Dynamic Stress Analysis Research Articles

3D nonlinear variable strain-rate-dependent-order fractional thermoviscoelastic dynamic stress investigation and vibration of thick transversely graded rotating annular plates/discs

In the present article, the idea of using the variable-order fractional-derivative thermoviscoelastic constitutive laws in dynamic stress and vibration analysis of the engineering structures, the required implementation backgrounds, and the relevant numerical solution procedures are investigated for the first time. In this regard, dynamic 3D stress and displacement fields and radial/transverse vibrations of transversely graded viscoelastic spinning thick plates/discs exposed to sudden thermoelastic loads are investigated. Instead of using the approximate plate theories, the exact thermoviscoelasticity theory is employed in the development of the governing equations. Since the variable fractional order is dependent on the localized deformation rates, the resulting thermoviscoelastic integro-differential equations are nonlinear. These equations are solved by utilizing a combination of the second-order backward/central/forward finite difference discretization of the spatial and time domains, numerical evaluation and updating of the Caputo-type fractional derivatives, updating the growing number of terms of the governing equations, and Picard's iterations. Various edge conditions are considered. Finally, comprehensive sensitivity analyses and various 3D plots are presented and discussed regarding the effects of the variable fractional order of the constitutive law, time variations of the nonuniformly distributed transverse loads, and edge conditions on the distributions and damping of the resulting displacement and stress components.

A Dynamic Model with Friction for Comprehensive Tubular-Stress Analysis

Summary A new model technique is described for comprehensive dynamic stress and displacement analysis of wellbore-completion tubulars, including friction loads with history. A dynamic model of tubing forces is necessary to predict local pipe velocity, which in turn determines the magnitude and direction of localized frictional contact. By tracking dynamic changes in axial force starting from the initial running state, a complete load history can be simulated for the installed casing and tubing through the service life of the well. The dynamic friction model subdivides the casing or tubing string joint by joint and uses an elastic pipe-momentum balance. Pipe velocity is related to axial force by the elasticity equation. Dynamically determined velocity is necessary to predict the magnitude and orientation of local node-friction vectors. Damping for the dynamic analysis is provided by annular fluid viscosity. The elastic equations are solved as a set of algebraic equations in terms of past and future values of pipe axial force and velocity. Key model inputs such as pressure, temperature, fluid, and wellbore-friction coefficients can be changed at each successive load step. Running loads and packer setting with slackoff or pickup loads determine the initial tubing-stress configuration. Given the initial configuration, each subsequent load case is calculated starting from the prior load and resultant friction state, allowing for full history dependence. The surface velocity profile of running individual stands is a key input. Unexpected magnitudes of downhole transfer of surface load are demonstrated. A change in the operation-load sequence is shown to produce significant differences in tubular axial loads, indicating that special attention to load history should be considered when performing a tubular-stress analysis. For slackoff, overpull, or packer-setting events, the model can track dynamic load response at downhole points, such as a packer or cement top. An example well with a deviated profile and a planned sequence of life-cycle operations including stimulation, production, and shut-in was simulated for a variety of load sequences. The model has been validated against field data using the actual hookload plot during installation of a single-trip, multizone intelligent completion in an offshore highly deviated extended-reach-drilling (ERD) well. Example calculations are given for a high-pressure/high-temperature (HP/HT) subsea well and a horizontal unconventional well. The dynamic friction model allows for the seamless integration of running loads with friction into a fully sequential stress analysis of subsequent well life-cycle loads for landed completion strings. Although dynamic analysis has been extensively applied to complex drilling phenomena such as drillstring vibration or bottomhole-assembly design, current industry models for completion tubulars such as casing and tubing separate the installation state from the in-service life envelope or attempt to solve the problem with a static analysis. This represents a critical deficiency in the current industry state of the art for completion tubulars, which the present work proposed herein strives to address. From a comparison with appropriate static analytic solutions and industry-standard drag-and stress-models, dynamics were found to affect friction-force directions and magnitudes, suggesting that tubular dynamics cannot be neglected.

