Kagome Truss Research Articles

Cooling performance of droplet-shaped Kagome truss structure combined with jet array impingement composite cooling structure

Gas turbine is one of the most efficiency conversion equipment of heat into power, which is widely used in aviation propulsion and power generation. With the gas inlet temperature of gas turbine skyrocketing recently, gas turbine can achieve higher efficiency but the super high temperature far exceeds the bearable temperature limits of blade material. This causes a great threaten in lifespan of turbine blades and making advanced and efficient cooling structures for blades essential. To enhance the cooling effectiveness of middle chord region of gas turbine blade, a novel droplet-shaped Kagome truss structure (DKTS) is proposed and investigated through experimental and numerical analysis. Subsequently, within jet impingement channel, DKTS is compared against circular pin-fins (CPF), droplet-shaped pin-fins (DPF), and circular Kagome truss structures (CKTS) for fluid flow and heat transfer performance. The experimental method is used to study effects on cooling characteristics between DKTS and CKTS under different operating conditions. The numerical method is used to study effects on cooling characteristics among CPF, DPF, CKTS and DKTS, and to study influences of investigated parameters on cooling performance of DKTS. Experimental results show that under equivalent windward areas, both heat transfer efficiency and flow performance of DKTS are better than those of CKTS. The results of numerical simulations indicate that at the same porosity across jet Reynolds numbers ranging 5000–50000, DKTS increases thermal-hydraulic performance by 11.1%–17.5% relative to CKTS. Moreover, DPF and DKTS reduce flow resistance and augment heat transfer capabilities as compared to CPF and CKTS. This shows that turbulators with droplet-shaped rods have better thermal-hydraulic performance. Finally, the effects of differing jet Reynolds numbers, diameter, tail angles, and inclination angles on fluid flow and heat transfer characteristics of DKTS are conducted. These results may provide a reference for further optimization researches or industrial applications of DKTS.

Experimental Study on Flow and Heat Transfer Characteristics of Jet Array Impingement Combined with Kagome Truss Structures with/without Cross-flow

Jet array impingement providing high heat transfer are widely used in heat exchangers. However, the target plate is easily damaged impinged by high-speed air flow constantly. To solve this issue, Kagome truss structure is combined with jet array impingement to improve cooling performance in this paper. The flow and heat transfer characteristics of this composite structure in a heat exchanger unit with/without cross-flow were experimentally studied. Additionally, Kagome truss structures of circular and water-drop-shaped rods were used respectively in jet space and the results showed that the latter was beyond 7% higher than the former for the comprehensive thermal performance. When cross-flow was not added, the comprehensive thermal performance factor of the latter reached to a maximum of 1.656 at the Reynolds number of 5000. When cross-flow was added, the comprehensive thermal performance got worse at the cross-flow-to-jet velocity ratio of 1.0, while the best comprehensive thermal performances were found at the cross-flow-to-jet velocity ratio of 0.6 and at the mass flow rate proportion of cross-flow of 0.5, respectively. These results can provide a basic experimental data as a reference for designing new structures in advanced heat exchanger.

Heat transfer characteristics of a channel filled with the array of drop-shaped Kagome truss cores

A staggered array of Kagome truss cores with drop-shaped rods is proposed as a new turbulator for a typical rectangular internal cooling channel at the trailing edge of a turbine blade. Under the Re range of 5000–25000, flow field and heat transfer characteristics in the channel are comparatively analyzed for two Kagome truss cores with drop-shaped (DRKTC) and common cylindrical (CYKTC). The effect of rod diameter (d = 1–3 mm) and tail angle (α = 45°–90°) for the DRKTC on the friction factor (f) and average Nusselt number (Nuave ) at the bottom wall of the channel were studied. The results show that the f of the DRKTC reduces by 29.4% and the comprehensive thermal coefficient (F) increases by 6.82% compared to the CYKTC under the same porosity and operating conditions. The parameter α has a greater influence on the f, which enhances about 1.2 times when the a changes from 45° to 90°, and the effect of the Nuave is small, which only increases by 4.09%. A small α is a good choice for reducing pressure drop. The size of the rod windward area depends on the rod diameter, when the d increases from 1 mm to 3 mm, the Nuave increases by 35.8%, and the f sharply increases by 153.6%. Based on the simulation results data, the fitting relations of the f and Nuave are fitted with a deviation of about 5%.

