Search

Loss of foliage in soybean crop through leaf eating insects and diseases is common in tropical and sub-tropical countries where farmers do not protect their crops adequately. Experiment was performed under sub-tropical condition (24°8' N, 90°0' E) with four levels of defoliations (0, 25, 50 and 75% from base of the canopy). Defoliations were imposed at the visible bud initiation stage to investigate the growth and yield attributes in two popular soybean varieties during January to April 2011. Results revealed that degrees of defoliations simultaneously decreased leaf area and total dry matter (TDM) production irrespective of varieties. Defoliation not only reduced source sizes but also decreased total sink (pod) production resulting in lower seed yields. However, basal 25% defoliation did not decrease TDM, seed weight/plant and seed yield/ha significantly indicating the fact that the soybean plant, in general, can tolerate 25% basal leaf loss of the canopy. Exceeding this threshold limit (>25%) of the canopy defoliation reduced TDM and seed yield significantly. Implication of the results in relation to pest management was also discussed.

A theoretical approach is developed and a computational procedure adaptable to a high speed digital computer is established for the evaluation of the blade pressure distribution of a marine propeller due to thickness and loading effects. The dual role of the blade thickness is considered. The contribution of the nonplanar thickness to the propeller loading and pressure distribution and the effect of the flow distortion thickness are studied by means of the thin body approximation. The surface integral equation which relates the unknown loading to the known velocity distribution on the blades is solved by the mode approach in conjunction with the lift operator technique. The analysis treats both design and off-design conditions in steady-state and unsteady flows, and the proper chordwise modes are selected for each condition. The numerical solution yields the blade loading and resulting hydrodynamic forces and moments and blade bending moments, and, in addition, the blade pressure distributions on each blade face due to both loading and thickness effects, thus providing information necessary for the prediction of cavitation inception. Calculations have been performed for a set of three 3-bladed propellers of different EAR operating in a screen-generated wake, for comparison with experimental data.

This study is a continuation of an earlier investigation dealing with the interaction of a propeller and its enshrouding nozzle when both are operating in a nonuniform inflow field. The present investigation complements the previous one by introducing thickness of both lifting surfaces and camber of the duct. Thus a complete analysis is available which takes into account the true geometry of the propeller and duct, including the propeller and duct thickness and duct camber distributions along with the camber and flow angle of the propeller and the conicity angle of the duct. A computer program adaptable to a high-speed digital computer has been developed which evaluates the steady and time-dependent pressure (loading) distributions on both lifting surfaces and the resulting hydrodynamic forces and moments generated by the propulsive device. Provision has also been made in the analysis and program to deal with a nonaxisymmetric nozzle and a tilted nozzle.

The mathematical model used in previous Davidson Laboratory adaptations of linearized unsteady lifting surface theory to marine propellers has been revised by removing the so-called 'staircase' approximation of the blade wake and replacing it by an 'exact' helicoidal blade wake. A new numerical procedure and program based on the present model has been developed to evaluate the steady and unsteady blade loading distributions, which are used to determine the bearing forces and moments. Systematic calculations of these forces and moments for a series of propellers show better agreement on the whole with experimental measurements than did the earlier calculations for the same series. In addition, the chordwise loading distributions are much smoother than obtained previously. However, the quantitative improvement must be weighed against the considerable increase in computer time over the old method.

A brief review is presented of the unsteady lifting surface theory and of the 'generalized lift operator' technique of inverting the 'downwash' integral equation. The integral equation approach is then employed to predice responses of various foils to pitching oscillations and to forward motion in a regular wave train. The agreement between theoretical predictions and experimental results is good for simple configurations without appendages, but not in the case of the AG(EH) configuration at low frequencies because the presence of the pod is not taken into account in the theoretical calculations. Although the attempt made to remove the spurious leading-edge singularity in the chordwise pressure distribution before inverting the integral equation is questionable, removal of the singularity after the inversion yields responses consistent with other theoretical and experimental trends. (Modified author abstract)

The propeller-rudder interaction problem is studied by means of the unsteady lifting-surface theory. Both surfaces of arbitrary geometry are immersed in a nonuniform flowfield (i.e., hull wake) of an ideal incompressible fluid. The boundary-value problem yields a pair of surface integral equations, the inversion of which is achieved by the so-called 'generalized lift operator' technique, a new approach developed by the authors, in conjunction with the presently used 'mode-collocation' method. The analysis demonstrates the mechanism of the interaction phenomenon by exhibiting the filtering effects of the propeller on the harmonic constituents of the wake which allow the rudder to be exposed only to the blade harmonic and multiples thereof. A numerical procedure adaptable to the CDC 6600 computer was developed which furnishes information about (1) the steady and time-dependent pressure distribution on both lifting surfaces, and (2) the resultant hydrodynamic force and moments. A limited number of calculations exhibits the importance of some parameters such as axial clearance, number of blades, and harmonic components of the hull wake. (Author)

The previous analysis of the propeller-rudder interaction problem by means of the lifting surface theory has been modified to include the effects of thickness of both surfaces. The effect of thickness on the 'flow displacement' in the field is taken into account by the 'thin body' approach. The blade thickness effect on the loading of the propeller blade due to its non-planar form, being small, is neglected. The resulting field are incorporated, together with the onset velocities due to hull wake and camber and incident angle of the surfaces, into the existing iterative procedure. The numerical procedure, adapted to the CDC-6600 high-speed digital computer, furnishes the steady and time-dependent pressure distributions on both lifting surfaces and the resulting hydrodynamic forces and moments. (Author Modified Abstract)