Yongbo Deng

Topology optimization of unsteady incompressible Navier-Stokes flows

This paper discusses the topology optimization of unsteady incompressible Navier-Stokes flows. An optimization problem is formulated by adding the artificial Darcy frictional force into the incompressible Navier-Stokes equations. The optimization procedure is implemented using the continuous adjoint method and the finite element method. The effects of dynamic inflow, Reynolds number and target flux on specified boundaries for the optimal topology of unsteady Navier-Stokes flows are presented. Numerical examples demonstrate the feasibility and necessity of this topology optimization method for unsteady Navier-Stokes flows.

A flexible layout design method for passive micromixers

This paper discusses a flexible layout design method of passive micromixers based on the topology optimization of fluidic flows. Being different from the trial and error method, this method obtains the detailed layout of a passive micromixer according to the desired mixing performance by solving a topology optimization problem. Therefore, the dependence on the experience of the designer is weaken, when this method is used to design a passive micromixer with acceptable mixing performance. Several design disciplines for the passive micromixers are considered to demonstrate the flexibility of the layout design method for passive micromixers. These design disciplines include the approximation of the real 3D micromixer, the manufacturing feasibility, the spacial periodic design, and effects of the Péclet number and Reynolds number on the designs obtained by this layout design method. The capability of this design method is validated by several comparisons performed between the obtained layouts and the optimized designs in the recently published literatures, where the values of the mixing measurement is improved up to 40.4% for one cycle of the micromixer.

Experimental investigation of passive micromixers conceptual design using the layout optimization method

This paper presents an experimental investigation of the novel efficient passive micromixers conceptual design using the flexible layout optimization method. Utilizing the layout optimization method when designing passive micromixers results in decreased reliance on the experience and intuition of designers. The detailed layout of passive micromixers is obtained by solving a variational optimization problem, in which the manufacturability and periodicity of passive micromixers can be considered by adding the corresponding design constraints. The obtained micromixers are fabricated by using polydimethylsiloxane soft photolithography techniques. The mixing performance is evaluated by stereoscopic and confocal microscopes. The effectiveness of the layout optimization method is confirmed by a comparison of the numerical and experimental results.

Optimization of no-moving part fluidic resistance microvalves with low reynolds number

This paper reports an effective optimization procedure for designing no-moving part microvalves where the diodicity of the optimized valves has better performance when compared with the typical Tesla valve. The detailed layout of microvalves is obtained by minimizing the fluidic resistance of fluidic channels for the forward flow under a user-specified design constraint about the fluidic work diodicity between the forward and reverse flows. A couple of novel valves which have different layout with the Tesla valve are presented. The numerical value of the fluidic resistance diodicity for a designed periodic valve is verified by experiments.

Combination of topology optimization and optimal control method

This paper presents the combination of topology optimization and optimal control method to find the optimal match between the material topology and control. In the presented method, the material topology is determined using the SIMP (Solid Isotropic Material with Penalization) method, which has been popularly used in topology optimization. In the SIMP method, the design variable is relaxed and bounded in the interval 0 , 1 ] , and the evolution of the design variable is usually implemented by the method of moving asymptotes (MMA), which can be used to deal with optimization problem with multiple integral constraints and bound constraint of the design variable. In the combination of topology optimization and optimal control method, the control variable appears along with the design variable. In order to evolve the control variable and design variable using MMA simultaneously, the control variable is regularized using a bound constraint and the corresponding bound constraint is projected onto the interval 0 , 1 ] , which is the same as the bound constraint of the design variable. The optimization problem is analyzed using the adjoint method to obtain the adjoint sensitivity. During the optimization procedure, the design and control variables are filtered by the Helmholtz filters to ensure the smoothness of the distribution. To ensure the minimum scale length and remove the gray area in the material topology, the filtered design variable is projected by the threshold method. The feasibility and robustness of the combination of these two methods are demonstrated by several test problems, including heat transfer, fluid flow and compliance minimization.

Optimization of micro Venturi diode in steady flow at low Reynolds number

Micro Venturi diodes have been broadly used in microfluidics to rectify liquid flow. A key feature of these diodes is that they have no moving parts. This article treats the numerical optimization of such a micro Venturi diode for the case of steady Newtonian flow, with Reynolds numbers less than 100, which typically applies to microfluidic devices. Key design factors are discussed, such as the ratio of length to width of the design domain, the values of lower and upper bounds for the constraint of the volume of the diodes, and the Reynolds number, all of which influence the outcome of the diode effect. Curved micro Venturi diodes are found by the optimization. The method presented provides a systematic way to design Venturi diodes for steady Newtonian flows.

