Abstract
The measurement of acceleration plays an essential role in evaluating the state of mechanical equipment. The acceleration transducers are the most widely used devices for measuring ...vibration, motion, and shock. This paper proposes a novel method of acceleration measurement based on auxetic honeycomb structure. By using this method, the change in the auxetic honeycomb structure’s transmittance caused by elastic deformation under acceleration can be converted into a change in solar cell’s output. Geometric analysis and experiments are performed to investigate the effectiveness of the proposed method. The results provide a new structural insight for acceleration sensors. In order to assess the efficacy of the proposed approach, geometric analysis and experiments are conducted. The resonance frequency of an acceleration measurement device using an auxetic structure is approximately 100Hz, while for a device using a non-auxetic structure, it is about 40Hz, both reaching the maximum wavelength variation. The results give potential paths for future study as well as new structural insights for acceleration sensors.
A dual implementation of the Kalman filter is proposed for estimating the unknown input and states of a linear state-space model by using sparse noisy acceleration measurements. The successive ...structure of the suggested filter prevents numerical issues attributed to un-observability and rank deficiency of the augmented formulation of the problem. Furthermore, it is shown that the proposed methodology furnishes a tool to avoid the so-called drift in the estimated input and displacements commonly encountered by existing joint input and state estimation filters. It is shown that, by fine-tuning the regulatory parameters of the proposed technique, reasonable estimates of displacements and velocities of structures can be accomplished.
•A novel dual Kalman filter is proposed for output-only state and input estimation.•Sparse pure acceleration measurements and a model of the structure are used.•The unobservability issues attributed to augmented Kalman filter are resolved.•The low frequency drift is properly tackled in an online and autonomous fashion.•The efficiency of the proposed method is verified by numerical simulations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Many engineering applications require the knowledge of input forces to mechanical systems. However, in practice, it is quite difficult to measure these forces directly. In order to obtain an estimate ...of the input forces to structural systems, Kalman filtering based techniques have recently been introduced. These state-estimation techniques allow estimating the forces concurrent with the states of a system, based on a limited number of measurements. In practice, acceleration measurements are most convenient to use in structural dynamics applications. This paper proposes an analytical analysis of the stability of the Kalman based force estimation techniques and shows that only using acceleration measurements inherently leads to unreliable results. In order to circumvent this issue, the addition of dummy-measurements on a position level is proposed. These fictitious measurements dictate the estimator to return to an undeformed state and lead to a stable estimation approach. The proposed method is validated through both a numerical and a practical experiment. Both experiments show the inadequacy of the augmented Kalman filter based on only acceleration measurements to provide stable results. The estimator with dummy measurements on the other hand provides good results in the case of an unbiased external load.
•An online time-domain method for input force estimation is developed.•A structural dynamics model is coupled with accelerometers through a Kalman filter.•Using on only acceleration measurements is not sufficient for stable estimates.•A dummy-measurement approach on a position level is proposed for stabilization.•The proposed methods are validated numerically and experimentally.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Monitoring and analysing the integrity of structures and machinery is important for economic, operational, and mission critical reasons. In recent years, there has been growing interest in performing ...structural health monitoring (SHM) by monitoring structural dynamic response via micro electro-mechanical system accelerometers. In addition, the possibility of embedding these devices within a wireless sensor network and allowing measured data to be wirelessly transmitted has contributed to the development of many new applications not possible just a few years ago. These sensors, for use in SHM applications, need to detect low-amplitude and low frequency vibrations, operations which are not always feasible with the conventional low-cost sensor boards. Since the late 1990s, several accelerometer board prototypes have been proposed for achieving accurate vibration monitoring. This paper presents a summary review of the systems developed in the ten years following 2006 with particular emphasis on the sensing characteristics, performances, and applications of the designed sensor boards for microvibration detection and analysis.
The temporal stability of millisecond pulsars is remarkable, rivaling even some terrestrial atomic clocks at long timescales. Using this property, we show that millisecond pulsars distributed in the ...galactic neighborhood form an ensemble of accelerometers from which we can directly extract the local galactic acceleration. From pulsar spin period measurements, we demonstrate acceleration sensitivity with about 1σ precision using 117 pulsars. We also present a complementary analysis using orbital periods of 13 binary pulsar systems that eliminates the systematics associated with pulsar braking and results in a local acceleration of (1.7±0.5)×10^{-10} m/s^{2} in good agreement with expectations. This work is a first step toward dynamically measuring acceleration gradients that will eventually inform us about the dark matter density distribution in the Milky Way galaxy.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
A quick and very accessible method for the measurement of acceleration due to gravity is presented. The experimental set-up employs a smartphone ambient light sensor as the motion timer for measuring ...the period of a simple pendulum. This allowed us to obtain an experimental value, 9.72 + 0.05 m s−2, for the gravitational acceleration which is in good agreement with the local theoretical value of 9.78 m s−2.
