A review on design criteria for vortex tubes

In this study, the past investigations of the design criteria of vortex tubes were overviewed and the detailed information was presented on the design of them. Vortex tubes were classified and the type of them was described. All criteria on the design of vortex tubes were given in detail using experimental and theoretical results from the past until now. Finally, the criteria on the design of them are summarized.     

Optimal design of structures subjected to follower forces

Summary The optimal design of columns, consisting of segments with arbitrary thickness and length, subjected to follower forces is considered in this paper. The solution is presented for the case of cross modal interaction of a vibrating system. Since the resulting boundary value problem is nonselfadjoint only approximate solutions are generally possible. Herein, for the solution the method of the generalised functional and the transfer matrix technique have been used. As typical examples, the solutions of Beck's, Reut's, Leipholz's and Hanger's column are investigated.

---

Übersicht Behandelt wird die optimale Auslegung von Stäben, die aus Abschnitten beliebiger Querschnittsfläche und Länge bestehen und durch Folgelasten beansprucht sind. Eine Lösung wird angegeben unter Berücksichtigung des Zusammenwirkens der Eigenformen des Systems. Da das zugehörige Randwertproblem nicht selbstadjungiert ist, sind im allgemeinen nur Näherungslösungen angebbar. Hier werden das Verfahren eines generalisierten Funktionais sowie das Übertragungsmatrizenverfahren verwendet. Als typisches Beispiel werden die Lösungen zu den Stäben von Beck, Reut, Leipholz und Hauger betrachtet.

---

---

Fellow of the Alexander von Humboldt Foundation 1978/1979, visiting the University of Hannover     

Experimental criteria for the determination of fractal parameters of premixed turbulent flames

The influence of spatial resolution, digitization noise, the number of records used for averaging, and the method of analysis on the determination of the fractal parameters of a high Damköhler number, methane/air, premixed, turbulent stagnation-point flame are investigated in this paper. The flow exit velocity was 5 m/s and the turbulent Reynolds number was 70 based on a integral scale of 3 mm and a turbulent intensity of 7%. The light source was a copper vapor laser which delivered 20 nsecs, 5 mJ pulses at 4 kHz and the tomographic cross-sections of the flame were recorded by a high speed movie camera. The spatial resolution of the images is 155 × 121 m/pixel with a field of view of 50 × 65 mm. The stepping caliper technique for obtaining the fractal parameters is found to give the clearest indication of the cutoffs and the effects of noise. It is necessary to ensemble average the results from more than 25 statistically independent images to reduce sufficiently the scatter in the fractal parameters. The effects of reduced spatial resolution on fractal plots are estimated by artificial degradation of the resolution of the digitized flame boundaries. The effect of pixel resolution, an apparent increase in flame length below the inner scale rolloff, appears in the fractal plots when the measurent scale is less than approximately twice the pixel resolution. Although a clearer determination of fractal parameters is obtained by local averaging of the flame boundaries which removes digitization noise, at low spatial resolution this technique can reduce the fractal dimension. The degree of fractal isotropy of the flame surface can have a significant effect on the estimation of the flame surface area and hence burning rate from two-dimensional images. To estimate this isotropy a determination of the outer cutoff is required and three-dimensional measurements are probably also necessary.     

A new rosette design for more reliable hole-drilling residual stress measurements

A new six-element strain gage rosette is presented that can greatly improve residual stress measurement accuracy when using the hole-drilling method. The proposed rosette consists of three pairs of sector-shaped radial and circumferential gages connected as half-bridges. This rosette design increases effective strain sensitivity by a factor of 2.3 compared with a standard ASTM rectangular rosette, and can identify stresses at one-third greater depths from the measurement surface. Experimental measurements confirm theoretical strain response calculations within 3–4 percent. Apart from a small increase in time to complete the electrical connections, the practical use of the proposed rosette is identical to that of a conventional three-element rosette.     

On the determination of inertial and gyroscopic forces in multibody systems

Based on three coordinate systems (one inertial and two noninertial), general motion equations have been deduced for a holonomic mechanical system withn degrees of freedom using Lagrandian equations of the second kind. The proposed method permits one to determine the Coriolis and gyroscope forces as well as to establish the differences among them. Universidade da Beira Interior, 6200 Covilha, Portugal. Published in Prikladnaya Mekhanika, Vol. 35, No. 12, pp. 100–107, December, 1999.     

