BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and...

27
W-ftof* wa TECHNICAL LIBRARY \ ~hM<i Q/al TECHNICAL REPORT ARLCB-TR-80046 BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE ELEMENT METHOD CONSISTENT IN SPATIAL AND TIME COORDINATES J. J. Wu November 1980 US ARMY ARMAMENT RESEARCH AND DEVELOPMENT COMMAND LARGE CALIBER WEAPON SYSTEMS LABORATORY BENET WEAPONS LABORATORY WATERVLIET, N. Y. 12189 AMCMS No. 36KA7000204 DA Project No. 1564018136GRN PRON No. 1A0215641A1A IDTIC QUALTTTINSPEUTBD 3 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

Transcript of BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and...

Page 1: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

W-ftof* wa TECHNICAL

LIBRARY \™~hM<i Q/al

TECHNICAL REPORT ARLCB-TR-80046

BEAM MOTIONS UNDER MOVING LOADS

SOLVED BY FINITE ELEMENT METHOD

CONSISTENT IN SPATIAL AND TIME COORDINATES

J. J. Wu

November 1980

US ARMY ARMAMENT RESEARCH AND DEVELOPMENT COMMAND LARGE CALIBER WEAPON SYSTEMS LABORATORY

BENET WEAPONS LABORATORY

WATERVLIET, N. Y. 12189

AMCMS No. 36KA7000204

DA Project No. 1564018136GRN

PRON No. 1A0215641A1A

IDTIC QUALTTTINSPEUTBD 3

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

Page 2: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

DISCLAIMER

The findings in this report are not to be construed as an official

Department of the Army position unless so designated by other author-

ized documents.

The use of trade name(s) and/or manufacturer(s) does not consti-

tute an official indorsement or approval.

DISPOSITION

Destroy this report when it is no longer needed. Do not return it

to the originator.

Page 3: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

SECURITY CLASSIFICATION OF THIS PAGE (When Data Entarad)

REPORT DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM

1. REPORT NUMBER

ARLCB-TR-80046

2. GOVT ACCESSION NO 3. RECIPIENT'S CATALOG NUMBER

4. TITLE f«ndSuJ)««e;

BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE ELEMENT METHOD CONSISTENT IN SPATIAL AND TIME COORDINATES

S. TYPE OF REPORT 4 PERIOD COVERED

6. PERFORMING ORG. REPORT NUMBER

7. AUTHORO) Julian J. Wu

8. CONTRACT OR GRANT NUMBERfs)

9. PERFORMING ORGANIZATION NAME AND ADDRESS

Benet Weapons Laboratory Watervliet Arsenal, Watervliet, NY 12189 DRDAR-LCB-TL

10. PROGRAM ELEMENT, PROJECT, TASK AREA ft WORK UNIT NUMBERS

AMCMS No. 36KA7000204 DA Project No. 1564018136GRN PRON No. 1A0215641A1A

11. CONTROLLING OFFICE NAME AND ADDRESS

U.S. Army Armament Research & Development Command Large Caliber Weapon Systems Laboratory Dover, NJ 07801

12. REPORT DATE

November 1980 13. NUMBER OF PAGES

20 14. MONITORING AGENCY NAME ft ADDRESSf" dl/faranf trom Controlling Olllca) 15. SECURITY CLASS, (of thim raport)

UNCLASSIFIED 15«. DECLASSIFI CATION/DOWN GRADING

SCHEDULE

16. DISTRIBUTION STATEMENT (ol thla Raport)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of Ota abatract antarad In Block 20, It dllfarant trom Raport)

IB. SUPPLEMENTARY NOTES

Published in Proceedings of the 26th Conference of Army Mathematicians, Cold Regions Research and Engineering Lab, Hanover, New Hampshire, 10-12 June 1980.

19. KEY WORDS (Contlnua on ravaraa alda It nacaaaary and Idantlty by block number) Moving Loads Finite Element Dynamics Vibrations Beam

20, ABSTRACT (XZotrtfmia am rararaa atdla ft nmuaaaary and Idantlly by block number) A solution formulation and numerical results are presented here for the time- dependent problem of beam deflections under a moving load which can be neither a force nor a mass. The basis of this approach is the variational finite ele- ment discretization consistent in spatial and time coordinates. The moving load effect results in equivalent stiffness matrix and force vector which are evaluated along the line of discontinuity in a time-length plane. Numerical results for several problems have been obtained, some of which are compared with solutions obtained by Fourier series explanations.