Cooling performance of a teardrop cross-section Kagome truss-filled array jet impingement composite cooling structure

The target surface is coupled to truss rods and the jet space to form a robust overall structure using 30 Kagome truss cores with 5 × 6 array configurations. This paper focuses on the cooling performances of the array jet impingement structure with the Kagome truss array in a 3D printing heat exchanger at Reynolds numbers (Re) ranging from 5000 to 50,000. The cooling characteristics of the Kagome truss-filled array jet impingement with a circular cross-section (CC) and a teardrop cross-section (TC) are comparatively studied through experiments and numerical simulations. The effects of the truss array arrangements, the diameter of the cross-section (d) and the trailing edge angle (α) on the cooling characteristics are studied by numerical simulation in the TC, where the truss array arrangements include an in-line arrangement and a staggered arrangement, d = 1–3mm and α = 45°–90°. The results indicate that when d is 3 mm and α is 45°, the TC has better cooling performance compared to the CC. The TC in the staggered arrangement has a smaller pressure loss coefficient (Cp), while that in the in-line arrangement has a higher average Nusselt number on the impingement target surface (Nuave). The comprehensive thermal factor (F) is increased by 6.58%–21.00% with the increase in d from 1 mm to 3 mm and decreased by 7.16%–8.90% with the increase in α from 45° to 90° in the TC. Two empirical correlations for the Nuave and the Cp for the TC have an accuracy of about 5%.

NUMERICAL SIMULATION ON FLOW AND HEAT TRANSFER CHARACTERISTICS IN A RECTANGULAR CHANNEL WITH KAGOME TRUSS CORES: THE INFLUENCE OF STRUT CROSS-SECTION ELLIPTICITY

The traditional Kagome trusses have circular cross-section ligaments. In this study, a Kagome truss with elliptical cross-sectional ligaments instead of circular cross-sectional ligaments is proposed. Additionally, a scheme for transforming the circular cross-sectional ligament into an elliptical ligament, which maintains the same cross-sectional area as the circular cross-sectional ligament, is proposed. Four Kagome truss structures with different cross-sectional ligaments are designed. Model-4 is a Kagome truss with traditional circular cross-sectional ligaments, whereas model-1, model-2, and model-3 are Kagome trusses of elliptical cross-sectional ligaments, with the major-to-minor axes ratio gradually decreasing from model-1 to model-3. Furthermore, the pressure drop and heat transfer performance of different models at different flow velocities are analyzed. A dimensionless number eta; characterizing the overall heat transfer performance is introduced to evaluate the overall performance. The results reveal that model-1, with a major-to-minor axes ratio of 4, achieved the most minor pressure drop at all velocities, and model-2 has the best heat transfer performance at high velocities. The average overall heat transfer performances of model-1, model-2, and model-3 are 5.9%, 16.3%, and 13.3% higher than that of model-4, respectively, thereby demonstrating the significance of elliptical optimization. The best overall heat transfer performance is exhibited when the major-to-minor axes ratio of the ellipse is 2.04.

Flexural behavior of composite beams of Kagome truss and fiber-reinforced cementitious composites

This paper presents an experimental and analytical study of the flexural behavior of composite beams of Kagome truss and fiber-reinforced cementitious composite (FRCC). Two types of FRCC—highly ductile (HD)-FRCC with a tensile ductility of 6.33 % and high-strength (HS)-FRCC with a compressive strength of 156.8 MPa—were designed. Three composite beams were manufactured. To investigate the flexural behavior of the beams, bending tests were performed. Test results showed that the flexural behavior of the Kagome truss composite beams was influenced by the types of FRCCs and reinforcement methods. The K-HS-HD beam reinforced at the tensile portion with HD-FRCC and at the compressive portion with HS-FRCC showed 4.5 and 4.9 times higher load-bearing capacities than those, respectively, of the K-HD and K-HS beams that were reinforced only at the tension region. While the analytical results and the experimental results were relatively consistent in the case of the beam reinforced with HD-FRCC, the analytical results were different from the experimental results in the nonlinear region in the case of the beam reinforced with HS-FRCC, due to local fracture of the material.

