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We investigate the energy spectra and optical absorption of a 3D quantum dot–double quantum ring structure of GaAs/Al0.3Ga0.7As with adjustable geometrical parameters. In the effective mass approximation, we perform 3D numerical computations using as height profile a superposition of three Gaussian functions. Independent variations of height and width of the dot and of the rings and also of the dot–rings distance determine particular responses, useful in practical applications. We consider that a suitable manipulation of the geometrical parameters of this type of quantum coupling offer a variety of responses and, more important, the possibility of a fine adjusting in energy spectra and in the opportunity of choosing definite absorption domains, properties required for the improvement of the performances of optoelectronic devices. [ABSTRACT FROM AUTHOR]

This paper proposes a new hierarchical robust control scheme for the multiple quadrotor unnamed aerial vehicles (UAVs) aerial transportation system with a suspended payload. The control system is decoupled into two parts: (1) the payload-loop subsystem for the payload's position and attitude control together with the cable's swing control, (2) the quadrotor-loop subsystem for the i-th quadrotor UAV's attitude control. The robust integral of the signum of the error (RISE) method and geometry control method are combined together for the control design of the payload-loop subsystem, which is used to address the problem that the position and attitude control of payload is limited and the mass of the payload is not uniformly distributed in the actual flight. The proposed control strategy does not require the high-order time-derivatives of the desired system state, and it is more practical and can achieve fast tracking for the desired trajectory of the payload. Taking the coupling dynamics between the payload and multiple UAVs into consideration, the modeling uncertainty of the suspended payload and the unknown external perturbations are compensated. In addition, a quadrotor-loop controller is designed for the UAV's attitude with the combination of the geometry control method and the sliding model control method, and the unknown aerodynamic effects are also compensated. Finally, the stability of the closed-loop system is provided via Lyapunov-based stability analysis, and a numerical simulation is performed. Simulation results show that the proposed hierarchical robust control scheme can compensate the effects of the uncertainties and the unknown external disturbances. And the proposed system can reach the specified position rapidly; meanwhile, the attitude of the payload can converge quickly. The overall assessment in comparison with the recent similar method indicates the success of the proposed method on the obstacle avoidance scenario. [ABSTRACT FROM AUTHOR]

In the new hall of the Institute for Materials and Structures, there was a need to control the geometry of the existing crane rails. In this paper, the methodology for determining the geometry of such a complex structure is presented, and the results of the applied method are also presented. The final product, i.e. the examined geometry of crane rails included numerical and graphical analysis of straightness, analysis of parallelism and analysis of horizontality of crane rails.

Cold wire gas metal arc (CWGMA) additive manufacturing (AM) is more productive and beneficial than the common electric arc processes currently used in wire arc additive manufacturing (WAAM). Adding a non-energised wire to the gas metal arc (GMA) system makes it possible to overcome a process limitation and decouple the energy input from the material feed rate. Two novel process control methods were proposed, namely, arc power and travel speed control, which can keep the required geometry accuracy in WAAM through a broad range of thermal conditions. The reinforcement area of the bead is kept constant with accurate control over the height and width while still reducing the energy input to the substrate; decreasing penetration depth, remelting, and the heat-affected zone (HAZ); and reaching a dilution lower than 10%. This work also presents improved productivity compared to all the other single-arc energy-based processes with a demonstrator part built using 9.57 kg h−1 with CWGMA AM. [ABSTRACT FROM AUTHOR]

Cold wire gas metal arc (CWGMA) additive manufacturing (AM) is more productive and beneficial than the common electric arc processes currently used in wire arc additive manufacturing (WAAM). Adding a non-energised wire to the gas metal arc (GMA) system makes it possible to overcome a process limitation and decouple the energy input from the material feed rate. Two novel process control methods were proposed, namely, arc power and travel speed control, which can keep the required geometry accuracy in WAAM through a broad range of thermal conditions. The reinforcement area of the bead is kept constant with accurate control over the height and width while still reducing the energy input to the substrate; decreasing penetration depth, remelting, and the heat-affected zone (HAZ); and reaching a dilution lower than 10%. This work also presents improved productivity compared to all the other single-arc energy-based processes with a demonstrator part built using 9.57 kg h−1 with CWGMA AM.