OD \ JAM'TS M73 EDITION OF 1 MOV 65 IS OBSOLETE UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE (Whan Data Entered)

Page 4: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

SECURITY CLASSIFICATION OF THIS PAOEfWh«o Dmtm Entmrmd)

SECURITY CLASSIFICATION OF THIS PAGEfWien Datm Entered;

Page 5: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TABLE OF CONTENTS Page

I. INTRODUCTION 1

II. SOLUTION FORMULATION FOR A MOVING FORCE PROBLEM 2

III. FORCE VECTOR DUE TO A MOVING CONCENTRATED LOAD 7

IV. A GUN DYNAMICS PROBLEM AND THE MOVING MASS PROBLEM 10

V. NUMERICAL DEMONSTRATIONS 13

REFERENCES 18

ILLUSTRATIONS

1. A Typical Finite Element Grid Scheme Showing the (l,j)th 19 Element and the Global, Local Coordinates.

TABLES

I. RELATIONSHIP BETWEEN (l,j) AND k IN EQUATION (16). 3

II. VALUES OF hip IN EQUATION (17). 8

III. DEFLECTION OF A SIMPLE SUPPORTED BEAM UNDER A MOVING LOAD 16 (T - 100 sec).

IV. DEFLECTION OF A SIMPLE SUPPORTED BEAM UNDER A MOVING FORC« 16 (T ■ 1.0 sec).

V. DEFLECTION OK A SIMPLE SUPPORTED BEAM UNDER A MOVING FORCE 17 (T = 0.1 sec)

Page 6: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

I. INTRODUCTION

A solution formulation and some numerical results are presented for beam

motions subjected to moving loads. Most of the work on this problem has been

related to rail and bridge design (see, for example, reference 1 and many

papers cited there from 1910 to 1971). However, the application of the analy-

sis can obviously be extended to tracks for rocket firing and to gun

dynamics.^

In Section II of this report, a variational formulation for a moving

force problem is described. Also given are the procedures which lead to

finite element matrix equation. A detailed description of the treatment of a

concentrated moving force is given in Section III. The variational problem

associated with a gun tube dynamics is presented in Section IV. This gun-tube

problem contains the moving mass problem as a special case. Finite element

solution can be derived from this formulation,' but the details of this more

complicated problem is omitted from the present report. Some of the numerical

problem are reported in the last section and are compared with results

obtained from series solutions.

^■Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

2Wu, J. J., "The Initial Boundary Value of Gun Dynamics Solved by Finite Element Unconstrained Variational Formulations," Innovative Numerical Analysis For the Applied Engineering Science, R. P. Shaw, et al.. Editors, University Press of Virginia, Charlottesville, 1980, pp. 733-741.

Page 7: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

II. SOLUTION FORMULATION FOR A MOVING FORCE PROBLEM

In this section, the solution formulation will be described In detail for

a moving force problem. The moving mass problem will be Included as a special

case of a more general problem of gun motions analysis given In a later

section.

Consider a vertical force P moving on an Euler-Bernoulll beam. The

differential equation Is given by

Ely"" + pAy = P6(x-x) (1)

where y(x,t) denotes the beam deflection as a function of spatial coordinate x

and time t. E, I, A, p denote elastic modulus, second moment of Inertia, area

and material density respectively. A Dirac function Is denoted by 6 , x = x(t)

Is the location of P, a prime (') denotes differentiation with respect to x

and a dot (•), differentiation with respect to t.

