0


RESEARCH PAPERS

J. Basic Eng. 1968;90(2):143-151. doi:10.1115/1.3605072.

A novel approach to gas servo design is presented which provides closed-center operation while eliminating close clearance sliding seals and elastic members. Pulse-length modulated pressure waves having zero quiescent pulse width are used to actuate a new type of switching valve termed a “floating flapper disk.” Signal generation and modulation as well as power-level flow control are shown to be possible using this novel valve. System performance is discussed and compared with that of an equivalent linear servo. A prototype system fabricated to demonstrate feasibility is described. The valving concepts described are adaptable to digital, bang-bang, and optimally switched fluid control systems.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):152-156. doi:10.1115/1.3605073.

A proof of a distributed parameter maximum principle is given by using dynamic programming. An example problem involving a nonhomogeneous boundary condition is also treated by using the dynamic programming technique and by extending the definition of the differential operator. It is thus demonstrated that for linear systems the dynamic programming approach is just as powerful as the variational approach originally used to derive the maximum principle.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):157-166. doi:10.1115/1.3605074.

As an alternative to the normal vibration mode approach to dynamic analysis and control of bending vibrations, such vibrations are studied in terms of the distributed parameter concepts of propagation, reflection, and characteristic termination. In particular, the dynamics of lateral vibration of a thin uniform beam are factored into a form that separates the process of propagation from boundary effects. This allows the effects of various terminal impedance matrices to be described in terms of a reflection matrix, which is a generalization of the concept of reflection coefficient for the wave equation. It is shown that the reflection matrix can be nulled by terminating a beam in its characteristic impedance matrix. Several special cases of terminal impedance matrix are considered in detail. The reflection matrices are derived for these cases, and the response of control systems incorporating these terminal impedance matrices is studied by analog simulation.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):167-174. doi:10.1115/1.3605075.

This paper describes an automatic roll mode control system for ground vehicles. The primary objective of the so-called “active suspension system” is to maintain a coordinated vehicle banking attitude during cornering and steering through traffic. Efforts were also made to render the vehicle insensitive to the undulation of the road surface, wind gusts, and other disturbance inputs. Emphasis was placed upon the development of design logic in the application of control system concepts to a physical system. Realization of the active suspension concept was achieved by parameter optimization of a simplified system on the analog computer and the design and construction of an experimental vehicle. Laboratory and road tests of the physical system confirmed the feasibility of the active suspension concept and brought to focus additional design considerations such as vehicle elastic mode and the effects of man vehicle coupling. For the road tests, a manual bias was incorporated in the automatic roll control loop to improve the transient response of the system, and the resultant man-machine multiloop interaction was investigated.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):175-180. doi:10.1115/1.3605076.

A high-speed, two-dimensional, nonsteady, electrical diffusion analog is discussed with emphasis on applications to heat conduction systems. The accuracy of the device is apparent from transfer function data for a one-dimensional system which compares favorably with analytical predictions. The analog was used to study automatic control aspects of surface temperature regulation. Results are presented in terms of frequency response, transient response, and stability limits. In addition, optimal design parameters are given for temperature control of both one and two-dimensional systems in the presence of random disturbances. To obtain the latter information, the analog was used to simultaneously optimize controller gain and the feedback temperature probe location.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):181-186. doi:10.1115/1.3605077.

The principles of calculus of variations are used to obtain necessary conditions for optimal control of dynamical systems that involve nonconstant time lags. Consideration is given to systems that can be represented mathematically by a finite set of ordinary nonlinear differential-difference equations with one or more time-dependent argument lags. Application of the general results to classes of linear systems with finite-time quadratic performance criteria is considered in detail. Optimal feedback control laws are given. Discussion of a proposed method for obtaining computational solutions for nonlinear systems with variable delays is included in the paper.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):187-194. doi:10.1115/1.3605078.

In this paper sensitivity analysis techniques are applied to two aspects of the nonlinear system design problem: The modeling of nonlinear systems and the compensation of nonlinear systems. In the modeling problem the free parameters of the model are selected to minimize an integral performance index where the integrand is a function of the response of the model and the response of the modeled system. Sensitivity functions, which indicate the sensitivity of the response of the model to changes in the free parameters are used in the minimization procedure. Similarly, in the compensation problem, the adjustable parameters of the compensated system are selected to minimize an integral performance index where the integrand is a function of the response of the compensated system and a desired response. Sensitivity functions, which indicate the sensitivity of the response of the compensated system to changes in the adjustable parameters, are again used in the minimization procedure. The sensitivity functions are obtained from multiple solutions of the general sensitivity equation subjected to various forcing functions. The general sensitivity equation is obtained by differentiation of the model equation or of the compensated system equation. The free or the adjustable parameters are determined as functions of some characteristic parameter which represents the magnitude of the input, the degree of the nonlinearity or some other performance characteristic of the system. All the required computations may be performed by a digital computer. Three nonlinear examples are given to illustrate the method.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):195-200. doi:10.1115/1.3605079.

