Compressed Elements Research Articles

Tapering-enhanced high-efficiency THz waveguide oscillator

Using a waveguide in a THz FEL has been shown to maximize the coupling and enable efficient extraction of relativistic electron beam energy from a single passage through a tapered helical undulator. An oscillator configuration can further boost energy extraction above the single-pass limits and open the door toward very high average power THz sources. Embedding the undulator in an oscillator cavity is particularly useful in combination with high repetition rate electron sources, even if at reduced peak brightness, since recycling a fraction of the radiation as an intense seed can compensate for lower single-pass gain. In this paper, we investigate the efficiency scaling of a tapering-enhanced waveguide oscillator, showcasing its capability for frequency-tuning operation and high-efficiency operation at different wavelengths. Using a thermionic-driven beamline equipped with compression elements, numerical start-to-end simulation results indicate a 16% efficiency at 200 GHz and a 2.1% efficiency at 1.5 THz, resulting in kW-level average power out-coupled in radiation pulses with few hundred μJ energy and tens of MW peak power. Published by the American Physical Society 2024

A compressible semi-resolved computational fluid dynamics-discrete element method coupling model for fluid–solid systems with heat transfer

A compressible semi-resolved computational fluid dynamics-discrete element method coupling model for fluid–solid systems with heat transfer

Reverse design for mixture proportions of recycled brick aggregate concrete using machine learning-based meta-heuristic algorithm: A multi-objective driven study

Construction and Demolition Wastes (CDW) have a significant impact on global waste streams. Brick waste stands out as a prominent type of CDW, and numerous studies have explored its recycling for the creation of environmentally-friendly concrete. Reverse design of recycled brick aggregate concrete (RBAC) mixture proportion is presented in this paper with a focus on four key objectives, that is: compressive strength, cost, and environmental elements (i.e., energy consumption and carbon emission). Based on compiled experimental datasets of 374 samples, the back propagation neural network (BP), random forest (RF), and four meta-heuristic algorithm optimization models were constructed to achieve the desired compressive strength objective. In all machine learning (ML) methods, the compressive strength of RBAC can be predicted with high accuracy, with the SSA-BP (optimized back propagation neural network model using the sparrow search algorithm) model achieving superior results (i.e., NSE=0.91, RPD=3.2). The SSA-BP is therefore used as the objective function for compressive strength. The economic objective is primarily influenced by material costs, and the objective functions of energy consumption and carbon emission are determined by various aspects of production, transportation, and their mixing processes. In order to obtain the optimal RBAC design, the Non-Dominated Sorting Genetic Algorithm (NSGA-III) was implemented considering imperative constraints. Results indicate that cement amount and recycled brick aggregate (RBA)-to-natural aggregate proportion have a positive impact on the compressive strength. The suggested design framework allows for the creation of RBAC composite designs with varying levels of RBA substitution rates and strength targets, providing valuable guidance for tackling the CDW challenge and optimizing RBA usage.

Resistance of compressed elements with small eccentricity taking into account actual height of the compressed concrete zone

Resistance of compressed elements with small eccentricity taking into account actual height of the compressed concrete zone

Tensegrity FlaxSeat: Exploring the Application of Unidirectional Natural Fiber Biocomposite Profiles in a Tensegrity Configuration as a Concept for Architectural Applications

Material selection is crucial for advancing sustainability in the building sector. While composites have become popular, biocomposites play a pivotal role in raising awareness of materials deriving from biomass resources. This study presents a new linear biocomposite profile, fabricated using pultrusion technology, a continuous process for producing endless fiber-reinforced composites with consistent cross-sections. The developed profiles are made from flax fibers and a plant-based resin. This paper focuses on the application of these profiles in tensegrity systems, which combine compression and tension elements to achieve equilibrium. In this study, the biocomposite profiles were used as compression elements, leveraging their properties. The methods include geometrical development using physical and digital models to optimize the geometry based on material properties and dimensions. A parametric algorithm including physics simulations was developed for this purpose. Further investigations explore material options for tension members and connections, as well as assembly processes. The results include several prototypes on different scales. Initially, the basic tensegrity principle was built and explored. The lessons learned were applied in a final prototype of 1.5 m on a furniture scale, specifically a chair, integrating a hanging membrane serving as a seat. This structure validates the developed system, proving the feasibility of employing biocomposite profiles in tensegrity configurations. Furthermore, considerations for scaling up the systems to an architectural level are discussed, highlighting the potential to enhance sustainability through the use of renewable and eco-friendly building materials, while promoting tensegrity design applications.

