Cross-sectional Configuration Research Articles

Numerical investigation on thermal-hydraulic performance of variable cross section printed circuit heat exchanger

CO2 transcritical power cycle (CTPC) systems have attracted considerable research focus in the fields of thermoelectric conversion and waste heat recovery. The regenerator is a key component affecting the CTPC system's efficiency. To improve the comprehensive performance of the regenerator, extensive research has been conducted to optimize the regenerator flow channel design. However, the optimization of the traditional Z-channel printed circuit heat exchanger structure (ZPCHE) is limited to constant cross-sectional configurations along the flow direction, which can lead to low channel space utilization. To solve this problem, an efficient variable cross section Z-channel structure (UAPCHE) is proposed in this study. The structure is designed with different cross-sectional shapes along the flow direction to fit the flow path of the main fluid. UAPCHE achieves a coordinated optimization of the heat transfer (Nu), flow (dP), and compactness performance (Q/V) by increasing the effective utilization of the channel space and weakening the damage to the fluid boundary layer. The design principle of the UAPCHE is introduced, and based on this, the structural parameters of the UAPCHE are optimized to achieve the best comprehensive performance. The results show that, compared with the ZPCHE, Nu of UAPCHE can be increased by 16.79%, dP can be reduced by 19.48%, and Q/V can be increased by 22.65%.

Crashworthiness analysis of Dragonfly inspired tubes under multiple load cases

Nature's creatures have developed remarkable geometric structures for environmental adaptation. Dragonflies have evolved a rapidly flipping symmetrical four-wing system to enhance hunting efficiency. Inspired by the unique double-symmetric wing structure of the dragonfly, a group of multi-cell elliptic tubes (METs) are developed to enhance the energy absorption capacity of thin-walled tube for multiple load cases. The finite element models of MET with different cross-sectional configurations are established and validated by quasi-static axial crushing tests. The crashworthiness of MET under different load angles θ have been explored and extensively studied by simulation method through LS-DYNA. The results indicate that the crashworthiness of MET could be influenced by the number of basic corner elements. Moreover, MET demonstrates higher energy absorption efficiency in oblique compression as compared to axial compression. Theoretical models of axial and oblique compressions are developed to predict the mean crushing force, which are obtained by summarizing the deformation modes of MET and employing simplified super folded unit theory. Finally, multi-objective particle optimization (MOPSO) algorithm is adopted to explore the MET crashworthiness optimization under oblique impact, with peak crushing force (PCF) and specific energy absorption (SEA) as targets and geometric parameters L, α, F and thickness t regarded as design variables. A new knee-point selection method is used to select MET from the pareto set of solutions of different schemes. The results show that different weight coefficients have great influences on the optimization results and further study is needed.

Bending and Vibration Behaviour of CLT-Steel Composite Beams

A strengthening of cross-laminated timber (CLT) by a composite effect with steel girders can widen the application of CLT ceilings to spans over 8 m. Most possible shear connectors are not stiff enough to ensure a completely rigid composite. At present, it has not been sufficiently clarified how the elastic bending behaviour is affected by the influences of the flexibility of continuously and discontinuously shear connectors, the number of transverse layers of the CLT and the span width. Thus, 4-point bending tests and vibration tests were performed with different cross-section configurations and two different shear connectors in continuous and discontinuous spacing in spans of 8.10 and 10.80 m. To date, no comparable bending tests have been carried out in these spans, with more than five CLT-layers and discontinuously arranged shear connectors. The composite beams deformed linear-elastically until the yield strength of the steel was reached. The composite effect increased the elastic bending stiffness up to twofold compared to no composite. Increasing the span resulted in a higher bending stiffnesses. The elastic bending stiffness of the composite beams with shear studs was significantly lower than with fully threaded screws. For a worthwhile composite effect, both materials should contribute a balanced share of the stiffness. A larger share of the CLT in the bending stiffness compared to the steel girder created a higher elastic limit load capacity but an equivalent bending stiffness. It is necessary to discuss which cross-sectional configurations are appropriate in terms of load bearing capacity, economic efficiency and sustainability. To assess the practical application potential in spans between 8 and 12 m, the tests were additionally evaluated for the equivalent load level for the serviceability limit state of office or industrial buildings. For spans of 8.10 m, the limits according to EC5 for the initial deflection of L/300 and fundamental frequency of 8 Hz can be met. For spans of 10.80 m, only less strict deflection limits are achieved. However, by increasing the degree of composite through more shear connectors, compliance with the limit values mentioned could already be possible with the cross-sections tested. In case of fire, it may be sufficient to consider only the CLT with the reduced cross-section method (EN 1995-1-2) for load transfer, even for longer fire durations.

