bluuebunny/crossref_metadata_2025 huggingface dataset:
PVCO Pipeline Performance Under Large Ground Deformation
Authors: Wham Brad P. , Argyrou Christina , O’Rourke Thomas D. , Stewart Harry E. , Bond Timothy K.
Published: January 2016

Technological advances have improved pipeline capacity to accommodate large ground deformation associated with earthquakes, floods, landslides, tunneling, deep excavations, mining, and subsidence. The fabrication of polyvinyl chloride (PVC) piping, for example, can be modified by expanding PVC pipe stock to approximately twice its original diameter, thus causing PVC molecular chains to realign in the circumferential direction. This process yields biaxially oriented polyvinyl chloride (PVCO) pipe with increased circumferential strength, reduced pipe wall thickness, and enhanced cross-sectional flexibility.

This paper reports on experiments performed at the Cornell University Large-Scale Lifelines Testing Facility characterizing PVCO pipeline performance in response to large ground deformation. The evaluation was performed on 150-mm (6-in.)-diameter PVCO pipelines with bell-and-spigot joints. The testing procedure included determination of fundamental PVCO material properties, axial joint tension and compression tests, four-point bending tests, and a full-scale fault rupture simulation. The test results show the performance of segmental PVCO pipelines under large ground deformation is strongly influenced by the axial pullout and compressive load capacity of the joints, as well as their ability to accommodate deflection and joint rotation. The PVCO pipeline performance is quantified in terms of its capacity to accommodate horizontal ground strain, and compared with a statistical characterization of lateral ground strains caused by soil liquefaction during the Canterbury earthquake sequence in New Zealand.
Using Tension Measurement Methods for Backfill Procedures in the Evaluation of Pipelines
Authors: Silva Sérgio P. P. , Seixas Renato , Pacheco Anderson , Amaral Claudio
Published: January 2016

The OPASC and the OSPAR are 10″ and 30″ pipelines, respectively, which interconnect the State of Santa Catarina and Paraná, crossing the Serra do Mar, in southern Brazil. In 2003, after conducting slope stabilization works on a point of geotechnical activity, vibrating string gauges were installed to monitor the stress in these pipelines, in addition to geotechnical instruments installed to monitor the slope. These gauges were installed in seven sections, with 3 instruments per section, along a span of 180 meters.

Although the geotechnical instrumentation has shown no evidence of movement in the slope, the gauges recorded an increase in stress values in some of the sections within three months from the time of installation, however, they remained stable in their values for the next ten years. In 2013, blind hole tests were performed to determine the stresses in these sections and to verify the proper function of the gauges. The combination of these two measurement techniques, vibrating string gauges and blind hole tests, allowed for the determination of the stress state in sections, over time. From there, equivalent stress could be determined and compared with allowable stresses defined in standards.

After the completion of the blind hole test and subsequent backfill, stress rose again at the same rate, returning to the level reached after the initial installation of the strain gauges. To reduce the stress level additional excavations have been made to relieve the stress on the pipeline, followed by backfilling performed in a controlled manner in order for the soil to properly compact, which reduced the stress value over the pipes. The graphs depicting variation over time of stress showed a significant reduction in the level of stress after the backfill.

The main conclusions are listed as follows: a) the evolution of stress observed by the extensometers was primarily caused by pipeline settling; b) the vibrating string gauges are functioning properly and provide reliable readings even after ten years of service; c) the blind hole testing performed in conjunction with monitoring by vibrating string gauges can provide approximate values of the full stress state; d) after stress relief, backfilling of the trench must be carried out by compacting the soil beneath the pipe in order to reduce bending stresses due to the weight of the soil; e) backfilling of the trench, when not properly performed, can cause compressive stress in bending, reaching 390 mPa over the next few months.
The Challenge of Geohazards in the Replacement of Hydrocarbon Pipelines
Authors: Zapata Posada Dario , Aristizabal Ceballos Jaime Hernan
Published: January 2016

The effects of changes in land use and the effects of climate change have led to an increase in the morphodynamic processes that affect rights-of-way in Colombia. However, in view of the fact that these rights-of-way are considered to be the best possible routes in some areas in which the geological and geotechnical components are fairly complex, specialists are facing the challenge of establishing different perspectives for coexisting with the geohazards in these areas. This paper describes the analytical methodology implemented within Ecopetrol’s Office of the Vice President for Transportation and Logistics (VIT-Ecopetrol), in order to take this reality into account within the framework of proper asset management.
Management System for the Control of Geotechnical Risk in the Camisea Pipeline Transport System
Authors: Velásquez M. Fernando Adolfo
Published: January 2016

The Camisea Pipeline Transport System [“Sistema de Transporte por Ductos”] consists of two parallel pipelines, one of which carries natural gas (NG) over a distance of 730 km, and the other which carries liquid natural gas (LNG) over a distance of 560 km, starting in the Amazon basin in Malvinas (Cusco). The LNG pipeline ends in Playa Lobería (ICA) and the NG pipeline ends at the City Gate located in Lurín (Lima).

