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The expanding capabilities and decreasing costs of additive manufacturing have resulted in the increased adoption of micro-unmanned aerial vehicles (micro-UAVs) among professionals and hobbyists. Due to safety regulatory requirements of UAV operations, weight is generally the overriding design features of interest for micro-drones, but it often comes as a trade-off against the durability, loading constraints, and other subsystem equipment. Nevertheless, ultra-lightweight structures can be realized through the adoption of both 3D-printing and topology optimization without compromising the structural integrity and overall strength and this article explores the use of these two technologies for designing and manufacturing optimized ultralight micro-UAVs. First, material properties of Nylon 12 (PA12) manufactured using selective laser sintering (SLS) were accurately characterized via mechanical testing and ultrasonic means. These properties were verified by comparing the mechanical response of 3-point and 4-point bending tests with corresponding finite element (FE) simulation. Next, topology optimization was performed to produce an optimized structure of a Z-split configured lightweight micro-quadcopter. The optimized design is then 3D-printed and subsequently validated through a load test for verification against the optimized FE simulation-based design. A close correlation was obtained between the numerical and experimental data, suggesting that topology optimization with 3D printing can be safely and reliably adopted for the design and rapid prototyping of micro-UAVs, whilst catering to different specifications and requirements. National Research Foundation (NRF) Submitted/Accepted version This research is jointly supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Medium-Sized Centre funding scheme, and ST Engineering Aerospace Ltd., under project titled ‘3D Printing of micro UAV’.

There is a pressing need in very small scale three‐dimensional (3D) inkjet printing to control and reduce agglomeration, as agglomeration often leads to nozzle clogging. While agglomeration within ultraviolet ink has been studied, there has been, to our knowledge, no extensive studies conducted for surface agglomeration of the ink on nozzle's wall. This numerical study therefore focuses on investigating if surfactants can effectively control surface agglomeration during nanodroplet formation. Many‐body dissipative particle dynamics is the numerical method of choice here. We found that small amount of surfactant of about 1 wt % is sufficient to effectively reduce ink deposition on the nozzle's wall. However, by using the properties of a commercially available surfactant, sodium dodecyl sulfate, it was found that the maximum reduction achieved by its addition is only 60%. Thus, further physical or chemical deagglomeration techniques are required, and we show that by considering these other techniques, reduction of surface agglomeration to nearly 92% can be achieved. Finally, we found that adding surfactants has the additional benefit of improving total kinetic energy of the ink compositions, lowering possibility of agglomerations within the ink. It also raises the nanodroplet velocity while reducing nanodroplet breakup time, which can help speed up the process of 3D printing process. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1615–1624

Using molecular dynamics (MD) simulations, we investigate the strength and fracture behavior of biphenylene based graphene (BG) monolayer subjected to uniaxial tensile deformation along the x- and y-directions. AIREBO potential is used for modeling the C-C atom interactions, and the simulations are carried out under isothermal conditions at a temperature of 300 K and strain rate of 10 10 s −1 using NVT ensemble. Defects such as cracks and voids are introduced in the monolayer to study their influence on the strength and mechanism of crack propagation. From the results, we conclude that monolayer strength and fracture behavior are dependent on the loading direction. Fracture in the monolayer is observed only when loaded along the x-direction and has comparatively lower strength. Further, the crack propagates by bond breaking along the four-membered rings in the biphenylene unit. As anticipated, the strength of the monolayer decreases in the presence of defects and the crack speed is estimated to be 7 × 10 3 m/s.

