained. And the circumferential stress has proportional relation with the reciprocal of squared length. The FEM results verified that the rapid stress calculation method could obtain accurate results.Research limitations/implicationsThe rapid mechanics analysis method is practiced to evaluate the strength of FS at the design stage of HD. And the complete model of HD could contribute to improving the accuracy of FEM results.Originality/valueThe rapid calculation method is developed based on mechanics analysis method of cylinder and equivalent additional bending moment model, through which the analytical relationship between circumferential stress and length of cylinder was obtained. The complete three-dimensional finite element model of HD takes the stiffness of bearing into consideration, which can be used in the numerical simulation in the future work to improve the accuracy.

Design of a CFD-DEM-based method for mechanical stress calculation and its application to glass bead-enhanced cultivations of filamentous Lentzea aerocolonigenes

The production of chemical and pharmaceutical substances by filamentous microorganisms is a wide and challenging field of study. The morphology of filamentous microorganisms, which can vary between loose mycelia and dense pellets, is influenced by process parameters like mechanical stress. The addition of glass particles of different sizes (0.2-2.1 mm) on the cultivation of Lentzea aerocolonigenes pellets was investigated. The glass bead-induced mechanical stress is made responsible for the increased product concentration of rebeccamycin. By coupling the discrete element method (DEM) with the computational fluid dynamics (CFD), a method for the calculation of the mechanical stress energy was developed and applied on first experimental results. As the mean stress energy was increased, the pellet diameter raised up to a maximum pellet size. This effect was explained by an increased pellet loosening and hence, a better oxygen supply. If the pellets were subject to even higher mean stress energies, the diameter decreased due to the assumed pellet fragmentation. In conclusion, to ensure high product concentrations, an optimal particle induced mechanical stress is necessary, which can be calculated with the developed method and validated with experimental cultivations. In future, this method enables the investigation of other process parameters and a process scale-up.

A Semi-Supervised Meta-Heuristic Shell Form-Finding Approach

This paper proposes a general semi-supervised form-finding approach for optimization of shells, where an initial geometry referred to as the “Directive Form (DF)” influences and directs the shape optimization process. The degree of the influence of the DF over the optimization process is controlled by the optimizer algorithm. A normal option involves stronger influence of DF within the early stages of the optimization process and a vanishing effect towards the later stages of the process. The method is illustrated through an example using the artificial intelligence for the optimization process. The selected problem is optimized with particle swarm optimization algorithm in MATLAB. The required structural analysis of the optimization steps is carried out by the finite element software SAP2000 which is linked up with the optimization algorithm via the application programming interface software. The coordinates of the nodes over the surface of the shell are selected as the optimization variables, and the semi-supervised algorithm finds the desired optimal form by minimizing the eccentricity of the forces as the target function. Finally, the paper presents a simple and workable stress calculation method for the optimized shells under gravitational loads.

Application of various shear stress calculation methods with respect to different bridge abutment lengths

When a bridge abutment occupies a significant part of the channel width, the water surface elevation in the upstream of the bridge rises in comparison to that which would occur without the bridge, and this phenomenon is called backwater effect. Due to the backwater in the bridge approach section, several of bed shear stress estimation methods shows an inaccurate result because approach uniform flow might not be assumed depending on the degree of backwater amount. Thus, in this laboratory study, seven widely used shear stress formulas are applied in the bridge approach section subjected to the backwater according to the abutment length, and the results are compared for their validation. For the detailed velocity and turbulence measurements, 3D downlooking Acoustic Doppler Velocimeter (ADV) was used and three different lengths of bridge abutment were constructed in the laboratory to simulate various degree of backwater effect for shear stress calculation in the approach section. The experimental comparison shows that the methods using Reynolds stress and Turbulence Kinetic Energy concept were the most suitable of calculating shear stress in the approach section under severe backwater condition. For other methods leading to inaccurate estimations, the calibrating coefficient is suggeste

Numerical calculation of crack width in prestressed concrete beams with bond-slip effect

Purpose The calculation of the crack width is necessary for the design of prestressed concrete (PC) members. The purpose of this paper is to develop a numerical model based on the bond-slip theory to calculate the crack width in PC beams. Design/methodology/approach Stress calculation method for common reinforcement after beam crack has occurred depends on the difference in the bonding performance between prestressed reinforcement and common reinforcement. A numerical calculation model for determining the crack width in PC beams is developed based on the bond-slip theory, and verified using experimental data. The calculation values obtained by the proposed numerical model and code formulas are compared, and the applicability of the numerical model is evaluated. Findings The theoretical analysis and experimental results verified that the crack width of PC members calculated based on the bond-slip theory in this study is reasonable. Furthermore, the stress calculation method for the common reinforcement is verified. Compared with the model calculation results obtained in this study, the results obtained from code formulas are more conservative. Originality/value The numerical calculation model for crack width proposed in this study can be used by engineers as a reference for calculating the crack width in PC beams to ensure the durability of the PC member.