In terms of complexity, the geographic, geological, and climate-related characteristics of the rain-forest, mountain, and coastal regions through which the pipeline passes set it apart from the rest of the world’s pipelines. The highest point in the area is 4,860 meters above mean sea level in its mountain portion in the Peruvian Andes.

The first 200 km, which pose the greatest operational challenges, are characterized by residual soils, slopes steeper than 45°, and rainfall of more than 6,000 mm per year — in addition to the logistical difficulties presented by the lack of vehicular access for the transport of personnel, materials, and equipment, such that maintenance work must be done by helicopter.

The purpose of this article is to illustrate the diversity of geotechnical scenarios in this geographical area, and to discuss the early identification of risks through the management and control cycle for geotechnical threats, which consists of the following stages:

• The Threat Identification System: This stage includes the continuous monitoring of the right-of-way in order to detect geotechnical problems, which are triggered primarily by rainfall.

• Risk assessment: This stage involves the use of a geotechnical risk matrix that was developed in accordance with the so-called “Safety Ratio” [“Relación de Seguridad”], which assimilates the parameters for the calculation of the Safety Factor used in slope stability analysis, thereby making it possible to establish the various risk levels.

• Structure design: Depending on the risk level, the corresponding engineering tasks are developed and prioritized in order to determine the designs, through the use of geotechnical engineering processes such as subsurface exploration, laboratory tests, mathematical modeling, and instrumentation.

• Implementation of the structures: The geotechnical stabilization structures are built during the dry season, i.e., from April to October of each year.

• Monitoring and surveillance: Once the stabilization structures have been built and the dry season has ended, continuous monitoring is performed during the rainy season (November to April), through ongoing inspections, topographic monitoring, and instrumentation at sensitive sites, using inclinometers, piezometers, and strain gauges.

Thanks to these working techniques and control measures, as implemented in an area with special topographic and climate-related characteristics, it has been possible to achieve a dramatic reduction in the geotechnical risks to which the Camisea transport system is exposed.
Monitoring Stress/Strain in Buried Pipelines Through the Use of Fiber Bragg Grating Sensors
Authors: Betancur Ríos Juan David , Eliécer Torres Camilo , Aristizabal Jaime Hernan , Galvis Adriana , Díaz Ronald Andrés , Trespalacios Diego , Cuevas Henry Osorio
Published: January 2016

ECOPETROL S.A. has been working since 2006 in Pipeline Integrity Management Process. In that process, the threat related to climate and external forces play an important role, because of the vulnerability of ECOPETROL pipelines to this threat, not only by the geomorphology of Colombia, but also because of the strong impact of climate phenomenon such as “La Niña”, that consists in an unusual quantity of rain precipitation, represented in the increasing of slopes instability that affects the rights of way. Due to these events and the evolution of optical strain sensors monitoring technology, ECOPETROL has introduced an instrumentation pipeline program for monitoring the strain and advanced in the understanding of the behavior of pipelines. This paper describes the technology selected, the criteria used to select the monitoring sites and the thresholds stress/strain. The results of monitoring are discussed for a particular case.
Management Plans Formulated Based on the Verification and Validation of Information Compiled in Right-of-Way Patrols
Authors: Aristizabal Ceballos Jaime Hernan , Rodríguez Jiménez Paula Andrea
Published: January 2016

In Ecopetrol’s Office of the Vice-president of Transportation and Logistics, one of the principal inputs for formulating plans for the management of sites with geotechnical findings is the verification and validation of the information compiled in right-of-way patrols, by a standardized database that contains the geotechnical findings according to a defined typology.

The purpose of doing this is to deal with, on a timely basis, geotechnically complex zones based on the identification and characterization of geotechnical findings (recurrence and activity, among others), and to provide feedback to the Geotechnical and Risk Zoning models, with a view toward their being much better adapted to reality and making it possible to identify the gaps that distract the analysis models from the actual condition of the asset. This document describes the experiences along this line that have been filed over the course of recent years and shows the relevance of each component to the objective of establishing management plans of a preventive nature.
Reconfiguring Smart Structures Using Approximate Heteroclinic Connections in a Spring-Mass Model
Authors: Zhang Jiaying , McInnes Colin R.
Published: January 2016