This article investigates the agile flight control design for a quadrotor unnamed aerial vehicle in the 3D environment. Due to the need for the high speed flight and aggressive manoeuver in practical scenarios, the kinematic and dynamic models of the unmanned quadrotor are described in SO(3) and the controller is designed in the rotation format, which can avoid the singularity in the Euler angle format and the unwinding issue in the quaternion format. Moreover, comparing with the other existing nonlinear control strategies for the unmanned quadrotor, the proposed controller has the advantage of easy implementation and good robustness to the modeling uncertainties and unknown external disturbances by using the robust‐integral‐signum‐error method. The stability of the closed loop system is proved via the Lyapunov based stability analysis, and the proposed nonlinear robust controller can guarantee the asymptotic convergence of the quadrotor's attitude and position tracking errors. The effectiveness of the proposed agile flight control design is validated via real‐time experiments in comparison with the classical cascaded PID controller. And the experimental results show that the proposed controller achieves much higher flight control accuracy in agile flights. [ABSTRACT FROM AUTHOR]

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Recent studies in wave energy have highlighted the need for a structured innovation approach in wave energy converter (WEC) design because cost-of-energy estimates have remained high. One such innovation being investigated by the National Renewable Energy Laboratory is WEC geometry control, which uses control surfaces in combination with an oscillating surge WEC (OSWEC) to increase device availability and power generation while limiting structural costs. This study performs the first analysis of annual performance for a novel OSWEC with geometry control to understand how the geometry control affects availability, annual power generation, and structural loadings like the power-take-off (PTO) torque or surge foundation force. Device hydrodynamic coefficients are calculated using linear potential theory for six geometry configurations. A nonideal PTO system is assumed and quadratic viscous damping losses are considered. Annual performance is evaluated and compared for three U.S. wave energy sites. The WEC geometry and PTO system are controlled on a sea-state basis to optimize for power capture while remaining under limits set on motion amplitude and structural loads. Results indicate that geometry control can increase availability up to 25 days in an average year depending on design limits, increase average power generation, and significantly reduce peak structural loads. • First analysis of the effects of geometry control on annual performance. • Annual performance irregular wave analysis includes viscous and nonideal PTO losses. • Performance compared for different control strategies, locations, and load limits. • Geometry control increases availability by up to 25 days in an average year. • Geometry control increases average annual power production by up to 7.5%. [ABSTRACT FROM AUTHOR]

The short-line match method (SLMM) is an effective and popular technology for accelerated bridge construction because it is characterized by a small construction area, minimal labor, and fast construction speed. However, a millimeter-sized error in the precast phase may be amplified to a meter-sized error at the end; therefore, SLMM has an extremely high requirement for geometric control. Construction project abandonment and rework accidents caused by geometric control failure frequently occur. Existing geometric control methods should be improved due to their incomplete consideration of geometric errors. This study presents a novel high-precision geometric control method (HPGCM) for SLMM. The proposed method includes the decoupling of deviation angles consisting of coupled components from different planes and the identification of deviation angles with different spatial positions. The effectiveness of the proposed method is verified through simulated and practical examples. The developed method exhibits high precision and reliable error-correcting ability. It can provide a reference for the construction of SLMM-based bridges in the future. [ABSTRACT FROM AUTHOR]

Highlights • Proposed a new analytical power capture bound for SRPAs based on dynamic response. • Proposed a new constraint equation relating the optimal float to spar impedance. • Numerically demonstrated how the bound can be approached. • Introduced inerters to wave energy community to implement optimal geometry control. • Proposed a new condition for null power capture of SRPAs based on geometry control. Abstract To be a competitive supply of renewable energy, the power capture performance of ocean wave energy converters must improve. This requires that wave energy converter designers identify and invest resources to develop devices that exhibit a strong Technology Performance Level early in the development process. We contend that completing this identification process at the conceptual design stage requires a generalized method to establish the power capture upper bound for any given wave energy converter architecture. This upper bound must reflect simultaneous implementation of both optimal geometry control and power take-off force control – components known to be essential to optimizing performance but difficult to envision for complex WEC architectures. In this work, we develop and demonstrate a procedure, built on the mechanical circuit framework, to identify this upper bound for a self-reacting point absorber with an inertial modulation mechanism performing the geometry control. We illustrate how the analytical procedure generates generic design guidance, required to achieve the bound, without committing to a specific technology. We follow by formally introducing a new technology into the wave energy community, the inerter, capable of implementing the design guidance to enact the required geometry control. Finally, we apply the analytics within a numerical case study of a previously published wave energy converter configuration, and compare the power capture production of that device to one with equivalent hydrodynamics, but with the new geometry control feature set suggested by the new analytical procedure. Our analysis reveals the potential for a ten-fold increase in power capture even under stringent relative displacement constraints. [ABSTRACT FROM AUTHOR]