A Study on Dual-Load-Zone Model of Overlying Strata and Evolution Law of Mining Stress

The changeable structure and movement law of overlying strata are the main contributor to the change of mining stress. Starting from the relevant theory of key stratum and particularly based on the theory of mine ground pressure and strata control, this research proposed a new solution to mining stress problem by establishing a dual-load-zone stratum structural model. Elastic foundation beam theory was used to solve the stress of overlying strata of the two load zones with superposition method, which revised the traditional calculation method of mining stress. The abnormal increase of lead abutment pressure in the mining area was explained effectively, through which the evolution law of mining stress in the case of hard rock was obtained. The results indicate that mining stress experiences a drastic change within the range of 50m ahead of the coal wall due to the collapse of main roof; under the influence of main key stratum and inferior key strata, the influence range of lead abutment pressure is extended up to approximately 120m in the working face; this remarkable increase can be attributed to the excessive length of sagging zone. Results from both the dual-load-zone model experiment and field measurement demonstrate high consistency. The model can predict the influence range of abutment pressure effectively and thus guide the safety production of mining.

基于Schwarz-Christoffel变换的圆形隧道围岩应力分布特征研究

The transformation method with which the surrounding rock stress was mapped to an actual area, has been more and more widely applied to engineering practice, which is of practical guiding significance to the stress calculation method and the study on stability of tunnel surrounding rock. A mechanical model was established for circular tunnels in rock mass, with a mapping function obtained from a unit circle to a polygonal rock mass in the complex plane through the Schwarz-Christoffel transformation method based on the complex variable function theory. Then the solution of the stress distribution in the polygonal rock mass was studied in the complex function field, and subsequently the formulas of complex stress functions Φ(ξ) and φ(ξ) for circular tunnels in irregular rock masses were derived based on the elasticity theory. Finally, the analytical formulas of stress components σ^ρ and σ^θ for any point in the surrounding rock mass were obtained. Analysis of examples indicates that the shape of the rock mass has large influence on the stability of circular tunnels. Here is the maximum stress distribution law for 4 shapes of rock masses: the maximum stresses in the roof and floor of the hexagon, the pentagon, the quadrilateral and the circle decrease in order; otherwise, those in the sidewalls of the circle, the quadrilateral, the pentagon and the hexagon decrease successively.

Maxwell scheme for internal stresses in multiphase composites

The paper focuses on the reformulation of classic Maxwell's (1873) homogenization method for calculation of the residual stresses in matrix composites. For this goal, we equate the far fields produced by a set of inhomogeneities subjected to known eigenstrains and by a fictitious domain with unknown eigenstrain. The effect of interaction between the inhomogeneities is reduced to the calculation of the additional field acting on an inhomogeneity due to the eigenstrains in its neighbors. An explicit formula for residual stresses is derived for the general case of a multiphase composite. The method is illustrated by several examples. The results are compared with available experimental data as well as with predictions provided by the non-interaction approximation (Eshelby solution). It is shown that accounting for interaction can explain many experimentally observed phenomena and is required for adequate quantitative analytical modeling of the residual stresses in matrix composites.

Exploration and practice of integrated control technology for tubing and sucker rod lopsided wearing in directional well

Changqing oil field generally used sucker rod pump. In 2015, the maintenance operations reached 42 thousand times, the cost is about 550 million RMB, the work caused by tubing and sucker rod lopsided wearing accounts for 42.8% of the total. This paper focused on the main factor of lopsided wearing which caused high frequency of maintenance work, a three-dimensional mechanical simulation model of sucker rod string was established based on the analysis of borehole trajectory, rod mechanics; A model for calculation the neutral point of double material composite pipe and steel tubing is carried out; The calculation method of allowable stress is modified; at the same time, the application conditions of the mature process is standardized, to achieve the integration of technology management. The sucker rod lateral force dynamic distribution and allowable stress calculation method, the sucker rod parameter optimization and real-time warning, optimization of structure and the amount of wear resistant pipe string have been applied in oilfield. Compared with 2015, The number of maintenance operations decreased more than 6000 wells, operation frequency by 0.99 times / year - wells decreased to 0.85 times / year - wells, which is composed of 14 thousand and 500 well tube and rod failure wells decreased to 13 thousand and 300 wells, decreased 8%, annual cost savings of nearly 60 million RMB. It will have important guiding significance to prolong the pump checking period and cost control.