Consideration of general linear models for transmission line systems (hydraulic, pneumatic, electrical, etc.) has so far been limited to the case of systems in which the lines exhibit no internal dispersion. In this paper, a simulation system for distributed dynamic systems which can include dispersive transmission elements will be described. The ideal transmission line, a lossless, nondispersive transmission line, is used with static junctions to form models of dynamic systems. A simple computational algorithm is obtained if the state of the model is expressed in terms of wave-scattering variables rather than by the pressure-flow or voltage-current type of state variables. A model for dispersive transmission lines is presented, and its feasibility is demonstrated.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):201-207. doi:10.1115/1.3605080.

The paper extends and modifies an approach to adaptive optimal control problems proposed by Kulikowski. The emphasis at the outset is placed upon optimizing the steady-state system performance in which the desired output of the plant is a periodic function of time. The formulation for type-one plants is modified to include the optimization of the total amount of input accumulation,

s = −∞t0u(τ)dτ,
which is present at the beginning of each period of steady-state operation.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):208-212. doi:10.1115/1.3605081.

A new method of generating Liapunov functions is described that is useful for time-varying nonlinear differential equations. Constant coefficient quadratic forms are often used as Liapunov functions for linear constant coefficient differential equations. However, if the differential equation coefficients are time-varying and nonlinear, better results are usually obtained by using variable quadratic forms as Liapunov functions. This variation in V often introduces undesirable terms in V̇, which are cancelled by modifying V by subtracting integrals of certain partial derivatives of V with respect to the dependent variables. With few restrictions, V is proved to remain positive definite after the modification. The method often directly extends a Liapunov function useful for constant coefficient differential equations to cover the case when the coefficients are time-varying and nonlinear. Two examples are presented, including the incremental circuit for a time-varying nonlinear transmission line with hysteresis and the equations for an N-body collision avoidance problem.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):213-221. doi:10.1115/1.3605082.

The concept of preview control (a control scheme in which an input is sensed before it reaches the controlled plant) is discussed and applied to the guidance of vehicles over statistically described surfaces. Two methods are presented for optimizing the trade-off between vehicle vibration and the clearance space required for excursions of a vehicle relative to a roadway. The first approach, based on Wiener filter theory, is used to synthesize the optimum characteristics (transfer function) of a free-configuration system. Since the transfer function synthesized in this manner is very difficult to mechanize, a parameter-search technique is used to optimize a fixed-configuration system which may be more easily realized in practice. The results of this study show the reduction in vibration and clearance space that a preview control system may bring about as compared to an optimized system that does not use preview information. Preview control may account for root-mean-square vibration reduction by as much as a factor of sixteen at constant clearance space or a decrease in clearance space by a factor of 232 at constant vibration level.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):222-230. doi:10.1115/1.3605083.

There are multivariable systems which have free motions dominated by a limited number of clearly separable modes. In some cases it is possible to specifically control these modes, thereby improving overall control of the system. This paper is a discussion of when and how modal control may be applied.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):231-240. doi:10.1115/1.3605084.

Prior to development of high-speed digital computers, the method of characteristics has not been readily available for pneumatic system design. The traditional organization of computations on a free-running grid is not ideal for machine work. In a 1953 paper, Hartree developed the mathematical foundation for method of characteristics computations on a rectangular grid of predetermined dimensions. The present paper develops in detail a rectangular grid scheme for pneumatic line analysis. An approximate method for tapered lines is presented. Line termination computations are discussed for the general case, together with examples developed in connection with recent resonance tube research conducted by the author. Some computed results for constant area and tapered resonance tube simulations are presented.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):241-248. doi:10.1115/1.3605085.

The isotach pattern in a bounded jet with an aspect ratio of 6 suggests the presence of a secondary flow structure. A physical flow model is presented, and further measurements substantiate the model and support the conclusion that three-dimensional effects are highly significant in bounded jets of modest aspect ratio, even in the mid plane between the bounding walls.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):249-261. doi:10.1115/1.3605086.

Cavitation inception and the associated bubble dynamics in turbulent boundary layers adjacent to surfaces roughened with triangular grooves is investigated in a two-dimensional recirculating water tunnel. The experiments result in the significant conclusion that the cavitation inception index is directly related to the skin friction coefficient for both smooth and rough boundaries. Cavitation is observed to occur away from the wall approximately in the center of the boundary layer, and is apparently the result of negative peaks in static pressure having a magnitude which exceeds 5 times the expected value of root mean square wall pressure. Mean velocity and skin friction data are correlated with existing theory for equilibrium boundary layers.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):262-268. doi:10.1115/1.3605087.

