Transdisciplinary approaches to urban computing

The research field of urban computing – defined as “the integration of computing, sensing, and actuation technologies into everyday urban settings and lifestyles” – considers the design and use of ubiquitous computing technology in public and shared urban environments. Its impact on cities, buildings, and spaces evokes innumerable kinds of change. Embedded into our everyday lived environments, urban computing technologies have the potential to alter the meaning of physical space, and affect the activities performed in those spaces. This paper starts a multi-themed discussion of various aspects that make up the, at times, messy and certainly transdisciplinary field of urban computing and urban informatics.

Boarding Control System - for Improved Accessibility to Offshore Wind Turbines

This paper considers the dynamic modelling and motion control of a Surface Effect Ship (SES) for safer transfer of personnel and equipment from vessel to-and-from an offshore wind-turbine. Such a vessel is a key enabling factor for operation and maintenance (O&M) of offshore wind-energy infrastructure. The control system designed is referred to as Boarding Control System (BCS). We investigate the performance of this system for a specific wind-farm service vessel–The Wave Craft. A two-modality vessel model is presented to account for the vessel free motion and motion whilst in contact with a wind-turbine. On a SES, the pressurized air cushion carries the majority of the vessel mass. The control problem considered relates to the actuation of the pressure such that wave-induced vessel motions are minimized. This leads to a safer personnel transfer in developed sea-states than what is possible today. Results for the BCS is presented through simulation and model-scale craft testing.

Design and characterization of in-plane MEMS yaw rate sensor

In this paper, we present the design and characterization of a vibratory yaw rate MEMS sensor that uses in-plane motion for both actuation and sensing. The design criterion for the rate sensor is based on a high sensitivity and low bandwidth. The required sensitivity of the yawrate sensor is attained by using the inplane motion in which the dominant damping mechanism is the fluid loss due to slide film damping i.e. two-three orders of magnitude less than the squeeze-film damping in other rate sensors with out-of-plane motion. The low bandwidth is achieved by matching the drive and the sense mode frequencies. Based on these factors, the yaw rate sensor is designed and finally realized using surface micromachining. The inplane motion of the sensor is experimentally characterized to determine the sense and the drive mode frequencies, and corresponding damping ratios. It is found that the experimental results match well with the numerical and the analytical models with less than 5% error in frequencies measurements. The measured quality factor of the sensor is approximately 467, which is two orders of magnitude higher than that for a similar rate sensor with out-of-plane sense direction.

Modeling of magnetostrictive materials and structures

The constitutive model for a magnetostrictive material and its effect on the structural response is presented in this article. The example of magnetostrictive material considered is the TERFENOL-D. As like the piezoelectric material, this material has two constitutive laws, one of which is the sensing law and the other is the actuation law, both of which are highly coupled and non-linear. For the purpose of analysis, the constitutive laws can be characterized as coupled or uncoupled and linear or non linear. Coupled model is studied without assuming any explicit direct relationship with magnetic field. In the linear coupled model, which is assumed to preserve the magnetic flux line continuity, the elastic modulus, the permeability and magneto-elastic constant are assumed as constant. In the nonlinear-coupled model, the nonlinearity is decoupled and solved separately for the magnetic domain and the mechanical domain using two nonlinear curves, namely the stress vs. strain curve and the magnetic flux density vs. magnetic field curve. This is performed by two different methods. In the first, the magnetic flux density is computed iteratively, while in the second, the artificial neural network is used, where in the trained network will give the necessary strain and magnetic flux density for a given magnetic field and stress level. The effect of nonlinearity is demonstrated on a simple magnetostrictive rod.

Reliability Analysis of Torsional MEMS Varactor

This paper discusses reliability issues in torsional MEMS varactor. Self-actuation due to high ac signals is analyzed, and solutions are proposed. The mode of failure at high actuation voltages is analyzed and established through experiments. Issues like stiction due to high voltages and effect of high residual stress are studied experimentally.

Optimal configurations of active fiber composites based on asymptotic torsional analysis - art. no. 641413

Active Fiber Composites (AFC) possess desirable characteristics over a wide range of smart structure applications, such as vibration, shape and flow control as well as structural health monitoring. This type of material, capable of collocated actuation and sensing, call be used in smart structures with self-sensing circuits. This paper proposes four novel applications of AFC structures undergoing torsion: sensors and actuators shaped as strips and tubes; and concludes with a preliminary failure analysis. To enable this, a powerful mathematical technique, the Variational Asymptotic Method (VAM) was used to perform cross-sectional analyses of thin generally anisotropic AFC beams. The resulting closed form expressions have been utilized in the applications presented herein.