Interpretation of coarse effect in simple shear behavior of binary sand-gravel mixture by DEM with authentic particle shape

The sand-gravel mixture is a binary geotechnical material widely used in construction. Its shear behavior is a significant factor influencing the relevant structure safety or slope stability. In this study, a large-scale direct simple shear test was used to study the effect of gravel content on the shear behavior of the mixture. From the experimental results, macro-mechanical properties of the mixture were acquired with various gravel contents and compression stresses. However, the deeper understanding of the shear behavior of the mixture requires a profound microscopic investigation on the specimens. Based on the experimental tests, a series of three dimensional (3D) discrete element model (DEM) analyses of simple shear tests were carried out. The 3D DEM analysis results agree well with the experimental results. The particle generation process and shear stress calculation method have been improved in this model. Moreover, the gravel particle with authentic particle shape scanned by CT system was used in the simulation. The load transformation of the contact force and the evolution of the force network automatically recorded by the DEM program contribute to further understanding the significant role of the gravel content. In summary, both the micro- and macroscopic analyses were utilized to investigate the shear behavior of the sand-gravel mixture. The findings acquired from this study are expected to help researchers to better understand the role of the gravel content in the shear behavior of sand-gravel mixture and the particle-to-particle interaction mechanism.

Design principle of active load spectrum for shafting components in wheel hub reducer of electric vehicle

Design principle of active load spectrum is proposed for the lightweight design of shafting components. The characteristics of fatigue and the strengthening effect of low-amplitude load are conducted according to the material properties of the shafting components. The stress–life curve and three-dimensional surface of low-amplitude strengthening load are established for the life calculation of shafting components. Fast calculation method of working stress for variable size of shafting components is obtained considering the road cycle in Shanghai, the load spectrum is extrapolated, the torque working condition which is equivalent to load spectrum of 3000 km is achieved, and the fatigue damage and strengthening proportion of working stress spectrum of shafting components are adjusted, finally the minimum size of shafting components is designed to meet the requirement of service life. The design principle of active load spectrum can provide a new idea for the lightweight design of automotive components.

Accurate calculation and measurement method for elongation of pre-stressed strand of Bridges

In the pre-stressed construction of bridge strands, tension stress is used as the control and strand elongation is used as the calibration and the elongation of strands directly affects the performance of the bridge structure. So, it must be very precise. In actual construction, due to inadequate grasp of basic theory by technicians, improper measurement methods or inaccurate selection of calculation formulas, neglecting the relationship between the actual elongation value and the tool/job clip withdrawal amount, resulting in the deviation between the actual measured value and the theoretical design value is beyond the standard, which is very unfavorable to the quality of the engineering structure. This article starts with the basic science theory, through numerical calculation and theoretical analysis, explains the work stress compensation retracting amount of the Work anchor and tool anchor, and the compensation stress calculation method due to the stress loss caused by the retraction. It shows the working principle of the pre-stressed equipment, and proposes and validates accurate calculation and measurement method of strand extension.

Control of local stress in semiconductor silicon structures

Residual stress distribution in multilayer semiconductor structure is complicated and has a significant impact on device characteristics and yield, therefore their study is one of the actual tasks of modern device engineering. Purpose of the present work was to develop methods of estimation of actual residual stress distribution at the whole area of semiconductor structure and its elements as well.The estimation of residual stress distribution at the area of semiconductor structure was carried out on the basis of determining of local deformation of some areas of the structure by Makyoh topography. This method is based on consequent measurements of intensity of Makyoh image elements of the structure along the chosen direction followed by calculation of micro-geometrical profile and curvature radius.The estimation of residual stress of topological elements Si–SiO system was carried out by means of calculation of interference pictures obtained in a film-substrate gap after separating of film edge from substrate along open window perimeter.Analytical expressions relating semiconductor structure image characteristics with their deformation were developed by means of finite elements method. The expressions allow determining of local residual stress of chosen area of the structure. The examples of stress calculations in real structures are given.Proposed residual stress calculation methods allow to take into consideration character and curvature form of substrate, and also to estimate their magnitude in real topological elements of semiconductor circuits.

Modeling of Reactor Dry Protection Stressed-Strain State Taking into Account Temperature and Radiation Exposure

The paper proposes the method of stress calculation in three-layer protecting structures of nuclear reactors under thermal and radiation effects. We consider the case of a plane deformed state. One-dimensional axisymmetric finite elements are used. The effect of indirect material heterogeneity on the stress-strain state of the structure is investigated.

