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In Japan, the disastrous effects of the 2011 Tohoku Earthquake has affected seismic design. Furthermore, there is an increasing need for dynamic nonlinear analysis that can consider large strain levels in assessing the seismic resilience of essential structures such as nuclear power plants. However, the applicability of dynamic nonlinear analysis methods to rock masses has not yet been fully evaluated. Their applicability needs to be confirmed by dynamic phenomena, such as shaking table tests. Herein, as a preliminary step, quasi-static analyses of cyclic direct shear tests were conducted to validate the constitutive model. Soft rock samples with relatively few fractures were used as the testing material. In the tests, the load was applied in multiple steps by increasing the loading amplitude at each step, with a loading frequency of 0.1 Hz. The quasi-static analyses revealed that, although an existing constitutive model generally reproduced the shear load–displacement relationship obtained in the tests from small displacement levels to peak strength, discrepancies emerged beyond peak strength. Therefore, we focused on the post-failure history damping characteristics of the soft rocks and added a damping constant after rock failure to the existing constitutive model. Consequently, the accuracy of the values of the stress history beyond peak strength was improved by more than 10%, and the reproducibility of the shear load–displacement relationship improved. Therefore, the applicability of the improved constitutive model was confirmed for conditions of quasi-static cyclic loading of soft rock with few fractures, from small displacement levels to beyond peak strength. [ABSTRACT FROM AUTHOR]

Abstract In Japan, the disastrous effects of the 2011 Tohoku Earthquake has affected seismic design. Furthermore, there is an increasing need for dynamic nonlinear analysis that can consider large strain levels in assessing the seismic resilience of essential structures such as nuclear power plants. However, the applicability of dynamic nonlinear analysis methods to rock masses has not yet been fully evaluated. Their applicability needs to be confirmed by dynamic phenomena, such as shaking table tests. Herein, as a preliminary step, quasi-static analyses of cyclic direct shear tests were conducted to validate the constitutive model. Soft rock samples with relatively few fractures were used as the testing material. In the tests, the load was applied in multiple steps by increasing the loading amplitude at each step, with a loading frequency of 0.1 Hz. The quasi-static analyses revealed that, although an existing constitutive model generally reproduced the shear load–displacement relationship obtained in the tests from small displacement levels to peak strength, discrepancies emerged beyond peak strength. Therefore, we focused on the post-failure history damping characteristics of the soft rocks and added a damping constant after rock failure to the existing constitutive model. Consequently, the accuracy of the values of the stress history beyond peak strength was improved by more than 10%, and the reproducibility of the shear load–displacement relationship improved. Therefore, the applicability of the improved constitutive model was confirmed for conditions of quasi-static cyclic loading of soft rock with few fractures, from small displacement levels to beyond peak strength.

Marine towing cable serves an important bridge of power and signal transmission between the ship and towed body in the towed seismic cable system. The steady-state equilibrium configuration and natural frequency of towing cable which are valuable for preliminary design will change with different working requirements. In this paper, the steady-state characteristics of marine towing cable are investigated with different towing parameters. Cable length and towing speed have a greater effect on the configuration than other parameters, and the impact of cable weight and cable length is more obvious for the natural frequency. Based on plenty of numerical results, a proper neural network using back-propagation neural network (BPNN) to predict the configuration and natural frequency is introduced and validated. Finally, an approximate equation including the weights and biases of BPNN, which can reduce the calculation cost greatly compared with traditional method, is suggested to obtain the steady-state characteristics of marine towing cable rapidly and accurately. [ABSTRACT FROM AUTHOR]

The air and structural loads of a 5-ton class light helicopter (LH) rotor in a 2.24 g pull-up maneuver are investigated using a coupling between the computational structural dynamics (CSD) and computational fluid dynamics (CFD) methods. The LH rotor is characterized by a five-bladed system with elastomeric bearings and inter-bladed dampers. The periodic trim solution along with the converged CFD/CSD delta airloads obtained in steady-level flight (advance ratio of 0.287) are used to perform the transient CSD maneuver analysis. The resulting vehicle attitude angles and velocity profiles of the aircraft are then prescribed in the quasi-static (QS) CFD maneuver analysis. It is demonstrated that the present QS approach provides an effective means for the maneuver loads' analysis. The important flow behaviors such as BVI (blade–vortex interaction)-induced oscillations and the negative pitching moment peaks met in maneuver flight are captured nicely with the proposed method. Either the vortex trajectories or the surface pressure distributions are examined to identify the sources of the oscillations. A loose CFD/CSD coupling (LC) is used to predict the blade elastic motions, structural moments, and pitch link loads at the specified maneuver revolution of the rotor and also to correlate these with the transient CSD-based predictions. A reasonable correlation is obtained. The LC results show more pronounced 5P (five per revolution) oscillations on the structural response than those of the CSD-based methods. [ABSTRACT FROM AUTHOR]

In the vehicle suspension system field, smart materials are contributing their top-notch characteristics in building up magneto-rheological (MR) dampers. Though MR fluid has good characteristics to absorb shock, sedimentation problem is a significant issue while performing an MR damper. MR grease eliminates the sedimentation problem and can be used a MR damper in vehicle suspensions system, in vibration control of large structures, biomedical, etc. This paper aims to conduct a numerical study based on coupled FEA and CFD and evaluate the damping force induced in the MR grease gap region for a different input current ranging from 0.1A to 0.4A at frequencies 1 Hz and 2 Hz. ANSYS CFX solver has been used with SST k-ω turbulence model and ‘Herschel-Bulkley’ model for the numerical simulation. At first the simulation approach/model was validated with the experimental results. Initially, the simulation was assumed to be a laminar flow, but as the piston of the damper moves for the stroke, the flow becomes turbulent. Without Shear Stress Transport (SST) turbulence model the simulation was unable to capture laminar to turbulent transition and suddenly stopped when the transition occurred without writing any result. Also, a comparison analysis between ‘Herschel-Bulkley’ fluid model and ‘Bingham’ model was done to prove that only the ‘Herschel-Bulkley’ fluid model can capture the rectangular curve of the damping force for MR Grease as it is stated by the authors who validated the experimental results for MR Grease. No numerical simulation has been found for characterizing MR Grease damper. The FEA has been used to determine the fluid properties due to various currents and frequencies, which were input for the CFD analysis to determine the damping forces and Quasi-static analysis. This simulation model could capture the hysteresis behavior correctly also. [ABSTRACT FROM AUTHOR]

