Flexible Connection Research Articles

Dynamics modeling and flight characteristics of folded multi-body aircraft

This paper studies the dynamic modeling method of fold-able multi-body aircraft based on the dynamics theory of multi-body system. Considering the multi-body aircraft as a complete multi-rigid body system, the dynamic model for the free unfolding process of the multi-body aircraft after horizontal launch is established. On the basis of the multi-body dynamics model, the coil spring moment model and the damping moment model for the flexible connection between the flight units are added. Taking a certain type of fold-able three-section wing aircraft as an example, the numerical simulation calculation is carried out. The influence of the flexible connection stiffness coefficient between the flight unit on the dynamic characteristics of the fold-able multi-body aircraft in the free deployment process and the relationship between the stiffness of the flexible connection and the maximum initial folding angle are studied. Finally, the stability envelope between the stiffness coefficient of the flexible connection and the maximum initial folding angle is determined.

Modular Seven-Leg Switched Reluctance Motor Drive With Flexible Winding Configuration and Fault-Tolerant Capability

This paper proposes a modular seven-leg switched reluctance motor (SRM) drive with flexible winding configuration and fault-tolerant capability. In traditional SRM drives, the winding connection is fixed, where the speed regulation range and fault-tolerant ability are both limited. To solve these issues, a modular seven-leg drive topology is proposed, where each phase winding is divided into two segments, and the winding connection can be flexibly switched to achieve a wide speed range. At low speed, the winding segments are connected in series for a higher output torque, while the parallel connection is employed at high speed to extend the speed range. In addition, a swift and smooth online winding switching process is achieved, where there are no current or speed shocks. Furthermore, owing to the flexible winding connection in the proposed topology, effective fault-tolerant strategies are developed to deal with the open-circuit faults in both series and parallel connections, which can maintain the output capability and avoid large torque ripples when open-circuit faults occur. Meanwhile, the proposed drive topology is constructed by commercial half-bridge modules and is suitable for industrial applications. Simulations and experiments are carried out on a three-phase SRM prototype to verify the feasibility of the proposed scheme.

Uplink Multiple Access With Semi-Grant-Free Transmission in Integrated Satellite-Aerial-Terrestrial Networks

This paper investigates a semi-grant-free (SGF) based transmission strategy to provide a flexible connectivity for various kinds of users in an integrated satellite-aerial-terrestrial network (ISATN). Herein, a high-altitude platform (HAP) termed as a grant-based user (GBU), which serves multiple mobile terminals (MTs) through space division multiple access (SDMA), wants to access a satellite network with multiple earth stations (ESs) termed as grant-free users (GFUs) simultaneously via non-orthogonal multiple access (NOMA) assisted SGF. To this end, we first propose two SGF-based uplink transmission schemes for both perfect channel state information (CSI) and imperfect CSI cases. When perfect CSI is available, a zero-forcing based beamforming (BF) scheme is used in HAP network while an adaptive transmit power allocation (ATPA) approach is adopted for SGF transmission. When only imperfect CSI is available, BF scheme employing the derived channel correlation matrix of HAP-MT link is proposed to achieve SDMA, and a novel ATPA strategy with rate probability constraint is proposed to guarantee quality-of-service of the GBU. Next, we derive the closed-form throughput expressions to evaluate the performance of the considered ISATN with the proposed two SGF-based schemes. Finally, computer simulations are conducted to validate the theoretical performance analysis and show the superiority of the proposed schemes over the related works. Moreover, our numerical results not only demonstrate a satisfactory performance of the proposed SGF-based scheme using imperfect CSI, but also reveal the impact of CSI errors on the system performance.

