基于有限元法的航空轮胎瞬态冲击性能分析

利用Abaqus软件建立航空子午线轮胎三维有限元模型,研究航空轮胎冲击地面瞬间橡胶基体和骨架材料的等效应力。结果表明：轮胎冲击地面时,轮胎与轮辋接触部位受力大于轮胎与地面接触部位,更容易发生疲劳失效;骨架材料中带束层帘布等效应力最大,是主要承载部件,冠带层等效应力较小,主要吸收胎面方向的冲击;胎面胶和带束层在胎肩部位出现等效应力峰值,胎面接地中心区域出现低应力区。     

带束层角度对子午胎结构性能影响的三维非线性有限元分析

根据轮胎的几何非线性、材料非线性和橡胶-帘线复合材料的各向异性以及轮胎接触非线性，采用三维非线性有限元法时195／60R14规格子午线轮胎在不同带束层角度情况下的应力分布进行了计算分析，得出轮胎与地面接触过程中轮胎的变形情况、载荷-变形关系、带束层及胎体应力分布等结果，为轮胎结构参数的优化设计提供了有效的指导。     

加强筋单元在轮胎带束层力学性能分析中的应用

根据轮胎材料非线性、接触非线性以及大变形等复杂的力学特性,利用加强筋单元描述钢丝帘线-橡胶复合材料,建立了10.00 R 20全钢载重子午线轮胎的三维非线性有限元模型.借助有限元分析软件MSC.MARC,分析了轮胎在充气压力、垂直载荷以及稳态滚动下各带束层中的应力分布情况.结果表明:在这3种工作状况下,各带束层中的应力分布和大小发生了较大变化;给出了带束层应力在此3种情况下的变化规律.     

带束层对子午线轮胎均匀性影响的有限元分析

以ANSYS通用分析软件为工具，以载重子午线轮胎9．00R20为例，采用层、体和接触单元建立子午线轮胎的三维有限元模型。分析在静态条件下子午线轮胎带束层厚度变化、左右偏移量以及局部密度变化对轮胎径向力波动和侧向力波动的影响。结果表明，在一定充气压力和下沉量下，轮胎径向力随带束层厚度增大单调增大；侧向力随带束层偏移量变化具有方向性，其绝对值单调改变；径向力及侧向力基本不受带束层局部密度变化的影响。     

轮胎骨架材料带束层的有限元分析

使用ABAQUS有限元分析软件,考虑了轮胎材料的非线性、接触非线性及轮胎结构非线性等因素,建立了195/65R15半钢子午线轮胎三维有限元分析模型。探讨充气工况和静负载工况下轮胎及轮胎骨架材料带束层受力变形的情况,并对带束层不同部位帘线的受力及胎肩部位变形情况进行了分析。结果表明,带束层帘线径向受力分布与轮胎接地区域应力分布相似,按照中心轴线对称分布,最大值出现在胎肩位置,约为142N;通过带束层帘线在胎肩部位变形分析可知,帘线在胎肩部位最大周向变形量约为16mm。     

基于Abaqus软件的轮胎有限元模型建立及仿真分析

基于Abaqus软件建立轮胎有限元模型,对305/75R24. 5全钢载重子午线轮胎的充气外缘尺寸、胎肩应力分布、带束层应力分布、胎圈与轮辋接触应力分布进行预测分析。有限元仿真结果表明:轮胎的充气外缘尺寸符合国家标准要求,静负荷状态下沉率满足轮胎的整体刚度要求;胎肩应力最大处位于3~#带束层端部;在充气和静负荷状态下,2~#带束层的应力均小于3~#带束层;胎圈与轮辋过盈配合处及其周围应力较大。     

载重子午线轮胎带束层部分的动态模拟

以12.00R20全钢载重子午线轮胎为研究对象,基于Abaqus软件和组合模型技术建立带复杂胎面花纹的轮胎全局模型,然后基于子模型技术建立带束层部分的三维精细网格模型进行有限元分析。结果表明:静负荷工况下,由全局模型与子模型计算得到的应力场比较一致,且Mises应力最大值均出现在胎体帘布层。自由滚动工况下,两层带束层帘线Mises应力分布非常不均匀,但基本关于中分面对称;第2带束层Mises应力高于第1带束层,且各带束层在胎冠部位Mises应力整体高于胎侧部位;胎冠部位两层带束层Mises应力分布变化不大,胎肩部位Mises应力增大,胎侧部位Mises应力减小;第1和第2带束层帘线Mises应力分布关于中分面的对称情况刚好相反。     

