conforming to the LSTM's requirement for
continuous temporal data inputs. The subsequent
phase involves the extraction of features, with the aim
of reducing the dimensionality of the data set and
thereby extracting meaningful information. This
process employs Root Mean Square (RMS) metrics
as a means of quantifying the variability of the data.
The RMS value, calculated over each time window,
represents an aggregate of vibration magnitude,
serving as a key indicator of bearing condition and
mechanical health. By transforming the data into this
comprehensive format, the preprocessing pipeline
equips the LSTM model with precise and statistically
comprehensive inputs, enhancing its ability to predict
future vibration trends accurately.
The LSTM neural network was implemented to
model time-series vibration data, thanks to its ability
to identify long-range dependencies. The LSTM
architecture comprises multiple layers that are
designed to handle the sequence prediction tasks that
are particular to the dataset. At its core, the network
comprises an input layer, followed by a series of
(LSTM) layers. These layers incorporate cells that are
structured to retain information across time steps
through gates, namely input, forget and output gates.
This enables the network to effectively retain memory
and learn sequences. The network uses a
configuration of hidden layers comprising LSTM
blocks stacked on top of each other. Each block
processes a specific aspect of the temporal data (Al-
Selwi et al., 2024). LSTM networks are an enhanced
form of recurrent neural networks (RNNs). The
hidden layer of an LSTM network has a gated unit,
also known as a gated cell. The LSTM consists of four
interconnected layers that produce the cell's output
and cell state. These two layers are then transferred to
the next hidden layer. LSTMs consist of three logistic
sigmoid gates and one tanh layer.
The forget gate is crucial to an LSTM network
because it discards information that is irrelevant for
the current prediction context. When the gate outputs
a value close to zero, the corresponding content is
effectively eliminated from the cell state. Conversely,
an output near one ensures that the information is
retained for subsequent time steps. The input gate
enables new data, relevant information to be
integrated into the cell state. This selective update is
derived from processed input data and modulated by
a learnt weight structure. Finally, the output gate
determines which parts of the current cell state are
propagated to the next layer or output. This shapes the
model's final prediction at that time step.
The LSTM models were trained and validated
using Python as the primary programming
environment and TensorFlow and Keras as the
frameworks for creating and refining the neural
network architecture. The LSTM model was designed
using a sequential layer setup to take full advantage
of Keras's high-level capabilities and streamline the
implementation process. In order to prepare the
network for rigorous testing, the model underwent
several iterations in order to calibrate
hyperparameters such as the number of hidden units,
learning rate, and batch size. The Python libraries
NumPy and Pandas were instrumental in the
management of data operations and the facilitation of
the execution of the training pipeline. Regular
checkpoints were conducted throughout the iterative
process to capture the model's state, guaranteeing a
robust recovery procedure if necessary. The
evaluation of the trained LSTM models was
conducted within the same framework, using a test set
that was separated at the outset of the data processing
workflow to ensure the maintenance of unbiased
evaluation metrics. The implementation of these
methodologies ensured the establishment of a reliable
predictive model capable of estimating future
vibration trends with a high degree of accuracy.
The visualisation of results and the evaluation of
prediction accuracy are critical components of the
research methodology, facilitating in-depth analysis
of the LSTM model's performance. For the purposes
of this study, the Python library Matplotlib was
utilised in order to create comprehensive
visualisations. These tools enabled the creation of
various plots, including line graphs showing
predicted and actual vibration trends over time,
thereby facilitating a clear visual comparison. The
assessment of the model's accuracy was conducted by
utilising standardised metrics, namely the mean
absolute error (MAE) and the root mean square error
(RMSE). These metrics offer quantifiable indicators
of prediction accuracy and are imperative for the
evaluation of the model's validity. The analysis was
enriched with graphical plots, which highlighting the
model's ability to track actual trends and identify
potential inconsistencies. This information forms the
basis for understanding the model's predictive
capacity in real-world aircraft and space CBM
scenarios.
3 RESULTS
The LSTM architecture demonstrated a strong
capability in forecasting future trends in RMS
vibration data, a critical aspect for the effective
implementation of condition-based maintenance in