Introducing nondimensional quantities

A A A

y = yM , x - x/A , t = t/T , (2)

where H is the length of the beam and T is a finite time, within 0 < t <

T, the problem is of Interest, Eq. (I) can be written as

y"" + Y2y = QS(x-x) (3)

Page 8: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

The hats (*) have been omitted In Eq. (3) and

C T

T

?Z2

Q - El

c2 = pAJl4

with

(4) El

Boundary conditions associated with Eqs. (1) or (2) will now be introduced in

conjunction of a variational problem. Consider

61 = 0 (5a)

with 11 •• - -

i = / J [y"y*" - Y2yy* - QS(x-x)]dxdt o o

+ J dt{k1y(0,t)y*(0,t) + k2y'(0>t)y*,(0,t)}

+ Y2/ dx{k5[y(x,0) - Y(x)]y*(x,l)} (5b)

where y*(x,t) is the adjoint variable of y(x,t). If one takes the first

variation of I considering y(x,t) to be fixed:

(6l)6y=0 = 0 (5a')

and consider 6y* to be completely arbitrary, it is easy to see that Eq. (5)

is equivalent to the differential equation (3) and the following boundary and

initial conditions.

Page 9: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

y-'CO.t) + kiy(0,t) - 0

y"(0,t) - k2y,(0,t) - 0 a < t < 1 (6a)

y"'(l,t) - k3y(l,t) = 0

y"(l,t) + k4y'(l,t) = 0 • y(x.O) = 0

and . 0 < x < 1 (5b) y(x,l) - k5[y(x,0) - Y(x)] = 0

Taking appropriate values for k^, k2, k3, and k^, problems with a wide range

of boundary conditions can be realized. The initial conditions in Eqs. (6b)

are that the beam has zero Initial velocity, and, if one takes k5 to be * (or

larger number compared with unity),

y(x,0) = Y(x)

The meaning for cases where k5 is not so, need not be our concern here.

To derive the finite element matrix equations, one begins with Eq.

(Sa*) and write

(fiDfiy-O = 0 (7a)

II . . _ _ = / / [y'^y*" - Y2y6y* - Q6(x-x)6y*]dxdt

+/ dt[k1y(0,t)6y*(0,t) + k2y,(0,t)6y*(0,t)

+ k3y(l,t)6y*(l,t) + k4y'(1,t)6y*'(1,t)]

+/ dXY2k5[y(x,0) - Y(x)]6y*(x,l) (7b)

Page 10: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

Introducing element local variables

(i) 5=5 = Kx-i+1

(8a)

(1) n = n = Lt-j+1

or 1

x = - (5+1-1) K

1 t = - (5+j-l)

L

(8b)

where K is the number of divisions in x and L, in t. (A typical grid scheme

is shown in Figure 2). Equation (7b) can now be written as

I I ll'llir y"(ij)6y*"(ij) - ~- y(ij)6y*(ij)]^dn i=l j=l 0 0 L K

L ,1 kl K2 + 1 / dn [— y(ij)(0,n)6y*(ij)(0,n) + k2 — y

,(ij)(0,n)6y*,(ij)(0,Ti) j-1 0 L

K 1 d5 + I / - [Y2k5(y(ij)(5.0)6y*(1:))(5,l))]

1=1 0 K

K L Q i ! _ _ =1 I -/ / 6(x-x)6y*(i1)(5.n)d5dn

i-1 j=l L 0 0

K Y2k5 i + I / d5 [i(i)(5)fiy*(iL)(5.l)l (9)

1=1 K 0

The shape function vector is now introduced. Let

y(ij)(5,n) = aT(5,n)Y(1j)

y*(ij)(5,n) = aT(5,n)Y*(lj) = Y*T(i:j)a(5,n) (10)

Page 11: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

Equation (9) then becomes

L rK3 T2L

I I 6Y*T(lj) {-- A - --- B} Y(lj)

1-1 J-l L ~ K ~ ~

M ^2K2

+ I 6Y*T(ij) ir Bl + "7" B2} K1^

L k3 k4K2

+ I SJ*T(Kj) I- B3 + --" B4} Y(ij)

K Y2k5 + I «Y*T(iL) {--- B5} Y(iL)

K L Q K Y2k5 I I 5J*T - F(lj) + I 6Y*T(1L) G(1) (11)

1=1 j=l ' L 1=1 ~ K "

where, as it can be seen easily, that

I 1

0 0 -»" - ,%%

.1 ,1

and

0 0 ~'n ~ ,n

Hi = / a(0,n)aT(0,n)dn , B2 = / a r(0,n)aT r(0,n)dn 0~~ - 0 -' ~ '