A new hold-down device for seismic applications in CLT buildings: Design, testing, analytical and numerical assessment

An hold-down device was designed and tested experimentally for seismic applications (Seismic Hold-Down, SHD). The magnitude of axial strength as well as the up-lift displacement capacity is mainly oriented to cross-laminated-timber (CLT) buildings with medium-to-high ductility. There is consensus in the design practice of hold-down devices for promoting, as dissipative mechanism, flexural yielding of the dowel-type connectors (e.g. nails, screws) combined to timber’s embedment. Few are the applications aiming at hold-down’s optimization as it emerges from up-to-date literature review. In this framework, SHD was conceived such that tension break-out of steel was promoted at a reduced segment (fuse) of the vertical flange. In the context of capacity design, a convenient overstrength was assumed for other failure mechanisms, e.g. anchor’s pullout, laterally-loaded steel-to-timber connection, shear-plug of timber. The mechanical response under axial load was consistently predicted by an application of the component method, i.e. global stiffness and strength were analytically-derived using simplified series of non-linear mechanical springs. Three-dimensional finite elements model was employed to investigate buckling of the fuse which might occur, during cycles, when up-lift displacement is recovering. In practical circumstances, it is recommend to design SHD devices of a CLT wall similarly to diagonal elements of steel bracings, i.e. neglecting the contribution of the compressed element. Finally, SHD is compared to traditionally-designed hold-down, which mostly dissipates (and fails) at steel-to-timber connection. Overall hysteretic response is somehow similar, although the inelastic mechanisms involved are different. For example, both the devices show pinching during cycles which for SHD is mainly caused by buckling of the fuse while, for traditional hold-down, is dominated by timber’s embedment.

Research of strength of unaxial compressed concrete elements reinforced with FRP

Research of strength of unaxial compressed concrete elements reinforced with FRP

Effect of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete structures

Introduction. Using loop joints of working reinforcement in flexural reinforced concrete members reduces labor costs when installing reinforcement cages at the construction site. However, the analysis of the available research showed that they were carried out mainly for flexural members. In this regard, additional experimental studies were carried out to assess the effect of various types of design solutions of loop reinforcement joints on the strength of normal sections of eccentrically compressed reinforced concrete elements.Aim. To obtain the results of experimental studies and assess the effect of design solutions of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete elements.Materials and methods. The research involved the results of tests of eccentrically compressed reinforced concrete elements with loop joints of working reinforcement. As part of the research, 7 series of samples with different design solutions of loop joints were tested. The total number of samples in the research comprised 22 items.Results. The research revealed the effect of design solutions of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete elements – on average from 3 to 14 %, depending on the design solution of the loop joint.Conclusions. It was found that the design of eccentrically compressed elements should be carried out taking into account the design of the loop joint of longitudinal reinforcement.

The Influence of Using Steel Tapes and Composite Materials on Reinforcing Hot-Rolled Steel Profiles.

Steel structure designers frequently encounter the need to reinforce hot-rolled compressed steel elements. This is particularly common in the case of compressed truss bars in steel truss girders. Typically, reinforcement is designed using bars or flat bars welded to the compressed element. However, welding technology is not always feasible in existing and operational steel halls due to fire safety concerns. To address this challenge, researchers investigated alternative reinforcement methods using bonded steel and CFRPs (carbon fiber-reinforced polymers/plastics) tapes. Laboratory tests and numerical analyses were conducted. Eleven 1.5 m long specimens made of 50 × 50 × 4 angle iron from S235 steel were subjected to axial compression testing. The test samples included three unreinforced samples, three samples reinforced with steel tape bonded using SikaDur-30 adhesive, and five samples reinforced with CFRP tape (SikaDur-30 adhesive was used for bonding in three cases, and 3M VHB GPH-160GF tape in two cases). The research conducted indicates that reinforcement using bonded steel tapes is the most effective method for limiting vertical displacements and deformations, as well as increasing the load-bearing capacity of the tested angles by 28.6% compared to the reference elements. Considering the high cost of composite tapes, this is valuable information from an economic analysis perspective. The absence of steel tape delamination suggests that the bonding technique can be successfully employed in this reinforcement method and can replace welding, for example in facilities where there is a high fire hazard.

