Swing Modes Research Articles

Compact Micro-Coriolis Mass-Flow Meter with Optical Readout.

This paper presents the first nickel-plated micro-Coriolis mass-flow sensor with integrated optical readout. The sensor consists of a freely suspended tube made of electroplated nickel with a total length of 60 mm, an inner diameter of 580 µm, and a wall thickness of approximately 8 µm. The U-shaped tube is actuated by Lorentz forces. An optical readout consisting of two LEDs and two phototransistors is used to detect the tube motion. Mass-flow measurements were performed at room temperature with water and isopropyl alcohol for flows up to 200 g/h and 100 g/h, respectively. The measured resonance frequencies were 1.67 kHz and 738 Hz for water and 1.70 kHz and 752 Hz for isopropyl alcohol for the twist and swing modes, respectively. The measured phase shift between the two readout signals shows a linear response to mass flow with very similar sensitivities for water and isopropyl alcohol of 0.41mdegg/h and 0.43 mdegg/h, respectively.

Double-Modal Locomotion of a Hydrogel Ultra-Soft Magnetic Miniature Robot with Switchable Forms.

Flexible miniature robots are expected to enter difficult-to-reach areas invivo to carry out targeted operations, attracting widespread attention. However, it is challenging for the existing soft miniature robots to substantially alter their stable shape once the structure is designed. This limitation leads to a fixed motion mode, which subsequently restricts their operating environment. In this study, we designed a biocompatible flexible miniature robot with a variable stable form that is capable of adapting to complex terrain environments through multiple movement modes. Inspired by the reversible stretching reaction of alginate saline gel stimulated by changes in environmental ion concentration, we manufactured a morphologically changeable super-soft hydrogel miniature robot body. According to the stretch and contraction shapes of the flexible hydrogel miniature robot, we designed magnetic fields for swing and rolling motion modes to realize multi-shape movement. The experimental results demonstrate that the deflection angle of the designed flexible miniature robot is reversible and can reach a maximum of 180°. The flexible miniature robot can complete forward swinging in the bar stretch state and tumbling motion in the spherical state. We anticipate that flexible hydrogel miniature robots with multiple morphologies and multimodal motion have great potential for biomedical applications in complex, unstructured, and enclosed living environments.

Design and simplified stability analysis of wide-area damping control with variable feedback delay

Poorly damped low-frequency inter-area oscillations are a major concern in large power systems. Wide-area damping controllers which modulate power flow using power electronic systems like HVDC links and FACTS can be used to improve the damping of the critical modes in a targeted manner. These controllers use wide-area measurements, which are communicated from several remote locations. The communication time delay is generally variable in nature, and the data from different locations arrive at the controller with different delays. The overall delay in synthesizing the controller input signal affects the closed-loop damping performance. This paper proposes a delay-handling strategy and derives a discrete-time model which is used to characterize its performance. The relative insensitivity of the mode shape of swing modes to the damping controller is used to facilitate a simplified analysis. A strategy for the adaptation of controller gain when the delays are excessive and persistent is also presented. A case study is presented to illustrate the delay-handling and gain adaptation strategies.

Multidirectional Dynamic Response and Swing Shedding of Grapes: An Experimental and Simulation Investigation under Vibration Excitation

During mechanized table grape harvesting, berries are subjected to vibration and collision, which can cause shedding and damage to the fruit. Research on table grape berry shedding has primarily focused on macroscopic swing modes, which are reflected in the integrated grape cluster structure and idealized particle interactions, as well as static response treatments. However, these approaches are unable to accurately explain the characteristics of berry wobbling during picking, predict shedding-prone areas, or identify factors affecting shedding. In this paper, we study the dynamic response characteristics of grape berries in the X, Y, and Z directions by establishing a dynamic model and combining harmonic response and random vibration characteristics with finite element analysis. Our studies revealed that grape berries exhibit various forms (swinging and rebounding) under the same stimulus during harvesting. The grape berry amplitude in the X, Y, and Z directions were 14.71, 12.46, and 27.10 mm, respectively, with the most obvious response being in the Z direction and the flattest response in the Y direction. Berries in the lower cob system part were relatively stable, while those in the upper right side were more prone to swinging and falling, with areas most likely to fall off concentrated in the upper right side. This system accurately predicted the dynamic response characteristics of fruit during vibration harvesting and provided an ideal basis for mechanized grape harvesting. Optimization and research on fruit collection equipment may benefit from this theoretical basis.