The joint's cyclic behaviour and energy-dissipation capacity are important in lattice shell structures' resisting wind and seismic load capacities. Based on the bending test and FE analysis of the novel steel dovetail joint in the previous study, a full-scaled FE model with six H-shaped beams was analysed using the Abaqus program to determine the boundary conditions for the FE models of hysteric analysis. In the cyclic analysis, 1/6 FE models of the novel steel dovetail joints (NDJGs) were established and analysed based on the boundary conditions of the full FE model in the bending analysis and Quasi-static analysis step. The loading protocol is defined, and the analysis is carried out considering different design parameters, including hub ring thickness, slot edge thickness, and teeth depth. The analysis results indicated that the hub ring thickness does not affect the cyclic bending capacity and stiffness of the novel steel dovetail joint; meanwhile, they increased gradually when the slot edge increased. At the same time, the bending capacity is negatively correlated with the teeth depth, where the bending capacity is reduced when the teeth depth increases. All skeleton curves for all joints of this study are compared, and their energy-dissipation capacities and ductility are calculated. Finally, the novel steel dovetail joint showed an excellent energy-dissipation capacity with high ductility performance under cyclic loads. [ABSTRACT FROM AUTHOR]

In order to study the seismic behavior of tenon-mortise joints with different pin types, as well as the influence of three parameters such as tenon height, tenon thickness, and column diameter on the mechanical properties of tenon-mortise joints, in this study, finite element software modeling was used for the quasi-static analysis of tenon-mortise joints, and the seismic indexes such as hysteretic curve, skeleton curve,and energy dissipation capacity of three types of specimens were obtained. The results showed that the hysteresis curves of the three types of tenon-mortise joints penetrating pin showed obvious Z-shape, and the pinch effect was obvious .The bearing capacity of three types of tenon-mortise joints with penetrating pin under repeated load was not significantly different. The tenon height, tenon thickness and column diameter had significant influence on the bearing capacity of tenon-mortise joints. The bearing capacity of joint increased with the increasing of tenon thickness and column diameter, and increased first and then decreased with the increase of tenon height. According to the skeleton curve of tenon-mortise with penetrating pin, a bending moment-turning angle bilinear model of the joint was established, which explored the influence of tenon height, tenon thickness and column diameter on the model parameters. In the design of wood structures, the influence of the size change of tenonmortise on the mechanical properties of joints should be considered comprehensively. [ABSTRACT FROM AUTHOR]

The paper provides the conclusions of a comparative analysis of various approaches, design models, methods for analysis of a loaded structural system and the results of such analysis for a sudden failure of a structural member. It shows that the analysis methods recommended by Russian and foreign standards are based on the same methodology. And the recommended options for choosing secondary design schemes in static, quasi-static and dynamic formulations have different complexity, however, give results which are close enough and acceptable for practical purposes. Some differences in the results are associated with different approaches to consider the reaction redistribution time for the removed structural member, i.e., in essence, with the mode of failure of this member. The issue of criteria for a special limiting state is also discussed. The authors present the expediency of including an additional criterion in regulatory documents that considers the second-order effects on the buckling of the structural elements under accidental impacts and, accordingly, provisions for protecting structural systems against the exhaustion of the bearing capacity due to the loss of stability. As such criterion, the achievement of the limiting equilibrium point on the diagram “axial force vs. transverse deflection” can be adopted.

The air and structural loads of a 5-ton class light helicopter (LH) rotor in a 2.24 g pull-up maneuver are investigated using a coupling between the computational structural dynamics (CSD) and computational fluid dynamics (CFD) methods. The LH rotor is characterized by a five-bladed system with elastomeric bearings and inter-bladed dampers. The periodic trim solution along with the converged CFD/CSD delta airloads obtained in steady-level flight (advance ratio of 0.287) are used to perform the transient CSD maneuver analysis. The resulting vehicle attitude angles and velocity profiles of the aircraft are then prescribed in the quasi-static (QS) CFD maneuver analysis. It is demonstrated that the present QS approach provides an effective means for the maneuver loads’ analysis. The important flow behaviors such as BVI (blade–vortex interaction)-induced oscillations and the negative pitching moment peaks met in maneuver flight are captured nicely with the proposed method. Either the vortex trajectories or the surface pressure distributions are examined to identify the sources of the oscillations. A loose CFD/CSD coupling (LC) is used to predict the blade elastic motions, structural moments, and pitch link loads at the specified maneuver revolution of the rotor and also to correlate these with the transient CSD-based predictions. A reasonable correlation is obtained. The LC results show more pronounced 5P (five per revolution) oscillations on the structural response than those of the CSD-based methods.

In this paper, we present a novel formulation for the time-dependent three-dimensional bending analysis of a viscoelastic solid by defining a time function with unknown coefficient. The advantage of this method is that there is no need to follow the time-displacement curve; instead, the time-dependent responses of the viscoelastic solid are obtained only by bending analysis of the elastic solid with low computational cost and high computational speed. The relationship between stress and strain is written for linear viscoelastic materials employing the Boltzmann integral law. The displacement field is approximated through the combination of two functions, a function of geometrical parameters and a function of time. The equilibrium discretized equations are written based on the virtual work principle using the finite element method. The numerical results are compared with other available references. To determine the effects of geometry and material on the coefficient of the time function, the results are extracted for square, rectangular, skew, circular, and triangular prismatic solids as well as for different materials. [ABSTRACT FROM AUTHOR]