Mine Size Effects on Coal Pillar Stress and Their Application for Partial Extraction

Coal is a nonrenewable resource. Hence, it is important to improve the coal recovery ratio and ensure the stability of coal mines for sustainable development of mining cities. Partial extraction techniques, such as strip pillar mining or room-and-pillar mining, are efficient methods to extract coal. Pillar stress is a critical property for pillar design and for the assessment of mine stability after partial extraction. Current pillar stress calculation methods can sometimes overestimate the pillar stress and unnecessarily large coal pillars may be left underground, which leads to a waste of coal resources. In this paper, the size effects of mining activity on the maximum vertical pillar stress were investigated using numerical simulations. Both strip pillar mining and room-and-pillar mining were considered as possible mining scenarios at different mining depths. The results show that the maximum pillar stress of a mine is primarily controlled by four factors: the mine size to mining depth ratio, the mining width to pillar width ratio, the overburden elastic modulus, and the mining depth. The maximum pillar stress of a mine gradually increases to an ultimate value as the mine size increases. Simplified formulas and methodology have been derived for stress calculations under consideration of mine size effects and, therefore, can reduce the waste of coal resources from the overestimation of pillar stress.

The Calculation of Negative Bias Illumination Stress-Induced Instability of Amorphous InGaZnO Thin-Film Transistors for Instability-Aware Design

We propose a systematic calculation method for negative bias illumination stress (NBIS)-induced instabilities in amorphous InGaZnO thin-film transistors (TFTs). The proposed method is based on activation energy window (AEW) in subgap energy range, and it can reproduce the NBIS time evolution of ${I}$ – ${V}$ characteristics without long-term stress test. Furthermore, it quantitatively explains the effect of oxygen content on the NBIS instability. The AEW, which is employed for emulating the oxygen vacancy ionization, peroxide formation, and hole trapping, has the order of magnitude of 1016–1017 cm−3 for the bias stress of −20 V and the commercial LED backlight of 300 cd/m2. The proposed method is expected to play such an important role in the instability awareness of amorphous oxide TFTs.

A simplified method for calculating surface stress of thick walled cylinder based on numerical calculation method

The maximum compound stress in the thick wall cylinder is usually the key factor that causes the thick wall cylinder to crack. The existing calculation method for stress–strain under thermo-mechanical impact in thick wall cylinder is suitable for stress analysis in the thermo-elastic range. However, the compound stress of the thick wall cylinder under the thermoplastic condition cannot be well analyzed. In this paper, a method to calculate the compound stress of the thick wall cylinder under the effect of thermal–mechanical impact is proposed, based on the finite difference method and the ideal elastic–plastic model and the Mises yield criterion. This method solves the problem of the compound stress calculation to the tube wall under the thermoplastic condition, which change as a result of the combined effect of thermo-mechanical impact. The compound stress in the wall close to the bore surface at different times during shooting is calculated, taking the firing process of a gun as an example. The calculation results well explain the cause of the formation of the crack and the distribution characteristics of the crack in the bore surface.

Shear lag analysis of I‐shaped structural members

SummaryI‐shaped structural members are widely used in civil engineering, mainly including I‐shaped shear walls and beams. In order to establish a unified method for analyzing the shear lag effect of I‐shaped structural members, first, the shear lag warping displacement is assumed as a quadratic parabola, and the additional deflection caused by shear lag effect is taken as the generalized displacement. The principle of minimum potential energy is used to establish the calculation method of the normal stress and deflection of I‐shaped shear walls and beams with 3 boundaries, which consider the self‐balancing conditions of shear lag warping stress. Then numerical examples are used to verify the accuracy of the calculation method; meanwhile, the shear lag characteristics of I‐shaped structural members are investigated. At last, the calculation method is used to study the shear lag effect of T‐shaped structural members. Studies show that the analytical results obtained by the calculation method are close to the finite element method results, and the calculation method can predict the flange normal stresses and negative shear lag phenomenon well. Moreover, the calculation method in this paper can be used to analyze the shear lag of T‐shaped structural members.

Analytical model for the load transmission law of rock bolt subjected to open and sliding joint displacements

The present study focuses on the load transmission law along the rock bolt and the efficacy for different anchored conditions. Shear displacement along the joint face is considered on the basis of traditional rock bolt stress calculation method with regard to joint open displacement. Combining the elastic foundation beam model and the rock bolt pull-out model, an analytical solution for the stress distribution along the rock bolt through a single joint face is derived. The performance of the proposed analytical solution is compared with an experimental result and a previous study. In addition, joint displacement, joint location, and dip angle of the joint face are set as variables to further explore the corresponding anchored effect. The results indicate that larger joint displacement along the joint face tend to cause a distinct increase of the shear and compressive stress along the rock bolt. When the joint face moves inward, the interaction force between the rock bolt and the surrounding rock mass decreases, suggesting that the strength of the rock bolt is not taken full use. Moreover, for a certain joint displacement and joint location, larger anchored angle between the rock bolt and the joint face contributes to better reinforcement effect.