Abstract
Focused ion beam (FIB) machining has been demonstrated to be capable of fabricating nano- and micro-scale structures. In this paper we demonstrate techniques to design and fabricate 45° ...micro-mirrors into the end of multi-core fibres using FIB processing. The mirrors are fabricated by a two-step process: a scanning process which is used to make a rough cut followed by a polishing process to create an optical surface finish mirror. The machined 45° mirrors can be accurately aligned with optical fibre cores, which avoids issues associated with the alignment of external turning mirror components. Proof-of-concept demonstration shows that the fabricated structure is capable of measuring two-axis acceleration interferometrically with a linear response from 0.2 to 4 g and an rms. error of 0.03 g. Acceleration measurements of frequency response up to 700 Hz and cross-sensitivity of ∼4.3% are demonstrated.
Abstract
Gl 758 B is a late-T dwarf orbiting a metal-rich Sun-like star at a projected separation of
ρ
≈ 1.″6 (25 au). We present four epochs of astrometry of this system with NIRC2 at Keck ...Observatory spanning 2010 to 2017 together with 630 radial velocities (RVs) of the host star acquired over the past two decades from McDonald Observatory, Keck Observatory, and the Automated Planet Finder at Lick Observatory. The RVs reveal that Gl 758 is accelerating with an evolving rate that varies between 2 and 5 m s
−1
yr
−1
, consistent with the expected influence of the imaged companion Gl 758 B. A joint fit of the RVs and astrometry yields a dynamical mass of
M
Jup
for the companion with a robust lower limit of 30.5
M
Jup
at the 4-
σ
level. Gl 758 B is on an eccentric orbit (
e
= 0.26–0.67 at 95% confidence) with a semimajor axis of
a
=
au and an orbital period of
P
=
yr, which takes it within ≈9 au from its host star at periastron passage. Substellar evolutionary models generally underpredict the mass of Gl 758 B for nominal ages of 1–6 Gyr that have previously been adopted for the host star. This discrepancy can be reconciled if the system is older—which is consistent with activity indicators and recent isochrone fitting of the host star—or alternatively if the models are systematically overluminous by ≈0.1–0.2 dex. Gl 758 B is currently the lowest-mass directly imaged companion inducing a measured acceleration on its host star. In the future, bridging RVs and high-contrast imaging with the next generation of extremely large telescopes and space-based facilities will open the door to the first dynamical mass measurements of imaged exoplanets.
This study aims to deal with the velocity and displacement estimation problem in civil structures through acceleration measurements. Nowadays, different schemes have been proposed to solve this ...problem, however, most proposed observer schemes generally require the Luenberger structure and sometimes any base transformation. In contrast, this paper provides a novel algebraic Proportional Integral (PI) observer based on the Algebraic Observability Condition (AOC), which allows the representation of the velocity and displacement terms as a function of the acceleration measurements, does not need a coordinate transformation, and uses proportional and integral correction of the estimation error. Moreover, a simple criterion for the observer gains selection is provided in order to ensure asymptotic convergence which leads to the fact that the gains can be assigned without using any numerical method to calculate them. An advantage of this observer is that it can be easily implemented for practical purposes. Finally, the effectiveness and accuracy of this estimation method are demonstrated experimentally via a reduced-scale five-story building prototype.
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•The observer relies on acceleration for estimation of displacement and velocity.•The proposed methodology does not require a Luenberger structure.•The algebraic observer is designed only with proportional integral error correction.•A simple criterion for observer gains selection is provided.•The observer’s performance is experimentally verified on a building prototype.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Mixed mechanical-metrological approach for fracture deformation characterisation based on system dynamics is provided•Correlation between degree of fatigue damage and surface morphology is studied ...via surface texture parameters•A comparative study of fracture deformation behaviour for both sides of the broken specimens is carried out•Analysis of total areas and individual zones shows strong links between fracture surface parameters and fatigue damage•Monotonic breaking stresses are directly related to the fracture surface parameters evaluated on the rupture zone
Non-destructive methods are powerful tools in modern industry to assess the structural integrity of engineering critical parts subjected to fatigue loading. This paper proposes a mixed mechanical-metrological approach able to account for the three-dimensional fractographic damage in samples subjected to fatigue bending loading histories based on the system dynamics. The system records the changes in the dynamic response, using uniaxial acceleration sensors, enabling the correlation of the stiffness variations with the crack length and the residual loading capacity. Fracture topologies are analysed via standard surface texture parameters, namely height, material volume and void volume parameters, for different degrees of fatigue damage. The results show a clear relationship between the changes in the recorded accelerations, which are associated with the degree of fatigue damage, and the values of the above-mentioned surface texture parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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