Research on the Connector Loads of a Multi-Module Floating Body with Hinged Connector Based on FMFC Model

VLFSs (Very Large Floating Structures) are often assembled by multiple modules through connectors where the connector structure is prone to stress concentration. Therefore, the loads at the connectors have become a significant focus in VLFS design. In this paper, the FMFC (Flexible Module Flexible Connector) method, which can account for the elastic deformation of each module and the connector, is established in order to predict the coupling response of the connector and the platform. The finite element model of a dual-module transfer platform with a hinged connector is established and the modal shape characteristics of the entire structure are analyzed. The accuracy of the method is verified through a model test, where the model was scaled as 1:50. Furthermore, the RAOs (Response Amplitude Operators) of connector loads were calculated. It was found that the horizontal loads (along the x and y directions) were more sensitive to the wave direction. Furthermore, the wave direction where the maximum short-term significant value appears was not consistent with the direction of the maximum RAO. The loads response law of the VLFS with a hinged connector is summarized in this paper and provides a reference for the design of connectors.

High-Performance Wearable Bi2Te3-Based Thermoelectric Generator

Wearable thermoelectric generators (w-TEGs) convert thermal energy into electrical energy to realize self-powering of intelligent electronic devices, thus reducing the burden of battery replacement and charging, and improving the usage time and efficiency of electronic devices. Through finite element simulation, this study successfully designed high-performance thermoelectric generator and made it into wearable thermoelectric module by adopting “rigid device—flexible connection” method. It was found that higher convective heat transfer coefficient (h) on cold-end leads to larger effective temperature difference (ΔTeff) and better power generation performance of device in typical wearable scenario. Meanwhile, at same h on the cold-end, longer TE leg length leads to larger ΔTeff established at both ends of device, larger device output power (Pout) and open-circuit voltage (Uoc). However, when the h increases to a certain level, optimization effect of increasing TE leg length on device power generation performance will gradually diminish. For devices with fixed temperature difference between two ends, longer TE leg length leads to higher resistance of TEGs, resulting in lower device Pout but slight increase in Uoc. Finally, sixteen 16 × 4 × 2 mm2 TEGs (L = 1.38 mm, W = 0.6 mm) and two modules were fabricated and tested. At hot end temperature Th = 33 °C and cold end temperature Tc = 30 °C, the actual maximum Pout of the TEG was about 0.2 mW, and the actual maximum Pout of the TEG module was about 1.602 mW, which is highly consistent with the simulated value. This work brings great convenience to research and development of wearable thermoelectric modules and provides new, environmentally friendly and efficient power solution for wearable devices.

The effect of precast concrete infill wall on the seismic performance of PCCSW

Lateral stiffness provided by infill walls to the building structures is generally neglected in designs. However, the infill walls, served as the main nonstructural component, have significant influence on the seismic behavior of the main structures during seismic events. To investigate the effects of the infill walls on the seismic behavior of the precast concrete (PC) coupled shear walls (PCCSW) with infill walls, lateral cyclic loading tests were conducted on three PC coupled shear walls, including two specimens with rigid and flexible connections between the PC coupled shear walls and infill walls, and a specimen without infill walls for comparison. The test results showed that the infill walls can improve the strength and stiffness of the PC coupled shear walls but at the cost of the ductility and energy dissipation, especially for the specimen PCCSW with rigid connection. In addition, the finite element analysis (FEA) models of the PC coupled shear walls were proposed, and the reliability and accuracy of the FEA models were validated based on the test results. Subsequently, a parameter study was conducted to assess the influence of the critical parameters on the mechanical behaviour of the shear wall. Finally, the simplified calculation methods for the peak strength of the shear wall were also proposed, and the theoretical results matched well with the test and simulation results.

RIS-Assisted Space-Air-Ground Integrated Networks: New Horizons for Flexible Access and Connectivity