Several new methods are proposed to reconfigure smart structures with embedded computing, sensors and actuators. These methods are based on heteroclinic connections between equal-energy unstable equilibria in an idealised spring-mass smart structure model. Transitions between equal-energy unstable (but actively controlled) equilibria are considered since in an ideal model zero net energy input is required, compared to transitions between stable equilibria across a potential barrier. Dynamical system theory is used firstly to identify sets of equal-energy unstable configurations in the model, and then to connect them through heteroclinic connection in the phase space numerically. However, it is difficult to obtain such heteroclinic connections numerically in complex dynamical systems, so an optimal control method is investigated to seek transitions between unstable equilibria, which approximate the ideal heteroclinic connection. The optimal control method is verified to be effective through comparison with the results of the exact heteroclinic connection. In addition, we explore the use of polynomials of varying order to approximate the heteroclinic connection, and then develop an inverse method to control the dynamics of the system to track the polynomial reference trajectory. It is found that high order polynomials can provide a good approximation to true heteroclinic connections and provide an efficient means of generating such trajectories. The polynomial method is envisaged as being computationally efficient to form the basis for real-time reconfiguration of real, complex smart structures with embedded computing, sensors and actuators.
Aerodynamic Applications of SMA FRP Structures: An Active Airfoil, From Idea to Real Hardware
Authors: Hübler Moritz , Nissle Sebastian , Gurka Martin , Breuer Ulf Paul
Published: January 2016

This contribution focuses on the application potential of active fiber reinforced polymer (FRP) structures with integrated shape memory alloy (SMA) elements for new aerodynamic functions. The advantages of hybrid SMA FRP structures are highlighted and promising application concepts are discussed. Main focus is the development of an active aerodynamic airfoil. Beginning with the idea of an adaptive airfoil, able to bear an application relevant down force at a relatively high deflection, the design process starts with an evaluation of different airfoil actuation concepts. A SMA powered bending beam is a part of the airfoil itself. Applying the finite element method with a suitable model for the active hybrid material, an effective selection of material and design is possible. After manufacturing and assembling of the active hybrid airfoil a comparison of experimental results and simulation is the first proof of success. Finally, the installation of an integrated hardware setup with power source, control and the active airfoil, demonstrating actuation on demand, verifies the potential of the new approach.
Modeling of a Symmetric Five-Bar Displacement Amplification Compliant Mechanism Using Energy Methods
Authors: Elsisy Moataz M. , Anis Yasser , Arafa Mustafa , Saleh Chahinaz
Published: January 2016

We present a symmetric five-bar compliant mechanism for the displacement amplification of mechanical vibration. When the proposed mechanism is connected to an energy harvester, amplification of the input excitation vibration amplitude leads to an increase in the harvested power. Displacements in the compliant mechanism are caused by deflections in its flexure hinges. The flexure hinges we use are either of the right-circular, or the corner-filleted types. The mechanism is analyzed using energy methods. The displacement amplification was verified analytically and numerically using a finite element model. Through our model we present relations governing the displacement amplification in terms of the design parameters, such as the geometry of the mechanism, the flexure hinges dimensions, in addition to the load caused by the harvester. The effects of the flexure hinge dimensions on displacement amplification, are also presented.
Design and Experimental Validation of a Novel Magnetorheological Damper With Internal Pressure Control
Authors: Golinelli Nicola , Spaggiari Andrea
Published: January 2016

In the present paper we investigated the behaviour of magnetorheological fluids (MRFs) under a hydrostatic pressure up to 40 bar. We designed, manufactured and tested a magnetorheological damper (MRD) with a novel architecture which provides the control of the internal pressure. The pressure was regulated by means of an additional apparatus connected to the damper that acts on the fluid volume. The MRD was tested under sinusoidal inputs and with several values of magnetic field and internal pressure. The results show that the new architecture is able to work without a volume compensator and bear high pressures. On the one hand, the influence of hydrostatic pressure on the yield stress of MRFs is not strong probably because the ferromagnetic particles cannot arrange themselves into thicker columns. On the other hand, the benefits of the pressure on the behaviour of the MRD are useful in terms of preventing cavitation.
A New Electrical Circuit With Negative Capacitances to Enhance Resistive Shunt Damping
Authors: Berardengo Marta , Manzoni Stefano , Thomas Olivier , Giraud-Audine Christophe
Published: January 2016

This article proposes a new layout of electrical network based on two negative capacitance circuits, aimed at increasing the performances of a traditional resistive piezoelectric shunt for structural vibration reduction. It is equivalent to artificially increase the modal electromechanical coupling factor of the electromechanical structure by both decreasing the short-circuit natural frequencies and increasing the open-circuit ones. This leads to higher values of the modal electromechanical coupling factor with respect to simple negative capacitance configurations, when the same margin from stability is considered. This technique is shown to be powerful in enhancing the control performance when associated to a simple resistive shunt, usually avoided because of its poor performances.
A Dynamic Spar Numerical Model for Passive Shape Change
Authors: Calogero Joseph , Frecker Mary , Hasnain Zohaib , Hubbard James E.
Published: January 2016