Appropriate computational techniques to model laser shock peening to retrieve residual stress results using finite element modeling are largely under investigation. Hence, this original study investigated a numerical modeling technique employing a quasi-static analysis (using ABAQUS CAE) to deliberately introduce approximation into the analysis by ignoring the inertia normally present in a conventional dynamic explicit laser shock peening analysis (which has good prediction capability of residual stresses) in order to reduce computational time. To compensate for the modeling approximation, the input pressure load spatial profile parameters were varied in an attempt to obtain similar surface residual stress results to those of a dynamic explicit analysis. Such a study has not previously been conducted. The outcome of the study showed that a quasi-static analysis accelerates the simulation time up to 29 times. In addition, when machine learning with a partial least squares algorithm (employing the PyCharm Python integrated development environment) was used on the quasi-static input spatial profile and output surface residual stress data sets (obtained from performing trial and error in order to match the dynamic explicit results closely), the quasi-static input spatial results were obtained in sub one second, aiding with computational efficiency. Applying the predicted profile to the quasi-static model resulted in the surface residual stress profiles correlating well for the first 0.5 mm, with a 7.88% difference to the dynamic explicit model and a 3.27% difference to the experimental result. However, this explorative study demonstrated that the quasi-static modeling technique produced unrealistic results when the other principal stress components are compared to the dynamic explicit model. It becomes clear that inertial effects are essential in modeling laser shock peening realistically. Therefore, when stress components other than the surface residual stress profile in one plane are required, the conventional dynamic explicit analysis technique should be employed. [ABSTRACT FROM AUTHOR]

Satellite systems undergo several operational phases during their service life, including the assembly phase, ground transportation phase, the launch phase, and the in-orbit operation phase. Among these phases, the one that imposes the highest level of loadings on the satellite is the launch phase. This phase involves a number of highly dynamic loads, all being imposed upon the satellite simultaneously. Investigation of the responses of the structural subsystem of a satellite to these loadings, namely its maximum deformations and maximum von Mises stresses, is critical if a reasonably high level of confidence is to be achieved. This confidence is in terms of ensuring that no material yielding develops in the structure as a result of the imposed launch loadings. In an earlier work, the structural subsystem of a conceptual microsatellite was designed, employing aluminum 6061 alloy as its material. It was then modified through introducing sets of parametrically defined geometric patterns as perforation patterns to remove material, towards reducing the structure's total mass, as an alternative to employing composite materials. That effort led to a mass reduction percentage of 23.15%. The current work's research effort focused on computing the responses of the perforated structure to three of the dynamic launch loads that are imposed upon satellites while being launched, namely quasi-static, random, and shock loads. These responses were then compared to those of the baseline, unperforated, version of the same structure. The values of these loads were taken from the relevant sources, with the values being nominal, and represented the loads that any satellite must qualify for before it can be accepted by the provider for inclusion in a launcher. After imposing these load values upon the structural design it was found that the structural responses indicated that the structure would successfully survive these loads without developing stresses that would lead to material yielding failure. This was deduced from computing the yield margins of safety for each loading case, and all margin values were positive, indicating that the structure, at its current development stage, did have sufficient capacity to withstand these loads without material yielding. This reinforced the conclusion of the earlier work, namely that the perforation concept did have sufficient merit to be further developed towards being implemented in future satellite designs. [ABSTRACT FROM AUTHOR]

The extraction of oil and gas from deep water is one of the most important challenges of the oil and gas industry today. FPSO is one of the leading platforms for deep waters. This study discussed the performance of FPSO deck modules under loads exerted on the hull of the ship. Modeling of the studied module was executed by SACS software and the effect of support using neoprene in the function of the module’s members was studied. The members of this module are divided into two general areas: the first area includes fulcrum members under the main deck of module and the second area includes installed members on the main deck and equipment of the module which is investigated in three directions; longitudinal, transverse and vertical. After analysis, it was confirmed that in the module which uses neoprene, the connected members to the neoprene have a significant decrease in relative stress, whereas, the transverse members exhibited increased relative stress. On the other hand, the vertical and longitudinal members displayed insignificant changes.

A numerical model capable of predicting the dynamic response of pre-stressed concrete transmission poles under both the mean and fluctuating components of synoptic wind loads is developed in this study. A full non-linear dynamic analysis is conducted under a time history variation of wind velocity. The peak total responses, such as conductors' reactions and poles' base moments, are determined from this analysis. The same analysis is repeated in a quasi-static manner. Dynamic amplification factors (DAF), defined as the ratio between the maximum response based on a non-linear dynamic analysis and the corresponding value based on a quasi-static analysis, are calculated for the poles and the conductors to quantify the dynamic impact of synoptic wind loads. This factor is used to assess the importance of including the resonant component while estimating the response of the transmission poles. In addition, gust response factors (GRF) defined as the ratio between the peak and mean responses are evaluated and compared to GRF recommended by ASCE-74 (2010). A parametric study is conducted on three pre-stressed concrete transmission line systems. The mean value of the incoming wind speed is the main variable included in the parametric study. It is found that the resonant effect is dominant in the conductors at low wind speeds and the poles exhibit high dynamic response at higher wind speeds. [ABSTRACT FROM AUTHOR]

When a ship is damaged at sea, it is important to predict its behavior as well as whether it is to sink or not. If the ship comes to an equilibrium, the equilibrium position and time should be estimated; otherwise, the time to sink should be estimated. Furthermore, flooding analysis should be carried out not only during the design stage of the ship for preventive reasons, but also after an accident for a better investigation of its causes. In addition, flooding analysis methods that can provide predictions in case of an accident are of particular importance, as there is no time for the required calculations in an emergency. For this purpose, a quasi-static flooding analysismethod for the damaged ship in the time domain is proposed in this study. There are a number of studies in which the equilibrium position and time were estimated by flooding analysis. However, most of them have not considered the air pressure effect in fully flooded compartments, and themethod of determining the fluid volume in these compartments was not accurate. In the present study, the virtual vent and accumulator method are used to calculate the reference pressure in the fully flooded compartments, and the compartment shape is considered by using polyhedral integration. Also, spilled oil and solid cargo items from the damaged ship are taken into account for realistic flooding analysis. Finally, the damage stability criteria were checked not only in the final state, but also during the entire time of the flooding, as the intermediate states can be more hazardous than the final state. To validate the feasibility of the proposed method, it was applied to a naval ship, which is considerably more stringent for damage stability. As a result, we checked the availability of this study. [ABSTRACT FROM AUTHOR]

