Dissipative Method Research Articles

Development of scanning capacitance force microscopy using the dissipative force modulation method

We have developed scanning capacitance force microscopy (SCFM) using the dissipative force in frequency-modulation atomic force microscopy. An SCFM signal depends on the dopant density and polarity of semiconductors, whose evaluation is important for developing electronic devices. Thus, improving the force sensitivity of SCFM can prove effective for investigating these devices. In a previous report, the dissipative force modulation method was developed to increase the force sensitivity for Kelvin probe force microscopy. Thus, the force sensitivity of SCFM can be increased using this method. In this study, we determined the theoretical formula for SCFM by using dissipative force. Because this force was modulated using a multiplication signal with the same phase as that of a cantilever excitation signal, the SCFM signal was detected from the deflection of the cantilever by using a demodulation circuit. In the conventional method, the SCFM signal is detected using the second resonance frequency of the cantilever with a high-quality factor. The minimum detectable force of SCFM was calculated to be 0.74 fN from the Brownian motion of the cantilever, which is smaller than that obtained using the conventional method. The differential capacitance of a patterned silicon sample was measured using the proposed method and conventional one. The modulation signal amplitude was reduced from 3.0 V to 1.5 V in increments of 0.5 V. Using the proposed method, the differential dopant regions could be distinguished under a modulation signal amplitude of 1.5 V. However, using the conventional method, the regions could not be observed under the modulation signal amplitude of 2.0 V. Therefore, the proposed method could reduce the modulation signal amplitude from 2.5 V to 1.5 V. In addition, the signal-to-noise ratio and the spatial resolution of the proposed method were found to be higher than that of the conventional one.

Replica exchange dissipative particle dynamics method on threadlike micellar aqueous solutions

The self-assembly of surfactant molecules can spontaneously result in a variety of micelle morphologies, such as spherical micelles, threadlike micelles, and vesicles, and it is therefore crucial to predict and control the self-assembly to achieve a helpful process in the fields of materials chemistry and engineering. A dissipative particle dynamics (DPD) method used in a coarse-grained molecular simulation is applied to simulate various self-assembling soft matter systems because it can handle greater length and time scales than a typical molecular dynamics simulation (MD). It should be noted that the thorough sampling of a system is not assured at low temperatures because of large complex systems with coarse-grained representations. In this article, we demonstrate that the replica exchange method (REM) is very effective for even a DPD in which the energy barrier is comparatively lower than that of a MD. A replica exchange on DPD (REDPD) simulation for threadlike micellar aqueous solutions was conducted, and the values of the potential energy and the mean aggregation number were compared. As a result, the correct values and a self-assembled structure within a low-temperature range can only be obtained through the REDPD.

Analysis of local density potentials.

Low resolution coarse-grained (CG) models are widely adopted for investigating phenomena that cannot be effectively simulated with all-atom (AA) models. Since the development of the many-body dissipative particle dynamics method, CG models have increasingly supplemented conventional pair potentials with one-body potentials of the local density (LD) around each site. These LD potentials appear to significantly extend the transferability of CG models, while also enabling more accurate descriptions of thermodynamic properties, interfacial phenomena, and many-body correlations. In this work, we systematically examine the properties of LD potentials. We first derive and numerically demonstrate a nontrivial transformation of pair and LD potentials that leaves the total forces and equilibrium distribution invariant. Consequently, the pair and LD potentials determined via bottom-up methods are not unique. We then investigate the sensitivity of CG models for glycerol to the weighting function employed for defining the local density. We employ the multiscale coarse-graining (MS-CG) method to simultaneously parameterize both pair and LD potentials. When employing a short-ranged Lucy function that defines the local density from the first solvation shell, the MS-CG model accurately reproduces the pair structure, pressure-density equation of state, and liquid-vapor interfacial profile of the AA model. The accuracy of the model generally decreases as the range of the Lucy function increases further. The MS-CG model provides similar accuracy when a smoothed Heaviside function is employed to define the local density from the first solvation shell. However, the model performs less well when this function acts on either longer or shorter length scales.