A three-dimensional constraint-driven numerical dynamic model of a flapping wing structure called the Dynamic Spar Numerical Model (DSNM) is introduced and implemented. The model currently includes a leading edge spar and a diagonal spar, attached to a body by revolute and spherical joints, respectively. The spars consist of a user-specified number of rigid links connected by compliant joints (CJs): spherical joints with distributed masses and three axis nonlinear torsional spring-dampers. The goal of this model is to quickly simulate mechanisms in a test platform to see how their CJ design properties and spatial distribution affect passive shape change and physical performance metrics. The results of this model can be used as a starting point for further refinement in compliant joint design for passive shape change. Previous research leading to and assumptions made for modeling CJ are presented. The constraints are established, followed by the formulation of a state model used in conjunction with a forward time integrator, and finally several example runs. Modeling the CJs as linear springs produces a nearly symmetric rotation angles through the flapping cycle, while bi-linear springs show the wing is able to flex more during upstroke than downstroke. Increasing damping ratio reduces high frequency oscillations during the flapping cycle and the number of cycles required to reach steady state. Coupling the spring stiffnesses allows an angle about one axis to induce an angle about another axis, where the magnitude is proportional to the coupling term. Modeling both the leading edge and diagonal spars show that the diagonal spar changes the kinematics of the leading edge spar verses only considering the leading edge spar, causing much larger axial rotations in the leading edge spar. The kinematics are very sensitive to CJ location, where moving the CJ toward the wing root causes a stronger response, and adding multiple CJs on the leading edge spar with a CJ on the diagonal spar allow the wing to deform with larger magnitude in all directions. Future work includes implementing a performance metric, experimental verification, applying loads to represent ambient and flight conditions, and using the model as an optimization tool for parameter and spatial optimization.
Ionic Polymer-Metal Composites (IPMCs) as Impact Sensors
Authors: Seidi M. , Hajiaghamemar M. , Tabatabaie E. , Shahinpoor M.
Published: January 2016

The aim of the present study was to investigate the potential of using IPMC as a flexible impact sensor to be used in typical impact protective devices like a protective headgear to estimate the severity level of head impacts. To that end, IPMC strips were embedded into two layers of protective dilatant material and several impact testings were performed. Results of output IPMC voltage and impact acceleration were captured and analyzed. IPMCs appear to present a potential as impact sensors. In so doing, small strips of either Platinum or Gold chemically-plated IPMCs were used. Results of IPMC voltage output and impact accelerations were reported. The results indicate that IPMCs can be used as flexible impact sensors.
On the Stability of Decentralized AVC/ASAC for Large-Scale Structures
Authors: Algermissen Stephan , Monner Hans P.
Published: January 2016

Active Vibration Control (AVC) and Active Structural Acoustic Control (ASAC) gained much attention in all kind of industries in the past. Promising results have been achieved in controlling the vibration and the noise emission/transmission of single panel structures. Especially for aircraft applications, concepts for the reduction of the turbulent boundary layer, rotor or jet noise are presented in the literature. In most cases the contributed work is focused on a single panel or a section of the fuselage/lining. However, an AVC/ASAC system can only be effective for the passengers when it is expanded to the entire fuselage structure. This expansion inevitably leads to a large number of sensors and actuators and thus to a controlled plant of high dimensions. For model-based control approaches especially, the system identification and the proof of stability would be challenging and probably not realizable.

In this paper a strategy for such large-scale problems is investigated. A decentralized control approach with collocated actuator-sensor pairs is proposed. Since adjacent control loops are highly coupled by the underlying structure, special attention has to be given to the global stability of the entire control system. Instead of proving local stability and setting a global master gain, a method for the tuning of the single collocated control loops is developed that takes the cross-couplings into account. Based on data of DLR’s experimental aircraft Dornier 728, it can be shown that the new method increases the performance of the control system compared to the master-gain method.
Reliability-Based Design Optimization for Nonlinear Energy Harvesters
Authors: Seong Sumin , Mullen Christopher , Lee Soobum
Published: January 2016

This paper presents reliability-based design optimization (RBDO) and experimental validation of the purely mechanical nonlinear vibration energy harvester we recently proposed. A bi-stable characteristic was embodied with a pre-stressed curved cantilever substrate on which piezoelectric patches were laminated. The curved cantilever can be simply manufactured by clamping multiple beams with different lengths or by connecting two ends of the cantilever using a coil spring. When vibrating, the inertia of the tip mass activates the curved cantilever to cause snap-through buckling and makes the nature of vibration switch between two equilibrium positions. The reliability-based design optimization study for maximization of power density and broadband energy harvesting performance is performed. The benefit of the proposed design in terms of excellent reliability, design compactness, and ease of implementation is discussed. The prototype is fabricated based on the optimal design result and energy harvesting performance between the linear and nonlinear energy harvesters is compared. The excellent broadband characteristic of the purely mechanical harvester will be validated.
Non-Contact Tension Sensing Using Fe-Ga Alloy Strip
Authors: Yoo JinHyeong , Restorff James B. , Wun-Fogle Marilyn
Published: January 2016