Creep damage constitutive model of rock based on the mechanisms of crack-initiated damage and extended damage

Since the classical element model cannot describe the nonlinear characteristics of rock during the entire compressive creep process, nonlinear elements and creep damage are generally introduced in the model to resolve this issue. However, several previous studies have reckoned that creep damage in rock only occurs in the accelerated creep stage and is only described by the Weibull distribution. Nevertheless, the creep damage mechanism of rocks is still not clearly understood. In this study, a reasonable representation of the damage variables of solid materials is presented. Specifically, based on the Gurson damage model, the damage state functions reflecting the constant creep stage and accelerated creep stage of rock are established. Further, the one-dimensional and three-dimensional creep damage constitutive equations of rock are derived by modifying the Nishihara model. Finally, the creep-acoustic emission tests of phyllite under different confining pressures are conducted to examine the creep damage characteristics of phyllite. And the proposed constitutive model is verified by analyzing the results of creep tests performed on saturated phyllite. Overall, this study reveals the relationship between the creep characteristics of rocks and the corresponding damage evolution pattern, which bridges the gap between the traditional theory and the quantitative analysis of rock creep and its damage pattern.

Mechanical properties of porous concrete during compression

Results of the experimental studies of the force resistance and deformation of compressed elements from porous concrete of 1200-1600 kg/m3 density of various structural modifications (fine grain and micro grain) are presented. On the basis of research date, mechanical properties are complexly characterized; a criterion number of strength and deformation characteristics of porous concretes with due regard for the influence of longtime processes due to concrete hardening and external force factors is proposed. On the basis of data on the long-term resistance of porous concrete and change in its strength in time, calculation characteristics and coefficients of operation conditions of porous concrete are established for calculation and design of structures. It is shown that according to structural indicators, porous concretes meet normative requirements and occupy the intermediate place between cellular and light concretes of equal strength with porous fillers.

Constitutive model of MWCNTs/PDMS composites considering volume change and electromechanical response characteristics under impact load

Multi-walled carbon nanotubes/polydimethylsiloxane (MWCNTs/PDMS) composites have excellent electromechanical conversion ability which can be applied in the field of intelligent sensing. However, the volume changes and electromechanical response mechanism of MWCNTs/PDMS under dynamic load remain unclear. In this paper, the electromechanical response of MWCNTs/PDMS with different mass ratio of MWCNTs are studied by quasi-static compression, SHPB experiment and finite element numerical simulation. The quasi-static compression results show that volume ratios of MWCNTs/PDMS are decreased with compression strain (0.845 when strain is 0.5), then, the Yeoh hyperelastic constitutive model is established considering volume change. When the mass ratio of MWCNTs is 1 wt%, MWCNTs/PDMS shows the best mechanical properties. The stationary phases of strain rate of MWCNTs/PDMS decrease with increasing of impact velocity, showing obvious viscoelastic mechanical properties. The impact induced voltages of MWCNTs/PDMS are generally larger than PDMS (10∼15 m/s). The flexoelectric effect of MWCNTs/PDMS under impact is further studied based on numerical simulations. The results show that the strain gradients are within 10−2∼10−1 m−1, the related flexoelectric coefficients are within 10−10–10−9 C/m. In summary, this study can further expand the application of MWCNTs/PDMS in the field of intelligent sensing.

