Full State Estimation of Continuum Robots From Tip Velocities: A Cosserat-Theoretic Boundary Observer

State estimation of robotic systems is essential to implementing feedback controllers which usually provide better robustness to modeling uncertainties than open-loop controllers. However, state estimation of soft robots is very challenging because soft robots have theoretically infinite degrees of freedom while existing sensors only provide a limited number of discrete measurements. In this paper, we design an observer for soft continuum robotic arms based on the well-known Cosserat rod theory which models continuum robotic arms by nonlinear partial differential equations (PDEs). The observer is able to estimate all the continuum (infinite-dimensional) robot states (poses, strains, and velocities) by only sensing the tip velocity of the continuum robot (and hence it is called a ``boundary'' observer). More importantly, the estimation error dynamics is formally proven to be locally input-to-state stable. The key idea is to inject sequential tip velocity measurements into the observer in a way that dissipates the energy of the estimation errors through the boundary. Furthermore, this boundary observer can be implemented by simply changing a boundary condition in any numerical solvers of Cosserat rod models. Extensive numerical studies are included and suggest that the domain of attraction is large and the observer is robust to uncertainties of tip velocity measurements and model parameters

2-(4-tert-Butyl­phen­yl)-5-{3,4-dibutoxy-5-[5-(4-tert-butyl­phen­yl)-1,3,4-oxadiazol-2-yl]-2-thienyl}-1,3,4-oxadiazole

In the title compound, C36H44N4O4S, the dihedral angles between the central thio­phene ring and the pendent oxadiazole rings are 12.7 (2) and 13.7 (2)°, and the dihedral angles between the oxadiazole rings and their adjacent benzene rings are 6.1 (2) and 17.5 (2)°. An intra­molecular C—H⋯O inter­action may help to establish the conformation

Concrete-encased CFST structures: behaviour and application

[EN] Concrete-encased CFST (concrete-filled steel tube) is a kind of composite structure comprised of a CFST component and a reinforced concrete (RC) component. The concrete encased CFST possesses superior ductility and higher stiffness. They are gaining popularity in high-rise buildings, large-span structures, bridges, subway stations and workshops. This paper initially reviews the recent research on concrete-encased CFST structures. The major research findings on bond performance, static performance, dynamic performance and fire resistance are presented. This paper also outlines some construction considerations, such as the utilization of materials, the fabrication of the steel tube, and the methods of casting the inner and outer concrete. Finally, some typical practical projects utilizing concrete-encased CFST members are presented and reviewed.The research reported in this paper is part of the Project 51678341 supported by the National Natural Science Foundation of China (NSFC). The financial support is highly appreciated.Han, L.; Ma, D.; Zhou, K. (2018). Concrete-encased CFST structures: behaviour and application. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 1-10. https://doi.org/10.4995/ASCCS2018.2018.7109OCS11

Analytical behavior of concrete-filled aluminum tubular stub columns under axial compression

[EN] This paper presents numerical investigation of circular concrete-filled aluminum tubular (CFAT) stub columns under axial compression. The numerical models were developed using the finite element (FE) package ABAQUS. The parameters commonly employed in conventional CFST FE modeling have been discussed in this study. The nonlinearities of concrete and aluminum materials and the interaction between concrete and aluminum tube were considered. Numerical models were validated against collected experimental data. The ultimate loads, load-axial strain relationship and failure modes from numerical simulations were compared with those from experiments. The verified FE model was used to analyze structural behavior of full histories of the corresponding load-deformation N-ε response. Load-deformation N-ε curves for both concrete and aluminum tube were also presented. Upon on validation of the FE models, additional structural performance data over a wide range of diameter-to-thickness ratios, aluminum grades and concrete strengths were generated for parametric studies. The influences of diameter-to-thickness ratios, aluminum grades and concrete strengths on the ultimate strength were presented in this paper.Zhao, H.; Wang, F.; Han, L. (2018). Analytical behavior of concrete-filled aluminum tubular stub columns under axial compression. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 373-378. https://doi.org/10.4995/ASCCS2018.2018.7135OCS37337

Numerical Behaviour of Composite K-Joints Subjected to Combined Loading and Corrosive Environment

[EN] Concrete filled steel tubular (CFST) truss structures have been adopted in various infrastructures worldwide for past several decades. Application of CFST truss is more prevalent especially in areas where harsh marine condition with chloride corrosion limits the design life of structures. Design of joints is one of the most complicated issues in CFST truss structures; and it becomes more critical when corrosion causes section loss in the outer steel tube. Improved designs in terms of economy and durability need to be suggested based on rational research on composite K-joints in corrosive environment, whilst such research is very limited up until now. This paper thus attempts to study the behaviour of circular concrete filled steel tubular (CFST) K-joints under combined effect of long-term loading and corrosion. A finite element analysis (FEA) model is presented and verified against existing test results. The model is then utilized to perform mechanism analysis of CFST K-joints under varying loading and corrosion situations. Failure modes, detailed propagation of yield and stress distribution between the core concrete in chord and the tubular steel is investigated, based on which a favourable mode of failure is suggested in terms of maximum joint capacity. Finally, a full range analysis of the load-deformation characteristics is carried out for various corrosion situations, with the corresponding joint strength as well as ductility predicted.Saleh, S.; Hou, C.; Han, L.; Hua, Y. (2018). Numerical Behaviour of Composite K-Joints Subjected to Combined Loading and Corrosive Environment. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 557-564. https://doi.org/10.4995/ASCCS2018.2018.6974OCS55756

Hexaaqua­cobalt(II) bis­(5-acetyl-2-hy­droxy­benzoate) dihydrate

In the title compound, [Co(H2O)6](C9H7O4)2·2H2O, the Co2+ cation lies on a twofold rotation axis and is coordinated by six water mol­ecules in a distorted octa­hedral geometry. In the 5-acetyl-2-hy­droxy­benzoate anion, the hy­droxy group links with the carboxyl­ate group via an intra­molecular O—H⋯O hydrogen bond and the acetyl group is twisted to the benzene ring at a dihedral angle of 16.99 (12)°. In the crystal structure, the cations, anions and water mol­ecules are linked by extensive O—H⋯O hydrogen bonding

Analytical behaviour of concrete-encased CFST box stub columns under axial compression

[EN] Concrete-encased CFST (concrete-filled steel tube) members have been widely used in high-rise buildings and bridge structures. In this paper, the axial performance of a typical concrete-encased CFST box member with inner CFST and outer reinforced concrete (RC) is investigated. A finite element analysis (FEA) model is established to analyze the compressive behavior of the composite member. The material nonlinearity and the interaction between concrete and steel tube are considered. A good agreement is achieved between the measured and predicted results in terms of the failure mode and the load-deformation relation. The verified FEA model is then used to conduct the full range analysis on the load versus deformation relations. The loading distributions of different components inclouding concrete, steel tube and longitudinal bar during four stages are discussed. Typical failure modes, internal force distribution, stress development and the contact stress between concrete and steel tube are also presented. The parametric study on the compressive behavior is conducted to investigate the effects of various parameters, e.g. the strength of concrete and steel, longitudinal bar ratio and stirrup space on the sectional capacity and the ductility of the concrete-encased CSFT box member.Chen, J.; Han, L.; Wang, F.; Mu, T. (2018). Analytical behaviour of concrete-encased CFST box stub columns under axial compression. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 401-408. https://doi.org/10.4995/ASCCS2018.2018.6966OCS40140