Application of the vibration method with additional mass to timber guardrail beams

This study examined whether or not weight, density, and Young’s modulus can be accurately measured by vibration test without weighing beams for timber guardrails. Bending vibration tests with and without the concentrated mass were performed on small clear round bars without the pith of spruce and cedar and on actual size round bars with the pith of cedar for the timber guardrail. The following results were obtained. The vibration method with additional mass could be applied to the round bar as well as the rectangular bar. It is possible that resonance frequency was decreased by the sawn split in the horizontal tapping. It is believed that the free ends condition is easier to realize than the fixed ends condition for cross beams for timber guardrails. The weight of the cross beam for the timber guardrail could be accurately estimated by the vibration method with additional mass under several testing conditions.     

Fixed–fixed flexural vibration testing method of actual-size bars for timber guardrails

Resonance frequencies of bars with various types of end supports were examined in terms of flexural vibration. Sugi (Japanese cedar, Cryptomeria japonica D. Don) was used for the specimens. Small rectangular bars with dimensions of 25?mm (R)?×?5?mm (T)?×?300?mm (L), small round bars of 25?mm in diameter and 250?mm in length, actual-size rectangular bars with the dimensions of 45?mm (R)?×?95?mm (T)?×?1500?mm (L) and actual-size round bars of 180?mm in diameter and 2000?mm in length were made. Varying compression stress was applied to the parts around both ends of test specimen, whereupon flexural vibration tests were performed. The measured resonance frequency rose rapidly early in the increasing compression load process and was nearly stable for the larger compression load. The significant increases in the resonance frequency for round bars are thought to be derived from the wide area between the round bar and jig. It is necessary to compare the resonance frequency of a bar tightly fixed to a post with that of the same bar loosely fixed to the post.     

现浇砼连续箱梁扣件式钢管支架的计算及施工

构造简单，安装方便，荷载作用下稳定性比较好的扣件式钢管支架，是目前桥梁施工中应用最广泛的一种支架。现就使用前在组合荷载作用下，格构式钢管支架整体稳定及单根钢管立杆局部稳定进行验算。安装时，支架立杆的纵距、横距及水平杆的步距要根据验算结果进行。安装顺序，立杆沿桥纵向由一端向另一端，水平杆由下向上进行。支架安装完成后，应做预压试验，以检查支架的压缩量及稳定性。     

Relationships between longitudinal and radial Picea genera sound vibration parameters

Longitudinal sawn wood are usually selected as samples in the study of sound properties of a musical instrument board. But in real production, radial sawn timber are cut and are also widely used as vibration component. Therefore, it is very important to evaluate the vibration properties of the board in the round, especially for the sound radiation characteristic of radial sawn timber and its relationship to longitudinal sawn timber. However, for the national and international experts, researches on radial sawn timber and its role and function in sound emission have not yet been developed. This paper describes a study of seven important spruces that grow up in the Sichuan and Heilongjiang provinces of China, and one Picea sitchensis specimen from North America. Under the high bending vibration mode, resonance frequency and other parameters of longitudinal and radial wood were tested. Analysis result disclosed the relationship between longitudinal and radial wood vibration property. An important conclusion of wood for musical instruments with proper anisotropy, fine toughness, and weak shear of longitudinal and radial vibration was inducted. __________ Translated from Scientia Silvae Sinicae, 2006, 42(3): 21–24 [译自: 林业科学, 2006, 42(3): 21–24]     

Elastic parameters of poplar wood with end-cracks

? In this study, longitudinal specific modulus of elasticity along the grain (specific MOE_L = MOE_L/ρ) as well as radial and tangential shear moduli (G _LR and (G _LT ) of Populus Deltoides wood were examined in free flexural vibration in a free-free bar method, where end-cracks produced manually in LT plane along and parallel to annual rings in four different sizes.

? The effects of four different crack sizes (0, 6, 12, and 18 cm) on elastic parameters of the bars were examined for their vibration properties based on Timoshenko bar equations, in order to find a procedure to make a confident choice of a clear specimen among the cracked ones, considering three initial modes of vibration.

? Based on research findings, a significant correlation existed between radial and tangential shear moduli of the clear bars as G _LR was approximately 15 percents higher than (G _LT . After making the shortest crack sizes, however, this correlation entirely faded. Statistically for 6 cm crack, decreases in specific MOE _L for measurement on the tangential impact were not significant though they were for longer cracks.

? It was also revealed that in specimen under the study if longitudinal specific modulus of elasticity from both LR and LT flexural vibrations were almost equal and G _LR was slightly larger than (G _LT , the user could be confident enough to consider the specimen without severe longitudinal cracks.