Investigation on surface roughness of piston in mini-magnetorheological damper using dissipative particle dynamics modeling

Mini-magnetorheological damper is modeled using dissipative particle dynamics method, as a molecular modeling technique by applying various arrangement patterns of rough sections on the surface area of piston as four proposed scenarios of A, B, C, and D to obtain optimal damper performance. Modeling is developed to achieve 10-N damping force utilized in micro-machines and compared to experimental results that show good conformity. Weierstrass–Mandelbrot function is used to apply rough surface profile on the piston, and bounce back boundary condition is utilized as no-slip boundary condition. Results of modeling show that 140-CG magnetorheological fluid is suitable as the agent fluid. Also, it is observed that by increasing fractal dimension of roughness profile, damping force has an initial enhancement and then trends to a constant value. Results shown by utilizing Bouc–Wen model and genetic algorithm method and fractal dimension of roughness profile of 1.5 using at the beginning and the end of the piston as presented in scenario B; by applying 20% magnetic field strength, considered damping force of 10 N is achieved within 2 s, while under conventional conditions, using the smooth surface area of piston, more damping time is needed and more electrical energy is used than the developed model.

Effectiveness of friction dampers on the seismic behavior of high rise building VS shear wall system

The increase in population especially in third world countries demands taller, more flexible, and lighter buildings. Most of these countries are subjected to a high risk of earthquakes, which requires more control of building seismic response. However, several techniques exist to minimize the vibrations induced by an earthquake shock. This paper will discuss the effectiveness of using friction dampers as a passive dissipative device and proposes some design optimization of the number and position of dampers in the building. Friction dampers offer a supplemental damping in conjunction with appropriate stiffness, offering an innovative and attractive solution for the seismic response control of tall structures in risky areas. The originality of this work is in the detailed seismic study of an asymmetric reinforced concrete (RC) building, located in a risky seismic zone and using real earthquake seismic waves. The seismic response of this dissipative structural method is compared with the response of the conventional method (shear wall system) for the high rise building. To accomplish this objective, a nonlinear modal time history analysis using the El Centro earthquake record for a 40‐storey RC high rise building, is performed with four different damper type formats using ETABS software. To illustrate the response improvement by dampers, storey accelerations, storey displacements, base shear forces, and storey drifts are compared with a conventional fixed base system (shear wall system) for the same building. Results show that using an optimum position and number of dampers, a tall building can remain operational during a seism.

Effect of non-uniform fields on DNA entering nano-channel

The translocation of deoxyribonucleic-acid (DNA) segments into a nanoscale channel from a bulk solution has significance to genome-related fields such as gene sequencing and genetic profiling. However, its dynamic characteristics are poorly understood because of complexities involving the size and character of the confining spaces, polymeric evolution, and driving sources. The DNA translocation was studied by mesoscale simulation using a worm-like-chain model of DNA and the dissipative particle dynamics method. Three driving sources — electric field, suction flow, and constant body force were individually applied to a λ-DNA entering a nanoscale cylindrical channel. Each source altered the translocation actions, mainly due to marked differences in conformational transformation processes. The suction flow uniquely induced strong extension of the DNA chain before channel entry. Consequently, the flow was more effective at overcoming the free-energy barrier with narrower confinements. Other driving sources permitted the DNA chain to enter in a more globular form, which was effective for larger entrances. Combining different sources is the most versatile means of controlling the trans-location of genetic materials in highly confined spaces.

Development of the formalism of the discrete element method for the study of the mechanical behavior of liquid-saturated porous materials on a pore scale

In the framework of a single computational approach (particle method), we developed a coupled microscale computer model of liquid-saturated micropores in a solid-phase carrier. Within the model, the solid-phase and liquid-phase components of the contrast system are modeled on the basis of the formalism of homogeneously deformable discrete elements. For computer simulation of flow of complex liquids (including aqueous solutions of drugs) in the micropore volume of the carrier, a new implementation of discrete elements has been developed. This implementation borrows key advantages of the dissipative particle dynamics method. Using the system of adjacent slit-shaped micropores in hydroxyapatite filled with water as an example, we showed an adequacy of the developed discrete element based formalism and its applicability for microscale study of the coupled problems including deformation of solid-phase skeleton and flow of liquids in micropore space.