Design and Analysis of an Active Swing Decoupling Compliant Mechanism With Multiple Co-Directional Input Branches

AbstractIn this work, we propose a novel bio-inspired swing decoupling mechanism supporting high precision motion systems, which is composed of multiple co-directional input branches with a rigid swing unit and an anti-rotational guiding unit. By actively adjusting the input displacements, the decoupling mechanism can switch between the swing and translational modes, where the parasitic rotations can be significantly suppressed by the anti-rotational guiding unit. With this, fully decoupled X and Y linear motions are obtained in the presence of co-directional input branches. A theoretical model of the decoupling mechanism is also established to accurately describe the decoupling behavior, which is verified by finite element simulations. A prototype of the proposed swing decoupling mechanism is fabricated and instrumented with comprehensive experimental apparatus, where the experimental results effectively validate the excellent decoupling performance and demonstrate good potentials to precision engineering applications.

A Vision Aided Initial Alignment Method of Strapdown Inertial Navigation Systems in Polar Regions.

The failure of the traditional initial alignment algorithm for the strapdown inertial navigation system (SINS) in high latitude is a significant challenge due to the rapid convergence of polar longitude. This paper presents a novel vision aided initial alignment method for the SINS of autonomous underwater vehicles (AUV) in polar regions. In this paper, we redesign the initial alignment model by combining inertial navigation mechanization equations in a transverse coordinate system (TCS) and visual measurement information obtained from a camera fixed on the vehicle. The observability of the proposed method is analyzed under different swing models, while the extended Kalman filter is chosen as an information fusion algorithm. Simulation results show that: the proposed method can improve the accuracy of the initial alignment for SINS in polar regions, and the deviation angle has a similar estimation accuracy in the case of uniaxial, biaxial, and triaxial swing modes, which is consistent with the results of the observable analysis.

Computation of the controllable swing mode spectrum of FACTS and HVDC in large power systems

This paper presents computation of swing modes of a large power system that could be significantly affected by power swing damping controllers in FACTS or HVDC devices at a given location. Modal controllability is a suitable measure to isolate these modes for analysis. Computation of the controllable swing mode spectrum is useful, especially in situations where the controller structure and feedback signals are not frozen (e.g., at the planning stage). This paper proposes two important steps that allow us to map the problem of finding highly controllable swing modes to the problem of finding the swing modes that have high transfer function residues (for which efficient algorithms are available). The steps are: (a) normalization of the eigenvectors corresponding to different modes and (b) identification of specific feedback signals for each type of FACTS/HVDC device such that the modal observability and modal controllability are tightly coupled. Once the mapping is done, a computationally efficient method like the Subspace Accelerated Dominant Pole Algorithm [16] (SADPA) can be adapted to find the highly controllable swing modes. The effectiveness of this approach is demonstrated by case studies of FACTS and HVDC devices in a 16-machine system and the Indian power grid.

A Model-Free Approach for Emergency Damping Control Using Wide Area Measurements

Rescheduling methods for mitigation of poorly damped power swings depend on a model-based evaluation of eigenvalue sensitivities and are slow to implement. This paper proposes an approach for an online model-free implementation of modulation-type control using Wide Area Measurement System (WAMS). Such a control measure can act as a primary line of defense before the slower rescheduling-type measures are taken. The proposed control measure utilizes special properties of swing modes derived analytically from a simplified system model to 1) synthesize a modal feedback signal as the input to the controller and 2) tune the controller parameters for adequate damping improvement, in a model-independent manner for certain FACTS devices and HVDC links. For a power system stabilizer (damping controller in a synchronous machine excitation system), the extent of model information required is limited to that of the well-known GEP $(s)$ transfer function and inertia constant of the concerned synchronous machine. Case studies with detailed system models provide the necessary proof-of-concept.