B3 = / a(l,Ti)aT(l,n)dn , B4 = J a r(l,n)aT r(l,n)dn 0~ ~, ~ O- ~

B5 = J a(5,l)aT(5,0)d5 0 ~

F(ij) - /0 /0 a(5,n)6(ij)(5-i)dCdn , G(i) - / a(5,1)Y(1)(C)d5

(12)

Page 12: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

Now Eq. (11) can be assembled in a global matrix equation

6Y*T K Y = 6Y* F (13)

By virtue of the fact that 6Y* is not subjected to any constrained

conditions, one has K Y = F (14)

which can be solved routinely. Numerical results of several problems in

this class will be presented in a later section.

III. FORCE VECTOR DUE TO A MOVING CONCENTRATED LOAD

We shall describe here the procedures involved to arrive at the force

vector contributed by a moving concentrated load. This force vector has

appeared in Eq. (12) as

F(ij) = / / a(5,n)6(i;j)(5-C)d^dTi (15)

The shape function a(5,Ti) is a vector of 16 in dimension. In the present

formulation we have chosen the form:

ak(e.n) = b1(Obj(n) , k = 1,2,3,... 16 (16) l,j = 1,2.3,4

The relations between k and i,j are given in Table I. These are the conse-

quences of the choice of the shape function such that Y(:M\, the generalized

coordinates of the (lj)th element, represent the displacement, slope, veloc-

ity, and angular velocity at the local nodal points. Thus

S - P-i MO = I bip5 (17)

P-l

The values of b^p are given in Table II.

Page 13: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TABLE I. RELATIONSHIP BETWEEN (l.J) AND k IN EQUATION (16)

1

2

3

4

5

6

7

8

(l.j)

(l.D

(2,1)

(1,2)

(2.2)

(3,1)

(4,1)

(3,2)

(4,2)

9

10

11

12

13

14

15

16

(l,j)

(1,3)

(2,3)

(1,4)

(2.4)

(3,3)

(4,3)

(3,4)

(4,4)

TABLE II. VALUES OF bip IN EQUATION (17)

1

2

3

4

i 1 1 2 3 4

1 1 0 -3 1

0 1 -2 1

1 o 0 3 -2

1 o 1 o I -1 I 1

Page 14: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

Now, let us consider 6(ij)(£-0• This "function" represents the

effect of the Dlrac delta function 6(x-x) on the (lj)th element. If the

curve of travel x = x(t) does not go through the element (l,j), 6 (ij) (£-£;)

= 0. If It passes through that element, one has

6(lj)(C K) = 6(x-x) = K6(£-i) (18a)

with

5 = 5(n) (18b)

The function £(ri) Is derived from x = x(t). For example. If the force

moves with a constant velocity, one has

x = x(t) = vt (19a)

It follows from Eqs. (8) that

- - vK 5 - 5(n) = -i+i + — (n-t-j-D (19b)

With Eqs. (16), (17), (18), and (19), one writes (15) as

r1 r1 " " F(li)k = Kj J aka,n)6U-Od5dTi (20a) J 0 0

,1 .1 - - p-1 q-1- - F(ij)k - K/ / bipbjq C n 6(5-£)d5dTi

0 0 (20b)

Equation (20) can then be evaluated easily once the exact form of K Is

written. For example. If 5 ■ H, Eq. (20) reduces to

Page 15: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

p=l q=l F(ij)k = ^ ^ k bip biq /0 ^ d5

4 4 kbipb^ ); I —Li5 (21)

p=l q=l P+q-1

IV. A. GUN DYNAMICS PROBLEM AND THE MOVING MASS PROBLEM

In this section, the solution formulation of a gun tube can be obtained

as a special case to the gun tube motion problem. The differential equation

of this problem can be written as:J

(Ely")" + [PU.Oy']' + pAy

= - P(x,t)y"(x,t)H(x-x)

- mp[x2y" + 2xy' + y]6(x-x)

+ (mp g cos a)6(x-x) + pA g cos a (22)

The notations are the same as in the previous section if they have already

been defined. The "gun tube" is replacing the "beam" whenever appropriate.