Crashworthiness analysis of novel cactus-inspired multi-cell structures under axial crushing

This study introduces an innovative cactus-inspired bionic tube (CBT) designed for enhanced energy absorption, drawing inspiration from the ribbed structure of cacti. Validation is achieved through quasi-static crushing experiments, confirming the numerical model's accuracy. Numerical simulations investigate critical factors, including structural mass, wall thickness, loading velocity, and cross-sectional configuration, revealing that proper cross-section design can boost the specific energy absorption (SEA) of the original CBT by 15.84 %. Additionally, a theoretical model is developed to forecast the mean crushing force of CBTs. Comparative analysis demonstrates the superior crashworthiness of CBTs over contemporary bionic and widely adopted multicell structures with the same mass, achieving a remarkable SEA of 11.44 J/g—exceeding maximum and minimum SEA values of these structures by 28.3 % and 127.9 %, respectively. This research significantly contributes to advancing the development of high-performance bionic energy-absorbing structures for crash applications.

Performance of seawater sea sand concrete-filled bimetallic tube (SSCFBT) stub columns under axial partial compression

This study presents the experimental findings on the mechanical performance of circular seawater sea sand concrete (SSC)-filled bimetallic tube (SSCFBT) stub columns under axial partial compression. The proposed cross-sectional configuration of the bimetallic tube consists of an external layer fabricated with carbon steel and an inside layer fabricated with stainless steel, by doing so to prevent the chloride ions in SSC from corroding the external carbon steel tube-layer. Axial partial compression tests are conducted on twelve SSCFBT specimens with steel endplates and six counterparts without endplates, and the corresponding parameters include the partial compression area ratio, endplate thickness, and specimen dimensions. The test findings suggest that the two layers of the bimetallic tube exhibit effective composite actions and the SSCFBT stub columns show favorable load-carrying capacity and ductility. The effects of various parameters on the failure mechanism, load-deformation relationship, load-carrying capacity, and strain development of SSCFBT stub columns are analyzed. Finally, the suitability of using different available design codes for conventional concrete-filled steel tubes (CFST) to predict the axial partial compressive strength of SSCFBT stub columns is evaluated.

Aerodynamic Characteristics of Circular and Noncircular Cross-Sectional Missile Configurations

This paper summarizes an investigation of the aerodynamic performance of missile configurations with axisymmetric and nonaxisymmetric cross sections. Configurations have either a circular, oval, pentagonal, triangular, or square cross section and were tested at three different flight conditions: Ma=1.17 and Reynolds number per inch of 3.88×105, Ma=2.49 and Reynolds number per inch of 6.88×105, and Ma=4.33 and Reynolds number per inch of 8.74×105. The influence of Mach number, shape, and fin deflection was investigated. A prescribed body motion was used to expedite the prediction of the missile aerodynamic forces and moments at different angles of attack compared to many static computational fluid dynamics simulations. The results show that the oval missile model is the most aerodynamically efficient body at all the tested speeds. At higher speeds, all nonstandard configurations produce more normal force and better aerodynamic efficiency than the circular body. The triangular configuration is much less stable than the other models.