Reliability analysis of torsional varactor

A torsional MEMS varactor with wide dynamic range, lower actuation voltage and isolation between actuation voltage and signal voltage has been proposed in C. Venkatesh et al. (2005). In this paper we address the effects of pull-in, residual stress and continuous cycling on the performance of torsional MEMS varactor.

Boarding control system for improved accessibility to offshore wind turbines: Full-scale testing

This paper considers the dynamic modelling and motion control of a Surface Effect Ship (SES) for safer transfer of personnel and equipment from vessel to-and-from an offshore wind-turbine. The control system designed is referred to as Boarding Control System (BCS). The performance of this system is investigated for a specific wind-farm service vessel—The Wave Craft. On a SES, the pressurized air cushion supports the majority of the weight of the vessel. The control problem considered relates to the actuation of the pressure such that wave-induced vessel motions are minimized. Results are given through simulation, model- and full-scale experimental testing.

Transient Momentum and Enthalpy Transfer in Packed Beds at High Reynolds Numbers

An experimental study for transient temperature response and pressure drop in a randomly packed bed at high Reynolds numbers is presented.The packed bed is used as a compact heat exchanger along with a solid-propellant gas generator, to generate room-temperature gases for use in control actuation, air bottle pressurization, etc. Packed beds of lengths 200 and 300 mm were characterized for packing-sphere-based Reynolds numbers ranging from 0.8 x 10(4) to 8.5 x 10(4).The solid packing used in the bed consisted of phi 9.5 mm steel spheres. The bed-to-particle diameter ratio was with the average packed-bed porosity around 0.43. The inlet flow temperature was unsteady and a mesh of spheres was used at either end to eliminate flow entrance and exit effects. Gas temperature and pressure were measured at the entry, exit,and at three axial locations along centerline in the packed beds. The solid packing temperature was measured at three axial locations in the packed bed. A correlation based on the ratio of pressure drop and inlet-flow momentum (Euler number) exhibited an asymptotically decreasing trend with increasing Reynolds number. Axial conduction across the packed bed was found to he negligible in the investigated Reynolds number range. The enthalpy absorption rate to solid packing from hot gases is plotted as a function of a nondimensional time constant for different Reynolds numbers. A longer packed bed had high enthalpy absorption rate at Reynolds number similar to 10(4), which decreased at Reynolds number similar to 10(5). The enthalpy absorption plots can be used for estimating enthalpy drop across packed bed with different material, but for a geometrically similar packing.

A dragonfly inspired flapping wing actuated by electro active polymers

An energy-based variational approach is used for structural dynamic modeling of the IPMC (Ionic Polymer Metal Composites) flapping wing. Dynamic characteristics of the wing are analyzed using numerical simulations. Starting with the initial design, critical parameters which have influence on the performance of the wing are identified through parametric studies. An optimization study is performed to obtain improved flapping actuation of the IPMC wing. It is shown that the optimization algorithm leads to a flapping wing with dimensions similar to the dragonfly Aeshna Multicolor wing. An unsteady aerodynamic model based on modified strip theory is used to obtain the aerodynamic forces. It is found that the IPMC wing generates sufficient lift to support its own weight and carry a small payload. It is therefore a potential candidate for flapping wing of micro air vehicles.

Elasto-Electrostatic Analysis of Circular Microplates Used in Capacitive Micromachined Ultrasonic Transducers

The active structural component of a capacitive micromachined ultrasonic transducer (CMUT) is the top plate which vibrates under the influence of a time-varying electrostatic force thereby producing ultrasound waves of the desired frequency in the surrounding medium. Analysis of MEMS devices which rely on electrostatic actuation is complicated due to the fact that the structural deformations alter the electrostatic forces, which redistribute and modify the applied loads. Hence, it becomes imperative to consider the electrostatics-structure coupling aspect in the design of these devices. This paper presents an approximate analytical solution for the static deflection of a thin, clamped circular plate caused by electrostatic forces which are inherently nonlinear. Traditionally, finite element simulations using some commercial software such as ANSYS are employed to determine the structural deflections caused by electrostatic forces. Since the structural deformation alters the electrostatic field, a coupled-field simulation is required wherein the electrostatic mesh is continuously updated to coincide with the deflection of the structure. Such simulations are extremely time consuming, in addition to being nontransparent and somewhat hard to implement. We employ the classical thin-plate theory which is adequate when the ratio of the diameter to thickness of the plate is very large, a situation commonly prevalent in many MEMS devices, especially the CMUTs. We solve the thin-plate electrostatic-elastic equation using the Galerkin-weighted residual technique, under the assumption that the deflections are small in comparison to the thickness of the plate. The evaluation of the electrostatic force between the two plates is simplified due to the fact that the electrostatic gap is much smaller than the lateral dimensions of the device. The results obtained are compared to those found from ANSYS simulations and an excellent agreement is observed between the two. The pull-in voltage predicted by our model is close to the value predicted by ANSYS simulations.