     

Permeability and meniscus phenomenon in four Korean softwood species

1 Introduction A number of studies have been carried out to examine the process of liquid impregnation into different kinds of wood (Stamm and Raleigh, 1967; Bolton and Petty, 1978; Olsson et al., 2001). Different techniques and methods have been developed so far to obtain quanti- tative and qualitative information about this process (Stamm, 1953; Stone, 1956; Rudman, 1965). Penetra- tion of liquid in wood depends on several factors. The penetration rate and amount varies in different spec…     

Inorganic elements in typical Japanese trees for woody biomass fuel

The inorganic element contents of trees were measured to evaluate the safety of using wood biomass as thermal power generation fuel. Twelve species of typical conifer trees and 17 species of typical broad-leaved trees in Japan plus 9 species of commonly imported trees were selected and analyzed for the main inorganic elements and several trace elements that are potentially harmful in combustion ash. The ash content in bark, especially in the inner bark, was higher than that in wood, but the highest concentration was in the leaves. In almost all parts of the trees, the order of inorganic element concentration was calcium ≥ potassium ≥ magnesium ≥ sulfur ≥ phosphorous. Among the trace elements, the boron content was high and the mercury content was recorded as being high in conifer bark.     

Chemical treatment of wood for musical instruments. Part I: acoustically important properties of wood for the Ranad (Thai traditional xylophone)

The purpose of this study is to determine the important acoustic properties of wood for making Ranad bars and the resonator box. The woods used in this study were separated into two groups. The first group is the type of wood that has been used to make Ranad for centuries: Ching-Chan (Dalbergia oliveri Gamble) and Ma-Had (Artocarpus lakoocha Roxb.) for making the bars, and Ka-Nun (Artocarpus neterophylla Lamk.) out of which the resonator box is made. The second group comprises woods that are abundant in Thailand and are genetically related to the first group. The physical and mechanical properties of the woods in both groups were measured including the specific dynamic Youngs modulus (E/), density (), hardness (H), acoustic conversion efficiency (ACE), and sound refraction coefficients (||). The results revealed that high and consistent || were crucial factors of the Ranad bar properties in addition to E/, , and H. The results from measurements made on the resonator box wood revealed that high E/, ACE, and high and consistent || were its crucial properties.     

Natural vibration analysis of clear wooden beams: a theoretical review

 In wood science, natural vibration analysis is being used to an increasing extent to characterise the longitudinal and the shear modulus of elacticity of various geometrical types of prismatic beams. A lateral or a axial percussion at one end of a beam set up on elastic support produces bending or longitudinal vibrations. Considering the hypothesis of the homogeneity of geometrical and mechanical properties of the beam, basic dynamics theorems can be applied to obtain the motion equations of longitudinal and transverse vibrations. The resolution of the differential equation for transverse motion leads to a search for solutions to the frequency equation. Because no exact analytical solution can be found, several approximate results are analysed. The application and validity range have to be defined to be able to achieve realistic results. The effects of the elastic support, the shear modulus and the height to length ratio are discussed. The conceptual bases help in understanding the analytical results and accuracy calculations can then be developed for practical applications. We present the most common theoretical models and define their validity range, application conditions, and accuracy levels with respect to measured values. Received 26 June 2000     

渐开线油锯导板的线型设计

在对现有油锯“三圆弧”导板的缺陷进行分析的基础上，提出了以渐开线作为油锯导板外廓线型的设想．并对有关问题进行了推导和讨论．分析表明，这种方法可消除锯链运动时导权头部与主体街接处产生加速度的突变现象，减轻导板与锯链间的横向冲击振动，改善锯链与导板间的运动动力学特性，从而达到提高锯切质量，延长导板使用寿命之目的．     

对变形钢筋套管连接技术的探讨

变形钢筋套管连接技术是采用机械式钢筋连接方法解决工程中的钢筋连接问题。本文从工作机理、挤压设备、操作工艺及技术经济等方面探讨了该技术在工程实践中的应用.并分析了技术经济特点及该技术的发展前景。     

LY12合金冷拉棒性能的研究

对淬火前的热挤压棒用不同的冷拉拔量进行拉拔，结果表明；冷拉拔量对棒材的组织和性能有不同的影响．当变形量达到10％时，经淬火后的棒材其组织是均匀的细晶组织．     

Palm “wood”

The fine structure of differentiating and mature sieve elements, tracheary elements and fibers of palms has been studied. The fine structure of sieve elements in general resembles that of the sieve elements in angiosperms except that not all the species of palms have P-protein. Material examined after taking precautions to minimize sudden release of pressure in the phloem indicate that the sieve-plate pores may be free of occlusions in intact sieve elements. Sieve elements in the basal parts of the stem estimated to be several decades old maintain their structural integrity and apparently remain functional throughout the life of the palm. Differentiating xylem elements are characterized by the presence of amoeboid plastids with electron-dense granular stroma. All the organelles normally present in meristematic cells are also present in differentiating tracheary elements. Bundles of microfilaments are often present in such elements. Structural changes that occur as the tracheary element matures are comparable to those observed in tracheary elements of other angiosperms. Xylem parenchymatous cells do not have the so called protective wall layer. The most striking ultrastructural feature in differentiating fibers of the root is the deep invagination of plasmalemma that traverses almost the entire width of the cell. The secondary wall of the fibers is characteristically multilayered.This paper was presented at the Eighth Cellulose Conference, Syracuse, New York, U.S.A.     

