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Self-centering bracing systems, by which residual deformations of structures after earthquakes can be minimized, are considered effective solutions to achieve seismic resilience. In this paper, a parametric study on the seismic response of intermediate and high-rise steel-framed buildings with novel self-centering tension-only braces (SC-TOBs) is numerically conducted. Three key parameters, the stiffness degradation factor, the activation strain, and the initial axial stiffness of the SC-TOBs, are investigated to explore the design space for the SC-TOB frames (SC-TOBFs) because of their unique tunability compared with traditional bracing systems. Identical steel frames equipped with buckling restrained braces (BRBs) are also designed and examined for comparison purposes. The results indicate that increasing the stiffness degradation factor can improve the second stiffness of SC-TOBFs and successfully make the distribution of interstory drifts more uniform; an increase in the activation strain leads to a larger activation deformation of SC-TOBFs, but it has a very limited effect on the interstory drifts; increasing the initial axial stiffness appropriately is beneficial to reduce the interstory drifts of the low stories. The lateral behavior of SC-TOBFs is comparable to that of BRB frames when a lower activation strain and a higher initial axial stiffness are selected. Furthermore, when a higher stiffness degradation factor and a lower initial axial stiffness are selected simultaneously, the seismic action on SC-TOBFs can be effectively reduced, and a relatively uniform distribution over the building height can be obtained. The SC-TOBFs are considered to be a type of performance-tunable structure, and tuning can be achieved by varying a frame’s adjustable parameters.

The self-centering tension-only brace (SC-TOB) is a new and innovative bracing system that provides both a flag-shaped recentering hysteresis and load mitigation to structures. This paper presents an extensive investigation of the nonlinear seismic response of multistory steel frames built with SC-TOBs to internal force, drift, and energy dissipation. Pushover analysis subjected to two lateral load distributions and nonlinear dynamic analysis under ground motion ensembles corresponding to four hazard levels were conducted. The SC-TOBs can be designed to serve as conventional tension-only braces (TOBs) only providing lateral stiffness during minor earthquakes, to function with energy dissipation as intensity increases, and to fully recenter a structure even after severe earthquakes. The findings show that with an increase in the earthquake intensity, both the force response and drift response of the SC-TOB frames (SC-TOBFs) increased, however, the force distribution and drift distribution shapes of the SC-TOBFs remained almost constant. The SC-TOBFs generally experienced more energy dissipation in the lower parts of the building, while the upper stories dissipated almost no energy under certain load conditions, suggesting that the bracings on those stories could be replaced by conventional TOBs for economy. It is demonstrated that the SC-TOBs have immense potential to effectively improve seismic resilience to structures such that rehabilitation costs and operational disruptions after earthquakes are minimized.

Permanent magnet couplings (PMCs) are widely used in underwater propulsion because it can solve the deep-sea sealing problem effectively. In this paper, a new type of conical permanent magnet coupling (CPMC) is proposed, which is able to match the tail shape of the underwater vehicle and make full use of the tail space to increase pull-out torque capability. Based on the three-dimensional finite element method (3D-FEM), the electromagnetic characteristics of an initial model for CPMC are analyzed. In order to facilitate the design and optimization of CPMC, an equivalent three-dimensional (3D) analytical method for the pull-out torque calculation is presented, and its accuracy is verified by comparison with the 3D finite element results. Finally, the influence of design parameters such as half-cone angle, pole pair, pole arc coefficient and permanent magnet thickness on maximum pull-out torque and torque density of CPMC is analyzed, and a preliminary optimization model is obtained.

Banki wind turbine is a kind of vertical axis wind turbine (VAWT) with high solidity, and has been proved to have a relatively high starting torque and maximum power coefficient under low wind conditions. This study introduces an arc-shaped windshield to further improve the performance of Banki wind turbines. The windshield is placed in front of the turbine to deflect wind and reduce the negative torque on the blades in the upwind direction. Computational investigations are carried out to study the influence of the angle of the arc-shaped windshield on the performance of the turbine using the commercial computational fluid dynamics (CFD) code Fluent 13.0. The results demonstrated that the maximum power coefficient of the Banki wind turbine was increased by 66.9% with the optimal windshield angle of 60°. The maximum power coefficient was found to be 0.2784 at a tip speed ratio of 0.5 in the presence of the windshield.

A drag-type vertical axis water turbine, like Savonius, experiences negative torque in the returning half cycle, which limits the power efficiency. A new drag-type turbine, which consists of several retractable blades that are mounted on a drum, is designed and analyzed in this paper. The open angle of each blade is controlled to achieve a high output performance. Kinematics analysis demonstrated that the returning blades can fit to the drum and negative torques can then be considerably deduced. Two-dimensional computational fluid dynamics simulations were performed to give detailed information about the output of the turbine. The simulation results show that the maximum averaged power coefficient is 0.2595, obtained at a flow coefficient of 0.4.

We demonstrate a widely tunable near-infrared source from 767 nm to 874 nm generated by the intracavity second harmonic generation (SHG) in an optical parametric oscillator pumped by a Yb:LYSO solid-state laser. The home-made Yb:LYSO oscillator centered at 1035 nm delivers an average power of 2 W and a pulse duration as short as 351 fs. Two MgO doped periodically poled lithium niobates (MgO:PPLN) with grating periods of 28.5–31.5 μm in steps of 0.5 μm and 19.5–21.3 μm in steps of 0.2 μm are used for the OPO and intracavity SHG, respectively. The maximum average output power of 180 mW at 798 nm was obtained and the output pulses have pulse duration of 313 fs at 792 nm if a sech2-pulse shape was assumed. In addition, tunable signal femtosecond pulses from 1428 nm to 1763 nm are also realized with the maximum average power of 355 mW at 1628 nm.

It is a pivotal step in the measurement of carrier-envelope phase offset frequency in optical femtosecond frequency combs that a stable octave-spanning super-continuum spectrum is generated. In this paper, a home-made Yb:YCOB femtosecond laser pulse is led into a tapered fiber in which some nonlinear effects like self pulse modulation are generated and the four-wave mixing is made to broaden a spectrum to more than one octave-spanning. A Yb:YCOB oscillator emits 130 fs, 620 mW and 76.8 MHz laser pulses, the center wavelength at 1052 nm. Such pulses are focused into a tapered single-mode fiber, and then more than one octave-spanning supercontinuum from 550 nm to 1350 nm has been produced. The coupling efficiency can reach 52% when 323 mW SC laser pulses are detected. Based on the experimental result, a new optical comb will be built with the Yb:YCOB solid state laser as the light source.

A self-starting mode-locked femtosecond laser is accomplished with an oxoborate self-frequency doubling crystal Yb:YCa4O(BO3)3 (Yb:YCOB) as the gain medium and a semiconductor mirror as the saturable absorber. Pumped by a 976-nm fiber-coupled diode laser with 50-μm core diameter, stable mode-locked laser pulses up to 430 mW were obtained at a repetition rate of 83.61 MHz under 5-W pump power. The autocorrelation measurement shows that the pulse duration is as short as 150 fs by assuming the sech2 pulse shape at a central wavelength of 1048 nm. This work has demonstrated a compact and reliable femtosecond laser source for prospective low-cost applications.