Space-air-ground integrated network (SAGIN) has emerged as a paradigm shifting architecture that offers largescale, flexible wireless coverage and seamless, high-rate connectivity to complement terrestrial communications. Nonetheless, unlocking the potentials of SAGIN is subject to addressing nontrivial challenges associated with their inherent time-variability, self-organization, and heterogeneity. Meanwhile, the concept of reconfigurable intelligent surfaces (RISs) is recognized as a disruptive technology that supports an unprecedented control of electromagnetic waves propagation and potentially offers significant enhancements in spectral efficiency, coverage expansion, and security, all achieved in a low-cost and energy-efficient manner. We anticipate that the integration of RISs into SAGIN will not only play a fundamental role in improving the quality of interand intra- layer communications, but will also provide complex interactions among the three network segments, and hence, opens the horizons for a new breed of applications across all industries. In this article, we explore the underlying opportunities and challenges of integrating RIS-enabled communications into SAGIN, and present a forward-looking overview of the crosslayer operational elements supported by RISs. Finally, we outline major enabling technologies and present a look ahead toward addressing open research issues.

ГИБКИЕ СВЯЗИ: ОСНОВНЫЕ УРАВНЕНИЯ И РАСЧЕТНЫЕ ХАРАКТЕРИСТИКИ.

The article presents a calculation model, which, according to the author, most adequately reflects the work of building elements replaced in the process of engineering analysis by flexible connections. The concept of "mounting extension" of a flexible element is introduced, the value of which fully determines the behavior of the flexible connection after installation. Based on the proposed model, it is possible to obtain the stiffness characteristics of flexible connections for the calculation of building structures using existing CAD systems [1,2].

Approximation algorithms for flexible graph connectivity

Approximation algorithms for flexible graph connectivity

Adaptability of precast concrete external wall panels to steel frame deformation with flexible connectors

A cantilever holder–girth (CHG) flexible connector was proposed for improving the adaptability of precast concrete (PC) external wall panels to the deformation of the steel frame under severe seismic loads. Three specimens of full-size single-span two-story steel frames with PC external wall panels (composite, open-window, and integral) were designed and tested. Low cyclic loading was applied to the steel frame, and a horizontal force was applied to the external wall panels as inertial force. The results showed that the external wall panels with flexible connectors had good adaptability to the deformation of the steel frame. The maximum deformation of the CHG flexible connector reached 27.16 mm even when the external wall panels were subjected to rare earthquakes such as a magnitude 9 earthquake. The displacement angle of the external wall panels was only 0.0026 rad when the steel frame reached a 2.4 % story drift angle.

Nonwoven Polymeric Nanofiber Sheets: Path Forward Toward a New Class of Hybrid Flexible Thermoelectrics

Hybrid flexible thermoelectric (TE) materials are widely being explored for wearable TEs, micro power generators, and self‐powered electronics. The commonly used methods for developing hybrid flexible TE materials are organic–inorganic composite which exhibits low TE performance and second is inorganic material deposition over organic substrate making it a two‐sheet structure that has sustainability concerns. In view of this, herein, a different class of highly flexible hybrid TE materials are designed using a network of electrospun 1D nanofibers (NFs) as a substrate which provides high surface area, better connectivity, and high flexibility. For the proof of concept, the NFs sheets of two polymers polyacrylonitrile (PAN) and cellulose acetate are used to deposit the well‐known Bi2Te3 as a case study. Herein, the directionally aligned PAN‐based NFs sheet exhibits good TE properties leading to the maximum PF ≈51.4 μW m−1 K−2 at 384 K for the P‐400 sample. Herein, the concept of a new class of hybrid TEs is successfully demonstrated by utilizing the flexible NF sheet as a substrate for inorganic TE materials, which will pave the way for sustainable flexible TE. Further, the TE performance can be enhanced by modulating certain factors such as the synthesis conditions of NFs and inorganic material, the thickness of deposition, and so on.