EFFECTS OF LIGAMENT MODELING APPROACHES ON LOAD TRANSFER AND RANGES OF MOTION IN AN INTACT LUMBAR SPINE: A FINITE ELEMENT INVESTIGATION

The complex biomechanics of the lumbar spine and its associated structures have been studied using finite element (FE) analysis. Several FE studies used simplified approaches to model the spinal ligaments, assuming that the significant effect of spinal ligaments is on the ranges of motion (ROM) rather than stress–strain distributions on the vertebral body. A comparison of different ligament configurations (tension-only and tension & compression) and their effects on ROM and stress–strain distribution is necessary to verify the above assumption. In this study, an FE model of the L1-L5 lumbar spine was developed and analyzed for three different cases of physiological movements (flexion, extension, and lateral bending). It was found that the spinal flexibility was almost equally constrained by both ligament configurations. The variation in ROM observed for tension-only ligament and tension & compression ligament model ranged between 0.5∘ and 4∘ under all loading cases. However, no considerable changes were observed in stress–strain distributions. The findings of this study indicate that assuming the impact of ligaments only in restricting the ROM is reliable and two-node tension-only or tension & compression elements are useful to model the spinal ligaments in FE studies.

Size effect on compressive behavior of GFRP bars

In the last three decades, studies investigating the use of Glass Fiber Reinforced Polymer (GFRP) bars as an alternative to conventional steel rebars have increased due to their corrosive resistance. In addition to corrosion resistance, GFRP bars utilize high specific tensile strength, which makes them highly desirable in civil engineering applications. However, major design guidelines for GFRP-reinforced concrete structures currently do not consider their compressive contribution. Nevertheless, there is a growing trend in utilizing GFRP bars as compressive elements, driven by various studies demonstrating their ability to bear compressive loads effectively. This increasing demand underscores the need to comprehend the mechanical properties of GFRP bars, particularly in terms of their compressive behavior. Furthermore, a standardized test method to evaluate their compressive properties has not yet been developed. Addressing these gaps, this research paper focuses on investigating the influence of specimen size on the compressive strength of GFRP bars, specifically emphasizing on the compressive properties of GFRP bars. Compressive tests were conducted on GFRP specimens with varying diameters while maintaining a constant slenderness ratio. The findings from these compression tests shed light on the critical role of size in the compressive behavior of GFRP. This research emphasizes the importance of considering size as a significant parameter in designing mechanical properties for GFRP reinforcements.

Analysis of the Adherent Cell Response to the Substrate Stiffness Using Tensegrity.

Cell's shape is dependent on the cytoskeleton mechanical properties. Hybrid models were developed that combine the discrete structure for the cytoskeleton and continuum parts for other cell organelles. Tensegrity-based structures that consist of tensile and compression elements are useful models to understand the cytoskeleton mechanical behavior. In this study, we are looking to examine the reaction of the cell to a variety of substrate stiffnesses and explain the relationship between cell behavior and substrate mechanical properties. However, which tensegrity structure is appropriate for modeling a living cell? Is the structure's complexity play a major role? We used two spherical tensegrities with different complexities to assess the impact of the structure on the cell's mechanical response versus substrate's stiffness. Six- and twelve-strut tensegrities together with membrane, cytoplasm, nucleoskeleton, and nucleus envelope were assembled in Abaqus package to create a hybrid cell model. A compressive load was applied to the cell model and the reaction forces versus deflection curves were analyzed for number of substrate stiffness values. By analyzing the difference due to two different tensegrities it became clear that the lower density structure is a better choice for modeling stiffer cells. It was also found that the six-strut tensegrity is sensitive to higher range of substrate stiffness.

A metaheuristic‐based method for analysis of tensegrity structures

SummaryTensegrity systems are construction system that offers solutions for lighter designs compared with a standard truss system consisting of tension and compression elements. Due to their structure, they are recommended in the design of space structures due to the use of lighter and easy‐to‐assemble structural elements such as cables, ropes, and similar to provide the desired durability. In this study, energy minimization was carried out to solve the structural element displacements. It is expected to reduce the total potential energy of the system with minimization. By minimizing the total potential energy of the tensegrity system models, the displacement of each building element is found for the equilibrium condition. Tensegrity models were analyzed by minimizing energy via the adaptive harmony search (AHS) algorithm. In this research, two distinct tensegrity structure specimens were employed. One comprised a cantilever beam, while the other adopted a cyclic model, forming eight equal octagons from eight nodes at both the base and the top. Additionally, an examination was conducted on a two‐layer iteration of the cyclic model. The method is robust for both space and planar tensegrity structures, allowing the determination of deformed shapes under various loads without design assumptions. The TPO/MA method demonstrates superiority in handling nonlinear and barely stable systems, as evidenced by examples illustrating its efficacy in maintaining structural form under increasing loads and challenging conditions.

