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This paper proposes a time-varying unmanned aerial vehicle (UAV) formation control method based on trajectory prediction and nonlinear model predictive control (NMPC). First, in formation control, the nominal controller is constructed using a linear model and consensus for theoretical stability assurance. The time-varying formation control of nonholonomic UAVs subsequently is achieved by integrating the nonholonomic model with the NMPC, using the desired state derived from the nominal controller. Furthermore, considering the optimal obstacle avoidance problem of moving obstacles, the transformer is used to predict the trajectory in the predictive horizon, the safety constraints are established in combination with the discrete control barrier function (DCBF), and the optimal obstacle avoidance is realized by reducing the additional motion generated during obstacle avoidance. Subsequently, the NMPC-DCBF-transformer is integrated to realize the optimal obstacle avoidance control of nonholonomic UAV time-varying formation. Finally, the algorithm's effectiveness was verified by numerical simulation, and the advantages of the algorithm were verified by comparison. [ABSTRACT FROM AUTHOR]

In this paper, a fast online guidance law generation method is proposed to resolve the flight time control guidance design problem for time adjustable flight consensus via an analytical polynomial shaping approach. The obtained guidance command is explicit such that fast online trajectory generation is applicable without blind parameters to be designed or tuned. Specifically, the polynomial shaping approach is employed to construct a reference relative range profile by a cubic polynomial in terms of a look angle-based auxiliary. The reference profile is solved by initial and terminal flight conditions. Meanwhile, the field-of-view limit is also achieved by explicitly deriving the conditions to be met for the reference profile's coefficients. Notably, the proposed technique does not rely on the error-prone time-to-go approximation. The trajectory generation command is derived using the guidance model under the expected relative range profile, and is finally presented as a proportional navigation guidance-like law which has simple structure and guaranteed effectiveness. Extensive numerical simulations under various flight consensus scenarios, comparison study, as well as Monte Carlo test under measurement errors and uncertainties are conducted to validate the proposed method. [ABSTRACT FROM AUTHOR]

Fiber-reinforced elastomeric isolators (FREIs) have been proposed as a cost-effective solution for expanding the use of seismic isolation to normal-importance structures. By using lightweight fiber reinforcement and eliminating the attachment plates, FREIs reduce cost while improving the isolation efficiency and reducing tensile stresses in the rubber. However, the flexural flexibility of the fiber allows cross-sectional distortions (i.e., warping) to occur, which significantly impacts the stability of these devices. This paper evaluates the buckling of rectangular, circular, and annular FREIs, taking into account shear warping effects. A planar buckling theory previously proposed by the authors is adapted for the three-dimensional problem, and effective warping rigidities and warping-related areas are derived for the above bearing geometries, accounting for rubber compressibility. To assess the adequacy of the proposed buckling theory and derived warping properties in predicting the buckling of FREIs, a parametric finite element study is conducted. The critical load predictions of the proposed analytical formulation are found to be in excellent agreement with those of the numerical simulations. It is shown that traditional estimations of the buckling load that neglect warping are significantly unconservative. Finally, design recommendations and resources are provided for practice-oriented applications. [ABSTRACT FROM AUTHOR]

This paper addresses the fixed-time, six-degrees-of-freedom control problem for the distributed spacecraft formation system subject to actuator saturation, considering limited communication resources. Since only a fraction of the follower spacecraft can contact the virtual leader, a distributed fixed-time observer is designed to reconstruct the leader's information. Subsequently, a distributed fixed-time, six-degrees-of-freedom controller is established, compensating the actuator's magnitude and the rate saturation problem with an auxiliary system. In particular, this paper proposes a novel event-triggered mechanism in the framework of the "adding a power integrator" technique, avoiding the unnecessary occupancy of communication resources significantly. Finally, numerical simulations demonstrate the advantages of the theoretical results. [ABSTRACT FROM AUTHOR]

An abstract of the paper "Modeling of Simultaneously Continuous and Stochastic Construction Activities for Simulation" by Vivek Puri and Julio C. Martinez is presented.

This paper proposes an analytic approach for impact time control guidance laws against stationary targets using biased proportional navigation. The proposed guidance scheme realizes the impact time control in two different ways: the first approach directly uses the exact time-to-go error to satisfy both the impact time control and the field-of-view constraint, while the second approach adopts a look angle tracking law to indirectly control the impact time, with the reference profile of the look angle generated using the exact time-to-go solution. The stability properties of the proposed guidance laws are discussed, and numerical simulations are carried out to evaluate their performance in terms of accuracy and efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a reinforcement learning–based adaptive attitude control (RLAC) method for a class of hypersonic flight vehicles (HFVs) output constrained nonaffine attitude control problems subject to unmatched disturbances. First, by considering the strong coupling of HFVs attitude dynamics, the uncertainty of aerodynamic parameters and the complexity of the flight environment, a second-order multivariable nonaffine nonlinear control system is obtained. Then, by introducing specific nonlinear function and coordinate transformation techniques, the output constrained nonaffine control problem is transformed into a stabilization problem of several new variables. Moreover, dual actor-critic networks and their adaptive weight update laws are designed to cope with unknown unmatched and matched structural uncertainties. Meanwhile, two super-twisting disturbance observers integrated with dual actor-critic networks are designed to compensate unknown unmatched and matched external disturbances. With the help of the Lyapunov direct method, output constraint, convergence of the estimated weights, and stability of the system are proved. Finally, the validity as well as superiority of the proposed method are verified by numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, a novel magnetohydrodynamic attitude adjustment method is proposed, which uses a spherical magnetohydrodynamic attitude control device for the three-axis attitude adjustment. This paper mainly studies the distribution characteristics of the magnetic field and liquid flow field, and it does not involve attitude control performance and other contents. The magnetohydrodynamic method is used to solve the liquid flow field, which is coupled with the magnetic field. Then, the angular momentum and output torque of the attitude controller are calculated. The calculations aim to investigate the effects of current intensity and frequency on the magnetic induction intensity, flow velocity, angular momentum, and output torque in the spherical magnetohydrodynamic attitude control device. It was found that the velocity, angular momentum, and output torque increased when the current frequency and intensity increased. In addition, to achieve a larger flow rate and more efficient performance of the output angular momentum, priority should be given to increasing the current intensity rather than the current frequency. Thus, an optimal combination of the current intensity and frequency is proposed based on the numerical results. Finally, some implications of the proposed method are further discussed. [ABSTRACT FROM AUTHOR]