Abstract Robot-guided Laser Metal Deposition (LMD) process offers an efficient and resource-friendly production of big complex metals parts. In order to produce high-quality parts with minimum post-processing time, a highly stable process is required. The LMD process is characterized by numerous influencing physical parameters that lead to melt-pool instability, which results in shape irregularities in the component, followed by longer post-processing time. For process stability, control systems are necessary, which react to the occurring process and part deviations. The harsh environmental and process conditions impose high mechanical and thermal stresses on the sensors, which impact the accuracy of the system. In this paper, the factors influencing the accuracy of the sensors have been presented. The usability and stability of geometry control strategies with sensors have been evaluated against strategies without sensors. Additionally, the sensor system requirements for irregularity detection have been reported along with the guidelines developed for the implementation of a robust sensor control system for robot-based LMD processes. [ABSTRACT FROM AUTHOR]

This paper reports on the development and fabrication of precast bridge piers with unique creative shapes and more accurate geometry control methods using building information modelling, a new form of information processing and collaboration in which data are embedded within 3D models. Panelized formworks were created by digital fabrication from the 3D design models and attached to common steel formworks. During fabrication of precast segments, key parameters for geometry control were captured by laser scanning. The design models from the algorithm modelling were compared to fabrication models to provide error adjustment during assembly. Before assembly of the segments at a construction site, instructions for geometry control were provided to ensure the final target geometry of the bridge piers. Information delivery from design to maintenance can be achieved by 3D information models and a new format for drawings that includes QR codes and 3D models. [ABSTRACT FROM AUTHOR]

The design space for ocean wave energy converters is notable for its divergence. To facilitate convergence, and thereby support commercialization, we present a new simple method for analysis and comparison of alternative device architectures at an early stage of the design process. Using Thévenin's theorem, Falnes crafted an ingenious solution for the monochromatic optimal power capture of heaving point absorber devices by forming a mechanical impedance matching problem between the device and the power take-off. However, his solutions are limited by device architecture complexity. In this paper, we use the mechanical circuit framework to extend Falnes' method to form and solve the impedance matching problem and calculate the optimal power capture for converter architectures of arbitrary complexity. The new technique is first applied to reprove Falnes' findings and then to assess a complex converter architecture, proposed by Korde. This work also provides insight into a master-slave relationship between the geometry and power take-off force control problems that are inherent to converter design, and it reveals a hierarchy of distinct design objectives unbeknownst to Korde for his device. Finally, we show how application of the master-slave principle leads to the reduction in the dimensionality of the associated design space. [ABSTRACT FROM AUTHOR]

Overtopping wave energy converters (OWECs) are designed to extract energy from ocean waves based on wave overtopping into a reservoir, which is emptied into the ocean through a set of low-head turbines, and typically feature a low crest freeboard and a smooth impermeable steep slope. In the process of optimizing the performance of OWECs, the question arises whether adapting the slope geometry to the variable wave characteristics at the deployment site (i.e., geometry control) can increase the overall hydraulic efficiency and overall hydraulic power compared to a fixed slope geometry. The effect of five different geometry control scenarios on the overall hydraulic efficiency and overall hydraulic power of OWECs has been simulated for three possible deployment sites using empirical prediction formulae. The results show that the effect of an adaptive slope angle is relatively small. On the other hand, adapting the crest freeboard of the OWECs to the wave characteristics increases the overall hydraulic efficiency and power. Based on the simulations, gains in overall hydraulic power of at least 30% are achievable when applying an adaptive crest freeboard compared to a fixed crest freeboard.