Two types of cracks are often encountered in engineering structural systems and these are the open cracks and the breathing cracks. Existence of open cracks often leads to the loss of physical stiffness, resulting in a mostly linear structure with reduced load bearing capacity and vibration frequencies. The development of breathing cracks not only reduces structural stiffness, but tends to render the otherwise linear structure to become nonlinear, due to their bilinear stiffness characteristics associated with open and closed states. The nonlinear structural vibration responses can then be investigated and potentially employed to detect and identify breathing cracks within a structural system. In the present study, breathing cracks are modeled based on fracture mechanics from which bilinear stiffness values are obtained. These values are then incorporated into finite element models to compute the first- and second-order frequency response functions (FRFs) based on a proposed correlation technique which is both very accurate and resilient against measurement uncertainties. The existence of well-defined second-order FRFs has been firmly established for the bilinear oscillator, as well as a cantilevered beam with breathing cracks. By expressing the bilinear restoring force as a polynomial series, analytical derivation of second-order FRFs of general structural systems such as the GARTEUR AG11 structure with breathing cracks has been established for the first time. Further, a method of identification has been developed to identify the physical parameters of breathing cracks using second-order FRFs. With these new developments that are presented in this paper, a solid foundation has been laid for the potential applications of higher-order FRFs to damage identification and assessment of general real structural systems. MOE (Min. of Education, S’pore)

Classical non-equilibrium molecular dynamics is employed to model short-strips of single-layered materials consisting of either carbon (graphene) or silicon (silicene) atoms. Both materials are modeled using their respective parameterizations of the Tersoff potential, and their thermal conductivities are then determined through non-equilibrium molecular dynamics. The present results indicate that both materials experienced increasing thermal conductivities as length increased, and graphene had far more rapid increases than silicene. Both armchair and zigzag chiralities in silicene has significant differences in thermal conductivities but not in graphene. Graphene possesses significantly higher thermal conductivities than silicene at every length scale and chirality, and this is found to be attributed to the fewer excitable phonon frequencies, as shown through the vibrational density of states.

In this study, classical molecular dynamics with the well-known van Beest, Kramer and van Santen potential are used for the first time to investigate the solid thermal conductivity of silica aerogel. Aerogel samples at various densities are obtained through negative pressure rupturing of dense silica samples, and reverse non-equilibrium molecular dynamics is employed to determine the thermal conductivity at each density. Results indicate that a power-law fit of the thermal conductivity obtained varies almost linearly with density, where decreasing density and increasing porosity led to an almost linear decrease in thermal conductivity. This is reflective of the trend observed in experimental bulk sintered silica aerogel. The results also showed that the thermal conductivity is of the same order of magnitude as bulk sintered aerogel. The power-law fit of the results also accurately reflected the variation found in bulk sintered aerogel.

In the present work, we present a systematic analysis of the chemisorption process pathway of hydrogen atoms onto the exterior wall of (5,5) carbon nanotubes using the ONIOM2 (B3LYP(6–31+G(d,p):UFF)) scheme, and we avoid the gross assumption of fixing any of the carbon atoms during the simulation. It is shown that the adsorption of hydrogen atoms onto the sidewall of CNTs are energetically favorable and the most stable state is to form two H–C σ-bonds while the original σ-bond between the carbon atoms is totally severed. In particular, we examined the molecular thermodynamics properties for the reaction at a range of temperatures from 77 K to 1000 K, and the results suggests that the reaction is possible at ambient temperature, but it is less favorable than that at lower temperatures.

A chemo-electro-mechanical formulation, referred to as the multi-effect-coupling pH-stimulus (MECpH) model, is presented in this paper for the analysis of the effects of the initial geometrical size on the responsive behavior of pH-sensitive hydrogels subject to the coupled stimuli of environmental solution pH and externally applied electric voltage. The model is composed of coupled nonlinear partial differential equations, and it accounts for the diffusion of ionic species, distributive electric potential and large mechanical deformation. In addition, the correlation between the diffusive hydrogen ion within the hydrogel and charge groups fixed to the polymeric network chains is incorporated quantitatively into this MECpH model. For the simulation of the response characteristics of the smart hydrogel, we solve the one-dimensional steady-state problem using the Hermite–Cloud meshless technique. For the MECpH model, the present numerical simulations were compared with experimental data available from literature to validate the accuracy and robustness of the model, and good agreement was observed. Several parameter studies were then carried out in the analysis of the hydrogel swelling when immersed in solution, and it was observed that the initial geometrical size has significant influence on the volume variations of these pH-responsive hydrogels.