The thermal effect has a significant influence on the performance of angular contact ball bearings and thus affects the motion accuracy and stability of spindle-bearing system of computerized numerical control (CNC) lathe. In this paper, a comprehensive coupled CNC lathe spindle-bearing model considering the thermal effect is proposed to predict the dynamic characteristics of system. The spindle is modeled as Timoshenko's beam by considering the centrifugal force and gyroscopic effects. The bearing is analyzed by a five degrees-of-freedom (DOF) quasi-static model considering the thermal effect in order to obtain the static deformations and thermal deformations of rolling bodies. The dynamic differential equation of system is established by the finite element method. Runge–Kutta integral method is used to solve the system equation numerically to study its nonlinear dynamic behaviors. The correctness of thermal model of CNC lathe spindle-bearing system is verified by testing the housing temperature. The simulation values of system response considering thermal effect or not are compared with the experimental results, which shows that the proposed model is feasible. Moreover, the effects of key parameters such as rotational speed, pulley eccentricity and bearing preload on the nonlinear characteristics of system are investigated. Single-periodic, multi-periodic, quasi-periodic and chaotic motions are observed by time history curve, 3-D frequency spectrum curve, phase diagram, Poincare section and bifurcation diagram under different operating conditions. The analytical model developed here can be also helpful to the design and optimization of CNC lathe spindle-bearing system. [ABSTRACT FROM AUTHOR]

Seismic analysis of earth and rockfill dams is generally done by two methods, quasi-static and dynamic. However, the quasi-static method provides dam safety with ease of use and simple assumptions. But sometimes it can lead to unsafe and uneconomical results. In the present study, the Rayleigh Damping rule has been used in calculating the pore water pressure of the Azadi earth dam and non-linear quasi-static and dynamic analyses have been used. Also, in numerical analysis, Abaqus software and simple elastoplastic behavior model based on the Mohr-Coulomb criterion have been used. To validate the data of Azadi Dam instrumentation, the pore water pressure of the core due to changes in reservoir water level after impounding was modeled by Abaqus software and compared with the instrumentation results in quasi-static mode. To match the observed and predicted data, multivariate regression and the criterion of the coefficient of explanation have been used. The value of R2= 0.9747 indicates a very good agreement between the observed and predicted data. A comparison of research results shows that the pore water pressure in the dynamic analysis is 39% higher than in quasi-static analysis. The maximum pore water pressure ratio (RU) in the dam core is 0.24, so according to the pore water pressure ratio, the obtained, hydraulic failure will not occur in the core. [ABSTRACT FROM AUTHOR]

Satellite systems undergo several operational phases during their service life, including the assembly phase, ground transportation phase, the launch phase, and the in-orbit operation phase. Among these phases, the one that imposes the highest level of loadings on the satellite is the launch phase. This phase involves a number of highly dynamic loads, all being imposed upon the satellite simultaneously. Investigation of the responses of the structural subsystem of a satellite to these loadings, namely its maximum deformations and maximum von Mises stresses, is critical if a reasonably high level of confidence is to be achieved. This confidence is in terms of ensuring that no material yielding develops in the structure as a result of the imposed launch loadings. In an earlier work, the structural subsystem of a conceptual microsatellite was designed, employing aluminum 6061 alloy as its material. It was then modified through introducing sets of parametrically defined geometric patterns as perforation patterns to remove material, towards reducing the structure’s total mass, as an alternative to employing composite materials. That effort led to a mass reduction percentage of 23.15%. The current work’s research effort focused on computing the responses of the perforated structure to three of the dynamic launch loads that are imposed upon satellites while being launched, namely quasi-static, random, and shock loads. These responses were then compared to those of the baseline, unperforated, version of the same structure. The values of these loads were taken from the relevant sources, with the values being nominal, and represented the loads that any satellite must qualify for before it can be accepted by the provider for inclusion in a launcher. After imposing these load values upon the structural design it was found that the structural responses indicated that the structure would successfully survive these loads without developing stresses that would lead to material yielding failure. This was deduced from computing the yield margins of safety for each loading case, and all margin values were positive, indicating that the structure, at its current development stage, did have sufficient capacity to withstand these loads without material yielding. This reinforced the conclusion of the earlier work, namely that the perforation concept did have sufficient merit to be further developed towards being implemented in future satellite designs.

The location of wagon gravity center for a loaded wagon is underestimated in a vehicle–track coupled system. The asymmetric wheel load distribution due to loading offset significantly affects the wheel-rail contact state and seriously deteriorates the curving performance in conjunction with the height of gravity center and cant deficiency. Optimizing the location of gravity center and cruising velocity, therefore, is of interest to prevent the derailment and promote the transport capacity of railway wagons. This study aims to reveal the three-dimensional influencing mechanism of mass distribution on vehicle curving performance under different velocities. The wheel unloading ratio is regarded as the evaluation index. A simplified quasi-static model is established considering essential assumptions to highlight the influence of lateral and vertical offset on curving performance. For a more accurate description, the MBS models with various locations of wagon gravity center are built and then negotiate curves in different simulation cases. The simulation results reveal that the distribution of wheel unloading ratio determined by loading offset is like contour lines of 'basin'. Based on the conclusions of quasi-static analysis and dynamics simulations, the regression equation is proposed and the fitting parameters are calculated for each simulation case. This paper demonstrates the necessity of optimizing the location of wagon gravity center according to the running condition and offers a novel strategy to load and transport the cargo by railway wagons. [ABSTRACT FROM AUTHOR]

A quasi‐static approach based on lumped equivalent circuits is presented and investigated for an efficient numerical analysis of miniature RF circuits. In this approach, the static capacitances and inductances including mutual capacitances and inductances of individual circuit components are first evaluated using the finite element method. An equivalent lumped circuit based on the calculated capacitances and inductances is then constructed for the entire circuit, whose analysis predicts the frequency responses of the circuit. The accuracy of this quasi‐static approach is investigated by comparing its solution with that of the full‐wave analysis based on Maxwell's equations. It is found that the quasi‐static analysis is very accurate for a miniature RF circuit whose electrical size is smaller than a fraction of the effective wavelength. [ABSTRACT FROM AUTHOR]

