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排序方式: 共有232条查询结果,搜索用时 15 毫秒
1.
Optimum design of steel frames with stability constraints 总被引:1,自引:0,他引:1
M.P. Saka 《Computers & Structures》1991,41(6):1365-1377
Optimum design algorithms based on the optimality criteria approach are proven to be efficient and general. They have the flexibility of accomodating variety of design constraints such as displacement, stress, stability and frequency in the design problem. The design methods developed recently, although considering one or more of these constraints, lack the necessity of referring to any relevant design code. The algorithm presented for the optimum design of street frames implements the displacement and combined stress limitations according to AISC. The recursive relationship for design variables in the case of dominant displacement constraints is obtained by the optimality criteria approach. The combined stress inequalities which include in-plane and lateral buckling of members are reduced into nonlinear equations of design variables. The solution of these equations gives the values of bounds for the variables in the case where the stress constraints are dominant in the design problem. The use of effective length in the combined stress constraints makes it possible to study the effect of the end rigidities on the final designs. The design procedure is simple and easy to program which makes it particularly suitable for microcomputers. A number of design examples are considered to demonstrate the practical applicability of the method. It is also shown that the design procedure can be employed in selecting the optimum topology of steel frames. 相似文献
2.
Domes are elegant and economical structures used in covering large areas. They are built in various forms. According to their
form, they are given special names such as lamella, network, and geodesic domes. In this paper, optimum topological design
algorithm is presented that determines the optimum number of rings, the optimum height of crown and tubular section designations
for the member groups of these domes. The design algorithm developed has a routine that generates the data required for the
geometry of these domes automatically. The minimum weight of each dome is taken as the objective function. The design constraints
are implemented according to the provision of LRFD-AISC (Load and Resistance Factor Design–American Institute of Steel Constitution).
The optimum topological design problem that considers these constraints turns out to be discrete programming problem. Improved
harmony search algorithm is suggested to determine its optimum solution. The design algorithm also considers the geometric
nonlinearity of these dome structures. Design examples are presented to demonstrate the effectiveness and robustness of the
design optimization algorithm developed. 相似文献
3.
AISI 5140 low alloy steel was ion nitrided under different process parameters including time (1, 4, 8 and 12 h), temperature (400, 450, 500 and 550 °C) and gas mixture ratio (0.05, 0.33, 1 and 3 N2/H2). By determining the fatigue strength, surface hardness, compound layer thickness and case depth, the optimum working conditions were determined by using a Taguchi design of experiment. After ion nitriding process, it is aimed to maximize fatigue strength, surface hardness and case depth as well as to minimize compound layer thickness. While the optimum conditions were determined, due to the goals (above aims) more than one being, the trade-off among goals was considered. First of all, each goal was optimised, separately. Then, all the goals were optimised together, considering the priority of the goals, and the optimum results were obtained at 0.05 N2/H2 gas mixture ratio, at the temperature of 450 °C and for 12 h process time. 相似文献
4.
Harmony search based algorithm for the optimum design of grillage systems to LRFD-AISC 总被引:1,自引:1,他引:0
Harmony search based optimum design method is presented for the grillage systems. This numerical technique imitates the musical
performance process that takes place when a musician searches for a better state of harmony. Jazz improvisation seeks to find
musically pleasing harmony similar to the optimum design process which seeks to find the optimum solution. The design algorithm
considers the serviceability and ultimate strength constraints which are implemented from Load and Resistance Factor Design—American
Institute of Steel Construction (LRFD-AISC). It selects the appropriate W-sections for the transverse and longitudinal beams
of the grillage system out of 272 discrete W-section designations given in LRFD-AISC. This selection is carried out such that
the design limitations described in LRFD-AISC are satisfied and the weight of the system is the minimum. Many design examples
are considered to demonstrate the efficiency of the algorithm presented. 相似文献
5.
Recently, the size of solder bump interconnects have been significantly reduced with the advent of high-density packaging,
and thus the evaluation of electromigration in solder bumps has become necessary. The present paper proposes a simple method
to test the electromigration resistance of Pb-free solders. One of the key points of the present method is the fabrication
of a simple solder sample that can produce sufficient current density to cause electromigration. Moreover, the actual local
temperature of a small area subjected to electromigration in the sample was measured by a direct method. A right-angled diamond-shaped
hole was introduced in a thin film of solder using a focused-ion-beam system. A direct current was supplied to the film far
from the hole, perpendicular to the diagonal of the hole. In this way, the current density was concentrated near to the corner
of the hole, and the value of this was obtained through a theoretical analysis. It was noted that the steady temperature in
the film along a line extending from the diagonal, remained constant, although the current density decreased gradually far
from the corner. Therefore, the temperature at a position near the corner, where electromigration takes place, can easily
be found by measuring the temperature far from the corner. The temperature was measured directly under current flow conditions
by utilizing the chemical reagents with known melting points. Finally, by measuring the ratio of hillock volume to the time
for the current supply as a measure of the atomic flux divergence due to electromigration, the corresponding resistances of
some Pb-free solders to electromigration were evaluated. 相似文献
6.
