Numerical Analysis of Finite Element Method for a Transient Two-phase Transport Model of Polymer Electrolyte Fuel Cell

AbstractIn this paper, we study a 2D transient two-phase transport model for water species in the cathode gas diffusion layer of hydrogen polymer electrolyte fuel cell (PEFC), the reformulation of water concentration equation is described by using Kirchhoff transformation, and its numerical efficiency is demonstrated by successfully dealing with the discontinuous and degenerate water diffusivity. The semi-discrete and fully discrete finite element approximations with Crank-Nicolson scheme are developed for the present model and the optimal error estimate in H1 norm and the sub-optimal error estimate in L2 norm are established for both finite element schemes

Auf dem Weg zum Cyberpunk (On the Way to Cyberpunk)

Cyberpunk is a word that is both familiar and unfamiliar to us. In some ways, it is familiar to us. As a sub-genre of science fiction, Cyberpunk is a popular futuristic theme that greatly influenced pop culture in the 21st century. We are fascinated by the bizarre but realistic fictional world, a dystopian society characteristic of high tech and low life for the majority population, it presents. In most works of this genre, an overwhelming technology company monopolies most social resources and dominates society like a leviathan . The majority population is alienated from the well-being brought by high technology. They are exploited by the social elites and forced to endure the scarcity of resources and terrible living standards. On the other hand, it is unfamiliar to us. We believe that such a dystopian world can only exist in artworks or literature. Natural rights, social contracts, and all men are created equal —these concepts have been deeply embedded in our laws and culture. After the USSR fall, most of us believe that we have reached the end of history. In this democratic system we proud of, there will be no more oppressors benefiting from exploiting others with their social power. At least, the organization that most likely to become a leviathan , the government, has been tamed by the democratic system we built. Naturally, people tend to believe in what they want to believe. A promise of a bright future is always more attractive than disturbing predictions. However, ignorance is always the outset of disaster. In the 21st century, cyber technology advances at an unprecedented pace. The rocketing up Internet market produces thousands of tech entrepreneurs every year. We once believed that the Internet\u27s development could lead to diversity and transparency and facilitate the free dissemination of information. Nevertheless, tech giants, such as Google and Facebook, are gradually taking over the world of the Internet. They overwhelm, annex the smaller companies and monopolize the dissemination of information. It is a dangerous sign. Once a group monopolizes information distribution, it can choose what people can know and control the minds. The church in the middle age dominated the era by fabricating information cocoons for the whole population. Being the judge of the truth and knowledge, they took away the people\u27s reason and forced them to follow its words blindly. With the power of faith, it became the leviathan of its time. The Enlightenment freed people\u27s reason from the leviathan by breaking the information cocoon. However, today, with the help of AI-algorithm and user experience design, the tech giants who dominate the information are trying to build information cocoons for each of us. Sadly, immersed in the convenience of the services they brought us, this time, we voluntarily give them our reason. These rising digital leviathans are once again closing the window of reason for humanity and driving us towards the world of Cyberpunk. This essay endeavors to demonstrate why our society in the 21st century is on the way to Cyberpunk. With Immanuel Kant and Karl Marx\u27s philosophical ideas, this essay will analyze the consequences that tech giants and their social media have on both individuals and society and why these consequences lead us towards the era of Cyberpunk

Modeling studies and numerical analyses of coupled PDEs system in electrohydrodynamics

Electrohydrodynamics (EHD) is the term used for the hydrodynamics coupled with electrostatics, whose governing equations consist of the electrostatic potential (Poisson) equation, the ionic concentration (Nernst-Planck) equations, and Navier-Stokes equations for an incompressible, viscous dielectric liquid. In this dissertation, we focus on a specic application of EHD - fuel cell dynamics - in the eld of renewable and clean energy, study its traditional model and attempt to develop a new fuel cell model based on the traditional EHD model. Meanwhile, we develop a series of ecient and robust numerical methods for these models, and carry out their numerical analyses on the approximation accuracy. In particular, we analyze the error estimates of nite element method for a simplied 2D isothermal steady state two-phase transport model of Proton Exchange Membrane Fuel Cell (PEMFC) as well as its transient version. On the aspect of hydrodynamics arising in the fuel cell system, the fluid flow through the open channels and porous media at the same time, both Navier-Stokes equations and Darcy\u27s law are involved in the fluid domains, leading to a Navier-Stokes-Darcy coupling problem. In this dissertation, we study a one-continuum model approach, so-called Brinkman model, to overcome this problem in a more ecient way. To develop a new fuel cell model based on EHD theory, in addition to the two-phase transport model of fuel cells, we carry out numerical analyses for Poisson-Nernst-Planck (PNP) equations using both standard FEM and mixed FEM, which are the essential governing equations involved by EHD model. Finally, we are able to further extend the traditional fuel cell model to more general cases in view of EHD characteristics, and develop a new fuel cell model by appropriately combining PNP equations with the traditional fuel cell model. We conduct the error analysis for PNP-Brinkman system in this dissertation

