Recent efforts on model-based simulation of engineering problems : multiphysics and multiphase interactions

Simulation-Based Engineering Science (SBES) is playing a more important role in gaining new knowledge and providing guidance for engineering activities, in particular, in the fields in which time scale and/or spatial scale make physical experiments dramatically expensive or even impossible. The success of SBES heavily relies on the development of algorithms that provide the bridge between the models describing physical and engineered systems and the computational devices that generate the digital representations of simulations. My efforts on the development of algorithms that simulate multiphysics and multiphase flow are presented in this dissertation. The first part of the dissertation describe the algorithms for the multiphysical model that simulates the laser drilling process. During laser drilling, heat conduction, melt flow, and vaporization occur in a very short time period. Vaporization also produces the recoil pressure that drives melt flow and complicates the heat transfer and material removal rate. To get a more realistic picture of the melt flow, a series of differential equations were developed that govern the process from pre-heating to melting and evaporation. In particular, the Navier-Stokes equation governing the melt flow is solved with the use of the boundary layer theory and integral methods. Heat conduction in a solid is investigated by using classic solutions with the corrections that reflect the change in boundary condition from constant heat flux to Stefan condition. The dependence of saturation temperature on the vapor pressure is taken into account by using the Clausius-Clapeyron equation. Both constantly rising radial velocity profiles and rising-fall velocity profiles are considered. In spite of the assumed varying velocity profiles, the new model predicts that the drilling hole profiles are very close to each other in a specific super alloy for given laser beam intensity and pulse duration. The numerical results show that the effect of melt flow on material removal can be ignored in some cases. The solutions derived can be applied to new cases to determine the role of melt flow and vaporization on laser drilling profile evolution and to study the solid material removal efficiency. The second part of this dissertation describes a new method that simulates the interaction between fluid and solid elements. The discrete element method (DEM) has been used to deal with the interactions between solid elements of various shapes and sizes, while the material point method (MPM) has been developed to handle the multi-phase (solid-liquid-gas) interactions involving failure evolution. A combined MPM-DEM procedure is proposed to take advantage of both methods so that the interaction between solid elements and fluid particles in a container could be better simulated. In the proposed procedure, large solid elements are discretized by the DEM, while the fluid motion is computed using the MPM. The contact forces between solid elements and rigid walls are calculated using the DEM. The interaction between solid elements and fluid particles are calculated via an interfacial scheme within the MPM framework. The proposed procedure is illustrated by representative examples. The convergence of numerical solutions and the factors affecting the simulation fidelity is also discussed

Extensional collapse of the Tibetan plateau: results of threedimensional finite element modeling

[1] Following their initial collision 50-70 Myr ago, the Indian and Eurasian plates have been continuously converging toward each other. Whereas the regional stress field is predominately compressive, the Late Cenozoic tectonics within the Tibetan Plateau features widespread crustal extension. Numerous causes of the extension have been proposed, but their relative roles remain in debate. We have investigated the major factors contributing to the Tibetan extension in a three-dimensional viscoelastic model that includes both lateral and vertical variations of lithospheric rheology and relevant boundary conditions. Constrained by the present topography and GPS velocity field, the model predicted predominately extensional stress states within the plateau crust, resulting from mechanical balance between the gravitational buoyancy force of the plateau and the tectonic compressive stresses. The predicted stress pattern is consistent with the earthquake data that indicate roughly E-W extension in most of Tibet and nearly N-S extension near the eastern margin of the Tibetan Plateau. We explored the parameter space and boundary conditions to examine the stress evolution during the uplift of the Tibetan Plateau. When the plateau was lower than 50% of its present elevation, strike-slip and reverse faults were predominate over the entire plateau, and no E-W crustal extension was predicted. Significant crustal extension occurs only when the plateau has reached $75% of its present elevation. Basal shear associated with underthrusting of the Indian plate beneath Tibet may have enhanced crustal extension in southern Tibet and the Himalayas, and a stronger basal shear during the Miocene may help to explain the development of the South Tibetan Detachment System

Early detection of pine wilt disease tree candidates using time-series of spectral signatures

Pine wilt disease (PWD), caused by pine wood nematode (PWN), poses a tremendous threat to global pine forests because it can result in rapid and widespread infestations within months, leading to large-scale tree mortality. Therefore, the implementation of preventive measures relies on early detection of PWD. Unmanned aerial vehicle (UAV)-based hyperspectral images (HSI) can detect tree-level changes and are thus an effective tool for forest change detection. However, previous studies mainly used single-date UAV-based HSI data, which could not monitor the temporal changes of disease distribution and determine the optimal detection period. To achieve these purposes, multi-temporal data is required. In this study, Pinus koraiensis stands were surveyed in the field from May to October during an outbreak of PWD. Concurrently, multi-temporal UAV-based red, green, and blue bands (RGB) and HSI data were also obtained. During the survey, 59 trees were confirmed to be infested with PWD, and 59 non-infested trees were used as control. Spectral features of each tree crown, such as spectral reflectance, first and second-order spectral derivatives, and vegetation indices (VIs), were analyzed to identify those useful for early monitoring of PWD. The Random Forest (RF) classification algorithm was used to examine the separability between the two groups of trees (control and infested trees). The results showed that: (1) the responses of the tree crown spectral features to PWD infestation could be detected before symptoms were noticeable in RGB data and field surveys; (2) the spectral derivatives were the most discriminable variables, followed by spectral reflectance and VIs; (3) based on the HSI data from July to October, the two groups of trees were successfully separated using the RF classifier, with an overall classification accuracy of 0.75–0.95. Our results illustrate the potential of UAV-based HSI for PWD early monitoring

