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20 results on '"Lu, Tianhang"'

1. Approximate Core Allocations for Edge Cover Games

Author

Lu, Tianhang, Xian, Han, and Fang, Qizhi

Subjects
Mathematics - Combinatorics, Economics - Theoretical Economics
Abstract

We study the approximate core for edge cover games, which are cooperative games stemming from edge cover problems. In these games, each player controls a vertex on a network $G = (V, E; w)$, and the cost of a coalition $S\subseteq V$ is equivalent to the minimum weight of edge covers in the subgraph induced by $S$. We prove that the 3/4-core of edge cover games is always non-empty and can be computed in polynomial time by using linear program duality approach. This ratio is the best possible, as it represents the integrality gap of the natural LP for edge cover problems. Moreover, our analysis reveals that the ratio of approximate core corresponds with the length of the shortest odd cycle of underlying graphs.

Published
2023

4. Approximate Core Allocations for Multiple Partners Matching Games

Author

Xiao, Han, Lu, Tianhang, and Fang, Qizhi

Subjects
Computer Science - Computer Science and Game Theory, Economics - Theoretical Economics, 05C57, 91A12, 91A43, 91A46
Abstract

The matching game is a cooperative game where the value of every coalition is the maximum revenue of players in the coalition can make by forming pairwise disjoint partners. The multiple partners matching game generalizes the matching game by allowing each player to have more than one possibly repeated partner. In this paper, we study profit-sharing in multiple partners matching games. A central concept for profit-sharing is the core which consists of all possible ways of distributing the profit among individual players such that the grand coalition remains intact. The core of multiple partners matching games may be empty [Deng et al., Algorithmic aspects of the core of combinatorial optimization games, Math. Oper. Res., 1999.]; even when the core is non-empty, the core membership problem is intractable in general [Biro et al., The stable fixtures problem with payments, Games Econ. Behav., 2018]. Thus we study approximate core allocations upon which a coalition may be paid less than the profit it makes by seceding from the grand coalition. We provide an LP-based mechanism guaranteeing that no coalition is paid less than $2/3$ times the profit it makes on its own. We also show that $2/3$ is the best possible factor relative to the underlying LP-relaxation. Our result generalizes the work of Vazirani [Vazirani, The general graph matching game: approximate core, arXiv, 2021] from matching games to multiple partners matching games., Comment: 12 pages

Published
2021

15. Analytical Calculation for Temperature Rise of Bearingless Switched Reluctance Motor Based on Lumped-Parameter Simplified Thermal Circuit Model

Author

Jingwei Zhang, Chao Tan, Sa Zhu, Honghua Wang, and Lu Tianhang

Subjects
Materials science, Control theory, Electromagnetic coil, Thermal resistance, 020208 electrical & electronic engineering, Direct current, 0202 electrical engineering, electronic engineering, information engineering, Magnetic bearing, 02 engineering and technology, Thermal analysis, Temperature measurement, Finite element method, Switched reluctance motor
Abstract

The magnetic bearings are more suitable in harsh environments, especially in which the bearings are the vulnerable part of system, and they can be integrated with switched reluctance motor to form bearingless switched reluctance motor (BSRM). However, the temperature rise of machine limits the performance of BSRM. Aiming at the analytical calculation of the temperature rise of dual-winding BSRM, the lumped-parameter (LP) thermal circuit method is used to build the LP simplified thermal circuit model of BSRM. Different from the switched reluctance motor, the heat performance for the dual-winding structure of the BSRM is considered. The temperature of machine case and windings are measured in the direct current thermal tests. Experimental results show that the proposed LP simplified thermal circuit model of BSRM obtains good accuracy for engineering application. The proposed model has less parameter with fast solving speed, which is more suitable for thermal analysis and thermal design of BSRM.

Published
2019

18. Multi-Physics Multi-Objective Optimal Design of Bearingless Switched Reluctance Motor Based on Finite-Element Method

Author

Sa Zhu, Jingwei Zhang, Honghua Wang, and Lu Tianhang

Subjects
Optimal design, multi-physics approach, Control and Optimization, Computation, Energy Engineering and Power Technology, Magnetic bearing, 02 engineering and technology, 01 natural sciences, Multi-objective optimization, lcsh:Technology, Control theory, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, Electrical and Electronic Engineering, optimal design, Engineering (miscellaneous), Fourier series, 010302 applied physics, lumped-parameter thermal model, Renewable Energy, Sustainability and the Environment, lcsh:T, 020208 electrical & electronic engineering, Finite element method, Switched reluctance motor, multi-objective optimization, Transient (oscillation), bearingless switched reluctance motor (BSRM), Energy (miscellaneous)
Abstract

The bearingless switched reluctance motor (BSRM) integrates the switched reluctance motor (SRM) with the magnetic bearings, which avoids mechanical bearings-loss and makes it promising in high-speed applications. In this paper, a comprehensive framework for the multi-physics multi-objective optimal design of BSRMs based on finite-element method (FEM) is proposed. At first, the 2-D electromagnetic model of a fabricated initial design prototype is built and solved by the open-source FEM software, Elmer. The iron loss model in Elmer based on the Fourier series is modified by a transient iron loss model with less computation time. Besides, a simplified lumped-parameter (LP) thermal model of the BSRM is applied to estimate the temperature rise of BSRM in the steady state. Then, the comprehensive framework for the multi-physics multi-objective optimal design of BSRMs based on FEM is proposed. The objectives, constraints, and decision variables for optimization are determined. The multi-objective genetic particle swarm optimizer is utilized to obtain the Pareto front of optimization. The electromagnetic performance of the final optimal design is compared with the initial design. Comparison results show that the average electromagnetic torque and the efficiency are significantly enhanced.

Published
2019

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