The dissipative particle dynamic (DPD) method is applied to simulate the DNA separation process based on a mechanism developed earlier by other authors, who demonstrated a micro-device for separating DNA molecules (>2 kbp) through an entropic trapping mechanism. The DPD is used to model the process because it is intrinsic to modeling hydrodynamic interactions, which is lacking in some earlier works. We use the worm-like chain model to represent DNA molecule and Lennard–Jones potential at mesoscopic level to avoid phantom collision between the chain beads. Our simulations show that longer DNA strands do move faster than shorter ones, as observed in available experimental data. We also confirm that the delayed entrance is the cause of entropic trapping. Contrary to some earlier reported data, we found that the corner trapping is not a contributor to DNA separation.

In this paper, the dynamic stability analysis of thin, laminated cylindrical panels under static and periodic axial forces is presented by using the mesh-free kp-Ritz method. The mesh-free kernel particle estimate is employed to approximate the 2D transverse displacement field. A system of Mathieu–Hill equations is obtained through the application of the Ritz minimization procedure to the energy expressions. The principal instability regions are then analyzed via Bolotin's first approximation. Effects of lamination schemes such as number of layers, ply-angle and boundary conditions on the instability regions are examined in detail.

The effect of Young's modulus on the behavior of pH-sensitive hydrogels is studied when subjected to coupled stimuli of solution pH and externally applied electric field. The study is the first instance for coupled stimuli numerical analysis of the hydrogels, in which a multi-effect-coupling pH-stimulus (MECpH) model is presented. The model considers ionic diffusion, electric potential, and large mechanical deformation. A correlation between diffusive hydrogen ion and charge groups fixed onto the hydrogel polymeric chains by the Langmuir absorption isotherm is incorporated into the model. To validate the model, the computed results by the meshless Hermite-Cloud technique are compared well with experimental data available from the literature. Then several case studies are conducted for the swelling hydrogel immersed in buffered solution subject to applied electric voltage, especially for the Young modulus effects on the volume variations of the hydrogels.

When exposed to an external solvent, a dry polymeric network imbibes the solvent and undergoes large deformation. The resulting aggregate is known as a hydrogel. This swelling process is diffusion driven and thus results in differential swelling during transient swelling. When subjected to external geometrical constraints, such as being rigidly fixed or attachment to a compliant substrate, wrinkles have been shown to appear due to mechanical instabilities. In the case of free swelling, there are no external constraints to induce the instabilities accounting for wrinkling patterns. However, during the transient swelling process, the swelling differential between the gel on the exterior and the interior causes compressive stresses and gives rise to mechanical instabilities. It is also observed that the time dependence of the swelling profile causes the wrinkles to evolve with time. In this work, we investigate this interesting phenomenon of transient wrinkle mode evolution using the finite element and state-space methods. From our simulations and prediction, we find that there is an inverse relation between critical wave number and time, which has earlier been observed in experiments.

In this paper, the free vibration of conical panels is analyzed by the mesh-free kp-Ritz method. Both 1-D and 2-D versions of the kp-Ritz approach are formulated for conical panels. For conical panels with two simply supported straight edges, the 1-D kp-Ritz version is used, where the kernel particle estimation is employed in hybridized form with harmonic functions to approximate the 2-D displacement field. For conical panels having arbitrary boundary conditions, the displacement field is approximated by the 2-D kp-Ritz version, with 2-D form of kernel particle functions employed. The classical thin shell theory based on Love's hypothesis is employed in the present analyses, and based on the kernel particle concept and Ritz technique, the eigenequations of the frequencies of the conical panels are obtained. To validate the accuracy of stability of the present method, convergence studies were carried out based on the influences of the support size and the number of nodes. Comparisons were also made with existing results available in the open literature. This study also examines in detail the effects of variation in the semi-vertex angle and boundary conditions, on the frequency characteristics of conical panels.

In this work, a novel true meshless numerical technique is proposed. It is termed the Hermite–Cloud method and is based on the classical reproducing kernel particle method except that a fixed reproducing kernel approximation is used instead. Another distinction is that the point collocation technique is used for the discretization of the governing partial differential equations. In this method, the Hermite theorem is employed for the construction of the interpolation functions. Through the constructed Hermite-type interpolation functions, we are able to generate the expressions of approximate solutions of both the unknown functions and the first-order derivatives, in a direct manner. A set of auxiliary conditions have also been developed so as to construct a complete set of PDEs with mixed Dirichlet and Neumann boundary conditions. Through several structural analysis examples, it is shown that the numerical results at the scattered discrete points generated by the Hermite–Cloud method are distinctly improved, for both the approximate solutions as well as the first-order derivatives.

