Abstract
Wave overtopping is a dangerous phenomenon that, in a port environment, takes place when waves that are higher than the port's breakwater meet it and water passes over the structure. This event can lead to property damage or physical harm to port workers. It is difficult to detect an overtopping, so this chapter proposes a solution to the overtopping detection problem by describing the design and development of a system that can detect an overtopping event in real-time and in a real environment. To achieve this goal, the proposed overtopping detection system is based on devices that use ultrasonic ranging sensors and communicate using the Sigfox low-power wide-area network, together with a backend that processes the data the devices send, issuing alerts to inform the interested parties that an overtopping took place.
TopIntroduction
Wave overtopping is a dangerous phenomenon that takes place when waves meet a submerged reef or structure. It also happens when waves meet an emerged reef or structure lower than the approximate wave height. The latter case is the one that affects a port’s breakwater and the one we want to measure.
When a wave overtopping occurs in a commercial port environment, the best-case scenario will be the disruption of activities and even this best-case scenario has a negative financial repercussion. Possessing a system that detects overtopping events would provide valuable information to port operators, allowing the minimization of the impact of overtopping: the financial impact, the property damage, or even physical harm to port workers.
During an overtopping, two processes take place: wave transmission and the passing of water over the structure. We want to measure the passing of water over the structure. This process can occur in three different ways, either independently of each other or combined:
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Green Water: It is the solid step of a certain volume of water above the crown wall of the breakwater due to the rise of the wave (run-up) above the exposed surface of the said breakwater.
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White Water: This occurs when the wave breaks against the seaside slope. This creates so much turbulence that air is entrained into the water body, forming a bubbly or aerated and unstable current and water springs that reach the protected area of the structure either by its impulse or as a result of the wind.
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Aerosol: It is generated by the wind passing by the crest of the waves near the breakwater. This is not an especially meaningful event, even in the case of storms. This case is the less dangerous, its impact on the normal development of port activities is negligible.
The more important overtopping types, in terms of the damage they could cause, are green and white water. To detect these events, we need to use a distance sensor, a type of sensor that allows detecting the location of objects without physical contact by outputting some kind of signal, (e.g. laser, ultrasonic waves, or IR LED) and reading how the signal has changed on its return. The change may occur in the strength of the returned signal or the time it takes the signal to return.
Once a potential overtopping is detected, a message has to be sent to a backend (server) that can process it. A port breakwater is usually several kilometers long and lacks wired internet connections and power supplies, so we need to use a Wireless network to send the data. Since the amount of data we need to send is small (only one message per overtopping event needs to be sent, and these events happen rarely), the best approach is to use a low-power wide-area network (LPWAN), a type of wireless telecommunication wide area network that allows long-range, low bit-rate communications among things (connected objects that conform the Internet of Thing, IoT), such as sensors operated on a battery (the case of the devices presented in this chapter). Right now, there are several types of IoT networks. One of them is Sigfox and it is the one the Overtopping Detection System uses.
The main objective of this chapter is to show how to use IoT, LPWAN technologies, and ranging devices to create a full system that can detect an overtopping event in real-time in a real environment.
This chapter provides an analysis of civil engineering applications of IoT, LPWAN technologies, and ranging devices. The chapter also considers the security aspect of the system which is an important consideration due to the nature of the problem and the energy supply solution for practical deployment.
The remainder of the chapter is organized into five sections. Section 2 presents the literature review of IoT, LPWAN, and ranging devices based solutions used to solve civil engineering problems. Section 3 presents the design and development of the measuring device that detects an overtopping event. Section 4 presents the design and development of the backend part of the system that is responsible for collecting the data of the device and issuing the alerts if necessary. Section 5 presents the future research directions based on the knowledge acquired in the development of the system this chapter presents and possible improvements to the system. In Section 6, the chapter concludes with the main points of the section 5.
Key Terms in this Chapter
Low Power Wide Area Networks: Low Power Wide Area Networks (LPWAN) are networks mainly used in the IoT. These networks can cover a large area and the devices that communicate using these networks can do it using very low power. These networks have been successfully used in the large-scale deployments of smart grids and smart cities, where sensors of different types are used to gather information of different nature, such as water level in the city reservoirs and power consumption but also to control the state of the city and traffic lights.