In this paper, a prescribed-time guidance law with approach angle constraint in the presence of an actuator fault is proposed. Firstly, a sliding mode manifold with prescribed-time convergence is given to ensure that the state of the system converges to the equilibrium point in the specified time. Then, in order to suppress the distrubance, an adaptive gain based on adaptive control is designed. Subsequntly, a augmentation term based on the Lyapunov method is presented to meet the prescribed-time convergence prpoperty when an actuator fault occurs. The prescribed-time convergence of the proposed guidance laws is proven. Numerical simulation results validate the effectiveness of the proposed prescribed-time guidance framework. [ABSTRACT FROM AUTHOR]

This paper presents a discrete element method (DEM) numerical model to elucidate mechanical behavior, particle crushing, and anisotropy evolution within a pressurized sand damper (PSD) subjected to cyclic loading. Computational simulations of the PSD under different initial pressures and stroke amplitudes were conducted and compared to experimental results. Good agreement was achieved between the DEM model and experimental results for the different cases. Force–displacement, particle crushing, shear, and normal stresses along with geometric and mechanical anisotropy degrees were closely monitored in different areas of the PSD. Dissipated energy was also monitored and used to calculate the specific damping capacity. Employing spherical particles, crushable clusters, and uncrushable clumps as sand particles revealed that the closest results to the experiments are obtained when using crushable clusters. The results show that the majority of crushing occurs in the vicinity of the center of the PSD and within the first loading cycle. Increasing stroke amplitude significantly influenced particle crushing, whereas increasing initial pressure was less considerable. In addition, a direct relationship between the PSD's direction of movement with shear and normal stresses and anisotropy degree was observed. Moreover, the contribution of mechanical anisotropy was more considerable than the geometric anisotropy to the overall anisotropy degree. Regarding dissipated energy, an increase in stroke amplitude resulted in higher dissipated energy whereas an increase in initial pressure had a minor influence on the dissipated energy. Based on the dissipated energy, it was found that the specific damping capacity was nearly equal to one for all cases studied. [ABSTRACT FROM AUTHOR]

Development of the fast model of phase transformations in the Pyrowear 53 steel was the objective of the paper. An upgrade of the JMAK (Johnson–Mehl–Avrami–Kolmogorov) was proposed. Coefficients in the model were introduced as modified Gauss functions of the temperature. Changes in the carbon and molybdenum concentrations due to precipitation were accounted for. Dilatometric tests were carried out across a wide range of cooling rates. Identification of the model was performed using inverse analysis for the results of these tests. Three austenitization cycles prior to transformations were applied and an influence of the grain size on the nucleation and kinetics of phase transformations was accounted for in the model. All the tests were carried out on the core samples with the nominal chemical composition and on the carburized samples. Numerical tests confirmed the good accuracy of the model for both compositions in the whole investigated range of the grain size. [ABSTRACT FROM AUTHOR]

Quantitative safety assessment of offshore platforms under ship collision is a hot topic. Numerical simulation is a powerful tool to evaluate the damage and failure mode of offshore structures under collision. This paper incorporates an element-coupling method into the simulation of ship-platform collision, in which the jacket platform is established using different elements to reduce the modelling costs of the traditional pure shell element modeling method. The coupling method for connecting the interfaces of different elements is proposed and validated through a case study. Further, numerical simulations are carried out for different collision scenarios with collision velocity from 1 to 5 m/s. According to the simulation results, three different types of failure modes of the jacket are identified namely as "Local denting," "Brace buckling," and "K-joint rupture" corresponding to low-energy collision, medium-energy collision, and high-energy collision scenarios, respectively. Also, the detailed failure mechanism of the collision area under a typical high-energy collision is assessed. The collision process is divided into six stages according to the analysis of collision force results. The safety of the jacket platform under collision is assessed through the overall results of vibration acceleration and horizontal displacement. The work in this paper can greatly reduce the modeling efforts and calculating costs, and is thus suitable for conducting numerical analysis of failure mode and collision process in a more efficient way. [ABSTRACT FROM AUTHOR]

The present paper attempts to study the flood wave propagation at a right-angled combining open channel junction utilizing the three-dimensional (3D) transient Reynolds-averaged Navier-Stokes (RANS) equations. The present study advocates using the 3D model over the depth-averaged two-dimensional (2D) model by comparing simulations obtained from 3D and 2D models for steady flows. The 3D model is validated against the experimental results of the flood routing in a single reach channel, available in the literature. The flood wave at the channel inlet is generated by a half-cycle of the sinusoidal function. Three different cases (Cases 1, 2, and 3) are considered by applying the flood wave at the inlet of the main channel, tributary channel, and both the channels, respectively. The steady-state junction flow with equal discharge in both the upstream channels is considered as the initial condition for the flood wave simulations. The rising flood flow of the main channel offers huge flow blockage to the tributary channel flow in Case 1, while vice versa in Case 2. The blockage causes significant flow accumulation leading to the stage rise. In Case 2, the flow reversal occurs as the flow in the main channel is entirely blocked by the rising flood flow of the tributary channel. The interplay of the flow blockage by the main channel to the tributary channel and vice versa results in water accumulation and release, alternatively. The maximum stage rise occurs in Case 3 due to the combined effects of the rising flood wave and flow blockage, simultaneously. The previous flood routing studies at the channel junction have disregarded the momentum equation. This may not be accurate as momentum exchange occurs between the main and tributary channel flow. Considering the dynamic interaction between the approaching flows, the present paper attempts to study the flood wave propagation at a right-angled combining open channel junction utilizing the fully three-dimensional numerical model. Three different simulation cases considered for investigating the flood wave propagation demonstrate the impact of the main channel flood wave on the tributary flow and vice versa. The alternate amplification and attenuation of the flow discharge in both the upstream channels continue to happen due to the interplay of the blockage offered by the main channel to the tributary channel and vice versa before the junction flow attains the base flow condition. The results of the present study improve the understanding of flood wave propagation at the channel junction. [ABSTRACT FROM AUTHOR]

Due to the strength reduction at the bent corners of fiber-reinforced polymer (FRP) stirrups, the high tensile strength of FRP reinforcement cannot be fully utilized in concrete structures. Although numerous experimental investigations have been conducted to study the reduced bent-corner strength, the mechanism of the strength reduction at bent corners has not been fully understood. This paper presents numerical research into the bent-corner strength of FRP stirrups with rectangular cross sections. Refined finite-element models are established based on Hashin's failure criterion and their validities are verified against six groups of 18 FRP stirrup specimens. Analyses of stress concentration in the elastic range and damage accumulation afterward are conducted to explain the mechanism of strength reduction at the bent corners of FRP stirrups. Further parametric analyses are conducted to quantitatively evaluate the contributing factors to the bent-corner strength and an empirical prediction equation is proposed. This research shows that the bond, compressive stress from concrete, and FRP material anisotropy are the critical contributors to the tensile stress concentration in the elastic range at the bent corners, which accounts for 7%, 48%, and 45% of the tensile stress concentration, respectively. The parametric analyses show that better bonding at the bent corners could potentially result in lower strength; the concrete properties and FRP width have limited influence on the bent-corner strength; and the bent-corner strength has logarithmic relation with the bent radius and thickness ratio of (R/t). This work reveals the critical mechanism of strength reduction of FRP stirrups at bent corners in concrete structures and potentially provides the opportunity for more efficient material use of FRP reinforcement. [ABSTRACT FROM AUTHOR]