Simulation of RBC dynamics using combined low dimension, immersed boundary and lattice Boltzmann methods

ABSTRACT A 3-D simulation of red blood cells (RBCs) described as deformable cells in plasma flow is an indispensable element of blood flow analysis in the human vessels. To numerically investigate RBC motion in shear and Poiseuille flow, a mesoscale low dimensional-RBC method based on dissipative particle dynamics method has been successfully combined with a hybrid lattice Boltzmann method-immersed boundary method. This new model decreases the computational cost compared to the low dimensional RBC method and models the deformation of red blood cell accurately. To evaluate and validate the present numerical method, the relationship between the RBC diameter and the force value derived by the low dimensional-RBC method is compared with numerical and experimental data. In addition, as a benchmark test, the deformation index as the function of the capillary number of RBC motion through a narrow cylindrical tube has been performed. The behaviour of RBC in a shear flow and Poiseuille flow has been investigated. The present results demonstrated that this model is applied to reduce the computational cost, while maintaining the model precision.

Dissipative particle dynamics with reactions: Application to RDX decomposition.

We present a general, flexible framework for a constant-energy variant of the dissipative particle dynamics method that allows chemical reactions (DPD-RX). In our DPD-RX approach, reaction progress variables are assigned to each particle that monitor the time evolution of an extent-of-reaction associated with the prescribed reaction mechanisms and kinetics assumed to occur within the particle, where chemistry can be modeled using complex or reduced reaction mechanisms. We demonstrate our DPD-RX method by considering thermally initiated unimolecular decomposition of the energetic material, cyclotrimethylene trinitramine (RDX), into a molecular gas mixture. Studies are performed to demonstrate the effect of a spatially averaged particle internal temperature and a local reaction volume term in the chemical kinetics expressions, where both provide implicit mechanisms for capturing condensed phase reactivity. We also present an analysis of the expansion of the product gas mixture during decomposition. Finally, a discussion of other potential applications and extensions of the DPD-RX method is given.

Magneto-rheological damper modeling by using dissipative particle dynamics method

A mesoscale modeling of magneto-rheological damper is performed by using dissipative particle dynamics method. Bounce-back and periodic boundary conditions are used, and the model is validated by Couette flow, Poiseuille flow and flow through a micro-tube. Shear stress and damping behavior are probed with considering hysteresis condition. Three electrical coils are placed inside MR damper, control damping force by applying magnetic strength distribution as step function pattern. Results show that by increasing both of average strength of magnetic field and shear rate, shear stress increases. The effects of different parameters such as frequency and amplitude of piston velocity, magnetic field strength, diameter of magnetic particles and strength of dissipative forces on damping force and hysteresis condition are investigated by using Bouc–Wen model. Results show by increasing frequency and decreasing amplitude and magnetic field strength, hysteresis range and strength of damping force reduce. Sensitivity analysis performed on MR fluid parameters reveals that the weight of magnetic particles and the dissipative force have the most effect on strength of damping force so that, by increasing dissipative force, damping force increases linearly, but enhancement in the weight of magnetic particles leads to damping force firstly increases and then reduces.

Dissipative networked filtering for two-dimensional systems with randomly occurring uncertainties and redundant channels

In this paper, the non-fragile dissipative filtering problem is investigated for the two-dimensional (2-D) systems subjected to randomly occurring uncertainties and redundant channel protocol. For the redundant channel transmission, if a signal fails to be transmitted through a certain channel, the next channel is immediately activated to transmit the signal once again. The norm-bounded uncertainties are introduced in the considered system, which are governed by two stochastic variables obeying the Bernoulli distribution law. The aim of this paper is to design a dissipative filter in a non-fragile manner such that the augmented filtering error system is not only asymptotically stable in the mean-square sense but also satisfies a strict 2-D (Q,S,R)−α-dissipativity performance index. Based on the Lyapunov theory and stochastic analysis, sufficient conditions are first given to guarantee the asymptotic stability of the 2-D system in the mean-square sense. Then, the non-fragile filter is designed to ensure that the 2-D system satisfies the strict 2-D (Q,S,R)−α-dissipativity performance index, under which the expressions of the non-fragile filter gains are given by solving certain matrix inequalities. Finally, a simulation example is provided to show the effectiveness of the proposed dissipative filtering method.