Topological design of the hybrid structure with high damping and strength efficiency for additive manufacturing

PurposeThree-dimensional (3D) printing provides more possibilities for composite manufacturing. Composites can no longer just be layered or disorderly mixed as before. This paper aims to introduce a new algorithm for dual-material 3D printing design.Design/methodology/approachA novel topology design method: solid isotropic material with penalization (SIMP) for hybrid lattice structure is introduced in this paper. This algorithm extends the traditional SIMP topology optimization, transforming the original 0–1 optimization into A–B optimization. It can be used to optimize the spatial distribution of bi-material composite structures.FindingsA novel hybrid structure with high damping and strength efficiency is studied as an example in this work. By using the topology method, a hybrid Kagome structure is designed. The 3D Kagome truss with face sheet was manufactured by selective laser melting technology, and the thermosetting polyurethane was chosen as filling material. The introduced SIMP method for hybrid lattice structures can be considered an effective way to improve lattice structures’ stiffness and vibration characteristics.Originality/valueThe fabricated hybrid lattice has good stiffness and damping characteristics and can be applied to aerospace components.

Seismic Strengthening of RC Structures Using Wall-Type Kagome Damping System

In this study, the Kagome truss damper, a metallic wire structures, was introduced and its mechanical properties were investigated through theoretical analyses and experimental tests. The yield strength of the Kagome damper is dependent on the geometric shape and diameter of the metallic wire. The Kagome damper has higher resistance to plastic buckling as well as lower anisotropy. Cyclic shear loading tests were conducted to investigate the energy dissipation capacity and stiffness/strength degradation by repeated loadings. The hysteretic properties obtained from the tests suggest that a modification of the ideal truss model with a hinged connection could be used to predict the yield strength and stiffness of the damper. For seismic retrofitting of a low-rise RC moment frame system, a wall-type Kagome damping system (WKDS) was proposed. The effectiveness of the proposed system was verified by conducting cyclic loading tests using a RC frame with/without the WKDS (story drift ratio limit 1.0%). The test results indicated that both the strength and stiffness of the RC frame increased to the target level and that its energy dissipation capacity was significantly enhanced. Nonlinear static and dynamic analyses were carried out to validate that the existing building structure can be effectively retrofitted using the proposed WKDS.

Impact resistant properties of Kagome truss reinforced composite panels

This paper presents an experimental study exploring impact resistant properties of Kagome truss reinforced composite panels. Three types of panels with different materials and reinforcements, i.e., ultra-high-performance mortar, steel fiber, and Kagome truss, were designed and manufactured. High-velocity projectile impact tests were performed to investigate the impact response of panels with dimensions of 200 mmx200 mmx40 mm. The projectile used in the testing was a steel slug with a hemispherical front; the impact energy was 1 557 J. Test results showed that the Kagome truss reinforcement was effective at improving the impact resistance of panels in terms of failure patterns, damaged area, and mass loss. Synergy effects of a combination of Kagome truss and fiber reinforcements for the improvement of impact resistance capacity of ultra-high-performance mortar were also observed.

Conjugate forced convective heat transfer in a sandwich panel with a Kagome truss core: The effects of strut length and diameter