As part of the LEAP (Liquefaction Experiments and Analysis Projects), many centrifuge model tests on a sheet pile retaining wall were conducted at six different centrifuge facilities around the world. Each centrifuge facility used containers of different W/H (width of container/height of wall) ratios to model the same plane strain prototype retaining wall. Predictions of the centrifuge tests that neglected wall friction, assumed plane strain conditions, and used the CycLiq constitutive model, exhibit reasonable general agreement with tests in terms of liquefaction response. However, an overprediction of the median response of sheet pile wall displacement was observed. The study presented in this paper was motivated by a concern that friction on the side walls might be biasing results from model containers with different W/H. A numerical simulation parametric study using FLAC3D is presented to illustrate the potential effects of interface friction and container geometry on the LEAP retaining wall test results. The results show that incorporation of appropriate container geometry and soil-container friction can reduce the error between simulated and experimental sheet pile wall displacements. Soil-container friction is also shown to affect the total earth pressure and especially its distribution on the sheet pile wall, causing the actual tests to deviate from the intended plane strain conditions. For the assessed liquefaction related cases, soil-container friction has the additional effect of significantly restricting the local development of excess pore pressure and subsequent soil deformation, further contributing to its influence on the centrifuge tests. The parametric study indicates that an interface friction angle of 17.6° and W/H>1 , 2, and 3 reduced horizontal wall displacements by 50%, 20%, and 10% respectively, compared to simulations neglecting wall friction. Use of containers with large W/H is therefore recommended for future centrifuge experiments. [ABSTRACT FROM AUTHOR]

A new generation of transport aircraft increasingly adopts T-tail configurations for their excellent aerodynamic, operating, and structural performance. However, flutter of T-tail configurations is a serious dynamic instability problem caused by aerodynamic and structural interactions between the vertical stabilizer and the horizontal stabilizer. The horizontal tailplane (HTP) is mounted on the vertical tailplane (VTP). Bending and twisting of the VTP induce rolling, yawing, and in-plane motion of the HTP, which has a significant effect on T-tail flutter. In this paper, a multiple input/multiple output (MIMO) linear quadratic Gaussian (LQG) controller is designed to suppress flutter for a T-tail. The state-space equations of the aeroservoelastic (ASE) T-tail model, which are composed of the state-space equations of the aeroelastic system and the actuator dynamics, are derived for the design of the control law. The controller is synthesized by posing and solving a weighted optimization problem with the goal of making the rudders collaborate deflection for flutter mode suppression and expand the boundary of the T-tail flutter. A thorough analysis of the performance achieved by the closed-loop system was performed through numerical simulations. The numerical results demonstrate that the proposed LQG controller can effectively suppress the T-tail flutter and expand the flutter boundary. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of a numerical simulation and subsequent variability analysis of the lateral load-resisting behavior of unbraced and chevron-braced glulam portal frames. Longitudinal tension/compression strengths of each glulam member were determined based on wood-size effect theory. The finite-element method (FEM) and an experimental study were carried out to determine the nonlinear mechanical behavior of glulam braces and bolted glulam beam-to-column connections. OpenSees "Pinching4" hysteresis models were adopted to model the mechanical behavior of both glulam braces and bolted beam-to-column connections. An FEM model of the glulam frames was developed to predict the lateral load-resisting hysteretic response of such frames. The stochastic finite-element method was used to calculate the frame capacity considering random distributions of connection and brace capacity. The FEM model presented can represent the nonlinear and hysteretic pinching behavior of an unbraced glulam frame whose behavior is dominated by splitting in the connection regions. Similarly, the strength softening and stiffness degradation of a chevron-braced glulam frame was also captured. Response surface method analysis was used to regress braced frame capacity from 200 analyses to a single set of capacity variables. The approach described in this paper demonstrates promise for optimizing the industrial-scale production of glulam portal frame structures. [ABSTRACT FROM AUTHOR]

In this paper, the finite-element (FE) method combined with smoothed particle hydrodynamic (SPH) method is used to simulate the bird strike process, and a new type of tail leading edge structure is designed. This kind of bird is represented by the SPH model, and the structure is simulated by traditional Lagrangian elements. The design for the novel structure can be described as incorporating a triangular reinforcement component into traditional tail leading edge structure. Numerical simulations of bird strikes with the novel structure indicate that the anti-bird-strike capacity of the new type of tail leading edge is greatly enhanced. Then, the corresponding bird strike tests are carried out to verify the numerical simulation model. The simulation results are in good agreement with the test results, indicating that the SPH-FE coupling method gives a useful tool for predicting the deformation and damage behavior of aircraft structure under bird impact, and for the design of bird-strike-resistant structure. Finally, through bird strike simulation and test of the horizontal tail leading edge with the new design of commercial aircraft, it can be observed that the front beam does not penetrate, which indicates that the new design meets the requirements of the China Civil Aviation Regulations (CCAR) Part 25 on the certification of the bird strike resistance of the wing leading edge. [ABSTRACT FROM AUTHOR]

The stochastic subspace algorithm is one of the most widely used structural identification techniques, which is generally involved with the stabilization diagram for estimating modal parameters. However, the conventional stabilization diagram has an inherent problem: some spurious modes may be identified as stable results, resulting in adverse effects on structural modal identification. To address this critical issue, this paper proposes an improved stochastic subspace algorithm involving a Monte Carlo–based stabilization diagram. Through a numerical simulation study, the good performance of the Monte Carlo–based stabilization diagram for discriminating the poles denoting the physical modes from those representing spurious modes is demonstrated. The numerical simulation results show that the proposed method can estimate structural modal parameters with high accuracy and robustness. Moreover, the proposed method is applied to field measurements on a 600-m-high skyscraper during Super Typhoon Mangkhut, and the results verify the applicability and effectiveness of the proposed method to field measurements. This paper aims to provide an effective tool for accurate estimation of modal parameters of civil structures. [ABSTRACT FROM AUTHOR]

