A general method for active surface adjustment of cable net structures with smart actuators

Pre-tensioned cable net systems are being increasingly used in building façades. Due to the geometrical nonlinearities exhibited by the cables, people have to resort to the nonlinear response history analysis approach for analyzing the seismic responses of cable net structures. This article studies the effectiveness of linear response spectrum analysis method for nonlinear cable net systems. An energy-based parameter is used to describe the structural stiffness, based on which the equivalent single-degree-of-freedom systems for cable net structures with various irregularities could be established. By means of a pseudo-energy-equivalent approach, the nonlinear equivalent single-degree-of-freedom systems are transformed into linear ones, whose seismic responses are reasonable approximations of the accurate nonlinear results. It is revealed that the vibrating period of the equivalent linearized system is close to that of the nonlinear equivalent single-degree-of-freedom system, indicating that the nonlinear effects on seismic responses of cable net structures are not serious. Inspired by the theoretical analysis, large-scale numerical computations are carried out to check the accuracy of linear response spectrum analysis for nonlinear cable net structures. In the numerical computation, four cable net models are excited by 80 seismic records. Considering 19 different degrees of earthquake intensity, a total number of 6080 nonlinear response history analyses are executed, and the results are compared with those obtained from the linear response spectrum analysis. From the numerical results, the linear response spectrum analysis yields proper overestimations of seismic responses with errors within 35%, which may lead to slightly conservative yet acceptable designs in engineering practice. Given all the aforementioned discussions, it is concluded that the linear response spectrum analysis method is effective for seismic response analysis and aseismic design of nonlinear cable net structures.

Non-parametric shape optimization method for designing cable net structures in form finding and stiffness maximization problems

Wave-based vibration control of large cable net structures

The active vibration control of cable net structures by piezoelectric stacked actuators is the subject of the present work. The focus of this paper lies on the proposal of a nonlinear method to address the vibration problem for such structures in the presence of uncertainties. To this end, a cable net structure with integrated piezoelectric stacked actuators is considered. For the structure, a nominal model is derived through the finite element method, and an uncertain model is constructed on the basis of the nominal model by taking into consideration the uncertainties. Based on the established uncertain model, a nonlinear state feedback control is deduced through the Lyapunov stability theory. This control guarantees that every uncertain system response enters and remains within a certain neighborhood of the zero state after a finite interval of time. To demonstrate the superiority of the proposed nonlinear control, a linear control based on the linear quadratic regulator is presented for comparison. Displacement responses and control voltages of the uncertain system under an impulse excitation are simulated for both the nonlinear and linear control cases. It is observed that the nonlinear method is feasible and robust as it stabilizes the uncertain system to a smaller size of the region of ultimate boundedness. Besides, the nonlinear approach improves the performance of the uncertain system by reducing the vibration to a lower amplitude within a shorter time.

Distributed acoustic sensing (DAS) is an emerging fiber-optic technology that can turn tens of kilometers long fiber-optic cables into dense acoustic sensor arrays. This technology is expected to bring new opportunities for geologic hazard characterization and mitigation. The cable structure and installation method are two critical factors affecting the performance of a DAS system. Here, we report laboratory tests performed in a sandbox to evaluate the acoustic response of different types of cables at variable sand densities and acoustic frequencies. Our initial results indicated that complex cable packaging structures had unfavorable impacts on the DAS amplitude response whereas the influence of sand density was dependent on cable structure and acoustic frequency. Further tests with refined measurement setup will improve the understanding of the combined effects of cable type, medium density, and acoustic frequency on DAS recordings.

A numerical strategy for relieving pretension of cable net structures by exchanging stiffness components

This paper develops a moving-magnet electromagnetic actuator for fast steering mirror (FSM).The actuator achieves a reasonable compromise between voice coil actuator and piezoelectric actuator.The stroke of the actuator is between the strokes of a piezoelectric actuator and a voice coil actuator, and its force output is a linear function of air gap and excitation current within our FSM travel range.Additionally, the actuator is more reliable than voice coil actuator as the electrical connection in the actuator is static.Analytically modeling the actuator is difficult and time-consuming.Alternatively, numerous finite element simulations are carried out for the actuator analysis and design.According to the design results, a real prototype of the actuator is fabricated.An experimental test system is then built.Using the test system, the force output of the fabricated actuator is evaluated.The test results validate the actuator analysis and design.

