Fast and Accurate Computation of Time-Domain Acoustic Scattering Problems with Exact Nonreflecting Boundary Conditions

This paper is concerned with fast and accurate computation of exterior wave equations truncated via exact circular or spherical nonreflecting boundary conditions (NRBCs, which are known to be nonlocal in both time and space). We first derive analytic expressions for the underlying convolution kernels, which allow for a rapid and accurate evaluation of the convolution with $O(N_t)$ operations over $N_t$ successive time steps. To handle the onlocality in space, we introduce the notion of boundary perturbation, which enables us to handle general bounded scatters by solving a sequence of wave equations in a regular domain. We propose an efficient spectral-Galerkin solver with Newmark's time integration for the truncated wave equation in the regular domain. We also provide ample numerical results to show high-order accuracy of NRBCs and efficiency of the proposed scheme.Comment: 22 pages with 9 figure

Computational Modeling of the Time-dependent Behavior of Cementitious Materials

Finite element procedures combined with microstructure development modeling are integrated to quantitatively predict the viscoelastic/viscoplastic relaxation of cement paste due to intrinsic calcium silicate hydrate viscoelasticity/viscoplasticity and microstructure evolution. The combined models are implemented in a computational routine to predict time-dependent stress and strain fields in cement paste. Besides predicting the time-dependent viscoelastic/viscoplastic properties of cement paste, the early-age desiccation shrinkage of cement paste is also computationally simulated utilizing this modeling approach. The model simulations suggest that inherent viscoelastic deformation caused by calcium silicate hydrate might not necessarily be the primary mechanism leading to the overall early-age time-dependent behavior of cement paste. The effect of time-dependent dissolution of load-bearing phases due to either the hydration reaction or the application of stress/strain can be substantial and should be considered as a significant mechanism for the apparent viscoelasticity/viscoplasticity of cement paste

Forecasting bus passenger flows by using a clustering-based support vector regression approach

As a significant component of the intelligent transportation system, forecasting bus passenger flows plays a key role in resource allocation, network planning, and frequency setting. However, it remains challenging to recognize high fluctuations, nonlinearity, and periodicity of bus passenger flows due to varied destinations and departure times. For this reason, a novel forecasting model named as affinity propagation-based support vector regression (AP-SVR) is proposed based on clustering and nonlinear simulation. For the addressed approach, a clustering algorithm is first used to generate clustering-based intervals. A support vector regression (SVR) is then exploited to forecast the passenger flow for each cluster, with the use of particle swarm optimization (PSO) for obtaining the optimized parameters. Finally, the prediction results of the SVR are rearranged by chronological order rearrangement. The proposed model is tested using real bus passenger data from a bus line over four months. Experimental results demonstrate that the proposed model performs better than other peer models in terms of absolute percentage error and mean absolute percentage error. It is recommended that the deterministic clustering technique with stable cluster results (AP) can improve the forecasting performance significantly.info:eu-repo/semantics/publishedVersio

A Coordination Model and Framework for Developing Distributed Mobile Applications

How to coordinate multiple devices to work together as a single application is one of the most important challenges for building a distributed mobile application. Mobile devices play important roles in daily life and resolving this challenge is vital. Many coordination models have already been developed to support the implementation of parallel applications, and LIME (Linda In a Mobile Environment) is the most popular member. This thesis evaluates and analyzes the advantages and disadvantages of the LIME, and its predecessor Linda coordination model. This thesis proposes a new coordination model that focuses on overcoming the drawbacks of LIME and Linda. The new coordination model leverages the features of consistent hashing in order to obtain better coordination performance. Additionally, this new coordination model utilizes the idea of replica mechanism to guarantee data integrity. A cross-platform coordination framework, based on the new coordination model, is presented by this thesis in order to facilitate and simplify the development of distributed mobile applications. This framework aims to be robust and high-performance, supporting not only powerful devices such as smartphones but also constrained devices, which includes IoT sensors. The framework utilizes many advanced concepts and technologies such as CoAP protocol, P2P networking, Wi-Fi Direct, and Bluetooth Low Energy to achieve the goals of high-performance and fault-tolerance. Six experiments have been done to test the coordination model and framework from di erent aspects including bandwidth, throughput, packages per second, hit rate, and data distribution. Results of the experiments demonstrate that the proposed coordination model and framework meet the requirements of high-performance and fault-tolerance