This paper describes a proof-of-concept non-contact strain sensor, using a magnetostrictive Fe-Ga alloy (Galfenol). Magnetostrictive materials demonstrate dimensional changes in response to a magnetic field. In contrast with typical piezoceramic materials, Galfenol is the most ductile of the current transduction materials and appears to have an excellent ability to withstand mechanical shock and tension. Galfenol also exhibits the inverse (Villari) effect: both the magnetization and permeability change in response to an applied stress. Galfenol has low hysteresis loses, less than ∼10% of its transduction potential over a range of −20 to +80 °C. The magnetization’s response to stress depends strongly on both magnetic field bias and alloy composition. Galfenol’s Villari effect can be used in various sensor configurations together with either a giant magnetoresistance (GMR) sensor, Hall Effect sensor or pickup coil to sense the magnetization / permeability changes in Galfenol when stressed. The sensor described in this paper utilizes the permeability change, which is not time dependent and can measure static loads. The design reported here targets low force, low frequency applications, such as inclination measurements and stress monitoring. The sensor was able to measure both static and dynamic stress. The static sensitivity was +3.64 Oe/kN for the Hall sensor close to the bias magnet and −1.49 Oe/kN for the Hall sensor at the other end of the Galfenol strip. We conclude that a Galfenol strain sensor is a viable candidate for bolt stress monitoring in critical applications.
Uncertainty Analysis of Dielectric Elastomer Membranes Under Multi-Axial Loading
Authors: Miles Paul , Guettler Adriane , Hussaini Yousuff , Oates William S.
Published: January 2016

A variety of models have been developed to simulate the behavior of electroactive elastomers. As with all modeling applications, there are varying levels of uncertainty associated with measurement limitations and lack of knowledge of the constitutive behavior. Methods of quantifying this uncertainty have been explored previously using Bayesian statistics under uniaxial mechanical loading. The research presented here expands prior developments to quantify constitutive model uncertainty under multi-axial mechanical loading at different electrostatic fields. Specifically, we experimentally characterize and simulate transverse loading of a pre-stretched membrane under different electrostatic fields. We also quantify the dielectric response from electric displacement versus electric field loops. Bayesian statistical methods are employed to quantify modeling uncertainties in light of the data conducted on the 3M elastomer, VHB 4910.
Experimental Characterization and Modeling of Photon Upconversion in Azobenzene Photomechanical Polymers
Authors: Chowdhury Sadiyah Sabah , Kent Catherine , Hill Sean P. , Baduell Enric , Hanson Kenneth , Oates William S.
Published: January 2016

Azobenzene polymers show promising photostrictive behavior for a broad range of applications in flow control, robotics, and energy harvesting applications. The conversion of solar energy directly into mechanical work provides unique capabilities in adaptive structures; however, the energy conversion of visible light into mechanical work presents several material chemistry challenges. Azobenzene strongly absorbs ultraviolet (UV) light and blue/green light which limits the efficiency of the photomechanical response under solar irradiation. Photon upconversion — combining two or more low energy photons (longer wavelength) to generate a higher energy excited state (shorter wavelength), provides an intriguing strategy to drive these high energy photochemical reactions with low energy light. We present an experimental study showing the feasibility to drive azobenzene photoisomerization using visible light via select up-conversion molecules in the fluidic state. Multi-physics modeling is then used to predict advances in photomechanical energy conversion when up-conversion molecules are introduced within an azobenzene polymer.
Implementation of the Large Time Increment Method for the Simulation of Pseudoelastic Shape Memory Alloys
Authors: Gu Xiaojun , Zaki Wael , Moumni Ziad , Zhang Weihong
Published: January 2016

The paper presents a numerical implementation of the Large Time Increment (LaTIn) method for the integration of the ZM model [1] for SMAs in the pseudoelastic range. LaTIn was initially proposed as an alternative to the conventional incremental approach for the integration of nonlinear constitutive models [2]. It is adapted here for the simulation of pseudoelastic SMA behavior and is shown to be especially useful in situations where the phase transformation process presents little to no hardening. In these situations, a slight stress variation during a load increment can result in large variation of the volume fraction of martensite within a representative volume element of the SMA. This can lead to difficulty in numerical convergence if the incremental method is used. LaTIn involves two stages: in the first stage a solution satisfying the conditions of static equilibrium is obtained for each load increment without considering the consistency with the phase transformation conditions, then in the second stage consistent increments of the local state variables are determined for the entire loading path. The two stages take place sequentially, in contrast to the incremental method that requires satisfying the global equilibrium and local consistency conditions simultaneously at a given load increment before proceeding to the next. The numerical integration algorithm consists of the following steps: 1. Division of the loading path into a finite number of increments, 2. Solution for all the load increments of the static equilibrium problem in which the local consistency conditions are relaxed, 3. Update of the state variables in accordance with the consistency conditions for all the load increments. Steps 2 and 3 are repeated until a solution is reached that satisfies simultaneously the equilibrium and consistency requirements. An algorithm is presented for the implicit integration of the time-discrete equations. The algorithm is used for finite element simulations using Abaqus, in which the model is implemented by means of a user material subroutine. The simulation results are discussed in comparison with those obtained using conventional step-by-step incremental integration.
The Contribution of LARES to Global Climate Change Studies With Geodetic Satellites
Authors: Sindoni Giampiero , Paris Claudio , Vendittozzi Cristian , Pavlis Erricos C. , Ciufolini Ignazio , Paolozzi Antonio
Published: January 2016