芳纶纤维在子午线轮胎中的应用

采用Abaqus有限元分析软件,研究芳纶纤维在子午线轮胎带束层和冠带层中的应用效果。结果表明:轮胎带束层采用芳纶纤维,第1和第2带束层轴向、横向对称面内周向应力以及带束层端点周向应力均有不同程度下降,提高了轮胎强度和承载能力;冠带层采用芳纶纤维,轴向接地中心线上冠带层肩部应力显著降低,冠带层端点周向应力大幅减小,应力分布均匀性显著提高,能够降低轮胎骨架材料端点破坏的可能性。     

全钢载重子午线轮胎带束层帘线受力的有限元分析

建立11.00R20规格全钢载重子午线轮胎结构力学分析的二维和三维有限元模型,模型考虑了轮胎分析中因大变形而产生的几何非线性和材料非线性问题及轮胎与轮辋和路面的接触问题.采用ABAQUS软件对轮胎模型的装配与充气过程和轮胎在静负荷条件下带束层帘线的受力情况进行了分析,得到的各层带束层受力结果可帮助轮胎结构工程师评价带束层的设计方案.     

带束层结构对高速轿车子午线轮胎印痕和制动性能的影响

利用MSC.Marc有限元软件模拟分析带束层结构对轿车子午线轮胎静态接地印痕、高速制动印痕和制动性能的影响,并将模拟结果与205/55R16 94W试制轮胎实测结果进行对比。结果表明：轮胎静态接地印痕的有限元模拟结果与实测结果接近,具有可靠指导意义;在相同的充气压力和负荷条件下,带束层宽度大的轮胎印痕短轴长度和印痕面积均大于带束层宽度小的轮胎,而印痕长轴长度较小,带束层钢丝帘线角度大的轮胎印痕短轴长度和印痕面积均大于带束层钢丝帘线角度小的轮胎,而印痕长轴长度较小,增大带束层宽度或钢丝帘线角度均能够增大轮胎印痕面积,通过改变带束层结构设计可以提高车辆安全性能;轮胎接地面积随着制动初始速度的提高而减小,导致轮胎接地压力增大,充气压力提高也会使轮胎接地面积减小,接地压力增大。     

Host selection behavior of bark beetles (Coleoptera: Scolytidae) attackingPinus ponderosa,with special emphasis on the western pine beetle,Dendroctonus brevicomis

Detection of weakened hosts from a distance by bark beetles through olfaction was investigated in field experiments. No significant numbers of Scolytidae were attracted to anaerobically treated pine bolts, stem disks, or sugar and ponderosa pine bark including phloem. Treatment of living trees with cacodylic acid induced attacks byDendroctonus brevicomis, D. ponderosae, Ips latidens, Gnathotrichus retusus, andPityophthorus scalptor, beginning two weeks after treatment. There was no significant difference between landing rates ofD. brevicomis andD. ponderosae on screened treated trees and screened controls. There was a significant increase in landing rates ofG. retusus andI. latidens, because both species had penetrated the screen and produced pheromones. Tree frilling alone did not increase the landing rate of bark beetles. Freezing of the lower trunk with dry ice did not increase significantly the landing rate ofD. brevicomis, D. ponderosae, G. retusus, orI. latidens on screened trees, whereas unscreened frozen trees were attacked by all four species. There was no significantly higher landing rate byD. brevicomis, D. ponderosae, I. paraconfusus, I. latidens, G. retusus, orHylurgops subcostulatus on screened trees evidencing symptoms of severe infection by the root pathogenVerticicladiella wagenerii, than on symptornless trees. These experiments show thatD. brevicomis, D. ponderosae, I. paraconfusus, I. latidens, andG. retusus land, apparently indiscriminately, on healthy and stressed hosts. Thus, in these species host discrimination must occur after landing and prior to sustained feeding.These studies were supported in part by the U.S.D.A. Forest Service, Cooperative State Research Services (2598-RRF.W-1 10) and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BM575-04223) to the University of California; and by the Canada Department of the Environment. The findings, opinions and recommendations are not necessarily those of the University of California or the funding agencies.From a thesis submitted by H.A. Moeck to the University of California, Berkeley, in partial fulfillment of the requirements for the degree Doctor of Philosophy in Entomology.     