Development of ABAQUS UEL/VUEL subroutines for scaled boundary finite element method for general static and dynamic stress analyses

User-defined element subroutines (UEL and VUEL) in Fortran are developed in ABAQUS, to implement the Scaled Boundary Finite Element Method (SBFEM), for general static and elastodynamic stress analyses of solids. The purposes are twofold: to increase the ease-of-use and acceptability of this relatively new numerical method; and to combine advantages of both the SBFEM and ABAQUS, namely, the former's semi-analytical solutions and flexibility in domain discretization, and the latter's powerful linear and nonlinear solvers and pre/post-processing modules, for modelling complicated problems with higher accuracy and fewer degrees of freedom than the traditional FEM. Using the developed UEL and VUEL, a few 2D and 3D problems, including homogeneous solids with and without cracks, composites with inclusions of random shapes, XCT-image converted concrete mesoscale models, are simulated. The results are compared favourably with FEM simulations in terms of accuracy and degrees of freedom.

A pore water pressure model calibration based on in-situ test results

This paper proposes a procedure for the calibration of a simplified pore water pressure model implemented in 1D effective stress dynamic analyses. The calibration procedure is based on the cyclic strength of the soils as quantified using empirical correlations with in-situ tests, CPT and SPT. Specific relationships have been directly defined among the parameters of the pore water pressure model and the results of in-situ tests. All the steps for the definition of these relationships are described in detail.The proposed calibration procedure has been used to simulate the seismic response of two well-documented reclaimed sites where widespread liquefaction occurred: Port Island, in Kobe (Japan) and Treasure Island in California (US), struck by the 1995 Kobe and the 1989 Loma Prieta earthquakes, respectively. The results of the analyses have been compared to the actual site response as recorded by downhole acceleration arrays, showing that the proposed approach leads to a good estimate of the site response. Guidelines for calibration of the proposed model are finally provided, and the advantages and limitations of its use are discussed in detail.

Linear wave-induced dynamic structural stress analysis of a 2D semi-flexible closed fish cage

Closed fish cages in the sea are proposed as a new concept in marine aquaculture, replacing the conventional net cages in order to meet ecological challenges related to fish lice and escapes. A closed fish cage can be compared to a floating tank structure with an internal free surface. Several types of closed cages have been suggested, and they are categorised according to structural properties as flexible membrane structures (fabric), semi-flexible structures (glass fibre) and rigid structures (steel or concrete). To be able to develop safe and reliable structures, more knowledge is required on the seakeeping behaviour of closed cages in waves and the structural response to the wave loads. This paper builds on a theory presented in Strand and Faltinsen (2019) on the linear wave loads on a 2D closed flexible fish cage. A modelling error has been found in Strand and Faltinsen (2019), however, all the main conclusions are in hold. The error has been corrected in the model in the present paper. The present paper extends the model to include bending in the structural model to be able to handle semi-flexible structures where bending stiffness is significant. In this paper, the linear theory of a 2D semi-flexible closed fish cage in waves is developed and analysed to investigate the structural response of the semi-flexible closed cage in waves. We have compared a quasi-static analysis with a fully coupled hydroelastic analysis to investigate if it is a valid and conservative assumption to assume that the stresses in the structure can be assumed quasi-static. If a hydroelastic analysis is necessary or not, is dependent on the stiffness of the structure. We have investigated what happens with the stress in the curved beam part of the closed fish cage for increasing and decreasing stiffness relative to a reference composite structure. One stiffer and two softer cases have been analysed. One major concern for the structural stresses in a closed cage is the effect of sloshing. Sloshing is internal wave motion inside the cage and have multiple resonance periods. The results indicate that to use the quasi-static assumption in structural stress calculation is conservative within the given frequency range for all examined stiffnesses and frequencies, except the frequencies very close to the second sloshing frequency. Close to the second sloshing frequency for all the examined stiffnesses, a localised peak can be observed in the coupled hydroelastic results. The second sloshing frequency is a frequency connected to a symmetric sloshing mode. Rigid body motion is not affected at the symmetric sloshing frequency for an assumed rigid structure, and are therefore also not visible in the stress results from the quasi-static analysis. The structural stress in irregular sea was calculated. These results show no indication of increased stress close to the second sloshing frequency. However, this is not a surprising result since the stress peak is very localised in frequency, and the accumulated effect on the stress standard deviation is therefore small.

