• Composites Research
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• v.17 no.4
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• pp.18-24
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• 2004

In this paper, active shape control of composite structures actuated by shape memory alloy (SMA) wires is presented. The thermo-mechanical behaviors of SMA wires were experimentally measured. Hybrid composite structures were established by attaching SMA actuators on the surfaces of graphite/epoxy composite beams using bolt-joint connectors. SMA actuators were activated by phase transformation, which induced by temperature rising over austenite finish temperature. In this paper, electrical resistive heating was applied to the hybrid composite structures to activate the SMA actuators. For (aster and more accurate shape/deflection control of the hybrid composite structure, PID feedback controller was designed from numerical simulations and experimentally applied to the SMA actuators.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.229-245
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• 2017

Post-earthquake observations revealed that seismic performance of beam-column connections in precast concrete structures affect the overall response extensively. Seismic design of precast reinforced concrete structures requires improved beam-column connections to transfer reversed load effects between structural elements. In Turkey, hybrid beam-column connections with welded components have been applied extensively in precast concrete industry for decades. Beam bottom longitudinal rebars are welded to beam end plates while top longitudinal rebars are placed to designated gaps in joint panels before casting of topping concrete in this type of connections. The paper presents the major findings of an experimental test programme including one monolithic and five precast hybrid half scale specimens representing interior beam-column connections of a moment frame of high ductility level. The required welding area between beam bottom longitudinal rebars and beam-end plates were calculated based on welding coefficients considered as a test parameter. It is observed that the maximum strain developed in the beam bottom flexural reinforcement plays an important role in the overall behavior of the connections. Two additional specimens which include unbonded lengths on the longitudinal rebars to reduce that strain demands were also tested. Strength, stiffness and energy dissipation characteristics of test specimens were investigated with respect to test variables. Seismic performances of test specimens were evaluated by obtaining damage indices.

• Steel and Composite Structures
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• v.44 no.3
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• pp.407-421
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• 2022

Prefabricated hybrid wind turbine towers (WTTs) are promising due to height increase. This study proposes the use of ultra-high performance concrete (UHPC) to develop a new type of WTT without the need to use reinforcement. It is demonstrated that the UHPC WTT structure without reinforcing bars could achieve performance similar to that of reinforced concrete WTTs. To simplify the design of WTT, a design approach for the calculation of stresses at the horizontal joints of a WTT is proposed. The stress distribution near the region of the horizontal joint of the WTT structure under normal operating conditions and different load actions is studied using the proposed approach, which is validated by the finite element method. A further parametric study shows that the degree of prestressing and the bending moment both significantly affect the principal stress. The shear-to-torsion ratio also shows a significant influence on the principal tensile stress.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2678-2686
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• 2023

This work demonstrates the results of full-scale numerical experiments of a hybrid thorium-containing fuel plant operating in a state close to critical due to a controlled source of D-T neutrons. The proposed facility represented a level of generated power (~10-100 MW_t) in a small pilot. In this work, the simulation of the D-T neutron plasma source operation in conjunction with the facility blanket was performed. The fission of fuel nuclei and the formation of spatial-energy release were studied in this simulation, in pulsed and stationary modes of the facility operation. The optimization results of neutronic and fluid dynamics studies to level the emerging offsets of the radial energy formed in the volume of the facility multiplying part due to the pulsed operation of the D-T neutron plasma source were presented. The results will be useful in improving the power control-based subcriticality monitoring method in coupled systems of the "pulsed neutron source-subcritical fuel assembly" type.

• Steel and Composite Structures
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• v.45 no.2
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• pp.231-248
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• 2022

Hybrid Steel-Trussed Concrete Beam (HSTCB) is structural typology suitable for light industrialization. HSTCBs usually cover long span with small depths, which lead to significant amount of longitudinal rebars. The latter make beam-column joints more prone to damage due to earthquake-induced cyclic actions. This phenomenon can be avoided using friction-based BCCs. Friction devices at Beam-to-Column Connections (BCCs) have become promising solutions to reduce the damage experienced by structural members during severe earthquakes. Few solutions have been developed for cast-in-place Reinforced Concrete (RC) and steel-concrete composite Moment Resisting Frames (MRFs), because of the difficulty of designing cost-effective damage-proof connections. This paper proposes a friction-based BCC for RC MRFs made with HSTCBs. Firstly, the proposed connection is described, and its innovative characteristics are emphasized. Secondly, the design method of the connection is outlined. A detailed 3D FE model representative of a beam-column joint fitted with the proposed connection is developed. Several monotonic and cyclic analyses are performed, investigating different design moment values. Lastly, the numerical results are discussed, which demonstrate the efficiency of the proposed solution in preventing damage to RC members, and in ensuring satisfactory dissipative capacity.

