prev

next

out of 67

View

217Download

0

Embed Size (px)

1 _L

NASA Technical Memorandum 101636

Stability and Dynamic Analysis of a Slender Column with Curved Longitudinal Stiffeners

Mark S . Lake

AUGUST 1989

(BlSA-Tfi-1Q1636) STABILITP AYD D P l A f l I C n89-27275 &IALTSXS OF A SLEIDEB COLUUII UITB CgBVED LOECITUDIBU, STIPFEHBBS ~ U A S ~ . #s Langley

Research Center) 67 p CSCL 20s Unclas 63/39 0224569

National Aeronautics and Space Administration

Langley Research Center Hampton, Virginia 23665

https://ntrs.nasa.gov/search.jsp?R=19890017844 2018-02-01T13:16:54+00:00Z

TABLE OF CONTENTS

Page .

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv LIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

CHAPTER 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 ReviewofResearch ....................... 2 1.2 Definition of Problem and Objectives . . . . . . . . . . . . 4

2. ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Cross-sectional Geometric Properties . . . . . . . . . . .

2.1.1 Effect of Stiffener Kinematic Attachment on Geometric Properties . . . . . . . . . . . . . . . . .

2.1.2 Calculation of Geometric Properties . . . . . . . . 2.1.3 Optimization Considerations for a Stiffened

Column . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Analysis of Stiffener Local Buckling . . . . . . . . . . . .

2.2.1 Functional Dependence of Stiffener Local

2.2.2 Derivation of Approximate Explicit Relationship Buckling on Geometric Design Parameters . . .

for Stiffener Local Buckling. . . . . . . . . . . . . 2.3 Column Design Algorithm . . . . . . . . . . . . . . . . . . .

10 10

11 14

17 19

20

24 29

3. EXAMPLES AND DISCUSSION . . . . . . . . . . . . . . . . . 33

i

3.1 Generation of Design Curves for Example Problems. . 33 3.2 Discussion of Results . . . . . . . . . . . . . . . . . . . . . . 39

4. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 REFERENCES . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 47 APPENDIX A

Derivation of Stiffener Cross-Sectional Inertias . . . . . . . . . . . . . 49 APPENDIX B - DEsign of Diffened a l u m n Code (DESTCO) . . . . . . . . . . . . . 51 APPENDIX C

Vibration Frequencies of the Stiffened Column . , . . . . . . . . . . . 57

LIST OF TABLES

Table Number 7 Title

Page Number

2.1 Mamx of Normalized Stiffener Local Buckling Stresses From VIPASA Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.1 Nominal Dimensions for Example Central Columns . . . . . . . . . . . 34 3.2 Design Data for Space Station Freedom Column. . . . . . . . . . . . . 34 3.3 Design Data for Precision Segmented Reflector Column. . . . . . . . . 34

c

... u1

Figure Number

1 .1

2.1

2.2

2.3

2.4

2.5

2.6

3.1

3.2

3.3

3.4

3.5

3.6

3.7

A. 1

B. 1

c . 1

LIST OF FIGURES

Page - Title Number

Section of a cylindrical column with curved deployable stiffeners . . . . . 2 Symmetry of stiffened column cross section. . . . . . . . . . . . . . . 14 Stiffened column cross-sectional geometric parameters. . . . . . . . . . 15 Stiffener local buckling mode due to uniform axial compression. . . . . . 20 Typical plot of curved stiffener as represented in VIPASA . . . . . . . . 25 Plot of normalized stiffener local buckling stresses from VIPASA analysis.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Comparison of normalized stresses from VIPASA and explicit expression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Stiffener thickness variation with arc angle for minimum mass designs . . 35 Minimum mass design curve for Space Station Freedom column . . . . . 36 Minimum mass design curve for Precision Segmented Reflector column. . 36 Verification of Space Station Freedom column design curve . . . . . . . 38

