Transcript Using CUDA for Solar Thermal Plant Computation

Capstone Spring 2009 – Team 5
Using CUDA for Solar Thermal Plant
Computation.

Solar Thermal Plants

Background

Problem

Energy

Solution

Algorithm

Polygon Clipping
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Why CUDA?

Progress
Our Team.

Claus Nilsson

Sahithi Chalasani

Pranav Mantini

Arun Kumar
Subramanian
Instructor:
Dr.Bun yue
Mentor:
Dr.Michel Izygon
Mr. Peter Armstrong
SOLAR THERMAL PLANT
 Solar Thermal power plants are used to generate
electricity from the energy of the sun.
Background

Structure
1. Central receiver
A type of solar furnace.
 Receives the sunlight
redirected by Heliostats.
2. Heliostat



A type of mirror.
redirects sunlight towards
the central receiver.
Background.

Field



Generally huge
Heliostats are placed in
a radial stagger
formation.
For the purpose of
computation the field
is broken into grids
containing cells.
Shading and Blocking.

Shading and Blocking.
•
•
•
The sunlight being received by one heliostat
can be blocked by the adjacent heliostats,
causing shading and blocking.
A field of heliostats suffers loss in efficiency
caused by shading and blocking.
For our purpose we assume that shading and
blocking occurs only within a cell.
Shading.
• Shading is the loss of illumination on a
given mirror due to the interception of
the incident sunlight by a neighbouring
mirror. [3]
SHADING
Blocking.

Blocking is the loss of illumination on the
central receiver due to the interception of
reflected sunlight by another neighbouring
mirror. [3]
BLOCKING
Energy.
 The energy generated by a heliostat
depends on many factors, one of them
being the area of the heliostats.
 The energy generated from a solar thermal
plant is directly proportional to the amount
of sunlight reflected on to the central
receiver.
Energy
• The amount of sunlight reflected onto the central
receiver depends on the total area of the heliostats
that is neither shaded nor blocked.
• To optimize the energy generated from a solar thermal
plant, the total area of the heliostats that is shaded
and blocked should be calculated.
Algorithm.


An algorithm was designed by Mr. Peter
Armstrong of Tietronix Software, Inc., to
calculate the shading and blocking among the
heliostats.[4]
This algorithm makes use of Vector Mathematics,
including vector projection and a polygon
clipping algorithm.
Algorithm.
 The algorithm calculates the co-ordinates of the
heliostats for a given configuration of the grid at a
certain location of the sun.
 These co-ordinates are used to find the interactions of
the heliostats.
 The algorithm uses vector projections to find, if one
heliostat shades or blocks another heliostat.
Algorithm.
 If a heliostat shades or blocks another heliostat, a
polygon clipping algorithm is used to find the vertices
of the unshaded region of the representative heliostat.
 This algorithm is applied for all the neighboring
heliostats and the area is added to the running total of
the area calculated.
Polygon Clipping.
 The area of the representative Heliostat that is shaded
or blocked does not contribute towards the power
generated.
 This area should be subtracted using a polygon
clipper.
 The Original program designed by Tietronix Software,
Inc. makes call to a general polygon clipping(gpc)
library.
Polygon Clipping
 This gpc is a huge library designed at The University
of Manchester.
 It has about 2500 lines of code.
 Most of the processing time for calculating the co-
ordinates is taken by the gpc.
Problem.



Solar thermal fields in general have considerably
large number of heliostats.
This computation algorithm takes significant
amount of time to calculate shading and blocking
for thousands of heliostat.
The objective is to decrease this computation
time.
Solution.


To increase the efficiency of this computation
algorithm, Tietronix Software, Inc. has proposed
to create an application that computes the shading
and blocking among the heliostats
simultaneously.
For this purpose, CUDA(Compute Unified
Device Architecture), a parallel computing
architecture was chosen.
Design
 As CUDA is extension to language c, the whole
computation algorithm and the polygon clipping
algorithm was first implemented in C and then later
converted to CUDA.
Polygon Clipping Issue
 The gpc library used for the original computation
could not be used for our purpose.
 As, the gpc library are located on the host, a call to the
function on the host from the device is lot more time
consuming.
 A polygon clipping algorithm that is more specific to
the computation algorithm has to be designed.
Polygon
Clipping
 The polygon clipping algorithm used for our design is
a paper, Efficient clipping of arbitrary polygons
proposed by GUNTHER GREINER and KAI
HORMANN.
 This algorithm is chosen because, it is relatively more
efficient than Sutherland Hodgman algorithm which
is more commonly used.
 The data structures used for the polygons are very
simple.
Polygon Clipping
 A doubly linked list is used in the algorithm to
represent the polygons.
 The clipping algorithm involves the calculation of all
the intersection points and the choosing among these
points to create the desired polygon.
CUDA

What is CUDA
◦
◦
Scalable programming model and
Software environment for parallel computing [2]
◦
Extension to the C programming language
CUDA

What CUDA does




Allows utilization of GPU
Allows parallel execution of code
Manages threads automatically
CUDA Requires
 One or more Nvidia GPUs (Graphics Processing Unit)
 Nvidia’s CUDA API
CUDA Example
GPU
Source: “Parallel Processing With CUDA” by Tom R. Halfhill [1]
CUDA
CUDA
 Challenges with CUDA
 No communication from device to host
 No dynamic memory allocation on device during run
 Only Single Precision on our devices
References
[1] Tom R. Halfhill. Parallel Processing With CUDA.
Microprocessor, 01/28/08-01,
www.nvidia.com/docs/IO/55972/220401_Reprint.pd
f
[2] Greg Ruetsch, Brent Oster. Getting Started with
CUDA.
http://www.nvidia.com/content/cudazone/download/
Getting_Started_w_CUDA_Training_NVISION08.p
df
References
[3] Lipps, F. W.; vant-Hull, L. L., Shading and
blocking geometry for a solar tower concentrator
with rectangular mirrors, American Society of
Mechanical Engineers, Winter Annual Meeting,
New York, N.Y., Nov. 17-22, 1974, 7 p. NSFsupported research.
[4] Peter Armstrong, An Algorithm For Shading And
Blocking Computation Of A Field Of Heliostats
Arranged In A Grid Layout.
Thank You!
Any Questions?