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African elephants (Loxodonta africana) use many sensory modes to gather information about their environment, including the detection of seismic, or ground-based, vibrations. Seismic information is known to include elephant-generated signals, but also potentially encompasses biotic cues that are commonly referred to as 'noise'. To investigate seismic information transfer in elephants beyond communication, here we tested the hypothesis that wild elephants detect and discriminate between seismic vibrations that differ in their noise types, whether elephant- or human-generated. We played three types of seismic vibrations to elephants: seismic recordings of elephants (elephant-generated), white noise (human-generated) and a combined track (elephant- and human-generated). We found evidence of both detection of seismic noise and discrimination between the two treatments containing human-generated noise. In particular, we found evidence of retreat behaviour, where seismic tracks with human-generated noise caused elephants to move further away from the trial location. We conclude that seismic noise are cues that contain biologically relevant information for elephants that they can associate with risk. This expands our understanding of how elephants use seismic information, with implications for elephant sensory ecology and conservation management. [ABSTRACT FROM AUTHOR]

To this day, the petroleum industry is still searching for alternative ways to improve the recovery of hydrocarbon from the reservoir. The residual oil blotches may consist of about 30%–40% or more of a volume fraction. Seismic stimulation has great potential for IOR (improved oil recovery), because of its advantages on low cost, high effectivity, and environment-friendly as they introduce no formation damage, etc. The investigation and application of seismic stimulation have been launched for over 70 years. In this study, a literature review on the mechanism for IOR, including laboratory and theoretical modeling work, and oilfield application, is present here. Firstly, four different manners of vibration are introduced, and the seismic vibration with 1 Hz–100 Hz (frequency) and 1 μm–100 μm (amplitude) is the commonly used; Secondly, the mechanisms of IOR by seismic stimulation are summarized as: effect on capillary pressure, pore deformation, relative permeability, thermal and degassing effects, however, further tests and understanding of the mechanisms are necessary. Thirdly, the reviews of experimental research and mathematical modeling based on the published literature are made. Especially, the mathematical modeling of seismic vibration for the real reservoir development (such as non-Darcy flow, low permeability reservoirs, the coupling of non-Newtonian fluid, etc.) is still insufficient. Finally, some successful oilfield applications (in Russia, North America, and China) and prospects are proposed in this work. It will be more efficient to stimulate the reservoirs if the seismic wave is at the formation's resonant frequency. In our work, we don't expect to provide an exhaustive review of the work presented. On the contrary, we hope that our work can provide an introduction for other researchers to get a brief understanding of the seismic stimulation technology and possible results under which conditions the seismic stimulation works well. • Mechanisms of seismic stimulation based on the published literature are introduced. • Reviews of experiments and mathematical modeling on seismic stimulation are made. • Mathematical modeling of seismic vibration for real reservoir is insufficient. • Seismic wave at the formation's resonant frequency can efficient stimulate reservoir. • Seismic stimulation can work together with some chemical-based EOR methods. [ABSTRACT FROM AUTHOR]

In this paper, a new adaptive viscous damper (AVD) is proposed and required equations are developed to describe its mechanical behavior. As opposed to conventional adaptive devices, the proposed damper is capable of adapting its own mechanical properties without any need for other devices such as sensors, processing unit, actuators, energy supplies, and wired or wireless connections. Eliminating such equipment not only reduces costs, but also removes related time lag and improves the efficiency of the control system. The proposed AVD includes a cylinder filled with viscous fluid and a piston with a nozzle at its head. The passing area of the nozzle is variable and as a result, the device can cover a range of damping coefficients. For non-extreme excitations, the damping coefficient is relatively small and consequently the damping force is reduced. Conversely, when extreme movements occur, the nozzle contracts a bit and generates relatively large control forces in order to protect the main structure efficiently. The mechanical model of the AVD is created in OpenSees and the damper is implemented in a two-story building example subjected to different earthquake records. The results show that compared to a typical viscous device, the proposed AVD can reduce the mean values of displacement, acceleration, and base shear by up to 52.5, 62.9, and 44.4% and increase the energy dissipation by up to 94.3% for extreme cases. Moreover, for non-extreme cases, the AVD shows a more flexible behavior and reduces the unfavorable damping forces. [ABSTRACT FROM AUTHOR]

