Multiple Span Research Articles

HAWT dynamic stall response asymmetries under yawed flow conditions

AbstractHorizontal axis wind turbines can experience significant time‐varying aerodynamic loads, potentially causing adverse effects on structures, mechanical components and power production. As designers attempt lighter and more flexible wind energy machines, greater accuracy and robustness will become even more critical in future aerodynamics models. Aerodynamics modelling advances, in turn, will rely on more thorough comprehension of the three‐dimensional, unsteady, vortical flows that dominate wind turbine blade aerodynamics under high‐load conditions. To experimentally characterize these flows, turbine blade surface pressures were acquired at multiple span locations via the NREL Phase IV Unsteady Aerodynamics Experiment. Surface pressures and associated normal force histories were used to characterize dynamic stall vortex kinematics and normal force amplification. Dynamic stall vortices and normal force amplification were confirmed to occur in response to angle‐of‐attack excursions above the static stall threshold. Stall vortices occupied approximately one‐half of the blade span and persisted for nearly one‐fourth of the blade rotation cycle. Stall vortex convection varied along the blade, resulting in dramatic deformation of the vortex. Presence and deformation of the dynamic stall vortex produced corresponding amplification of normal forces. Analyses revealed consistent alterations to vortex kinematics in response to changes in reduced frequency, span location and yaw error. Finally, vortex structures and kinematics not previously documented for wind turbine blades were isolated. Published in 2000 by John Wiley & Sons, Ltd.

Optimised dispersion management scheme for long-haul optical communication systems

Using the distributed under-compensation scheme (DUCS) in every fibre span, the overall transmission distance of 10 Gbit/s NRZ and RZ multiple span systems is doubled. The benefits of such a dispersion management scheme are clarified by defining a new figure of merit.

Slab behavior and approximation of transverse strain increase due to the change of support conditions from rigid to elastic supports

When existing multiple simple span bridges are converted into a continuous span in order to increase the load carrying capacity by connecting each opposite ends of the simple beams, the rigid support conditions (pin and roller supports) have to be changed to elastic supports in order to absorb and distribute the energy of large horizontal motion due to earthquake loading. However, it may overlook the development of additional stress in the transverse direction of the slab due to the relative vertical displacement of the elastic support. In this study, a simple span bridge specimen of 1/6 scale is tested and analyzed by the use of F.E.M. to investigate strain increase in the transverse direction of the slab when the rigid supports are replaced by the elastic supports. Both test and analytical results exhibit a notable increase of transverse stress throughout the whole feasible range of the vertical support stiffness.

Fast heuristic principle for spare capacity placement in mesh-restorable SONET / SDH transport networks

The authors propose a useful new insight into the problem of spare capacity design for mesh-restorable networks. A straightforward heuristic of average case complexity O(S) based on the new principle is within 21% (13% on average) of the minimum capacity and runs 8.5-80 times faster than the optimal integer program (IF). Application to evaluate benefits from six new span addition candidates in a 53 node, 81 span network yielded the correct rank-order of merit 650 times faster than optimal methods. This contributes to a practical assault on the problem of finding the globally best single or multiple new span additions in the evolution of large transport networks.

North American approach to the design of continuous Z- and C- purlins for gravity loading with experimental verification

The design of cold-formed, through fastened, roof purlins requires a significant number of assumptions. The usual North American practice is to make the following major assumptions: constrained bending, full continuity through the lapped section, and a lap strength equal to the sum of individual purlin strengths. To verify these assumptions, test results of multiple span purlin systems were gathered from 10 laboratories. Of the 45 test results reported, 24 were found to be sufficiently documented for complete evaluation. Comparison of the test results and analysis/design procedures using the above assumptions and AISI specification provisions showed that the assumptions are valid.

