Large scale physical model testing on the ultimate strength of a steel stiffened plate structure under cyclic compressive loading

See the pdf fil

Large scale physical model testing on the ultimate compressive strength of a steel stiffened plate structure at cryogenic condition

Ship structures are typical examples of large plated structures which are made of large number of structural elements composed into system structures to be strong enough, while keeping the structural weight at minimum, to survive varying loads arising from cargo (e.g. weight and cryogenic condition due to LNG cargo), waves, winds or other environmental conditions (e.g. cold temperature due to Arctic operation). The design of ship structures are today designed based on limit states which are defined by the description of a condition for which a particular structural member or an entire structure would fail to perform the function designated beforehand. Four types of limit states are relevant, namely SLS (serviceability limit state), ULS (ultimate limit state), FLS (fatigue limit state) and ALS (accidental limit state). At the preliminary design stage, structural scantlings and materials of ship structures are determined based on the ULS, and ultimately other types of limit states are integrated to ensure so that the different parts of a ship structure will meet safety requirements and survive environmental and operational conditions during the life time period of some 25 years. \ua0The stiffened plate structures in the bottom, the deck and the side-shell are the most important parts of a ship in association with a ship’s integrity, safety and survivability. The design criteria for determining the scantlings of stiffened plate structures are the ultimate limit states (or ultimate strength). If applied loads exceed the ultimate strength then the stiffened plate structures fail to perform the function, leading to total loss of the ship. Therefore, it is of vital importance to accurately and efficiently compute the ultimate strength of stiffened plate structures. The behavior of stiffened plate structures until and after the ultimate strength is reached is highly nonlinear involving geometric nonlinearities (e.g. buckling and large deflection) and material nonlinearities (e.g. yielding, plasticity and material failure or fracture). Various types of collapse modes, including overall buckling collapse, beam-column type collapse, web buckling induced collapse and flexural-torsional buckling induced collapse, are relevant. Today\u27s large merchant ship structures are made of different grades of steel materials that should meet specific requirements for yield strength, ductility, brittleness, ultimate tensile strength resistance to corrosion in association with operational and environmental conditions.\ua0\ua0As of today, the ultimate strength of stiffened plate structures has been studied and applied in room temperature conditions. However, ships now operate in Arctic region at cold temperatures as climate change causes Arctic ice to melt at an alarming rate. A shipping company MAERSK recently navigates a 200m long container ship through the Arctic waters for the first time without the help of icebreakers. The average ambient temperature in Arctic region during winter season is -40 deg. C and the lowest temperature is reportedly -68 deg. C. Furthermore, the number of LNG-fueled ships is increasing in terms of resolving the issues associated with CO2 emissions. LNG-fueled ships need to have LNG fuel tanks in a large size, and hazards of LNG leakage always exist. The temperature of LNG is -163 deg. C. The collapse behavior of ship stiffened plate structures is vulnerable to cold temperatures or cryogenic condition in association with catastrophic failure, leading to total loss of ships that can affect personnel, assets and the environment, where brittle facture must be playing a significant role on the ultimate strength behavior. Theoretical methods are almost impossible to apply for computing such a highly nonlinear behavior of ship stiffened plate structures involving buckling, yielding and brittle fracture. Advanced computational models should be developed for that purpose. However, it is highly demanding to obtain physical model test database which shall be used to validate the accuracy and applicability of the advanced computational models.\ua0The purpose of the present study is to obtain physical model test database on the ultimate strength characteristics of ship stiffened plate structures subject to extreme loads and cold temperatures (due to LNG leakage). Physical model testing on a large scale ship stiffened plate structure is undertaken at cryogenic condition (-160 deg. C). Elastic-plastic large deflection behavior of the test model under axial compressive loads is measured until and after the ultimate strength is reached. Material properties at cryogenic temperature are tested in separate material experiments. Details of the test database are documented

Report on the Observation of a Dark morph Tree Sparrow (Passer montanus) in Daejeon Metropolitan City

AbstractOn March 16th, 2010, at 13:35, a single count of dark morph tree sparrow (Passer montanus) was observed for approximately 15 minutes while it was resting with approximately 30 ordinary tree sparrows at a terrace land on water (east longitude 127°21′31.4”, north latitude 36°18′20.2”) under Gasuwon Bridge (Gasuwongyo) of Gasuwon-dong, Seo-gu in Daejeon Metropolitan City. Dark morph tree sparrow has not been observed in nature for 16 years since its observation in Pyeongtaek-gun of Gyeonggi-do by the Korean Avian Association in 1994

Electric field control of nonvolatile four-state magnetization at room temperature

We find the realization of large converse magnetoelectric (ME) effects at room temperature in a multiferroic hexaferrite Ba$_{0.52}$Sr$_{2.48}$Co$_{2}$Fe$_{24}$O$_{41}$ single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62 $\mu$$_{B}$/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients

Realization of giant magnetoelectricity in helimagnets

We show that low field magnetoelectric (ME) properties of helimagnets Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 can be efficiently tailored by Al-substitution level. As x increases, the critical magnetic field for switching electric polarization is systematically reduced from ~1 T down to ~1 mT, and the ME susceptibility is greatly enhanced to reach a giant value of 2.0 x 10^4 ps/m at an optimum x = 0.08. We find that control of nontrivial orbital moment in the octahedral Fe sites through the Al-substitution is crucial for fine tuning of magnetic anisotropy and obtaining the conspicuously improved ME characteristics

Visceral Myopathy of Intestinal Pseudoobstruction

Intestinal pseudoobstruction is a syndrome complex caused by a variety of disorders of various etiology. It can be classified pathologically as visceral myopathy and visceral neuropathy. The sporadic form of visceral myopathy is characterized histologically by vacuolar degeneration and fibrosis of smooth muscle but differs from the familial form only by the absence of other affected family members. We studied 6 cases with intestinal pseudoobstruction classified as sporadic visceral myopathy. They were four boys and two girls, and were two neonates, two infants and two children. The duration of symptoms ranged from two days to two years. Two babies were dead from pneumonia and sepsis. Others were alleviated after surgical resection of the bowel. Both small and large intestines were found affected in autopsy cases. Histopathologic features were vacuolar degeneration of muscularis propria, disproportionate hypoplasia of outer muscle layer, abnormal muscle direction of muscularis propria, submucosal and/or interstitial fibrosis and extra muscle layering. It is presumed that a variety of histopathologic features accounts for visceral myopathy of intestinal pseudoobstruction