A hybrid method of modified NSGA-II and TOPSIS for lightweight design of parameterized passenger car sub-frame

Dengfeng Wang,Rongchao Jiang,Yinchong Wu 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.11

This paper presents a hybrid method integrating modified NSGA-II and TOPSIS, used for lightweight design of the front sub-frame of a passenger car. Firstly, the FE model of the sub-frame is constructed and is validated by modal test. Then, the strength performance of the sub-frame is analyzed under four typical load conditions consisting of braking, acceleration, steady state cornering and vertical bump. After that, a parameterized model of the sub-frame, in which 12 geometric parameters are defined as design variables, is developed based on the mesh morphing technology. Subsequently, modified NSGA-II is employed for multi-objective optimization of the sub-frame considering weight, maximum von-Mises stress and first order natural frequency as three conflicting objective functions. Accordingly, a set of Pareto-optimal solutions are obtained from the optimization process. Finally, the entropy weight theory and TOPSIS method are adopted to rank all these solutions from the best to the worst for determining the best compromise solution. In addition, the effectiveness of the proposed hybrid lightweight design method is demonstrated by the comparisons among baseline design and optimum solutions.

A New Definition of Short-circuit Ratio for Multi-converter HVDC Systems

Dengfeng Liu,Dongyuan Shi,Yinhong Li 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.5

In this paper, a new definition of short-circuit ratio concept for multi-converter HVDC systems is proposed. Analysis results of voltage interaction between converters show that the reactive power-voltage characteristic of a converter has a dominant effect on voltage interaction level compared with its active power-voltage characteristic. Such a relation between converter reactive power and voltage interaction level supports taking the former into account in the definition of short-circuit ratio concept for multi-converter systems. The proposed definition is verified by the method of maximum power curve for various system configurations. Furthermore, a formula to calculate transient overvoltage for multi-converter systems is derived based on the proposed definition, and the efficiency of the derived formula is verified.

Investigations on the effect of guide vane thickness and solidity on shock and unsteady flow characteristic of VNT

Dengfeng Yang,Li’ang Cao,Ce Yang,Dazhong Lao,Harold Sun 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

In this work, the influence of thickness and solidity of guide vane on the unsteady flow of a radial inflow turbine with variable nozzle has been numerically studied. Three vanes with the thickness changes from 0.3 to 0.1 and the solidity changes from 1.43 to 2.86, were chosen for this study. By investigating the unsteady flow field, it is found that the vane with low thickness and high solidity (vane B) can reduce shock by 75 % compared to the vane with high thickness and low solidity (base model); meanwhile, it can also mitigate the nozzle endwall leakage flow thus improves the flow uniformity of rotor inlet. As the intensity of shock and nozzle leakage flow were mitigated, the aerodynamic loading fluctuation of rotor blade can be weakened effectively, which will lead to improved rotor blades forced response. However, at small opening, vane B shows about 0.5 % lower efficiency than the base model; at large open condition, the efficiency degradation of vane B is up to 1.4 %. Therefore, there is a trade-off between the efficiency and forced response when choosing the nozzle vane solidity and thickness.

Multiplicity of solutions for biharmonic elliptic systems involving critical nonlinearity

Dengfeng Lu,Jianhai Xiao 대한수학회 2013 대한수학회보 Vol.50 No.5

In this paper, we consider the biharmonic elliptic systems of the form [수식] where Ω ⊂ RN is a bounded domain with smooth boundary Ω, △2 is the biharmonic operator, N ≥ 5, 2 ≤ q < 2∗, 2∗ = 2N N−4 denotes the critical Sobolev exponent, F ∈ C1(R2, R+) is homogeneous function of degree 2∗. By using the variational methods and the Ljusternik-Schnirelmann theory, we obtain multiplicity result of nontrivial solutions under certain hypotheses on λ and δ. In this paper, we consider the biharmonic elliptic systems of the form [수식] where Ω ⊂ RN is a bounded domain with smooth boundary Ω, △2 is the biharmonic operator, N ≥ 5, 2 ≤ q < 2∗, 2∗ = 2N N−4 denotes the critical Sobolev exponent, F ∈ C1(R2, R+) is homogeneous function of degree 2∗. By using the variational methods and the Ljusternik-Schnirelmann theory, we obtain multiplicity result of nontrivial solutions under certain hypotheses on λ and δ. .

Experimental and numerical investigation on a novel gas turbocharging system for diesel engine power recovery at high altitude

Dengfeng Yang,Li’ang Cao,Yang Liu,Zhilian Zhang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10

Based on the analysis of the plateau performance for a 6 cylinder 8.6 L turbocharged diesel engine, a novel gas turbocharging system (GTS) is proposed to recover the engine power at high altitudes. Besides, a rolling-reflux combustor is designed to meet the structural requirements of GTS as well as to reduce the flow loss. Both the structure of the rolling-reflux combustor and the cycle thermal calculation of the GTS were described in detail in present work. The performance changes and the fuel consumption rate with engine speed at different altitudes of the GTS are compared to the original engine. Results show that when the altitude changes from 3 km to 5 km, the torque and power of the diesel engine with GTS can be recovered to that at sea level. Then, the particle image velocimetry (PIV) test is performed to study the cold flow field at the cylinder head of the rolling-reflux combustor, and the flow conditions are analyzed in detail. Finally, the flow bench is built and the aerodynamic experiment is carried out to verify the effectiveness of GTS.