地震作用下高层钢结构的最优MTMD控制策略及设计

基于一般 MTMD,导出了 MTMD( )、MTMD( )和 TMD的动力放大系数 ( DMF)。以具有 MTMD( )、MTMD( )或 TMD结构的动力放大系数最大值中的最小值为优化准则。基于优化准则 ,列表显示了MTMD( )、MTMD( )和 TMD的最优参数。同时研究了最优参数对振型参与系数的敏感性。提出了 MTMD( )、MTMD( )和 TMD结构 -MTMD( )、MTMD( )和 TMD系统的优化设计方法。数值模拟表明 ,MTMD( )、MTMD( )和 TMD能有效地减小高层钢结构的地震反应     

Toward more accurate resudual-stress measurement by the hole-drilling method: Analysis of relieved-strain coefficients

In residual-stress measurement by the holedrilling technique, accuracy can be enhanced if the proper values for the relleved-strain coefficients are employed. These values are obtained by double integration of the relieved strain over the area of the grid. In this paper, several methods customarily used in the literature for the calculation of these coefficients are discussed. A comparison of the coefficients from these methods and those derived by double integration demonstrate the increased accuracy of the latter.     

A direct approach to design of geometry and forces of tensegrity systems

In the process of designing a tensegrity system, some constraints are usually introduced for geometry and/or forces to ensure uniqueness of the solution, because the tensegrity systems are underdetermined in most cases. In this paper, a new approach is presented to enable designers to specify independent sets of axial forces and nodal coordinates consecutively, under the equilibrium conditions and the given constraints, to satisfy the distinctly different requirements of architects and structural engineers. The proposed method can be used very efficiently for practical applications because only linear algebraic equations are to be solved, and no equation of kinematics or material property is needed. Some numerical examples are given to show not only efficiency of the proposed method but also its ability of searching new configurations.     

Direct determination of multi-axial elastic potentials for incompressible elastomeric solids: an accurate,explicit approach based on rational interpolation

With a novel approach based on certain logarithmic invariants, we demonstrate that a multi-axial elastic potential for incompressible, isotropic rubber-like materials may be obtained directly from two one-dimensional elastic potentials for uniaxial case and simple shear case, in a sense of exactly matching finite strain data for four benchmark tests, including uniaxial extension, simple shear, bi-axial extension, and plane-strain extension. As such, determination of multi-axial elastic potentials may be reduced to that of two one-dimensional elastic potentials. We further demonstrate that the latter two may be obtained by means of rational interpolating procedures for uniaxial data and shear data displaying strain-stiffening effects. Numerical examples are presented in fitting Treloar’s data and other data.     

地震作用下高层钢结构MTMD控制参数取值及优化设计研究

本文对地震作用下结构－MTMD系统的动力特性及优化设计进行了探讨,通过数值分析研究了MTMD系统各设计参数间的关系,给出了MTMD系统最优参数取建设,提出了MTMD系统优化设计及结构－MTMD系统优化设计方法,最后,算例说明了本文方法的应用及MTMD对结构地震反应控制的有效性。     

Application of pressure-sensitive paint for determination of the pressure field and calculation of the forces and moments of models in a wind tunnel

The visualization and measurements of aerodynamic effects on a 3D aircraft model were conducted using an optical pressure measurement system, based on the pressure-sensitive paint (PSP) technique. PSP technology provides a good understanding of the flow around the wind tunnel model. The PSP technique can be used to carry out absolute pressure measurements on a surface of the model and to determine additional aerodynamic data using scientific-grade cameras and image processing techniques. Surface pressures from the top, bottom, left, and right viewing directions were obtained using the DLR-PSP system on the entire surface, which can be observed by eight CCD cameras. Finally, the measured pressures can be integrated to calculate the forces and moments of the complete model, or parts thereof.     

A Taguchi approach for determination of optimum design parameters for a heat exchanger having circular-cross sectional pin fins

The present work submits an investigation about the optimal values of design parameters and performance analysis for a heat exchanger having cylindrical pin fins positioned in a rectangular channel. The experiments covered the following range: Reynolds number 13,500–42,000, the clearance ratio (C/H) 0, 0.33 and 1, the interfin spacing ratio (S _y /D) 1.208, 1.944 and 3.417. In the experimentation, Taguchi method was employed, and Nusselt number and friction factor were considered as performance parameters. While the optimum parameters were determined, due to the goals (above aims) more than one being, the trade-off among goals was considered. First of all, each goal was optimized, separately. Then, all goals were optimized together, considering the priority of goals, and the optimum results were found to be Reynolds number of 42,000, fin height of 50 mm and pitch of 3.417. The performance analysis also was made under a constant pumping power constraint, and the results showed that the use of cylindrical pin fins may lead to an advantage on the basis of heat transfer enhancement.