A Robust Wide-Area Measurement-Based Damping Controller for Networks With Embedded Multiterminal and Multiinfeed HVDC Links

Control strategies for power swing damping which use wide-area feedback signals need to be robust to partial/complete loss of communication and changes in operating points and topology. In addition, they should have a positive effect on all controllable swing modes and ensure adequate stability margins to avoid destabilization of untargeted modes. This paper proposes a control strategy for multiple embedded dc links (multiterminal or multiinfeed), which has all these attributes and is inherently able to provide wideband damping. The strategy uses only a limited set of nonlocal signals. These signals may be directly communicated to the dc links without having to be centrally collated with other system-wide measurements, thereby reducing communication delays. The strategy can easily be adapted during power system operation to achieve targeted damping of the critical swing modes.

Particle-Based Modeling of Asymmetric Flexible Fibers in Viscous Flows

AbstractThe present paper follows our previous work [Yang et al., Phys. Rev. E, 90 (2014), 063011] in which the bending modes of a symmetric flexible fiber in viscous flows were studied by using a coupling approach of smoothed particle hydrodynamics (SPH) and element bending group (EBG). It was shown that a symmetric flexible fiber can undergo four different bending modes including stable U-shape, slight swing, violent flapping and stable closure modes. For an asymmetric flexible fiber, the bending modes can be different. This paper numerically studies the fiber shape, flow field and fluid drag of an asymmetric flexible fiber immersed in a viscous fluid flow by using the SPH-EBG coupling method. An asymmetric number is defined to describe the asymmetry of a flexible fiber. The effects of the asymmetric number on the fiber shape, flow field and fluid drag are investigated.

A Novel Method to Directly Analyze Dissolved Acetic Acid in Transformer Oil without Extraction Using Raman Spectroscopy

Analyzing the concentration of low molecular acids dissolved in oil is vital in the oil-paper insulation aging diagnostic procedure of power transformers. The existing methods cannot distinguish between different acid types and their strengths. In this study, an improved solution Raman detection platform is fabricated. The direct measurement of dissolved acetic acid, a kind of low molecular acids, is observed in transformer oil without extraction. The Raman shift line of oil-dissolved acetic acid at 891 cm−1 corresponding to H–C–H symmetrical swing and O–H swing modes is taken as its characteristic value. Taking Raman shift line of pure oil at 932 cm−1 as an internal standard, a linear regression curve for quantitative analysis is obtained with a slope of 0.19. The best platform parameter of accumulation number is 300, which is determined by Allan deviation analysis. The current concentration detection limit and accuracy for oil-dissolved acetic acid are obtained at about 0.68 mg/mL and 91.66%, separately. The results show that Raman spectroscopy could be a useful alternative method for evaluation insulation aging state of an operating power transformer in the future.

Bending modes and transition criteria for a flexible fiber in viscous flows

The present paper follows our previous work in which a coupling approach of smoothed particle hydrodynamics (SPH) and element bending group (EBG) was developed for modeling the interaction of viscous incompressible flows with flexible fibers. It was also shown that a flexible object may experience drag reduction because of its reconfiguration due to fluid force on it. However, the reconfiguration of deformable bodies does not always result in drag reduction as different deformation patterns can result in different drag scales. In the present work, we studied the bending modes of a flexible fiber in viscous flows using the presented SPH and EBG coupling approach. The flexible fiber is immersed in a fluid and is tethered at its center point, while the two ends of the fiber are free to move. We showed that the fiber undergoes four different bending modes: stable U-shape, slight swing, violent flapping, and stable closure modes. We found there is a transition criterion for the flexible fiber from slight swing, suddenly to violent flapping. We defined a bending number to characterize the bending dynamics of the interaction of flexible fiber with viscous fluid and revealed that this bending number is relevant to the non-dimensional fiber length. We also identified the critical bending number from slight swing mode to violent flapping mode.