The new notations are defined here:

P(x,t) = irR2(x)p(t) - axial force in the tube due to internal

pressure alone

R(x) * inner radius of tube

p(t) = internal pressure

3J. J. Wu, "A Computer Program and Approximate Solution Formulation For Gun Motions Analysis," Technical Report ARLCB-TR-79019, US Army Armament Research and Development Command, Benet Weapons Laboratory, June 1979.

10

Page 16: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

o, J0 pAdx P(x,t) = [-P(0,t) + g(sln a) J pAdx] (23)

0 j1 pAdx o

= recoil force Including tube inertia in axial direction.

H(x) = Heaviside step function

x = x(t) = position of the projectile

mp = mass of projectile

g ■ gravitational acceleration

a = angle of elevation

With similar nondimensionalization as before and assuming that the cross-

section is uniform, ballistic pressure is not time dependent. Equation can be

written in dimensionless form

y"" + [-P + g sin otHU-x^']' + Y2y

= - P y"H(x-x)

- Y2mp[x2y" + Zxy' + y]6(x-x)

+ mp g(cos a)6(x-x) + g(cos a) (24)

Where, now, everything is dimensionless and

C2 1 pA*> T2 = (25)

T2 T2 El

It is also clear that if one drops the second term on the left hand side and

the first and the last terms on the right hand side in the above equation, the

equation becomes that for a moving mass problem.

11

Page 17: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

A varlatlonal problem associated with the differential equation of

Eq. (24) can be obtained through Integratlon-by-parts.

12 3

with

and

61 = (6l)y = I (SI1)y - I (fijj) » 0 (26a) 1-1 j-1

Ii - J J y"y*"dxdt ; I2 = (P-g sin a) J y'y*'dxdt 00 Z 00

?fl A" -A A I3 " -1 i J yy*dxdt ; I4 = -PJ J y,y*,H(x-x)dxdt

I5 = -P/ / y'y*'6(x-x)dxdt ; I6 = -m32Y2/ J t2y'y*•6(x-x)dxdt

I7 = -me2Y2/ / ty'y*'6'(x-x)dxdt ; I8 = 2m3Y2/ / ty'y*6(x-x)dxdt

ll**-- ll*-- I9 = -mY2/ / yy*6(x-x)dxdt ; I^Q = -mY2/ / yy*6(x-x)dxdt

111 = /0 {kiy(0,t)y*(0,t) + k2y(0,t)y*(0,t) +

k3y(l,t)y*(l,t) + l^y'(l,t)y*«(l,t)fdt

llZ - k7/ y(x,0)y*(x,l)dx (26b)

r1 r1 Ji = -g cos a J J y*dxdt

0 0

r1 r1 " " J2 = -gm cos a J J y*6(x-x)dxdt

.1 J3 = kyj Y(x)y*(x,l)dx (26c)

12

Page 18: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

The varlational problem also produces the following initial and boundary value

conditions in addition to the differential equation:

y(x,o) = o

- 1 y(x,l)[l + mS(- g-x)] + kyEyU.O) - Y(x)] = 0 (27a)

and

y"(0,t) - k2y,(0,t) = 0

y"(l,t) + k4y'(l,t) = 0

y'^'CC^t) + kiyCO.t) + (-P+g cos a)y,(0,t) + Py,(0,t)H(- 3t2) 2

+ m32y'(0,t)6(- gt2) = 0 2

y"'(l,t) - k3(l,t) + Py'(l,t)H(- 0t2-l) + m32y,(1,t)6(- 3t2-l) = 0 2 2

(27b)

Other than the fact that the present problem is much more complicated than the

one associated with a moving force, the basic concept of solution used previ-

ously does not change and we shall omit the details of solution formulation

here.

V. NUMERICAL DEMONSTRATIONS

Some numerical results obtained will now be presented. Let us consider a

simply-supported beam subjected to a unit moving force with a constant

velocity

i v = -

T

As T varies from " to 0, the velocity varies from 0 to o".

