• Structural Engineering and Mechanics
• /
• 제5권5호
• /
• pp.491-505
• /
• 1997

This paper deals with the formulation and solution of a wide class of structures, in the presence of both geometric and material nonlinearities, as a particular mathematical programming problem. We first present key ideas for the nonholonomic (path dependent) rate formulation for a suitably discretized structural model before we develop its computationally advantageous stepwise holonomic (path independent) counterpart. A feature of the final mathematical programming problem, known as a nonlinear complementarity problem, is that the governing relations exhibit symmetry as a result of the introduction of so-called nonlinear "residuals". One advantage of this form is that it facilitates application of a particular iterative algorithm, in essence a predictor-corrector method, for the solution process. As an illustrative example, we specifically consider the simplest case of plane trusses and detail in particular the general methodology for establishing the static-kinematic relations in a dual format. Extension to other skeletal structures is conceptually transparent. Some numerical examples are presented to illustrate applicability of the procedure.

• 대한가정학회지
• /
• 제25권1호
• /
• pp.43-50
• /
• 1987

Non-durable flame retardant finish, borax/boric acid mixed solution, was applied to cotton fabric with pad-dry method. The LOI(limited oxygen index) was measured as the measare of the flame retardant effect. The TGA was investigated to know the thermal behavior of the samples. In addition, the solubility of the solutions was investigated. The results were as follows: 1) There was a synergism of flame retardant effect in the borax/boric acid mixed solution treatment and the maximum synergism was shown around the ratio of 7 : 3 2) After the borax/boric acid solution treatment, the degradation temperature was lowered and degraded at the larger temp range with slower rate. The residual char length also increased. 3) The solubility of borax/boric acid become higher when the ratio of borax/boric acid became similar. Compositions from 80/20 to 40/60 borax/boric acid mixtures were solubilized well in room temperatuare or warmwater therefor there was no problem for home use.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1992년도 가을 학술발표회 논문집
• /
• pp.7-19
• /
• 1992

An efficient approach to limit analysis is presented whereby a continuous perfectly plastic structure is replaced by a discrete mathematical model. It is formulated as a mathematical programming problem using the static theorem of plasticity. The discretization is accomplished by writing the governing equilibrium equations in finite difference form, and is combined with piecewise linearization of the nonlinear yield curve, thus converting the formulation into a linear programming exercise. Examples of reported cases involving plates and shells are solved to illustrate the ease of application of the present method, its flexibility and accuracy - features which it make attractive to practising engineers.

• Structural Monitoring and Maintenance
• /
• 제4권4호
• /
• pp.301-329
• /
• 2017

Impedance-based damage detection method has been known as an innovative tool with various successful implementations for structural health monitoring of civil structures. To monitor the local critical area of a structure, the impedance-based method utilizes the high-frequency impedance responses sensed by piezoelectric sensors as the local dynamic features. In this paper, current advances and future challenges of the impedance-based structural health monitoring are presented. Firstly, theoretical background of the impedance-based method is outlined. Next, an overview is given to recent advances in the wireless impedance sensor nodes, the interfacial impedance sensing devices, and the temperature-effect compensation algorithms. Various research works on these topics are reviewed to share up-to-date information on research activities and implementations of the impedance-based technique. Finally, future research challenges of the technique are discussed including the applicability of wireless sensing technology, the predetermination of effective frequency bands, the sensing region of impedance responses, the robust compensation of noise and temperature effects, the quantification of damage severity, and long-term durability of sensors.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
• /
• pp.25.3-26
• /
• 2008

The direct way to the moon is to start from the parking orbit by using impulsive thruster In previous domestic research, the direct way has been studied by using a single impulsive shot. However, when a single impulsive shot occurs to go into a Translunar orbit, gravity losses occur because thruster is not impulsive shot but the finite burns and it causes the gravity losses. To make up for the weak point of a single impulsive shot, this paper divides TLI (Trans Lunar Injection) into several small burns. Therefore, departure loop trajectory and the Translunar trajectory. This method is useful not only to reduce the gravity losses but also to check the condition of satellite. By using this method, this paper demostrates the optimized trajectory from Earth parking orbit to lunar mission orbit which minimizes the fuel, and the SNOPT (Sparse Nonlinear OPTimizer software) is used to find optimal solution. Also, this paper provides lunar mission profile which includes the mission schedule when TLI, LOI (Lunar Orbit Insertion) maneuvers occur, a mount of fuel when thruster is used and other mission parameters.