In this paper, we consider the free vibration analysis of thin conical shells under different boundary conditions. The analysis is carried out using the element-free kp-Ritz method. The present study is based on the classical thin-shell theory. The kernel particle (kp) functions are employed in hybridized form with harmonic functions to approximate the two-dimensional displacement field. In order to examine the numerical stability of the present approach, convergence studies are performed based on the influences of the support size and the number of nodes. To verify the accuracy of this method, comparisons of the present results are made with results available in the open literature. This study also examines in detail the effects of semi-vertex angles and boundary conditions on the frequency characteristics of the conical shells.

A meshfree method based on the reproducing kernel particle approximate is employed for the free vibration and buckling analyses of shear-deformable plates. In this approach, the first order Mindlin/Reissner plate theory (FSDT) is used, and the displacement shape functions are constructed using the reproducing kernel approximation satisfying the consistency condition. The essential boundary conditions are enforced by a transformation method. Numerical examples considering various aspect ratios, skew angles and boundary conditions are demonstrated to show the validity of the proposed method, and satisfactory results were obtained when comparisons are made with the exact and other available numerical results existing in the literature.

In this paper, a micropump actuated by electrostatic forces is dynamically analyzed. Coupled electro-mechanical effects are considered in the evaluation of the performance of the electrostatic micropump. The boundary element method is employed here to solve the quasi 3-D Laplace equation that the potential difference satisfies in order to obtain the surface charge density and corresponding electrostatic force. First order shear deformation theory is used to model the electrode membrane of the pump. Geometric non-linearity arises due to the inclusion of von Karman strains. The finite element method is employed to discretize the governing equations and Newton's iteration method is employed to solve the discretized equations. With the electro-mechanical coupling effects considered within the framework of linear plate theory, i.e., ignoring the von Karman strains, similar response trends are obtained for the 2-D plate analysis as that of 1-D analysis found in open literature. The present study is extended to non-linear analysis with von Karman strains included and non-linear load–deflection relationship is demonstrated. Variation of the amplitude and frequency of the potential difference applied across the two electrodes are investigated and responses are compared with those of linear analysis. Qualitatively different responses are observed. Also, the effects of the length-to-thickness ratio of the electrode plate are examined in detail.

In this paper, the free vibration of laminated two-side simply-supported cylindrical panels is analyzed by the mesh-free kp-Ritz method. In this latest form of the Ritz technique, the reproducing kernel particle estimation is employed in hybridized form with harmonic functions to approximate the two-dimensional displacement field. The present analysis is based on the energy functional of the classical thin-shell theory based on Love's hypothesis. To validate the accuracy of the results and the stability of the present method, convergence studies were carried out based on the influences of the support size and the number of nodes. Comparisons of the present results were also made with existing results available in the open literature and good agreement obtained. This study also examines in detail the effects of different curved-edge boundary conditions on the frequency characteristics of cylindrical panels.

A hybrid meshless–differential order-reduction (hM-DOR) method is presented in this paper. It uses an order-reduction approach for high-order partial differential equations and combines a point collocation technique with a fixed reproducing kernel approximation. One of its advantages is that it can directly discretize the overlapping boundary conditions, which is a difficult procedure to carry out with existing collocation-based meshless approaches. Following numerical convergence studies on the newly developed method for the bending problems of thin simply supported circular and semicircular plates, the method is employed for the control simulation of the deformation profile of the uniformly loaded smart circular plates integrated with piezoelectric sensors/actuators. These validate the efficiency and accuracy of the proposed meshless hM-DOR technique.