Numerical investigation on energy absorption characteristics of impact-resistant lightweight structure of bio-mimetic micro aerial vehicle

With the increasing development of micro aerial vehicle, the impact resistance of the structure has gradually become a research hotspot. The beetle's exoskeleton not only provides important protection for its body and flexible wings but also ensures its good flight performance. Therefore, the beetle's exoskeleton has become an important research content in the field of bio-mimetic micro aerial vehicles. In this study, taking the internal structure of the beetle's exoskeleton as the research object, a kind of bio-mimetic lightweight thin-walled impact-resistant structure that can be used in the micro aerial vehicle is proposed. The energy absorption characteristics of the bio-mimetic structure under axial impact loading are calculated and analyzed by the numerical simulation method, and the important parameters such as impact angle, protective layer thickness, and wall thickness are optimized and discussed. The main results include that the filling method of the hollow column has a certain correlation with the energy absorption characteristics of the structure under different impact angles, and among the different cross-sectional shapes, the hollow column with a circular cross-sectional configuration has the best energy absorption ability. In addition, as the internal space of the structure increase exponentially, the decrease of specific energy absorption value of the bio-mimetic structure is relatively small. Finally, the wall thickness with good energy absorption characteristics is about 1.5 mm, while the preferred span length of the structure is between 90 and 120 mm.

Analysis of optimized combined microchannel and heat pipes for electronics cooling

In this work, innovative heat sink designs consisting of Microchannel Heat Sinks (MCHS) and Flat Plate Micro Heat Pipes (FPM-HP) are investigated to improve thermal management in electronic components. The three-dimensional finite volume method is used to analyze the fluid flow and heat transfer in the heat sinks. The validity of the numerical models is confirmed by comparison with pertinent experimental data. The thermal performances of the new heat sink designs are compared to that of double-layer microchannel heat sinks with parallel flow (DLPF MCHS) and counter flow (DLCF MCHS) configurations, as two of the more efficient heat sink designs in the industry. The investigated configuration of Silicon-Water Counter Dual MCHS with rectangular cross-section improves the temperature uniformity by 43–50 % and 26–31 % compared to DLPF and DLCF MCHSs, respectively, and the triangular cross-section configuration improves it by 38–47 % and 21–26 %, respectively. The thermal resistance of heat sinks is reduced by 10–15 % compared to DLPF MCHS and by 2–8 % compared to DLCF MCHS. Additionally, innovative hybrid heat sink designs combined with MCHS and FPM-HP are proposed to optimize hotspot management in electronics cooling applications that involve local high heat generation. The hybrid DLPF MCHS & FPM-HP reduces the maximum temperature and surface temperature gradient of the heat sink by 13–23 % and 20–49 %, while these are reduced by 16–40 % and 27–64 % for the hybrid DLCF MCHS & FPM-HP compared with the corresponding copper base (no heat pipe) designs. The hybrid Counter Dual Rectangular MCHS & FPM-HP reduces the maximum temperature and surface temperature gradient of the heat sink by 15–24 % and 29–65 % compared with the DLCF MCHS with copper base (no heat pipe) design, while these are reduced by 10–26 % and 24–63 % for the Counter Dual Triangular MCHS, respectively.

Switchable photothermal conversion efficiency for reprogrammable actuation

Reprogrammable soft matter brings flexibility to soft robots so that they can display various motions, which is flourishing in soft robotics. However, the reprogramming of photoresponsive materials used in soft robots is time-consuming using existing methods. In this study, we promote a strategy for rapid reprogramming via switchable photothermal conversion efficiency (PCE). The liquid crystalline elastomers doped with semiconductor bismuth compounds (Bi-LCE) used in this work exhibited large photothermal actuation with over 35% shrinkage in 5 s at high PCE state, which demonstrated little deformation at low PCE state. Furthermore, the material was capable of being reprogrammed up to 10 times, with only 20 min required for one PCE reversible switch. Based on this switchable PCE effect, the same Bi-LCE film displayed various shape changes through different programmable pattern. Additionally, a reprogrammable hollow tube made of PCE reprogrammable materials could tune the diameter, cross-section configuration, and surface morphology, which was crucial for microfluidics field. Reprogrammable materials provide endless possibilities for reusability and sustainability in robotics.

Fast Probing Amyloid Polymorphism via Nanopore Translocation.