Heat exchangers with a cellular metal core have become an alternative to those with louvered fins due to their high heat transfer performance and mechanical strength. Because of the multi-functionality, they are mostly used in systems such as rockets and space vehicles or in others in need of both high heat transfer performance and mechanical strength. The geometrical parameters of the unit cell of cellular metals have important effects on both fluid and heat transfer characteristics and these effects need to be studied. Accordingly, conjugate forced convective heat transfer in a sandwich panel with a Kagome truss core both with a constant heat flux (CHF) and a constant temperature (CT) boundary condition was studied numerically in this study for various values of the Reynolds number, strut length, and strut diameter. The 3D turbulent flow and heat transfer was modeled by the RNG k-epsilon turbulence model. The near-wall behavior of the flow was modelled by enhanced wall treatment. The channel was extended before and after the Kagome core to avoid entrance and exit effects. The computational results were obtained for the Reynolds numbers in the range of about 6000–17000, for the strut lengths of 3, 5 and 7 mm, and for the strut diameters of 1.3 and 1.6 mm. A nonlinear regression analysis was also performed for the pressure loss coefficient and average Nusselt number. The numerical results show that complex flow structures develop in the flow field due to the presence of unit cells. The results also show that the pressure drop along the Kagome core increases considerably with decreasing strut length and increasing strut diameter. The average Nusselt number increases significantly when the strut length is decreased and shows a small increase with an increase in the strut diameter. The effect of strut diameter on average Nusselt number becomes marginal for strut length of 3 mm. The average heat transfer rate for a fixed pumping power shows a considerable increase with a decrease in the strut length and a small increase with the strut diameter for high values of strut length. On the other hand, for the strut length of 3 mm, it shows a small decrease with an increase in the strut diameter for the CT case and remains almost constant for the CHF case.

Mechanical hysteresis model of a metal-wire Kagome truss for seismic strengthening for building systems

ABSTRACT In this study, we introduce a metal-wire Kagome truss damper and investigate its mechanical properties through theoretical analyses and experimental tests. The Kagome damper had high resistance to plastic buckling and low anisotropy. We propose an equation to estimate the yield strength of the damper, which was dependent on the geometric shape and thickness of the metal wire. We conducted cyclic shear loading tests to investigate the energy dissipation capacity and stiffness/strength degradation of the damper through repeated loading. Based on the hysteretic properties revealed by the tests, we found that modification of the ideal truss model with a hinged connection could predict the yield strength and stiffness of the damper. We present a numerical example to improve the seismic performance of a five-story reinforced concrete structure by installing Kagome dampers.

Performance of strut-reinforced Kagome truss core structure under compression fabricated by selective laser melting

Lattice structures are regarded as an excellent candidate for lightweight applications owing to their high specific strength and stiffness. In this paper, a novel lattice design is proposed, and its compressive properties are investigated. The Kagome lattice design is modified to form a new lattice core structure, namely, strut reinforced Kagome (SRK) with the presence of extra vertical strut. Ti-6Al-4V SRK unit structures with different aspect ratio are fabricated through selective laser melting. The compressive properties, elastic modulus and peak strength are predicted using analytical solution and are compared with the finite element analysis results and experimental measurements. The SRK unit structures outperformed Kagome unit structures of the same relative density by 13.42% and 12.87% in terms of peak strength and effective modulus, respectively. The sub-β-transus heat treatment on the SRK and Kagome unit structure has led to an increase in the effective moduli, ductility, and energy absorption with a slight decrease in the peak strength.

Vibration and damping characteristics of 3D printed Kagome lattice with viscoelastic material filling

Constrained layer dampers (CLD) are in widespread use for passive vibration damping, in applications including aerospace structures. However, the introducing of the damping layer can reduce the stiffness of the sandwich structures. A viscoelastic material filling (VMF) is chosen to balance structural and vibrational performance of lattice truss in this work. The recently brought forward 3D Kagome truss with face sheet was manufactured by selective laser sintering technology and the thermosetting polyurethane was chosen as the viscoelastic filling material. A novel complex modal analysis finite element method for Hybrid composite lattice truss sandwich is introduced in this paper. Dynamic analysis experiment results show that the VMF method is found to be effective in reducing the vibration amplitude and it has the potential for band-gap design. The VMF method can provide high stiffness at low mass and considerable vibrational performance at low cost and it can be considered as a general vibration design method in lattice truss manufacture.