In conventional analyses of composite laminates, the assumption of perfect bonding of adjoining layers is well accepted, although this is an oversimplification of the reality. It is possible that the bond strength may be less than that of the laminae. Thus, the study of weak bonding is an interesting focus area. In this study, an elastic bonding model based on three-dimensional theory of elasticity in a layerwise framework is used to study composite laminates. The differential quadrature (DQ) discretization is used to analyze the layerwise model. The present model enables the simulation of actual bonding stress states in laminated structures. The interfacial characteristics of transverse stress continuity as well as the kinematic continuity conditions are satisfied through the inclusion of the elastic bonding layer. The present model is employed to investigate the free vibration of thick rectangular cross-ply laminates of different boundary conditions and lamination schemes.

In an effort to overcome the limitations of existing rigid bonding analysis of composite laminates, the current three-dimensional elastostatic model is proposed. In this model, the three-dimensional interlaminar elastic stress field is determined using the technique of layerwise differential quadrature. The new formulations allowed us to determine the influence of a natural bonding layer upon the field variables in the laminated structure. The interfacial characteristics of continuity and discontinuity satisfy the kinematic continuity conditions through the elastic-bonding layer. A number of case studies are examined, comparisons with rigid bonding and finite element analyses are provided, and the influence of the pertinent parameters on the interlaminar stress field is evaluated and discussed.

By using the generalized differential quadrature (GDQ) method, this paper presents the orthotropic influence of composite materials on frequency characteristics for a rotating thin truncated circular symmetrical cross-ply laminated composite conical shell with different boundary conditions. The present governing equations of free vibration include the effects of initial hoop tension and the centrifugal and Coriolis accelerations due to rotation. Frequency characteristics are obtained to study in detail the orthotropic influences. Effects of boundary condition, rotating speed, circumferential wave number and geometric property are also discussed. To ensure the accuracy of the present results by the GDQ method, comparisons are made with those available in open literature and very good agreements are achieved.

In this paper, the free vibration of laminated composite cylindrical panels is solved by the meshfree (meshless) approach. The reproducing kernel particle approximation is employed to model the two-dimensional displacement functions. The effects of the particle distribution and the size of the domain of influence, on the convergence behavior, are studied. This study examines in detail the effects of different boundary conditions on the frequency characteristics of the cylindrical panels. The effects of the curvature of the cylindrical panels as well as the lamination scheme, on the frequencies of the panels, are also investigated. The present results are verified by comparison against results available in the open literature, with very good agreement being attained.

A non-linear vibration model for fluid–membrane coupling is developed for simulating the behaviour of valveless micropumps. The analytical solution for fluid–membrane coupling vibration has been approximated using the Galerkin and small parameter perturbation methods. Specifically, the vibration response of the membrane and the mean flux through a valveless membrane micropump are investigated in detail. The effects of the pressure loss coefficients of the diffuser and the coupling parameter on the mean flux are examined. An optimal working frequency range for the valveless membrane micropump is obtained. Numerical examples are presented to demonstrate the effectiveness of the present model for the designing of valveless micropumps.

In this paper, the dynamic model of the prototyped piezoelectric ceramic (PZT) linear actuator is established and optimized to obtain optimal performance. The PZT linear actuator construction is a cylindrical block with two cylindrical brass blocks attached to each side via PZT plates in between. Previous experimental and analytical studies on the prototyped PZT actuator concluded that velocity of the actuator had to be increased. Also, for practical applications, low voltages (applied across the PZT plates) were included as a criterion in the design scheme. The Sequential Quadratic Programming (SQP) method was employed in the optimization process. Optimization of the velocity was performed in detail, with important design parameters being the driving voltages and system parameters such as the masses of the metal blocks constructing the system, linear parameters of PZT, and coefficient of friction. Various waveforms of driving voltage were explored in an attempt to make the actuator move faster.