Neurodegenerative diseases are characterized by the presence of cross-β-sheet amyloid fibrils and a rich mesoscopic polymorphism, requiring noninvasive detection with high fidelity. Here, we introduce a methodology that can probe via a sensitive synthetic nanopore the complex polymorphism of amyloid fibrils by an automated and fast screening protocol. Statistically analyzing the translocation events on two model amyloid systems derived from β-lactoglobulin and lysozyme allows extracting the cross-sectional configuration of hydrated amyloid fibrils from current block amplitude and correlating dwell time with fibril length. These findings are consistent with the amyloid polymorphs observed in solution by atomic force microscopy. Furthermore, the ionic current signal of a single translocation event can reveal abnormally aggregated conformations of amyloid fibrils without potential artifacts associated with microscopy methods. This study introduces an effective approach to physically discriminating and separating amyloid and may serve in the rapid diagnosis of early aggregating pathological amyloidosis.

Hamel's field variational integrator for simulating dynamics of thin-walled geometrically exact beams with warping effects

Using discrete variational principle, a Hamel's field variational integrator (HFVI) for simulating dynamics of thin-walled geometrically exact beams with warping effects is originally proposed. Firstly, a spacetime independent interpolation way for thin-walled beam elements is established on SE(3) × R space by using Hamel's formalism. Then, a new discretization formulation of convective velocity and convective strains on Lie algebra is proposed by using frame operators, which helps to reduce the system's nonlinearity. After that, the variations of discrete convective velocity and discrete convective strain are decoupled from the cross-section configuration variables. This way can avoid the computation of nonlinear exponential map's tangent map and reduce the computation complexity significantly. According the Hamiltonian form of proposed HFVI, the warping variables and discrete convective strains can be independently solved by using discrete compatibility equations on Lie algebra. Finally, the efficiency and accuracy of HFVI is validated by six static and dynamic examples.

A simplified analysis of a configuration of geosynthetic reinforcement in GRPS embankments

Geosynthetic-reinforced and pile-supported (GRPS) embankments are increasingly used in recent years to reduce the differential settlement and increase the bearing capacity of the embankments. A new theoretical model is proposed to calculate the tensile force distribution and cross-sectional configuration of the geosynthetic reinforcement used in the Geosynthetic-reinforced and flexible pile-supported GRRPS and Geosynthetic-reinforced and rigid pile-supported GRFPS embankments. The accuracy of the proposed methods is verified by the results from laboratory model tests, centrifuge model tests and theoretical models in the literature. It is found that the tensile forces along the geosynthetic are distributed unevenly both in GRRPS and GRFPS embankments with the maximum and minimum magnitudes located at the edge and centre of the pile cap, respectively. The soil arching effect contributes more to the bearing capacity of the GRPS embankment than the membrane effect. It is found through the analyses of the centrifuge and model tests data that the soil arching effect contributes 65–75% of the total load transfer efficiency.

A new approach to the stability design of Ramberg–Osgood material struts

An energy formulation employing total potential energy principles is presented to derive a governing equation for strength predictions of struts made from materials following the Ramberg–Osgood constitutive law such as stainless steel, cold-formed steel, and aluminium alloys. The formula is generic and applicable to arbitrary cross-sections and all strut slendernesses for which flexural buckling is critical. Extensive comparisons against experimental data on square and rectangular hollow section struts as well as finite element simulations demonstrate the accuracy of the developed formula, while the effect of varying material parameters is examined through comprehensive parametric studies. Owing to its simplicity and its derivation based on mechanical principles, arbitrary configurations of material parameters and cross-sections can be analysed, making the formula suitable for use in design practice, representing effectively a non-iterative alternative to the widely accepted design load employing the tangent modulus. With the aid of the formula, new column buckling design provisions are developed, which show excellent agreement with experimental data and meet the reliability requirements specified within the structural Eurocodes.