ASSESSMENT OF ORTHOPEDIC TREATMENT LATE RESULTS OF PATIENTS WITH FIXED PARTIAL DENTURES DUE TO THE FUNCTIONAL STATE OF ABUTMENT TEETH

The scientific work highlights the results of an index assessment of the periodontal condition of patients abutment teeth with dentition defects which were replaced with metal-ceramic fixed partial dentures due to partial teeth loss. Since during the preparation of abutment teeth there is sometimes a need for endodontic treatment of them due to medical indications, we investigated the state of the periodontium before, during and after treatment and compared index indicators of pulpless teeth with teeth in which the vascular-nerve bundle was preserved. It was established that the periodontium of the vital tooth recovers and functions much better in comparison with the surrounding dental tissues of a nonvital tooth. Where there are inflammatory changes, which are objectively caused by pronounced swelling and bleeding of the gingival papilla. It is caused due to rubber dam pressure, which in turn is confirmed by reliable data of index indicators determined in various the terms of the treatment.
 After conducting a detailed examination of patients with vital abutment teeth with defects in the hard tissues of the teeth, we found that in the age group of 30-39 years, the most common defect in the hard tissues of the teeth was caries damage, which was observed in 8 patients (72.7%), damage due to injuries was found in 2 patients (18.2%), enamel hypoplasia was found in 2 patients (18.2%).
 Treatment of partial adentia involves the preparation of abutment teeth followed by the manufacture of fixed bridge prostheses. However, the vitality of the abutment tooth should be taken into account and the reserve forces of the periodontium should be taken into account in order to prevent functional overload. It is also necessary to monitor the hygienic condition of the oral cavity during the treatment and at various times after its completion.
 The peculiarity of the proposed method of preparation of vital upper and lower abutment teeth consists in the creation of a champfer on the vestibular surface with the transition to an imitation of a champfer on the oral surface, under constant control of the thickness of the peripulpal dentin using a dentometer with the use of full water cooling and subsequent fixation of provisional crowns. The use of a complex of diagnostic techniques for full control of the effectiveness of treatment during and after prosthetics at different times is substantiated and proposed.
 The gnathodynamometric study was carried out using an advanced device, the VIZIR E1000 gnathodynamometer: the plates placed between the opposing teeth were bitten, as a result of which the load was digitized using a flexible connection through an analog-digital converter and displayed on the display of a computer program, displayed graphically in newtons (N), the time of the masticatory load was also recorded in seconds.
 Using data from clinical indices, it was determined that the preservation of vital teeth is a reliable criterion of the effectiveness of the use of partial fixed prostheses than the use of pulpless teeth. The absence of periapical trauma in vital teeth, which occurs in pulpless teeth due to extirpation of the neurovascular bundle, is demonstrated by the Russel index, and other indices also demonstrate mucosal irritation caused by the use of rubber dams due to the need for quality endodontic treatment.

A Coupled Hydrodynamic–Structural Model for Flexible Interconnected Multiple Floating Bodies

Evaluating the structural safety and seakeeping performance of very large floating structures (VLFS) using the rigid module flexible connector (RMFC) method remains challenging due to the complexity of the coupled hydrodynamic–structural responses in this system. In this study, a coupled hydrodynamic–structural frequency–time domain model is developed based on the RMFC method employing the planar Euler–Bernoulli beam elements to investigate the dynamic responses of multi-module floating systems. To reveal the dynamic characteristics of the systems, the coupled hydrodynamic–structural responses are investigated using a frequency–time-domain numerical model with viscous correction, in which the mass and stiffness attributes of connectors are incorporated into the system. Given the effects of hydrodynamic interaction, consideration is given to the case of three modular boxes connected by flexible beams aligned in series in shallow water to validate the present model. Higher efficiency and accuracy can be found in the system using viscous correction in potential flow theory and introducing state–space model to replace the convolution terms in the Cummins equation for the time domain. Moreover, this model can be extended to a considerable number of floating modules, which provides possibilities to analyze N-module floating systems.

Dynamic responses of serially connected truss pontoon-MOB – A numerical investigation

Very large floating structures (VLFS) are typically made up of several modules of offshore platforms, such as semi-submersibles, connected by mechanical connectors. The proposed Truss Pontoon Mobile Offshore Base (TP-MOB) is a new type of offshore platform based on the truss pontoon semi-submersible design. The design of the connectors is crucial for the functionality of the structure. In this study, the flexible connectors are modeled with a 3D source distribution method and the wave forces are estimated with 3D linear potential theory. The open-source finite element-based numerical model, HYDRAN-XR, is used to analyze the structural responses and connector forces in both regular and irregular wave conditions. The results indicate significant differences in responses between single and multi-module cases, especially in extreme waves. Loads on the connector change greatly for three- and five-module cases, with maximum values at specific wave angles.