Magnetically actuated propulsion at low Reynolds numbers: towards nanoscale control

Significant progress has been made in the fabrication of micron and sub-micron structures whose motion can be controlled in liquids under ambient conditions. The aim of many of these engineering endeavors is to be able to build and propel an artificial micro-structure that rivals the versatility of biological swimmers of similar size, e. g. motile bacterial cells. Applications for such artificial ``micro-bots'' are envisioned to range from microrheology to targeted drug delivery and microsurgery, and require full motion-control under ambient conditions. In this Mini-Review we discuss the construction, actuation, and operation of several devices that have recently been reported, especially systems that can be controlled by and propelled with homogenous magnetic fields. We describe the fabrication and associated experimental challenges and discuss potential applications.

Electro-magnetically Actuated Minute Polymer Pump Fabricated using Packaging Technology

Design, fabrication and preliminary testing of a flat pump with millimetre thickness are described in this paper. The pump is entirely made of polymer materials barring the magnet and copper coils used for electromagnetic actuation. The fabrication is carried out using widely available microelectronic packaging machinery and techniques. Therefore, the fabrication of the pump is straightforward and inexpensive. Two types of prototypes are designed and built. One consists of copper coils that are etched on an epoxy plate and the other has wound insulated wire of 90 mu m diameter to serve as a coil. The overall size of the first pump is 25 mm x 25 mm x 3.6 mm including the 3.1 mm-thick NdFeB magnet of diameter 12 mm. It consists of a pump chamber of 20 mm x 20 mm x 0.8 mm with copper coils etched from a copper-clad epoxy plate using dry-film lithography and milled using a CNC milling machine, two passive valves and the pump-diaphragm made of Kapton film of 0.089 mm thickness. The second pump has an overall size of 35 mm x 35 mm x 4.4 mm including the magnet and the windings. A breadboard circuit and DC power supply are used to test the pump by applying an alternating square-wave voltage pulse. A water slug in a tube attached to the inlet is used to observe and measure the air-flow induced by the pump against atmospheric pressure. The maximum flow rate was found to be 15 ml/min for a voltage of 2.5 V and a current of 19 mA at 68 Hz.

Structural vibration control using resistively shunted piezoceramics

Application of piezoceramic materials in actuation and sensing of vibration is of current interest. Potential and more popular applications of piezoceramics are probably in the field of active vibration control. However, the objective of this work is to investigate the effect of shunted piezoceramics as passive vibration control devices when bonded to a host structure. Resistive shunting of a piezoceramic bonded to a cantilevered duralumin beam has been investigated. The piezoceramic is connected in parallel to an electrical network comprising of resistors and inductors. The piezoceramic is a capacitor that stores and discharges electrical energy that is transformed from the mechanical motion of the structure to which it is bonded. A resistor across the piezoceramic would be termed as a resistively shunted piezoceramic. Similarly, an inductor across the piezoceramic is termed as a resonantly shunted piezoceramic. In this study, the effect of resistive shunting on the nature of damping enhancement to the host structure has been investigated. Analytical studies are presented along with experimental results.

An Improved Compact Compliant Mechanism for an External Pipe-Crawler

An external pipe-crawling device presented in this paper aids the inspection of pipes in hazardous environments and areas inaccessible to humans. The principal component of our design, which uses inchworm type motion, is a compliant ring mechanism actuated using shape memory alloy (SMA) wire. It was fabricated and tested and was reported in our earlier work. But this device had a drawback of low crawling speed (about 1 mm/min) owing to the delay in heating and cooling of the SMA strips in the linear actuation. Additionally, that design also had the difficulties of mounting on pipes with closed ends, large radial span, and the need for housing for electrical insulation and guiding of the SMA wire. In this paper we present a compact design that overcomes the difficulties of the earlier design. In particular, we present a compact compliant mechanism with two halves so as to enable mounting and un-mounting on any closed or open pipe. Another feature is the presence of insulation and guiding of the SMA wire without housing. This design results in a reduction of the radial span of the ring from 22 mm to 12 mm, and the stiffness of the mechanism and the SMA wire are matched. An SMA helical spring is to used in the place of an SMA strip to increase the crawling speed of the device. A microcontroller-based circuitry is also fitted to cyclically.activate the SMA wires and springs.