Cantilever assembly method with cable inclined pulling and buckling system is usually used for long-span truss arch bridge construction. The complex structural mechanical behaviors and construction technology bring difficulties to the bridge construction. The construction technologies which are applied on several domestic long-span steel truss arch bridges are summarized, compared and analyzed, such as general construction scheme, system transformation processes, geometry control methods, unstressed closure of arch and rigid tie bar, cable inclined pulling and buckling system erection, etc. We obtained construction technology and methods for different situations. [ABSTRACT FROM AUTHOR]

This paper uses topology optimization to optimize the layout of discrete objects, such as fixed-shape void, stiffening, or functional inclusions, in structures and periodic materials. The methodology follows a material distribution approach and the Heaviside Projection Method (HPM) is manipulated to ensure that the designed objects are discrete, of fixed size (length scale) and shape, and satisfy minimum spacing requirements. These restrictions are achieved implicitly through projection without additional constraints or heuristics. The methodology is built in the spirit of free-form topology optimization and thus discrete objects are shown to appear, vanish, or translate across the design domain during the design evolution. The technique is demonstrated on problems governed by mechanical stiffness including the design of structures and material microstructures whose elastic stiffness is to be enhanced by optimizing the location of stiff, circular inclusions. [ABSTRACT FROM AUTHOR]

The Incheon Bridge is a continuous span steel deck cable-stayed bridge with six traffic lanes in dual direction. Its total length is 1480 m including an 800 m centre span. The pylon was designed as an inverted Y-shaped concrete structure of 238 m in height. The pylon consists of four parts, namely the lower part, cross beam, middle part and upper cable anchorage part. The pylon was constructed by being divided into 57 lots of 4 m height, and auto-climbing form was applied. The cross beam was prefabricated at the factory to save construction time and was erected by using a floating crane. In order to control the geometry and secure the stability during construction, temporary tie and struts were installed and tensioned. For the superstructure erection, the side span was fabricated as four large blocks, which weighed 27 000 kN at the factory and was erected on temporary bents by using a 30 000 kN floating crane. The centre span was fabricated as a 15 m long block weighing 3000 kN and erected by a derrick crane along with the stay cables. A total of 208 cables were installed in a semi-fan shaped arrangement and four cables were stressed simultaneously. An integrated geometry control system was developed and applied for geometry control and cable adjustment during the erection. Four systems, namely, data integrated management system, structural analysis system, error adjustment system and measurement system, were employed. Approximately 6 to 7 days of cycle time was achieved for the superstructure erection within the allowable limits of geometry and cable tension. This paper presents the construction and geometry control system applied in the Incheon cable-stayed bridge. [ABSTRACT FROM AUTHOR]

Abstract: Asymmetric Janus ZnO spheres with partially attached PS spheres were prepared by both protecting layer mask technique and Pickering emulsion template in presence of polyelectrolyte (poly(allylamine hydrochloride)). The scanning electron microscopy images showed that the surface of ZnO sphere was clearly divided into two parts, one of which was densely packed with PS particles, and the other one was bare. As compared with Janus ZnO formed by Pickering emulsion, the protecting layer mask technique gave rise to more regular masked area on the ZnO spheres, thereby producing quite regular morphology of the PS patterned. More importantly, this approach provided a facile way to tune the Janus balance by controlling the geometry of the Janus ZnO spheres, which was achieved by adjusting the thickness of the wax layer. [Copyright &y& Elsevier]