Design and Experimental Validation of a Rapidly Deployable Folding Floating Bridge Based on Rigid-Flexible Combination

As a temporary means of water transportation, floating bridges play an important role in the military and other fields. However, traditional floating bridges have limitations such as large size, heavy weight, and slow construction time. In this paper, we propose a rigid-flexible composite folding floating bridge. The main structure of the floating bridge consists of three layers: the bridge deck, airbag, and water bag. The floating bridge units are connected by flexible connectors to allow for pre-connection and folding of the bridge, reducing storage and transportation space, and improving construction efficiency. The proposed floating bridge also has a complete engineering application design and has been checked for safety and reliability (including the strength, buoyancy, and bearing capacity of the connections). We used AQWA software to simulate and analyze the anchorage scheme of the floating bridge and its response to wave loads and conducted a ballast test on a floating bridge model to verify its feasibility as a main bearing body. The results show that the floating bridge we designed has the advantages of being lightweight, having fewer consumables, having a small storage and transportation space, and being able to be constructed quickly.

Influence of gravity connections and damper activation forces on the seismic behavior of steel CBF buildings with dissipative floor connectors

AbstractThis paper investigates the influence of typical gravity connections on the seismic demands of steel concentrically braced frame (CBF) buildings with friction dampers as dissipative floor connectors. The investigated connections include (i) typical shear tab, (ii) clip angle, (iii) flush end‐plate and (iv) shear tab connections with bottom T‐stub. It is shown that the seismic behavior of the gravity framing system (GFS) is practically insensitive to the gravity connection type because the supplemental damping provided by the dissipative floor connectors dominates the seismic response of the GFS. While flush end‐plate and shear tab connections with bottom T‐stub generally exhibit smaller rotational demands than more flexible gravity connections, the resultant lateral drift demands in the GFS are more‐or‐less identical in all cases due to the elastic contribution of the gravity columns. A simplified method is proposed to evaluate the influence of the damper activation forces on the seismic response of multi‐story CBF buildings equipped with floor sliding friction dampers. First, the building is transformed into an equivalent single‐degree‐of‐freedom system. Subsequently, dual graphics called P‐spectra are generated through nonlinear response history analysis. These graphics allow to estimate the peak floor absolute acceleration demands and peak/residual roof displacements of the GFS as a function of the activation forces of the sliding friction dampers. An application example demonstrates that the proposed method can be reliably employed in a pre‐design phase to identify the range of damper activation forces through which an optimal performance of the steel CBF building may be anticipated.

The cellular architecture of memory modules in Drosophila supports stochastic input integration.

The ability to associate neutral stimuli with valence information and to store these associations as memories forms the basis for decision making. To determine the underlying computational principles, we build a realistic computational model of a central decision module within the Drosophila mushroom body (MB), the fly's center for learning and memory. Our model combines the electron microscopy-based architecture of one MB output neuron (MBON-α3), the synaptic connectivity of its 948 presynaptic Kenyon cells (KCs), and its membrane properties obtained from patch-clamp recordings. We show that this neuron is electrotonically compact and that synaptic input corresponding to simulated odor input robustly drives its spiking behavior. Therefore, sparse innervation by KCs can efficiently control and modulate MBON activity in response to learning with minimal requirements on the specificity of synaptic localization. This architecture allows efficient storage of large numbers of memories using the flexible stochastic connectivity of the circuit.