Sliding Mode Robust Control Based Active-Power Modulation of Multi-Terminal HVDC Transmissions

This paper presents a sliding mode robust control based active-power modulation (SMAPM) for voltage source converter based multi-terminal HVDC (VSC-MTDC) systems, which could enhance the stability of the onshore power system subjected to disturbances by fast changing transmitted power of onshore VSCs. The development of the SMAPM includes three steps. First, the onshore disturbed ac system could be divided into two areas with generators sharing different swing modes. The center of the inertia (COI) reference frame is utilized to be the representative of the area's behavior. Secondly, an index called sensitive index is proposed to quantify the sensitivity of generator angular speed to the active-power change of an onshore VSC. A strategy is developed to determine the modulation direction and intensity of each onshore converter. Thirdly, the final control law is derived based on sliding mode variable structure control method. Simulation verifications are run in a four-machine ac system and a modified New England 39-bus system.

Robust Global Control Strategies for Improvement of Angular Stability using FACTS and HVDC Devices

Abstract System-wide feedback signals made available by Wide-Area Measurement Systems technology can be used in FACTS/HVDC based controllers for the improvement of angular stability. These global signals can facilitate the efficient use of controller effort to stabilize critical swing modes. This paper introduces a restricted global strategy which involves the use of specific global feedback signals which are available at the HVDC/FACTS locations. The strategy is expected to be robust to changes in the power grid as well as communication uncertainties. This paper presents a heuristic introduction to this strategy using a circuit analogy of a simplified model of a power system. Preliminary results on a small system are also presented.

소화근처 헵탄 풀화재의 화염불안정성

액체연료를 사용하는 풀화재에서 화염불안정성에 대하여 산화제 유속변화와 농도변화의 효과를 알아보기 위해 컵버너 실험을 수행하였다. 연료는 헵탄을 사용하였고, 산화제는 공기에 질소와 이산화탄소를 희석하였다. 소화근처에서 축방향 및 화염 밑면에서 두 가지 형태의 대표적인 불안정성이 관찰되었다. 화염 밑면에서 발생되는 불안정성은 셀, 스윙, 회전 모드로 특성화 할 수 있고, 산화제의 유속이 증가할수록 모든 불활성기체에서 셀, 스윙 모드에서 회전모드로 천이하였다. 이러한 화염밑면 불안정성에 영향을 미치는 변수들을 파악하기 위하여 초기혼합률, Le 수, 단열화염온도에 대해서도 함께 조사되었다. 이 중 Le 수가 불안정성 모드와 가장 큰 상관관계를 보이고 있지만 보다 정확한 관계를 규명하기 위해서는 더 많은 실험조건에서의 결과가 요구된다. 또한, 소화농도근처의 화염에서는 유속이 작거나 큰 경우에는 축방향 주기적인 진동불안정성이 나타나지 않고, 적절한 산화제 속도 영역에서만 관찰된다. 이는 작은 유속에서는 증발하는 연료속도가 임계유속이하이며, 큰 유속에서는 반응중인 연료유속과 산화제 유속이 유사하기 때문으로 판단된다.

Numerical investigation on the dynamic characteristics of an automotive A/C hose

The objective of this study is to investigate the dynamic deformation characteristics of an automotive A/C hose assembly using the finite element method and experimentation. The finite element analysis consisted of two analyses, specifically, a modal and a transient analysis. The dynamic modal analysis was conducted to assess the dynamic characteristics of the A/C hose structure, and the dynamic transient analysis was performed to investigate the dynamic stresses of an automotive A/C hose by dynamic loading with particular emphasis on the reinforced braid. Furthermore, the analyses results are expected to provide useful reference data in the design optimization of the hose layout related to the constrained design space. Modal testing was undertaken to verify the FE model. The FE result was in good agreement with the experimental results. The modal analysis result showed that the bending and swing modes of the hose occurred in the first six natural frequencies. The dynamic transient result showed that the maximum stress in the hose components occurred in the reinforced braid layers, which are particularly damage-prone.