Overtopping wave energy converters (OWECs) are designed to extract energy from ocean waves based on wave overtopping into a reservoir, which is emptied into the ocean through a set of low-head turbines, and typically feature a low crest freeboard and a smooth impermeable steep slope. In the process of optimizing the performance of OWECs, the question arises whether adapting the slope geometry to the variable wave characteristics at the deployment site (i.e., geometry control) can increase the overall hydraulic efficiency and overall hydraulic power compared to a fixed slope geometry. The effect of five different geometry control scenarios on the overall hydraulic efficiency and overall hydraulic power of OWECs has been simulated for three possible deployment sites using empirical prediction formulae. The results show that the effect of an adaptive slope angle is relatively small. On the other hand, adapting the crest freeboard of the OWECs to the wave characteristics increases the overall hydraulic efficiency and power. Based on the simulations, gains in overall hydraulic power of at least 30% are achievable when applying an adaptive crest freeboard compared to a fixed crest freeboard. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the effects that geometry and control have on the absorption characteristics of wavemakers. It presents the hydrodynamic coefficients for piston and bottom hinged flap wavemakers and also for two novel wavemaker profiles. Absorption efficiencies are presented for wavemakers using one, two and three control coefficients for reactive control. This is then used to analyse the absorption efficiency of each of the different wavemakers based upon the geometry and the control strategy used. It is shown that the amount of absorption for a given paddle differs greatly depending on the choice of control coefficients used to implement complex conjugate control. Increased absorption can be achieved over a broader bandwith of frequencies when the geometry of the wavemaker is optimised for one specific frequency. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we described how to control the magnetic junction critical dimension (CD) and profile defined by ion beam milling and its implication to device performance. The impact of standing waves on breaking the photo-resist and on the resultant junction defects have been highlighted. The ideal device profile and geometry are also discussed. [Copyright &y& Elsevier]

Stonecutters Bridge is the second longest cable-stayed bridge in the world and the first major bridge with a twin-box girder superstructure. It has a number of innovative structural features which made the construction of the bridge a significant challenge. This paper describes the fabrication and erection procedures for the bridge towers and the main span superstructure. These were developed in close interaction between the contractor and his construction engineering consultant to ensure a safe and effective construction. A stage-by-stage analysis was set up to model every step of the main span erection. The results were first used in the verification analyses to establish the adequacy of the permanent works throughout construction. In parallel, extensive wind tunnel testing as well as numerical analyses were performed to ascertain the effects of typhoon wind loads on the structure. The structural deformations predicted by the erection analysis were incorporated into a comprehensive geometric control procedure. This paper describes the construction methodologies developed and the related engineering input. It outlines studies undertaken to achieve an effective construction, ensure structural adequacy of all erection stages, ascertain an acceptable aerodynamic performance of the bridge, and exercise full control over the bridge geometry throughout erection. [ABSTRACT FROM AUTHOR]

We propose a control method that changes the geometry of a fishing net into an arbitrary geometry. To control the net geometry, an automatic control system was constructed by integrating the data assimilation method into a fishing net dynamics simulation. This study focused on the function of the data assimilation method to estimate the unknown parameter needed to control the net geometry. By applying the parameter estimation, the length of the material and loading were set as unknown parameters and estimated to be an intended geometry of the fishing net. Further, geometry control experiments consisting of numerical simulations were conducted for validation. This was achieved by using a simplified plane net model and a trawl net model. An automatic control system using the extended Kalman filter was applied. In addition, we confirmed that the net geometry can be controlled in real space by the automatic control system. For validation, the results of experiments conducted in an experimental flume tank were compared with the numerical simulation results of the plane net geometry by using the automatic control system that integrated an ensemble Kalman filter. The numerical simulation results were found to be congruent with those of the flume tank experiments, confirming the validity of the proposed control system. [ABSTRACT FROM AUTHOR]

Geometry of single tracks has a significant influence on the forming efficiency, surface accuracy and internal quality of metal additive manufacturing parts. Herein, a 3D numerical model of 7075 aluminum alloy single tracks forming process during liquid metal flow rapid cooling additive manufacturing was established to reveal the effect of thermal behaviors and fluid flow on the geometry of 7075 aluminum alloy single tracks. The 7075 aluminum alloy single tracks with controllable geometries were fabricated by self-developed liquid metal flow rapid cooling additive manufacturing equipment. The results show that the variation of the solidification volume of 7075 aluminum alloy melt in spreading stage and the solidification velocity in accumulation stage results in the variety of the spreading and accumulation kinetic energy of 7075 aluminum alloy melt, which decide the geometry of 7075 aluminum alloy single tracks. The geometry of 7075 aluminum alloy single tracks can be controlled by adjusting the process parameters such as nozzle travel speed and melt temperature, which have a significant effect on the solidification volume and solidification velocity during single tracks forming process of liquid metal flow rapid cooling additive manufacturing. [ABSTRACT FROM AUTHOR]