A New Test Method for the Determination of the Flexural Modulus of Spirally Wound Paper Tubes

A new static test method to determine the flexural modulus of spirally wound paper tubes is described. The experimental method is based on the standard three-point-bend procedure. The method requires testing the tube at multiple (two or more) span lengths. The testing can be performed on either a rigid frame fixture under constant static load or in a universal testing machine under monotonically increasing quasi-static load. The test data are analyzed with a modified form of a classical Euler-Bernoulli beam theory. The modified theory accounts for nonbending deflection components that are obtained with the three-point-bend test. The effect of time-dependent creep deflection on the modulus prediction is also discussed. Extensive testing of a variety of paper tubes was conducted to verify the proposed test method. The accuracy of the method was determined by comparison with dynamic bending modulus predictions obtained from modal tests on the tubes. The dynamic modulus predictions were based on Euler-Bernoulli beam theory. Results of tests performed on a specially designed static frame fixture and tests performed on a universal testing machine are compared. It is found that the bending modulus predictions using the new analysis method are considerably closer to the dynamic bending modulus than those predictions obtained by classical beam theory.

Variability in Long‐Term Concrete Deformations

The deformation properties of concrete significantly influence the behavior of complex concrete structures. These properties are subject to large variabilities and it is therefore not possible to accurately predict the structural response. The sources of these variabilities are first examined, and an example is then presented of the long term deformation calculations in a multiple span bridge. Finally, a procedure using the finite element method, is proposed for predicting the variability in the shortening of the bridge. A number of analyses are performed for selected combinations of material properties, and the deformation at different time steps are calculated. Polinomial models are then fitted to the results at each time step. These models are used to calculate the distribution of the response, the confidence limits and estimates of the decomposition of the variance of the response. The results indicate that the variability in the response can be reduced by performing selected tests on the actual mater...

Approaches to the economic evaluation of agroforestry farming systems

The economics of agroforestry systems can be approached in a purely analytical fashion with mathematical equations and diagrams explaining the principles of analysis. This paper argues that such an approach may be useful for teaching purposes but has little practical relevance. There is an urgent need for a practical tool with which multi-disciplinary teams can asses agroforestry systems. The simplest and most common approaches to the economic analysis of farm management problems are various forms of budgeting. Recent advances in micro-computer technology provide the means by which the principles of partial budgeting can be adapted to the needs of agroforestry taking account of its multiple component nature, seasonal variability and long life span. The paper sets out the specifications for such an approach and indicates how it might be used.

多径間連続げたのパイルベント橋脚の設計・施工

本稿は橋長約510m, 12径間の連続げた高架橋の設計及びその下部工の施工について述べたものである。 基礎ぐいは大口径リバースぐい, 橋脚はRC, H形橋脚であり, 両者とも主鉄筋は太径鉄筋D51を用いている。 また, 橋脚には設計方針上, 橋軸方向たわみ性を求めており, パイルベント的挙動を示すので, その性能を保持させるため橋脚変位拘束防止工を施している。 なお, RC橋脚には, 美観上の配慮から化粧目地として縦目地を入れ, 脚柱をスレンダーに見せる努力をしている。

Finite mode bond graph representation of vehicle-guideway interaction problems

Classical modal analysis techniques for the prediction of vehicle-guideway dynamics are developed and interpreted with bond graph representations. Bond graphs are shown to allow easy generalization to multiple span guideways incorporating virtually any dynamic boundary conditions at the support locations. In addition, non-linear vehicle models can be used with any vehicle displacement-time history desired. Straightforward formulation procedures are also provided through the bond graph representation. The analysis procedure is demonstrated for a two-span Bernoulli-Euler Guideway with first-order dynamic boundary conditions. The results for a vehicle traveling at different speeds are shown to compare favorably with current literature.

Multiple and Continuous Span Elevated Guideway-Vehicle Dynamic Performance

Analyses are developed to determine the dynamic performance of vehicles interacting with single, multiple, and continuous span elevated structures. Operating conditions in which multispan resonant conditions occur are identified, and the resulting resonant amplitudes computed. Guideway design examples considering tracked, levitated vehicles are described to illustrate the influence of span configuration and vehicle speed and suspension properties upon guideway span design for vehicle-guideway systems required to provide specified passenger comfort levels. For the 150 and 300 mph (242 and 483 km/h) vehicle systems considered, continuous and multispan guideway configurations were found to have reduced span material requirements in comparison to single span systems which provide the same level of passenger comfort.