This paper considers the problem of designing a state-feedback controller with both passive base isolation (PBI) and active structural control (ASC). In order to improve control performance, state-feedback gains are designed based on the linear quadratic regulator (LQR) method that optimizes a new performance index containing absolute acceleration, and inter-story drifts and velocity. Simulations on a model of an eleven degree-of-freedom shear building for four earthquake accelerograms are used to verify this method. Comparison studies show that, compared with PBI, the combination of PBI and ASC improves control performance; and this method yields better control results than the conventional ASC, which considers relative displacement and relative velocity of each story. The results are also discussed from the viewpoint of control system structure regarding the location of system zeros. In addition, the effect of weights in the LQR on control performance is discussed. A method for selecting the weights is presented by using the infinity norm of a system as a criterion to visualize their effect. [ABSTRACT FROM AUTHOR]

Lasers having sub-Hz linewidth and long-term stability better than a few parts in 1 0 16 is an unavoidable requisite to achieve unprecedented accuracy in the optical atomic clocks, intercomparing distributed atomic clocks and their networking, establishing coherent optical fibres, precision time & frequency transfer, production of optical qubits, and many more. For these wide ranges of applications, ultrastable Fabry–Pérot (FP) cavities, which act as the reference optical resonator, have got lots of attention. Designing such a FP cavity is a challenge due to the requirements of suppressing instabilities from all the thermo-mechanical noise sources at the highest degree. In this article, we report a comprehensive study to elucidate detailed design steps and associated numerical analysis procedures to build such a FP cavity. For this, we considered all sources of noises arising from: improper optical and opto-mechanical settings, ground vibrations transmitted to the cavity, deformations due to self-weight as it worsens the stability due to acoustic noise coupled to it, and temperature fluctuation. We present quantitative assessments of the instabilities for different shapes, geometries, and constituent materials of the cavities. In order to model the vibration-induced instability, we developed a novel forced-vibration based technique for accurate estimation of the instabilities, that reciprocates the experimental results reported in the literature, and the method is found to be superior compared to the other approaches, therefore estimating the overall cavity stability more accurately. We found in short term (¡ 10 s), the instability of the cavity is limited by temperature fluctuation, and in the long term (¿ 10 s), Brownian noise dominates the instability, therefore demands adequate precautions to reach the desired level of stability. Through systematic simulations, we have identified the best criteria for minimization of all these noises and obtain stabilities of 8. 5 × 1 0 − 17 and 5. 1 × 1 0 − 17 using dielectric and crystalline mirror coatings, respectively, which are similar to the best-reported results among its homologue cavities. [Display omitted] • Stabilities of 8. 5 × 1 0 − 17 and 5. 1 × 1 0 − 17 using the dielectric and crystalline mirrors are useful for cutting edge research & technologies. • A comprehensive and systematic presentation for designing a room-temperature ultrastable Fabry–Perot cavity. • Guidance for selecting the constituent materials, shapes, geometries, and mounting structure to cover different applications of such cavity. • Instability estimation for thermo-mechanical and instrumentation noises together with their methodologies are described. • A novel approach for accurate calculation of the vibration-induced instability is presented. [ABSTRACT FROM AUTHOR]

A new method of active structural control, which suppresses vibrations in civil structures due to seismic shocks, has been developed. It is based on the equivalent-input-disturbance (EID) approach, which estimates the effect of a seismic shock and produces an equivalent control signal on the control input channel to compensate for it. A system designed by this method can be viewed as a conventional state-feedback control system with an EID estimator plugged in. Unlike conventional control systems, this one has two degrees of freedom, which yields better control performance. Simulations on a model of a ten-degree-of-freedom building demonstrated the validity of the method. In addition, the effect of the parameters of the low-pass filter in the EID estimator on the vibration suppression performance was examined. A comparison revealed that this method is superior to a linear-quadratic regulator and sliding-mode control. [ABSTRACT FROM AUTHOR]