A fast frequency sweep approach based on analytic extension of eigenvalues (AEE) is presented and investigated for an efficient analysis of miniature passive RF circuits. In this approach, an eigenvalue decomposition is performed to the Z-parameters of the circuit components at one or a few frequencies, and analytic extension is applied to obtain the eigenvalues at all other frequencies within the band of interest. For electrically small circuit components, the frequency-independent characteristic inductances and capacitances, as well as the frequency-dependent resistances, are extracted from the eigenvalues at the sampling frequencies. The extracted characteristic parameters are then used to approximate the Z- and Y-parameters and predict the responses of the circuit over the entire frequency band. The accuracy of this approach is evaluated by comparing it with the results from a full-wave analysis. It is found that the proposed AEE is very accurate with a relative error of less than 1% for miniature RF circuits whose electrical sizes are smaller than one tenth of the wavelength and is more general and powerful than the one based on lumped equivalent circuits. [ABSTRACT FROM AUTHOR]

Since ancient times, different techniques have been favoured to provide the integrity of masonry buildings at risk from earthquakes. Earthquake consciousness and determination of related effective techniques have always been a challenging subject. In this study, morphologic characteristics affecting structural resistance of dry-joint masonry towers, and their impact on each other are examined with the help of the statistical analysis. The effectiveness of each characteristic is discussed in relation to the earthquake risk level of the regions to decipher awareness of precautions necessary for structural resistance of dry-joint masonry under earthquake risk in ancient periods. The methodology includes gathering morphologic data with the conventional site survey techniques of architectural restoration; visual analysis of the dataset; design of hypothetical towers by combining possible characteristics of real towers; quasi-static tilt analysis of hypothetical towers with MsPhysics 1.0.3 software; regression analysis of the collapse limits for different morphologic configurations with EViews 4 software, and the proposition of a vulnerability framework and application of the framework to case studies. The parameters affecting structural resistance are listed in the order of high to low impact as a staggering ratio, stone depth, ratio between block length and height, proportional relationship between height and length, opening area, number and position and the distribution of header stones. The application of the framework to case studies indicated consciousness awareness of the risk and the taking of precautions against lateral loading of dry-joint masonry in ancient periods. [ABSTRACT FROM AUTHOR]

High-strength flexible net barriers have achieved a certain effect in mountainous debris flow prevention, but research on the mechanism of structural stress and deformation is still developing. This study first presents an analytical model based on the quasi-static mechanical equilibrium to evaluate the geometric nonlinearity and the load performance of the structure and then conducts a flume experiment to reveal the load mechanism of the structure. Then, a full-scale simulation is performed to investigate the deformation and failure of the flexible net barrier impacted by the debris flow via PFC3D software. The results show that the deformation of the flexible net barrier occurs not only in the direction of flow but also in other directions to make the structure force balanced under debris flow impact. The load impacting on the barrier is far less than the total impact force exerted by debris flow. The flexible barrier has an obvious effect to block a coarse debris flow, and the blocking capacity is related to the volume of debris flow and the slope gradient of the flume. The displacement patterns of loaded cable in the experiment and the simulation are different, but the cable under non-debris flow impact is only dragged by the mesh rope showing a regular parabolic shape, and the tension inside the flexible mesh is far less than that of the transverse cable. In addition, the model shows the failure characteristics of flexible barrier under large-scale debris flow, which plays a guiding role in practical engineering design of the structure. [ABSTRACT FROM AUTHOR]

The objective of this work is to develop an efficient method to carry out the preliminary design of the mooring system for a wave energy converter. A practical mooring design procedure is applied to a specific case of study, and it can be replicated for other cases. Firstly, the static analysis is performed for a configuration with three mooring cables with different pre-tensions on fairlead, diameters of the cables, and materials. Based on these configurations from the static analysis, a quasi-static analysis is carried out in the frequency domain and a preliminary design is conducted according to DNV rules. Then, a 3-h dynamic analysis in the time domain is performed on several selected configurations, considering the same environmental conditions in the quasi-static analysis using the finite element method. Extreme dynamic responses of the system, such as extreme surge motion and mooring tensions, are estimated by the global maximum method, which is performed by fitting 20 individual maximum observations by Gumbel distribution. The quasi-static method is validated by comparing the results of extreme tension and displacement with the coupled time domain analysis. In addition, the influence of pre-tensions and cable diameters on the static and dynamic responses of the mooring system are discussed.

The present study aimed at quasi-static compressive test on 6061-O aluminum cylindrical absorbers with internal networking. The cylindrical cellularization was in such a way that a square is welded to a thin-walled cylindrical at the middle of the sides. As one of the design of experiments (DOE) techniques the response surface method (RSM) was used to examine the effect of the parameters on energy absorption, peak force (PF), specific energy absorption per unit mass (SEA) and energy absorption per length (EA). The variables of thickness, height and length of square of the thin-walled cylindrical were considered in three levels. The samples were performed under a quasi-static compressive test at a constant speed of 10 mm/min. Then, the numerical simulation was performed using the finite element software (ABAQUS). The results obtained from the experiments and simulations were consistent. In accordance to the equations obtained from the experimental results, the multi-objective optimization was conducted considering maximum SEA conditions, EA conditions, and minimum PF conditions. The results indicated a direct relationship between thickness and length of square with responses, nonlinear relationship between height and responses, and the effect of thickness was greater than other parameters in all responses. Except for PF response, there was an interaction between the parameters in EA and SEA responses. [ABSTRACT FROM AUTHOR]