This paper proposes a sliding mode controller for a novel kind of quadcopter called tilt-rotor quadcopter. The controller is modeled in SIMULINK and implemented on a Pixhawk 2 flight controller board. First, this paper presents the dynamic model of the tilt-rotor quadcopter. Second, the proposed smart sliding mode controller for simulation studies is presented. Third, the hardware platform is discussed in detail with the controller implementation. Finally, numerical simulation results for the smart sliding mode controller for various scenarios (wind disturbances, faulty motors) are presented following which the preliminary hardware tuning results are presented. Simulation results of the tilt-rotor platform hovering at a position with a nonzero attitude are also shown. This paper also presents a discussion on the challenges faced transitioning from a simulation environment to hardware testing and plausible ideas to address the challenges. [ABSTRACT FROM AUTHOR]

Compact tether-based actuation is a suitable approach for the deployment of femto/picosatellite bodies from CubeSats using ultrasmall electrodynamic tethers for fuel-free propulsion and deorbiting. Despite the advantages of tethered satellite systems, control technologies for these have yet to mature in several domains including robustness to structural faults and unmodeled dynamics. A proposed solution for the identification of disturbances to tethered satellite dynamics is to use a data-driven algorithm to learn the system's behavior over previous orbits and then provide an estimated prediction for the evolution of system states. To achieve the goal of state prediction via a globally linearized system model, this paper employs the Koopman operator constructed from observed dynamics to extrapolate future motion of a tethered subsatellite subject to unknown disturbances while being deployed from its mothership. Numerical simulations of the constructed model versus the nonlinear model of the tethered satellite system demonstrate the effective prediction capabilities of the proposed Koopman operator-based numerical algorithm for the general flight characteristics many orbits into the future. [ABSTRACT FROM AUTHOR]

With the increasing demand for vertical isolation in the engineering field, the compressive behavior of low–shape factor (LSF) lead-rubber bearings (LRBs) needs to be further explored. However, the conventional simulation method of lead boundary conditions cannot accurately capture the actual compressive behavior of LSF bearings. Some scientific literature has reported this, but there is a lack of detailed studies to explain it. By comparing the experimental data and numerical simulation results of LSF bearings, the problem of this research is put forward. Thus, a refined numerical simulation method of lead boundary conditions is proposed in this paper based on the manufacturing process of LRBs. Assumed contact types, friction coefficients, and filling ratios of the lead plug are considered as variables of lead boundary conditions. The first shape factor and lead plug diameter are considered bearings variables. The compressive behavior of LRBs, including stiffness, deformation, and stress–strain distribution, are discussed through detailed analysis. The main study results indicate that contact types and filling ratios of lead plugs have a significant influence on the compressive behavior of LSF bearings, and the friction coefficient is negligible. The proposed refined simulation method is capable of capturing LRBs' mechanical behavior with better accuracy than the conventional model under different stresses, especially LSF bearings. However, the conventional numerical modeling method is recommended for LRBs with high shape factors (e.g., 30–50). Finally, an empirical formula is established based on refined simulation results. [ABSTRACT FROM AUTHOR]

Long-cantilever transmission towers are drawing more and more attention in ultrahigh-voltage (UHV) transmission projects. To meet the requirements of high-voltage safety clearance, the structural characteristics of long-cantilever transmission towers are significantly different from traditional ones. Aiming to ensure the safety of long-cantilever transmission towers during service, this paper investigates their static and dynamic characteristics under various extreme loading conditions based on full-scale tests and numerical simulation. With the strain data tested in seven typical cases, the bending moments and axial forces of the main members were back-calculated and the initial imperfections were calculated based on these results. Using a stochastic subspace identification algorithm, the evolution of the modal parameters during the full-scale test was revealed. The damage position of the main members was identified according to the mode shape changes, and the dynamic collapse process was analyzed via the measured dynamic responses and recorded videos. Numerical simulation was conducted in ANSYS using the calculated initial imperfections, and the results were in good agreement with the full-scale test. The results show that torsion action was not dominant for this tower and the failure mode was still the bending failure at the tower body. The proposed imperfection quantification method makes up for the deficiency of the empirical values, and using experimental results to guide numerical simulation proves practical. The modal parameters vary greatly under different loading conditions, which can be attributed to the damage after each loading case. [ABSTRACT FROM AUTHOR]

In previous decades, shale gas production has been given special attention as a clean source of energy. Technological advancements in multi-well especially horizontal drilling and hydraulic fracturing, have raised more research on how to produce shale gas commercially while studying its challenges. CH4 gas production by using CO2 injection is a combination of several parameters, including both fracking and geologic parameters. This paper investigated the influence of aligned and staggered multiwell placement patterns to enhance CH4 gas recovery and CO2 sequestration. A three-dimensional reservoir model was built and simulated, and the influence of reservoir and fracking parameters was analyzed. The results revealed that the staggered well pattern is the best pattern for CH4 gas recovery during continuous injection, with a 37% increase of recovery with late CO2 breakthrough, compared with the aligned well pattern, which had 31% increase recovery, associated with early CO2 breakthrough. In terms of CO2 gas storage, the aligned well pattern had a significant amount of CO2 storage during continuous injection and huff and puff injection by storing 4% more carbon dioxide during continuous injection and 7% more during huff and puff injection than that in the staggered well pattern. Different injection timings of 1, 2, and 3 years, and injection cycles of one, three, and five cycles were analyzed during huff and puff injection. The results showed that five cycles of injection had the highest methane gas recovery, 23% and 21%, in aligned and staggered well patterns, respectively. Furthermore, the influence of injection start time also was analyzed, and results showed that injection after 10 years of production produced higher methane gas recovery and CO2 storage in both aligned and staggered well patterns, followed by injection after 5 years of production, after 3 years of production, and during the first year of production. Sensitivity analysis revealed that horizontal matrix permeability, vertical matrix permeability, initial reservoir pressure, reservoir temperature, injection pressure, injection rate, fracture porosity, and fracture spacing played a vital role in both methane gas recovery and carbon dioxide gas storage in both well patterns. In addition, results showed that methane recovered during continuous injection is higher than during huff and puff injection in both aligned and staggered well patterns. Results obtained from this paper can help to improve shale gas production in multiwell placements, and save time and cost. This paper should motivate more research into the mitigation of global warming through CO2 geosequestration. [ABSTRACT FROM AUTHOR]