13

Page 19: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

It will be helpful to compare v with some reference velocity which is a

characteristic of the given beam. It is known that for a simply-supported

beam, the first mode of vibration has a frequency (see, for example,

reference 4)

w 1 TT2 ir

f, = — => — [—J = — (cycles per seconds) 2ir 2ir C 2C

and the period,

2C Ti = -

TT

where

C2 = El

Consider the vibration as standing waves. They travel at a speed

■ni, vi = 2Afi - —

C

Hence, the relative velocity - v C Tx v = — = — = —

vi iiT 2T

IT

We shall take C = 1.0 for the moving force problems. Thus, fi = - 2

1.5708 Hz. Ti ' 0.6366 sec. and

1

nT

^K. N. Tong, Theory of Mechanical Vibration, John Wiley, New York, 1960, p. 257; p. 308.

14

Page 20: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

Using a grid scheme of 4 x 4, Tables III, IV, and V show the deflections

as the concentrated force Q = 1.0 moves from the left end to the right end of

the beam. Since we have defined that T Is the time required for the load to

travel from one end to another, t = 0.5T, for example, denotes the point when

the load is at the mldspan of the beam If v Is constant. At t = 1.0 T, the

force has reached the other end and the deflection should be zero In the

static case.

Solutions by Fouries series [1] are also obtained and they are also given

In these tables (numbers in parentheses) for close comparisons.

Table III shows that for T - 100 sec, v = 1/300 or more or T Is more than

300 times the natural frequency T^, the deflections as P moves across the beam

is nearly the static deflection. The dynamic effect of the load In the case T

= 100, as indicated by the deflection curve at t -1.0 T is indiscernible. For

v = 1/3 and v = 3.33, the dynamic effect is very much pronounced as indicated

by Table IV and V. The agreement between the present results compared reason-

ably well with the series solution in Tables II and III. It is extremely well

In case of nearly static cases as shown in Table III.

15

Page 21: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TABLE III. DEFLECTION OF A SIMPLY SUPPORTED BEAM UNDER A MOVING LOAD (T =■ 100 sec.)

y(x,t)/i [x lO"1]

t/T x/A

0.

0.25

0.50

0.75

1.00

0.

0. (0.)

0. (0.)

0. (0.)

0. (0.)

0. (0.)

0.25

0. (0.)

.1172 (.1167)

.1431 (.1433)

.0908 (.0916)

-.0047 (-.0002)

0.50

0. (0.)

.1432 (.1426)

.2082 (.2085)

.1427 (.1438)

-.0066 (-.0003)

0.75

0. (0.)

.0911 (.0907)

.1431 (.1434)

.1168 (.1176)

-.0046 (-.0002)

1.00

0. (0.)

0. (0.)

0. (0.)

0. (0.)

0. (0.)

TABLE IV. DEFLECTION OF A SIMPLY SUPPORTED BEAM UNDER A MOVING FORCE (T = 1.0 sec.)

cT* t/T

0.

0.25

0.50

0.75

1.00

0.

0. (0.)

0. (0.)

0. (0.)

- 0. (0.)

0. (0.)

y(x,t)/£ [x lO"1] -1-

0.25

0. (0.)

.09489 (.09795)

.20542 (.20802)

.03869 (.05829)

-.10200 (.01994)

0.50

0. (0.)

.11349 (.11414)

.30402 (.30257)

.09522 (.09397)

(.05191) (.03148)

0.75

0. (0.)

.07108 (.06942)

.21491 (.21126)

.09641 (.08092)

(.11574) (.02405)

1.00

0. (0.)

0. (0.)

0. (0.)

0. (0.)

0. (0.)

16

Page 22: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TABLE V. DEFLECTION OF A SIMPLY SUPPORTED BEAM UNDER A MOVING FORCE (T = 0.1 sec.)

y(x,t)/A [x lO"1]

1 xM "1 It/T 0. 0.25 0.50 0.75 1.00 i

1 0. .0 .0 .0 .0 .0 (.0) (.0) (.0) (.0) (.0)1

I 0.25 .0 .0619 -.0148 .0043 .0 I (.0) (.0645) (-.0149) (.0033) (.0)1

I 0.50 .0 .2002 .1228 -.0494 .o 1 (.0) (.1952) (.1262) (-.0479) (.0)1

I 0.75 .0 .3007 .3837 .0770 .0 1 (.0) (.2929) (.3849) (.0801) (.0)1

1 1.00 .0 .4601 .4912 .5767 .0 1 (.0) (.4018) (.4880) (.5959) (.0)1

17

Page 23: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

REFERENCES

1. L. Fryba, Vibrations of Solids and Structures Under Moving Loads,

Noordhoff International Publishing Company, Groningen, 1971.