A method is developed for approximating the transverse velocity component in the incompressible two-dimensional boundary layer equations. The method is restricted to flows that are symmetrical in the transverse coordinate, and it facilitates easy numerical integration in such problems as the prediction of jet and wake flows. The prediction of velocity profiles and diameters for free exiting Poiseuille flows, under the influence of both gravity and surface tension, is then undertaken. Analytical results obtained by the present method are found to agree very closely with experiments. The experiments also show that, in low Weber number situations, contact angle at the exit plane can dominate the early relaxation of the exit profile.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):269-274. doi:10.1115/1.3605088.

A summary is given of two-dimensional, steady-state, nonlinear theory for two finite-cavity models and their solutions. Two applications are described. First, the influence of the foil’s depth of submersion below a free surface on cavity length and foil performance is described. Second, the effect of a blunt nose on a circular-arc hydrofoil is examined.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):275-284. doi:10.1115/1.3605089.

The wake behind a six-to-one spheroid was studied for a Reynolds number equal to 2.75 × 106 at 12 sections from 0.25 dia upstream to 18 dia downstream from the stern of the body. The flow pattern was determined and an analytical expression was derived to express the manner in which the mean characteristics of the wake develop in the established flow region. The Reynolds stresses were measured throughout the flow and their magnitudes were checked through the momentum and mean-energy equations.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):285-291. doi:10.1115/1.3605090.

The Griffith criterion for fracture of brittle materials is based on a model of a continuum in which infinitely sharp cracks are distributed with random orientations. This study extends the Griffith analysis to cracks of finite sharpness. While the Griffith criterion predicts a compressive strength of eight times the tensile strength, the extended criterion predicts a compressive strength of any value from three to eight times the tensile strength depending on the sharpness of the cracks. To test the validity of the extended criterion, tests were conducted on porous zirconia under ratios of compressive to tensile stress of 0, 3, and 5, and under compressive stress. A specimen was designed and test procedures developed so that the average bending stress was 1.99 percent. A test program was designed so that a statistical confidence limit could be assigned to the test results. The test results of the proposed criterion fell within a 99 percent confidence band, while all other criteria fell outside of the band for many combinations of tensile and compressive stress. The average compressive strength of the porous zirconia was approximately 7.1 times the tensile strength.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):292-294. doi:10.1115/1.3605091.

The relationship of flow stress to the interparticle path of two phase alloy systems is discussed and the similarity of two phase alloy systems to wire or fiber reinforced composites is described. Experiments were performed on iron wire reinforced 6061 aluminum alloys which show that the flow stress in these systems can be expressed by a similar relationship as documented for two phase alloy systems, namely, σflow = C1 log λ + C2 , where C1 and C2 are constants, σflow is the flow stress, and λ is the interwire spacing within 4, 6, and 8 wire aluminum alloy composites.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):295-296. doi:10.1115/1.3605092.

An experiment was performed to determine the nature of the elastic stress system in the vicinity of an elliptical aperture in a plate subjected to uniform in-plane uniaxial tension, when the aperture is oblique to the plate midsurface. It was found that the maximum circumferential stress is somewhat higher than predicted by the Inglis solution for the “corresponding” plane problem. The possible relevance of these findings to elastic fracture mechanics is discussed.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):297-300. doi:10.1115/1.3605093.

This paper presents an analysis of the tensile instability phenomenon in a thin-walled membrane shell of revolution undergoing creep while subjected to a time-dependent internal pressure. Time-independent plastic deformation due to biaxial stress, including strain hardening and biaxial-stress creep, are included. The theory is applied to an example of a typical closed-end cylindrical pressure vessel to emphasize the importance of considering both plastic and creep deformations due to biaxial stress in calculations of ductile creep rupture.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):301-312. doi:10.1115/1.3605094.

Equations have been developed [1] which describe the flow in a steady, two-dimensional, incompressible, laminar boundary layer on a curved surface. The method of “similar solutions” yields a fourth-order, nonlinear, ordinary differential equation which may be solved on a digital computer. Account is taken of the effects of both surface curvature and displacement thickness, and in this paper attention is given to the influence of these effects on other boundary-layer properties up to and including the position of flow separation.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Basic Eng. 1968;90(2):313-314. doi:10.1115/1.3605095.
Abstract
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):314-316. doi:10.1115/1.3605096.
Abstract
Topics: Yaw
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(2):316-318. doi:10.1115/1.3605097.
Abstract
Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In