Porous structures of silica aerogels are generated using classical molecular dynamics, with the Tersoff potential, which has been re-parametrized for modeling silicon dioxides. This work demonstrates that this potential is superior to the widely used BKS potential in terms of characterizing the thermal conductivities of amorphous silica, by comparing the vibrational density of states with previous experimental studies. Aerogel samples of increasing densities are obtained through an expanding, heating and quenching process. Reverse non-equilibrium molecular dynamics is applied at each density to determine the thermal conductivity. A power-law fit of the results is found to accurately reflect the power-law variation found in experimental bulk aerogels. The results are also of the same order of magnitude as experimental bulk aerogels, but they are consistently higher. By analyzing the pore size distribution on different simulation length scales, we show that such a disparity is due to finite sizes of pores that can be represented, where increasing simulation length scales lead to an increase in the largest pore size that can be modeled. ASTAR (Agency for Sci., Tech. and Research, S’pore)

This study investigates the distribution and propagation of potential energy in graphene under tearing loads. Before crack extension, high potential energy accumulates at the crack tip. The distributions of the high potential energy are symmetrical and asymmetrical in pristine graphene and bi-crystal graphene with misorientation angle of [Formula: see text], respectively. When a C–C bond breaks during the fracture of graphene, numerous energy waves successively arise from the crack tip, i.e., the two atoms linked by the broken bond. These atoms lose one bond constraint and turn into unstable states, and they displace with high accelerations. In pristine graphene, the energy waves present as hexagonal geometries, while the waveforms near the loading areas are compressed to flatter geometries. In bi-crystal graphene, the refractions of potential energy waves are observed when the energy waves propagate to the grain boundary (GB) and interact with it, and the waveforms are changed after the wave crosses the GB. For both pristine graphene and bi-crystal graphene, wrinkles are generated when the crack tip extends to the site sufficiently close to the vertical free boundary, and the wrinkles are always nearly parallel to the horizontal free boundary and move along with the motion of the crack tip.

Classical molecular dynamics with the AIREBO potential is used to investigate and compare the thermal conductivity of both zigzag and armchair graphene nanoribbons possessing various densities of Stone–Thrower–Wales (STW) and double vacancy defects, within a temperature range of 100–600 K. Our results indicate that the presence of both kinds of defects can decrease the thermal conductivity by more than 80% as defect densities are increased to 10% coverage, with the decrease at high defect densities being significantly higher in zigzag compared with armchair nanoribbons. Variations of thermal conductivity in armchair nanoribbons were similar for both kinds of defects, whereas double vacancies in the zigzag nanoribbons led to more significant decreases in thermal conductivity than STW defects. The same trends are observed across the entire temperature range tested.

Classical molecular dynamics with the AIREBO potential is used to investigate the thermal conductivity of both zigzag and armchair graphene nanoribbons possessing different densities of Stone–Thrower–Wales (STW) defects. Our results indicate that the presence of the defects can decrease thermal conductivity by more than 50%. The larger the defect density, the lower the conductivity, with the decrease significantly higher in zigzag than in armchair nanoribbons for all defect densities. The effect of STW defects in the temperature range 100–600 K was also determined. Our results showed the same trends in thermal conductivity decreases at all temperatures. However, for higher defect densities there was less variation in thermal conductivity at different temperatures.

The superior thermal, optical, acoustical, and mechanical properties of a nano-porous and ultra-light material called silica aerogel have been known to science since the 1930's. In this study, we propose a new analytical–numerical model of a silica aerogel to predict its Young's modulus. The molecular dynamics (MD) simulation method was adopted to model and simulate the backbone of silica aerogels with different densities in an improved negative pressure rupturing method, and their mechanical properties were investigated. To generate the model using MD, the traditional method was improved by changing the sequence of its procedures, and it was proven to be a more stable and physically representative method. In the prediction, we proposed a two-level nano-porous structure model according to our simulations and the widely accepted fractal structure of silica aerogels. The Young's modulus of a silica aerogel, which is shown in a power–law relationship with the density of samples, was derived by the two-level hierarchical model and uniaxial tension tests. We envisage that this new model can be applied in more analytical–numerical studies to reveal other interesting mechanical properties of silica aerogels.

Modeling is conducted in this paper for analysis of the influence of Young's modulus on the response of soft active hydrogels to environmental solution pH changes. A chemo–electro–mechanical formulation termed the multi-effect-coupling pH-stimulus (MECpH) model, which was developed previously according to linear elastic theory for small deformation description, is improved in this paper through incorporation of the finite deformation formulation into the mechanical equilibrium equation. The model is expressed by coupled nonlinear partial differential equations and solved via the meshless Hermite-cloud method with the modified Newton iteration technique. The improved MECpH model is examined by comparison between the computational and published experimental results. Numerical studies are then done on the influence of Young's modulus on the distributive variations of the diffusive ion concentrations and electric potential, and on the deformation variations of the pH-stimulus-responsive hydrogels within different buffered solutions.