2. J. J. Wu, "The Initial Boundary Value of Gun Dynamics Solved by Finite

Element Unconstrained Variatlonal Formulations," Innovative Numerical

Analysis For the Applied Engineering Science, R. P. Shaw, et al.. Editors,

University Press of Virginia, Charlottesville, 1980, pp. 733-741.

3. J. J. Wu, "A Computer Program and Approximate Solution Formulation For Gun

Motions Analysis," Technical Report ARLCB-TR-79019, US Army Armament

Research and Development Command, Benet Weapons Laboratory, June 1979.

4. K. N. Tong, Theory of Mechanical Vibration, John Wiley, New York, 1960, p.

257; p. 308.

18

Page 24: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

1

T

t

/

- j111 COLUMN

/

0.8T i ^

O.BT

0.4 T

■ th m A ^— lin

N

0.2T

n X

0. .2 .4 .6 .8 1.0

FIGURE 1. A Typical Finite Element Grid Scheme Showing the (i,j)th Element and the Global, Local Coordinates.

19

Page 25: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TKCHKICAL RKPORT KXTKRNAL DISTRIBUTION LIST

NO. car COPIES

NO. OF COPIKS

ASST SEC OF THE ARMY RESEARCH & DEVELOPIiENT ATTN: DEP FOR SCI & TECH 1 THE PENTAGON WASHINGTON, D.C. 20315

CCUMANDER US ARMY MAT DEV & READ. CH^D ATTN: DRCDE 1 5001 EISENHOWER AVE ALEXANDRIA, VA 22333

CaMANDER US ARMY ARRADCCM ATTN: DRDAR-LC 1

-ICA (PIASTICS TECH 1 EVAL CEN)

-LCE 1 -LCM 1 -LCS 1 -LCW 1 -TSS(STINFO) 2

DOTER, NJ 07801

CCMT^ANDER US ARMY ARRCCM ATTN: DRSAR-LEP-L 1 ROCK ISLAND ARSENAL ROCK ISLAND, IL 61299

DIRECTOR US Army Ballistic Research Laboratory ATTN: DRDAR-TSB-S (STINFO) 1 ABERDEEN PROVING GROUND, MD 21005•

COMMANDER US ARMY ELECTRONICS CCMD ATTN: TECH LIB 1 FT MONMOUTH, NJ 07703

CQvMANDER US ARMY MOBILITY EQUIP R&D CCM) ATTN: TECH LIB 1 FT BELVOIR, VA 22060

NOTE: PLEASE NOTIFY CCMMANDER, ARRADCCM, ATTN: BENET WEAPONS LABORATORY, DRDAR-LCB-TL, WATERVLIET ARSENAL, WATERVLIET, N.Y. 12189, OF ANY REQUIRED CHANGES.

CfWMANDER US ARMY TANK-AUTMV R&D CCMD ATTN: TECH LIB - DRDTA-UL

MAT LAB - DRDTA-RK WARREN MICHIGAN 48090

CCMMANDER US MILITARY ACADEMY ATTN: CHMN, MECH ENGR DEPT WEST POINT, NY 10996

CCMMANDER REDSTONE ARSENAL ATTN: DRSMI-RB

-RRS -RSM

ALABAMA 35809

CCMMANDER ROCK ISLAND ARSENAL ATTN: SARRI-ENM (MAT SCI DIV) ROCK ISLAND, IL 61202

CCMMANDER HQ, US ARMY AVN SCH ATTN: OFC OF THE LIBRARIAN FT RUCKER, ALABAMA 36362

CCMMANDER US ARMY FGN SCIENCE & TECH CEN ATTN: DRXST-SD 233 TTH STREET, N.E. CHARLOTTESVILLE, VA 22901

CCMMANDER US ARMY MATERIALS & MECHANICS

RESEARCH CENTER ATTN: TECH LIB - DRXMR-PL WATERTOWN, MASS 02172

1

2 1 1

Page 26: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TECHNICAL REPORT EXTERNAL DISTRIBUTION LIST (CONT.)