Satellite Laser Ranging (SLR) makes an important contribution to Earth science providing the most accurate measurement of the long-wavelength components of Earth’s gravity field, including their temporal variations. Furthermore, SLR data along with those from the other three geometric space techniques, Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and DORIS, generate and maintain the International Terrestrial Reference Frame (ITRF) that is used as a reference by all Earth Observing systems and beyond. As a result we obtain accurate station positions and linear velocities, a manifestation of tectonic plate movements important in earthquake studies and in geophysics in general. The “geodetic” satellites used in SLR are passive spheres characterized by very high density, with little else than gravity perturbing their orbits. As a result they define a very stable reference frame, defining primarily and uniquely the origin of the ITRF, and in equal shares, its scale. The ITRF is indeed used as “the” standard to which we can compare regional, GNSS-derived and alternate frames. The melting of global icecaps, ocean and atmospheric circulation, sea-level change, hydrological and internal Earth-mass redistribution are nowadays monitored using satellites. The observations and products of these missions are geolocated and referenced using the ITRF. This allows scientists to splice together records from various missions sometimes several years apart, to generate useful records for monitoring geophysical processes over several decades. The exchange of angular momentum between the atmosphere and solid Earth for example is measured and can be exploited for monitoring global change. LARES, an Italian Space Agency (ASI) satellite, is the latest geodetic satellite placed in orbit. Its main contribution is in the area of geodesy and the definition of the ITRF in particular and this presentation will discuss the improvements it will make in the aforementioned areas.
Effect of Heat Treating on Precipitate Phases in NiTiHf
Authors: Carl Matthew , Garcia Victoria , Van Doren Brian , Schlegel Scott , Young Marcus
Published: January 2016

Recently, NiTiHf-based HTSMAs have been shown to exhibit unique precipitation and mechanical behavior. In this study, a rolled plate of NiTiHf HTSMA was homogenized and heat treated at various times and temperatures and characterized using a barrage of analytical techniques including high-energy synchrotron X-ray diffraction (SR-XRD). Neither homogenization nor any of heat treatments studied significantly affect the austenitic or martensitic transformation temperatures. H-phase was observed to precipitate at heat treating times below 30 minutes and then to subsequently dissolve away for times of 30 minutes and above. The presence of H-phase dramatically increases the material strength by almost a factor of 2, Lastly, an over-aging effect occurs with increasing time due to the disappearance of the H-phase.
Non-Linear Impedance-Based Structural Health Monitoring for Damage Detection and Identification
Authors: Albakri Mohammad I. , Malladi Sriram , Tarazaga Pablo A.
Published: January 2016

Impedance-based structural health monitoring (SHM) is a non-destructive, active technique for real-time structural damage assessment. Conventional impedance-based SHM practices apply a sinusoidal signal of fixed amplitude to excite the piezoceramic patch and obtain the impedance signature over a certain frequency range. Damage is then detected by comparing the measured impedance signature to a baseline measurement taken at the pristine state.

In this work, the amplitude of the driving signal, which is directly related to the magnitude of the excitation force acting on the structure, is introduced as an additional variable, and sweeps over both frequencies and amplitudes are performed. Several structural defects, such as cracks and loose joints, are nonlinear in nature. Therefore, changing the excitation force will allow the detection of such damage induced nonlinearities and track their evolution.

Numerical simulations are carried out to study the effects of nonlinearities on the impedance signature using a single mode model. Several types of structural nonlinearities, such as hardening, softening, and nonlinear damping are studied with the assumption that the piezoelectric actuator stays in its linear regime. Experiments are conducted on a single beam and a lap joint, and impedance signatures in the range of 12–15 KHz are measured at different levels of excitation. Nonlinear damping and softening behavior are detected experimentally by examining the measured impedance signatures. Numerical and experimental findings suggest the possibility of detecting and tracking structural nonlinearities using impedance measurements.
Mechanical Properties Adaptivity by the Design and Exploitation of Metastable States in a Modular Metastructure
Authors: Harne R. L. , Wu Z. , Wang K. W.
Published: January 2016