In-Depth Analysis of Supramolecular Interfacial Polymerization via a Computer Simulation Strategy

The supramolecular interfacial polymerization induced at the interface of water and oil phases is scrutinized with a dissipative particle dynamics simulation method coupled with a stochastic reacti...

Insight into the Polymerization-Induced Self-Assembly via a Realistic Computer Simulation Strategy

The dynamic process of polymerization-induced self-assembly (PISA) is simulated by the dissipative particle dynamics method coupled with the stochastic reaction model. Meaningful comparisons betwee...

Dissipative particle dynamics simulation of the soft micro actuator using polymer chain displacement in electro-osmotic flow

ABSTRACTIn this research, the numerical simulation of a soft polymer micro actuator performance has been investigated using the dissipative particle dynamics method in electro-osmotic flow. Effective factors including electro-osmotic flow and polymer chain parameters have been studied. First of all, considering a wide range of electro-osmotic parameters, the validation of analytical results is carried out in a simple micro channel. The electric field and zeta potential changes are linearly related to the flow rate, and the kh parameter behaves nonlinearly to around the kh = 10. In the following, a convergent–divergent channel is used for the soft micro actuator simulation in which a polymer chain as a heart of actuation is embedded in the middle. As the main control parameter, the direction of the electric field is changed every 4 s, and it leads to a reciprocating motion. The numerical results indicate that the displacement of the soft polymer chain will be increased by enhancing the electric field, the number of beads, decreasing the harmonic bond coefficient and also exposing more length of a polymer chain in front of fluid flow. The results of this study may be useful for some future applications such as artificial fibres and muscles.

Dissipative Particle Dynamics Simulations of the Self-assembly Mechanisms of Fluorinated Ordered Mesoporous Carbon in the Aqueous Phase

To clarify the preparation mechanisms of fluorinated ordered mesoporous carbon materials (FOMCs), the dissipative particle dynamics method was used to simulate the self-assembly process of the amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer Pluronic F127 in the aqueous system. The self-assembly mechanisms in aqueous phase and the formation mechanisms of micropores and mesopores were investigated. It was found that the mesoporous structure of the FOMCs was formed by the hydrophobic segments of F127, while the pore wall was formed by both the hydrophilic segments and the carbon precursor in the system. The microporous structure on the pore wall was constructed by the carbon source in the hydrophilic segments’ spaces after the template was removed. Our findings could provide understanding and knowledge for the synthesis of mesoporous carbon by the self-assembly method on the mesoscopic scale.

Influence of pH on the formation of a polyelectrolyte complex by dissipative particle dynamics simulation: From an extended to a compact shape.

This work aims to investigate the influence of pH on the mechanism of assembly of macromolecules. We studied the effect of the pH on the interaction of two polyelectrolytes of opposed charge, having the same size, by means of dissipative particle dynamics method. The system consisted of a strong cationic and a weak anionic polyelectrolyte in an aqueous solution containing monovalent counterions. The analysis was made by varying the pH of the solution, which modifies the charge fraction of the weak anionic polyelectrolyte with a dissociation acid constant pKa of 5.5, while the polycation is fully charged in all the pH range used, characteristic of a strong polyelectrolyte. In order to describe the influence of pH on the complexation process, we have analyzed the pair radial distribution functions polyanion-counterion, polycation-counterion, and polyanion-polycation. The complex conformation was studied by means of the radius of gyration and the end-to-end distance of both chains as the pH varied from 1 to 14. A relevant finding obtained here was the relationship between the radial distribution functions and the counterion release from the polyelectrolytes, which leads to a reduction in the size of the complex when pH increased. Surprisingly, a transition from an extended to a compact polyelectrolyte complex was obtained when the pH reached the dissociation acid constant pKa of the weak polyelectrolyte. This systematic study can help to understand a large number of more realistic problems in biological systems such as protein complex, chromatin phase transition, or in complex systems applied in biomedical science.