Seismic performance of block-type quay walls with liquefiable calcareous sand backfill

Block-type gravity quay walls are widely used in remote oceanic regions due to their cost and construction efficiency, where backfill and foundation soil often consist of liquefiable calcareous coral sand. The lack of connection between blocks and hence structure integrity can result in poor seismic performance of block-type quay walls, especially in liquefiable soil. Based on laboratory element tests on calcareous sand, centrifuge shaking table test, and high-fidelity numerical simulation, this paper investigates the seismic performance of block-type quay walls with liquefiable calcareous sand backfill. Undrained cyclic torsional shear tests are conducted on South China Sea calcareous coral sand to determine its dynamic properties, which are used to calibrate the unified plasticity model for large post-liquefaction shear deformation of sand. A centrifuge shaking table test is conducted to obtain the basic physical seismic response of a block-type quay wall in liquefiable calcareous backfill sand. Utilizing the understanding from laboratory tests, fully coupled dynamic effective stress analysis using the calibrated constitutive model is conducted. The influence of seismic input, quay wall structure, and backfill sand properties on the seismic response of the quay wall is analyzed. Input motion intensity and frequency are shown to be influential to the seismic response of the quay wall. Increase of backfill soil density, permeability, and block to block connection can significantly improve the seismic performance of the quay wall.

The dynamic stress analysis of an infinite piezoelectric material strip with a circular cavity

The scattering of SH guided wave by a circular cavity in an infinite piezoelectric material strip is analyzed by using “mirror image method” and guided wave theory, and the analytical expressions of guided wave function satisfying stress free and electric insulation conditions on the upper and lower horizontal boundaries of the strip domain are obtained. The analytical expression of the scattered wave around a circular cavity is constructed by using the method of multiple mirror superposition and wave function expansion. The integral equations are established and solved by the boundary conditions of the circular cavity, and the analytical expressions of the dynamic stress concentration factor and the electric field intensity factor are obtained. The effects of incident wave frequency, dielectric parameters and circular cavity position on electric field intensity concentration factor (EFICF) and dynamic stress concentration factor (DSCF) are analyzed by numerical examples. Besides, the analytical solutions obtained in this article are compared with the finite element solutions and the analytical solutions in previous literature to verify the correctness and accuracy of the conclusions in this article. And the conclusions in this article are of great reference value to the selection and ultrasonic nondestructive testing of anti-seismic materials.

Dynamic Stress Analysis of a Circular‐Lined Tunnel in Composite Strata‐SH Wave Incidence

It is necessary to study the problem of seismic wave scattering in composite stratum for tunnel engineering because the existence of composite strata will make the stress of tunnels more complicated during earthquakes. In this thesis, a series solution of the scattering wave field of the composite strata and lining is obtained using the complex function method. According to the stress and displacement boundary conditions between the composite stratum and the lining, a series of equations are established and are solved by means of Fourier transformation and finite term truncation, and the calculation errors are also discussed. Through programming calculations, the dynamic stress concentration factor (DSCF) of circular tunnels in the two types of composite strata, “hard‐over‐soft” and “soft‐over‐hard,” is analyzed when SH waves propagate, and certain conclusions on the scattering of SH waves that are distinguished from the case of single homogeneous layers are reached. The research in this article reveals some phenomena. For the Q345 steel lining in the calculation examples, it is found in this paper that increasing the thickness of the lining is effective to reduce the influence of the DSCF. But, for C30 concrete, increasing the thickness of the lining reduces the DSCF of the outer surface while increasing the DSCF of the inner surface.