Defensive strategy of twoHypselodoris nudibranchs from Italian and Spanish coasts

Hypselodoris nudibranchs from different geographic areas (Spain and Italy) have been studied in order to investigate their general defensive strategy. Longifolin (1) and nakafuran-9 (2) are the main ichthyodeterrent allomones used by the mollusks to avoid predation. Evidence of their dietary origin is presented and the very effective strategy against predators, which includes secretion of allomones into the mucus and their storage into specific mantle dermal formations (MDFs), is also discussed.F.P.I.-M.E.C. Spanish fellowship (University of Barcelona) at the I.C.M.I.B.     

Cuticular Hydrocarbons as Chemotaxonomic Characters of Pine Engraver Beetles (Ips spp.) in the grandicollis Subgeneric Group

Cuticular hydrocarbons were extracted, identified, and evaluated as chemotaxonomic characters from all species of adult Ips pine engraver beetles in the grandicollis subgeneric group. The grandicollis group consists of Ips grandicollis (Eichhoff), I. cribricollis (Eichhoff), I. lecontei Swaine, I. montanus (Eichhoff), I. paraconfusus Lanier, I. confusus (LeConte), and I. hoppingi Lanier. In order to provide outgroups for a phylogenetic analysis, cuticular hydrocarbons were also analyzed from Orthotomicus caelatus (Eichhoff), I. latidens (LeConte) (latidens subgeneric group), and I. pini (Say) (pini subgeneric group). Two hundred forty-eight hydrocarbon components were identified by gas chromatography–mass spectrometry. The members of the grandicollis group provided 206 of these compounds. The components represented eight classes: n-alkanes, alkenes, alkadienes, terminally branched methylalkanes, internally branched methylalkanes, dimethylalkanes, trimethylalkanes, and tetramethylalkanes. Different populations of O. caelatus, I. grandicollis, I. lecontei, I. montanus, I. paraconfusus, I. confusus, and I. hoppingi provided no evidence for interpopulational variation in cuticular hydrocarbons. Single populations only were analyzed for I. latidens, I. pini, and I. cribricollis. Sexual dimorphism in cuticular hydrocarbons occurred only in I. lecontei where females produced eight unique components with a pentatriacontane parent chain. Several phylogenetic analyses based on hydrocarbon phenotypes agreed in general with the established morphologically based system of relatedness and with published phylogenies reconstructed from protein and nucleic acid characters. Nearly all hydrocarbon analyses suggested a close relationship between I. grandicollis and I. cribricollis; between I. lecontei and I. montanus; and among the sibling species I. paraconfusus, I. confusus, and I. hoppingi. The presence or absence of specific n-alkanes (n-docosane, n-triacontane); certain dimethylalkanes (terminally branched with octacosane and triacontane parent chains and internally branched with heptacosane, hentriacontane, and docotriacontane parent chains); and 3,7,11-; 3,7,15-trimethylheptacosane permit facile discrimination of I. paraconfusus, I. confusus, and I. hoppingi. These three sibling species are difficult to resolve by external morphology. These data support the species status of I. hoppingi rather than it being considered a host race of the I. confusus complex. They also support the species status of I. cribricollis rather than it being considered part of I. grandicollis. In contrast to other published phylogenies reconstructed from molecular data, phylogenies reconstructed from cuticular hydrocarbons repeatedly place I. lecontei as an integral part of the grandicollis subgeneric group. Thus, cuticular hydrocarbon and pheromone alcohol composition of I. lecontei support its inclusion in the grandicollis subgeneric group.     

Extracts of Flourensia cernua (L): Volatile Constituents and Antifungal, Antialgal, and Antitermite Bioactivities

The chemical components of tarbush (Flourensia cernua) leaves were fractionated by extracting successively with hexanes, diethyl ether, and ethanol. Volatile profiles of each fraction were identified by using GC-MS. The hexanes fraction contained mostly monoterpenoids, while the ethanol fraction volatiles were primarily sesquiterpenoids. Crude fractions were tested for activity against fungi, algae, and termites. Application of as little as 1 g of the essential oil from the hexanes fraction was sufficient to provide visible antifungal activity in bioautography assays. The diethyl ether fraction showed selective activity against the cyanobacterium responsible for the 2-methylisoborneol-induced off-flavor sometimes associated with catfish farming operations. All three fractions exhibited a high degree of antitermite activity.     