Recent studies on periodic metamaterial systems have shown that remarkable properties adaptivity and multifunctionality are often products of exploiting internal, coexisting metastable states. Yet to realize such attractive potential, effecting coexisting metastable states in material systems may require the determination of a periodic constituent which promotes a non-uniqueness when composed within the whole system, thus creating a need for costly, multiscale design. To surmount such concerns, this research first focuses on the development of adaptable, metastable modules: once assembled into modular metastructures, synergistic properties adaptation is found to be a natural byproduct of the strategic module design. Using this approach, it is seen that modularity facilitates a direct pathway to create and effectively exploit metastable states for massive, metastructure properties adaptivity, including a near-continuous variation of mechanical properties or stable topologies and adjustable hysteresis. A model is developed to understand the source of the synergistic characteristics, and theoretical findings are found to be in good agreement with experimental results. Important design-based questions are raised regarding the modular metastructure concept, and a genetic algorithm routine is developed to elucidate the sensitivities of the properties variation with respect to the statistics among assembled module design variables. To obtain target multifunctionality and adaptivity, the routine discovers that particular degrees and types of modular heterogeneity are required. Future realizations of modular metastructures are discussed to illustrate the extensibility of the design concept and broad application base.
Magnetically Responsive Droplet Interface Bilayer Networks
Authors: Brahmbhatt Khushboo , Zhao Wujun , Deng Zhaojie , Mao Leidong , Freeman Eric
Published: January 2016

This work explores incorporating ferrofluids with droplet interface bilayer (DIB) membranes. Ferrofluids contain magnetic nanoparticles in solution with a stabilizing surfactant, providing a magnetically-responsive fluid. These fluids allow for remote mechanical manipulation of ferrofluid droplets through magnetic fields, and will allow for better control over the characteristics of networks of stimuli-responsive cellular membranes created through by DIB technique.

This work involves several phases. First, a suitable biocompatible ferrofluid is synthesized, containing a neutral pH and a biocompatible surfactant. Once a proper ferrofluid is identified, it is tested as the aqueous phase for the creation of DIB membranes. Interfacial membranes between ferrofluid droplets are created and compared to non-ferrofluid DIB membranes. The interfacial membrane between two ferrofluid droplets was tested for leakage and stability, and the electrical characteristics of the interfacial membrane were studied and compared to non-ferrofluid DIB membranes.

Once it is confirmed that the ferrofluid droplets do not negatively interfere with the formation of the artificial cellular membranes through the electrical measurements, the magnetically-responsive nature of the ferrofluid droplets are used to form large networks of DIB membranes through a simple magnetic field. These networks are easy to assemble and may be remotely manipulated, providing a significant step towards the rapid and simple assembly of DIB networks advancing towards the tissue scale.
A Novel Thermomagnetic Rotational-Actuator
Authors: Cheng Chih-Cheng , Chung Tien-Kan , Chen Chin-Chung , Wang Hsin-Min
Published: January 2016

In this article, we demonstrate a novel thermomagnetic rotational-actuator. The actuator consists of thermomagnetic material Gadolinium sheets, thermoelectric generators, a rotary aluminum cantilever beam with NdFeB hard magnets fixed on the free-end of the beam, a stainless steel bearing, and a mechanical frame. As conventional magnetic rotational-actuators are controlled by using electromagnetic-induction-based magnetic-force interaction produced by electromagnets or coils, our actuator is controlled by using a heating-induced magnetic force interaction produced by the thermomagnetic generators. Experimental results show that our actuator is successfully rotated by a controlled sequence of temperature-difference generated by the TEGs.
Deformation Behavior of Capsule-Type Micro Actuator Using Palladium
Authors: Goto Kenta , Higuchi Takehiro , Fuchiwaki Ohmi , Nakao Wataru
Published: January 2016

Deformation behavior of a capsule-type micro actuator using palladium as a hydrogen storage alloy was investigated. The capsule-type micro actuator using hydrogen storage alloys (HSA-CMA) drives by the volume change of the hydrogen storage alloy induced by the absorption and discharge of hydrogen gas. It was developed as a compact, lightweight and energy-saving actuator mounted on the super multi-link manipulator to capture space debris. In the present work, a palladium foil was used as the hydrogen storage alloy. It was confirmed that the actuator of 10 mm in diameter fabricated with palladium has deformed by the introduction and evacuation of hydrogen gas. The height change and deformation rate have increased with the cycle between hydrogen introduction and evacuation.
Vertically Aligned Lead Titanate Nanowire Arrays for High Temperature Energy Harvesting
Authors: Nafari Alireza , Bowland Christopher C. , Sodano Henry A.
Published: January 2016