Dynamic stress analysis of anisotropic gun barrel under coupled thermo-mechanical loads via finite element method

Abstract This work focused on the stress response of anisotropic 30SiMn2MoVA steel gun barrel under coupled thermo-mechanical loads, namely, the contact pressure and friction of projectile, thermal load and pressure of propellant gas. The effect of temperature on the mechanical properties of gun barrel was considered. Two thermal-displacement coupled finite element models (FEM) were built by ABAQUS software. The first was the interaction model of projectile and barrel which was to calculate the stress of barrel engraved by copper jacket and steel jacket projectile. The results of barrel in the interaction model, as an initial condition, were imported to the second FEM which was applied with thermal load and pressure of propellant gas. The results show that the rifling at chamber throat has the largest stress and circumferential stress under coupled loads. It gives a request that the gun barrel should have the better circumferential mechanical properties. The plastic deformation of the rifling at the chamber throat is observed which indicates that 30SiMn2MoVA gun barrel has a low service life due to the poor mechanical properties.

Vehicle-induced dynamic stress analysis of orthotropic steel decks of cable-stayed bridges

Orthotropic steel deck (OSD) is widely used in long-span cable-stayed bridges, but vehicle-induced dynamic stresses at its deck-to-rib (DTR) joints often make OSD vulnerable to local failure or fatigue damage. This paper presents a framework for vehicle-induced dynamic stress analysis of DTR joints of OSD in a cable-stayed bridge. The multi-scale finite element model of the bridge is first developed using solid elements to simulate DTR joints of OSD interacted with pavement (local model), shell elements to simulate the most vulnerable girder segment (intermediate model), and beam/truss elements to simulate the rest part of the bridge (global model). Road vehicles are modelled as a combination of several rigid bodies connected by a series of springs, dampers and pivots. The vehicle-induced dynamic stress responses at the DTR joints of a long-span cable-stayed bridge are finally computed to assess the effects of bridge dynamics, vehicle dynamics, asphalt pavement temperature, roughness and vehicle velocity. The results show that the dynamically coupled vehicle-bridge system should be considered and that pavement temperature and roughness are two profound factors affecting the stress responses of DTR joints.

Dynamic non-local stress analysis of two collinear semi-permeable mode-I cracks in a piezoelectric medium

This article investigates the dynamic non-local stress analysis of two collinear semi-permeable mode-I cracks in a piezoelectric medium under the harmonic waves by using the generalized Almansi theorem and the Schmidt method. Based on the Fourier transform technique, this problem is formulated into coupled dual integral equations. The dynamic stress and the dynamic electric displacement fields at the crack tips are obtained by solving the derived dual integral equations. Numerical examples are provided to show the effects of the crack length, the distance between the two collinear cracks, the lattice parameter, the electric permittivity of the air inside the crack, and the characteristics of the harmonic wave on the dynamic stress field and the dynamic electric displacement field near the crack tips. The dynamic stress and electric displacement decrease with increasing the distance between two collinear cracks and lattice parameter in a piezoelectric medium. Meanwhile, the dynamic field will impede or enhance crack propagation in piezoelectric medium depending on the circular frequency of the incident wave. Different from the classical solutions, the present solutions exhibit no stress and electric displacement singularities at the crack tips. This work is expected to be helpful for theoretical modeling of piezoelectric medium at nanoscale.

Graphene Oxide and Its Inorganic Composites: Fabrication and Electrorheological Response.

Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the fabrication mechanisms of GO/inorganic composites and their ER response when suspended in a non-conducting medium, including steady shear flow curves, dynamic yield stress, On-Off tests, and dynamic oscillation analysis. Furthermore, the morphologies of these composites, dielectric properties, and sedimentation of the ER fluids are covered.