This paper deals with the formulation and validation of the discrete fresh concrete (DFC) model to simulate the rheological behavior of self-consolidating, ordinary, and printable concrete in the fluid state immediately after mixing. The DFC model is formulated within the framework of the discrete-element method (DEM), and it models the interaction among coarse aggregate particles embedded in a fine mortar. The formulation is based on stress-strain constitutive equations through which the behavior of fresh concrete can be described by parameters with clear physical meaning. This study presents a rigorous methodology for estimating the model key input parameters by the comparison of numerical simulations with experimental data. This methodology includes (1) a series of sensitivity analyses and simulations to establish the relationship between constitutive parameters and macroscopic properties; and (2) numerical simulations of experimental tests commonly used to characterize the fresh state behavior of concrete. Finally, the paper discusses the application of the DFC model to the simulation of concrete additive manufacturing. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the fundamental characteristics of plasticity in microheterogeneous continuum materials. Plasticity in such materials is a multiscale phenomenon with contrasting characteristics at different scales. A hollow sphere model, including a matrix embedding an oblate spheroidal pore, is considered as a sample representative elementary volume (REV) of a microheterogeneous material where, at the local level (microscale), a simple Drucker–Prager plasticity model is assumed for the matrix obeying the classical continuum theory of plasticity. The plasticity model is Lode angle independent with associated plastic flow and no hardening. We perform finite element numerical simulations on the REV to investigate the characteristics of the homogenized plasticity of the REV. It is seen that the homogenized plasticity shows complex characteristics such as Lode angle dependency, presence of cap, hardening, and nonassociativity. Well-established as these aspects are in the literature, they are often presumed in the plasticity models of heterogeneous materials in an ad hoc form. In contrast, we present here a systematic and lucid way to capture these aspects as emergent phenomena of heterogeneous microstructures. This has crucial implications in guiding the theoretical constitutive developments for elastoplastic materials toward adopting a multiscale approach that properly considers the effect of microstructure and naturally captures these aspects without the need for ad hoc assumptions. A fundamental assumption in the classical theory of plasticity is the plastic flow rule postulate, which states that the direction of plastic strain increment is governed only by the current state variables, independent of the loading increment direction. We show, through a stress probing exercise in 3D principal stress space, that the flow rule, assumed for the microscale plasticity, is not valid for the macroscopic plasticity. Indeed, the homogenized plastic flow direction in heterogeneous materials is governed by the current state variables and loading increment direction. Finally, we show that the plastic response is also a function of the stress path taken prior to loading. As such, nonclassical characteristics are observed for the plasticity of microheterogeneous materials. These nonclassical characteristics for the simple REV considered in this work (the hollow sphere model) align with some of the results observed in experiments or only reported for microdiscrete materials; herein, we show they are also valid for a broader range of materials endowed with microstructure, i.e., microcontinuous materials, and, as such, the fundamental assumptions in the classical theory of plasticity require revision before being applicable to the plastic behavior of heterogeneous materials. [ABSTRACT FROM AUTHOR]

Soft-core sandwich structures subjected to coplanar compression loading might exhibit wrinkling behaviors, which will reduce significantly the support capability of the structure. In order to prevent the wrinkling behaviors of sandwich structures, this work attempts to improve stiffness of face sheets reinforced by carbon nanotubes (CNTs). To achieve such a goal, the following work is to be required. First, an equivalent single-layer model will be proposed to accurately analyze the wrinkling behaviors of sandwich structures because only layerwise models possess the capability to accurately predict wrinkling behaviors of sandwich structures, but these models are often computationally expensive. Second, the influence of distributions of the CNTs through thickness on the buckling and wrinkling behaviors for the sandwich beams will be investigated in detail. Moreover, the translation mechanism between the buckling deformation and the wrinkling deformation has been also explored. The proposed model has been verified by using the quasi three-dimensional (3D) elasticity solutions and the 3D finite-element results (3D-FEM). Third, by selecting the proper distributions of the CNTs through the thickness of sandwich structures, the wrinkling behaviors of sandwich structures can be effectively prevented. Thus, a scheme resisting wrinkling deformation of sandwich structures has been proposed, which can provide a reference for other investigators. Sandwich structures are extensively used in many engineering applications due to their high strength to weight ratios and ease of manufacture. However, sandwich structures subjected to in-plane compressive loads might encounter wrinkling failure. In practical applications, this phenomenon is so common, but when it occurs, the sandwich structures will become unstable and cannot withstand higher loads. Therefore, it is crucial to take effective measures to avoid the occurrence of such unfavorable phenomena. To this end, a strategy was presented, where carbon nanotubes are proposed to be added to the face-sheet of sandwich structures. In order to verify the effectiveness of this method, a computational model was also proposed to analyze the wrinkling behaviors. By comparing with the 3D-FEM results of computer simulations, it was proven that the proposed model is correct and effective. In addition, it was found that different volume fractions and distributions of carbon nanotubes have the different influences resisting wrinkling deformation. In practical applications, structural engineers might get some inspirations to avoid the instability of sandwich structures from the research results of this paper. [ABSTRACT FROM AUTHOR]

Temporary shoring structures are used in the construction of reinforced concrete buildings to transmit the loads of newly poured slabs onto the lower floors. The main problems involved in the use of shores/props are: (1) the possibility of having higher loads than those initially foreseen, and (2) the structural efficiency and cost of the system, which is normally oversized due to being designed to bear the maximum load of the most demanding building operation. This paper describes a test carried out on a full-scale one-story building to analyze the behavior of load limiters (LLs) installed on shores under actual construction loading conditions. The theoretical approach and development of this new LL concept were described in previous papers. Because these LLs still had not been tested in actual buildings, this paper covers the existing need for a test in the form of a "proof of concept." It also includes computer simulations and recommendations for the use of LLs. [ABSTRACT FROM AUTHOR]

The paper titled " HT ht Sequestration and Enhanced Shale Gas Recovery by HT ht Injection: Numerical Simulation Method", published online on February 15, 2022, has been retracted at the request of the authors. "CO2 Sequestration and Enhanced Shale Gas Recovery by CO2 Injection: Numerical Simulation Method." The authors discovered data-processing software errors that have affected the accuracy of the conclusions made in the paper. [Extracted from the article]

Accurate numerical modeling of structural components is necessary for both performance-based designs of new structures and performance assessments of existing structures. Steel special concentrically braced frames (SCBFs) represent a large portfolio of steel buildings in areas of high seismicity, especially in North America. Therefore, it is necessary to critically study the accuracy of available numerical models for SCBFs and propose improvements to them, if necessary. This requires forming a database of high-fidelity benchmark experimental results for SCBFs against which models can be compared. This paper presents multielement hybrid simulations on a steel SCBF, as a representation of systems with highly unsymmetrical hysteretic response. A representative buckling brace specimen is developed and verified through reversed-cyclic tests to physically capture the response of SCBFs in the experiments. 2-element and 4-element pseudo-dynamic hybrid simulations are carried out on the reference SCBF using the University of Toronto Ten-Element Hybrid Simulation Platform (UT10). The experimental results from the multielement tests are compared with numerical simulations in detail using the available numerical models, which are observed to predict the response well. [ABSTRACT FROM AUTHOR]

