A Multisegment Dynamic Model of Ski Jumping

This paper presents a planar, four-segment, dynamic model for the flight mechanics of a ski jumper. The model consists of skis, legs, torso and head, and anns. Inputs include net joint torques that are used to vary the relative body configurations of the jumper during fiight. The model also relies on aerodynamic data from previous wind tunnel tests that incorporate the effects of varying body configuration and orientation on lift, drag, and pitching moment. A symbolic manipulation program, "Macsyma," is used to derive the equations of motion automatically. Experimental body segment orientation data during the fiight phase arc presented for three ski jumpers which show how jumpers of varying ability differ in flight and demonstrate tlie need for a more complex analytical model than that previously presented in the literature. Simulations are presented that qualitatively match the measured trajectory for a good jumper. The model can be used as a basis for the study of optimal jumper behavior in fiight which maximizes jump distance

Hydrodynamics and Pressure Fluctuation of Spouted Beds

This experiment studied with standard deviations and pressue drop. And discuss the effects of different cone angle, particle size and bed height on the minimun spouting velocity and analyzed these data with wavelet transform. The results showed that satndard deviations of pressure drop not only exactly describe the transition of regime but also determine minimun spouting velocity. We find minimun spouting vwlocity increase with bed height, cone angle and particle diameter. After wavelet transform, these data could be divided into several scales are responded to the hydrodynamic changes.本實驗量測壓降與壓力擾動標準偏差變化，觀察其與流態變化之關係，並探討不同圓錐角不同粒子，不同床高下的噴流情形，研究以上各操作變數對最小噴流化速度的影響；並用wavelet transform將原始數據轉換作分析。結果顯示，壓力擾動可以準確判斷流態變化。實驗中當床高，粒徑及圓錐角增加時，所對應的最小噴流化速度會隨之上升。又將原始數據經wavelet轉換後，依不同的頻率大小分成不同的區間，可利用其中的幾個頻率區域的擾動變化，與內部流態之改變相惢較，以準確的判斷噴流床的操作情形

Analysis of Pressure Fluctuation Signals of an L-valve

本實驗裝置採用內徑為 80mm 的壓克力管所製成之下降管和 L-閥。實驗中以量測 L-閥中的固體流量及壓力擾動訊號，探討不同上升床流速、通氣位置、通氣方向和通氣深度對 L-閥的固體流量、壓力差和壓力擾動標準偏差所造成之影響。 結果顯示，固體流量隨通氣位置的降低而增加。當通氣量增加，使下降管中產生大型氣泡時，壓力擾動之標準偏差有急劇增加的現象。由不同通氣方向來看，通氣方向向下時的固體流量雖略小於水平方向通氣，但可使下降管中的壓力擾動明顯減少，即可得到較穩定的操作。以不同的通氣方向，在本實驗之最低通氣位置操作 L-valve 時，比較實驗結果可發現，當下降管底部和 L- valve 水平段所量測到之壓力值幾乎不再增加時，可推測下降管所能產生的壓力差已達到最大值，即已達到其操作上限值。The experimental apparatus consist of the downcomer and L-valve made by the transparent Plexiglas column, 80mm i.d. The influence of the riser velocity, position of aeration tap, aeration direction and aeration depth was determined by the measurement of solid flow rate, pressure drop and pressure fluctuations at various pressure probe position. The results show that the solid flow rate of L-valve increased with lower position of aeration taps. The standard deviation of pressure signals increased sharply with the formation of large gas bubbles in the downcomer. The solid flow rate of downflow of inlet gas was slightly less than that of horizontal flow of inlet gas. But the standard deviation of pressure signals of downflow of inlet gas decreased significantly, causing more stable operation. From comparing the results of different aeration directions by aerating at the lowest position of aeration tap, when the pressure measured in lower part of the downcomer and the horizontal section of L-valve was no more increased, that could suppose that the pressure drop of the downcomer was its maximum value

Compaction Behavior and Mechanical Properties of Uniaxially Pressed Bi-W Composites

Powder metallurgy is a useful route to forming particulate composite materials; however, the densification of hard and soft powder mixtures is usually inhibited by the more refractory phase. The Bi-W powder compacts were uniaxially pressed at room temperature and the compaction behavior and mechanical properties were evaluated. Pressing was performed in incremental steps from ~1 to 540 MPa. After each step, the pressure was relieved and the thickness and sound-wave transit time were measured in situ (in the die), in order to determine the density and sound-wave velocity in the compact. The data show that the unreinforced Bi powder compacts to ~98 pct density at 540 MPa. The W reinforcement inhibits the densification process, resulting in increased levels of residual porosity. The compaction behavior was evaluated using a modified Heckel equation, while the porosity dependence of the ultrasonically determined elastic modulus was described by a site percolation approach. Postcompaction sound-wave velocity and Vicker’s hardness measurements show <5 pct anisotropy between the axial (pressing) and radial directions. The mechanical characterization illustrates the competing effects of the W reinforcement and the associated residual porosity