In this paper, the effect of parameter and spatial discretization errors on the closed-loop behavior of distributed-parameter systems is analyzed for natural controls. If the control force designed on the basis of the postulated system with the parameter and discretization errors is applied to control the actual system, the closed-loop performance of the actual system will be degraded depending on the degree of the errors. The extent of deviation of the closed-loop performance from the expected one is derived and evaluated using operator techniques. It has been found that the extent of the deviation is proportional to the magnitude of the parameter and discretization errors, and that the proportional coefficient depends on the structures of the natural controls.

Cellular materials have two important properties: structures and mechanisms. These properties have important applications in materials design; in particular, they’re used to determine the modulus and yield strain. The objective of this study is to gain a better understanding of these two properties and to explore the synthesis of three-dimensional (3D) compliant cellular materials (CCMs) with compliant porous structures (CPSes) generated from modified hexagonal honeycombs. An orthotropic constitutive CCM model in the Cartesian coordinate system is constructed using the strain energy method, which uses the deformation of hinges around holes and the rotation of links. A finite element (FE) based simulation is conducted to validate the analytical model. The moduli and yield strains of the 3D CCMs with an aluminum alloy are about 1.2GPa and 0.4% in the longitudinal direction and about 0.08MPa and 30% in the lateral direction. The CCMs have extremely high positive and negative Poisson’s ratios ν x y * ∼ ± 30 due to the large rotation of the link member in the transverse direction caused by an input displacement in the longitudinal direction. This paper demonstrates that compliant me so structures can be used for next generation materials design in tailoring mechanical properties such as moduli, strength, strain, and Poisson’s ratios.

In an effort to tailor functional materials with customized anisotropic properties — stiffness and yield strain, we propose porous materials consisting of flexible mesostructures designed from the deformation of a re-entrant auxetic honeycomb and compliant mechanisms. Using an analogy between compliant mechanisms and a cellular material’s deformation, we can tailor in-plane properties of mesostructures; low stiffness and high strain in one direction and high stiffness and low strain in the other direction. Two mesostructures based on hexagonal honeycombs with positive and negative cell angles are generated. An analytical model is developed to obtain effective moduli and yield strains of the porous materials by combining the kinematics of a rigid link mechanism and deformation of flexure hinges. A numerical technique is implemented to the analytical model for nonlinear constitutive relations of the mesostructures and their strain dependent Poisson’s ratios. A Finite Element Analysis (FEA) is used to validate the analytical and numerical model. The moduli and yield strain of a porous aluminum alloy are about 6.3GPa and 0.26% in one direction and about 2.8MPa and 12% in the other direction. The mesostructures have extremely high positive and negative Poisson’s ratios, ν x y * (∼ ±40) due to the large rotation of the link member in the transverse direction caused by the input displacement in the longitudinal direction. The mesostructures also show higher moduli for compressive loading due to the contact of slit edges at the center region. This paper demonstrates that compliant mesostructures can be used for a next generation material design in terms of tailoring mechanical properties; moduli, strength, strain, and Poisson’s ratios. The proposed mesostructures can also be easily manufactured using a conventional cutting method.

Investment casting processes are influenced by a variety of parameters. Many researches considering viscosity as a constant have been conducted up to this point. In particular, however, viscosity with temperature change has not been much accounted for solidification and heat transfer simulation of molten metal in the investment casting process. In addition, analysis of behavior of metal flow as well as air gap problems for complex network structures have not been investigated much. The aim of this study is to build transient metal flow and velocity profile models considering temperature dependent viscosity in investment casting processes of cellular structures. In this study, a Computational Fluid Dynamics (CFD) modeling tool was used for metal flow and velocity profile in investment casting processing using User Defined Function (UDF) for temperature dependent viscosity. The results of the metal flow and velocity profile inside of the simple cylindrical geometry are represented. It is shown that for the validation of the numerical simulation, the velocity profile between analytical and numerical approaches showed very good agreement. Analytical approaches showed that velocity was reduced with the increase in viscosity, which is applied as a function of temperature. In particular, rapid decreasing in velocity was shown from under the melting temperature of the molten metal. There was no movement on metal flow at the room temperature. Numerical approaches showed that the liquid metal began to be solidified from the wall surface inside of the mold. For the same simulation time, it was shown that the metal flow in a cylinder that has 1 mm diameter showed better fluidity rather than that of the cylinder that has 2 mm diameter due to the increase in adhesion between liquid metal and the surface of the mold and surface tension between molten metal and air. The effective diameter by solidification is decreased with the time change.

Motivated by our previous study on the flexibility and low local stress of auxetic hexagonal honeycombs in uni-axial loading, we explore the dynamic characteristics of a flexible auxetic hexagonal lattice structure when it is used as the flexible spokes of a non-pneumatic tire. In this study, a modal analysis and the steady state vibration characteristics of NPTs with cellular spokes are investigated with a series of vertical loads and rolling speeds using a commercial finite element code, ABAQUS/Explicit. The angular velocity and the displacement at the hub center and the reaction force on the ground were investigated in the time and frequency domains for the steady state rolling condition for vehicle speeds of 60km/h and 80km/h. The orthotropic properties of the honeycomb spokes create different modal behaviors compared with those of pneumatic tires; e.g., the in-plane shear at the initial mode. The discrete spoke geometry induces a non-homogeneous mass (non-uniformity) distribution, which also causes local vibration effects.