Design optimization of a diesel engine connecting rod

Rotary motion is generated from a crankshaft’s piston alternating motion using a connecting rod. The engine combustion gases and components motion of inertia exert pressures that induces compressive and tensile stress in the connecting rod respectively [1], [2]. Connecting rods fail due to its overloading, bearing failure, irregular adjustments of the bolts and faulty assembly or fatigue [3]. It is important for connecting rods to be able to withstand the complex high tensile loads that acts on them. As a result, numerous design technology, material selection, working and fatigue test of a connecting rod have been studied and presented [4]. Mechanical properties (such as hardness, tensile strength, rigidity and fatigue resistivity) of the materials used in the manufacture of a connecting rod need vehicles depends on the design of the connecting rod. Failure of connecting rod is attributed to the in availability of much strength needed to hold the load. This can be overcome with the life cycle extended by increasing the strength [5].
 Finite element analysis of connecting rod have been conducted and presented by a lot of researchers. In [6], theoretical and FEA of an IC engine connecting rod was conducted. The result of the analysis obtained shows the causes of failure at the fillet of both ends due to the induced stress. In [7] static FEA for fatigue, deformation and weight optimization of a connecting rod using ANSYS workbench is carried out and presented. From the suggested design changes obtained from the weight optimization result, the failure result is further updated to achieve a better result. In a paper by Bansal, dynamic stress analysis was carried out on a single cylinder four stroke diesel engine connecting rod of Aluminum material using FEA. The optimization was also done under dynamic loading with the boundary conditions and inputs determined from the pressure-volume diagram and engine specification chart respectively are carried out with different meshing size for an accurate result. [8].
 FEA is the commonly employed computational tool for testing and modifying engineering structures within certain design limit. It involves diving in to small units known as ‘elements’ for static and dynamic analysis of simple to complex model under different design constraints. Further investigation can also be done to improve the design for optimal performance and lifespan with regards to design failure [9].
 Many kinds of literature have worked on weight optimization. Gaikwad in his paper modifies a roller conveyor by performing weight optimization after carrying out static analysis on the roller conveyor [10] In another paper by [10] the weight of a roller conveyor was reduced thereby saving the materials under specific load constraints using finite element method.
 In this paper shape optimization with target weight reduction rate of 20 to 60% with an interval of 10 under a static loading of 100N. Further analysis for structural optimization is also done to determine a new optimized structure with new deformation and stress values respectively. The analysis is carried out in ANSYS static structural, mechanical solver with a tensile force of 100N acting on its larger end.

Computational fluid dynamic and thermal stress analysis of coatings for high‐temperature corrosion protection of aerospace gas turbine blades

AbstractThe current investigation presents detailed finite‐element simulations of coating stress analysis for a three‐dimensional, three‐layered model of a test sample representing a typical gas turbine component. Structural steel, titanium alloy, and silicon carbide are selected for main inner, middle, and outermost layers respectively. ANSYS is used to conduct three types of analysis—static structural, thermal stress analysis, and also computational fluid dynamic erosion (via ANSYS FLUENT). The specified geometry, which corresponds to corrosion test samples exactly, is discretized using a body‐sizing meshing approach, comprising mainly of tetrahedron cells. Refinements were concentrated at the connection points between the layers to shift the focus toward the static effects dissipated between them. A detailed grid independence study is conducted to confirm the accuracy of the selected mesh densities. The momentum and energy equations were solved, and the viscous heating option was applied to represent the improved thermal physics of heat transfer between the layers of the structures. A discrete phase model (DPM) in ANSYS FLUENT was used, which allows for the injection of continuous uniform air particles onto the model, thereby enabling an option for calculating the corrosion factor caused by hot air injection. Extensive visualization of results is provided. The simulations show that ceramic (silicon carbide) when combined with titanium clearly provide good thermal protection; however, the ceramic coating is susceptible to cracking and the titanium coating layer on its own achieves significant thermal resistance. Higher strains are computed for the two‐layer model than the single layer model (thermal case). However even with titanium only present as a coating the maximum equivalent elastic strain is still dangerously close to the lower edge. Only with the three‐layer combined ceramic and titanium coating model is the maximum equivalent strain pushed deeper towards the core central area. Here the desired effect of restricting high stresses to the strongest region of the gas turbine blade model is achieved, whereas in the other two models, lower strains are produced in the core central zones. Generally, the CFD analysis reveals that maximum erosion rates are confined to a local zone on the upper face of the three‐layer system which is in fact the sacrificial layer (ceramic coating). The titanium is not debonded or damaged which is essential for creating a buffer to the actual blade surface and mitigating penetrative corrosive effects. The present analysis may further be generalized to consider three‐dimensional blade geometries and corrosive chemical reaction effects encountered in gas turbine aero‐engines.