Determining Compressed Concrete Element Limit States Based on the Widths and Depths of Cracks Caused by Transverse Deformations.

In the modern theory of compressed concrete elements, the most attention is paid to longitudinal deformations, whereas transverse ones are rarely considered and just within Poisson's coefficient limits (i.e., elastic concrete behavior in the transverse direction). However, transverse deformations significantly develop beyond the limits corresponding to Poisson's coefficient, where they lead to longitudinal crack initiation and development. In-depth experimental and numerical investigations of transverse deformations in the inelastic stage showed that it is necessary to consider crack propagation. The present study proposes simultaneous consideration of longitudinal and transverse deformations, as well as the appearance of cracks and their widths and depths. This allowed us to obtain a complete compressed concrete element behavior pattern at all performance stages in two types of limit states (based on longitudinal and transverse deformations). Consequently, new ultimate limit states by the depth and width of cracks caused by transverse deformations are proposed to be included in modern design practices and codes.

Optimal data compression for Lyman-α forest cosmology

ABSTRACT The Lyman-α three-dimensional correlation functions have been widely used to perform cosmological inference using the baryon acoustic oscillation scale. While the traditional inference approach employs a data vector with several thousand data points, we apply near-maximal score compression down to tens of compressed data elements. We show that carefully constructed additional data beyond those linked to each inferred model parameter are required to preserve meaningful goodness of fit tests that guard against unknown systematics, and to avoid information loss due to non-linear parameter dependences. We demonstrate, on suites of realistic mocks and Data Release 16 data from the Extended Baryon Oscillation Spectroscopic Survey, that our compression approach is lossless and unbiased, yielding a posterior that is indistinguishable from that of the traditional analysis. As an early application, we investigate the impact of a covariance matrix estimated from a limited number of mocks, which is only well conditioned in compressed space.

TENSEGRITY INSIGHTS: UNRAVELING THE MECHANICAL BEHAVIOR OF SUBCELLULAR ORGANELLES THROUGH A 3D FINITE ELEMENT MODEL STUDY

This study delves into the intricate mechanical behavior of subcellular organelles by employing a sophisticated 3D finite element model that embraces the principles of tensegrity structures. Tensegrity, a structural concept characterized by a balance of tension and compression elements, has been increasingly recognized as a crucial framework for understanding the dynamic nature of cellular components. Through our computational approach, we explore the biomechanical responses of subcellular organelles, shedding light on their structural integrity, deformation patterns, and overall mechanical functionality. The insights gained from thisstudy contribute to the growing understanding of cellular biomechanics, offering potential applications in fields such as cell biology, bioengineering, and medicine.

An Investigation of the Antimicrobial Efficacy of a Nonwoven CMC PHMB Dressing and the Ability of the Dressing to Absorb Wound Slough

Objective. To conduct an in vitro investigation into the slough absorption and retention attributes of a gelling fiber dressing composed of CMC fibers and PHMB (Dressing A), and to assess its antimicrobial efficacy under compression. Materials and Methods. Dressing A is indicated for use with secondary dressings or bandaging, and conditions that replicate this compression element were applied. Dressing A was compared with 5 other dressings. Antimicrobial efficacy testing was conducted over a 7-day challenge period. Results. Dressing A absorbed an average of 33 g/100 cm2 per sample of viscous solution, 28% more than the other dressings tested. A greater than or equal to 6-log reduction of all microorganisms tested was achieved within 168 hours with Dressing A. Conclusion. The CMC PHMB gelling fiber dressing is able to absorb and retain viscous solutions (simulated slough). The antimicrobial efficacy of the dressing under compression was demonstrated by total eradication of all microorganisms tested.