Assessment of Modal Characteristics of Steel–Concrete Composite Girder Bridge with V-Shaped Piers

As the standards of bridge design and construction continue to improve, more and more combination bridges are being put into use. The public’s demand for aesthetically pleasing bridges is also increasing, making it necessary to use the special structure of steel–concrete combinations, continuous V-shaped piers, and continuously stiffened bridges. This structure has the structural and mechanical characteristics of both a continuous girder and a V-shaped pier bridge. The span can be reduced to a certain extent because the support of the V-shaped piers can be applied directly to the main girder. The spanning capacity of the bridge is generally greater than that of a combined steel–concrete girder bridge with vertical piers. The whole bridge is continuous, without expansion joints, making it more stable and safe for traffic. At present, research on this structural bridge type is not yet complete. In this paper, the structural system and dynamic characteristics of this bridge are investigated in the context of real-life engineering. Firstly, the self-vibration characteristics of the three structures were analyzed, and their effects on the self-vibration characteristics were studied by varying the height of the crossbeam at the V-shaped piers’ support, the main beam stiffness, and the V-shaped piers’ stiffness in the three structures. The results show that the increase in main beam stiffness can effectively improve the vertical stiffness of the three structures, with the most obvious effect on structure one and the least effect on structure two; the increase in V-shaped pier stiffness causes a huge improvement in the transverse stiffness of the three structures. Subsequently, a two-unit rod system model of the background bridge was established using the finite element method, and the original model was improved by calculating the equivalent shear stiffness of the shear nail group so that it could simulate the shear joints more accurately. The effects of the shear connectors on the self-vibration characteristics of the steel–concrete combined continuous beam–V-shaped piers and continuous rigid-frame bridge were investigated through theoretical analysis and finite element simulation. It was found that due to the existence of flexible shear connectors, the interface between the steel beam and concrete slab in the combined beam has a slippage effect which causes the deformation to become unsynchronized, and there is a certain difference between vibration patterns. The stiffness of the shear connectors has a certain effect on the self-vibration frequency of the bridge. The damage to the local shear connectors does not have a large effect on the self-vibration frequency of the overall structure, but the damage to the shear connectors at the beginning of the connection between the V-shaped piers and the main beam is greater than that of the other areas. Damage to shear joints should be given special consideration in comparison to other areas.

Experimental and finite element analysis: Out-of-plane mechanical performance of infill walls with flexible connection

Flexible connection between the wall and the frame can improve the seismic performance of the structure, thus minimizing the pushing effect of the infill wall on the main frame. Masonry infill walls with flexible connection have lower out-of-plane stability than walls with rigid connection. However, local collapses are more likely to occur. A comparative study was conducted on the load-carrying capacity, initial stiffness, deformation and ductility of different wall structures based on a monotonous static load test, and the out-of-plane mechanical properties exhibited by flexible masonry infill walls were investigated. A simplified separated finite element model of masonry infill wall was built in accordance with the test results, and then the monotone out-of-plane static loading was performed. The structural configuration, the wall-frame connection method, and the spacing between structural columns were found to have significant effects on the out-of-plane mechanical behavior of the infill wall. The wall structural configuration was found to have the strongest effect, followed by the wall-frame connection method. Under the conditions of flexible connection, when the wall structure was in the “grid-beam” form, and the spacing between structuring columns was 2.5–3.0 m, the frame-infill wall was found with the best restraint effect, so the optimal out-of-plane comprehensive mechanical performance would be achieved.

USE OF FLEXIBILITY IN DISTRIBUTION NETWORKS

The Electricity Market Act stipulates that the distribution system operator is encouraged to use flexibility, including participation in congestion management in distribution network in coordination with transmission system operator, to increase efficiency, develop the distribution system and promote energy efficiency measures. DSO can access flexibility in one or more of the following ways: market-based procurement of flexibility services, distribution network tariffs, flexible (non-firm) connection agreements, rules based (regulated) approach, in combination or separately. The categories are not necessarily mutually exclusive and the inherent regulatory incentives and implemented measures may overlap. Member States and national regulatory authorities should, therefore, carefully evaluate the interactions when implementing new forms of access to flexibilities or when enhancing existing ones. The paper reviews the mentioned possibilities of using flexibility in the distribution network.