Dynamic Stress Analysis of Multilayered Structure With Radial Gaps of Cylindrical Pressure Vessel Under Plane Strain Conditions

Radial gaps were found in multilayered cylindrical vessels which experience inner explosion accidents in chemical plants in the past few years worldwide. It is necessary to investigate the dynamic response of multilayered structures with radial gaps to ensure the vessel safety. This paper presented a numerical modeling of the dynamic response of a multilayered structure with radial gaps of cylindrical pressure vessel under plane strain conditions by using the ANSYS/ls-dyna package. The effects of the dynamic loading profile and the radial gap height are considered in the investigation. The stress spatial distribution, the stress and the plastic deformation variation curves with time are emphatically analyzed. The results show that the stress variation of the entire loading process can be divided into four stages: the oscillation stage, the yield stage, the fast increase stage, and the redistribution stage. The layer stress distributes discontinuously at the gaps between layers and distributes unevenly in any single layer. The inner layer stress is not always larger than the outer layers' during the whole loading process. The effect of loading profile on the dynamic response is not as obvious as the gap height. As the gap height increases, the stress oscillation stage is suppressed and becomes shorter. While the loading recovers to the operation pressure, the stress and the plastic deformation of inner layers increases and vice versa for the outer layers.

Safety assessment for a shield tunnel in a liquefiable deposit using a practical dynamic effective stress analysis

Shield tunnels are widely constructed throughout urban areas with most of their sections being fully or partially embedded in liquefiable deposits. The possible damage to shield tunnels caused by soil liquefaction should be considered in their seismic design. Thus, this paper proposes a FDM-based analysis method to study this issue. Several dynamic time history analyses were performed for a shield tunnel embedded at different positions in ground with a liquefiable layer. It was found that the liquefied soil behaves like a fluid, and the tunnel uplifts due to buoyancy if the tunnel is fully embedded in a liquefied soil deposit. However, if the tunnel is only partially embedded in the liquefied deposit, with its top or bottom section in a non-liquefied deposit, the interaction behavior is quite complex and differs from that of a tunnel fully embedded in liquefied soil. To check the safety of the lining, the internal forces of the lining were monitored and compared with its strength curves throughout the shaking history. The proposed framework can be used as a reference for a practical engineer to consider the dynamic behavior of a shield tunnel in a liquefiable deposit.

The dynamic stress analysis of a piezoelectric bi-material strip with an inclusion

With the aid of guided wave theory, the scattering of SH guided wave by a circular inclusion in an infinite piezoelectric bi-material strip is considered. Firstly, a harmonic out-of-plane line source force is applied on the vertical boundary of a strip. By the means of the repeated image superposition method, Green’s function is constructed, which satisfies the stress-free and electric insulation conditions on the upper and lower horizontal boundaries. Secondly, the bi-material media is divided into two parts along the vertical boundary, and a pair of anti-plane forces and a pair of in-plane electric fields are applied on the vertical boundary. According to boundary conditions, the first kind of Fredholm integral equations are established by ‘the conjunction method’, then the integral equations are reduced to the algebraic equations by effective truncation. Finally, the dynamic stress concentration factor (DSCF) and electric field intensity concentration factor (EFICF) around the circular inclusion are calculated, besides, the influences of the order of guided wave, the position of the inclusion, the combination of parameters, etc. on the DSCF and EFICF are discussed.