A Simulation Model for Heat Pump Dryer Plants for Fruits and Roots.

Dryer design requires food properties, drying rate and mass-heat transfer coefficients. These values change continuously during drying due to changes in food fractions, particularly the water fraction. The high energy demand and costs allied to inefficient devices, creates a great need for new processing equipment. Along these guide-lines, several heat pump drying research projects were established at the Norwegian University of Science and Technology. The heat pump dryer provides high quality final product as its drying conditions can be controlled. Its efficiency and non-polluting operation come from closed air-refrigerant circuits and from its ability to fully recover the latent heat of moist air as it exits the drying chamber. Most of the above features are quite the opposite of the conventional dryer characteristics. Several experiments were made on heat pump drying of fruits and roots at temperatures from -22.5 to 40°C to obtain data and correlations on thermophysical properties, specific enthalpy and rehydration. Also, tests were done on drying rate, moisture content, drying constant, effective mass diffusivity and heat and mass transfer equations. The next important phase is the development of a simulation model to predict the performance and characteristics of the heat pump dryer plant. The objectives of the present work are to develop and lo test a heat pump dryer simulation model. The simulation provides results on the characteristics of both plant and components which are integrated by heat and mass transfer equations. The program has menus with click-on icons, input and output pop-up dialogue boxes. The usual commands such as, file-open, file-save, edit-delete are available in this program simply called Hpdryer. The model contains moist air psychrometric. natural and conventional refrigerant property libraries. Ammonia is a time-tested, self-alarming and natural refrigerant. It has been used extensively in the past, and it has better thermodynamic and transport properties than halocarbons. Safety is easily attained by design and its restrictive standards have helped increase its use in several countries. There are 36 ammonia installations in Norway and in the United Kingdom, including a drying plant. Ammonia has zero Odp, zero Gwp and the recent R&D has led to viable small-sale heat pump plants. Ammonia and dichlarodifluoromethane refrigerants were used in the test cases simulated by Hpdryer madel.     

Recognition of aphid parasitoids by honeydew-collecting ants: The role of cuticular lipids in a chemical mimicry system

The aphidiid waspLysiphlebus cardui parasitizes in ant-attendedAphis fabae cirsiiacanthoidis colonies without causing aggressive behavior in the antLasius niger. By contrast,Trioxys angelicae, another aphidiid parasitoid of aphids, is rapidly recognized and vigorously attacked by the ants.L. niger workers also responded differently to dead individuals ofL. cardui andT. angelicae. DeadL. cardui parasitoids were often ignored when encountered byL. niger, whereas deadT. angelicae individuals were immediately grasped by ants that discovered them. However, hexane-washed parasitoids caused a similar reaction pattern in the ants, in that both aphidiid species were tolerated in the aphid colony. Lure experiments demonstrated that chemical stimuli on the cuticle are major cues for the ants to distinguish between the parasitoids. The hexane extract ofL. cardui transferred to washed individuals ofT. angelicae resulted in ant responses characteristic towardsL. cardui, andL. niger workers displayed the typical removal pattern they normally showed towardsT. angelicae whenT. angelicae extract was applied toL. cardui individuals. Both parasitoid species treated with the hexane extract ofA. fabae cirsiiacanthoidis were similarily treated by the ants as were aphid control individuals. The suggestion that the aphidiid waspL. cardui uses chemical mimicry is discussed.     

ON ESTIMATING THRESHOLDS IN AUTOREGRESSIVE MODELS

Abstract. The problem of estimating the threshold parameter, i.e., the change point, of a threshold autoregressive model is studied. By introducing smoothness into the model, sampling properties of the conditional least-squares estimate may be obtained. Artificial and real data are used for illustrations.     