Dry reforming of methane using a novel microreactor fabricated from stacking of stainless steel wire-mesh support catalysts

We fabricated a novel microreactor with stainless steel wire-mesh supports coated with Ni-based hydrotalcite catalysts for dry reforming of methane (DRM) reaction. Catalytic performance and long-term stability of microreactor was tested by stacking the stainless steel wire-mesh support catalysts to allow parallel and cross-sectional flow to stacking configurations. Conversion rates of CH4 and CO2 were measured and found to be 92% and 95% respectively, and syngas ratio of 0.92 was obtained. Only a small decrease of about 3–4% in conversion rates was observed after 100 h of reaction which could be due to whisker like carbon formation as carbon nanofibers (CNFs). Investigation of spent catalysts revealed that surfaces of support catalysts were not fully covered with CNFs, leaving active sites for reactant gases with little effect on long-term stability. In addition to CNFs, in situ formation of γ-Al2O3 flakes were obtained during long-term DRM reaction from the parent FeAl powder that was used for annealing of stainless steel wire-mesh supports to increase the adhesion of hydrotalcite-derived spinel catalysts. Effect of γ-Al2O3 flakes on microreactor's performance turned out to be very useful because sites of γ-Al2O3 flakes further prevented the deposition of carbon on surface and acted as active sites for reactant gases. Moreover, stacking of stainless steel wire-mesh support catalysts for parallel and cross-sectional flow configurations caused the better mixing of reactant gases due to the tortuosity of the narrow porous microstructure of the support. The excellent throughput was verified by numerical calculations using CFD simulations.

Performance Analysis of Variable Cross-Section TEGs under Constant Heat Flux Conditions

In this paper, five shapes of thermoelectric generator (TEG) models (cylindrical, barrel shaped, hourglass shaped, cup shaped, and inverse cup shaped) are built under the boundary conditions of heat flux at the hot end and convection at the cold end of the TEGs. Based on the numerical simulation results, the configuration of the variable cross-section can effectively boost the performance of TEGs. Remarkably, the hourglass-shaped TEG generated the maximum output power and efficiency, which were 69.62% and 70.96% higher than that of the conventional cylindrical TEG, respectively. The results indicate that the hourglass shape is beneficial to enlarge the temperature difference between the two ends of the TEG, which results in performance improvement. In addition, the effects of heat flux and convection on the performance of TEGs are explored and discussed. After choosing the appropriate boundary conditions, the relationships between the maximum output power and efficiency and the shape factor of the hourglass-shaped TEG are obtained according to the fitting results. Finally, some conclusions are drawn to provide guidance for TEG applications.

An efficient technique in dynamic modeling and analysis of soft fluidic actuator

Soft actuators with embedded fluidic channels are promising for soft robotics, but their continuous nature presents challenges in accurate and efficient modeling. Existing studies on dynamic behavior have shown that both approximate and exact methods have limitations in accurately predicting the deflection of soft actuators. Additionally, conventional methods require experimental parameter extraction for each individual actuator. To address these challenges, we propose a modified analytical method and use finite element analysis as the defined correction functions to improve accuracy and computational efficiency, providing a promising tool for the design and control of soft robotic systems. In this work, we propose a solution methodology for simulating the dynamic behavior of fluidic soft actuators, which are widely used in soft robotics applications. Our approach takes into account the cross-sectional geometry and the number of channels in the actuator’s configuration. By scrutinizing various fluidic actuation designs, we can deduce the most suitable cross-sectional configuration for optimal performance. Compared to existing analytical methods, our approach is more accurate and does not require additional calculation time. As the method is adaptable with experimental models, it can be used to design and optimize soft actuators while can be refined and improved through experimental model updating.

Bending performance of nail-laminated bamboo-timber panels made with glubam and fast-grown plantation Chinese fir

This study attempts to develop a novel structural nail-laminated panel constructed of engineered bamboo and local fast-grown plantation Chinese fir. An experimental program is reported in this paper on static bending behaviors of such nail-laminated bamboo-timber (NLBT) panel. Twelve NLBT specimens, including five short span specimens without butt joints and seven long span specimens with different butt joints were manufactured and tested. The panel span, species of sawn timber boards, the cross sectional configuration, and reinforcement measures of butt joints were chosen as the experimental parameters in the current investigation. The typical failure mode of the short span NLBT panels exhibited a multiple-fracture process caused by the tension failure of timber layers, while the overall collapse was much delayed or avoided attributed to the residual bending capacity provided by glubam layers. Test results demonstrate that the use of fast-grown Chinese fir instead of imported dimension lumber to combine glubam does not obviously reduce the bending performance of NLBT panels. The proposed vertical nailing reinforcement for butt joints can significantly improve the bending stiffness of the long span NLBT panels, and it is convenient for processing and assembling of NLBT components. Based on the ratio of bamboo and timber, a simple linear relationship is proposed for predicting the elastic modulus of the NLBT through regression analysis. The observed performance evaluation also reveals that the bending performance of the proposed NLBT structural panels is sufficient to meet the design requirements for using as the structural floors in offices and residential buildings. This research provides a feasible and reasonable approach for developing local fast-grown species as structural components.