EXISTENCE AND CONCENTRATION RESULTS FOR KIRCHHOFF-TYPE SCHR¨O DINGER SYSTEMS WITH STEEP POTENTIAL WELL

Dengfeng Lu 대한수학회 2015 대한수학회보 Vol.52 No.2

In this paper, we consider the following Kirchhoff-type Schr¨odinger system −(a1 + b1 ∫R3 |∇u|2dx)△u + γV (x)u = 2α/α+β|u|α−2u|v|β in R3, −(a2 + b2 ∫R3 |∇u|2dx)△u + γV (x)u = 2β/α+β|u|α|v|β−2v in R3, u, v ∈ H1(R3), where ai and bi are positive constants for i = 1, 2, γ > 0 is a parameter, V (x) and W(x) are nonnegative continuous potential functions. By applying the Nehari manifold method and the concentration-compactness principle, we obtain the existence and concentration of ground state solutions when the parameter γ is sufficiently large.

Dynamic Control Allocation Algorithm for a Class of Distributed Control Systems

Dengfeng Zhang,Shen-Peng Zhang,Zhi-Quan Wang,Baochun Lu 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.2

The control allocation algorithm is developed for a class of distributed control systems with hierarchical structure and similar models of the subsystems, to solve the real-time cooperative control taking the dynamics and possible variations of subsystems into consideration. The augmented state-space model of the subsystems is first established for the control allocation. Based on robust control theory, the constrained and convex optimization is then developed with LMIs form to design the gain matrix of the dynamic control allocation. Furthermore, the closed-loop stability of the distributed control system is analyzed on the basis of stable upper-level main control law. Finally, simulations on the four-corner leveling control system of an advanced hydraulic press demonstrate the effectiveness of the proposed control allocation algorithm.

A New Definition of Short-circuit Ratio for Multi-converter HVDC Systems

Liu, Dengfeng,Shi, Dongyuan,Li, Yinhong The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.5

In this paper, a new definition of short-circuit ratio concept for multi-converter HVDC systems is proposed. Analysis results of voltage interaction between converters show that the reactive power-voltage characteristic of a converter has a dominant effect on voltage interaction level compared with its active power-voltage characteristic. Such a relation between converter reactive power and voltage interaction level supports taking the former into account in the definition of short-circuit ratio concept for multi-converter systems. The proposed definition is verified by the method of maximum power curve for various system configurations. Furthermore, a formula to calculate transient overvoltage for multi-converter systems is derived based on the proposed definition, and the efficiency of the derived formula is verified.

MULTIPLICITY OF SOLUTIONS FOR BIHARMONIC ELLIPTIC SYSTEMS INVOLVING CRITICAL NONLINEARITY

Lu, Dengfeng,Xiao, Jianhai Korean Mathematical Society 2013 대한수학회보 Vol.50 No.5

In this paper, we consider the biharmonic elliptic systems of the form $$\{{\Delta}^2u=F_u(u,v)+{\lambda}{\mid}u{\mid}^{q-2}u,\;x{\in}{\Omega},\\{\Delta}^2v=F_v(u,v)+{\delta}{\mid}v{\mid}^{q-2}v,\;x{\in}{\Omega},\\u=\frac{{\partial}u}{{\partial}n}=0,\; v=\frac{{\partial}v}{{\partial}n}=0,\;x{\in}{\partial}{\Omega},$$, where ${\Omega}{\subset}\mathbb{R}^N$ is a bounded domain with smooth boundary ${\partial}{\Omega}$, ${\Delta}^2$ is the biharmonic operator, $N{\geq}5$, $2{\leq}q$ < $2^*$, $2^*=\frac{2N}{N-4}$ denotes the critical Sobolev exponent, $F{\in}C^1(\mathbb{R}^2,\mathbb{R}^+)$ is homogeneous function of degree $2^*$. By using the variational methods and the Ljusternik-Schnirelmann theory, we obtain multiplicity result of nontrivial solutions under certain hypotheses on ${\lambda}$ and ${\delta}$.

EXISTENCE AND CONCENTRATION RESULTS FOR KIRCHHOFF-TYPE SCHRÖ DINGER SYSTEMS WITH STEEP POTENTIAL WELL

Lu, Dengfeng Korean Mathematical Society 2015 대한수학회보 Vol.52 No.2

In this paper, we consider the following Kirchhoff-type Schr$\ddot{o}$dinger system $$\{-\(a_1+b_1{\int}_{\mathbb{R^3}}{\mid}{\nabla}u{\mid}^2dx\){\Delta}u+{\gamma}V(x)u=\frac{2{\alpha}}{{\alpha}+{\beta}}{\mid}u{\mid}^{\alpha-2}u{\mid}v{\mid}^{\beta}\;in\;\mathbb{R}^3,\\-\(a_2+b_2{\int}_{\mathbb{R^3}}{\mid}{\nabla}v{\mid}^2dx\){\Delta}v+{\gamma}W(x)v=\frac{2{\beta}}{{\alpha}+{\beta}}{\mid}u{\mid}^{\alpha}{\mid}v{\mid}^{\beta-2}v\;in\;\mathbb{R}^3,\\u,v{\in}H^1(\mathbb{R}^3),$$ where $a_i$ and $b_i$ are positive constants for i = 1, 2, ${\gamma}$ > 0 is a parameter, V (x) and W(x) are nonnegative continuous potential functions. By applying the Nehari manifold method and the concentration-compactness principle, we obtain the existence and concentration of ground state solutions when the parameter ${\gamma}$ is sufficiently large.