Identification and Distribution of Oviposition Stimulants for Monarch Butterflies in Hosts and Nonhosts

Flavonol glycosides that act as oviposition stimulants for monarch butterflies were surveyed from a range of asclepiad hosts and some nonhosts. Major stimulants also were identified as quercetin-3-O-(2-O--xylosyl)--D-galactoside and quercetin-3-O--D-galactoside from Asclepias syriaca and A. incarnata, respectively. The flavonol glycosides in A. curassavica, A. tuberosa, A. incarnata, A. syriaca, A. humistrata, A. albicans, A. eriocarpa, Calotropis procera, Cynanchum acutum, Vincetoxicum (Cynanchum) nigrum and in nonhosts Hoya australis and Nerium oleander were compared and characterized by HPLC and spectral studies. There was great variation in quercetin glycoside content. On the basis of the sugar moieties attached to quercetin, the asclepiad glycosides were classified broadly as those containing: (1) galactose, glucose, and rhamnose; (2) galactose, glucose, and xylose; and (3) galactose, glucose, xylose, and rhamnose. In most cases, galactose was attached to the 3-O-position (1) of quercetin and other sugars were attached either to the 2 or 6 position of galactose. The sugars of triglycosides were attached at both 2 and 6 positions. A geographical pattern of flavonol distribution that may have affected the evolution of host recognition by the butterflies is suggested.     

Attraction of Dibrachys cavus (Hymenoptera: Pteromalidae) to its Host Frass Volatiles

The European grapevine moth, Lobesia botrana (Lepidoptera: Tortricidae), is a polyphagous insect able to develop on grapes and wild plants. We tested the hypothesis that the parasitoid Dibrachys cavus (Hymenoptera: Pteromalidae) uses the larval frass in its host search. A two-armed olfactometer was used to measure the attractiveness of L. botrana larvae, their silk, or their frass after larvae were fed on different host plants. Frass of three Lepidoptera (L. botrana, Eupoecillia ambiguella, Sphinx ligustri) and one Orthoptera (Chorthippus brunneus) was assayed, but only L. botrana was used to test an effect of the larval host plant (two grape cultivars and three other plant species) to D. cavus females. Larvae without frass did not attract D. cavus whatever their origin, but their frass was attractive at a dose of 2–3 days equivalent of larval frass production. The silk produced by a single larva (L. botrana) was not attractive to D. cavus. The parasitoid was most attracted to the odor of S. ligustri; the frass of L. botrana was more attractive than that of E. ambiguella, irrespective of the species on which D. cavus had been reared. There was no difference in attractiveness of frass collected from L. botrana raised on food containing different plants. Chemical extracts using five different polarity solvents (acetone, dichloromethane, hexane, methanol, and water) differed in attractiveness to D. cavus. Water and dichloromethane were the most attractive. This suggests that a complex volatile signal made from intermediate to polar volatiles may be involved in attraction. D. cavus used frass to discriminate between different potential host species. Our results revealed that the larval food of L. botrana did not modify frass attractiveness, but that the moth species did.     

Interspecific activity of semiochemicals among sibling species ofPissodes (Coleoptera: Curculionidae)

Pissodes strobi, P. approximatus, andP. nemorensis are sibling species of pine weevils that can hybridize in the laboratory but are presumed to be reproductively isolated in nature. Males of all three species produce the terpenoids grandisol and grandisal; these compounds serve as an aggregation pheromone forP. approximatus andP. nemorensis when deployed with odors from pine bolts. A series of field experiments examined the possibility of cross-attraction among the three species. Tests in New York and Florida found that parapatrically distributedP. approximatus andP. nemorensis were cross-attractive, but different photoperiodic conditioning was required for pheromone production in males of the two species. Long-day pheromone production (P. approximatus-type.) was inherited in interspecific hybrids. Other tests showed thatP. strobi males, or hybrid males from crosses ofP. strobi withP. approximatus, were not attractive to sympatricP. approximatus. When the response ofP. strobi was assessed to males of eitherP. strobi orP. approximatus confined on white pine leaders (the breeding site ofP. strobi), no evidence of cross-attraction or pheromone activity was found;P. strobi were caught in equal numbers onP. strobi-baited leaders,P. approximatus-baited leaders, and unbaited leaders. Tests of interspecific interactions found that maleP. strobi produce an allelochemical signal that interrupts the response ofP. approximatus to its natural or synthetic aggregation pheromone. This interspecific response is apparently adaptive for members of both species (classified as an allomone-kairomone or synomone) because it may ultimately serve to prevent interspecific matings that would lower the fitness of the parents.