Dynamic load and stress analysis of a large horizontal axis wind turbine using full scale fluid-structure interaction simulation

A dynamic load and stress analysis of a wind turbine is carried out using transient fluid-structure interaction simulations. On the structural side, the three 50 m long commercial glass-fiber epoxy blades are modelled using shell elements, accurately including the properties of the composite materials. On the fluid side, a hexahedral mesh is obtained for every blade and for the hub of the machine. These meshes are then overlaid to a structured background mesh through an overset technique. The displacements prescribed by the structural solver are imposed on top of the rigid rotation of the turbine. The atmospheric boundary layer (ABL) is included using the k-epsilon turbulence model. The computational fluid dynamics (CFD) and computational solid mechanics (CSM) solvers are strongly coupled using an in-house code. The transient evolution of loads, stresses and displacements on each blade is monitored throughout the simulated time. The ABL induces oscillating axial displacements in the outboard region of the blade. Furthermore, the influence of gravity on the structure is accounted for and investigated, showing that it largely affects the tangential displacement of the blade. The oscillating deformations lead to sensible differences in the torque provided by each blade during its rotation.

Evaluation of gap influence on the dynamic response behavior of pump-turbine runner

Purpose The gaps between runner and nearby structures play an important role in the dynamic response of runner, especially for pump-turbines. This paper aims to evaluate the gap influence on the added mass and dynamic stress of pump-turbine runner and provide an improved method to predict the resonance of runner. Design/methodology/approach Acoustic-structural coupling method was used to evaluate the added mass factors of a reduced scale pump-turbine with different axial and radial gap size between runner and nearby rigid walls. Improved one-way fluid-structural interaction (FSI) simulation was used to calculate the dynamic stress of the runner, which takes into account fluid added mass effect. The time-dependent hydraulic forces on the runner surfaces that were obtained from unsteady CFD simulation were transferred to the runner structure as a boundary condition, by using mesh-matching algorithm at the FSI surfaces. Findings The results show that the added mass factors increase as the gap size decreases. The axial gaps have greater influence on the added mass factors for the in-phase (IP) modes than the counter-phase (CP) and crown-dominant (CD) modes, while the CP and CD modes are very sensitive to the radial gaps. The largest added mass factor is observed in (2 + 4)ND-CP mode (resonance mode). The results reveal that the transient structural dynamic stress analysis, with the consideration of gaps and fluid added mass, can accurately predict the resonance phenomenon. Resonance curve of the pump-turbine has been obtained which agrees well with the test result. The gap fluid has great influence on the resonance condition, while for non-resonance operating points, the effect of gaps on the dynamic stress amplitude is quite small. Originality/value This paper provides an accurate method to analyze the dynamic response during runner design stage for safety assessment. The resonance curve prediction has more significance than previous methods which predict the resonance of runner by modal or harmonic analysis.

Dynamic stress analysis for fatigue damage prognosis of long-span bridges

For fatigue damage prognosis of a long-span steel bridge, the dynamic stress analysis of critical structural components of the bridge under the future dynamic vehicle loading is essential. This paper thus presents a framework of dynamic stress analysis for fatigue damage prognosis of long-span steel bridges under the future dynamic vehicle loading. The multi-scale finite element (FE) model of the bridge is first developed using shell/plate elements to simulate the critical structural components (local models) and using beam/truss elements to simulate the rest part of the bridge (global model). With the appropriate coupling of the global and local models, the multi-scale FE model can accurately capture simultaneously not only the global behavior in terms of displacement and acceleration but also the local behavior in terms of stress and strain. A vehicle traffic load model is then developed for forecasting the future vehicle loading based on the recorded weigh-in-motion (WIM) data and using the agent-based traffic flow microsimulation. The forecasted future vehicle loading is finally applied on the multi-scale model of a real long-span cable-stayed bridge for dynamic stress analysis and fatigue damage prognosis. The obtained results show that the proposed framework is effective and accurate for dynamic stress analysis and fatigue damage prognosis.