Transportation Vehicle/Beam-Elevated Guideway Dynamic Interactions: A State-of-the-Art Review

The importance of elevated guideway/vehicle dynamics to the design of advanced ground transportation systems is discussed and the general vehicle-suspension-guideway interaction problem is outlined. Simplifying assumptions valid for many practical beam-type elevated guideway systems are described including the Bernoulli-Euler beam assumptions, support conditions, and simplified vehicle models. The theoretical and experimental literature on beam-guideway/vehicle dynamics is reviewed and recent computer-based analytical techniques (lumped mass, finite difference and modal analysis) are discussed. Available simulation programs are described and published results for wheeled, air cushion and magnetically levitated vehicles operating over beam-elevated guideways are reviewed. The influences of critical system parameters on guideway deflection and vehicle vibrational acceleratior (ride comfort) are illustrated through simple limiting case analyses. Low ratios of vehicle-suspension to guideway natural frequency and distribution of vehicle weight over finite pressure pads as in air or magnetic suspensions reduce guideway structural requirements for specified ride comfort. Continuous guideway beams on simple supports provide lower static deflection and greater dynamic range than simply supported single or multiple span beams. Severe resonance problems which may occur in synchronous vehicle systems are illustrated using a point-force vehicle model.

Unsteady Subsonic Aerodynamic Loadings Caused by Control Surface Motions

A numerical method is presented for the prediction of unsteady aerodynamic loadings on lifting surfaces that are due to oscillations of trailing edge control surfaces having sealed gaps in subsonic compressible flow. The development is applicable to planform configurations having full span or multiple partial span control surfaces located anywhere along the planform trailing edge. The final form of the downwash integral equation is formulated by separating the singular terms from the non-singular terms of the integral equation. A systematic solution process is developed to remove and separately evaluate the discontinuities in the kinematic downwash distribution. A suggestion is made for modifying the boundary conditions to include local velocities due to airfoil thickness effects within the solution process. Comparisons of theoretical and experimental pressure data indicate that reasonably accurate pressure distributions may be obtained for a wide range of control surface configurations.

BÉSM-2M computer calculation of beam type structures on elastic foundations (method, algorithm, program)

The approximate method of computing multiple span beams with variable cross section and elastic supports and connections, in any area of contact with the elastic foundation for static loads and temperature variation effects was elaborated by the author at the Leningrad Department of the Gidroproekt. For this purpose a foundation model based on Winkler's hypothesis, an elastic, isotropie medium of finite depth, one of infinite depth (the plane and the space probtems),~and a combined medium (the plane and the space problems) were investigated. The method is based on the general theory of structural mechanics of bar systems with the application of the integral equations of Fredholm and of the methods of numerical analysis. The computational formulas are given in matrix form. The above mentioned method is completely developed in the B-l-10 program for the BESM-2M computer. Let us examine a multiple span beam of variable height h(x) and constant width bb having a portion of its length supported by an elastic foundation and undergoing the influence of a complex of external factors F. The external factors include concentrated and distributed forces Pi, q(x) and moments Mi, m(x), temperature gradients AT(x), initial rotations vl(x) and displacements v~.(x) of the supports and connections, the load on the foundation surface qel(X). We will consider the connections and supports as elastic and completely independent of the foundation (Fig. la). As unknowns we select the normal forces r(x) which appear at the contact between the beam and the foundation and the internal forces xi (0-<i _<n) in the supports and connections. Tim friction on the contact surface is neglected. It we assume that r(x) is a known function, the structure can be considered as a multiple span beam (Fig. lb): We consider the basic system as a cantilever beam with a connection at the right. In the case when there is no connection we introduce fictitious constraints preventing the rotation or the vertical displacement. The rotation angle ~ and the vertical displacement v of the actual constraints will be supplementary unknowns. The reduced system of canonical equations of the mixed method with respect to Xi, ~, and v will be in the most general case 7: