Transition to an optimal periodic gait by simultaneous input and parameter optimization method of Hamiltonian systems

This paper is concerned with a gait transition to an optimal periodic gait by a simultaneous input and parameter optimization technique of Hamiltonian systems. First, a continuous-time dynamics of a passive walking/running robot between the touchdown and lift-off is considered as a Hamiltonian system. Then, the control input and some robot parameters, such as the mass, inertia, link length, and so on, are optimized using learning optimal control of Hamiltonian systems, which has been developed by the authors. This method allows one to simultaneously obtain an optimal feedforward input and optimal parameters, which (at least locally) minimize a given cost function. The main advantage is that the precise model of the dynamics of the plant system is not required using a symmetric property of Hamiltonian systems, called variational symmetry. We formulate an optimal gait generation scheme via the learning optimal control, where the robot keeps walking and the gait is optimized with respect to the control input and some adjustable robot parameters simultaneously. As a result, the gait transition to an optimal periodic one is achieved.     

Full‐parallax autostereoscopic display with scalable lateral resolution using overlaid multiple projection

Abstract— A method to increase the viewing resolution of an autostereoscopic display without increasing the density of microlenses is proposed. Multiple projectors are used for the projection images to be focused and overlaid on a common plane in the air behind the microlens array. The multiple overlaid projection images yield multiple light spots inside the region of each elemental lenslet of the microlens array. This feature provides scalable high‐resolution images by increasing the number of projectors. Based on the proposed method, a prototype display that includes 15 projectors was designed and built. 3‐D images were successfully reproduced on the prototype display with full parallax and a wide viewing angle of 70°.     

Robust dynamic ship positioning control system design and applications

This paper describes the robust control system design for a ship dynamic positioning system. The control design is based on an approximate linear model derived from the nonlinear hydrodynamic equations governing the horizontal motions of the ship. The nonlinear models of the ship, seawaves, current, wind and thrusters are derived and simulated for control design verification. The H_∞ control design technique is employed to design the controller. The control problem is formulated in state‐space form and the design specifications are translated into requirements on the weighting functions of the error signal and the thrusters input. A tuning procedure is proposed based on the wind and wave disturbances. The controller is initially tested on the nonlinear ship model and simulation results are presented to demonstrate the robustness of the H_∞ controller. Tank tests results are then presented to assess the controller performance. Copyright © 2001 John Wiley & Sons, Ltd.     

XPS study of carbon nitride films deposited by hot filament chemical vapor deposition using carbon filament

Amorphous carbon nitride, a-CN_x, thin films were deposited by hot filament CVD using a carbon filament with dc negative bias voltage on the substrate. The effects of the negative bias and the filament components on the binding structure of the films are investigated by XPS. The composition ratio of graphite to amorphous carbon in the filaments affects the bonding structure of carbon and nitrogen in the films, although the nitrogen content in the films is almost same as 0.1. The nitrogen content in the films changes from 0.1 to 0.3 as the negative bias changes from 0 to − 300 V.     

Effect of air-oxidation on the pore-structure of coals and cokes or chars obtained from oxidized coals

Seven kinds of coals (C, 77.8–89.8 wt% daf) were oxidized with air at 150 °C for 1, 5 and 10 h. The oxidized coals were heat-treated at various temperatures between 300 and 1500 °C with intervals of 50 or 100°C. The pore-structure of the oxidized coals and the cokes or chars obtained from the oxidized coals was compared with those of parent coals and their cokes or chars. True densities were measured in methanol and straight-chain hexane and pore volumes were determined by the Dubinin-Polanyi procedure. For the coals, the methanol-density increased with extent of oxidation; the hexane-density increased at first, but then decreased and again increased in the course of the oxidation. The air-oxidation of coals has a marked and controlling effect on the development of the pore-structure of cokes and chars in the course of the carbonization.     

Determination of the diffusion coefficients of NiCl2, ZnCl2, and CdCl2 in aqueous solution

The diffusion coefficients of NiCl₂, ZnCl₂, and CdCl₂ in the aqueous solution systems of MC1₂ and MC1₂-HC1 were measured at 298 K using a diaphragm-cell method. The data are listed as a function of molar concentrations of MC1₂ at the HC1 concentrations of 0, 0.1, 0.5, 1.0, and 2.0 mol dm^-3. It was found that the concentration dependencies of the diffusion coefficients for these metal chlorides in single-electrolyte solutions differed from each other. This could be explained in terms of changes in the mean activity coefficients of chloride and in the viscosities of those solutions. The diffusion coefficient of metal chloride in MC1₂-HC1 solution was greatly affected by the HC1 concentration; however, the behavior of the diffusion coefficients varied, depending on the kind of chloride involved. In NiCl₂-HCl solutions, an increase in HC1 con-centration caused a decrease in the diffusion coefficient value, while in ZnCl₂-HCl solutions, the addition of 2 mol dm^-3 HC1 caused an increase in the diffusion coefficient of ZnCl₂. These phenomena are quite different from those of the sulfate systems reported in our previous work. It was also demonstrated that the concentration dependency of the diffusion coefficients of MC1₂ in aqueous MC1₂-HC1 solutions could be attributed to the diffusion potential as well as the changes in the mean activity coefficient and viscosity. Masami Aoki, formerly Graduate Student, Department of Met-allurgy, Kyoto University.     

Mechanical Properties of Woodceramics: A Porous Carbon Material

The mechanical properties of woodceramics, which are new porous carbon materials utilizing the natural structure of wood, were investigated. The effects of burning temperature and amount of impregnated phenol resin on Young's modulus, compressive strength and fracture toughness were measured. The fracture morphology was then observed, and simplified mechanical models of the woodceramics were discussed to explain the mechanical properties. The fracture was initiated at the cell walls that were located in vertical direction against the applied stress. The effect of impregnated phenol resin on the Young's modulus and the compressive strength was reasonably explained by a wall-bending model.     

Development of moisture loss models in steam turbines

This paper describes physics‐based moisture loss models for designing wet‐steam turbines. Steam turbines operating under wet‐steam conditions experience thermodynamic and mechanical losses caused by the presence of moisture. The developed moisture loss models are composed of six categories: supersaturation loss, condensation loss, acceleration loss, braking loss, capturing loss, and pumping loss. These losses are calculated according to the wetness levels in the stationary blade and moving blade rows, and defined by the functions of steam properties and design factors of turbine stages. The supersaturation loss produced by non‐equilibrium expansion of the wet steam is modeled using the pressure ratio and the isentropic exponent of the supersaturated steam. The loss models are compared to full‐size test turbine data for prediction of the overall moisture losses. As a result, the developed loss models are found to be very effective for estimating the moisture losses of turbine stages. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(7): 651–664, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20395