Dynamic Modeling and Vibration Analysis for the Vehicles with Rigid Wheels Based on Wheel-Terrain Interaction Mechanics

The contact mechanics for a rigid wheel and deformable terrain are complicated owing to the rigid flexible coupling characteristics. Bekker's equations are used as the basis to establish the equations of the sinking rolling wheel, to vertical load pressure relationship. Since vehicle movement on the Moon is a complex and on-going problem, the researcher is poised to simplify this problem of vertical loading of the wheel. In this paper, the quarter kinetic models of a manned lunar rover, which are both based on the rigid road and deformable lunar terrain, are used as the simulation models. With these kinetic models, the vibration simulations were conducted. The simulation results indicate that the quarter kinetic model based on the deformable lunar terrain accurately reflects the deformable terrain's influence on the vibration characteristics of a manned lunar rover. Additionally, with the quarter kinetic model of the deformable terrain, the vibration simulations of a manned lunar rover were conducted, which include a parametric analysis of the wheel parameters, vehicle speed, and suspension parameters. The results show that a manned lunar rover requires a lower damping value and stiffness to achieve better vibration performance

‘Brotherly strangers’: historicising and disaggregating Kenya and Zambia’s relations with China (1961-2000)

This thesis examines post-colonial Kenya and Zambia’s relations with the People’s Republic of China from ideological, political, economic and social perspectives, encompassing encounters between Kenyans, Zambians and Chinese as well as between their states. China’s growing significance in Africa is a popular subject in the press and academia but hitherto has been little analysed from a historical dimension. Through the triangulation of the global Cold War, African history, and Chinese history, the thesis examines the encounters, conflicts, and dynamics of China-Kenya/Zambia relations from 1961 until 2000, as well as the basis on which historical narratives regarding Chinese encounters with Kenyans/Zambians have been constructed. In doing so, it explains the on-going development of these relationships and sheds light on the historical underpinnings – or lack thereof – on contemporary China-Africa relations. The thesis title, ‘brotherly strangers’, identifies two key ostensibly contradictory aspects of China-Africa relations: ‘strangers’ in the sense of their diverse historical trajectories, but ‘brotherly’ in terms of an asserted shared historical lineage of western domination. The dynamics of their changing relations across a wide span of time are examined by the comparative studies of Kenya and Zambia’s respective relations with China. From a Chinese state perspective, Zambia has been primarily of political/strategic importance, whereas Kenya, although politically estranged and even hostile, has been of greater economic significance. Their distinctive historical legacies, and the variation in China’s relations with specific African states, challenges both the ‘taken for granted’ role of the China-Africa historical lineage in contemporary analyses, as well as its tendency to assume uniformity in these relationships.</p

âBrotherly strangersâ: historicising and disaggregating Kenya and Zambiaâs relations with China (1961-2000)

This thesis examines post-colonial Kenya and Zambiaâs relations with the Peopleâs Republic of China from ideological, political, economic and social perspectives, encompassing encounters between Kenyans, Zambians and Chinese as well as between their states. Chinaâs growing significance in Africa is a popular subject in the press and academia but hitherto has been little analysed from a historical dimension. Through the triangulation of the global Cold War, African history, and Chinese history, the thesis examines the encounters, conflicts, and dynamics of China-Kenya/Zambia relations from 1961 until 2000, as well as the basis on which historical narratives regarding Chinese encounters with Kenyans/Zambians have been constructed. In doing so, it explains the on-going development of these relationships and sheds light on the historical underpinnings â or lack thereof â on contemporary China-Africa relations. The thesis title, âbrotherly strangersâ, identifies two key ostensibly contradictory aspects of China-Africa relations: âstrangersâ in the sense of their diverse historical trajectories, but âbrotherlyâ in terms of an asserted shared historical lineage of western domination. The dynamics of their changing relations across a wide span of time are examined by the comparative studies of Kenya and Zambiaâs respective relations with China. From a Chinese state perspective, Zambia has been primarily of political/strategic importance, whereas Kenya, although politically estranged and even hostile, has been of greater economic significance. Their distinctive historical legacies, and the variation in Chinaâs relations with specific African states, challenges both the âtaken for grantedâ role of the China-Africa historical lineage in contemporary analyses, as well as its tendency to assume uniformity in these relationships.</p

