Furuno WR2120 Installation Manual page 60

Assessment of annual number ��
According to the statistic information provided by the National Environment Agency of Singapore,
average thunderstorm days per year (��
will be leaded as follows:
I. Number of dangerous events ��
may be evaluated as the product:
��
��
where
is the lightning ground flash density [ ��������ℎ����/����
��
��
is the collection area of the structure [ ��
��
��
is the location factor of the structure, 0.5 for CWRP
��
��
1) Determination of the collection area ��
For isolated structures on flat ground, the collection area ��
intersection between the ground surface and a straight line with 1/3 slope which passes
from the upper parts of the structure (touching it there) and rotating around it. Determination
of the value of ��
For an isolated rectangular structure with length L, width W, and height H on flat ground, the
collection area is then equal to:
where L, W and H are expressed in meters.
Figure A.2: Collection area ��
2) Relative location of the structure
The relative location of the structure, compensating for surrounding structures or an
exposed location, will be taken into account by a location factor ��
CWRP, �� = 0.5 (Structure surrounded by objects of the same height or smaller).
��
II. Assessment of the average annual number of dangerous events ��
a structure
may be evaluated as the product:
��
��
where
2
[ ��������ℎ����/���� /�������� ] ��
is the collection area of flashes striking near the structure [ ��
��
��
of dangerous events:
��
) at Changi is 168. The lightning ground flash density ��
��
= 16.8 [ ��������ℎ����/����
�� ≁ ��. 1 ��
�� ��
for the structure
��
�� = ��
�� ��
will be performed graphically or mathematically.
��
= �� × �� + 2 × ( 3 × �� ) × ( �� + �� ) + π × ( 3 × �� )
��
��
H
L
of an isolated structure (IEC 62305-2)
��
�� = ��
��
is the lightning ground flash density
��
54
2
/�������� ]
−6
× �� × �� × 10
�� ��
2
/�������� ]
2
]
��
��
1:3
3H
V
IEC 2637/10
−6
× �� × 10
�� ��
is the area defined by the
2
. For the weather radar at
��
due to flashes near
��
2
]
��