Creep Behavior of Hot-Mix Asphalt due to Heavy Vehicular Tire Loading

The objective of this study is to characterize the creep behavior of hot-mix asphalt (HMA) at intermediate (20°C) and at high temperatures (40°C). To accomplish this objective, a nonlinear time-hardening creep model, characterized through laboratory testing, was incorporated into a three-dimensional (3D) finite-element (FE) model, which was used to calculate permanent creep strains after applying repetitive vehicular loading cycles at the pavement surface. Two different tire configurations were simulated representing a typical dual-tire assembly and a newly introduced wide-base tire (dual-tire: 275/80R22.5 and wide-base tire: 455/55R22.5). Results of the 3D FE model were successfully verified against pavement response measurements in the field at the Virginia Smart Road. While the elastic or linear viscoelastic FE model may not simulate permanent deformation or shear creep strains after repetitions of vehicular loading, a nonlinear time-hardening creep model could predict primary rutting damage in HMA and shear creep strains at the edge of the tire imprint caused by different tire configurations.     

A Service-Oriented Middleware for Building Collaborative UAVs

For a while, Unmanned Arial Vehicles (UAVs) use was limited to military applications, however recently UAVs are also used for a wide range of civilian applications. Some of these UAV applications may involve multiple UAVs that must cooperate to achieve a common goal. This kind of applications is termed collaborative UAV applications. This paper investigates the collaborative aspects and challenges of multiple UAV systems. One of the main issues for multiple UAV systems is developing an effective framework to enable the development of software systems for collaborative UAV operations. One possible approach is to rely on service-oriented computing and service-oriented middleware technologies to simplify the development and operations of such applications. This paper discusses how the service-oriented middleware approach can help resolve some of the challenges of developing collaborative UAVs. The paper also proposes a service-oriented middleware architecture that can satisfy the development and operations of such applications.     

Causal state-feedback parameterizations in robust model predictive control

In this paper, we investigate the problem of nonlinearity (and non-convexity) typically associated with linear state-feedback parameterizations in the Robust Model Predictive Control (RMPC) for uncertain systems. In particular, we propose two tractable approaches to compute an RMPC controller–consisting of both a causal, state-feedback gain and a control-perturbation component–for linear, discrete-time systems involving bounded disturbances and norm-bounded structured model-uncertainties along with hard constraints on the input and state. Both the state-feedback gain and the control-perturbation are explicitly considered as decision variables in the online optimization while avoiding nonlinearity and non-convexity in the formulation. The proposed RMPC controller–computed through LMI optimizations–is responsible for steering the uncertain system state to a terminal invariant set. Numerical examples from the literature demonstrate the advantages of the proposed scheme.     

A new finite volume method for flux-gradient and source-term balancing in shallow water equations

We present a new finite volume method for flux-gradient and source-term balancing in the numerical solution of shallow water equations on nonflat topography. The method consists of a predictor stage for discretization of gradient terms and a corrector stage for treatment of source terms. The numerical fluxes at the interfaces of each triangle are reconstructed using an upwind scheme along with slope limiters to obtain high accuracy in the method. Using a three-sided decomposition, the source terms are balanced in the corrector stage. The proposed method is implemented on unstructured meshes and verifies the exact conservation property (C-property). We also discuss a mesh adaptive procedure by monitoring the water depth in the computational domain. Several standard test examples are used to verify high accuracy, exact C-property and good resolution properties for smooth and discontinuous solutions.     

Reach a nonlinear consensus for MAS via doubly stochastic quadratic operators

This technical note addresses the new nonlinear protocol class of doubly stochastic quadratic operators (DSQOs) for coordination of consensus problem in multi-agent systems (MAS). We derive the conditions for ensuring that every agent reaches consensus on a desired rate of the group's decision where the group decision value in its agent's initial statuses varies. Besides that, we investigate a nonlinear protocol sub-class of extreme DSQO (EDSQO) to reach a consensus for MAS to a common value with nonlinear low-complexity rules and fast time convergence if the interactions for each agent are not selfish. In addition, to extend the results to reach a consensus and to avoid the selfish case we specify a general class of DSQO for reaching a consensus under any given case of initial states. The case that MAS reach a consensus by DSQO is if each member of the agent group has positive interactions of DSQO (PDSQO) with the others. The convergence of both EDSQO and PDSQO classes is found to be directed towards the centre point. Finally, experimental simulations are given to support the analysis from theoretical aspect.     