In this paper, we conduct a computational analysis of the effects of initial fixed charge density on the responsive performance of pH-sensitive hydrogels to environmental change in solution pH. The analysis is based on a chemo-electro-mechanical formulation previously termed the multi-effect-coupling pH-stimulus (MECpH) model. In this work, we improve the MECpH model by incorporating the finite deformation formulation into the mechanical equilibrium equation. The present model consisting of coupled nonlinear partial differential equations is solved via a meshless numerical technique called the Hermite-cloud method with the modified Newton iteration methodology. After validation of the MECpH model by comparing the computational results with experimental data available in the literature, several computational case studies are carried out for analysis of the effects of initial fixed charge density on the distributive variations of the diffusive ion concentrations and electric potential and on the deformation of the pH-stimulus-responsive hydrogels, when they are immersed in different buffered solutions.

We simulate DNA suspension microchannel flows using the dissipative particle dynamics (DPD) method. Two developments make this simulation more realistic. One is to improve the dynamic characteristics of a DPD system by modifying the weighting function of the dissipative force and increasing its cutoff radius, so that the Schmidt number can be increased to a practical level. Another is to set up a wormlike chain model in the DPD framework, according to the measured extension properties of a DNA molecule in uniform flows. This chain model is then used to study flows of a DNA suspension through microchannels. Interesting results on the conformation evolution of DNA molecules passing through the microchannels, including periodic contraction-diffusion microchannels, are reported.

In this paper, the effects of size of the chains composed of the drop and initial velocity of the drop on the drop terraced spreading are studied. The chain size effects on the base radius of drop are studied at zero initial velocity. A logarithm dependence of the drop base radius on the time is found for 2-atom to 16-atom flexible chain systems with large lattice dimension of solid and a power law t1/2 for small lattice dimension of solid. The longer the chain, the slower is the spreading. With a nonzero initial velocity, the drop base radius increases with increasing initial velocity before the drop splits into smaller separated drops. As the initial velocity increases, the transition from a logarithm to a power law t1/2 relation for the time dependence of the drop base radius is first noted here.

A polymer network can imbibe copious amounts of solvent and swell, the resulting state is known as a gel. Depending on its constituents, a gel is able to deform under the influence of various external stimuli, such as temperature, pH-value and light. In this work, we investigate the photo-thermal mechanics of deformation of temperature sensitive hydrogels impregnated with light-absorbing nano-particles. The field theory of photo-thermal sensitive gels is developed by incorporating effects of photochemical heating into the thermodynamic theory of neutral and temperature sensitive hydrogels. This is achieved by considering the equilibrium thermodynamics of a swelling gel through a variational approach. The phase transition phenomenon of these gels, and the factors affecting their deformations, are studied. To facilitate the simulation of large inhomogeneous deformations subjected to geometrical constraints, a finite element model is developed using a user-defined subroutine in ABAQUS, and by modeling the gel as a hyperelastic material. This numerical approach is validated through case studies involving gels undergoing phase coexistence and buckling when exposed to irradiation of varying intensities, and as a microvalve in microfluidic application.

In this paper, the dynamic stability of rotating cylindrical shells under static and periodic axial forces is investigated using a combination of the Ritz method and Bolotin’s first approximation. The kernel particle estimate is employed in hybridized form with harmonic functions, to approximate the 2-D transverse displacement field. A system of Mathieu–Hill equations is obtained through the application of the Ritz energy minimization procedure. The principal instability regions are then obtained via Bolotin’s first approximation. In this formulation, both the hoop tension and Coriolis effects due to the rotation are accounted for. Various boundary conditions are considered, and the present results represent the first instance in which, the effects of boundary conditions for this class of problems, have been reported in open literature. Effects of rotational speeds on the instability regions for different modes are also examined in detail.