Sound Isolation Characteristic of Wall System Using Kagome Truss Panel

This study investigated the sound isolation characteristic of wall system using the Kagome truss panel through sample and full-scale sound isolation experiments. Samples (1×1 m2 , depth:100 mm) of Kagome truss panel were first tested in the rectangular chamber. The samples consisted of various surface materials (steel plate, CRC board, gypsum board, and plywood), Kagome truss and filling materials (urethane foam, aerated concrete and light-weight concrete). Results of sample test showed that the Kagome truss panel with steel plate and urethane foam had best sound isolation performance (48 dB in Rw). Additional sound isolation experiment with wall panel (3.9×2.4 m2 , depth: 270 mm) in full-scale was conducted in the reverberation chamber. The wall system was comprised of gypsum board, air-space, C-stud with glass wool and the Kagome truss panel with steel plate and urethane foam, which was used in the sample test. It was shown that sound isolation performance of the triple wall system using the Kagome truss panel was 58 dB in Rw. The sole Kagome truss panel showed sound isolation performance of 44 dB in Rw, which is lower than result in sample test. It was also shown that sound isolation performance was increased by about 5 dB in Rw after installing gypsum board and glass wool, respectively. Computational analysis of sound transmission for the wall system was also conducted and compared with the results of experiment.

Ultralight shape memory actuator from wire-woven Kagome truss

In this paper, a novel actuator in the form of a Kagome truss composed of shape memory alloy (SMA) wires and common metallic wires is described. In the actuator, the SMA wires play dual roles as load supporters and actuating elements. The intersections between the SMA wires and between the SMA wires and the common metallic wires were joined by using shrinkable tubes, which induced the kinematically compatible buckling of the columns of SMA wires under compression, consequently enabling the large actuation displacement of up to 30% of the height with some sacrifice of the load capacity. An analytic solution was derived using the elementary mechanics of buckling and geometric relation of curved column, which gave fairly good estimation of the behavior of the Kagome actuator for the deformation and actuation stages, based on the behavior of a single SMA wire. The lightness and large actuation range of this actuator appear to be useful for practical applications.

Printing and characterisation of Kagome lattice structures by fused deposition modelling

Sandwich structures with lattice cores exhibit high specific bending strength and stiffness when compared to monolithic structures. Additive manufacturing is able to further expand the available design space to fabricate novel core structures with complex features. In this paper, the compressive performance of the Kagome truss unit cell of acrylonitrile butadiene styrene (ABS) ABSplus™ fabricated by fused deposition modelling is investigated. The influences of part build orientation, truss radius and surface roughness on strength and stiffness are critically explored. The change in build orientation improved the average peak strength and effective stiffness by 23% and 19%, respectively. 90% (v/v) acetone was used to polish the printed surfaces and 5min chemical treatment was optimal based on the measured surface roughness, strength and stiffness values. These single cell studies will help to understand the macroscopic behaviour of the beams and plates with Kagome cores under quasi-static bending and impact loading scenarios.

Seismic Strengthening Effects Based on Pseudodynamic Testing of a Reinforced Concrete Building Retrofitted with a Wire-Woven Bulk Kagome Truss Damper

A passive damper with a wire-woven bulk Kagome truss design was recently developed; its applicability as a passive damper to improve the seismic performance of building systems, including shear hysteresis behavior, energy dissipation capacity, and fatigue, was confirmed by material tests. The Kagome truss, a periodic cellular metal type, is composed of evenly distributed helical wires with a constant pitch and helical radius in six directions. The purpose of this study was to develop a new passive damper system for seismic strengthening of existing reinforced concrete (RC) frames. The proposed external connection methodology uses a wire-woven bulk Kagome truss (i.e., a Kagome damper external connection (KDEC) system), to dissipate earthquake energy using the dynamic interaction among an existing building, a support structure, and the Kagome damper installed between them. Four test specimens were designed and then strengthened with the KDEC system. Cyclic loading and pseudodynamic tests were conducted; lateral load-carrying capacity, deformation, and hysteresis characteristics were investigated, as well as the maximum response strength, response ductility, and earthquake damage degree, and compared to a control sample. Test results revealed that the KDEC system effectively dissipated the earthquake energy, showing considerable resilience under large-scale earthquake conditions.