• Smart Structures and Systems
• /
• 제28권6호
• /
• pp.761-777
• /
• 2021

This study presents a numerical investigation on the sensitivity of electromechanical (EM) impedance responses to inner damaged concrete of a prestressed anchorage zone. Firstly, the Ottosen yield criterion is selected to simulate the plasticity behavior of the concrete anchorage zone under the compressive loading. Secondly, several overloading cases are selected to analyze inner damage formations in the concrete of the anchorage zone. Using a finite element (FE) model of the anchorage zone, the relationship between applied forces and stresses is analyzed to illustrate inner plasticity regions in concrete induced by the overloading. Thirdly, EM impedance responses of surface-mounted PZT (lead-zirconate-titanate) sensors are numerically acquired before and after concrete damage occurrence in the anchorage zone. The variation of impedance responses is estimated using the RMSD (root-mean-square-deviation) damage metric to quantify the sensitivity of the signals to inner damaged concrete. Lastly, a novel PZT skin, which can measure impedance signatures in predetermined frequency ranges, is designed for the anchorage zone to sensitively monitor the EM impedance signals of the inner damaged concrete. The feasibility of the proposed method is numerically evaluated for a series of damage cases of the anchorage zone. The results reveal that the proposed impedance-based method is promising for monitoring inner damaged concrete in anchorage zones.

• 한국응용과학기술학회지
• /
• 제23권3호
• /
• pp.252-263
• /
• 2006

It is attempted to develop flame retardant polyurethane coatings, which have received significant attention in recent years. It is the purpose of this study to synthesize new reactive polyurethane coatings containing halogen. Lactone based modified polyester polyols, using trichlorobenzoic acid as chlorine moiety (TBAOs) were synthesized. These polyesters were cured with isophorone diisocyanate (IPDI)-isocyanurate at room temperature (TBAPUs). Physical properties of these flame retardant coatings were similar with those of non-flame retardant coatings. The flammability of coatings was strongly dependent on the chlorine contents. We found that the increasing chlorine contents showed better flame retarding properties and that, however, they also resulted in more smog generation during combustion. The detailed results of flammability test using various methods indicated $24{\sim}26%$ in LOI and $3.7{\sim}5.3\;cm$ char length in $45^{\circ}$ Meckel burner method.

• 한국응용과학기술학회지
• /
• 제17권3호
• /
• pp.203-211
• /
• 2000

Pyrophosphoric lactone modified polyester(PATT) that contains two phosphorous functional groups in one unit base resin structure was synthesized to prepare a non-toxic reactive flame retardant coatings. Then the PATT was cured at room temperature with isocyanate, Desmodur IL, to get a two-component polyurethane flame retardant coatings(PIPUC). Comparing the physical properties of the films of PIPUC with the film of non-flame retardant coatings, there was no degradation observed in physical properties by the introduction of a flame-retarding component into the resin. We found that the char lengths measured by $45^{\circ}$Meckel burner method were $3.1{\sim}4.4cm$ and LOI values recorded $27{\sim}30%$. These results indicate that the coatings prepared in this study is good flame retardant one. The surface structure of coatings investigated with SEM does not show any defects and phase separation.

• 한국염색가공학회지
• /
• 제9권2호
• /
• pp.1-9
• /
• 1997

This paper was carried out to introduce flame retardant and antibiotic properties to polyester(PET) and polyester/cotton(P/C) blend fabrics. PET and P/C blend fabrics were treated by a paddry-cure method in the aqueous solutions of the finishing agents(JA 6034, JA 6050, DC-5700). The corona discharge technique was applied to increase the polar group of the polymer surface. The characteristics of the treated fabric were investigated by means of scanning electron microscope (SEM) and electron spectroscopy for chemical analysis(ESCA), and water penetration time, limiting Oxygen index(LOI), and K/S value were also measured. Wettability of the fabrics was increased considerably with the corona discharge treatment. ESCA was used to elucidate the surface chemical composition of the fabrics treated with the corona discharge. Relative Ols intensity increased and oxygen was incorporated in the form of -C-O-, -C=O, and O=C-O on the polymer surface. The current study indicated that corona discharge treatment was effective for modifying the polymer surface.

• 한국의류산업학회지
• /
• 제5권3호
• /
• pp.273-282
• /
• 2003

Effect of fixation methods and relaxation treatment on the flame retardant(FR) and physical properties of MDPP/HMM treated cotton weft-knitted fabrics were studied. Combination of four different fixation methods - relaxation, swelling agent treatment, pad dry cure fixation, and wet fixation - were applied to flame retardant finish of cotton weft-knitted fabric with MDPP/HMM. As the results, 1. Swelling agent and wet fixation method helps FR agent penetrate the fiber efficiently. Interlock showed relatively higher values of LOI than single jersey. 2. Interlock showed relatively higher values of bending rigidity(B), shear rigidity(G) and coefficient of friction(MIU) than those of single jersey before and after flame resistant treatment. 3. An increase in internal volume of cotton fiber by relaxation treatment increased the bending rigidity(B), shear rigidity(G) and compressional energy(WC). 4. The cotton weft-knitted fabric treated wet fixation, which crossliked FR agent efficiently, showed higher bending rigidity, shear rigidity(G) and lower compressional energy(WC). Retention of swelling ability of cotton weft-knitted fabrics treated with MDPP/HMM, which increased the internal volume of cotton weft-knitted fabric, showed lower bending rigidity.