The performances of an angular contact ball bearing (ACBB) are influenced by its geometric dimensions that can have uncertainty due to manufacturing tolerances. Uncertainty of these geometric dimensions results in uncertainty of the performances. This study performed robust design optimization considering the uncertainty of the geometric dimensions which affect the performances of an ACBB, mounted on the main shaft of a grinder. Six geometric parameters and an axial preload were selected as design variables. Among these design variables, three geometric variables were regarded as random design variables that have significant uncertainty of geometric dimensions. To ensure manufacturing precision of the grinder, simultaneously maximizing means and minimizing standard deviations of both axial and radial stiffness values were defined as objective functions. Constraints were imposed to consider uncertainty of the performance functions. A quasi-static analysis was employed to evaluate the bearing performances. The means and standard deviations of the performances were evaluated by the enhanced dimensional reduction method. Robust design optimization was performed using the progressive quadratic response surface method. The robust optimum design revealed that the performance and robustness of both stiffness values were improved than the initial design of the ACBB while satisfying all constraints. [ABSTRACT FROM AUTHOR]

This paper presents a finite element analysis based study of web crippling failures in cold-formed steel unlipped channel sections with their flanges fastened to supports under one-flange load cases (EOF and IOF). Currently no design equations are available in the current cold-formed steel specifications to determine the web crippling capacities of unlipped channel sections with restrained flanges under one flange load cases. Hence the web crippling behaviour of unlipped channel sections was first investigated experimentally using 28 tests and suitable coefficients were proposed for the current web crippling design equation. However, the applicability of the proposed coefficients was limited to the tested channel sections. In this study advanced finite element models were developed in ABAQUS/CAE and validated in terms of ultimate failure loads, load versus deflection curves and failure modes. The developed models were analysed using nonlinear static and quasi-static analysis based on implicit and explicit integration schemes. This study addressed the effects of mesh size, element type, mechanical property model and inertia of support and loading plates. Also, the effects of two enhancement techniques of explicit analysis such as mass scaling and artificial loading rates with different thicknesses were investigated and the results are presented. A detailed parametric study was then conducted using the validated finite element models. New and improved design equations were proposed to determine the web crippling capacities of unipped channel sections using the results from both finite element analysis based parametric study and experiments. • Investigated web crippling behaviour of unlipped channel sections fastened to supports. • Finite element models with contacts were developed and validated using test results. • Web crippling coefficients are not available for unlipped channels fastened to supports. • Proposed improved web crippling coefficients for AS/NZS4600/AISI S100 equations. • Proposed improved web crippling equations based on numerical and experimental studies. [ABSTRACT FROM AUTHOR]

This paper addresses an analytical method for determining the static equilibrium position of beam axle suspension systems used of motor vehicles. This method is applicable to most types of suspension systems and is based on the definition of the spatial positioning of the guiding mechanism as a result of the forces and torques acting in the suspension system. The static model is defined in analytical form, in terms of virtual work, considering the system of applied forces and reactions in the elastic suspension elements (springs, bumpers, anti-roll bar and bushings), whose deformations are determined by the spatial positioning of the guiding mechanism. The proposed method is based on an iterative algorithm by which, for a given set of contact forces on wheels, the equilibrium position is identified by scanning the entire vertical motion domain of the wheels and selecting the configuration that ensures minimal static function. The results obtained by the algorithmization of the method and computer programming allow an accurate assessment of the static behaviour of a beam axle suspension system (in terms of equilibrium configuration and reaction forces) in various regimes, without the need for costly experimental testing. [ABSTRACT FROM AUTHOR]

Laminated glass fulfills the demands on safety and security in transparent structural elements used in architecture and other fields of engineering. It can be constructed as forced-entry, bullet, or blast resistant. The basic three-layer configuration consists of two glass panes connected with a polymer or ionomer interlayer; the advanced products contain also other layers. The foil ensures shear coupling and provides post-breakage resistance and damping. For the design of laminated glass structures and their analysis, knowledge of mechanical properties of interlayers is essential. In numerical simulations, the interlayer is most typically described by the generalized Maxwell chain ‒ a classical viscoelastic model which can capture the time/temperature-dependent response of polymers under shear. Its parameters can be found for common interlayer types in the literature. However, they differ even for the same material, because of a slightly different content of additives, different test setups, and different data processing procedures. In this contribution, the dependence of the response of a laminated glass element on the material parameters of the polymer interlayer is studied by means of numerical modelling and experiments. Two examples are shown and discussed, i.e., quasi-static analysis of a simply-supported beam and modal analysis of a free-free beam. Numerical predictions are obtained by a layer-wise model based on the finite element method. These predictions are validated against the detailed experimental data. We demonstrate that using the Maxwell model parameters from the literature determined even for the same material type but not for the concrete foil may lead to unrealistic predictions.

Automotive side impacts are particularly dangerous as location of impact is very close to the passenger, who can be immediately reached by the impacting vehicle. FMVSS 214 static is a US safety regulation for occupant safety during side impacts, in which the vehicle is tested at static loading conditions to measure its load baring capacity and integrity of side closures. The CAE load case, virtually simulating the test, was handled as a quasi-static problem in this study. Impact beam is a component that helps in improving vehicle passive safety performance during side impacts by minimizing door intrusion to the occupant cabin. It plays an important role in achieving side impact regulatory norms. Through this study, a mass optimized front door impact beam design was developed for a passenger car with the help of CAE simulations; FMVSS 214S regulation norms are met. Component thickness, material and cross section shape were the design variables considered for the study. A methodology to perform the component level simulation of the impact beam loading such that it replicates component behaviour during full vehicle simulation was developed. This has helped in reducing the total problem calculation time in solver. This also has minimized the computational cost for the project. CAE simulations required for the study were done using LS-DYNA. ANSA and PRIMER were used as preprocessors and hyper-graph and meta-post were used for post processing. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an advanced numerical technique is proposed for a low-frequency electromagnetic field simulation. The finite difference time domain (FDTD) method is one of the best methods for analyzing electromagnetic field problems, which require high levels of precision, such as a heterogeneous whole-body voxel human model. However, directly using the standard FDTD method in the quasi-static frequency band requires an extra-large number of iterations. We overcome this drawback using the hybrid of surface equivalence theorem and quasi-static FDTD (QS-FDTD) method. The surface equivalence theorem is used to consider arbitrary shape of source and the QS-FDTD is applied to obtain electromagnetic response quickly in the low-frequency region. The results of the proposed method are in good agreement with those from a commercial electromagnetic simulator. The proposed method is valid where the quasi-static approximation is satisfied. [ABSTRACT FROM AUTHOR]