Rigid bone fixation plates made of stainless steel or a titanium alloy are used as supplemental support structures when a fracture occurs in a long bone. These fixation plates are about an order of magnitude higher in elastic modulus than that of cortical bones, which may cause high interface stress between the fixation plate and the bone. Moreover, when they are used for a bone fracture in a child, they may prevent bone growth due to their high stiffness in the longitudinal direction. In this study, we suggest a novel fixation plate that controls for the stiffness and elastic elongation in the uni-axial loadings, namely tension and compression. Using a flexure based compliant mechanism and cellular structures, uni-axial load-deflection curves are generated in tensile and compression loads. A commercial finite element (FE) code, ABAQUS, is used for a parametric study of the geometric effect of the cellular structures on stiffness and elastic elongation. Performance of the designed fixation plate is validated by an FE analysis for bone tension and compression under a contact condition between the bone and fixation plate.

With an increasing demand to reduce CO 2 emissions, sustainable transportation tools are drawing attention. After having reported on our initial design of a folding bike as an easy-to-carry sustainable transportation tool, we now explore lateral stiffness as well as other dynamic properties, including modal behaviors and steady state vibration characteristics. In this study, we investigate the lateral force of a separable polyurethane solid tire with varying slip and camber angles. Nonlinear hyperelastic material models are used with a commercial finite element code, ABAQUS/Standard. Transient and steady state dynamic properties of the separable bike wheel and tire are also investigated with the ABAQUS/Explicit code, and the results are compared with those of the pneumatic counterpart.

An understanding of the flow around a tire in contact with the ground is important for when designing a fuel efficient tire as aerodynamic drag accounts for about one third of an entire vehicle’s rolling loss [1]. Recently, non-pneumatic tires (NPTs) have drawn attention mainly due to their low rolling resistance associated with the use of low viscoelastic materials in their construction. However, an NPT’s fuel efficiency should be re-evaluated in terms of aerodynamic drag: discrete flexible spokes in an NPT may cause more aerodynamic drag, resulting in greater rolling resistance. In this study, the aerodynamic flow around an NPT in contact with the ground is investigated for i) stationary and ii) rotating cases using the Reynolds-Averaged Navier-Stokes (RANS) method. The NPT has a more complex flow and a higher drag force than does the pneumatic counterpart.

With an increased interest in a non-pneumatic tire (NPT) and its possible performance on safety in driving and low rolling resistance, extensive research on mechanical properties including dynamic characteristics are required to explore for the commercialization of NPTs. In this study, we explore the dynamic characteristics of NPTs with flexible hexagonal lattice spokes. A steady state vibration characteristic of NPTs is investigated with a series of load carrying capability and rolling speed for two hexagonal spokes using a commercial finite element code, ABAQUS. The obtained vibration characteristics are compared with those of conventional pneumatic tires, which are available in the literature.

For an accurate evaluation of the failure stress of tire and pavement materials, both the tire and pavement need to be modeled as nonlinear materials. In this study, a hyperelastic model of a truck tire and an elasto-viscoplastic model for pavement are implemented and their interaction effect on contact stresses is investigated. Finite element (FE) analysis with ABAQUS is used to simulate the interaction models of the truck tire and pavement. The interaction of hyperelastic and elasto-viscoplastic models for a truck tire and pavement shows accurate contact pressure for the truck tire and accurate stress distribution of the pavement.

A passive morphing may improve the aerodynamic characteristics through structural shape change by aerodynamic loads during the flight, resulting in improving fuel efficiency. The passive morphing structure should have a capability to be highly deformed while maintaining a sufficient stiffness in bending. Honeycombs may be good for controlling both stiffness and flexibility. This paper investigates a honeycomb airfoil’s static deformations through the fluid-structure interaction using computational fluid dynamics and structural finite element analysis. The structural performance will be investigated with varying honeycomb geometries including regular, auxetic and chiral meso-structures.

Contact pressure distribution has been an important issue on the tire design due to its significant effect on passengers’ comfort, vehicle handling, wear, and noise. Motivated by our previous finite element results on contact pressure reduction with a non-pneumatic tire (NPT) of two-dimensional (2D) lattice spokes, we explore structural performance of a NPT tire with three-dimensional (3D) lattice spokes. In this study, static contact pressure of a NPT with 3D lattice spokes is investigated as a function of vertical load and is compared with that of a pneumatic tire. Finite element based numerical simulation of the contact pressure of a NPT is conducted with ABAQUS for varying vertical forces and 3D lattice spoke geometries.

With increasing awareness of energy depletion and environmental pollution, bikes have been paid more attention as an important transportation tool. Folding or separable part design of a bike may increase a use of bikes due to its portable capability. In this study, we suggest a novel separable solid bike tire for a folding bike use. Finite element model with ABAQUS is used to model a polyurethane (PU) separable solid tire. Vertical stiffness and contact pressure are compared with those of a conventional pneumatic bike tire. Elliptical hollow cross-sections of a PU solid tire are investigated to match a vertical stiffness and contact pressure of a conventional pneumatic bike tire. The suggested PU solid tire with an elliptical hollow cross-section shows a lower contact pressure than a pneumatic bike tire when they are designed to be the same load carrying capability.

Nonlinear material models of a tire and a pavement appear to be important to precisely evaluate both tire performance and stresses of a pavement. In this paper, nonlinear tire and pavement material models are used and their contract pressures of a tire and stresses of a pavement are investigated. The results with the nonlinear material models are compared with those of simplified tire and pavement models. Finite element (FE) analysis with ABAQUS is used for simulating four different interaction models of tire and pavement. An interaction model with a hyperelastic tire and an elasto-viscoplastic pavement shows accurate contract pressures of a tire and stress distributions of a pavement.