Design curve for Space Station Freedom column including 10% mechanism mass. . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Comparison of approximate and exact design curves for Space Station Freedom column including 10% mechanism mass . . . . . . . . . . . . 41 Family of approximate general stiffened column design curves . . . . . . 42 Cross-sectional parameters for stiffener moments of inertia. . . . . . . . 50 Flow chart of DESTCO program . . . . . . . . . . . . . . . . . . . . 51 General Stiffened column design curves with vibration frequency increase . 59

iv

LIST OF SYMBOLS

c1

N

cross-sectional area

coefficient expressions defined for use in equations for moment of inertia

constants used in bilinear equation for stiffener local buckling stress

distance between discrete stiffener attachment locations

width of flat plate

constant in column vibration frequency equation

percent increase in stiffened column mass from that of the central column

percent increase in stiffened column buckling load from that of the central column

Young's modulus

summation index

general cross-sectional moments of inertia

equivalent cross-sectional moments of inertia of stiffened column

cross-sectional moments of inertia of central column and stiffener

column length

stiffener deployment mechanism mass as a percentage of the mass of the central column

mass density

number of data points used in least-squares approximation of stress function

V Poisson's ratio

V

r

0,

t

8

a, P

0

critical buckling load of column

arc angle of stiffener

deployment angle of stiffener

deployment angle of stiffener which maximizes cross-sectional moment of inertia

radius of curved shell

radius of gyration of cross section

inner and outer radii of central column, and outer radius of stiffener

average radius of stiffener

local buckling stress of stiffener

Euler buckling stress

thickness of curved shell

thickness of central column

thickness of stiffener

orientation angle of moment of inertia reference axis

surrogate angles defined for use in equations for moment of inertia

vibration frequency of stiffened column

vibration frequency of colunin without stiffeners

vi

CHAPTER 1

INTRODUCTION

A significant percentage of future manned and unmanned space flight missions will involve very large spacecraft whose components will be of such size and/or number as to require on-orbit assembly and integration. Although the goals of these missions may be quite different, the design of these spacecraft gives rise to at least one significant common technological requirement. This requirement is to develop the ability to construct and operate large, lightweight structures in space.

Most of these structures share the characteristic that their design is primarily driven by stiffness as opposed to strength considerations. This along with the constraint of low packaged volume allowances tends to drive the use of very long slender truss members. However, many of these structures are also required to withstand significant loads due to thermal gradients, spacecraft operations, and attitude control maneuvers. Consequently, stability of these slender members becomes a design concern. As a compromise, concepts have been developed for truss members which exhibit high buckling loads and, yet, package very efficiently.

One of these concepts consists of a cylindrical central column having three deployable longitudinal stiffeners each of which are sections of a right circular cylinder with an inner diameter equal to the outer diameter of the central column as shown in Fig. 1.1. While packaged, the stiffeners lie flush around the outside of the central column, and when deployed, the stiffeners are rotated outward to an angle which maximizes the moment of inertia of the cross section. This thesis is the summary of a study of the deployable curved stiffener concept. Results presented herein demonsrate the stability characteristics of columns employing these stiffeners, and outline a procedure for designing these columns for application to large space structures.

1

* Isometric view shows only a

r C e n t r a l column

Stiffener Deployment angle

Deployed

Figure 1.1. Section of a cylindrical column with curved deployable stiffeners.

1.1 Review of Research

Technology development programs have been in existence for more than ten years to address the problem of constructing and operating large, lightweight structures in space. From these programs, concepts have been developed for large truss systems to support a variety of large aperture antennas and platforms (1,2) and a permanently manned Space Station (3). Typically, these truss systems share the design goals of high stiffness, low weight, and low packaged volume (4, 5). Constrained optimization studies have been conducted to determine geometric proportions of minimum mass structures using constant diameter cylindrical columns (6,7, 8). Results from these studies support the use of truss members having the maximum diameters allowed for packaging, and lengths which are set by local buckling or vibration requirements.