This paper presents unified solutions for elastic–plastic expansion analysis of a cylindrical or spherical cavity in an infinite medium, adopting a flow theory of strain gradient plasticity. Previous cavity expansion analyses incorporating strain gradient effects have mostly focused on explaining the strain localization phenomenon and/or size effects during infinitesimal expansions. This paper is however concerned with the size-dependent behaviour of a cavity during finite quasi-static expansions. To account for the non-local influence of underlying microstructures to the macroscopic behaviour of granular materials, the conventional Mohr–Coulomb yield criterion is modified by including a second-order strain gradient. Thus the quasi-static cavity expansion problem is converted into a second-order ordinary differential equation system. In the continuous cavity expansion analysis, the resulting governing equations are solved numerically with Cauchy boundary conditions by simple iterations. Furthermore, a simplified method without iterations is proposed for calculating the size-dependent limit pressure of a cavity expanding to a given final radius. By neglecting the elastic strain increments in the plastic zone, approximate analytical size-dependent solutions are also derived. It is shown that the strain gradient effect mainly concentrates in a close vicinity of the inner cavity. Evident size-strengthening effects associated with the sand particle size and the cavity radius in the localized deformation zone is captured by the newly developed solutions presented in this paper. The strain gradient effect will vanish when the intrinsic material length is negligible compared to the instantaneous cavity size, and then the conventional elastic perfectly-plastic solutions can be recovered exactly. The present solutions can provide a theoretical method for modeling the size effect that is often observed in small-sized sand-structure interaction problems. [ABSTRACT FROM AUTHOR]

The mechanical properties of a broad range of thermoset foams based on tannin were investigated through destructive compression tests, either with or without rigid plates glued to the opposite faces of the samples, and through a rather new, non-destructive, quasi-static method. The main objective was to compare both techniques, as well as the effect of the presence of plates, and to discuss the relevance of each for properly characterising the materials. Gluing stiff plates to the samples was found to be a key point for the appropriate determination of the elastic modulus of brittle foams, whereas it did not affect that of elastic-plastic foams. In contrast, the compressive strength did not depend on the kind of test. The results obtained by destructive compression were then compared to those of the new non-destructive technique, proving that the latter was suitable for characterising elastic-plastic foams but not brittle foams. However, the new method allowed determining Poisson ratio and loss factor, which had never been measured so far for this kind of materials. [ABSTRACT FROM AUTHOR]

Quasi-static analysis of electromagnetic scattering from a radially uniaxial (RU) sphere is presented in this paper. RU dielectric sphere is placed in an unbounded fractional dimensional space. We investigate effects of fractional dimensional space on behavior of potential distribution due to the RU sphere. For this purpose, numerical results of electric potential for different dimensions of the fractional space have been presented and discussed. [ABSTRACT FROM AUTHOR]

The gearboxes of machines generally operate under a time-varying state rather than under steady-state conditions. However, it is difficult to investigate the nonlinear dynamics of a time-varying gear system. A gear system model of a railway vehicle was proposed in consideration of its time-varying mesh stiffness, nonlinear backlash, transmission error, time-varying external excitation, and rail irregularity. To obtain the nonlinear behaviors of a time-varying stochastic gear system, a quasi-static analysis was performed to observe its doubling-periodic bifurcation, chaotic motion, and transition from a lower to a higher power periodic motion. Based on the energy comparison results, the time-varying stochastic gear system was degraded to a time-varying system to simplify the calculation. Furthermore, the nonlinear response of the time-varying system was computed using the Runge-Kutta method and was compared with the results of a quasi-static analysis that employed a short-time Fourier transform method. The results of the quasi-static analysis were consistent with the results of the time-frequency analysis for the time-varying gear system except for the result at 3180 r/min, which represented a short period wherein the process transitioned to chaos. Hence, the comparison demonstrates the applicability of the quasi-static analysis for the nonlinear behavior analysis of a time-varying stochastic system. [ABSTRACT FROM AUTHOR]

Offshore wind turbine energy has recently attracted significant attention and many researchers have attempted to develop cost-efficient offshore wind turbine support structures to reduce capital costs. This paper proposes a new hybrid support structure using driven piles that eliminates the disadvantages of conventional support structures for offshore wind turbines. The hybrid support structure proposed here is a piled concrete foundation (PCF) structure, which combines a concrete base with a steel shaft and is supported not only by gravity type foundations but also by driven piles. The soil was modeled as an elastic foundation, and the added mass was calculated using the Added mass method to determine the effects of water surrounding the support structure. To evaluate the feasibility of the PCF, quasi-static analysis, natural frequency analysis and seismic analysis were performed using environmental conditions at the Southwest Coast of Korea. In quasi-static analysis, the lateral displacement did not exceed the allowable displacement, and natural frequency analysis confirmed the superiority of the dynamic behavior of the PCF. Seismic evaluation through response spectrum analysis and time-history analysis demonstrated that the PCF is safe. The proposed PCF was confirmed to have sufficient structural stability for applications in real-site conditions in Korea. Optimization of the structure using the preliminary design resulted in an efficient structure that reasonably reduces fabrication costs. [ABSTRACT FROM AUTHOR]

The continuum robot undergoes extremely high deflection when it is actuated. In this paper, mathematical model of continuum robot has been presented. Here, only the quasi-static analysis is considered neglecting the inertial part. One of major components of this kind of continuum robot is the flexible beam. A thorough analysis of highly-flexible beam has been carried out in this work. Main challenge in this context is to solve the equilibrium/governing equations. In this work, a novel way has been explored to handle flexible beam with multiple point-loads. Specifically, problem becomes extremely complex for the analysis of the multi-segment continuum robot. The similar concept of domain decomposition has been employed to integrate the governing equations. Numerical integration is done by Runge-Kutta 5 th order method. The nonlinear boundary value problem in each sub-domain has been solved by shooting method by taking help of the bisection technique. An important issue in domain-decomposition is to pass boundary information among the connected sub-domains. This newly developed method is easily implementable and can handle large number of segments without posing any extra difficulty. [ABSTRACT FROM AUTHOR]