Daily prediction of short-term trends of crude oil prices using neural networks exploiting multimarket dynamics

This paper documents a systematic investigation on the predictability of short-term trends of crude oil prices on a daily basis. In stark contrast with longer-term predictions of crude oil prices, short-term prediction with time horizons of 1–3 days posits an important problem that is quite different from what has been studied in the literature. The problem of such short-term predicability is tackled through two aspects. The first is to examine the existence of linear or nonlinear dynamic processes in crude oil prices. This sub-problem is addressed with statistical analysis involving the Brock-Dechert-Scheinkman test for nonlinearity. The second aspect is to test the capability of artificial neural networks (ANN) for modeling the implicit nonlinearity for prediction. Four experimental models are designed and tested with historical data: (1) using only the lagged returns of filtered crude oil prices as input to predict the returns of the next days; this is used as the benchmark, (2) using only the information set of filtered crude oil futures price as input, (3) combining the inputs from the benchmark and second models, and (4) combing the inputs from the benchmark model and the intermarket information. In order to filter out the noise in the original price data, the moving averages of prices are used for all the experiments. The results provided sufficient evidence to the predictability of crude oil prices using ANN with an out-of-sample hit rate of 80%, 70%, and 61% for each of the next three days’ trends.     

Effect of Frictions on the Ballistic Performance of a 3D Warp Interlock Fabric: Numerical Analysis

3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2? fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.     

Hydroelastic Behavior of a Floating Ring-Shaped Plate

The interaction between incident surface water waves and floating elastic plate is studied. This paper considers the diffraction of plane incident waves on a floating flexible ring-shaped plate and its response to the incident waves. An analytic and numerical study of the hydroelastic behavior of the plate is presented. An integro-differential equation is derived for the problem and an algorithm of its numerical solution is proposed. The representation of the solution as a series of Hankel functions is the key ingredient of the approach. The problem is first formulated. The main integro-differential equation is derived on the basis of the Laplace equation and thin-plate theory. The free-surface elevation, plate deflection and Green’s function are expressed in polar coordinates as superpositions of Hankel and Bessel functions, respectively. These expressions are used in a further analysis of the integro-differential equation. The problem is solved for two cases of water depth infinite and finite. For the coefficients in the case of infinite depth a set of algebraic equations is obtained, yielding an approximate solution. Then a solution is obtained for the general and most interesting case of finite water depth analogously in the seventh section. The exact solution might be approximated by taking into account a finite number of the roots of the plate dispersion relation. Also, the influence of the plate’s motion on wave propagation in the open water field and within the gap of the ring is studied. Numerical results are presented for illustrative purposes.     

Electrical properties and longitudinal modulus of superconductor/polymer NdBa2Cu3O7−δ/PVC composites

High temperature superconductor NdBa₂Cu₃O_7–/poly(vinyl chloride) (Nd123/PVC) composites have been prepared by cold press and hot press methods. Addition of PVC resulted in increase of the electrical resistivity with percolation occurring between 0.3 and 0.5 Nd123 volume fraction for both preparation methods. Although the samples showed some form of magnetic levitation at liquid nitrogen temperature, they do not show any zero-resistance temperature indicating the lack of effective superconducting percolative path. The density deviates from the linear calculated value with increasing Nd123 content at 0.3 volume fraction for the cold press and at 0.6 for the hot pressed samples due to increasing porosity. X-ray powder diffraction patterns suggest that the Nd123 crystals tend to align when the composites are prepared by hot press method. A resistance anomaly is observed at 90 K in the hot press composites indicating improved electrical contact between the aligned Nd123 grains. The longitudinal modulus increases as Nd123 content is increased.     

On experimental investigation of failure process of woven-fabric composites

In this paper an experimental investigation is performed to describe the fracture behavior and failure mechanisms of woven fabrics composites, under static loading, using a compact tension test (CT). We studied the development of the different damage phases using the digital image correlation and the compliance method. The crack length was estimated at in the front of the notch tip. The approach of the effective crack length via the compliance procedure was compared to the measures of the damage in the epoxy/glass fiber composite obtained by the digital image correlation (DIC).