In the framework of generalized plasticity theory, this paper presents a new elastoplastic model to characterize complicated softening/hardening and dilation/contraction behaviors of sand–gravel composites in triaxial tests. The model has six parameters that are determined by the conventional triaxial test directly, which is of great practical interest to engineers. The dilatancy equation that is able to describe the dilatancy of sand–gravel composites during the whole shearing process is incorporated into the model. The advantage of the proposed model in predicting the dilatancy behavior of sand–gravel composites is demonstrated by comparing it with three widely used dilatancy equations. A set of drained triaxial compression tests were launched to examine the performance of the proposed model. In addition, the applicability of the model is also confirmed by sand–gravel composites tests covering a wider range of confining pressure in previous literature. The generality of the model on other granular materials including rockfill, Ottawa sand, calcareous sand, cement-sand–gravel material, and glass beads mixtures is also verified by comparing the experimental results with the corresponding fitting results. Furthermore, the proposed model is programmed into the nonlinear finite element program GEODYNA and applied to the numerical simulation of high concrete-faced sand–gravel dams. Summarizing the fitting and numerical results comprehensively, the constitutive model proposed in this study is capable of characterizing the mechanical behaviors of granular materials and can provide a powerful tool for geotechnical engineering. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of time-dependent bond slip on the delayed failure of RC frames. The time-dependent model of bond slip is formulated based on the mechanism of subcritical damage accumulation along the steel–concrete interface. A kinetic model of the time dependence of slip under sustained loading is developed through numerical simulations. The model is incorporated into a recently developed reduced-order numerical model for simulations of the progressive collapse of RC frames. It is shown that the present model captures the essential deformation mechanisms of the frame under both monotonic loading and sustained loading, and that the time dependence of bond slip has a profound influence on the delayed failure of RC frames, especially under moderate sustained loading. This finding highlights the importance of understanding and accounting for the time dependence of bond slip for future study of the delayed progressive collapse of RC structures. [ABSTRACT FROM AUTHOR]

In comparison with conventional thin-cylindrical tethers, tape-shaped tethers have obvious advantages in orbital applications such as electron collection, satellite deorbit, and reliability. There are many differences between them not only in appearance but also in dynamics. Hence, this paper studies the dynamics of a tape-shaped flexible tethered satellite during free deployment. First, an approximate model for the system, in which the tape-shaped tether is divided into a series of rigid elements connected by massless spherical joints, was structured. The bending stiffness of the tether was analyzed, and the tension force along the tether length direction was ignored. In particular, three types of constraint equations for rigid elements were built to help identify tether deployment. Then, the kinetic friction force between the tape-shaped tether and deployment device, as well as the atmospheric drag/lift on the system, were discussed. Finally, numerical simulations demonstrated that the deployment dynamics of the tape-shaped tethered system are sensitive to the bending stiffness, friction force, and orbital altitude. [ABSTRACT FROM AUTHOR]

The present paper concerns the introduction of a mixed analytical-numerical method for the estimation of the maximum lift coefficient of box-wing aircraft in unflapped configuration. The analytical aspect is related to the adaptation of the method included in the United States Air Force (USAF) Stability and Control Data Compendium (DATCOM) by means of an approach built on the characteristics of the optimal lift distribution of the box-wing and implemented through simplifying assumptions. Since the formulation depends on parameters of the considered aircraft, numerical simulations are performed through a vortex-lattice method to complete the input data set. The method is first presented and then validated for the case of the 2-seater amphibious PrandtlPlane (PrP) and is then applied to two test cases: a 300 passenger midrange PrandtlPlane and a regional hybrid-electric PrandtlPlane. Results are presented and discussed, and the links between the proposed method and relevant parameters of the box-wing design, such as taper ratios and wing loading repartition among the two wings is analyzed. [ABSTRACT FROM AUTHOR]

This paper focuses on the guidance of an unpowered reusable launch vehicle (RLV) with aerosurface failure in the terminal area energy management (TAEM) phase. The aerosurface failure will limit the bank capability, and has a great influence on the range and turning radius of RLV. To this end, a new TAEM guidance scheme with the ability of online profile reconstruction is proposed in this paper for the bank-constrained RLV. The 3-dimensional (3D) profile is reconstructed online by directly adjusting the parameters of the dynamic pressure profile and the two-external-tangent-circle-based ground track profile. As the coupling between vertical and lateral motion is considered in the trajectory propagation, the reconstruction accuracy is guaranteed. Then, a closed-loop TAEM guidance law is proposed to track the reconstructed 3D profile. The effectiveness and robustness of the guidance scheme are verified by numerical simulations with a variety of initial states and model deviations. [ABSTRACT FROM AUTHOR]

Gyratory compaction has widely been used to evaluate the compactability of hot asphalt mixtures. Existing efforts on modeling of gyratory compaction have largely been devoted to sophisticated high-fidelity numerical simulations. This paper presents a one-dimensional nonlocal model for gyratory compaction. The model is anchored by the principle of mass conversation, in which the local densification rate is formulated as a function of the nonlocal packing fraction. The nonlocal model involves a material characteristic length scale, which is independent of the specimen size. The nonlocality gives rise to strong effects of the specimen height on the overall compaction curve as well as on the profile of the local packing fraction. A set of gyratory compaction experiments is performed on specimens of different heights. It is shown that the model is able to capture the measured size effect on the compaction curves. A parametric study is carried out to investigate the effects of nonlocality and model parameters on the predictions of compaction curve and profile of packing fraction. [ABSTRACT FROM AUTHOR]

Hydraulic experiment courses in engineering education usually require students to follow a 'standard procedure.' Students are expected to learn the underlying theories through manipulating the equipment, observing the phenomena of fluid mechanics, and analyzing the data recorded in the laboratory. However, the procedures are usually complicated and require large amounts of preparation to ensure the success of the experiment. In this research, current paper-based preparations are improved by providing virtual equipment that can provide instant and realistic feedback, with the ability to deliver these over the Internet. This research selected the Venturi tube experiment as a case study. Five steps were defined in the development process: (1) defining the experiment procedure, (2) building a three-dimensional (3D) virtual reality model, (3) adding procedure controllers, (4) adding physics rules to the virtual world, and (5) adding 3D manipulation functions. The virtual experiment of Venturi tube was implemented and evaluated in a real class, with the involvement of 48 undergraduate students in National Taiwan University. The students were separated randomly into two groups, one using paper-based preparation and the other using the virtual equipment for experiment preparation. The results showed that the students who prepared using the virtual equipment performed significantly better in both speed and skill application in the real experiment. Their attitudes toward learning were also significantly more positive than that of the other group. [ABSTRACT FROM AUTHOR]