Concrete foundations have received attention as offshore wind turbine support structures because of their various advantages. However, because of the lack of information on structural analysis and the design method of complex marine environmental loads, concrete foundations cannot be applied on actual sites. Therefore, the structure behavior mechanism and concrete reinforcement design need to be evaluated based on soil-structure interactions. Herein, an efficient method for analysis of piled concrete foundations (PCFs) is presented, and the stability of PCF structures is evaluated under environmental conditions of the coast in Korea for a 3-MW wind turbine. Three analytical parameters for PCF models were defined to consider soil-structure interaction. The results of each model were compared with the displacement, stresses, and natural frequencies. Using the analysis results, a prestressing reinforcement design for concrete foundations was proposed. Quasi-static analysis showed that maximum displacement was sufficiently small and the maximum stresses did not exceed the allowable stresses. PCF showed excellent dynamic performance and structural stability. In addition, stiffness of the soil spring model influenced the natural frequency rather than the stiffness of the pile type. Detailed analysis of the connections between piles and concrete need to be studied in the future.

Marine renewable energy devices require mooring and foundation systems that suitable in terms of device operation and are also robust and cost effective. In the initial stages of mooring and foundation development a large number of possible configuration permutations exist. Filtering of unsuitable designs is possible using information specific to the deployment site (i.e. bathymetry, environmental conditions) and device (i.e. mooring and/or foundation system role and cable connection requirements). The identification of a final solution requires detailed analysis, which includes load cases based on extreme environmental statistics following certification guidance processes. Static and/or quasi-static modelling of the mooring and/or foundation system serves as an intermediate design filtering stage enabling dynamic time-domain analysis to be focused on a small number of potential configurations. Mooring and foundation design is therefore reliant on logical decision making throughout this stage-gate process. The open-source DTOcean (Optimal Design Tools for Ocean Energy Arrays) Tool includes a mooring and foundation module, which automates the configuration selection process for fixed and floating wave and tidal energy devices. As far as the authors are aware, this is one of the first tools to be developed for the purpose of identifying potential solutions during the initial stages of marine renewable energy design. While the mooring and foundation module does not replace a full design assessment, it provides in addition to suitable configuration solutions, assessments in terms of reliability, economics and environmental impact. This article provides insight into the solution identification approach used by the module and features the verification of both the mooring system calculations and the foundation design using commercial software. Several case studies are investigated: a floating wave energy converter and several anchoring systems. It is demonstrated that the mooring and foundation module is able to provide device and/or site developers with rapid mooring and foundation design solutions to appropriate design criteria. [ABSTRACT FROM AUTHOR]

Shear walls have high stiffness and strength; however, they lack energy dissipation and repairability. In this study, an innovative slotted shear wall featuring vertical slots and steel energy dissipation connectors was developed. The ductility and energy dissipation of the shear wall were improved, while sufficient bearing capacity and structural stiffness were retained. Furthermore, the slotted shear wall does not support vertical forces, and thus it does not have to be arranged continuously along the height of the structure, leading to a much free arrangement of the shear wall. A frame-slotted shear wall structure that combines the conventional frame structure and the innovative shear wall was developed. To investigate the ductility and hysteretic behavior of the slotted shear wall, finite element models of two walls with different steel connectors were built, and pushover and quasi-static analyses were conducted. Numerical analysis results indicated that the deformability and energy dissipation were guaranteed only if the steel connectors yielded before plastic hinges in the wall limbs were formed. Finally, a modified D-value method was proposed to estimate the bearing capacity and stiffness of the slotted shear wall. In this method, the wall limbs are analogous to columns and the connectors are analogous to beams. Results obtained from the modified Dvalue method were compared with those obtained from the finite element analysis. It was found that the internal force and stiffness estimated with the modified D-value method agreed well with those obtained from the finite element analysis. [ABSTRACT FROM AUTHOR]

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In nanopositioning system, the compliant tripod stages have proved to have enormous advantages for out-of-plane (z/tip/tilt) positioning in turns of compactness, simplicity in structure, and economic cost. However, most of the present-day compliant tripod stage undergo manufacturing problems due to a complicate structure, and little study has been carried out to formulate the tri-inputs and tri-outputs relationship, which is essential for precise positioning. Accordingly, this paper presents the quasi-static analysis of a novel compliant tripod stage with an equivalent plane model to achieve precise position analysis for nanopositioning. Three-plane compliant lever mechanisms and cylindrical flexure hinges with high length–diameter ratio are employed, which mitigate couple influence and enable easy fabrication via planar manufacturing processes. The spatial output motions of the compliant tripod stage are first split among inputs of the three-plane compliant lever mechanisms, where the lateral translations of the compliant tripod stage are included. Then the displacement equations of the plane compliant lever mechanism are formulated through Castigliano’s second theorem. The model is further verified by finite element analysis. Finally, an experimental test system is set up and the test results validate the proposed approach. [ABSTRACT FROM AUTHOR]

Kresling is one of the most well-known and widely-used origami patterns. Its outstanding features, such as deployability, bistability, and coupled extensional-rotational motion, have attracted considerable attention from many engineering applications, including aerospace structures. In this research, three approaches for the geometrical design of Kresling modules are investigated and their capabilities are compared. The first two approaches are based on the quasi-static analysis. The third one is an analytical approach focusing on the frequently-used type of Kresling module with two zero-energy stable states. Moreover, based on the number of stable configurations, the amount of potential energy, and the height of the module in the stable state (in monostable cases), Kresling modules are categorized into six groups. According to this classification, design maps are represented for these approaches. Parametric studies are also conducted to clarify the effects of the influencing parameters on the general mechanical behavior of the Kresling modules. Due to the exploiting dimensionless parameters, the presented results are highly useful in the preliminary design of the Kresling origami for applications requiring lightweight and deployable structures. [ABSTRACT FROM AUTHOR]