Over the past few decades, the increasing demand for self-powered devices has led to an immense amount of research in the field of energy harvesting from renewable mechanical energies. Often, most of these abundant energy sources are wasted in the form of structural vibrations, acoustic waves or impact energy. Recently, nano-electromechanical systems (NEMS) consisting of piezoelectric nanowires have shown excellent electromechanical coupling coefficients which can efficiently convert small amplitude vibrations into useful electrical energy for compact and low power wireless electronic devices. Specifically, high aspect ratio piezoelectric nanowires have shown to have a better deformability and hence produce higher piezoelectric response to low level induced stress. However, current materials are not well suited for energy harvesting from extreme environments. In this study, ultra-long high aspect ratio vertically aligned lead titanate nanowires (45 μm long, AR = 75) are synthesized through a two-step hydrothermal reaction in which sodium titanate nanowires serve as the precursor. Their application in harvesting vibrational energy at temperatures above 300 °C is demonstrated through the characterization of open circuit voltage and power measurements. The results show that the ultra-long vertically aligned lead titanate nanowire array energy harvester can produce up to 22.3 mW m−2 at room temperature and up to 13 mW m−2 at 375 °C. Thus, it is shown that the energy harvester can provide enough energy density for many self-powered, high-temperature applications.
Incorporating Stimuli-Responsive Bacteria in Microfluidic Droplets
Authors: Chukwurah Kengelle Q. , Yang Yaping , Wang Jian , Yan Yajun , Freeman Eric C.
Published: January 2016

Model cellular membranes respond to chemical and electrical stimuli, regulating transport and exchange between two neighboring aqueous droplets. This regulated exchange may prove useful for controlling aqueous micro-environments for studying stimuli-responsive encapsulated bacteria. This concept is explored in this work, focusing on characterizing the bacterial response within a synthetic cellular environment.

In the droplet interface bilayer (DIB) approach, aqueous micro-droplets deposited in an oil reservoir with dissolved lipids are coated with lipid monolayers and arranged into artificial cellular networks. This approach has been explored for potential use as a biologically-inspired smart material, but new material transduction pathways are necessary. This may be accomplished by combining this bottom-up approach to synthetic biology with living organisms such as stimuli-responsive bacteria.

Bacteria encapsulation within the microfluidic droplets begins with a strain of Escherichia coli (E. coli), XL1-Blue. These flagellated bacteria naturally respond and move towards chemoattractants such as casamino acids, and their motion may be tracked through differential interference contrast (DIC) and fluorescent microscopy. Chemotaxis of XL1-Blue was assessed through low-flow perfusion of the chemoattractant (casamino acids) into a buffer solution containing the bacteria through a tailored capillary tube. Next, the response of bacteria within asymmetric DIB networks separating the bacteria and the chemoattractant were studied.
Postbuckling Behavior of Axially-Compressed Strips With Discrete Rigid Constraints: A Numerical Study
Authors: Liu Suihan , Hu Nan , Burgueño Rigoberto
Published: January 2016

Axially-compressed columns, or strips, with bilateral continuous rigid constraints (CRC) are known to be able to attain multiple snap-through buckling events in their elastic postbuckling response that lead to the sudden release of strain energy from the system. This feature allows this structural prototype to be used as energy concentrators for smart applications. However, the parameters controlling the postbuckling response for such system are limited. The structural prototype discussed in this paper is that of an axially compressed strip provided with discrete rigid constraints (DRC), whereby the layout of the lateral constrains provides increased design freedom to control the strip’s postbuckling features. The study is based on numerical simulations using the finite element method. Using a previously characterized CRC strip as a baseline, two DRC design groups were considered in symmetric and asymmetric layouts for a total of 15 different arrangements. Results show that DRC strips can attain elastic postbuckling responses with distinct characteristics and that the far postbuckling response can be controlled by modifying the number and the location of the constraints. Compared to CRC strips, some DRC patterns allow attaining higher mode transitions and larger kinetic energy release after the first buckling event. The ability to design for such postbuckling response features can be potentially used for energy harvesting and other sensing and actuation applications.
Thermo-Responsive Polymer Grafted Aluminum Surface to Actively Modulate Water Wettability
Authors: Zhang Feini , Lai Shuqi , Jacobi Anthony M. , Braun Paul V.
Published: January 2016

Thermo-responsive wettability is studied for adaptive surface, which can potentially help to enhance the performance of thermal devices under various operation conditions. Poly(N-isopropylacrylamide) or PNIPAAm polymer brush can be grafted onto solid surfaces so that at temperatures below the lower critical solution temperature (LCST), the surface is hydrophilic, while at temperatures above LCST, it automatically becomes more hydrophobic. In this study, PNIPAAm is grafted on to aluminum alloy 6061, which is a multipurpose alloy commonly used in thermal mechanical systems. It is demonstrated by water static contact angle experiment at varies temperature that, the surface is hydrophobic at temperatures above LCST, and hydrophilic below LCST. The results are compared with bare aluminum surface at similar temperatures. Grafting PNIPAAm polymer brush on roughened aluminum surface would result in the ability to automatically switch between superhydrophobic state and superhydrophilic state in response to temperature change.