Additional Fire Exposure Time for the Effect of Spalling in Reinforced Concrete Columns

AbstractConcrete exposed to fire can experience spalling when the pore pressure increases due to water evaporation resulting in damage to part of the concrete cross-section which causes the loss of the initial cross-sectional symmetry, both thermal and geometrical. This may lead to what is, in essence, a biaxial bending problem in reinforced concrete columns. This study does not deal with the prediction of the occurrence of spalling for which a fully coupled hygro-thermo-mechanical analysis would be required. This work evaluates the consequences that corner spalling and surface spalling have on the fire resistance of reinforced concrete columns and presents a methodology based on the determination of a modified fire resistance time. An advanced fiber based numerical model for evaluating the fire resistance of RC sections exposed to fire is used as a tool to analyse the effect that spalling has on the performance of the columns. The model is able to generate the interaction surfaces of the columns subjected to uniaxial or biaxial bending and 4-sided exposed to the standard fire curve ISO 834. After a parametric analysis, it is observed that the negative effect of spalling can be quantified by means of an additional fire exposure time, which ranges between 0–35 min and depends on the column cross-section configuration, dimensions and load level. Finally, a proposal for the calculation of the modified fire resistance time for the effect of spalling is presented, which may be beneficial for practitioners in design.

Energy absorption and recoverability of Moore space-filling thin-walled structures

This paper proposes novel thin-walled structures inspired by Moore space-filling curves. Nine designs, featuring three fractal hierarchies (1st, 2nd, and 3rd orders) with three different relative densities (20%, 30%, and 40%), were used as cross-sectional configurations of the thin-walled structures. Specimens were manufactured using a material extrusion additive manufacturing technique, fused filament fabrication, with a carbon fiber-reinforced composite. Quasi-static compression tests from in-plane direction were conducted to investigate the influences of fractal hierarchy and relative density on the energy absorption capacity. Finite element models were developed to compare with the experiments and to further explore the 4th order structures. A certain level of compliance and snap-in instability were observed in all the structures. These properties show great potential for such thin-walled structures to absorb more energy by enduring large strain. Among them, the 2nd order structures exhibited the best energy absorption capacity. Furthermore, loading and unloading compression tests were performed on the 2nd and 3rd order structures (relative density of 20%) to evaluate their resilience toward displacement and damages. The residual strain and dissipated energy ratio demonstrated that the 2nd order structure outperformed the 3rd order structure owing to its less compliant feature. The integration of Moore curves with thin-walled structures contributes to great compliance and snap-in instability, offering a new approach to designing lightweight energy absorption structures.

Shape and non-shape unified isogeometric optimal design for extremal band gaps

A unified shape and non-shape design optimization for lattice structures is performed to obtain extremal band gaps in an isogeometric computational framework, which uses the same NURBS basis functions as used in CAD description. Using a precise numerical model in both response and shape sensitivity analyses, enhanced response and sensitivity can be obtained, which leads to a precise optimal design. A plane wave propagation in infinite periodic lattice is analyzed within a representative unit cell using the Bloch theory with periodic boundary conditions. The ligaments of lattice structures are modeled using geometrically exact beams whose cross-sectional area and configuration are regarded as design variables, which are parameterized by the NURBS basis functions. The design variables are controlled by a mathematical programming algorithm with efficient adjoint design sensitivity. The obtained optimal lattice structures of triangular, squared, hexagonal, and Kagomé structures are fabricated using a 3D printing machine to be validated by physical experiments. Through harmonic response analysis and physical experiment for the optimal and the original designs, the wave attenuation properties are compared to demonstrate the validity of the obtained optimal design.