In this paper, a method has been proposed to use artificial neural networks for the modeling of concrete gravity dams with nonlinear hysteretic response under earthquake loading. The main advantage of this method is that it makes it possible to design an analysis tool for a specific dam based on the data obtained from monitoring said dam; hence, it is expected that the analysis tool could provide more precise results than analysis software presently available. This advantage is especially pronounced when the dam is to be analyzed under strong earthquakes where its response is nonlinear and hysteretic. The modeler neural network, referred to here as the neuro-modeler, offers considerable possibilities. For example, the nonlinear analysis of dams under earthquake loading requires considerable time; one advantage of designing neuro-modelers for dams is that they can give practically precise results about the response in a short time. As the first study on the subject to prepare a controlled precise data for the training and testing of the neuro-modeler so that the precision of the method could be evaluated, an analysis software was used to simulate the experiment. The smeared crack model, which has been one of the models used successfully in the literature to model concrete gravity dams, has been used in this study as well. Multilayer feed-forward neural networks have also been used. The first step in this method is to analyze the dam under study as it is subjected to different earthquake simulations to collect large data about its linear and nonlinear response. The second step is to train a neuro-modeler, based on the collected data, to implicitly learn the nonlinear hysteretic response of the dam being subjected to the training earthquakes. The third step is to test the precision and generalization capabilities of the neuro-modeler where it is used for the analysis of the dam under a number of selected earthquakes of different properties including both near- and far-field excitations. After passing the tests successfully, the neuro-modeler is expected to be able to provide reliable and precise results about the response of the dam under any given earthquake. Three concrete gravity dams with differing characteristics and in different geographical locations including the Koyna, Pine Flat, and Sefid-Rud dams, which have been both numerically and experimentally studied because they had experienced considerable damage during earthquakes, have been utilized as examples. A neuro-modeler has been trained for each of the dams and tested. The results are reported in this paper. The dam neuro-modelers have been successful in providing precise results in this numerical simulation of the nonlinear hysteretic behavior of dams. [ABSTRACT FROM AUTHOR]

The paper presents the identification process of inelastic (viscoplastic) properties for two aluminum alloys at a temperature of 120°C. The material parameters are calculated on the basis of uniaxial tension tests. Twelve tests at elevated temperature for each alloy have been performed--three tests for four different strain rates. The main purpose of the paper is to identify the Bodner-Partom viscoplastic model parameters for two aluminum alloys. The additional purpose of the research is the comparison of the parameter values at elevated temperatures for two types of aluminum alloys. The results have been successfully verified by numerical simulation of the laboratory tests. [ABSTRACT FROM AUTHOR]

The paper presents the experimental and numerical study of a mild steel replaceable dissipation device. The dissipater is made of a milled-down mild steel bar that is confined by a steel tube filled with either grout or epoxy. The use of a reduced area concentrates yielding and plastic straining over a defined length while the tube prevents buckling. The device has been widely adopted in posttensioned rocking systems, and extensive experimental research was carried out on wall and beam-column subassemblies using this external dissipater. As part of those experimental programs, some component testing was carried out; nevertheless, a more comprehensive study was necessary to cover a wider range of geometric and mechanical parameters. The main objective of this research was to calibrate and suggest design parameters to support the design of the dissipation device. The paper shows a comprehensive experimental program under quasi-static cyclic loading carried out with varying geometrical parameters. This work forms the basis for the development of more refined analytical and numerical models to simulate the behavior of the device. In particular, the onset of the dissipater interaction with the confining tube and its buckling mechanism were targeted. Further numerical simulations made use of a fiber element–based model that was capable of capturing the full range of deformation mechanisms highlighted in the experimental program. Using this model, an extensive parametric analysis was carried out to determine significant design parameters, such as the maximum force in the dissipater and the buckling onset strain. Analytical models were also presented to predict the monotonic behavior of the dissipater and provide calibration of the hysteretic force-displacement rule proposed in the final part of the paper. [ABSTRACT FROM AUTHOR]

Long-term exposure to a harsh environment leads to irreversible degradation of mechanical properties of fiber-reinforced polymer (FRP) profiles. Understanding the aging effects on pultruded FRP composites due to long-term exposure is essential. The moisture diffusion process plays a significant role in understanding material degradation of E-glass/polyester-reinforced polymer composite laminates exposed to hygrothermal environments. In this paper, the moisture diffusion process in pultruded (GFRP) composite bridge members is numerically simulated using the finite-element method. The moisture diffusion parameters were calibrated by gravimetric tests of pultruded composite thin plates. Gravimetric tests of three different rectangular specimens were conducted to investigate three-dimensional moisture diffusion at different temperatures and environments. The calibrated mass diffusion parameters were validated by comparing the average time-dependent moisture concentration obtained from non-Fick finite-element (FE) simulation with experimental results. [ABSTRACT FROM AUTHOR]

Jacking force is one of the most important parameters in pipe jacking engineering, and also the key in pipe jacking design. A lot of research has been done on the prediction of jacking force of a single pipe. However, the research on jacking force of a row of steel pipes is relatively rare. A case of pipe jacking project is studied in this paper. In construction the test pipes were successfully jacked into the designed position, but the subsequent pipes were stuck because the jacking machine could not provide enough jacking force. Based on this phenomenon, the influence on the jacking force from the pipe spacing and the number of pipes have been jacked around the pipe being jacked is studied by field measurement and numerical simulation. The mechanism of the steel pipes stuck after the test pipes is analysed in detail. The results show that the jacking force decreases nonlinearly with the increase of the pipe spacing, and the influence range of pipe jacking is three times the pipe diameter; the jacking force increases with the increment of the number of pipes that have been jacked, but the increasing trend gradually slows down. Based on the above results, the pipe group effect of jacking force is proposed which is verified by the measured data. The results indicate that the amplification and superposition effect of the jacking force should be considered in the design stage to avoid pipes stuck in the jacking process. [ABSTRACT FROM AUTHOR]

Unreinforced masonry structures, particularly façade walls, are seismically vulnerable due to their weak connections with adjacent walls, floors, and/or roofs. During an earthquake, such walls formulate local mechanisms prone to out-of-plane collapse. This behavior has been largely investigated using classical rocking theory, which assumes the structure responds as a rigid body undergoing rocking motion, with energy dissipation at impact. Due to the complexity of the problem, however, e.g., number of degrees of freedom or boundary conditions, numerical block-based modeling is gaining momentum. However, numerical models lack a consistent and reliable treatment of the energy loss at impact. This paper bridges the gap between the well-established energy loss of classical rocking theory and the treatment of damping in numerical modeling. Specifically, it proposes an equivalent viscous damping model through novel ready-to-use predictive equations that capture the dissipative phenomena during both one-sided and two-sided planar rocking motion. The results reveal a satisfactory performance of the proposed model through comparisons with experimental results from literature and highlight its universality and robustness through applications of the model in fundamentally different block-based numerical modeling software. [ABSTRACT FROM AUTHOR]