Highly Effective Cell Equalization in a Lithium-Ion Battery Management System

This paper proposes a highly effective voltage cell equalization method for lithium-ion (Li-ion) battery management systems (BMSs) for several applications, such as nearly zero energy buildings, microgrids, and electric vehicles. The concept of the suggested method is the proper control of the charging current of each cell of a battery stack through the suitable regulation of the gate source of each cell's parallel-connected mosfet . Thus, the mosfet can act as a controllable current source for providing the proper equalization current according to the specific needs of each battery cell. The correct voltage level of the gate-source of each mosfet is determined by a cell equalization controller through the comparison of the performance of each cell of a battery stack with the healthier cell, which is detected by an aging estimation algorithm based on the evaluation of the internal resistor and the capacity fade of each cell. Therefore, smoother and faster cell equalization is achieved compared to the conventional dissipative method. The practicality and the high effectiveness of the proposed cell equalization technique have been experimentally validated. Several experimental results are presented to demonstrate the operational improvements of the proposed cell equalization technique against the conventional one.

Hybrid Flux Method in Monotonicity-Preserving Scheme for Accurate and Robust Simulation in Supersonic Flow

The fifth-order monotonicity-preserving (MP5) scheme is an accurate and low dissipative numerical method. As a finite-volume method, MP5 adopts the Roe-flux scheme for solving the numerical flux in the compressible Euler equation. However, due to the deficiency of the MP limiter and Roe-flux in maintaining positive density and pressure, the calculation could fail in cases of extreme flow involving small values of density and pressure. In this study, to overcome such a limitation but still to achieve a high-accuracy of MP5, we propose a hybrid flux method: the Roe-flux is used in the global computational domain, but the first-order Lax-Friedrich (LF)-flux is adopted only for trouble grids. The numerical results of shock-tube and complicated interaction problems indicate that the present scheme is more accurate at discontinuities and local extrema compared to the previous scheme, maintaining positive density and pressure values. For two-dimensional applications, a supersonic jet is explored with different Mach numbers and temperature conditions. As a result, small vortices induced by the shear layer can be clearly captured by the proposed scheme. Furthermore, a simulation was successfully conducted without blow-up of calculation even in the extreme jet flow condition.

A new fourth-order energy dissipative difference method for high-dimensional nonlinear fractional generalized wave equations

In this paper, a new energy dissipative fourth-order difference scheme for the high-dimensional nonlinear fractional generalized wave equations is constructed. Then, the discrete energy dissipation property of the system is exhibited in detail. Next, we prove that the proposed scheme is uniquely solvable. By the discrete energy method, it is shown that the proposed scheme achieves the optimal convergence rate of O(Δt2+hx4+hy4) in the discrete L2- norm, and is unconditionally stable. Besides, the presented convergence analysis is unconditional for the time step size in terms of space mesh sizes. Lastly, some numerical results are given to illustrate the physical effects of the nonzero damping terms and support our theoretical analysis.

Dissipative particle dynamics modeling of a mini-MR damper focus on magnetic fluid

Mini-magneto rheological damper modeled by using dissipative particle dynamics method as molecular modeling technique and effects of agent magnetic fluid properties on damping force are investigated. To validate results of modeling with experimental data, modified Bouc-Wen model is used as computational strategy and no-slip condition on the solid surfaces implemented by utilizing bounce back boundary condition which shows good conformity. Results of molecular modeling indicate by increasing in number density and non-dimensional weight of magnetic particles, damping force has parabolic pattern so that first increases then decreases to a constant value; while, by increasing in diameter of magnetic particles damping force increases uniformly. Also, the effect of different magnetic field distributions with enhancement rates of 10%, 30% and 50% on quality and quantity of damping force and shear stress is investigated. Results show by using number density, non-dimensional weight and diameter of magnetic particles of 0.25, 0.6 and 0.55 μm, respectively, when magnetic field with power function pattern is utilized considered damping force of 10 N obtained in less damping time and electrical energy consumption; so, modeled damper is an optimal version of its experimental model.