Sigfox: Sigfox is both the name of a private company and the name of the Low Power Wide Area Networks (LPWAN) developed and commercialized by this company. Like other types of LPWAN, Sigfox uses narrow bands for its operation and it also has a large coverage and low energy consumption. Sigfox is popular due to its simplicity because the company has already deploy communication towers in many countries, so the users do not have to install it themselves (or rely on other public interested party that provides it) such is the case in LoRaWAN.
Wave Overtopping: Wave Overtopping is a phenomenon that takes place when a water wave meets a submerged structure (or reef) or when the water wave meets a structure (or reef) with a height lower than the approximate wave height. Part of the wave is reflected and part passes over the structure. Wave Overtopping is the part of the wave that overpasses the structure.
Telegram: Telegram is an instant messaging and voice service. It is cloud-based and works over the IP protocol. As a messaging tool, it can be used to send messages and exchange multimedia and files of any type. Telegram also offers an API for developers called the Bot API. This API allows creating programs, called bots, that use Telegram messages for an interface. Bots can be used to send customized notifications and information instantaneously. Bots do not require an additional phone number to communicate, they serve as an interface for code running on the developer's server. This communication is encrypted by default.
Ultrasonic Sensor: Ultrasonic sensors are a type of sensors that emit and read ultrasonic sound waves that reflect on objects. This type of sensors can measure several parameters of the reflected wave and determine the distance and velocity of the object that reflected the wave. By using sound waves, these sensors can be used to measure some type of objects in some kind of environment where optical sensors such as lasers can not be used. For instance, ultrasonic sensors can be used with liquids, clear objects, uneven surfaces, and objects in an environment with dust that could affect optical sensors.
Internet of Things: Internet of Things (IoT) is a system composed mainly of interrelated computing devices and digital or mechanical machines, but even objects, animals and people can be a part of the IoT. This interrelation is achieved by the ability of the things to transfer data over a network without the need for human interaction. Currently, wireless communication technologies are the most extended. The data the things send and receive can be a reading of a sensor that measures a parameter of the thing or its environment and an action to be taken by a thing with the ability to operate actuators. A system, such as a server, can read and send data to things.
MQ Telemetry Transport: MQ Telemetry Transport (MQTT) is an international standard (ISO and OASIS) lightweight network protocol that allows sending messages between constrained devices and low bandwidth, high-latency or unreliable networks. MQTT is usually run over TCP/IP but it can potentially be used over any network protocol that meets the MQTT requisites. MQTT is based on a publish-subscribe model where devices can publish its data to several topics and they can also subscribe to several topics, receiving the data that is sent to the topics they are subscribed to. The topics can be created ad-hoc, so there is no need for a fixed topic hierarchy. MQTT is a protocol widely used in the Internet of Things world, and in systems where bandwidth and battery power are restringed and must be conserved.
European Telecommunications Standards Institute: The European Telecommunications Standards Institute (ETSI) is a European independent, not-for-profit, standardization organization that operates in the telecommunications industry and produces standards that are applied globally. The ETSI standards regulate fixed, mobile, radio, converged, broadcast and internet technologies. They have a special role in Europe, where they created standards that are recognized as European Standards at the European legislative level.
Civil Engineering: Civil Engineering is a professional engineering discipline. Civil engineering is divided into several sub-disciplines. Civil engineers belonging to this sub-disciplines are responsible for the design, construction, and maintenance of large public man-made works such as ports, roads, railways, bridges, dams, airports, and water supply systems but also structures built by nature. Civil engineers can work both in the public and private sectors.
Structural Health Monitoring: Structural Health Monitoring (SHM) is the process of detecting and characterizing damages in engineering structures to ensure structural integrity and safety of buildings, bridges and all kinds of engineering structures). The monitoring is automated and can continuously monitor and detect state (such as strain, stress, and temperature) and damages (such as cracks, holes, and ruptures) of structures with minimum human intervention. Using SHM we can optimize the maintenance of the structures maximizing the service life of the structure and the safety of its usage.