GCMMANDER US ARMY RESEARCH OFFICE. P.O. BOX 12211 RESEARCH TRIANGLE PARK, NC 27739

CCWMANDER US ARMY HAR-^f DIAMOND UB ATTN: TECH LIB 2800 POWDER MILL ROAD ADELPHIA, MT 20783

DIRECTOR US ARMY INDUSTRIAL BASE ENG ACT ATTN: DRXPE-lvCT ROCK ISLAND, XL 61301

CHIEF, MATERIALS BRANCH US ARMY R&S GROUP,, EUR BOX 65, FPO N.Y. 09510

CCMMANDER riAVAL SURFACE WEAPONS CEN ATTN: CHIEF, MAT ;SCIENCE DIV DAHIGREN, VA 22^8

DIRECTOR .US NAVAL RESEARCH LAB ATTN: DIR, MECH DIV

CCTE 26-27 (DOC LIB) WASHINGTON, D. C. 20375

NO. OF NO. OF COPIED

CCMMANDER DEFENSE TECHNICAL INFO Ce^TER

COPIFS

1 ATTN: DTIA-TCA CAMERON STATION ALEXANDRIA, VA 22314

METAI^ 4 CERAMICS INFO CEN

U

1 BATTELLE COLUMBUS TAB 1 505 KING AVE COLUMBUS, OHIO 43201

MECHANICAL PROPERTIES DATA CTR BATTELLE COLUMBUS LAB 505 XING AVE COLUMBUS, OHIO A3201

MATERIEL SYSTIM3 ANALYSIS ACTV ATTN: DRXSY-MP ABERDEEN PROVING GROUND MARYLAND 21005

1 1

NASA SCIENTITIC & TECH INFO FAC. P. 0. BOX 3757, ATTN: ACQ BR BALTIMORE/WiSHINGTCN INTL AIRPORT MARYLAND 21240

NOTE: PLEASE NOTIFY CCWMANDER, ARRADCCM, ATTN: 3ENET WEAPONS LABORATORY, DRDA.~-LCB-TL, WATERVLIET ARSENAL, WATERVLIET, N.Y. 12189, OF ANY REQUIRED CHANGES.

Page 27: BEAM MOTIONS UNDER MOVING LOADS SOLVED BY FINITE …^ Fryba, L. , Vibrations of Solids and Structures Under Moving Loads, Noordhoff International Publishing Company, Groningen, 1971.

TECHNICAL RKPORT INTERNAL DISTRIBUTION LIST

DIRECTOR, OPERATIONS DIRECTORATE

DIRECTOR, PROCUREMENT DIRECTORATE

DIRECTOR, PRODUCT ASSURANCE DIRECTORATE

NO. OF COPIES

COMMANDER

CHIEF, DEVELOPMENT ENGINEERING BRANCH ATTN: DRDAR-LCB-DA

-DM -DP -DR -DS -DC

CHIEF, ENGINEERING SUPPORT BRANCH ATTN: DRDAR-LCB-SE

-SA

CHIEF, RESEARCH BRANCH ATTN: DRDAR-LCB-RA

-RC -RM -RP

CHIEF, LWC MORTAR SYS. OFC. ATTN: DRDAR-LCB-M

CHIEF, IMP. SIMM MORTAR OFC. ATTN: DRDAR-LCB-I

TECHNICAL LIBRARY 5

ATTN: DRDAR-LCB-TL

TECHNICAL PUBLICATIONS § EDITING UNIT 2

ATTN: DRDAR-LCB-TL

NOTE: PLEASE NOTIFY ASSOC. DIRECTOR, BENET WEAPONS LABORATORY, ATTN: DRDAR-LCB-TL, OF ANY REQUIRED CHANGES.