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic. \ua9 2017 American Chemical Society

Environmental benefits of innovation policy : China's national independent innovation demonstration zone policy and haze control

In recent years, China has focused its development on technological innovation, trying to achieve a win–win situation between environmental protection and economic growth, and it has formulated a series of policies to promote technological innovation. Taking China's national independent innovation demonstration zone (NIIDZ) policy as an example, this paper empirically investigates the impact of China's innovation policy on haze pollution by using a difference-in-differences (DID) model. The results show that the NIIDZ policy promotes the governance of urban haze pollution and confirms the applicability of the experimentalist governance model in the practice of innovation policy in developing countries. Dynamic analysis shows that the NIIDZ policy has an experience accumulation effect. This policy can continue to promote haze control for at least 6 years, and the policy effect increases year by year. Action mechanism analysis shows that the NIIDZ policy can inhibit urban haze pollution by promoting urban technological innovation and high-tech industrial agglomeration. The estimation results of the spatial DID model show that the NIIDZ policy not only inhibits haze pollution in NIIDZ cities but also has an inhibitory effect on haze pollution in the surrounding non-NIIDZ cities and the NIIDZ cities, which confirms the positive externality characteristics of policy diffusion theory and environmental governance. The conclusions of this paper have important theoretical value for understanding the ecological effect of innovation policy and provide experience for developing countries to implement an experimentalist governance model

The role of top leadership team's cognitive framework in COVID-19 control and economic recovery in China

This study aims to discuss how China’s top leadership team’s (CTLT) cognitive framework helped them quickly minimize the impact of COVID-19 and enter economic recovery. We find that cognitive framework of CTLT based on Yin-Yang philosophy balancing exerted the following effects: (1) It helped CTLT determine the relative significance of COVID-19 control and economic recovery from a higher level goal of Chinese people’s life and health. (2) It helped CTLT determine opportunities conducive to economic recovery from COVID-19. (3) It helped Chinese leaders quickly identify the central paradox in COVID-19 and mobilize the available resources to address it

[In Press] The Eastern construction of paradoxical cognitive framework and its antecedents : a Yin-Yang balancing perspective

Purpose: In the face of external paradoxical requirements, the cognitive framework of managers and employees use to perceive, interpret and reconstruct information is important to ease anxiety and improve job performance. The Yin-Yang balancing of eastern philosophical thought is particularly good at explaining and predicting changes and conflict environments. For this reason, this study aims to propose the eastern construction of the paradoxical cognitive framework based on the Yin-Yang balancing theory and its antecedent framework. Design/methodology/approach: This paper contrasts the similarity and differences between Chinese and Western philosophy’s thoughts on paradoxes. On this basis, the eastern construction of the paradoxical cognitive framework is proposed. Then, the paper puts forward the antecedent framework of managers’ cognitive framework and employees’ paradoxical cognitive framework. Findings: This paper proposes the eastern construction of the paradoxical cognitive framework includes the following three dimensions: the unity-in-diversity of paradoxical elements, the asymmetric balance of paradoxical elements and mutual transformation of paradoxical elements. In addition, this paper proposes an antecedent framework of the eastern construction of the paradoxical cognitive framework – the paradoxical requirement of organizational environment exerts a direct impact on managers’ and employees’ paradoxical cognitive framework; managers’ paradoxical cognitive framework has a positive impact on paradoxical leadership; paradoxical leadership exerts an indirect impact on employees’ paradoxical cognitive framework through the collective paradoxical cognitive framework; paradoxical leadership directly affects employees’ paradoxical cognitive framework. Research limitations/implications: This paper focuses on comparing the similarities and differences of the individual paradoxical cognitive framework in Chinese and Western cultures and proposes the eastern construction of the paradoxical cognitive framework and its antecedent framework. Future research needs to further verify the theoretical framework proposed in this paper. Originality/value: This paper makes a detailed comparison of the paradox views in Chinese and Western philosophy. It is the first to propose the eastern construction of the paradoxical cognitive framework and its antecedent framework, laying a theoretical foundation for future empirical research

Understanding Singaporeans’ pro-environmental behaviors : a theoretical expansion of the influence of presumed media influence

Using the influence of presumed media influence (IPMI) model as the theoretical framework, this study aims to explain the influence of individuals’ attention to pro-environmental media messages on their pro-environmental behavioral intentions. Specifically, we examine both direct and indirect media effects on individuals’ pro-environmental behavioral intentions, and integrate the constructs of attitudes, descriptive, subjective, and injunctive norms into the model. Furthermore, we used the expanded model to examine the influences on three dimensions of pro- environmental behavioral intentions, namely energy conservation, recycling, and civic engagement. We tested the proposed extended framework on a random sample of 1,144 Singaporeans utilizing computer-assisted telephone interviewing (CATI).Bachelor of Communication Studie