The optimum design of base isolation system to control seismic vibration considering uncertain system parameters are usually performed by minimizing the unconditional expected value of mean square response of a structure without any consideration to the variance of such responses due to system parameter uncertainty. However, the unconditional mean square response based designed may have larger variance of responses due to uncertainty in system parameters and the overall system performance may be sensitive. But, it is desirable that the optimum design should reduce both the mean and variance of dynamic performance measure under system parameter uncertainty. The present study deals with robust design optimization (RDO) of base isolation system considering random system parameters characterizing the structure, isolator and ground motion model. The RDO is performed by minimizing the weighted sum of the expected value of the maximum root mean square acceleration of the structure as well its standard deviation. A numerical study elucidates the importance of the RDO procedure for design of base isolation system by comparing the proposed RDO results with the results obtained by the conventional stochastic structural optimization procedure and the unconditional response based optimization. [ABSTRACT FROM AUTHOR]

The optimum design of a base isolation (BI) system in the framework of total probability theory cannot be applied in many real situations when the required detailed information about the uncertain parameters are limited and the maximum possible ranges of variations are only known and can be modeled as an uncertain but bounded type. The interval analysis based bounded design optimization usually applied in such cases are the worst case measures and unsuitable for practical design. Moreover, such a design method does not consider the variation of the performance of an isolated system due to uncertainty and may not correspond to an optimum design yielding maximum performance with its minimum dispersion. The robust optimization requiring only the bounds on the magnitude of the uncertain parameters will be a viable alternative in such situations. The present study deals with the robust optimization of BI system for seismic vibration mitigation of structures characterized by bounded uncertain parameters. The robust optimization is performed by using a two-criteria equivalent optimization problem, where the weighted sum of the nominal value of the maximum root mean square acceleration of the superstructure and its dispersion is optimized. The bounded design optimization is also performed to demonstrate the effectiveness of the proposed robust optimization approach. A five-storied building frame with attached isolator elucidates the effectiveness and importance of the proposed design approach by comparing the present robust optimization results with the results obtained by the bounded design optimization procedure. [ABSTRACT FROM PUBLISHER]

The possibility of controlling two modes of structural vibration due to earthquake excitation by considering the sloshing action in the vertical limbs of the liquid column vibration absorber (LCVA) has been explored in this paper. The structure has been modeled as a linear, viscously damped multi-degree-of-freedom (m.d.f.) system. The governing differential equations of motion for the damper liquid and for the coupled structure-LCVA system have been derived from dynamic equilibrium. The nonlinear orifice damping in the LCVA has been linearized by a stochastic equivalent linearization technique. A displacement transfer function formulation for the structure-LCVA system has been presented. The study has been carried out on a 2-d.f. example structure for which both the modes have significant contribution to the total response. The performance of the LCVA has been evaluated in the frequency domain with the base input characterized by a white noise power spectral density function and through a simulation study by subjecting the example structure-LCVA system to a recorded accelerogram. The results are compared with that of the liquid column damper and indicate superior performance of the LCVA. Furthermore, an LCVA has been designed for the example structure. [ABSTRACT FROM PUBLISHER]

• The interfacial parameters in boiling flow were measured by four-sensor conductivity probe under static and vibration conditions. • The time-averaged local parameters under vibration conditions were analyzed. • The instaneous change of local void fraction was analyzed by adopting the phase partitioning method. • The additional forces induced by mechanical vibration were calculated and compared with each other. • The effect of vibration frequency on local void fraction was studied. In this paper, the subcooled boiling flow experiments in a vertical annulus were conducted to study the effect of vibration on local interfacial characteristics. The local interfacial parameters including void fraction, bubble velocity, interfacial area concentration and Sauter mean diameter were measured by four-sensor conductivity probe. The time-averaged local parameters under vibration conditions were firstly measured and analyzed. It is found that the effects of vibration on time-averaged void fraction and interfacial area concentration are very limited. Therefore, we have developed the phase partitioning method to obtain the instantaneous variation of void fraction for further investigation. The instantaneous void fraction along the radial direction varies periodically with the vibration phase. The additional forces induced by vibration are analyzed and compared with each other. Among them, the tangential force is the dominant, which can account for the change tendency of void fraction under vibration. Besides, the variations of void fraction depend on different working conditions. The change tendencies of void fraction near the inner wall and outer wall are opposite in relatively low averaged void fraction regime while those in relatively high averaged void fraction regime are consistent. [ABSTRACT FROM AUTHOR]