A flange can also be a plate or ring to form
a rim at the end of a pipe when fastened to the pipe. A blind flange is a plate
for covering or closing the end of a pipe. A flange joint is a connection of
pipes, where the connecting pieces have flanges by which the parts are bolted
together.
Although the word flange generally refers to
the actual raised rim or lip of a fitting, many flanged plumbing fittings are
themselves known as 'flanges':
There are many
different flange standards to be found worldwide. To allow easy functionality
and interchangeability, these are designed to have standardised dimensions.
Common world standards include ASA/ASME (USA), PN/DIN (European), BS10
(British/Australian), and JIS/KS (Japanese/Korean). In the USA, ANSI stopped
publishing B16.5 in 1996, and the standard is ASME B16.5
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Measuring the propagation path loss and antenna effect of the actual jungle environment
China is a country with limited forest cover and a fragile ecological system, making it highly susceptible to climate-related impacts and frequent forest fires. These fires are sudden, destructive, and pose significant risks. They rank among the most common, challenging, and severe natural disasters globally. Various factors—such as natural causes like lightning, human activities such as burning, hunting, or improper disposal of fire sources—can trigger these fires. Between 2001 and 2015, China experienced a total of 116,171 forest fires, covering an area of 3,522,582 hectares, with 1,429,477 hectares affected. These events have serious consequences, highlighting the urgent need for robust forest protection measures and effective fire prevention strategies.
Forest fire prevention follows the principle of "prevention first, active suppression." Prevention is the foundation of any successful strategy, and establishing a reliable forest monitoring and communication system is crucial. To achieve this, understanding the propagation characteristics of radio waves in forest environments is essential, as it forms the basis for developing efficient communication systems in such areas.
In densely built-up regions, tree coverage might be overlooked, but in forests, vegetation plays a critical role in radio wave propagation. Trees can cause signal blockage, scattering, and absorption, leading to significant path loss. This issue was notably observed during World War II in tropical forests, where wireless communication devices often failed. Studies later revealed that the complex electromagnetic environment and harsh climate were major contributors to communication interference. With the expansion of mobile communications into rural and forested areas, ensuring consistent communication quality has become increasingly important.
Forests attract many adventurers and are also strategically relevant for military purposes. However, their dense and unpredictable nature—affected by weather, humidity, and tree density—makes radio wave propagation highly uncertain. Research on forest communication began in the 1950s, with significant efforts made during the Vietnam War to address communication challenges. The U.S. conducted extensive field studies in Thailand, while China also carried out similar experiments in its native forests. Over time, research expanded from high-frequency (HF) and very high-frequency (VHF) bands to ultra-high-frequency (UHF) bands, reflecting the growing need for integrated communication solutions in forested environments.
Theoretical and experimental approaches are both essential in studying forest communication. Theoretical work focuses on the propagation mechanisms of electromagnetic waves, while experimental research involves measuring path loss and antenna effects in real jungle settings. One of the most influential models is the Tamir forest model, which treats the forest as a lossy medium. By simulating received field values, researchers explore how factors like tree height, distance, and signal frequency influence path loss.
Path loss increases with transmission distance, showing exponential growth at short distances and linear behavior at longer ranges. Higher frequencies generally result in greater path loss. Similarly, the dielectric constant of the forest medium significantly affects path loss, with higher values leading to more signal attenuation. Signal frequency also plays a key role, with higher frequencies causing greater losses.
Additional loss depends on factors like the height of the receiving antenna, the depth of the forest layer, and the joint depth between transmitting and receiving antennas. As the receiving antenna height increases, additional loss decreases linearly. A taller forest layer leads to higher additional loss, especially at higher frequencies. Joint depth also directly influences loss, with larger depths resulting in more significant signal degradation.
Total path loss combines basic and additional losses, and it varies exponentially with distance. At higher frequencies, the loss becomes more pronounced, but after a certain point, the increase slows down. When designing forest communication systems, selecting the right frequency and antenna height based on environmental conditions is vital to meet technical requirements and ensure reliable communication in forested areas.