Nutrient cycle of planted forest of Pinus tabulaeformis in the Miyun Reservoir Watershed, Beijing

We studied the nutrient cycle of a planted forest of Pinus tabulaeformis in the Miyun Reservoir Watershed, Beijing. Results show that the total biomass of P. tabulaeformis stands at age 29 in the experimental area is 92627 kg/hm², and the total nutrient store is 695.17 kg/hm² including nitrogen (N), phosphorus (P), kalium (K), calium (Ca) and magnesium (Mg). The sequence of their contents in different organs was given as follows: needle>branch> trunk>root. The annual amount of 85.37 kg/hm² of five nutrient elements were assimilated by P. tabulaeformis, about 0.34% of the total store in soil, and 3.30% of available nutrient store in soil depth from 0 to 30 cm. The nutrient annual retention is 35.92 kg/hm², annual returning 49.46 kg/hm², the rain input 26.04 kg/hm² to the five nutrient elements. The parameter absorption coefficient, utilization coefficient, cycle coefficient and turnover period were cited to describe the nutrient elements cycle characteristic of the planted forest ecosystem of P. tabulaeformis. The absorption coefficient is the ratio of plant nutrient element content to soil nutrient element content, and its sequence of five nutrient elements was given as follows: N>P>K>Ca>Mg. Utilization coefficient is the ratio of the nutrient element annual uptake amount to the nutrient element storage in standing crops, and its sequence of five nutrient elements was: Mg>K> P>N>Ca. The big utilization coefficient means more nutrients stored in the plant. The cycle coefficient is the ratio of the nutrient element annual return amount to the nutrient element annual uptake amount, its sequence: Ca>N>P>K>Mg. Turnover period is the ratio of the nutrient storage in the crops to the annual returning, its sequence: Mg>K>P>N>Ca. __________ Translated from Journal of Beijing Forestry University, 2008, 30(3): 51–56 [译自: 北京林业大学学报]     

Presence of double‐stranded RNA in Heterobasidion annosum

A search for double‐stranded RNA (dsRNA) was conducted among 204 European isolates of the pathogenic fungus Heterobasidion annosum. Nucleic acids were extracted and purified by cellulose CF‐11 chromatography or lithium chloride precipitation. dsRNA was present in eight of the isolates and was confirmed by nuclease digestion. The dsRNA elements ranged between 1.8 and 2.4 kbp and were found in two H. annosum intersterility groups, S and P. Partial amino acid sequence information from one dsRNA element showed significant homology to RNA‐dependent RNA polymerases from several fungal partitiviruses. This is the first report of the presence of dsRNAs in H. annosum. Possible implications of dsRNA for the biology of the fungus and the potential for biological control are discussed.     

Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba)

Vibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry (Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tanδ), storage (elastic) modulus (E′) and specific modulus (E′/γ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by dynamic mechanical analysis. Native wood had a quite low E _L′/γ but its tanδ was smaller than expected, and the anisotropy of tanδ and E′/γ was very low. Removal of extractives caused tanδ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tanδ _L by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E′/γ was nearly unchanged after extraction in methanol or hot water, while tanδ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance.     

Identification of defect position in a wooden beam from the power spectrum of longitudinal vibration

The inverse solution procedure that enables the identification of the defect position in a beam from the resonance frequency was exploited. Resonance frequency shifts of a power spectrum due to defects in a longitudinally vibrating beam when both ends are free were investigated by both numerical and experimental analysis. Calculation by a transfer matrix method showed that the frequency shift was large when the defect position coincides with a node of vibration and that no shift occurs when it coincides with a loop of vibration. The frequency shift could be approximated by a sinusoidal curve. Calculation results agreed well with those of the experiment in which artificial round holes were drilled as the defect model. Experimental equations predicting the amount of the frequency shift in function of the defect position were obtained. In the inverse procedure, the defect position was determined by comparing the resonance frequencies between the experimental and estimated power spectra so that the coincidence factor S(x) became a minimum. The results showed the validity of the proposed method to identify the defect positions of fewer than two predominant defects.     

TH42160龙门加工中心的动态特性分析

建立了HT42160型数控龙门加工中心的左、右立柱和整机的三维及有限元模型,并分别进行了静、动态分析,借助ANSYS、分析软件,得到了左、右立柱及整机在自由和约束状态下的前五阶固有频率和主振型,并在此基础上找出该龙门加工中心结构的薄弱环节,为龙门加工中心的结构优化设计提供理论依据和技术支持。