유사동적실험에 의한 외부접합형 카고메 트러스 제진장치가 설치된 RC 라멘조 공동주택의 내진성능 평가

최근 새로운 3차원 와이어 다공질 형태의 카고메 트러스 이력형 제진장치가 개발되어, 건축물의 내진성능 개선을 위한 제진장치로서의 적용가능성이 재료실험을 통하여 검증되었다. 본 연구에서는 카고메 트러스 이력형 제진장치를 RC 라멘조 공동주택에 외부접합 한 새로운제진구조시스템을 제안하였다. 카고메 외부접합형 제진구조시스템은 대상건물, 카고메 제진장치, 지지구조물로 구성되어 있으며, 기존 층간에 설치된 제진시스템과 달리 외부 지지 구조물과 대상 건축물의 상호작용을 이용하여 제진장치가 지진 에너지를 흡수하는 시스템이다. 본 연구에서 제안한 카고메 외부접합형 제진공법의 유효성을 검증 할 목적으로 LH공사 시범적용용 RC 라멘조 20층 공동주택의 골조를 대상으로 유사동적실험을 실시하여 내진성능 개선효과를 검토하였다. 그 결과, 국내에서 발생 가능한 지진규모 (200gal)에서 비보강 골조는 중규모의 지진피해가 예상되었지만, 카고메 외부접합형 제진보강법으로 보강한 골조는 경미한 지진피해가 예상되었으며, 대규모 지진(300gal)을 상정한 경우에도 중규모 이하의 지진피해가 예상되어 본 연구에서 개발한 카고메 제진보강법의 내진성능 개선 효과의 유효성이 검증되었다고 사료된다. Recently a new damper system with Kogome truss structure was developed and its mechanical properties were verified based on the laboratory test. This paper presents a Kagome truss damper external connection method for seismic strengthening of RC frame structural system. The Kagome external connection method, proposed in this study, consisted of building structure, Kagome damper and support system. The method is capable of reducing earthquake energy on the basis of the dynamic interaction between external support and building structures using Kagome damper. The pseudo-dynamic test, designed using a existing RC frame apartment for pilot application of LH corporation, was carried out in order to verify the seismic strengthening effects of the proposed method in terms of the maximum load carrying capacity and response ductility. Test results revealed that the proposed Kagome damper method installed in RC frame enhanced conspicuously the strength and displacement capacities, and the method can resist markedly under the large scaled earthquake intensity level.

Performance of bio-inspired Kagome truss core structures under compression and shear loading

Additive manufacture of titanium structures allows the realisation of advanced design strategies not achievable through traditional manufacturing methods. This work analyses the performance of Ti-6Al-4V Kagome truss core structures produced by selective laser melting (SLM) for composite sandwich structures. These bio-inspired core structures can be manufactured for truss diameters larger than 0.6mm and internal truss angles of less than 60° without requiring additional support structures. Mechanical testing is conducted to determine the deformation and failure of the core structure in compression and shear. A finite element model validates the structural performance and can further optimise the unit cell design. Design charts show that the performance of the proposed titanium core in both compression and shear is superior (strength) or equal (stiffness) to honeycomb cores for aerospace applications.

Tuning of Bandgap Structures in Three-Dimensional Kagome-Sphere Lattice

In this manuscript, acoustic wave propagation in a novel three-dimensional porous phononic crystal-Kagome lattice, is studied by using finite element method. Firstly, a Kagome-sphere structure is established based on Kagome truss. For lattice with fixed rods (sphere radius varied) or fixed spheres (rod radius varied), the band structures are calculated in order to clarify the influence of geometrical parameters (sphere and rod sizes) on the bandgap characteristics in Kagome-sphere lattice. The vibration modes at the band edges of the lowest bandgaps are investigated with the aim to understand the mechanism of the bandgap generation. It is found that the emergence of the bandgap is due to the local resonant vibration of the unit cell at the adjacent bands. The width and position of this bandgap can be tuned by adjusting the geometrical parameters. An equivalent mass-spring model is proposed and the equivalent system resonance frequency can be evaluated which predicts well the upper and lower edges of the complete bandgaps. Moreover, the critical geometrical parameter is formulated which gives the critical geometrical condition for the opening of the complete bandgaps. The results in this paper are relevant to the bandgap structure design of three-dimensional porous phononic crystals (PPCs).