Hysteresis phenomenon occurs in all smart material-based sensors and actuators, such as shape memory alloys, piezoceramics and magnetostrictive actuators (Bank & Smith, 2000; Tan & Baras, 2004). In order to study this phenomenon, different models were proposed (Brokate & Sprekels, 1996; Visintin, 1994). Normally, hysteresis models are classified into two categories, physics-based model such as Jiles-Atherton model (Jiles & Atherton, 1986) and phenomenology-based model such as Preisach operator (Brokate & Sprekels, 1996; Visintin, 1994) and Duhem model (Visintin, 1994). From control systems point of view, hysteresis is generally non-differentiable, nonlinear, and unknown. As a result, systems with hysteresis usually exhibit undesirable inaccuracies or oscillation and even instability. Mitigating the effect of hysteresis becomes necessary and important, thus it has received increasing attention in recent years (Tao & Kokotovic, 1995, Su, et al, 2000, Su, et al, 2005). Many of these studies are related to modeling of hysteresis and their control issues. With the development of artificial intelligent (AI), AI is being applied to dealing with nonlinearities in systems (Ge & Wang, 2002). Only a few studies have been carried out by using NN to tackle hysteresis modeling and compensation (Makaveev, et al, 2002; Kuczmann & Ivanyi, 2002; Beuschel et al, 1998; Zhao & Tan, 2006). In the paper (Makaveev, et al, 2002), a NN model is used to describe the hysteresis behavior in different frequencies with the knowledge of some properties of magnetic materials, such as loss separation property to allow the separate treatment of quasi-static and dynamic hysteretic effects. Beuschel et al used (Beuschel et al, 1998) a modified Luenberger observer and NN are used to identify a general model of hysteresis. These researches demonstrate that NN can work as an unknown function approximator to describe the characteristics of hysteresis. Recently, two papers (Zhao & Tan, 2006; Lin et al 2006) applied the approximation property of NN to coping with the identification of Preisach-type hysteresis in piezoelectric actuator, and the hysteresis estimation problem for piezo-positioning mechanism based on hysteresis friction force function, respectively. It should be noted that the aforementioned results share a common assumption that the output of hysteresis is measurable. In practical systems, smart actuators are integrated into the systems, which makes the measurement of output of hysteresis hard. Hence it is a challenge to design an observer for

Branched cable communications are carriers of fire load, they are tracks along which fire spreads in buildings and structures. Therefore, currently, fire safety of cables is one of the most important tasks of the cable industry. The spread of flames in vertical bunch wiring depends on the following factors: the amount of combustible material that is exposed to high temperatures, geometric shapes of cables and their mutual location when laying, the ignition temperature of gases emitted by cables, the volume of combustible gases emitted by cables at a certain elevated temperature, the room capacity and volume of air passing through the cable structure, cable devices. Analysis of regulatory documents revealed some key differences in the methodology of standards. It was found that the spread of fire is not only affected by the volume of laid cables, but also by their mutual placement in space. A direct correlation was found between the influence of the crosssection of the cable core and preservation of the cable line in case of fire. Parameters were determined for the preservation of serviceability under fire exposure in the case of bunch and in the case of single wiring. It has been determined that it is impossible to spread the results of fire tests in case of single wiring in accordance with GOST IEC 60331-21-2011 and in case of bunch wiring in accordance with GOST IEC 60332-3-22-2011 to the results of tests in accordance with GOST R 53316-2009 for the preservation of operability of cable lines. The parameters of fire resistance and operability of cable products under the influence of flame depending on the type of cables and the method of their installation have been determined.

<div class="section abstract"><div class="htmlview paragraph">Turboelectric propulsion is a technology that can potentially reduce aircraft noise, increase fuel efficiency, and decrease harmful emissions. In a turbo-electric system, the propulsor (fans) is no longer connected to the turbine through a mechanical connection. Instead, a superconducting generator connected to a gas turbine produces electrical power which is delivered to distributed fans. This configuration can potentially decrease fuel burn by 10% [<span class="xref">1</span>]. One of the primary challenges in implementing turboelectric electric propulsion is designing the power distribution system to transmit power from the generator to the fans. The power distribution system is required to transmit 40 MW of power from the generator to the electrical loads on the aircraft. A conventional aircraft distribution cannot efficiently or reliably transmit this large amount of power; therefore, new power distribution technologies must be considered. Two critical components in the power distribution system that must be redesigned are the cables and power converters.</div><div class="htmlview paragraph">Sizing algorithms for a conventional copper cable and a superconducting cable have been developed to determine the best method of power transmission. In order to create the sizing models, cable structure and materials were selected for both cable types. The sizing models determine the dimensions and weight of the cables as a function of system nominal voltage and cable length. A range of values were used for the design variables to produce sizing data; then, the data was regressed to create simple equations that can be used to estimate cable size. A turboelectric propulsion system required the use of inverters and rectifiers. Converter structures and control schemes will be explored and the optimal alternatives for this application will be modeled. The final goal of this research is to estimate the weight of the cables and performance of the converters to determine the optimal combination of power distribution technologies for a turboelectric propulsion system.</div></div>