Rao-Blackwellized Unscented Particle Filter for a Handheld Unexploded Ordnance Geolocation System using IMU/GPS

The existence of Unexploded Ordnance (UXO) is a serious environmental hazard, especially in areas being converted from military to civilian use. The detection and discrimination performance of UXO detectors depends on the sensor technology as well as on the processing methodology that inverts the data to infer UXO. The detection systems, typically electro-magnetic induction (EMI) devices, require very accurate positioning (or geolocation) in order to discriminate candidate UXO from non-hazardous items. For this paper, a hand-held geolocation system based on a tactical-grade IMU, such as the HG1900, was tested in the laboratory over a small, metre-square area in sweep and swing modes. A camera position system was used to emulate GPS or alternative ground-based external ranging systems that control positioning errors. The proposed integration algorithm is a combination of linear filtering (Extended Kalman Filter) and nonlinear, also non-Gaussian filtering (Unscented Particle Filter) in the form of the Rao-Blackwellized Particle Filter (RBPF). The test results show that the position accuracy was improved by applying nonlinear filter-based smoothing techniques in both the straight and curved sections of the sweep and swing trajectories.

Robust low-order controller design for multi-modal power oscillation damping using flexible AC transmission systems devices

Damping of multi-modal oscillation through supplementary control of a single flexible AC transmission system (FACTS) device is illustrated here. This often requires multiple feedback signals in a centralised multi-input single-output framework for which extension of the classical control design approaches is not straight forward. Past contributions have either focused on decentralised design of low-order PSS in an SISO or MIMO framework; or alternatively, on robust control design techniques which of course, result in higher order controllers. An attempt to design a fixed (low)-order controller, which is robust and is able to damp multiple swing modes with a single FACTS device is presented. The control design problem is formulated as a multi-objective parameter optimisation and solved using a standard evolutionary optimisation technique. Possible post-contingency operating conditions are considered explicitly during the design phase itself to reduce the conservativeness. The present exercise is a step forward towards use of wide area measurement systems for closed-loop supplementary control (around the primary voltage and/or power flow control loop) of the FACTS devices to improve the transfer capacity of the existing corridors.

Electronic Structures and Vibrational Properties of a Carbon Nanotube with Adsorption of Small Hydrocarbon Radicals

We employ density functional theory to investigate electronic structures and vibrational properties of a (7,0) carbon nanotube with adsorption of CH, CH2, or CH3 on the outer wall. We find that the edge states or gap states are induced in the band structure by the adsorption of CH, CH2, or CH3. This predicts that a carbon nanotube can be functionalized by the adsorbed radicals. Furthermore, the calculated vibrational density of states shows that, apart from the common C−H stretching and bending modes, each adsorbed radical introduces new vibrational modes, such as the swing modes, in the low frequency region below 500 cm−1. In addition, different numbers and different frequencies of the stretching modes for the radicals can be used to identify the adsorbed radicals each other.

Status of the experiments on measurement of the Newtonian gravitational constant

Due to the weakness of gravity, the accuracy of the Newtonian gravitational constant G is essentially below the accuracy of other fundamental constants. The current value of G, recommended by CODATA in 2006, based on all results available at the end of 2006, is G = (6.67428 ± 0.00067) × 10−11 m3 kg−1 s−2 with a relative error of 100 ppm. The accuracy of the best experimental results is 15–40 ppm, although the scatter of the results is large enough. Therefore new experiments at a level of accuracy of 10–30 ppm are rather topical. One of the problems of improving accuracy of G is a precision measurement of the period of eigen oscillations of a torsion balance. The nonlinear behavior of the torsion balance with five degrees of freedom has been studied. It was shown that swing modes are excited by the acting environmental noise. A coupling of the swing modes to the torsional mode has been revealed. Methods of suppressing the effect of mode couplings have been considered.