Realistic time history simulation of drilled pier/pile-soil systems under dynamic and static loading is essential for the development of effective performance-based earthquake designs of deep foundations. This paper presents the results of the numerical simulation of a series of static and dynamic tests on drilled piers performed at the University of California, Berkeley. A nonlinear soil model was implemented based on multiaxial cyclic bounding-surface plasticity within a general finite-element framework, OpenSees. The model requires a small number of parameters that can be easily obtained through conventional site investigations. The results of the simulations show that the model can reasonably simulate nonlinear response of the soil and that it does a good job of capturing the actual load deformation curves obtained from in situ dynamic and static pier load tests. Although the model is suitable for a fully nonlinear total stress analysis of soil-pile systems under multidirectional shaking, further studies are needed to enhance the model capacity by incorporating the cyclic stiffness and strength degradation caused by full stress reversals. [ABSTRACT FROM AUTHOR]

Current state-of-the-art tools allow for the accurate modeling of complex construction operations using discrete-event simulation and their realistic postprocessed three-dimensional animation. Due to the postprocessed nature of these animations it is not possible to interact with them so as to affect the remaining course of actions. The next logical step in the evolution of simulation modeling and visualization in construction is for simulations and animations to run concurrently and in a manner that allows interaction with the animation to affect the course events in the simulation. This effectively enables the creation of virtual environments with logic based on discrete-event simulation. This paper presents the user interaction architecture that accomplishes this. In particular, the paper presents: (a) the conceptualization developed to design the components for user interaction and (b) the design of the components with a focus on (i) empowering model developers to enable user interaction in their models and (ii) extensibility to enable the development of more advanced user interaction techniques. [ABSTRACT FROM AUTHOR]

This paper presents a new, simple, and exact solution to the formation keeping of satellites when the relative distance between the satellites is so large that the linearized relative equations of motion no longer hold. We employ a recently proposed approach, the Udwadia-Kalaba approach, which makes it possible to explicitly obtain the desired control function without making any approximations related to the nonlinearities in the underlying dynamics. We use an inertial frame of reference to describe the motion of a satellite and since no approximations are made, the results obtained apply to situations even when the distance between the satellites is arbitrarily large. The paper deals with a projected circular formation, but the methodology in this paper can be applied to any desired configuration or orbital requirements. Numerical simulations confirm the brevity and the accuracy of the analytical solution to the dynamical control problem developed herein. [ABSTRACT FROM AUTHOR]

Rapid growth of residential construction in the city of Edmonton, Alberta, Canada has led to an increased demand for lot grading (LG) inspectors. The traditional inspection process has contributed to inspection delays, backlog, and decreased customer satisfaction. The aim of the research presented in this paper is to study, evaluate, and optimize the existing LG approval process. Data from past years were collected and analyzed to establish a baseline performance level. Flowcharts were developed to visualize the process and a survey was conducted to determine potential areas of improvement from the perspectives of different shareholders. Lean thinking principles were applied to identify and reduce the nonvalue added activities and improve performance. The final phase of the research involved the simulation of the process to evaluate the impact of the implementation of various recommendations. Based on the simulation results, final recommendations were made and later implemented with the help from the city’s Information technology department. These modifications to the existing process produced significant gains in quality and productivity, as predicted by the simulation model. [ABSTRACT FROM AUTHOR]

This paper introduces the concept of microscopic simulation system scalability for the purpose of reducing the computational requirements of microsimulation modeling of large-scale traffic networks. This exploratory stage of research investigates scalability of both lane-changing and car-following behavior. The main objective of the proposed methodology is to create a reduced-scale network (microcosm) that retains most of the significant characteristics of the full-scale network (prototype). To achieve this objective a systematic downsampling procedure has been applied to a case study of a one-lane homogeneous freeway corridor in order to create a geometrically, kinematically, and behaviorally equivalent microcosm environment. This paper examines the scalability of lane-changing behavior, assuming a shifted negative exponential headway distribution, and investigates the scalability of car-following behavior under various operating conditions and downsampling ratios. The paper focuses on the tradeoff between performance and scalability of microscopic simulation systems. For each of the 48 cases considered, optimal behavioral parameters were determined based on two optimization methods: (1) Microscopic based on minimization of trajectory errors in both environments and (2) macroscopic derived from minimization of density errors in both environments throughout the simulation period. The results show that both optimization solutions were consistent in determining the optimal behavioral parameters. [ABSTRACT FROM AUTHOR]

Evaluation of the concrete cracking induced by rebar corrosion is necessary for accurately clarifying the durability and predicting the service life of reinforced concrete (RC) structures. The fact that rust penetration into cracks might decrease corrosion expansion has been realized but not sufficiently investigated. In this paper, a numerical approach in terms of the mesoscopic structure of concrete is used to simulate the corrosion-induced concrete cracking, and the lattice network model to account for rust penetration into cracks is developed by assuming that the movement of rust is driven by moisture convection. The total rust amount is calculated based on Faraday's law, and the rust expansion is transformed to a radial displacement boundary condition for both uniform and nonuniform conditions. Rust penetration is assumed to be a convection process governed by Darcy's law. The proposed model is confirmed by comparing cracking pattern, corrosion pressure, surface crack width, mass ratio of penetrated rust to total rust (ΔWpe/ΔWtotal), and volume ratio of cracks occupied by rust to total cracks (Vrustcrack/Vcracktotal) with available experimental and numerical results. It is found that the distribution and the amount of penetrated rust are closely related to the volume of cracks and the connection of crack networks. Besides, through sensitivity analysis of influencing factors for rust penetration, it is found that a higher dissolved degree of rust in moisture induces a higher ΔWpe/ΔWtotal , but it doesn't influence Vrustcrack/Vcracktotal. A larger relative water content at the concrete-steel interface will induce higher ΔWpe/ΔWtotal and Vrustcrack/Vcracktotal , while the initial relative water content in concrete has no significant difference on either ΔWpe/ΔWtotal or Vrustcrack/Vcracktotal. [ABSTRACT FROM AUTHOR]

Subcritical flow in a short expansion tends to become detached from its sidewalls and create turbulent eddies. This phenomenon can cause undesirable losses of flow energy and channel erosion. This paper numerically investigates the effects of a triangular hump fitted at the bottom of the expansion on flow separation reduction. The results are validated using available experimental data. This paper reports quantitative details of the velocity field, eddy structures, and flow streamline separation in expansions of different divergence angles under various conditions of the Froude number. The results show that the flow of water can separate along either of the two sidewalls, possibly due to bistability. The use of appropriate humps can effectively reduce separation and turbulent eddies because they force the flow to accelerate and hence create a favorable pressure gradient. The results from this paper are useful for the optimal design of expansions as an important part of irrigation and water systems. [ABSTRACT FROM AUTHOR]