It is widely suggested that step gains in wave energy converter power capture performance must be realized to achieve economic viability. One method of fulfilling power capture gains is to invoke resonant conditions between the device and the incoming ocean wave. However, a general method that can establish the prerequisites for achieving resonant conditions in an arbitrarily complex wave energy converter architecture is nonexistent. In this work, we present an analytical procedure, built on the mechanical circuit framework, for identifying the resonant conditions of an arbitrarily complex wave energy converter architecture. To demonstrate the procedure, we select three complex two body point absorber devices as a case study, each with a geometry controllable feature set. Through invoking resonant conditions in each architecture, we illustrate how the choice of topology has significant influence on the power capture characteristics of the WEC device. Selecting the highest performing architecture, we then reveal how the analytical equations can be applied to promote technology innovation by supplying design criterion prior to locking down the WEC design. Finally, we apply the analytics within a numerical case study and present a hierarchy describing the incremental performance improvements realized through implementing steps in control complexity for this device. • Proposed an analytical method to solve for the optimal phase control condition(s) in an arbitrarily complex WEC architecture. • Proposed a generic analytical constraint equation for achieving resonant control via the optimal spar mechanical impedance. • Demonstrated how the choice of WEC topology has a strong influence on the power capture potential of a self-reacting point absorber WEC. • Numerically demonstrated how an inerter can be used to implement this constraint equation. • Demonstrated via case study a hierarchy of WEC control objectives in relation to their step increases in power capture potential. [ABSTRACT FROM AUTHOR]

To date, one of the difficulties with wave energy devices is modulating the power transfer from the waves to the generator. In wind turbines, this is achieved by turbine pitch control, leading to the ubiquitous flat power curve. Recently, a wave energy converter, having moveable vanes, has been developed by the National Renewable Energy Laboratory (NREL) in the US. This paper described the development of a compact hydrodynamic model for the NREL device, based on multiple linear hydrodynamic modelling (Murray-Smith and Johansen, 1997), which can be used to model the hydrodynamic behaviour of the device across its full operational spectrum of vane angles. To show the utility of the model, we demonstrate a flat power curve for the WEC, using the vane angles as a control input. • Parametric modelling of a wave energy converter with moveable flaps. • Introduction of the hydrodynamic gain concept. • Power absorption control in regular waves. • Parallel is shown between the studied wave energy converter and wind turbines. [ABSTRACT FROM AUTHOR]

Integrating a plasmonic metal and a semiconductor at the nanoscale is of great importance for exploring their optical coupling properties. However, the synthesis and fine structural control of such nanostructures remain challenging. Herein we report the facile aqueous-phase Se-mediated overgrowth of metal selenides onto Au nanocrystals. Taking plasmonic Cu 2-x Se as an example, the introduction of a Se template allows deposition of large Cu 2-x Se crystalline grains onto Au nanocrystal seeds in various shapes, including spheres, rods, and plates. Moreover, the configuration of Au-Cu 2-x Se hybrids can be tuned from core-shell to heterodimer structure by controlling the growth behavior of the Se template. Se overgrowth depends critically on the absorption strength of stabilizers on Au seeds: a strongly absorbing stabilizer inhibits isotropic overgrowth, which is in agreement with molecular dynamics simulations. The resultant Au-Cu 2-x Se hybrid nanocrystals possess multiple surface plasmon resonance modes. Finally, our synthetic strategy can be extended to prepare other Au-metal selenide hybrids such as Au-Ag 2 Se and Au-CdSe with controllable morphologies.

A facile and ultrafast method for geometry controllable and vertically transformative 3D graphene architectures is demonstrated. The 2D stacked graphene layers produced by exfoliation of graphite were transformed, e.g., from horizontal to vertical, by applying electric charge (-2 V with 1-3 μAh/cm2). The three-dimensionally transformed graphene layers have maximized surface area as well as high specific capacitance, 410 F g(-1) in LiClO4/PC electrolyte, which is 4.4 times higher than that of planar (stacked) graphene layers. Furthermore, they can remarkably exhibit 87% of retained capacitance as the scan rate is increased from 100 to 1000 mV s(-1), unlike planar graphene, which displays 61% retention under the same conditions.