Low-Ag-based Pb-free solder and its evaluation for electromigration (EM) reliability are research areas of active development. This paper studies the effect of adding Ni and Ge microelements on the EM behavior of low-Ag-based SnAgCu solder. Comparative measurements of the EM resistance of Sn1.0Ag0.5Cu (SAC) and Sn1.0Ag0.5Cu0.07Ni0.01Ge (SACNG) solders (in wt?%) were conducted. In these experiments, SACNG showed a higher EM resistance than SAC. It was concluded that adding Ni and Ge enhanced the EM resistance of low-Ag-based SnAgCu solders. This shows the same effect of Ni and Ge on the EM resistance as that which has been reported for Sn3.5Ag0.5Cu solder. An analysis of these observations suggests that grain boundary sliding plays a dominant role in stress relaxation and causes hillock growth. Based on this assumption, a possible mechanism was proposed to explain the effects of Ni and Ge on the EM resistance of SnAgCu solder. 相似文献
7.
Four mechanical parameters of physical vapor-deposited (PVD) hard coatings were obtained, which were the residual strain, Young's modulus, film toughness, and interface toughness, concerning titanium aluminum nitride (TiAlN) and titanium nitride (TiN) coatings deposited on WC-Co substrates. The results were quantitatively compared with the author's previous trials for the case of chemical vapor-deposited (CVD) diamond coatings. Due to the significant difference in the mechanical properties between PVD hard coatings and CVD diamond coatings, it was necessary to develop new experimental techniques, which could properly evaluate those parameters for the case of PVD hard coatings. As a conclusion, film toughness of PVD hard coatings was surprisingly brittle. It was an order of magnitude smaller than that of CVD diamond coatings. In contrast, no significant difference was found in interface toughness between these different kinds of coatings. Concerning the residual strain, TiN had far larger level than the other two. These differences in mechanical properties were further discussed in relation to the difference in their wear behavior. 相似文献
8.
Miguel Rio Andrea di Donato Frank Saka Nicola Pezzi Richard Smith Saleem Bhatti Peter Clarke 《Journal of Grid Computing》2003,1(4):329-343
This paper reports on different efforts to provide quality of service (QoS) Networking to Grid applications done in the context of the MB-NG, GRS and DataTAG EU projects. These are leading edge network research projects involving more that 50 researchers in the UK, Europe and North America, concerned with the development and testing of protocols and standards for the next generation of high speed networks. We have implemented and tested the Differentiated Services Architecture (DiffServ) in a multi-domain, 2.5 Gbits/s network (the first such deployment) defining appropriate Service Level Agreements (SLAs) to be used between administrative domains to guarantee end-to-end Quality of Service. We characterised several hardware implementations of DiffServ and concluded on their appropriateness for several network scenarios. Since current and future Grid applications will have to use modified mechanisms of congestion control we have evaluated old and new TCP implementations over a Differentiated Services Networks. These quality of service tests have also included innovative MPLS (Multi-Protocol Label Switching) experiments to establish guaranteed bandwidth connections to Grid applications in a fast and efficient way. We have also developed a software based bandwidth broker architecture for Grids based on IETF standards which allows applications to transparently request dynamic and advanced reservations and implemented it in a real experimental network. We finally report on experiences delivering Quality of Service networking to high performance applications like Particle Physics data transfer and High Performance Computation. This includes quantitative results on the performance improvements that QoS brought to real data transfers in the context of High Performance Computing. 相似文献
9.
Cafer Saka Mustafa Salih Eygi̇ Asım Balbay 《International Journal of Hydrogen Energy》2021,46(5):3876-3886
Inorganic acids such as hydrochloric acid (HCl), nitric acid (HNO3) and sulphuric acid (H2SO4) are generally used in the acid modification of clays. Here, CoB catalyst was synthesized on the acetic acid-activated kaolin support material (CH3COOH -kaolin- CoB) with an alternative approach. This prepared catalyst, firstly, was used to catalyze the hydrolysis of NaBH4 (NaBH4-HR). The structure of the raw kaolin, kaolin-CH3COOH, and CH3COOH-kaolin-CoB samples were characterized by X-ray diffraction spectroscopy (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), and nitrogen adsorption. At the same time, this catalyst performance was examined by Co loading, NaBH4 concentration, NaOH concentration, temperature and reusability parameters. The end times of this hydrolysis reaction using raw kaolin-CoB and CH3COOH-kaolin-CoB were found to be approximately 140 and 245 min, respectively. The maximum hydrogen generation rates (HGRs) obtained at temperatures 30 °C and 50 °C were 1533 and 3400 mL/min/gcatalyst, respectively. At the same time, the activation energy was found to be 49.41 kJ/mol. 相似文献
10.
Saka O. Gbadamosi Sumbo H. Abiose Rotimi E. Aluko 《International Journal of Food Science & Technology》2012,47(4):731-739
Functional properties, amino acid compositions, in vitro protein digestibility, electrophoretic and thermal characteristics of conophor defatted flour (CDF), conophor protein concentrate (CPC), isoelectric protein isolate (CII) and neutral protein isolate (CNI) were evaluated. The isolates (CII and CNI) showed significantly lower (P < 0.05) water and oil absorption capacities, emulsifying and gelling capacities, but higher emulsion stability and foaming capacity. In vitro protein digestibility, enthalpy and denaturation temperature varied between 52.28% and 73.4%, 1.62–4.04 J g?1 protein and 79.7–89.3 °C, respectively. The native proteins were comprised of subunits with molecular weights ranging between 15.3 and 129.3 kDa. The major amino acids in all the samples were aspartic acid, glutamic acid and arginine, whereas the percentages of essential amino acids in CDF, CPC, CII and CNI were 39.35%, 40.46%, 44.54% and 46.04%, respectively. Conophor protein products could be used as functional ingredients in food formulations and for enriching low quality protein diets. 相似文献