Polymeric microlens array fabricated with PDMS mold-based hot embossing

This study presents a simple, flexible and cost-effective process to fabricate microlens arrays. The polymeric microlens arrays are fabricated using a polydimethylsiloxane (PDMS) mold-based hot embossing process. The desired profile of the lens is achieved with the use of air pressure to deform the PDMS membrane. The deformation of the PDMS membrane is determined by numerical simulation. Simulation results show that the sag height of the PDMS membrane varies nearly linearly along with the change of the negative pressure. The shape of the PDMS membrane is transferred to the PDMS mold with UV curing and casting processes. Then, PDMS is used as a mold insert, and polycarbonate microlens arrays with different sag heights are fabricated with the hot embossing technique. The surface profile of the fabricated microlens keeps spherical with the variation of the sag height induced by the negative pressure. For the negative pressure -3600 and -5900 Pa, sag heights with 40 and 65 mu m are obtained and the corresponding focal lengths are changed from 1.0 to 0.6 mm. Good uniformity and imaging quality of the microlenses is confirmed by the experimentally evaluated and measured optical properties of the replica.

Topology Optimization-Based Computational Design Methodology for Surface Plasmon Polaritons

This paper presents the topology optimization-based computational design methodology for nanostructures in surface plasmon polaritons. Using the proposed method, nanostructures can be designed solely based on the user’s desired performance specification for the surface plasmon polaritons. This topology optimization-based computational design methodology is implemented based on the material interpolation with hybrid formulation of logarithmic and power law approaches, to mimic the metal surface with exponential decay of the electromagnetic field. The constructed computational design problem is analyzed using the continuous adjoint method, and the filter and projection techniques are utilized to ensure the minimum length scale in the obtained nanostructures. The outlined design methodology is used to investigate the nanostructures for localized surface plasmonic resonances, extraordinary optical transmission, and surface plasmonic cloaking, respectively. For localized surface plasmonic resonances and extraordinary optical transmission, the metallic nanostructures are designed with spectra peaks at the prescribed wavelengths and the shift of the spectra peak is controlled by solving the computational design problem corresponding to a different incident wavelength; for surface plasmonic cloaking, the cloak covered at a curved metal-dielectric interface is designed to bound the surface plasmon polariton at the interface and remove the radiation, where the conventional simple isotropic dielectric readily available in nature is used instead of the material possessing gradient electromagnetic properties with challenges on realization for optical frequencies.

Hydrodynamic particle focusing design using fluid-particle interaction.

For passive sheathless particles focusing in microfluidics, the equilibrium positions of particles are typically controlled by micro channels with a V-shaped obstacle array (VOA). The design of the obstacles is mainly based on the distribution of flow streamlines without considering the existence of particles. We report an experimentally verified particle trajectory simulation using the arbitrary Lagrangian-Eulerian (ALE) fluid-particle interaction method. The particle trajectory which is strongly influenced by the interaction between the particle and channel wall is systematically analyzed. The numerical experiments show that the streamline is a good approximation of particle trajectory only when the particle locates on the center of the channel in depth. As the advantage of fluid-particle interaction method is achieved at a high computational cost and the streamline analysis is complex, a heuristic dimensionless design objective based on the Faxens law is proposed to optimize the VOA devices. The optimized performance of particle focusing is verified via the experiments and ALE method.

Topology optimization for three-dimensional electromagnetic waves using an edge element-based finite-element method

This paper develops a topology optimization procedure for three-dimensional electromagnetic waves with an edge element-based finite-element method. In contrast to the two-dimensional case, three-dimensional electromagnetic waves must include an additional divergence-free condition for the field variables. The edge element-based finite-element method is used to both discretize the wave equations and enforce the divergence-free condition. For wave propagation described in terms of the magnetic field in the widely used class of non-magnetic materials, the divergence-free condition is imposed on the magnetic field. This naturally leads to a nodal topology optimization method. When wave propagation is described using the electric field, the divergence-free condition must be imposed on the electric displacement. In this case, the material in the design domain is assumed to be piecewise homogeneous to impose the divergence-free condition on the electric field. This results in an element-wise topology optimization algorithm. The topology optimization problems are regularized using a Helmholtz filter and a threshold projection method and are analysed using a continuous adjoint method. In order to ensure the applicability of the filter in the element-wise topology optimization version, a regularization method is presented to project the nodal into an element-wise physical density variable.