Transcript Progress_Report_102711.ppt

The Effects of Engineering Assumptions
when Designing a Plate Panel/Stiffener
System Under a Uniformly Distributed Load
Bernard Nasser
Master of Engineering in Mechanical Engineering
Rensselaer Polytechnic Institute
Hartford, Connecticut
December, 2011
(For Graduation May, 2012)
Purpose
•Study focuses on the effect of engineering assumptions made when designing a plate
panel/stiffener system under a uniformly distributed load.
•Initial engineering assumptions design the panel using Classical Deflection
Theory (small deflection theory) for a flat rectangular plate under a uniformly
distributed load that is either fixed or clamped around the edges.
•Stiffeners are initially designed as beams under a uniformly distributed load that
are either simply supported or fixed at the ends.
•Initial panel and stiffener sizes generated are an approximation, as a finite element
analysis is required to evaluate and authorize the final configuration.
•Final configurations can be very different from the simple initial closed form
evaluations, as stress issues and fabrication constraints are accounted for.
•Comparative analysis between the closed form solutions (stress and deflection for a
fixed or pinned rectangular plate with a uniformly distributed load) and the values
generated by a finite element analysis.
•How close are FEA results to initial assumptions?
Panel System
Stiffeners
Top Plate
Figure 1: Pressurized Tank with top
plate stiffened
Side Plates
Panel System
Externally applied
pressure uniformly across
plate
Externally applied
pressure uniformly across
plate
Externally applied
pressure uniformly across
plate
Side plate clamped to
ground
T-frame stiffener “butted”
into side plates
Figure 3: Section view showing
stiffener design “butting” into shell
side plate
Side plate clamped to
ground
Externally applied
pressure uniformly across
plate
Externally applied
pressure uniformly across
plate
Externally applied
pressure uniformly across
plate
Side plate clamped to
ground
T-frame stiffener “sniped
into side plates
Figure 4: Section view showing
stiffener design sniped prior to
reaching shell side plate
Side plate clamped to
ground
Externally applied
pressure uniformly across
plate
Externally applied
pressure uniformly across
plate
Externally applied
pressure uniformly across
plate
Side plate and stiffener
clamped to ground
T-frame stiffener wrapped
around edge, extends to
ground
Side plate & stiffener
clamped to ground
Figure 5: Section view showing
stiffener design wrapped around
plates
Numerical Analysis
Clamped Rectangular Plate Under Uniformly Distributed Load

 po b 4
Et 3
α = 0.0138 (given, for a/b = 1)
po = 100 psi
b = 30in
E = 30 x 106 psi
t = 0.75in
  0.088
 max 
1 pob 2
t2
 max  49247
β1 = 0.3078 (given, for a/b = 1)
po = 100 psi
b = 30in
t = 0.75in
Numerical Analysis
Simply Supported Plate Under Uniformly Distributed Load

 po b 4
Et 3
α = 0.0444(given, for a/b = 1)
po = 100 psi
b = 30in
E = 30 x 106 psi
t = 0.75in
  0.284
 max 
1 pob 2
t2
 max  45984
β1 = 0.2874 (given, for a/b = 1)
po = 100 psi
b = 30in
t = 0.75in
FEA Analysis
Mesh Density
6x6
8x8
12 x 12
16 x 16
Deflection
Stress
(Numerical w max = 0.088)
(Numerical σmax = 49248 psi, σcenter = 22176 psi)
FEA
% Difference FEA (max) % Difference FEA (@center) % Difference
0.085777
2.59
44111
11.65
21260
4.31
0.086898
1.27
45992
7.08
21514
3.08
0.087762
0.27
47640
3.38
21766
1.88
0.088064
-0.07
48306
1.95
21862
1.44