Transnational networks of Africans and Chinese : global South imaginaries, decolonisation and the Cold War

This paper introduces Sun’s postdoc project which explores the exchanges of people and ideas between decolonising African countries and the People’s Republic of China during the Cold War. Following the end of the Second World War, the African continent experienced a growing ‘wind of change’ that called for an end to the global colonial order; the United States and the Soviet Union replaced European empires to become the new superpowers. China, although led by Mao Zedong and his Communist Party, claimed to be a leader of the ‘Third World’. This research will examine a range of Africans’ experiences including but not limited to politicians of initiating, deepening or negotiating relations with China at the time of global ideological contest. Through a close reading of national archives, English and Chinese newspapers, left-wing political pamphlets, and in-depth interviews, it will illustrate how transnational networks infused with a real and imagined shared colonial past, competing ideologies, and the developmental state contributed to and shaped the distinctive trajectories of China-Africa relations.A comprehensive investigation into the history of African decolonisation and the Cold War through the lens of China-Africa social networks is of both historiographical importance and great contemporary significance. Postcolonial African states, societies, ideas and practices need to be understood within what Jeremi Suri described as the ‘historical intersections’ of an on-going decolonisation, global waves of social mobilisation, and Cold War realpolitik. This study will also contribute to the emerging but uneven literature on the social history of Africa’s Cold War. The question of how the ‘global’ is revealed and remade through the ‘local’ is as crucial as that of how global forces shape local experiences. Bringing in China’s ‘alternativeness’ in engaging with African actors, this project will challenge the conventional understanding of the divisions of East and West, North and South in the context of the decolonising Cold War

The Elastic Property of Bulk Silicon Nanomaterials through an Atomic Simulation Method

This paper reports a systematic study on the elastic property of bulk silicon nanomaterials using the atomic finite element method. The Tersoff-Brenner potential is used to describe the interaction between silicon atoms, and the atomic finite element method is constructed in a computational scheme similar to the continuum finite element method. Young’s modulus and Poisson ratio are calculated for [100], [110], and [111] silicon nanowires that are treated as three-dimensional structures. It is found that the nanowire possesses the lowest Young’s modulus along the [100] direction, while the [110] nanowire has the highest value with the same radius. The bending deformation of [100] silicon nanowire is also modeled, and the bending stiffness is calculated

A New and Efficient Boundary Element-Free Method for 2-D Crack Problems

An efficient boundary element-free method is established for 2-D crack problems by combining a pair of boundary integral equations and the moving-least square approximation. The displacement boundary integral equation is collated on the on-crack boundary, and a new traction boundary integral equation is applied on the crack surface without the separate consideration of the upper and lower sides. In virtue of integration by parts, only singularity in order 1/r is involved in the integral kernels of new traction boundary integral equation, which brings convenience to the numerical implementation. Meanwhile, the integration by parts produces the new variables, the displacement density, and displacement dislocation density, and they are the coexisting unknowns along with the displacement and displacement dislocation. With the high-order continuity of the moving-least square approximation, these new variables are directly approximated with the nodal displacement or displacement dislocation, and the final system of equations contains the unknowns of nodal displacements and displacement dislocations only. The boundary element-free computational scheme is established, and several examples show the efficiency and flexibility of the proposed method

The Application of Mesh-Free Method in the Numerical Simulation of Beams with the Size Effect

The mesh-free method is employed to implement the numerical simulation of the bending behavior of beams with the size effect. On the basis of the classical Bernoulli-Euler beam theory, two higher-order strain components are involved in the beam model. The intrinsic bulk length and the directional surface length components are introduced into the constitutive relationship to describe the size effect, and the variation of the total potential is provided. The moving-least square approximation is used to construct the shape function and its second- and third-order derivatives, and the choice of the scaling factor is discussed in detail. A mesh-free scheme is built to implement numerical simulation, in which the higher-order strains are directly approximated with the nodal components due to the higher-order continuity of the shape function. The convergence of method is illustrated in virtue of an example of the simply supported beam, and the effect of the intrinsic bulk length and the directional surface length components are studied