The concept of microwave-driven smart material actuators was envisioned anddeveloped as the best option to alleviate the complexity and weight associatedwith a hard-wire-networked power and control system for smart actuator arrays.The patch rectenna array was initially designed for high current output, but hasundergone further development for high voltage output devices used in shape controlapplications. Test results show that more than 200 V of output were obtained from a6 × 6 array at a far-field exposure (1.8 m away) with an X-band input power of 18 W. The6 × 6 array patch rectenna was designed to theoretically generate voltages up to 540 V,but practically it has generated voltages in the range between 200 and 300 V.Testing was also performed with a thin layer composite unimorph ferroelectricdriver and sensor and electro-active paper as smart actuators attached to the6 × 6 array. Flexible dipole rectenna arrays built on thin-film-based flexible membranes are mostapplicable for NASA’s various missions, such as microwave-driven shape controls foraircraft morphing and large, ultra-lightweight space structures. An array of dipolerectennas was designed for high voltage output by densely populating Schottky barrierdiodes to drive piezoelectric or electrostrictive actuators. The dipole rectenna array willeventually be integrated with a power allocation and distribution logic circuit andmicrobatteries for storage of excessive power. The roadmap for the development of wirelesspower drivers based on the rectenna array for shape control requires the development ofnew membrane materials with proper dielectric constants that are suitable for dipolerectenna arrays.

Significant advances in smart material actuators have taken place in the past decade. The holy grail of actuator research is an architecture that can generate high displacement and force throughout a broad frequency range while not consuming a significant amount of electrical power. The large appeal of using smart material actuators stems from their high mechanical energy density. However, all smart material actuators generally have at least one shortcoming involving either mechanical stroke, force, or frequency capability. Whenever speed is a consideration, piezoelectric actuation is the most commonly employed. The purpose of this paper is to review the most current trends in piezoelectric actuation architectures. The paper does not present the theoretical details of each actuator, but instead strives to highlight the novel concepts used in each design to overcome the stroke limitation of the material.

Smart Actuators in Robotics

Piezoelectric solid-state actuators continue to gain in technical and economic significance for a great variety of applications such as quick fine-positioning tasks, control of structural stability and active noise and vibration control due to the high driving forces, short reaction times and compact construction of these actuators. Microelectronics and signal processing must be combined intelligently to form `smart actuators' in order to do justice to the growing demand for precision, miniaturization, efficiency and cost. Energy transducers with piezoelectric PZT ceramics (PZT: lead-zirconate-titanate) simultaneously possess actuator and sensor capacities. An important requirement for the construction of smart actuators is fulfilled by separating the sensor information (charge approximately external force) from the actuator control quantities (elongation approximately electric field strength). A closed-loop control structure with digital signal processing and a voltage controlled power amplifier were developed to enable nearly load-independent linearization of the actuator's response characteristic (elongation-voltage curve) even under dynamic operating conditions by making use of the `self-sensing' effect and without using extra force or displacement sensors. The effectiveness of the developed approach for realizing smart actuators was verified and specified with the help of a computerized large-signal measurement set-up using a low-voltage piezoelectric ceramic stack as an example.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Smart actuators, made of smart materials, are becoming more attractive in many applications because smart materials are not subjected to wear and does not require lubrication during services. Piezoelectric materials are a group of the many attractive smart materials that are being investigated for many applications today. Piezoelectric materials show fast responses, high efficiency/accuracy and operate on a large bandwidth. Composite materials are of interest because of their design flexibility and because they are lighter than other materials commonly used in aircraft and other applications. For the research reported here, a piezoelectric material was embedded in a composite material to form a piezoelectric composite actuator. This research was conducted to expand our knowledge of piezoelectric composite material actuators, and originated from the need to control air flow separation over an airfoil. There is a need to build a profound knowledge about such actuators before they can be implemented in an airfoil, and to understand which parameters influence the behaviour of piezoelectric composite material actuators under static and dynamic operating conditions. The actuators were manufactured and tested under static and dynamic conditions and the experimental results were compared to the finite element models. The models were incorporated with piezoelectric material properties that were determined experimentally. The results showed that a piezoelectric material’s response to an input stimulant, e.g. electric voltage and frequency, influences the actuator’s behaviour.