• Progress in Superconductivity and Cryogenics
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• v.25 no.4
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• pp.28-31
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• 2023

This study presents a comprehensive procedure for the low cycle fatigue test of ultrasonically welded (UW) coated conductor (CC) lap-joints. The entire process is examined in detail, from the robust fabrication of the UW REBCO CC joints to the reliability testing under a low number of repeated cycle fatigue conditions. A continuous I_c measurement system enables real-time monitoring of I_c variations throughout the fatigue tests. The study aims to provide a step-by-step procedure that involves joint fabrication, electromechanical property (EMP) tests under uniaxial tension for stress level determination, and subsequent low-cycle fatigue tests. The joints are fabricated using a hybrid method that combines UW with adding In-Sn soldering, achieving a flux-free hybrid welding approach (UW-HW flux-free). The selected conditions for the low cycle fatigue tests include a stress ratio of R=0.1 and a frequency of 0.02 Hz. The results reveal some insights into the fatigue behavior, irreversible changes, and cumulative damage in the CC joints.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.04a
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• pp.395-400
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• 1994

Most of Commercial Remote Center Compliance(RCC) devices have been designed using deformable structures. In this work, we propose another type of assembly devices which generate the compliance effects by attaching the compliances (or spring) at the joints of the given mechainsm. The compliance models are derived for a serial-type, parallel-type, and hybrid-type mechanisms, respectively. In particular, a planar three-degree of freedom parallel structure is shown to have RCC points at the center of the workspace for its symmetric configuratings.

• Journal of Mechanical Science and Technology
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• v.14 no.3
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• pp.338-349
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• 2000

Neck muscle forces and spinal loads at the C4/5 level were estimated that result from isometric voluntary ramp efforts gradually developing to maximums in flexion, extension, left lateral bending and right lateral bending. Electromyographic (EMG) activities, a three-dimensional anatomic data of the neck and a hybrid model, EMG-assisted optimization (EMGAO) model, were used. The model computed the cervical loads at 25%,50%,75%, and 100% of peak moments. The highest model-predicted C4/5 joint compressive forces occurred during flexion; $361\;({\pm}164)\;N,\;811\;({\pm}288)\;N,\;1207\;({\pm}491)\;N\;and\;1674\;({\pm}319)\;N$ in 25%, 50%, 75% and 100% of peak moment respectively. Variations in load distribution among the agonistic muscles and co-contractions of antagonistic muscles were estimated during ramp efforts. Results suggest that higher C4/5 joint loads than previously reported are possible during isometric, voluntary muscle contractions. These higher physiological loads at C4/5 level must be considered possible during orthopedic reconstruction at this level.

• Journal of Korean Institute of Industrial Engineers
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• v.39 no.5
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• pp.440-449
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• 2013

We consider a reverse supply chain with a production facility and a recovery facility, and address the joint control of production and disposal decisions for sustainable operations. Demands are satisfied from on-hand inventory of serviceable products, replenished via manufacturing or remanufacturing. Sold products may be returned after usage and each returned product is disposed of or accepted for recovery. Accepted returned products are converted into serviceable products after remanufacturing process. Formulating the model as a Markov decision process, we characterized the structure of the optimal production and disposal policy as two monotone switching curves under a special condition. Three types of heuristic policies are presented and their performance is numerically compared.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.15-21
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• 2010

The transported probability density function(PDF) model has been applied to simulate the turbulent nonpremixed piloted jet flame. To realistically account for the mixture fraction PDF informations on the turbulent non-premixed jet flame, the present Lagrangian PDF transport approach is based on the joint velocity-composition-turbulence frequency PDF formulation. The fluctuating velocity of stochastic fields is modeled by simplified Langevin model(SLM), turbulence frequency of stochastic fields is modeled by Jayesh-Pope model and effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate the present approach, the numerical results obtained by the joint velocity-composition-turbulence frequency PDF model are compared with experimental data in terms of the unconditional and conditional means of mixture fraction, temperature and species and PDFs.